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Annexure-I
IETP Process - BASIS OF DESIGN
EFFLUENT SEGREGATION & COLLECTION
Following Collection and segregation philosophy is adopted for various effluent generated in refinery.
The refinery has two sections, viz., Fuel refinery (FR) and Lube refinery (LR). Refining of crude is a complex
process, which involves physical separation of products on the basis of difference in their boiling points. This is
achieved in the primary operations like atmospheric distillation units and vacuum distillation units. Secondary
processing units include catalytic cracking of low value heavier hydrocarbon products to yield lighter hydrocarbon
products and lube refining processes such as solvent extraction, solvent de-waxing and solvent de-asphalting.
Finally, product treatment is done in order to maintain product quality conforming to required standards.
One of the most pertinent aspects in the design of any effluent treatment plant is the effluent collection scheme.
A segregated system of collection not only makes the refinery operations easier but also makes control on the
effluent quality more effective. For effective operation of biological section of the ETP, sea cooling water streams
shall never be allowed to enter into the ETP feed network.
Effluents from the different refinery units are segregated depending upon the stream quality to achieve optimum
sizing of specific treatment sub-systems, thereby reducing the overall costs of installation and operation of the
treatment plant. The principal contaminants in different streams include the following:
Stream Description Principal Contaminants
Process (Oily) Effluents Oil, BOD/COD, TSS, Phenols, Sulfides
Spent Caustic Sulfides, Phenols, BOD/COD, Oil
Contaminated Rain Water Oil, BOD/COD, TSS
Sanitary Waste BOD, TSS
After reviewing the existing effluent collection system, various modifications have been proposed in the same.
NEW INTEGRATED ETP FEED STREAMS
The following effluent streams are to be routed to the new Integrated ETP for treatment:
Process Streams
Following Streams from process area have been considered as a part of process streams:
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Stripped / Un-stripped sour water from GFEC-SWS (Sour Water Stripper)
Stripped / Un-stripped sour water from DHDS – SWS (Sour Water Stripper)
Sour water from existing FCCU
Spent caustic streams from existing refinery units
Spent caustic streams from GFEC units
Catch basin water & Spent caustic streams from NMP-I/II/III
FR/FRE flare seal drum & flare K.O. drum
LR flare seal drum & PDA K.O. drum
Tank farm drains
Miscellaneous streams from FR/FRE
Miscellaneous streams from LR/LRE
Effluent from proposed LOBS project
ATF Wash Water
Hexane-NMP ejector condensate water
The above stream are routed to new Integrated ETP.
Non-Process Streams
The non-process effluent mainly consists of the following:
1. Floor washes
2. Gland cooling water
3. Cleaning / washing of units
4. Boiler blow down
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These non-process effluent streams other than boiler blow down are also be treated in the new Integrated ETP
during dry weather flow conditions, whereas the same shall be treated in the existing API bays over and above
the design capacity of the new Integrated ETP during wet weather flow condition.
Contaminated Rain Water
No separate system exists in the refinery to divert Contaminated Rain Water (CRW). In view of this, contaminated
and un-contaminated rainwater along with various other effluent streams (including floor washes, leakages /
spillages, pump gland leaks, laboratory drains / washings, canteen waste, sampling drains, etc.) are to be routed
to the dirty water sewer (DWS) / oily waste sewer (OWS) system as per existing philosophy. During dry weather
flow conditions, these streams are to be treated in the new Integrated ETP. However, during wet weather flow
conditions, these streams along with contaminated / un-contaminated rain water are to be treated in the existing
API separators for oil recovery over and above the design capacity of the new Integrated ETP.
COOLING WATER STREAMS
For sustainable operation of any effluent treatment plant, it is of utmost concern that salt water shall never be
allowed to mix with the effluent streams. An ETP (conventional or advanced) cannot handle salty effluent which
has TDS more than 5000 ppm on a sustained basis. In case of HPCL-Mumbai Refinery, the predominant sea
cooling water streams, which enters the existing gravity sewer network leading to ETPs/API shall be diverted to
as per the following philosophy.
FR / FRE / LEU coolers back-flushing waste
Sea cooling water back-flushing and draining (to MAT) wastes from various coolers of FR/FRE are presently being
diverted to the dirty water sewer. All these back-flushing and draining wastes to be routed to storm water sewer
(SS) with a connection to clean water sewer (CWS) so that the operator may decide to route the back-flushing
waste either to SS or to CWS depending on the oil leakage observed. Necessary piping works for diversion of
these streams to SS/CWS has been considered under the scope of this project.
LR/LRE coolers back-flushing waste
Sea cooling water back-flushing and draining (to MAT) wastes from various coolers of LR/LRE are presently being
diverted to the oily waste sewer (OWS). All these back-flushing and draining wastes shall be collected in a
common header and shall be routed to the new API separators proposed at the inlet section of the Skim pond.
Necessary piping works for diversion of these streams has been considered under the scope of this project.
DHDS / SRU coolers back-flushing waste
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Sea cooling water back-flushing and draining (to MAT) wastes from various coolers of DHDS/SRU are presently
being diverted to the dirty water sewer. CWS does not exist in this area. All these back-flushing and draining of
identified Cooler shall be connected to SWC only which exists on the west side of the unit.
SANITARY EFFLUENT
Exiting sanitary lines to Imhoff tank within new Integrated ETP battery limit are to be re-routed to make space
available for the new Integrated ETP.
A new package treatment plant has been envisaged to treat sanitary effluent and new administration building
canteen waste. Treated sanitary effluent shall be disposed off to sea with a provision to further treat in biological
section of new Integrated ETP in case of non-availability of sufficient feed to the new Integrated ETP.
SUMMARY OF EFFLUENTS TO BE TREATED IN NEW INTEGRATED ETP
A brief description of the effluent streams to be treated in the proposed new Integrated ETP along with their
proposed routing to new Integrated ETP is given in the previous sections. Summary of these effluent streams and
their design flow is given below:
Sr.
No.
Effluent Stream Design Flow
(m3/h)
Basis
1. Stripped / Un-stripped sour water from GFEC /
Existing units
120* Note-1
2. Stripped / Un-stripped sour water from DHDS 17* Note-2
3. Sour Water from Existing FCCU 12* Note-2
4. Spent Caustic (GFEC streams) 2* GFEC design basis
5. Spent Caustic from PC-D-200 Drum:
Existing streams (1.75 m3/h)
HM unit boot water (1.5 m3/day)
FR/FRE stabilizers boot water
ATF caustic bubbler effluent
Rock salt filter entrained water
3 Note-2
6. Effluent from ATF Effluent Tank: 5 Note-2
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ATF Wash Water (1.25 m3/hr)
Hexane-NMP ejector condensate water (3 m3/h):
Note-6
7. Effluent from P-175 Sump:
Catch basin water from NMI-I, II & III (3 m3/h-1 m3/h
from each unit)
LR flare seal drum & PDA K.O. drum (2 m3/h)
FR/FRE flare seal drum (2 m3/h)
7 Note-2
8. Spent caustic from New Spent Caustic Collection
Drum NMP-I, II & III Spent Caustic Streams)
1 Note-2
9. Miscellaneous non-process effluent streams from
DWS-ETP Feed Pit:
Floor washes (by non-salty water), Leakages/spillages
and Pump gland leaks (25 m3/h)
Desalter desludging waste (5 m3/h)
Tank Farm drains (5 m3/h)
Lab drains / washing & Slop oil from storm water oil
catchers (5 m3/h)
Sampling drains (1 m3/h)
Contaminated rain water (not included in design
capacity of the new Integrated ETP and to be treated
in the existing API separators)
41 Note-3
10. Miscellaneous non-process effluent streams from
new LR/LRE Floor wash API separator:
Floor washes (by non-salty water),
leakages/spillages and pump gland leaks (20 m3/h)
Tank Farm drains (5 m3/h)
Canteen waste (1 m3/h)
27 Note-3
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Sampling drains (1 m3/h)
Contaminated rain water (not included in design
capacity of the new Integrated ETP and to be treated
in the new LR-API separators
11. Crude Tank Drains from LR/LRE ETP Feed Pumps 30 Note-3
12. Effluent from Proposed LOBS project 7 Note-2
13. Sanitary Effluent – 21 m3/h and New Admin Building
Canteen waste – 4 m3/h (to be mixed at inlet of the
biological section of the new Integrated ETP after
treatment in the new Sanitary Effluent Treatment
Package)
25 Note -3
14 Oily Effluent Streams (excluding spent caustic and
sanitary effluent )
Additional Design Margins (10%)
TOTAL
266
26.6
292.6
300 (say)
Note 2
15 Treated Sanitary Effluent & New Admin Building
Canteen Waste
25 Note 2
16 Spent Caustic Streams 6 Note 2
*These effluent to be routed to the New Integrated ETP under ongoing GFEC project. No new routing is
envisaged for these streams under the new Integrated ETP project.
Notes:
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Refer Design Basis for GFEC – Sour Water Stripper
These figures are based on operating data furnished by HPCL.
Design basis for various flows shall be as follows.
Basis for FR/FRE/LEU/DHDS/SRU/GFEC Floor Wash Flow Rates:
Location No. of
Operating
Hoses
Average Flow Rate
(m3/hr)
Operating Hours
(Hr)
Total Flow
(m3/day)
FR 12 6 2 144
FRE 6 6 2 72
LEU 4 6 2 48
DHDS/SRU 6 6 2 72
GFEC 6 6 2 72
Miscellaneous 10 6 2 120
Total Floor Wash Flow (m3/day) 528
Average Floor Wash Flow (m3/hr) 22
Average Floor Wash Flow Considered (m3/hr) 25
Basis for LR/LRE Floor Wash Flow Rates:
Location No. of Operating
Hoses
Average Flow Rate
(m3/hr)
Operating Hours
(Hr)
Total Flow
(m3/day)
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LR 15 6 2 180
LRE 10 6 2 120
Miscellaneous 10 6 2 120
Total Flow (m3/day) 420
Average Floor Wash Flow (m3/hr) 17.5
Average Floor Wash Flow Considered (m3/hr) 20
Basis for Sanitary Effluent Flow Rates:
Number of persons = 1500 (HPCL personnel) + 500 (Additional)
Average Effluent (as per Sewage Manual) = 250 liter /day / person
Total Sanitary Effluent = 2000 x 250 / 1000 x 24 =20.8 m3/hr
Total Sanitary Effluent Considered = 21 m3/hr
Basis for New Admin Building Canteen Waste Flow Rates:
Number of persons = 1500
Average Effluent = 50 liter/day/person
Total Canteen Effluent = 1500 x 50 / 1000 x 24 = 3.2 m3/hr
Total Sanitary Effluent Considered = 4 m3/hr
Basis for LR Canteen Waste Flow Rates:
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Number of persons = 1500
Average Effluent = 50 liter/day/person
Total Canteen Effluent = 500 x 50 / 1000 x 24 = 1.0 m3/hr
Total Sanitary Effluent Considered = 1m3/hr
Basis for New Crude Tank Drains
Capacity of one Crude Tank = 90,000 m3
BS&W (Average) = (1.0 - 0.05) % = 0.95%
Water to be drained from Each Tank = 855 m3/day
Average Crude Tank Drains = 35.6 m3/hr
ETP to be designed for the following capacity:
Oily effluent streams ( 300 m3 / Hr)
Spent caustic streams ( 6 m3 / Hr)
Sanitary effluent streams, for which New Sanitary effluent treatment package is proposed. (25 m3 / Hr)
RAW EFFLUENT CHARACTERISTICS
The effluent to be treated in the new Integrated ETP can be broadly classified as:
Oily effluent streams
Spent caustic effluent streams
Sanitary effluent streams
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A. OILY EFFLUENT STREAMS
Oily effluent streams from various parts of the refinery is collected and routed to the Battery Limit of ETP for
treatment.
Design Flow (Oily Effluent Streams): 300 m3/hr
Parameter Concentration
Temperature 25 Deg C
pH 5.5 – 9.0
Oil 1000 - 20000
Total Suspended Solids 200
BOD @ 270C, 3 Days 1000
COD 1700
Total Sulphide as S 235
Phenols 100
Total Dissolved Solids 5000
Organophosphate as PO4 10
Conductivity, micro mho/cm 9000
M Alkalinity as CaCO3 2000
Calcium Hardness as CaCO3 190
Magnesium Hardness as CaCO3 2380
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Chlorides as Cl 300
Sulphates as SO4 830
Nitrate + Phosphate as PO4 + NO3 78
Ammonia as NH3 90
Iron as Fe 1
Parameter Concentration
Total Silica as SiO2 25
Reactive Silica as SiO2 22.5
SDI Out of Range
KMnO4 consumption at 370 C 10
All other Metals Traces
All units are in mg/l except pH or as specified.
Notes :
The New IETP will be designed for maximum TDS Load of 5000 mg / lit.
Free Oil handling units will be designed for maximum oil of 20,000 ppm.
For Emulsified Oil, units will be designed for 500 mg/l.
Free and emulsified portion to be considered at 80% and 20% respectively for normal oil conc of 1000 mg/l in the
raw effluent stream.
Total Sulphide levels also include Mercaptant.
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B. SPENT CAUSTIC STREAMS
Spent caustic streams from refinery units will be stored within IETP battery limit before feeding to the New IETP
at controlled rate for the treatment of its high sulfide concentration and other contaminants. The treatment
envisaged for this stream is Oxidation by Hydrogen peroxide treatment.
Design flow: 6 m3/hr
Parameter Concentration
pH 13.6
Oil & Grease 200
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Total Suspended Solids 2200
BOD27 deg. C, 3 days 25000
COD 60000
Total Sulfides (as S) 6500
Phenols 2000
Mercaptans 5
Sodium Thiosulphate 9%
Sodium Carbonate 11.5%
Crystallates 0.5%
Sulphates 400
Ammonical Nitrogen 25
Total Dissolved Solids 125000
All units are in mg/l except pH or as specified.
C. SANITARY EFFLUENT
Sanitary waste from the refinery complex and canteen effluent from the canteen of New Admin Building will be
routed to a sanitary effluent treatment package unit. The quantity and quality of sanitary waste will be as under.
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Design flow: 25 m3/hr
Parameter Concentration
BOD 200
COD 400
TSS 200
All units are in mg/l .
TREATED EFFLUENT CHARACTERISTICS
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A. Treated Effluent Characteristics AT PLANT OUtLET
The treated effluent will be of fresh water quality and will be recycled as D.M. plant feed / Floor wash water
network. It should meet the following design parameters.
SR.NO. PARAMETER CONCENTRATION
1 pH 6.7 - 7.8
2 Turbidity 1.0 NTU
3 Total Suspended Solids 1.0
4 Total Dissolved Solids 120
5 Total Cation/Total Anion as CaCO3 100
6 BOD BDL
7 COD 3
8 KmnO4 value @ 100 degree C 5
9 Oil & Grease NIL
10 MO-Alkalinity as CaCO3 66.0
11 Chloride as Cl 30
12 Sulphate as SO4 17
13 Total Silica as SiO2 1.0
All units are in mg/l except pH or as specified.
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Effluent from the plant, if required to be disposed off, will meet the quantitative and qualitative limits of
parameters stipulated in Minimal National Standards (MINAS-Refineries) as given below:
SR. NO. Parameter Limiting value for
concentration (mg/l,
except for pH)
Limiting value for
quantum (kg/1000
tonne of crude
processed, except for
pH)
Averaging Period
Parameters to be monitored daily: grab samples for each shift with 8-hours interval.
1. pH 6.0 – 8.5 - Grab
2. Oil & Grease 5 2 -do-
Parameters to be monitored daily: composite sample (with 8-hours interval) for 24-hours flow
weighted average.
3 BOD3 days 27 deg.C, 15 6 24-hours
4. COD 125 50 -do-
5. SS 20 8 -do-
6. Phenols 0.35 0.14 -do-
7. Sulphides 0.5 0.2 -do-
8. CN 0.2 0.08 -do-
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Parameters to be monitored once in a month: composite sample (with 8-hours interval) for 24 hours
flow weighted average.
9. Ammonia as N 15 6 -do-
10. TKN 40 16 -do-
11. P 3 1.2 -do-
12. Cr (VI) 0.1 0.04 -do-
13. Total Cr 2.0 0.8 -do-
14. Pb 0.1 0.04 -do-
15. Hg 0.01 0.004 -do-
16. Zn 5.0 2 -do-
17. Ni 1.0 0.4 -do-
18. Cu 1.0 0.4 -do-
SR. NO. Parameter Limiting value for
concentration (mg/l,
except for pH)
Limiting value for
quantum (kg/1000
tonne of crude
processed, except for
pH)
Averaging Period
19 V 0.2 0.8 -do-
Parameters to be monitored once in a month: grab samples for each shift with 8-hours interval.
20. Benzene 0.1 0.04 Grab
21. Benzo (a)
Pyrene
0.2 0.08 -do-
B. RAW & TREATED EFFLUENT CHARACTERISTICS AT SBR INLET & OUTLET
The following is the quality and quantity of Raw and Treated effluent characteristics for the SBR unit.
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SR. NO. PARAMETER CHARACTERISTICS (MG/L)
RAW EFFLUENT
TREATED EFFLUENT
1 Flow (m3 / hr) 300 300
2 BOD 27 deg @ 3 days 1000 ≤20
3 COD 1700 ≤100
4 Sulphides 50 ≤30
5 Phenols 100 ≤20
6 Suspended Solids 100 ≤10
7 Total Nitrogen 115 ≤10
8 Ammonical Nitrogen 74 ≤2
9 Phosphorous 10 ≤1
10 Oil and Grease 10 ≤10
C. TREATED EFFLUENT CHARACTERISTICS AT MBR OUTLET
The following is the quality and quantity of Raw and Treated effluent characteristics for the MBR unit.
SR. NO. PARAMETER
UNIT INFLUENT EFFLUENT
Flow m3 / hr 300 300
Raw water Temperature Deg. 25 (minimum) NA
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(Note 1) Centigrade 35 (maximum)
BOD3 days 27 deg.C mg/l 100 < 5
COD mg/l 200 < 20 (Note 2)
Oil (max) mg/l 10 < 5 (Note 3)
TSS mg/l 20 < 3
Phenols mg/l 50 < 0.35 (Note 4)
Sulphides mg/l 40 < 0.5 (Note 5)
Total Nitrogen mg/l 35 < 7.0 (Note 6)
Phosphorous mg/l 3 < 3.0
Minimum Alkalinity (Note 7) mg/l 2000 NA
TDS mg/l 5,000 NA
SDI - NA < 3.0
pH - 7 – 8 6 – 8.5
Cyanide mg/l 1.0 < 0.2 (Note 7)
Note 1 : Minimum raw water temperature has been assumed to be 25 deg. Centigrade.
Note 2 : An effluent COD < 20 mg/l is achievable if the non-biodegradable portion of influent COD is < 20
mg/l.
Note 3: Oil present in the raw water should not be free oil. The effluent value is achievable if oil present is
biodegradable in nature.
Note 4: The effluent value is achievable if phenols present are biodegradable in nature.
Note 5: It is assumed that Sulphides are all in metal form and there is not H2S present.
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Note 6: We have designed to achieve TN<7 mg/L. This effluent can be achieved based on the following
assumptions
Influent TN to MBR: 35 mg/L
TN in suspended form: 10 mg/L. It is assumed that this concentration will be maintained in suspended form and
will be rejected by the membrane system.
TN in soluble form: 25 mg/L. It is assumed that influent TKN: 15 mg/L and NO3-N: 10 mg/L
Maximum non-biodegradable content of soluble TN: 0.5 mg/L
Note 7: The effluent value is achievable if cyanide present are biodegradable in nature.
Note 8: Alkalinity of 2,000 mg/L in the influent.
Note 9: Maximum TDS value of 5,000 mg/L in the influent.
D. TREATED EFFLUENT CHARACTERISTICS AT RO OUTLET
SR.
NO. PARAMETER INFLUENT EFFLUENT
1 pH 7 6.7 - 7.8
2 Turbidity --- ≤1.0 NTU
3 Total Suspended Solids <5 1.0
4 Total Dissolved Solids 5000 120
5 BOD <5 BDL
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6 COD
<20 BDL
7 Oil & Grease Nil BDL
8 Total silica as SiO2 25 <1
All units are in mg/l except pH or as specified.
E. TREATED CHARACTERITICS OF SANITARY EFFLUENT
SR.NO. PARAMETER
CONCENTRATION
1 Flow, m3/hr 25
2 BOD, mg/l < 10
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3 TSS, mg/l < 20
F. EQUIPMENT DESIGN PHILOSOPHY
Overall water recovery from the plant – 65% (min.) based on design conditions
Hydraulic Turn Down requirements - 30%
On stream factor – Plant should be able to operate round the year
PRINCIPLES OF TREATMENT
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The wastewater contains pollutants that can be seen from the data presented under the design specifications,
which require different types of treatment to reduce their presence in the effluent to acceptable levels.
The processing scheme has broadly following types of treatment:
Physical Treatment
Chemical Treatment
Biological Treatment
Tertiary Treatment
Sludge Treatment
VOC Treatment
Sewage Treatment
The major operations involved in these processing scheme are:
Free Oil Removal
Emulsified Oil Removal
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Sulphide Treatment
Biological Treatment
RO Treatment
Sludge Thickening & Centrifugation
Bio-Remediation
VOC Treatment
Sewage Treatment
The principles of the above operations are described below:
A. FREE OIL REMOVAL
Oil & grease in the wastewater can be present in essentially two main forms namely “FREE OIL” and “EMULSIFIED
OIL”. During transit of the oil contaminated water, various factors such as flow turbulence, temperature, presence
of other chemicals breaks the oil in smaller globules. The fraction of oil that under quiescent conditions can
coalesce and separate from the water phase due to the gravity differential of the two phases is termed as FREE
OIL. Generally, oil globules of above 60 micron are removed by API Oil Separators and less than 60 micron by TPI
Oil separators.
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a. API Oil Separator
The separation of oil from water by gravity differential is based on the rise rate of oil globules. Since the oil
globules present will have varying sizes,for practical purposes the design is based on the rise rate of globules
having a diameter of 60 microns. The separation basins are designed to have low velocity (0.6 m/s) and minimum
cross or eddy currents, and sufficient retention time to permit the globule to coalesce and rise to the surface.
During its upward travel to the surface, particles coalesce to form a film of oil, which is mechanically skimmed and
recovered.
b. TPI Oil Separator
The current trend is to satisfy the increased separating area requirements by providing a number of stacked
plates. Thus, the separating surface area is increased vertically. The area is further increased by selecting
corrugated plates. The plates are located one on top of the other at specific distance from one another. The
entire plate pack is placed in a tank at an approx. angle of 45 degrees. Hence the unit is called as “Tilted Plate
Interceptor (TPI)”. The wastewater enters the plates either parallel to corrugations in “Counter Current Flow” or
at right angles to the corrugations in “Cross Flow” under laminar flow conditions. The short distance between the
inclined plates is now the only distance over which the oil globule has to rise before it is intercepted and
separated from the water. Due to the laminar flow conditions the separated oil globules coalesce into large
droplets and gradually rise to the surface. The film formed on the surface is then skimmed off through slotted
pipes.
B. EMULSIFIED OIL REMOVAL
An intimate, two - phase mixture of two immiscible liquids with one phase dispersed as minute globules in the
other phase is defined as an EMULSION. In the case of refinery wastes, the oil phase is intimately dispersed in the
water phase. Various factors contribute to the stability of this dispersion. The minute globules are stabilized by an
interfacial film or stabilizing agent such that the globules do not coalesce and do not respond to gravity settling. A
major factor contributing to the formation and stability of emulsions is the electrical charge carried by the
emulsified particles. In general, globules of oil in an oil-water emulsion may be broken by an electrical current or
by electrolytes supplying a sufficient concentration of effective ions which neutralize the surface charges on the
emulsified oil globules, permitting them to coalesce into larger globules.
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Dissolved Air Flotation (DAF) is a process commonly used in refineries to remove emulsified oil and suspended
solids from gravity separator effluent. The process involves pressurizing the influent to DAF Unit and then
releasing the pressure, which creates minute bubbles that float suspended and oily particulates to the surface.
The floated material is collected by a mechanical froth skimmer.
If a significant portion of the oil is to be emulsified, chemicals are used for breaking the emulsion and enhancing
the separation. Chemicals normally used are Aluminum/ Iron salts and polyelectrolytes.
D. SULPHIDE TREATMENT
Sulphur is an inherent impurity in most crude oils, and its concentration depends on the source of the crude.
During the crude refining process, this impurity is separated from the product and discharged as a liquid effluent.
During the processing step the sulphur is converted to sulphide. The sulphides present in the effluent may be in
the form of free sulphides or as hydrogen sulphide depending on the pH of the stream. These compounds are
toxic in nature and need to the treated / removed prior to disposal of the effluent.
Sulphides are removed by chemically oxidizing them to elemental Sulphur or Sulphate using strong oxidising
agents such as Hydrogen Peroxide (H2O2), Ozone & Chlorine. In view of its various advantages, Hydrogen
Peroxide is normally the preferred chemical.
The reactions involved are as under:-
Acidic Range / Neutral Conditions
In acidic range and neutral conditions, sulphides in the effluent are mostly present in the form of H2S. The H2O2
reacts with H2S to give products of oxidation – water and elemental sulphur as shown below:
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H2O2 + H2S 2 H2O + S
(Stoichiometrically 1.06 kg of H2O2 is required for 1 kg of sulphide)
Alkaline Range
In alkaline range, sulphides present in the effluent are generally in the form of Na2S. The H2O2 reacts with Na2S
to give end products as water and Na2SO4 (relatively harmless and impose no oxygen demand), as shown below.
4 H2O2 + Na2S Na2SO4 + 4 H2O
(Stoichiometrically 4.25 kg of H2O2 is required for 1 kg of sulphide.)
E. BIOLOGICAL TREATMENT
Organic matter, phenols, residual sulphides, non-recoverable oil and hydrocarbons contribute to the effluent’s
Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). BOD is indicative of the quantity of
oxygen required to biologically stabilize the organic matter present in the waste water, while the COD indicates
the oxygen requirement for oxidizing the organic matter by a strong chemical in an acidic medium, at elevated
temperature. In order to stabilize the organic matter, biological treatment of waste water is to be accomplished
by aerobic digestion of the organic matter. Most modern effluent treatment plants (ETP) in refineries employ
Sequential Batch Reactor (SBR) followed by Membrane Bio Reactor (MBR) systems for treatment of organics.
Sequential Batch Reactor (SBR)
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in Sequential Batch Reactor system a Cyclic Activated Sludge Treatment (C-Tech) technology is used. It provides
highest treatment efficiency possible in a single step biological process. The C-Tech system is operated in a batch
reactor mode. This eliminates all the inefficiencies of the continuous processes. A batch reactor is a perfect
reactor, which ensures 100% treatment. Two or more modules are provided to ensure continuous treatment. The
complete process takes place in a single reactor, within which all biological treatment steps take place
sequentially as described below.
STEP 1: Fill-Aeration (F/A)
STEP 2: Settlement (S)
STEP 3: Decantation (D)
These phases in a sequence constitute a cycle, which is then repeated. During the period of a cycle, the liquid
volume inside the Reactor increases from a set operating bottom water level. During the Fill- Aeration sequence
mixed liquor from the aeration zone is recycled into the Selector. Aeration ends at a predetermined period of the
cycle to allow the biomass to flocculate and settle under quiescent conditions. After a specific settling period, the
treated supernatant is decanted, using a moving weir Decanter. The liquid level in the Reactor is so returned to
the bottom water level after which the cycle is repeated. Solids are wasted from the Reactor during the decanting
phase.
The C-Tech system selected is capable of achieving the following:
1. Removal of Organics
The effluent free from free oil & emulsified oil shall be taken up for Biological treatment for the removal of
organics, nitrogen and phosphorus. The activated sludge bio system is designed using Cyclic Activated Sludge
Technology which operate on extended Aeration activated sludge principle for the reduction of carbonaceous
BOD, Nitrification, Denitrification as well as phosphorous removal, using energy efficient fine bubble membrane
diffused aeration system, with automatic control of oxygen uptake rate, resulting in 20–30% power savings. The
practice of manipulating activated sludge reaction environments to obtain maximum nitrogen and phosphorous
removal has been optimized, using cyclic activated sludge technology, by co-current nitrification denitrification
mechanism. In its simplest form, the sequences of fill, aeration, settle and decant are consecutively and
continuously operated all in the same tank, allowing up to 30-40% space saving. No secondary clarifier system is
required to concentrate the sludge in the reactor. The return sludge is recycled and the surplus sludge is wasted
from the C-Tech basin to the Bio sludge sump.
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2. Nitrification
Any oxidation must be coupled with reduction, and oxygen satisfies this requirement in the aerobic
microorganisms. Extended Aeration system, with high c values, ensures uniform nitrification performance.
Nitrification results from the oxidation of ammonia present in the sewage by Nitrosomanas to nitrite and the
subsequent oxidation of the nitrite to nitrate by Nitrobacter. The nitrifying organisms are strict aerobic
autotrophes and use carbon source present in the sewage, in the presence of oxygen, maintained at 2 mg/l in the
SBR to avoid oxygen limitation. The nitrification of ammonia can be represented as given below:
Nitrosomonas + 2 NH4+ + 3O2 ---------> 2 NO2- + 2 H2O + 4 H+ + New Cells
Nitrobactor + 2 NO2- + O2 ----------------> 2 NO3- + New Cells
The diffused aeration system is sized so that sufficient oxygen is provided for carbonaceous treatment, sludge
stabilisation, nitrification and maintaining the DO at the specified level of 2 mg/l, taking into account the
reduction in oxygen demand due to denitrification. The capacity of diffused aeration in each SBR basin will be
sufficient to ensure good mixing conditions during Fill Aeration phase of the cycle of operation.
3. Denitrification
The wastewater enters the Selector zone in the front end of the SBR, where anoxic conditions are maintained.
Part of the wastewater along with return sludge from the aeration SBR basin is recycled here, using RAS Pumps.
With the incorporation of biological Selector there is no need for an Anoxic – Mixing sequence and is therefore
replaced by a simple Fill – Aeration sequence. As the microorganisms meet high BOD, low DO condition in the
Selector zone, natural selection of phosphate accumulating microorganisms and floc-forming microorganisms
takes place. This is very effective in containing all of the known low F/M bulking microorganisms and eliminates
the problems of bulking and surface foaming. Also, due to the anoxic conditions in the Selector zone,
denitrification and phosphorous removal occurs by co-current nitrification & Denitrification. Complete
nitrification and denitrification pathways take place with nitrification taking place external to the activated sludge
flocs and denitrification taking place within the interior of the flocs. This denitrification pathway is not bound to
the absence of dissolved oxygen in the liquid phase but requires diffusion of nitrate into the anoxic parts of the
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floc with a probable use of stored intracellular carbon or adsorbed organic carbon for denitrification. During
anaerobic conditions, all phosphorous that is released to the liquid phase is totally contained within the bio solids
layer. Biological denitrification in the Selector zone by recycling of mixed liquor from aeration zone requires
nitrification of all ammonical nitrogen in the incoming wastewater in the aeration zone. This requirement of plant
design is met by operating the SBR under Extended Aeration Process with higher C values, which ensure co-
current nitrification and denitrification in the aeration zone.
Denitrification releases nitrogen which escapes as an inert gas to the atmosphere, while the oxygen released stays
dissolved in the liquid and thus reduces the oxygen input needed for the aeration.
4. Carbonaceous BOD Removal
The aeration zone of SBR is provided with diffused aeration to oxidize the organic matter including phenol, by
Extended Aeration Process. An extended aeration activated sludge process operates in the endogenous
respiration phase of the growth curve where the microorganisms are forced to metabolize their own protoplasm
without replacement, since the concentration of food available is at a minimum. During this phase, the nutrients
remaining in the dead cells diffuse out to furnish the remaining cells with food. This system has been developed
for application where minimum solids production is desirable. Less solids production is achieved by using a larger
fraction of the entering organic material for energy rather than for synthesis. This means that more oxygen will be
consumed per unit mass of organic material removed.
The activated sludge process is capable of converting most organic wastes to more stable inorganic forms or to
cellular mass. In this process, the soluble and colloidal organic material is metabolized by a diverse group of
microorganisms to carbon dioxide and water. At the same time, a sizable fraction of incoming organic matter is
converted to cellular mass that can be separated from the effluent by settling.
Activated sludge comprises a mixed microbial culture wherein the bacteria are responsible for oxidizing the
organic matter, while protozoa consume the dispersed un-flocculated bacteria and rotifers consume the
unsettled small bio-flocs in the treated wastewater, performing the role of effluent polishers.
The utilization of substrate by a bacterial cell can be described as a three-step process:
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1. The substrate molecule contacts the cell wall.
2. The substrate molecule is transported into the cell
Metabolism of the substrate molecule by the cell. However, as the bacteria require the molecule in the soluble
form, colloidal, spherically incompatible molecules, which cannot be readily biodegradable, have to be first
adsorbed to the cell surface and then broken down or transformed externally to transportable fractions by
exoenzymes or wall-bounded enzymes. The organic matter will be utilized by the bacteria resulting in cell
synthesis and energy for maintenance.
The following reactions best describe the organic utilization by the aerobic bacteria:
Oxidation
COHNS + O2 + Bacteria ---------> CO2 + NH3 + Other End Products + Energy
Synthesis
COHNS + O2 + Bacteria -----------> C5H7O2N (New Bacterial Cell)
Endogenous Respiration
C5H7O2N + 5O2 --------------> 5CO2 + NH3 + 2H2O + Energy
Nutrients available in the wastewater or from external source of supplements cater to the nutrient requirements
of the aerobic microorganisms and to enhance the activity of the aerobic microbes. In addition to the nutrient
requirements, the aerobic microbes require oxygen to sustain their microbial activity. Oxygen also functions as a
terminal electron acceptor in the energy metabolism of the aerobic heterotrophic organisms indigenous to the
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activated sludge process. In other words a portion of the organic material removed is oxidized to provide energy
for the maintenance function and the synthesis function.
5. Phosphorous Removal
The key to Phosphorous removal is exposure of microorganisms to alternating aerobic and anaerobic conditions.
The alternating condition stresses the microorganism to uptake higher concentration of dissolved phosphorous,
from the effluent thereby reducing the Phosphorous level in the effluent. This phenomenon is called as Enhanced
Phosphorous Uptake. Phosphorous is also used by the microorganism for cell maintenance, synthesis, energy
transport and is also stored for future requirements.
Hence in C-Tech system, the removal of phosphorous from the wastewater is accomplished by the enhanced
phosphorous uptake rate and consumption of P for the cell growth with selector/aeration compartments.
6. Sulphides Removal
The removal of sulfides from the wastewater is accomplished during the Fill-Aeration phase in the aeration zone
of C-tech, by oxidation with oxygen present in the diffused air.
The oxidation of sulphides is represented as:
S2- + O2 SO2
7. Phenol Removal
Phenol is a complex organic matter. This can be oxidized in aerobic biological system with acclimatized biological
environment. Ideal treatment conditions such as maintenance of DO levels, good settling sludge, higher SRT, good
process control, etc. will further enhance the phenol removal. C-Tech system provides ideal conditions of
biological environment for phenol degradation.
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Process Microbiology
Bacteria are the most important type of microorganisms concerned with organics removal. There are
essentially two types of microbes in terms of metabolism, namely, Heterotrophs and Autrotrophs. Heterotrophic
bacteria utilize organic material as a source of carbon and energy, while Autotrophic bacteria generally
depend on the oxidation of inorganic compounds such as NH3 and H2S for energy requirements, and utilize
CO2 or carbonates or bicarbonates, as a carbon source (eg. Nitrifying and Sulfur oxidizing bacteria).
All microbial species in the activated sludge process utilize oxygen as the final electron acceptor in the oxidative
biochemical reaction. For certain species, presence of oxygen is absolutely essential, without which they would
die out. These are called `Obligate Aerobes'. However, there are many bacterial species which utilize oxygen
under aerobic conditions, but in the absence of oxygen switch over to a fermentative or anoxic metabolic
route. This class of microbes are called “Facultative Anaerobes”.
Bacterial genera most frequently occurring in activated sludge are as follows:- Pseudomonas,
Flavobacterium, Achromobacter, Chromobacterium, Azotobacter, Micrococcus, Bacillus, Alcaligenes,
Arthrobacter, Acinetobacter, Mycobacterium, Nocardia, Lophomonas, Escherichia, Zoogloea. Activated
sludge also frequently contains undesirable filamentous organisms: Sphaerotilus, Thiothrix, Beggiatoa,
Geotrichum, Nocardia, Microthrix. These organisms are associated with `Sludge Bulking', where the
activated sludge has poor thickening and settling characteristics.
Protozoa and Rotifiers The protozoa act as polishers of the effluents from biological waste treatment
processes by consuming bacteria and particulate organic matter. Various types of protozoa may be
present, namely, amoeba, flagellates, ciliates (both stalked and free swimming). Rotifers are multi-cellular
organisms. They are also effective in consuming dispersed and flocculated bacteria and particulate organic
matter. As in the case of protozoa, their presence in an effluent indicates a highly efficient and stabilized
aerobic biological process.
Physical Characteristics of Activated Sludge
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Visually activated sludge from sewage treatment has a light brown colour. However, in the case of industrial
waste treatment the colour of the activated sludge could vary depending on the waste being treated. For
example, activated sludges in the treatment of coal carbonization effluents have a very dark colour (almost
black). Well stabilized sludges appear to be well flocculated, with rapidly settling flocs leaving a clear
overflow. The activated sludge has a musty odour in the case of sewage treatment. This odour, however, may
be not apparent in the case of treatment of industrial effluents having a strong odour of their own.
Factors Affecting the Process
Numerous factors influence the performance of the activated sludge process. Some of the factors are:-
- Variability in Waste Water Flow and Quality
- Sludge Retention Time (SRT)
- Hydraulic Retention Time (HRT)
- Organic Loading (F/M ratio)
- Macronutrient (Nitrogen and Phosphorus) Levels
- Mixed Liquor Suspended Solids (MLSS) concentration
- Mixing and Aeration Intensity/Pattern
- Mixed Liquor Temperature
- Mixed Liquor pH Value
- Mixed Liquor Dissolved Oxygen levels
- Influent Waste concentrations
Characteristics of sludge
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Membrane Bio Reactor (MBR)
Based on the process requirements and influent characteristics, a Modified Ludzack-Ettinger (MLE) process was
selected for MBR system.
This design consists of the influent being fed into an anoxic zone followed by an aerobic zone. Nitrate formed in
the aerobic and membrane zones, is recycled back to the anoxic zone where it is denitrified. Having the anoxic
zone as a first zone, allows for maximum influent BOD utilization for denitrification (maximized the C:N ration).
The effluent of the SBR treatment will be collected in an MBR feed tank where submersible pumps will transfer
wastewater into the Bioreactor Splitter Box. Wastewater is combined with the recycled mixed liquor from the
membrane trains and is equally distributed into two biological trains. Supplemental carbon will be added in the
Splitter Box should the influent carbon be insufficient for the biological process. Sodium hydroxide and antifoam
agents will be added if required. A bypass of the SBR is included should the influent to the MBR be deficient in
nutrients which will affect the biological process.
Mixed liquor flows through each biological process train by gravity from the anoxic to the aerobic zone and into
the Bioreactor Collector Channel. Foam and scum are collected in a foam trap located at one end of the overflow
channel via a motorized downward opening gate. Dry-pit centrifugal pumps will transfer foam, scum and waste
activated sludge to the sludge handling facility.
Mixed liquor recirculation pumps will transfer mixed liquor from the Bioreactor Collector Channel into the
Membrane Tank Splitter Channel. Mixed liquor flows by gravity into (4) parallel ZeeWeed® membrane tanks via
partially submerged sluice gates, which are designed to ensure equal flow distribution to all the membrane tanks
and same water level in all tanks. The mixed liquor overflows to the Membrane Tank Collector Channel and it
flows by gravity to the Bioreactor Splitter Box where it is combined with the influent before entering the anoxic
zones.
Clean water is withdrawn from the mixed liquor through the membrane using a dedicated permeate pump and is
discharged to a common collector header discharging to the Treated Effluent Tank for RO feed. Permeate will be
used from this tank for backpulsing and cleaning the membranes.
The system is completed with membrane tank drain pumps. These pumps are common to all membrane trains
and will drain the membrane tanks when required.
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F. REVERSE OSMOSIS
The treated effluent after Membrane Bio Reactor is taken for the tertiary treatment. The tertiary treatment
mainly consists of Reverse Osmosis System.
The Reverse Osmosis (RO) unit essentially works at the molecular level. It separates the molecular impurities from
the water thus making one stream rich in salt molecules and other stream lean in salts thus reducing the TDS and
silica of the water.
Process of Reverse Osmosis:
Osmosis is a natural process involving fluid flow across a membrane, which is said to be ‘semi-permeable’. A semi-
permeable membrane is selective in that certain components of a solution, usually the solvent can pass through,
while others, usually the dissolved solids cannot pass through it. Its chemical potential determines the direction of
solvent flow, which is a function of pressure, temperature and concentration of dissolved solids. In case pure
water is available on both sides of a semi-permeable membrane at equal pressure and temperature, no resultant
flow can occur across the membrane, as the chemical potential is equal on both the sides. However, if any soluble
salt is added on one side of the membrane, the chemical potential of the water on that side is reduced. The
osmotic flow from the pure water on one side to the salt solution on the other side will occur across the
membrane until equilibrium of solvent chemical potential is restored.
The Thermodynamic requirement for osmotic equilibrium is that the chemical potential of the solvent be the
same on both sides of the membrane. No such condition is imposed on the solute, since the membrane prevents
its passage. The Equilibrium State occurs when the pressure differential on the two sides is equal to the osmotic
pressure, a solution property that is independent of the membrane.
The application of external pressure to the solution side, which equals the osmotic pressure, will also accomplish
equilibrium. A further increase in pressure will increase the chemical potential of the water in the solution and
will cause a reversal of the osmotic flow towards the pure water side which is at a lower solvent chemical
potential relative to the solution. This phenomenon is termed as Reverse Osmosis and is the basis for a process to
desalinate water without phase change.
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Reverse Osmosis System:
The treated water from MBR is further polished into RO plant to get the product water which can be use as feed
to DM plant, floor wash etc.
In order to prevent the precipitation of the salts on reject side, an antiscalant is added at the inlet of the cartridge
filter, which will result in inhibition of scales. Furthermore Sodium bisulfite shall be dosed to remove free chlorine
present in the feed water. Presence of free chlorine in the feed water will irreversibly damage the RO
membranes. 30 - 33 % HCl acid is also continuously dosed inlet of the cartridge filter to adjust the pH of the feed
water.
Micron cartridge filter is provided in order to remove micron size particles, which is additional safety. Water is
then pumped using high-pressure pumps through R.O. module for removal of TDS. Reverse Osmosis module
consists of thin film composite Polyamide Membranes. On continuous running the R.O. membranes get fouled
with fine colloids, bacterial debris or some times carbonate scales. These need to be removed and cleaned from
the surface of the membrane. For each type of flocculant, there is a recommended chemical cleaning procedure,
which is convenient to perform with CIP system.
The permeate from the RO plant is then stripped into degasser tower for reduction of CO2 in water.
Degasser Tower is filled with PP packing rings. Air is forced from the bottom of the tower by Centrifugal Blowers,
while the water flows down through the packed bed of PP rings. The carbonic acid present in the water splits up
into carbon dioxide gas and water.
This carbon dioxide gas is stripped off and escapes from the top of the tower. The degassed water is collected in
the degassed water tank and is pumped further for polishing.
The RO treated water will be pumped for reuse as DM plant feed (in DHDS and GFEC units) and floor wash. The
RO treated water will also be used in suck back tank.
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G. SLUDGE THICKENING AND CENTRIFUGE OPERATION
Biological sludge generated from SBR & MBR is thickened for volume reduction. Thickening is done by gravity belt
thickener and then dewatered by centrifuge operation. Polyelectrolyte is used to increase efficiency of the
centrifuge operation. The dewatered sludge send for further treatment and secured landfill.
The oily & chemical sludge generated from API, TPI Oil Separators, DAF, RO & DM plant is thickened in a gravity
thickener. The thickened sludge is dewatered by centrifuge operation. Polyelectrolyte is used to increase
efficiency of the centrifuge operation. The dewatered sludge is send to bioremedation unit for further treatment.
H. BIOREMEDATION
The Bioremediation process is a biological method to reduce the Total Petroleum Hydrocarbon (TPH) level in the
oily sludge to make it suitable for non hazardous land fill site.
The process involves biological processing of the oily sludge in a confined Bioreactor using specially designed
bacterial columns and advanced fermentation methods to degrade the petroleum hydrocarbon in the sludge
producing a non hazardous sludge with very low level of hydrocarbon. The TCLP analysis of the remediated sludge
is within US EPA guideline for land fill in a non hazardous site.
The Bacterial mass is naturally selected and acclimated with a careful blend of nutrients and surfactants. The
reactor conditions promote growth of highly active microbial population which rapidly converts the TPH into
carbon dioxide and water.
The contents of the bio reactor are closely monitored for temperature, pH, aeration intensity and nutrients. Each
batch is treated for approximately 10-15 days after which the bioremediated sludge is removed from the reactor
using discharge pumps.
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I. VOC TREATMENT
Recently, several environmental regulations have been enacted that require industries to limit gaseous and
aqueous emissions containing Volatile Organic Compounds “VOC’s”. These new laws have greatly increased the
number of regulated VOC’s and expanded the categories of emissions from industrial facilities. For example,
reduction of VOC gaseous emissions is now made mandatory under new Environmental Pollution Act and all the
new facilities are now being asked through No objection certificate to adopt VOC control and treatment
measures. This also requires a reduction of the emission of Hazardous Air Pollutants (HAP’s), many of which are
VOC’s and regulate the levels of VOC’s in both air emissions and wastewater. This regulation also requires the
control of "fugitive" VOC’s from processing units. A significant number of VOC's have also been added to the TC
(Toxicity Characteristic) Rule, which is part of the hazardous waste regulations. In addition, chemical-specific
effluent limitations are being added to wastewater standards. These are extremely stringent and apply to a large
number of VOC's.
In response to the need to find cost-effective ways of reducing VOC’s emissions, many industrial initiatives have
occurred. These initiatives have led to the realization that pollution prevention provides the most comprehensive
and efficient strategy for reducing VOC’s emissions. Furthermore, it has been realized that any successful
pollution prevention strategy should address management and technical concerns. For example, management
concerns addressed within a corporate pollution strategy are reduced liability, improved corporate image within
the community, and reduced uncertainty relative to waste shipments from the company to some disposal party.
Examples of technical concerns are waste reduction process efficiency, economics of recovery and recycle of
wastes, and energy efficiency.
Within the past decade, significant academic efforts have been devoted to the development of systematic tools
and robust design methodologies that could be incorporated within a corporate pollution strategy to allow the
systematic development of environmentally acceptable process designs. These tools and methodologies are
designed to address the technical and, in many cases, the management concerns of a company with respect to
their corporate pollution strategy. Prior to presenting the systematic tools and design methodologies that have
been developed for use in designing VOC separation systems, several pollution prevention terms should be
defined. Additional information on these definitions can be found in Noyes (1993) and Freeman (1990). The
following is a brief discussion of these terms. In addition following figure is included as a hierarchical
representation of these definitions.
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Pollution Prevention Waste Minimization
Source ReductionToxic Chemical
Use SubstitionRecycling
Use or Reuse Reclamation
A Hierarchical Representation of Pollution Prevention Definitions
Pollution Prevention Definitions as Used by the Environmental Protection Agency
Waste : Non-product outputs of processes and discarded products,
regardless of the environmental medium impacted.
Pollution Prevention : “Industrial pollution prevention” and pollution prevention refer to
the combination of source reduction and toxic chemical use
substitution. It does not include any recycling or treatment of
pollutants. It also does not include substituting a nontoxic product
made with nontoxic chemicals for a nontoxic product made with
toxic chemicals.
Waste Minimization : Current RCRA definition indicates that waste minimization refers to
source reduction and recycling activities, but does not include
treatment and energy recovery activities.
Recycling
: Recycling techniques are categorized as use, reuse and reclamation
techniques. These techniques allow potential waste materials to be
put to a beneficial use rather than going to treatment, storage or
disposal.
Use or Reuse
: Use and reuse involves the return of a potential waste material
either to the originating process as a substitute for an input material,
or to another process as an input material.
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Reclamation
: The recovery of a useful or valuable material from a waste stream is
referred to as reclamation.
Source Reduction : Source reduction is any practice that :
Reduces the amount of any hazardous substance, pollutant, or
contaminant entering any waste (pollutant) stream or otherwise
released into the environment prior to recycling, treatment, and
disposal.
Reduces the hazards to public health and the environment
associated with the release of such substances, pollutants, or
contaminants.
This term also includes:
Equipment or technology modifications
Process or procedure modifications
Reformulation or Redesign of products
Substitution of raw materials
Improvements in housekeeping, maintenance, training or inventory
control
Toxic Chemical Use
Substitution
: This term refers to the replacement of toxic chemicals with less
harmful chemicals.
Toxic Use Reduction
: Source reduction activities whose intent is to reduce, avoid or
eliminate the use of toxic substances in processes and/or products.
VOC Separation Systems for Gaseous Wastes
Several technologies exist that can be used for recovery & treatment of VOC’s from gaseous wastes. The most
widely used technologies for recovering VOC’s from gaseous wastes are liquid absorption using heavy
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oils/hydrocarbons, activated carbon adsorption, and condensation using coolants/refrigerants. In addition,
recently developed membrane-based technologies can be used in conjunction with one of the above technologies
to improve system efficiency and/or overall operating.
The activated carbon adsorption system is considered for the control and treatment of VOC based on the merit of
the system and techno-economic superiority on other systems.
Activated Carbon Adsorption
Description
VOC gaseous emissions flow into the top or bottom of an adsorption column, filled with porous
activated carbon, & is distributed throughout the carbon bed.
Two adsorption processes exist, temperature-swing adsorption (TSA) and pressure-swing adsorption
(PSA). Temperature-swing adsorption is the approach commonly used for VOC recovery and the
process description, advantages, and disadvantages listed in this section correspond to the
temperature-swing adsorption process.
Carbon adsorption beds can be fixed or moving, with respect to the carbon. For moving beds, the flow
of activated carbon is countercurrent to the flow of the gas; however, fixed beds are more common in
industry.
The VOC is adsorbed onto the surface of the activated carbon and onto the surface of the pores. At
some point the carbon becomes saturated with VOC and loses its capacity for additional adsorption.
This results in the concept of “breakthrough” where significant quantities of VOC become apparent in
the gas stream exiting the adsorption process. When this occurs the carbon must be regenerated for
re-use or replaced with virgin carbon.
Multiple fixed beds are generally employed so that as one or more beds are adsorbing at least one bed
can be regenerating. Regenerating a bed of activated carbon typically involves the direct injection of
steam, hot nitrogen or hot air to the bed which causes VOC to release from the carbon & exit the bed
via a vapor or condensate stream. The regenerated stream, containing a higher concentration of the
VOC than the original wastewater stream, is subsequently condensed. If the VOC is immiscible in
water, the condensate will form an aqueous layer & a solvent layer that can be separated using a
decanter. If the VOC is miscible in water, additional distillation can be used to further separate the VOC
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& water.
“VOC-free” gas exits the adsorber after contacting the activated carbon.
Advantages
A widely used technology with well established performance levels.
Can achieve high recovery efficiencies (90-98%).
Can be used for a wide range of gas flow rates (100-60,000 cfm).
Can handle a wide range of inlet VOC concentrations (20-5,000 ppm).
Can efficiently handle fluctuations in gas flow rates and VOC concentration.
Disadvantages
VOC having high adsorption heats (typically ketone)can cause carbon bed fires.
Carbon attrition properties (permanent bonding of small quantities of VOC through each adsorption
cycle) requires the periodic replacement of carbon with virgin or reactivated carbon. Spent carbon may
need to be disposed of as a hazardous waste depending on the VOC(s) adsorbed.
Carbon efficiency decreases for high humidity (>50% r.h.) air streams.
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Activated Carbon AdsorbersVOC Gaseous Waste
Clean Air
Adsorption Mode
Steam or Hot Nitrogen
Regeneration Mode
Condenser
Decanter
To Atmosphere
or Carbon Adsorber
Recovered VOCRecycled or Sent to Distillation
Water EffluentDischarged or Sent to
Air or Steam Stripping
Vapor
Liquid
A Schematic Representation of a Carbon Adsorption Process for VOC Gaseous Wastes
J. SEWAGE TREATMENT
1. Screening
This is the first unit operation encountered in sewage treatment plants. A screen is a device with openings,
generally of uniform size, that is used to retain coarse solids found in wastewater. A screen with parallel rods or
bars is called a Bar Rack or Bar Screen. These devices are used to protect downstream equipment such as pumps,
lines, valves etc from damage and clogging by rags and other large objects. The important criteria involved are
effluent velocity and hydraulic head loss through the bar screen, which increases with clogging of the screen.
2. Biological Treatment
The “Dorr Completreator” unit is provided for removal of organics from sewage. The Completreator is a complete
on site sewage treatment plant, specifically designed to accommodate all treatment facilities viz. contact
chamber, digestion chamber, stabilization chamber, clarifier mechanism as well as chlorination chamber in a
single tank installation.
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The Dorr Completreator Aeration plant employs the contact stabilization complete mixing flow sheet to provide
treatment for domestic waste. The raw sewage is aerated and completely mixed by high efficiency aeration grids.
The aerated influent is directed to the clarifier where the sludge settles. The settled sludge from the clarifier is
transferred to the stabilization chamber and digestion chamber by a sludge recirculation pump. The aerobic
digestion chamber overflows to the stabilization chamber. The stabilization chamber in turn overflows to the
contact chamber to mix with incoming raw sewage.
Any floating scum, which collects on the contact chamber, is carried into a launder, which runs the full width of
this chamber. The clarifier is kept clean of scum by a continuous mechanical skimmer, which also collects the
scum from the contact chamber and then pumps it for disposal into aerobic digester with the help of sludge
recycle pumps.
The “Dorr Completreator” has the following advantages:
This compact unit considerably reduces the land area required.
The erection costs are extremely low as compared to conventional plants.
It needs very little maintenance and supervision.
The Dorr Recirculation system eliminates the danger of bad smell and fly nuisance.
The plant can be located in the Hotel / Residential Premises, and hence it is unnecessary to install a long and
expensive sewer system.
The plant can be augmented in future by providing additional units.
The treated sewage from the clarifier is disposed to sea or can be routed to SBR inlet.
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PROCESS DESCRIPTION
Refer P & ID -A1-2070846 -601-1123 to 1141.
The detailed process scheme is as described below.
Oily effluent from various units gravitates to the existing API Separators (601-API-1001 A/B/C). Free floating oil
from all API Separators is removed by the installed oil skimmers, and gravitates to the Wet Slop Oil Sump (601-TK-
1050). The settled oily sludge is periodically withdrawn by gravity, and collected in the Oily & Chemical Sludge
Sump (601-TK-1045). The overflow from all the API units flows by gravity to the TPI Separator (601-TPI-1001
A/B/C).
In the TPI Oil Separators (601-TPI-1001 A/B/C), the effluent flows counter-currently downwards through the
corrugated plate pack. The residual free oil fraction separates in the plates and collects at the water surface in the
TPI unit, while the clarified waste passes down through the plate pack and overflows via the overflow launder
.The free floating oil collected at the TPI separator water surface removed by slotted pipe oil skimmer and
diverted to Wet Slop Oil Sump (601-TK-1050) by gravity while the settled sludge is withdrawn periodically and
transferred to the Oily & Chemical Sludge Sump (601-TK-1045).
From TPI separator the effluent gravitates to the Flash Mixing Tank (601-TK-1001 A). Hydrochloric acid (HCl) and
Caustic is dosed in the Flash Mixing Tank (601-TK-1001 A) for pH adjustment by HCl Solution Dosing Pumps (601-
P-1019 A/B/C) and Caustic Solution Dosing Pumps (601-P-1022 A/B/C) respectively. FeCl3 is also dosed by FeCl3
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Solution Dosing Pumps (601-P-1033 A/B) for demulsification of emulsified oil present in the effluent. Hydrogen
peroxide (H2O2) is added as required in the flash mixing tank for removal of sulphide in the effluent by means of
H2O2 Dosing Pumps (601-P-1017 A/B/C/D). Flash Mixing Tank Agitator (601-AG-1001 A) is provided in the Flash
Mixing Tank (601-TK-1001 A ) for proper mixing of all these chemicals with the effluent.
The effluent from Flash Mixing Tank (601-TK-1001 A) is gravitates to Flocculation Tank (601-TK-1002 A). The
deoiling polyelectrolyte solution is dosed in the flocculator by DOPE Solution Dosing Pumps (601-P-1023 A/B) for
flocculation of the demulsified effluent. Flocculation Tank Agitator (601-AG-1002 A) is provided in the
flocculation tanks for proper mixing and flocculation.
The effluent then gravitates to DAF Tanks (601-TK-1004 A/B). A side stream of clarified effluent from the DAF unit
is pumped by means of the DAF Recycle Pumps (601-P-1002 A/B/C) to Saturation Vessel (601-V-1001) into which
air is supplied under pressure from the DAF Air Compressors (601-K-1001 A/B). Air dissolves at high pressure in
this side stream, which is then allowed to enter the DAF unit via a pressure release valve, along with the main
flocculated effluent stream. On sudden release of pressure in the side stream effluent to atmospheric pressure,
the excess dissolved air in the over saturated effluent precipitates out as very fine air bubbles, which attach with
the free oil globules and flocculated solids in the main effluent stream and carry them to the surface as floating
sludge froth. The froth from DAF is removed periodically by means froth skimmer and flows by gravity to Wet Slop
Oil Sump (601-TK-1050). Settled solids are withdrawn periodically from the DAF underflow and diverted to Oily &
Chemical Sludge Sump (601-TK-1045) by gravity. The effluent from DAF overflow gravitates to pH Adjustment
Tank (601-TK-1005).
In the pH Adjustment Tank (601-TK-1005) based on requirement Hydrochloric acid (HCl) and Caustic is dosed for
pH adjustment by HCl Solution Dosing Pumps (601-P-1019 A/B/C ) and Caustic Solution Dosing Pumps ( 601-P-
1022 A/B/C) respectively. DAP & Urea Solution is dosed as required in the pH adjustment tank by Nutrient
Solution Dosing Pumps (601-P-1024 A/B). DAP & Urea are added as a source of Nitrogen 'N' & Phosphorous “P”
which are macro nutrients required for growth of microorganisms in biological systems. The effluent from pH
adjustment tank pumped to Sequential Batch Reactor – C Tech (056-SBR-1001) by SBR Feed Pumps (601-P-1003
A/B/C).
The C-TECH – System is operated in a batch reactor mode, which eliminates all the inefficiencies of the continuous
processes. A batch reactor is a perfect reactor, which ensures 100% treatment. Three modules are provided to
ensure continuous treatment. The complete process takes place in a single reactor, within which all biological
treatment steps take place sequentially.
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No additional settling unit / secondary clarifier is required.
The complete biological operation is divided into cycles. Each cycle is of 3-6 hrs duration (6 hours as design basis),
during which all treatment steps take place.
Explanation of cyclic operation:
A basic cycle comprises:
Fill-Aeration (F/A)
Settlement (S)
Decanting (D)
These phases in a sequence constitute a cycle, which is then repeated.
A Typical Cycle
During the period of a cycle, the liquid is filled in the C Tech Basin up to a set operating water level. Aeration
Blowers are started for aeration of the effluent. After the aeration cycle, the biomass settles under perfect
settling conditions. Once Settled the supernatant is removed from the top using a DECANTER. Solids are wasted
from the tanks during the decanting phase.
These phases in a sequence constitute a cycle, which is then repeated.
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A Typical C Tech Cycle
C Tech Components:
The C Tech system comprises the following features,
Flow Equalisation
C-TECH CAN HANDLE FLOW FLUCTUATION
Biological Selector zone
ENSURES NO FOAMING AND BULKING PROBLEMS
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Dissolved Oxygen Control to automatically control and optimise power consumption
ENSURES 20 - 30% POWER SAVINGS.
Co Current Nitrification and De nitrification, Phosphorous removal
PROVIDES NITROGEN AND PHOSPHOROUS REMOVAL TO REMOVE NUTRIENTS MAKING THE WATER SAFE FOR
WATER DISCHARGE
Decanter assembly in Stainless steel equipped with VFD to automatically control rate of decanting based on input
feed condition.
ENSURES NO CORROSION, LONG EQUIPMENT LIFE, NO MAINTENANCE
Diffusers for Aeration
OUTLET
INLE
T
DECANTER SELECTOR
AERATION
GRID
RAS/SAS PUMPS
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HIGHEST AERATION AND OXYGEN TRANSFER EFFICIENCY
Return sludge (RAS) recycle and Surplus sludge (SAS) pumps for sludge wasting from reactor only
REDUCES SPACE REQUIREMENT. NO SECONDARY CLARIFIER IS USED WHICH DRASTICALLY REDUCES CIVIL COST
AND CONSTRUCTION COST
PLC unit for complete automatic cycle control and operation
REDUCE MANPOWER COST. COMPLETE OPERATION CAN BE HOOKED TO CENTRAL CONTROL DESK.
Equalization tank
In refinery effluent where wide fluctuations are expected in the feed quality, it is very critical to provide an
equalization tank, which can normalize all input variations. This equalization facility has been provided inbuilt
within the C Tech basins.
Typically, for treating wastewaters with characteristics as mentioned in the inlet analysis, a Hydraulic detention
time of 36 to 40 hours is sufficient for C-Tech. However, we have provided 42.2 Hours detention time considering
additional 2.2 hours to cater to fluctuating load conditions. In effect, the Equalization tank is built into the C-Tech
basin.
The C-Tech basin has a fixed volume (for containing the biomass) and a variable volume (for containing the
effluent to be treated). This variable volume is designed such that it can hold fluctuating flow rates. In effect, this
volume acts like a equalization tank. C-Tech can absorb shock loads, as it is a batch process. Every batch is
completely treated and then discharged.
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The C-Tech system can take variable flow rate ranging from 30% to 100% of design flow.
Biological SELECTOR zone
The incorporation of a biological SELECTOR in the front end of the C-TECH- Systems distinguishes it from most of
the technologies. The raw effluent enters the SELECTOR zone, where ANOXIC MIX conditions are maintained. Part
of the treated effluent along with return sludge from the aeration basin is recycled in here, using RAS pumps. As
the microorganisms meet high BOD, low DO condition in the SELECTOR, natural selection of predominantly floc-
forming microorganisms takes place. This is very effective in containing all of the known low F/M bulking
microorganisms, eliminates problems of bulking and sludge foaming. This process ensures excellent settling
characteristics of the bio sludge. SVI of treated effluent of less than 120 is achieved in all seasons.
A coarse bubble aeration grid is provided in the selector to agitate sludge initially at the beginning of each cycle.
This operation is done for few minutes in each cycle through PLC controlled auto valve.
Also due to the anoxic conditions in the SELECTOR zone, Denitrification and phosphorous removal occurs in case
the Ammonical nitrogen and phosphorous levels are high in the effluent.
The instrument and control philosophy of selector zone is as follow:
Selector zone receives flow from the inlet channel. A motorized gate opens automatically as soon as the tank is
ready for next fill cycle based on timer settings. Once the filling is started, RAS pump starts automatically and
sludge recycle starts. There is no any speed control of the pump. It is again a timer controlled function linked to
time sequence of basin operation. When the filling period is over, RAS pump also stops. In the present case, the
sludge recycle is maintained at 2.16 times feed flow.
Another function in selector is operation of selector air valve. The selector air valve is opened during the start of
the aeration cycle for a preset time (which can be adjusted through HMI). During the settling and decanting
operation, the selector valve is in continuously open position.
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Dissolved Oxygen Control
The C Tech process uses measurement of dissolved oxygen (DO) levels in the basin to enhance treatment
efficiency and optimise power consumption. The DO concentration in the basin is continuously monitored using a
DO sensor. Once DO level is measured in the basins, a variable frequency drive automatically alters the aeration
blower rpm to maintain desired DO levels in the basin. This methodology provides a true in-basin method for the
efficient use of energy.
Decanter Assembly
The clean supernatant is removed from the basin using a Decanter assembly complete in stainless steel
construction. During decanting there is no inflow to the basin. The moving weir DECANTER is motor driven and
travels slowly from its “park” position to a designated bottom water level. Once the Decanting phase sets in, the
decanter automatically lowers to the required bottom level. Variable frequency drives are provided to control the
rate of movement of the Decanters.
VFD in decanter controls and adjusts the speed of the decanter as per system requirements. During aeration and
settling phase, decanter is stationed at PARK position. At the start of the decanting period, decanter moves up to
few centimetres above Top Water Level (TWL) at maximum speed so that the time taken is minimum. As soon as
it reaches TWL (sensed by float switch attached to decanter), it moves down at specified speed till it reaches
Bottom Water Level (BWL). During decanting, it moves at very slow speed to achieve desired decanting rate.
After the required level of supernatant is removed the Decanter is returned to its “park” position through reversal
of the drive. The basin is now ready for the next cycle to begin.
Operational Simplicity - Fully PLC based intelligent control
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The complete C-Tech plant operation is controlled automatically through a PLC system, which is a major factor in
reducing operating costs. This also prevents malfunctioning of the various set process parameters within the
plant. All key functions like, RAS, sludge wasting, aeration intensity, cycle time control, decanting rate etc are
automatically controlled without operator intervention as well as data logged. Complete historical records of
plant operation are available on touch of a button. All interlocks are shown in the P&I drawing.
The effluent from pH adjustment tank pumped to Sequential Batch Reactor – C Tech (056-SBR-1001) by SBR Feed
Pumps (601-P-1003 A/B/C). Based on the cyclic operation one of the Inlet Gate (GT-3001, 3002, 3003) will open
and effluent will be filled in one of the SBR Tank (601-SBR-1001 A/B/C). SBR Air Blower (601-K-1002 A/B/C/D/E/F)
will start and air will be introduced in the SBR Tank (601-SBR-1001 A/B/C) in which effluent is being filled. Also the
respective Return Sludge Pump (601-P-1004 A/B/C) will start and will recirculate the biosludge near the inlet.
After the set time interval, the aeration will stop in the SBR Tank (601-SBR-1001 A/B/C) which is under Fill &
Aeration Mode and settling will start. Also respective Return Sludge Pump (601-P-1004 A/B/C) will stop. At the
same time the Inlet Gate (GT-3001, 3002, 3003) of another SBR Tank (601-SBR-1001 A/B/C) will open and effluent
will be filled in this tank. Aeration will start in this tank and also respective Return Sludge Pump (601-P-1004
A/B/C) will start. After the set time interval for settling, the treated effluent from SBR Tank (601-SBR-1001 A/B/C)
will be decanted at the outlet launder by SBR Decanter Mechanism (601-P-1036 A/B/C). The cyclic operation - Fill
& Aeration, Settling and Decanting will continue and effluent will be treated continuously.
For detailed operation of SBR system (C-Tech), refer process operating manual of C-Tech submitted by SFC
Environmental Technologies Pvt. Ltd.
The treated effluent from SBR System (601-SBR-1001) is collected in MBR Feed Tank (601-TK-1034). It is then
pumped to Membrane Bio Reactor (MBR) System (601-MBR-1001).
The effluent of the SBR treatment will be collected in an MBR feed tank where submersible pumps will transfer
wastewater into the Bioreactor Splitter Box. Wastewater is combined with the recycled mixed liquor from the
membrane trains and is equally distributed into two biological trains. Supplemental carbon will be added in the
Splitter Box should the influent carbon be insufficient for the biological process. Sodium hydroxide and antifoam
agents will be added if required. A bypass of the SBR is included should the influent to the MBR be deficient in
nutrients which will affect the biological process.
Mixed liquor flows through each biological process train by gravity from the Anoxic Zone (601-TK-1042 A/B) to the
Aerobic Zone (601-TK-1043 A/B) and into the Bioreactor Collector Channel. Foam and scum are collected in a
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foam trap located at one end of the overflow channel via a motorized downward opening Weir Gate (GT-3301).
Foam/Was Pumps (601-P-1038 A/B) will transfer foam, scum and waste activated sludge to the sludge handling
facility.
Mixed Liquor Recirculation Pumps (601-P-1037 A/B/C) will transfer mixed liquor from the Bioreactor Collector
Channel into the Membrane Tank Splitter Channel. Mixed liquor flows by gravity into (4) parallel ZeeWeed®
Membrane Tanks (601-TK-1044 A/B/C/D) via partially submerged Sluice Gates (GT-3101/3102/3201/3202), which
are designed to ensure equal flow distribution to all the membrane tanks and same water level in all tanks. The
mixed liquor overflows to the Membrane Tank Collector Channel and it flows by gravity to the Bioreactor Splitter
Box where it is combined with the influent before entering the anoxic zones.
Clean water is withdrawn from the mixed liquor through the membrane using a dedicated MBR Permeate Pump
(601-P-1039 A/B/C/D) and is discharged to a common collector header discharging to the RO Feed Collection Tank
(601-TK-1007). Permeate will be used from this tank for back pulsing and cleaning the membranes by Backpulse
Pumps (601-P-1006 A/B).
The system is completed with membrane tank Drain Pumps (601-P-1040 A/B). These pumps are common to all
membrane trains and will drain the membrane tanks when required.
The membrane net flux is the most important parameter when designing a membrane filtration system. The
selection of conservative membrane flux depends on a number of factors including the minimum operating
temperature, flow rates, and assumed sludge characteristics. Our flux selection is based on design curves
developed from years of experience from full scale operating MBR plants under different conditions.
The membrane design for HPCL MBR consists of four (4) membrane trains with three (3) cassettes per train, each
cassette having 40 modules and each module having 31.59 m2 of surface area. This corresponds to 3,790.8 m2 of
membrane area installed per train and a total of 15,163.2 m2 of membrane area installed in the four (4) trains.
Each cassette has a maximum capacity of 48 modules, which means that a 16.7% spare space is included within
the installed cassettes. This percentage is within the range of our typical design (15-20% spare space).
Carbon Source Dosing Pumps (601-P-1041 A/B) will add a carbon source (i.e. methanol) to the Bioreactor Splitter
Box should the influent carbon be insufficient for denitrification.
Antifoam Dosing Pumps (601-P-1042 A/B) will add antifoam agents (approved by GEWPT) to the Bioreactor
Splitter Box should it be required.
A pH transmitter is located on the permeate collector header for monitoring purposes. As per specifications,
analyzers for silica, conductivity and TOC are also installed on the permeate collector header. A common
turbiditymeter is installed on the permeate collector header. A solenoid valve arrangement allows the
turbiditimeter to monitor each train and the common discharge.
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An SBR Bypass line is included in the design should the biological process require it. This by-pass provides
flexibility to the operation of the system as the influent wastewater might be deficient of nutrients affecting the
MBR biological process. The by-pass will provide nutrients to the system to maintain the biomass.
The two biological trains are identical. Each biological train is designed with two Anoxic Zone (601-TK-1042 A/B)
and two Aerobic Zone (601-TK-1043 A/B). Each anoxic zone has a dedicated Submersible Mixer (601-SM-1001
A/B) to ensure homogeneous mixed liquor, maximizing denitrification and alkalinity recovery.
From the anoxic zones, the mixed liquor flows to the aerobic tanks which are equipped with one (1) independent
fine bubble aeration grid that supplies oxygen necessary for the biological process as well as keeps the mixed
liquor fully mixed. The dropleg on each aeration grid is equipped with a motorized valve which allows aeration to
be cycled between zones. Process aeration is provided by a common group of positive displacement Process
Aeration Blowers (601-K-1003P D/E/F) completed with variable frequency drives. The air flow rate can be
regulated to control the DO level in the aerated zones. On each process train, the second aerobic zone has a
Dissolved Oxygen probe.
The mixed liquor flows by gravity from the aeration basins to the Bioreactor Collector Channel through partially
submerged gate valves to allow foam to pass.
The foam and scum are collected in the Foam/WAS Tank (601-TK-1053) located at one end of the Channel via a
motorized downward opening Weir Gate (GT-3301). Foam, scum and waste activated sludge are removed from
the system via Foam/Was Pumps (601-P-1038 A/B).
The mixed liquor is transferred to the Membrane Tank Splitter Channel via Mixed Liquor Recirculation Pumps
(601-P-1037 A/B/C) with a design flow rate of 5 times the influent flow (5Q).
The mixed liquor flows from the Channel into four (4) identical ZeeWeed® membrane trains. Each train is
equipped with partially submerged weir manual Sluice Gates (GT-3101/3102/3201/3202) which are designed to
ensure equal flow distribution and same water level in all Membrane Tanks (601-TK-1044 A/B/C/D. To protect
the membrane cassettes, a deflector plate is installed on the inlet of each tank.
Each train is designed with a dedicated MBR Permeate Pump (601-P-1039 A/B/C/D) (variable speed). The
permeate pump will generate a slight vacuum that draws water from the mixed liquor through the membranes.
Permeate flowrate demand is based on the influent flow with trim to the level in the bioreactor via control loops
in the programmable logic controller (PLC).
Since the membrane system operates under a slight vacuum, there will be a tendency for dissolved air to be
released from the water. In order to prime the permeate system, an ejector system (per membrane train) is
provided which incorporates the use of compressed air.
The permeate pumps discharge the treated water into a common collector header that discharges into the RO
Feed Collection Tank (601-TK-1007). Backpulse water will be from this tank. Chemicals for membrane cleaning
(i.e. sodium hypochlorite and citric acid) will be directly injected into the permeate header. Sodium Hypochlorite
Dosing Pumps (601-P-1027 A/B) and Citric Acid Dosing Pumps (601-P-129 A/B) are provided for the same.
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In order to maintain and chemically clean the membranes, permeate is used for backpulsing the membrane
trains. A common pair of Backpulse Pumps (601-P-1006 A/B) is used to service all membrane trains.
Membrane aeration is provided by a common group of air scour blowers. MBR Membrane Aeration Blowers (601-
K-1003M A/B/C) will discharge to a common air supply header leading to the membrane tanks. Each membrane
train is designed with two air headers in order to cycle air within each train via cyclic air valves.
The membrane tanks are drained by Drain Pumps (601-P-1040 A/B) that discharge to the Membrane Tank
Collector Channel.
The activated sludge flows by gravity to the Membrane Tank Collector Channel which terminates in a pipe that
recirculates the combined mixed liquor to the head of the bioreactor. The recirculated mixed liquor flow rate will
be 4 time the influent flow rate.
Common cleaning chemical dosing pumps with dedicated installed standby units are used to service all
membrane trains.
Membrane Cleaning Requirements
Cleaning is necessary to ensure a smoothly operating MBR. ZeeWeed® modules are based on a hollow fibre
geometry which is more versatile as cleaning can be carried out quickly, easily, and automatically.
GEWPT incorporates a multi-level approach to maintaining membrane performance in every MBR system. We
offer several cleaning strategies for membranes that ensure optimum permeate production with a minimum
investment in time and resources. The cleaning systems included for HPCL Refinery MBR System incorporate fully
automated processes such as relaxation, backpulsing, maintenance cleaning and recovery cleaning. The cleaning
methodology is very flexible and the system can be optimized to reduce the frequency of chemical cleaning based
on site specific conditions.
During normal operation, the GEWPT system is operated with a repeated filtration cycle, which consists of a
production period (permeation) followed by a relaxation or backpulse period. ZeeWeed® MBR systems have the
unique capability to operate in either relaxation or backpulse mode. Under normal conditions the system is
operated in relaxation mode, whereas during start-up or under conditions of poor sludge filterability the system
can be operated in backpulse mode. Details of the filtration cycle with relaxation and backpulse are provided
below.
The membrane filtration system, including membranes, headers and mechanical equipment is sized to produce
the design net flow rates under all operating scenarios.
Relaxation
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While operating in relax mode, the MBR Permeate Pump (601-P-1039 A/B/C/D) for each train is stopped
sequentially for a short period of time (30-45 sec) every 12-15 minutes to allow air scouring of the membrane
without permeation. No chemical or permeate is used during relaxation mode.
Process Flow Schematic – Relaxation Mode
Backpulse or Backwash
Under certain fouling conditions or when experiencing poor sludge characteristics, the ability to backpulse is
essential to maintaining a clean membrane. This feature allows for flexible and reliable system performance
during unexpected influent or process operating scenarios. Applying the backpulse cleaning option is one of the
simplest methods to ensure that immersed membranes retain optimum permeability throughout all operating
conditions.
Backpulsing involves reversing the flow through the membranes to slightly expand the membrane pores and
dislodge any particles that may have adhered to the membrane fibre surface. An entire membrane train is
backpulsed at a time using permeate stored in the RO Feed Collection Tank (601-TK-1007) with no addition of
chemicals.
For HPCL Refinery MBR System design, the Backpulse Pumps (601-P-1006 A/B) will provide the reverse flow at low
pressures.
An optimized backpulse cleaning schedule can ensure that the plant benefits from:
High membrane permeability;
Efficient plant operation with minimal downtime;
Reduced frequency of chemical cleans;
Lower consumption of cleaning chemicals.
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Process Flow Schematic – Backpulse Mode
Maintenance Clean
Sodium hypochlorite is used to oxidize organic foulants and citric acid to remove inorganic scaling.
For this project, maintenance cleaning is recommended up to once per week using sodium hypochlorite and once
per week using citric acid.
The maintenance cleaning procedure incorporates the following features;
Fully automated and the frequency is set by the operator;
Performed without draining the membrane tank;
< 1 hour duration per clean per train
Based on the site specific requirements, cleaning procedures can be modified to obtain effective cleaning and
maximize chemical savings.
Recovery Clean
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Recovery cleaning is required to restore the permeability of the membrane once the membrane becomes fouled.
A recovery clean should be initiated when permeability declines to less than 50% of initial stable permeability.
This will generally occur when the trans-membrane pressure (TMP) consistently exceeds 4-5 psi (vacuum) under
normal flow conditions. The recovery cleaning procedure consists of a chemical backpulse sequence, followed by
a chemical soak period. The cleaning chemical concentrations typically used to soak the membranes are sodium
hypochlorite (NaOCl) for the removal of organic foulants and citric acid for the removal of inorganic foulants.
For inorganic cleaning the acid soak concentration should have a pH between 2.5 – 3. Based on an influent
alkalinity of 1,730 mg/L as specified on table 1.2, citric acid will not be sufficient to reduce the pH to the target.
Therefore, addition of a strong acid, i.e. hydrochloric acid (HCl) is required. The amount of HCl required depends
solely on the water quality and it is not possible to determine. The process for adding this strong acid is fully
manual:
Dose citric acid to a concentration of 2,000 mg/L
Operator to measure pH in cleaning solution.
If pH > 2.5-3.0, add HCl manually to the tank
Aerate for 1 min to mix the acid and measure again
Repeat steps until desired pH is reached
Key features of the recovery cleaning procedure for ZeeWeed® membrane filtration system are:
Fully automated and initiated by the operator;
Cleans all membrane cassettes in a train at the same time;
Recommended up to four times per annum
Requires moderate chemical concentration
Spent cleaning chemicals will be neutralized with mixed liquor
For detailed process operation of MBR system refer Process Operating Manual of MBR system submitted by GE
Water & ZENON Membrane.
The treated effluent from MBR system outlet is RO system. The RO permeate from RO system is recycled back to
main process plant for reuse and RO rejects are disposed to sea.
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Reverse Osmosis Plant:
Osmosis is a natural process involving fluid flow across a membrane, which is said to be ‘semi-permeable’. A semi-
permeable membrane is selective in that certain components of a solution, usually the solvent can pass through,
while others, usually the dissolved solids cannot pass through it. Its chemical potential determines the direction of
solvent flow, which is a function of pressure, temperature and concentration of dissolved solids. In case pure
water is available on both sides of a semi-permeable membrane at equal pressure and temperature, no resultant
flow can occur across the membrane, as the chemical potential is equal on both the sides. However, if any soluble
salt is added on one side of the membrane, the chemical potential of the water on that side is reduced. The
osmotic flow from the pure water on one side to the salt solution on the other side will occur across the
membrane until equilibrium of solvent chemical potential is restored.
The Thermodynamic requirement for osmotic equilibrium is that the chemical potential of the solvent be the
same on both sides of the membrane. No such condition is imposed on the solute, since the membrane prevents
its passage. The Equilibrium State occurs when the pressure differential on the two sides is equal to the osmotic
pressure, a solution property that is independent of the membrane.
The application of external pressure to the solution side, which equals the osmotic pressure, will also accomplish
equilibrium. A further increase in pressure will increase the chemical potential of the water in the solution and
will cause a reversal of the osmotic flow towards the pure water side which is at a lower solvent chemical
potential relative to the solution. This phenomenon is termed as Reverse Osmosis and is the basis for a process to
desalinate water without phase change.
The treated effluent from MBR is further polished into RO plant to get the product water which can be use as feed
to DM plant, floor wash etc.
The treated effluent from MBR is collected in RO Feed Collection Tank (601-TK-1007). The effluent then pumped
to Cartridge Filters (601-CF-1001 A/B/C/D) by Cartridge Feed Pump (601-P-1007 A/B/C). In order to prevent the
precipitation of the salts on reject side, an antiscalant is added at the inlet of the cartridge filter by Antiscalant
Dosing Pumps (601-P-1028 A/B), which will result in inhibition of scales. Furthermore sodium bisulphite shall be
dosed by Sodium Bisulphite Dosing Pumps (601-P-1030 A/B) to remove free chlorine present in the feed water.
Presence of free chlorine in the feed water will irreversibly damage the RO membranes. HCl acid if required is also
dosed inlet of the cartridge filter to adjust the pH of the feed water by Acid Dosing Pumps –RO (601-P-1020 A/B).
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Micron cartridge filter is provided in order to remove micron size particles, which is additional safety. These
Cartridges are disposable type and should be replaced if differential pressure across cartridges approaches pre-
specified level.
The cartridge filter outlet is pumped to two stages Reverse Osmosis Train 1/2/3 (601-RO-1001 A/B/C) by high
pressure RO Feed Pumps (601-P-1008 A/B/C) for removal of TDS. In order to have flux balancing between two
stages inter stage Turbocharger (601-TC-1001 A/B/C) is provided between RO stage I & stage II.
Reverse Osmosis module consists of thin film composite Polyamide Membranes. On continuous running the R.O.
membranes get fouled with fine colloids, bacterial debris or some times carbonate scales. These need to be
removed and cleaned from the surface of the membrane.
The permeate from the RO plant is then stripped into Degasser Tower (601-DG-1001) for reduction of CO2 in
water.
Degasser Tower is filled with PP packing rings. Air is forced from the bottom of the tower by Centrifugal Blowers,
while the water flows down through the packed bed of PP rings. The carbonic acid present in the water splits up
into carbon dioxide gas and water. The reaction is as follows:
H2CO3 H2O + CO2
This carbon dioxide gas is stripped off and escapes from the top of the tower. The degassed water is collected in
the Permeate Water Storage Tank (601-TK-1009) and then treated water is pumped to DM Plant/Floor Wash by
Treated Water Transfer Pumps (601-P-1031 A/B/C). The pH of the treated water is maintained by dosing NaOH in
the RO permeate after degasification.
RO Membrane Fouling & Prevention
Fouling is the accumulation of foreign materials from feed water on the active membrane surface and/or on the
feed spacer to the point of causing operational problems. The term fouling includes the accumulation of all kinds
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of layers on the membrane and feed spacer surface, including scaling. More specifically, colloidal fouling refers to
the entrapment of particulate or colloidal matter such as iron flocs or silt, biological fouling (biofouling) is the
growth of a biofilm, and organic fouling is the adsorption of specific organic compounds such as humic substances
and oil on to the membrane surface.
Scaling refers to the precipitation and deposition within the system of sparingly soluble salts including calcium
carbonate, calcium sulfate, etc.
Pretreatment of feed water must involve a total system approach for continuous and reliable operation. For
example, an improperly designed and/or operated clarifier will result in loading the sand or multimedia filter
beyond its operating limits. Such inadequate pretreatment often necessitates frequent cleaning of the membrane
elements to restore productivity and salt rejection. The cost of cleaning, downtime and lost system performance
can be significant.
The proper treatment scheme for feed water depends on:
Feed water source
Feed water composition
Application
The type of pretreatment system depends to a large extent on feed water source (e.g., Industrial wastewater).
Industrial wastewaters have a wide variety of organic and inorganic constituents. Some types of organic
components may adversely affect RO membranes, inducing severe flow loss and/or membrane degradation
(organic fouling), making a well-designed pretreatment scheme imperative.
Scaling of RO membranes may occur when sparingly soluble salts are concentrated within the element beyond
their solubility limit. For example, if a reverse osmosis plant is operated at 50% recovery, the concentration in the
concentrate stream will be almost double the concentration in the feed stream. As the recovery of a plant is
increased, so is the risk of scaling.
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Due to water scarcity and environmental concern, adding a brine (RO concentrate) recovery system to increase
recovery has become more popular. To minimize precipitation and scaling, it is important to establish well-
designed scale control measures and avoid exceeding the solubility limits of sparingly soluble salts. In an RO
system, the most common sparingly soluble salts encountered are CaSO4, CaCO3, and silica. Other salts creating a
potential scaling problem are CaF2, BaSO4, SrSO4, and Ca3(PO4)2.
Most natural surface and ground waters are almost saturated with CaCO3. The solubility of CaCO3 depends on
the pH, as can be seen from the following equation:
Ca2 + + HCO3 H+ + CaCO3
By adding H+ as acid, the equilibrium can be shifted to the left side to keep calcium carbonate dissolved.
CaCO3 tends to dissolve in the concentrate stream rather than precipitate. This tendency can be expressed by the
Langelier Saturation Index (LSI) for brackish waters and the Stiff & Davis Stability Index (S & DSI) for seawaters. At
the pH of saturation (pHs), the water is in equilibrium with CaCO3.
The definitions of LSI and S & DSI are:
LSI = pH – pHs (TDS < 10,000 mg/L)
S & DSI = pH – pHs (TDS > 10,000 mg/L)
To control calcium carbonate scaling by acid addition alone, the LSI or S & DSI in the concentrate stream must be
negative.
Acid addition is useful to control carbonate scale only.
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Scale inhibitors (antiscalants) can be used to control carbonate scaling, sulfate scaling, and calcium fluoride
scaling. There are generally three different types of scale inhibitors: sodium hexametaphosphate (SHMP),
organophosphonates and polyacrylates.
Organophosphonates are more effective and stable than SHMP. They act as antifoulants for insoluble aluminum
and iron, keeping them in solution. Polyacrylates (high molecular weight) are generally known for reducing silica
scale formation via a dispersion mechanism.
Polymeric organic scale inhibitors are also more effective than SHMP. Precipitation reactions may occur, however,
with negatively charged scale inhibitors and cationic polyelectrolytes or multivalent cation (e.g., aluminum or
iron). The resulting gum-like products are very difficult to remove from the membrane elements. Hence dosage
rates on all antiscalant needs to be carefully selected in consultation with antiscalant manufacturers during
operation of the plant. Overdosing should be avoided. Make certain that no significant amounts of cationic
polymers are present when adding an anionic scale inhibitor.
Colloidal fouling of RO elements can seriously impair performance by lowering productivity and sometimes salt
rejection. An early sign of colloidal fouling is often an increased pressure differential across the system.
The source of silt or colloids in reverse osmosis feed waters is varied and often includes bacteria, clay, colloidal
silica, and iron corrosion products. Pretreatment chemicals used in a clarifier such as aluminum sulfate, ferric
chloride, or cationic polyelectrolytes are materials that can be used to combine these fine particle size colloids
resulting in an agglomeration or large particles that then can be removed more easily by either media or cartridge
filtration. Such agglomeration, consequently, can reduce the performance criteria of media filtration or the pore
size of cartridge filtration where these colloids are present in the feed water. It is important, however, that these
pretreatment chemicals become incorporated into the agglomerates themselves since they could also become a
source of fouling if not removed. In addition, cationic polymers may co precipitate with negatively charged
antiscalant and foul the membrane. Several methods or indices have been proposed to predict a colloidal fouling
potential of feed waters, including turbidity, Silt Density Index (SDI) and Modified Fouling Index (MFI). The SDI is
the most commonly used fouling index. The guideline is to maintain SDI15 at <3 is recommended.
CIP system is provided for cleaning of RO membranes. This system is consists of RO Cleaning Solution Tank (601-
TK-1011), RO Clean-up Pumps (601-P-1016 A/B) and Cartridge Filters (601-CF-1002 A/B). Based on the
requirement acid or caustic solution is prepared in Cleaning Solution Tank (601-TK-1011) by transferring required
amount of acid or caustic by Conc. HCl Unloading /Transfer Pumps (601-P-1018 A/B) and Caustic Lye Unloading /
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Transfer Pumps (601-P-1021 A/B). Then the solution is pumped to RO Train by RO Clean-up Pumps (601-P-1016
A/B) through Cartridge Filters (601-CF-1002 A/B).
Refer RO Process Operating Manual submitted by Aqua Tech Systems for detailed process operation of RO
system.
Spent Caustic Effluent Treatment
Spent caustic effluent is collected in Spent Caustic Storage Tank (601-TK-1003 A/B). It is pumped to Flash Mixing
Tank (601-TK-1001 B) by Spent Caustic Pumps (601-P-1001 A/B). In the flash mixing tank if required HCl is added
for pH corrections by HCl Solution Dosing Pumps (601-P-1019 A/B/C ). Also H2O2 is added for removal of sulphide
from spent caustic effluent by H2O2 Dosing Pumps (601-P-1017 A/B/C/D).. Flash Mixing Tank Agitator (601-AG-
1001 B) is provided in the tank for proper mixing of H2O2 & HCl . The effluent is then gravitates to Flocculation
Tank (601-TK-1002 C) in which DOPE is added if required. Flocculation Tank Agitator (601-AG-1002C) is provided
for proper mixing of DOPE with the effluent by DOPE Solution Dosing Pumps (601-P-1023 A/B). The treated spent
caustic effluent is either discharged to sea for disposal or can be diverted to DAF Tanks (601-TK-1004 A/B) based
on the quality of treated spent caustic effluent.
Sludge Treatment
The biosludge from SBR and MBR is collected in Biosludge Sump (601-TK-1047) and transferred to Biosludge
Thickener (601-ST-1002) by Biosludge Transfer Pump (601-P-1011 A/B). In the thickener feed DWPE (Bio) Solution
is added by DWPE (Bio) Solution Dosing Pumps (601-P-1026 A/B) to enhance the thickening of sludge. Belt
Cleaning Pump (601-P-1048) is provided for cleaning of belt of gravity belt thickener. The thickened biosludge
from thickener underflow collected in Thickened Biosludge Sump (601-TK-1048 A/B) which is provided with
Thickened Biosludge Sump Agitators (601-AG-1004 A/B) for uniform mixing of thickened sludge. It is then pumped
to Dewatering Biosludge Centrifuge (601-G-1002) by Thickened Biosludge Transfer Pump (601-P-1012 A/B). In the
centrifuge solid liquid separation take place. Polyelectrolyte is dosed at centrifuge inlet by DWPE (Bio) Solution
Dosing Pumps (601-P-1026 A/B) to enhance the solid liquid separation. Solid cakes from centrifuge discharge are
collected in a trolley and then send to further treatment / secure landfill. The centrate from centrifuge is collected
in a Supernatant Sump (601-TK-1049) and then transferred to API inlet by Supernatant Transfer Pump (601-P-
1013 A/B).
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The sludge from TPI, API, DAF and LR/LRE and drains from Flash Mixing Tanks, Flocculation Tanks is collected in
Oily & Chemical Sludge Sump (601-TK-1045). It is then pumped to Oily & Chemical Sludge Thickener (601-ST-
1001) by Oily & Chemical Sludge Transfer Pump (601-P-1009 A/B). In the thickener feed DWPE (Oily) Solution is
added by DWPE (Oily) Solution Dosing Pumps (601-P-1025 A/B) to enhance the thickening of sludge. The
thickened sludge is withdrawn from thickener underflow and collected in Thickened Oily & Chemical Sludge Sump
(601TK-1046 A/B. Thickened Oily & Chemical Sludge Sump Agitators (601-AG-1003 A/B) are provided in the sump
for uniform mixing of sludge. The sludge is then pumped to Dewatering Oily & Chemical Centrifuge (601-G-1001)
by Thickened Oily & Chemical Transfer Pump (601-P-1010 A/B). In the centrifuge solid liquid separation take
place. Polyelectrolyte is dosed at the centrifuge inlet by DWPE (Oily) Solution Dosing Pumps (601-P-1025 A/B) to
enhance the solid liquid separation. Solid cake from centrifuge discharge is send to Bioremediation Unit. Solid
cake from centrifuge discharge is collected in a trolley and then sends to further treatment / secure landfill. The
centrate from centrifuge is collected in a Supernatant Sump (601-TK-1049) and then transferred to API inlet by
Supernatant Transfer Pump (601-P-1013 A/B).
The wet slop oil from API, TPI & Spent Caustic Storage Tanks is collected in Wet Slop Oil Sump (601-TK-1050). It is
then transferred to Wet Slop Oil Storage Tank (601-TK-1010 A/B) by Wet Slop Oil Transfer Pump (601-TK-1014
A/B). LP/MP Steam is injected in Wet Slop Oil Sump as well as in Wet Slop Oil Storage Tank for separation of Oil.
Oil from Wet Slop Oil Storage Tank (601-TK-1010 A/B) is pumped to Refinery Slop Oil Tank by Dry Slop Oil Transfer
Pump (601-P-1015A/B).
Bio-Remediation
The treatment scheme for the bio-remediation of oily sludge is as follow:
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The treatment scheme consists of following treatment units:
Oily Sludge sump
Bioreactor Feed pumps
Bioreactor Tanks with air diffuser system
Air blowers
Nutrient Feed tank
Surfactant Feed tank
Acid/Alkali Feed tank
NUTRIENTS
SURFACTANT
ACID/ALKALI
AIR
BIO-REMEDIATED
SLUDGE FOR
DISPOSAL TO NON
HAZARDOUS LAND
FILL SITE
BIO-
REACTOR
SLUDGE SUMP
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Oily sludge generated from existing units of ETP- II and skim pond is collected in Oily Sludge Sump (601-TK-1052).
Characteristics of the sludge such as pH, TPH, TSS & Temperature are measured for pre-conditioning the sludge
before feeding it into Bioreactor (601-R-1037 A/B) by Bioreactor Feed Pumps (601-P-1045 A/B). Acid/Alkali is
added in bioreactor if required to keep the pH near neutral. Acid Feed Tank (601-TK-1038) and Alkali Feed Tank
(601-TK-1039) are provided for the same. Measured quantity of nutrients and surfactants are also added in
bioreactor. Nutrient Feed Tank (601-TK-1040) and Surfactant Feed Tank (601-TK-1041) are provided for the same.
Then the sludge is thoroughly mixed by recirculation using the feed pump.
The treatment in the bio-reactor is a batch process. There are two bio-remediation reactors provided. After pre-
conditioning, the oily sludge from the storage sump is pumped into the reactor. Required quantity of inoculum is
already present in the reactor (from the previous batch). For the first batch, required quantity of inoculums in the
form of fresh bacterial culture also needs to be added in the feed sump.
After filling the bio-reactor with required quantity of sludge and other chemicals, the contents are thoroughly
aerated using positive displacement Air Blowers (601-K-1006 A/B/C). A coarse bubble aeration system is installed
at the bottom of the reactor. This coarse bubble aeration system consists of air header and laterals with holes.
Aeration supplies required quantity of oxygen to bacteria and ensures degradation of oil in the sludge. The
process may take around 10 to 15 days.
After the treatment, sludge meets the outlet standards of US EPA for non hazardous landfill sites. The same
Bioreactor Feed Pumps (601-P-1045 A/B) can be used to withdraw sludge from the bio-reactors and pump to
disposal point.
During the degradation process, the bio-reactor requires minimum monitoring. Regular preventive maintenance
shall be made for blowers, etc. Flushing of lines prior and after feeding/discharge of sludge is required.
Refer Bio-remediation Process Operating Manual submitted by EWT Enviropro Water Tech for detailed process
operation of bio-remediation system.
VOC System
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Facilities are provided for Handling of Volatile Organic Compounds (VOC) in terms of their collection from oil-
handling units, routing to centralized VOC handling and control facilities to meet the VOC emission norms as per
statutory standards.
Carbon adsorption system is considered for the control of VOC based on the merit of the system and techno-
economic superiority on other systems as narrated in previous sections. The VOC has been estimated based on
the USEPA model for estimation of VOCs. System design / sizing calculations have been done based on the VOCs
estimated from the USEPA model and the breathing losses or displacement losses account for the volume
entering the VOC control system or due to volatility of the compound.
The VOC Control System consists closed loops of vents, carrying pipes, valves, ID fans, flame arrestors, carbon
filters and a vent to take out the VOC stripped air from the system. System is designed for compactness &
minimization of operation cost by putting up the VOC Control unit in the vicinity where VOC emissions are
generated.
The system is designed to accommodate the estimated flow rates and concentrations of the system, meet the
emission requirement of minimum 90% capture rate, and minimize pressure drop. The quantity of Carbon used
may vary based on actual operating conditions.
Carbon use rate is estimated based on the compounds present as identified. It is very difficult to estimates the
concentrations of various compounds that may appear at a particular time as refinery operations are diversified in
nature. Their concentrations may not necessarily be able to be specified in the incoming stream and the same are
estimated using chemical formulas and EPA guidelines/programs/model. As a precautionary note, it is
emphasized that this data is estimated only and actual operation will vary and may require operational
adjustments.
Another area of concern of the carbon adsorption system is that a high concentration level of some VOCs may
cause the carbon to generate heat on the bed since the adsorption is an exothermic reaction. This heat may
eventually build into a fire. Therefore the quantities of VOC’s in the dilution air need to remain below the Lower
Explosive Limit (LEL) to avoid the risk of fire. It may be necessary to use a LEL monitor or other device as
suggested to meter the level of VOC’s and add dilution air as necessary. As a design precaution, water quenching
and temperature measurement at the adsorption system are envisaged.
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The presence of higher concentrations of VOCs that may be present will shorten the life of the carbon beds.
Carbon needs replenished when the adsorption level drops below 90%. The main unit that is considered to be the
largest source of VOC is API separators. It has been observed that in a waste water treatment plant, VOC
emanating from API accounts for the Majority of the total VOC emissions from the ETP. The design of the system
uses the oil as the primary air borne VOC since the oil is taken as 100% on the liquid phase on top of the water.
The balance of VOCs is minor concentrations in comparison and consumes low levels of carbon.
For better safety, Thermocouple connections are provided in the carbon bed. The pipe length are optimized for
best plant layout and system is distributed in such a way that a balanced flow achieved in each of the sub-system.
The diameter is sized to maintain a good design velocity at full flow.
The VOC control system design provides the following benefits:
The system is designed to meet emission control requirements.
Low air pressure drop thus low operating cost
ID fans are designed to keep the flow rate in the pipe as required for the estimated concentration of VOC and well
below of LEL to improve safety of the system.
System flexibility to handle normal and minimum flows, pressures and temperatures. Field adjustment may be
required.
VOC emanating from API Separators (601-API-1001 A/B/C), TPI (601-TPI-1001 A/B/C), Flash Mixing Tank (601-TK-
1001 A/B), Flocculation Tank (601-TK-1002 A/B/C), Slop Oil Tank (601-TK-1050) and DAF Tank (601-TK-1004) is
collected by pipelines and send to Activated Carbon Filters (601-ACF-1001 A/B/C) through Flame Arrester (601-
FA-1002). Also VOC emanating from Slop Oil Storage Tanks (601-TK-1010 A/B) are fed by ID Fans (601-K-1007 A/B)
to the pipeline of above units through Flame Arrester (601-FA-1001). Volatile Organic Compounds are adsorbed
on the activated carbon surface and the outlet of activated carbon filters is vent off to atmosphere through Vent
Stack (601-VS-1001) by using ID Fans (601-K-1008 A/B). Hydrocarbon gas detectors are provided at the inlet and
outlet of Activated Carbon Filters.
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Refer VOC Process Operating Manual submitted by IIT, Roorkee for detailed process operation of VOC system.
Chemical Dosing & Handling Systems
HCl Dosing System
Concentrated HCl is unloaded from Acid Tanker to Conc. HCl Storage Tank (601-TK-1013) by Conc. HCl
Unloading/Transfer Pumps (601-P-1018 A/B). Service water and treated effluent is stored in Service Water Tank
(601-TK-1042) located above chemical house. The service water from this tank is taken into HCl dosing tanks for
dilution of HCl to about 10%. Conc. HCl is then transferred to HCl Solution Dosing Tanks (601-TK-1014 A/B) by
Conc. HCl Unloading/ Transfer Pumps (601-P-1018 A/B). The HCl Solution Dosing Pumps (601-P-1019 A/B/C) are
provided for dosing of HCl into pH Adjustment Tank (601-TK-1005), Flash Mixing Tanks (601-TK-1001 A/B) at a
controlled rate . Provision is also made to recycle the HCl solution from HCl dosing pumps to HCl dosing tanks.
Acid Solution Dosing Pumps-RO (601-P-1020 A/B) are provided for dosing acid at the inlet of Cartridge Filter (601-
CF-1001 A/B/C/D). Also Conc. HCl is transferred to RO Cleaning Solution Tank (601-TK-1011) by Conc. HCl
Unloading /Transfer Pumps (601-P-1018 A/B).
Caustic Dosing System
Caustic Lye is unloaded from Caustic Tanker to Caustic Lye Bulk Storage Tank (601-TK-1015) by Caustic Lye
Unloading / Transfer Pumps (601-P-1021 A/B). Caustic lye is transferred to Caustic Solution Dosing Tanks (601-TK-
1016 A/B) by Caustic Lye Unloading / Transfer Pumps (601-P-1021 A/B). The service water from Service Water
Tank (601-TK-1042) is taken into Caustic dosing tanks for dilution of caustic to about 10%. The Caustic Solution
Dosing Pumps (601-P-1022 A/B/C) are provided for dosing of caustic into pH Adjustment Tank (601-TK-1005),
Flash Mixing Tanks (601-TK-1001 A) and MBR System at a controlled rate . Provision is also made to recycle the
caustic solution from caustic dosing pumps to caustic dosing tanks. Also Caustic Lye is transferred to RO Cleaning
Solution Tank (601-TK-1011) by Caustic Lye Unloading / Transfer Pumps (601-P-1021 A/B).
DOPE Dosing System
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DOPE Dosing Tanks (601-TK-1017 A/B) with DOPE Dosing Tank Agitators (601-AG-1006 A/B) are provided for
preparation of DOPE solution. The service water from Service Water Tank (601-TK-1042) is taken into the dosing
tank so that the agitator’s blades are submerged in the water. Agitator is started and the required quantity DOPE
is added slowly into the tank. The service water is added up to the overflow nozzle. Agitators are stopped after
about 1-2 hrs. The DOPE solution is dosed into the Flocculation Tanks -601-TK-1002 A/B/C) by DOPE Solution
Dosing Pumps (601-P-1023 A/B).
DWPE (Oily) Dosing System
DWPE (Oily) Dosing Tanks (601-TK-1019 A/B) with DWPE (Oily) Dosing Tank Agitators (601-AG-1008 A/B) are
provided for preparation of DWPE solution. The service water from Service Water Tank (601-TK-1042) is taken
into the dosing tank so that the agitators blades are submerged in the water. Agitator is started and the required
quantity DWPE (Oily) is added very slowly into the tank. The service water is added up to the overflow nozel.
Agitators are stopped after about 1-2 hrs. The DWPE (Oily) solution is dosed into the Oily & Chemical Sludge
Thickener (601-ST-1001) and Dewatering Oily & Chemical Sludge Centrifuge (601-G-1001) by DWPE (Oily)
Solution Dosing Pumps (601-P-1025 A/B).
DWPE (Bio) Dosing System
DWPE (Bio) Dosing Tanks (601-TK-1020 A/B) with DWPE (Bio) Dosing Tank Agitators (601-AG-1009 A/B) are
provided for preparation of DWPE solution. The service water from Service Water Tank (601-TK-1042) is taken
into the dosing tank so that the agitators blades are submerged in the water. Agitator is started and the required
quantity DWPE (Bio) is added very slowly into the tank. The service water is added up to the overflow nozel.
Agitator is stopped after about 1-2 hrs. The DWPE (Bio) solution is dosed into the Bio Sludge Thickener (601-ST-
1002) and Dewatering Bio Sludge Centrifuge (601-G-1002) by DWPE (Bio) Solution Dosing Pumps (601-P-1026
A/B).
FeCl3 Dosing System
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FeCl3 Solution Dosing Tanks (601-TK- 1026 A/B) with FeCl3 Solution Dosing Tank Agitators (601-AG-1015 A/B) are
provided for preparation of FeCl3 solution. The service water from Service Water Tank (601-TK-1042) is taken
into the dosing tank so that the agitator blades are submerged in the water. Agitator is started and the required
quantity FeCl3 is added slowly into the tank. The service water is added up to the overflow nozel. Agitator is
stopped after about 1-2 hrs. The FeCl3 solution is dosed into the Flash Mixing Tank (601-TK-1001 A) by FeCl3
Solution Dosing Pumps (601-P-1033 A/B).
Nutrients Dosing System
Nutrients Solution Dosing Tanks (601-TK1018 A/B) with Nutrients Solution Dosing Tanks Agitators (601-AG-1007
A/B) are provided for preparation of nutrients solution. The service water from Service Water Tank (601-TK-1042)
is taken into the dosing tank so that the agitator blades are submerged in the water. Agitator is started and the
required quantity Nutrients (DAP & Urea) is added slowly into the tank. The service water is added up to the
overflow nozel. Agitator is stopped after about 1 hrs. The nutrients solution is dosed into the pH Adjustment Tank
(601-TK-1005).
H2O2 Dosing System
H2O2 is unloaded from the H2O2 tanker to H2O2 Storage Dosing Tanks (601-TK-1012 A/B) by H2O2 Unloading
Pumps (601-P-1023 A/B). The H2O2 is dosed into the Flash Mixing Tanks (601-TK-1001 A & B) by H2O2 Dosing
Pumps (601-P-1017 A/B/C/D).
Sodium Hypochlorite (NaOCl) Dosing System
Sodium Hypochlorite Dosing Tank (601-TK-1021) is provided for preparation of NaOCl solution. The service water
from Service Water Tank (601-TK-1042) is taken into the dosing tank and required quantity of NaOCl (approx
10.8%) is added manually into the tank. The service water is added up to the overflow nozzle. The diluted NaOCl
solution is dosed by Sodium Hypochlorite Dosing Pumps (601-P-1027 A/B) to the membrane installed in MBR
Tanks during cleaning step of MBR system operation.
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Citric Acid Dosing System
Citric Acid Dosing Tank (601-TK-1023) is provided for preparation of citric acid solution. The service water from
Service Water Tank (601-TK-1042) is taken into the dosing tank and required quantity of citric acid (approx 50%) is
added manually into the tank. The service water is added up to the overflow nozzle. The diluted citric acid
solution is dosed by Citric Acid Dosing Pumps (601-P-1029 A/B) to the membrane installed in MBR Tanks during
cleaning step of MBR system operation.
Carbon Source Dosing System
Carbon Source Dosing Tank (601-TK-1035) is provided for preparation of carbon source (methanol) solution. The
service water from Service Water Tank (601-TK-1042) is taken into the dosing tank and required quantity of
methanol is added manually into the tank. The service water is added up to the overflow nozzle. The diluted
methanol solution is dosed by Carbon Source Dosing Pumps (601-P-1041 A/B) to the Bioreactor Splitter of MBR
System.
Antifoam Dosing System
Antifoam Dosing Tank (601-TK-1036) is provided for preparation of Antifoam solution. The service water from
Service Water Tank (601-TK-1042) is taken into the dosing tank and required quantity of liquid antifoam is added
manually into the tank. The service water is added up to the overflow nozzle. The antifoam solution is dosed by
Antifoam Dosing Pumps (601-P-1042 A/B) to the Bioreactor Splitter of MBR System.
Sodium Bisulphite Dosing System
Sodium Bisulphite Dosing Tanks (601-TK- 1024 A/B) with Agitators (AG-013 A/B) are provided for preparation of
Sodium Bisulphite solution. The service water from Service Water Tank (601-TK-1042) is taken into the dosing
tank so that the agitator blades are submerged in the water. Agitator is started and the required quantity Sodium
Bisulphite is added slowly into the tank. The service water is added up to the overflow nozzle. Agitator is stopped
after about 1-2 hrs. The Sodium Bisulphite solution is dosed into the inlet of Cartridge Filter (601-CF-1001
A/B/C/D) by Sodium Bisulphite Dosing Pumps (601-P-1030 A/B).
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Antiscalant Dosing System
Antiscalant Dosing Tanks (601-TK- 1022 A/B) with Agitators (AG-011 A/B) are provided for preparation of
Antiscalant solution. The service water from Service Water Tank (601-TK-1042) is taken into the dosing tank so
that the agitator blades are submerged in the water. Agitator is started and the required quantity Antiscalant is
added slowly into the tank. The service water is added up to the overflow nozzle. Agitator is stopped after about
1-2 hrs. The Antiscalant solution is dosed into the inlet of Cartridge Filter (601-CF-1001 A/B/C/D) by Sodium
Bisulphite Dosing Pumps (601-P-1030 A/B).
Sanitary Waste Treatment
Sanitary effluent is collected in Sanitary Sewage Sump (601-TK-1051). The raw sewage is then pumped to a
Completreator (601-CT-1001). Completreator is a complete on site sewage treatment plant, specifically designed
to accommodate all treatment facilities viz. Bar Screen Chamber (601-BS-1001), Digestion Chamber (601-TK-
1028), Stabilization Chamber (601-TK-1029), Contact Chamber (601-TK-1030), Secondary Clarifier (601-CL-1033)
and Treated Sanitary Waste Tank (601-TK-1031) in a single tank installation.
The incoming raw sewage is passed through Bar Screen Chamber (601-BS-1001) where floating (suspended)
material will be removed. The raw sewage is then aerated and completely mixed by high efficiency aeration grids
in Digestion Chamber (601-TK-1028), Stabilization Chamber (601-TK-1029), Contact Chamber (601-TK-1030). The
air is supplied to aeration grids by Air Blowers (601-K-1005 A/B). The aerated influent is directed to the Secondary
Clarifier (601-CL-1033) where the sludge settles. The settled sludge from the clarifier is transferred to the
stabilization chamber and digestion chamber by Sludge Recycle Pump (601-P-1035 A/B). The aerobic digestion
chamber overflows to the stabilization chamber. The stabilization chamber in turn overflows to the contact
chamber to mix with incoming raw sewage. The floating scum in clarifier is collected in sum pit and recycled back
to digestion chamber by recycle pumps. The treated sewage from clarifier overflows to Treated Sanitary Waste
Tank (601-TK-1031). Treated sewage is send to SBR system or disposed into sea by Treated Sewage Transfer
Pump (601-P-1049 A/B).
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Tender 12000123-HD-48002 Annexure-1, Page No.77
INSTRUMENTATION & CONTROL PHILOSOPHY
Running/stop indications of all drives (motors, agitators. etc.) are provided in the control room. A dedicated
PC/PLC based control system has been envisaged for the ETP and the same is housed in a Control Room located in
the Chemical House building within the IETP area. For all types of tanks/sumps/pits, Non Contact type SMART
Radar type Level Transmitters (including the interface level) are used as primary level measurement device and
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Tender 12000123-HD-48002 Annexure-1, Page No.78
for secondary level measurement, mechanical float operated gauges are provided. Switching action will be in PLC.
Level transmitter will be used for local & control room level indication and for tripping purposes (including low &
high levels alarms in the control room). Switching will be in PLC.
Incoming and Outgoing Lines
Suitable type of flow measurement systems (orifice type for fluids without solid particles and magnetic type for
fluid with solid particles) with local and control room indication along with recording and totalizing facilities (in
Control Room) are provided on incoming effluent feed (pressure lines) & utility lines (except instrument air &
drinking water), and outgoing lines (e.g. treated effluent, slop oil, etc.) with PG and double block valves with a
spectacle blind provision at IETP battery limit.
The following are flow transmitters are provided on the incoming and outgoing lines.
Sl no
Tag No. Type of Instrument Service
1. 601-FIT-2301 Magnetic Type Flow transmitter 8" Line from Crude Desalter FR /FRE
2. 601-FIT-2302 Magnetic Type Flow transmitter 8" Line from Sour water stripper -GFEC
3. 601-FIT-2303 Magnetic Type Flow transmitter 4" Line from LR units
4. 601-FIT-2304 Magnetic Type Flow transmitter Effluent from ATF effluent transfer Pumps
5. 601-FIT-2305 Magnetic Type Flow transmitter Effluent from P-175 Sump
6. 601-FIT-2306 Magnetic Type Flow transmitter Effluent from DWS ETP feed pumps
7. 601-FIT-2307 Magnetic Type Flow transmitter Effluent from LR/LRE floor wash pumps
8. 601-FIT-2308 Magnetic Type Flow transmitter Effluent from new LR/LRE ETP feed pumps
9. 601-FIT-2309 Magnetic Type Flow transmitter
Common Header of spent caustic lines coming
from OSBL area.
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10. 601-FIT-2310 Magnetic Type Flow transmitter Sludge from LR/LRE sludge pumps
11. 601-FIT-2311 DP Type flow transmitter Service water header from B/L
12. 601-FIT-2312 DP Type flow transmitter LP steam from B/L
13. 601-FIT-2313 DP Type flow transmitter Plant air header from B/L
14. 601-FIT-2316 Magnetic Type Flow transmitter Spent caustic from CR-LPG units (GFEC)
15. 601-FIT-2317 Magnetic Type Flow transmitter Spent caustic from NHTISOM / NHTCCR (GFEC)
16. 601-FIT-2318 Magnetic Type Flow transmitter Spent caustic from PC-D-200 pumps
17. 601-FIT-2319 Magnetic Type Flow transmitter
Spent caustic from NMPI / NMP II/NMP III spent
caustic pumps
18. 601-FIT-2401 Magnetic Type Flow transmitter Oily effluent from units to API separators.
19. 601-FIT-2501 DP Type flow transmitter
Treated water transfer pump (601-P-1031-A/B)
header
Sanitary Sewage Sump (601-TK-1051) & Raw Sewage Transfer Pumps (601-P-1034 A/B)
The sump is provided with Non Contact SMART Radar type Level Transmitter (LT 2901), secondary level
measurement device Level Indicator (LI-2902), with local & control room indication, high/low alarms in control
room and interlocks to trip the Raw Sewage Transfer Pump (601-P-10330 A/B) at low-low level. Downstream of
these pumps, there is Magnetic Type Flow Transmitter (FIT-2901) with local and control room indication along
with totalizing facilities in Control Room.
Secondary Clarifier (601-CL-1033)
The clarifier drive mechanism has been provided with a Torque Indication (TQSH 2903) as well as interlock for
high torque alarm and drive motor auto trip.
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Treated Sanitary Waste Tank (601-TK-1031)
The tank is provided with a Level Transmitter (LIT 2902) and indicator controller with local and control room
indication. Also provided with high and low level alarm in the control room as well as interlock for auto trip of
Treated Sewage Transfer Pump (601-P-1049 A/B) at low-low level in the tank.
Treated Sewage Transfer Pump (601-P-1049)
Orifice Type Flow Transmitter (FIT-2903) has been provided in the pump discharge line with local and control
room indication and also totalizing facility.
DAF System - DAF Tank (601-TK-1004 A/B), Saturation Vessel (601-V-1001), Recycle Pumps (601-P-1002 A/B/C) &
Air Compressor (601-K-1001 A/B)
Magnetic Type Flow Transmitter (FIT-2403 & FIT-2404) with local & Control Room Indication with associated
piping are provided at a suitable point to help measure and control (by means of the pressure regulating valve or
manually by globe valve) the recycle flow to individual compartments of the Flotation Tank. Air supply line to
Saturation Vessel is provided with air filter, air supply pressure gauge, pressure regulator, pressure gauge
(downstream of Pressure regulator), and Flow Indicator (FI-2405) for local indication, check valve, etc. as required
to ensure the required quantity of air taken to the system. Saturation Vessel is provided with safety relief valve,
pressure gauge, Level Gauge (LG-2404), and Level Transmitter (LIT-2403) with corresponding high/low alarms. A
solenoid valve is provided on the air supply line to saturation vessel and the solenoid valve will be auto activated
by the level in the vessel to close at low level and open at high level. Pressure regulating valve is installed near the
inlet to the Flotation Unit.
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pH Adjustment Tank (601-TK-1005) & Biological Feed Sump
It is ensured that appropriate quantity of the acid/caustic is dosed in the pH adjustment tank in relation to adjust
pH of the effluent. On-line pH Analyzer (AE-2403) and auto pH-Adjustment facility is provided for the same which
will control the dosing rate of acid/caustic by variation in dosing pump speed (VFD Control). Biological feed sump
is provided with Non Contact SMART Radar type Level Transmitter (LIT-2404), secondary level measurement
device - Level Indicator (LI-2403), local & control room indication, high/low alarms in control room and interlocks
to trip tank agitator and SBR Feed Pumps at low level.
Permeate Water Storage Tank (601-TK-1009) and Treated Water Transfer Pumps (601-P-1031 A/B/C)
Permeate Water Storage Tank (601-TK-1009) is provided with Non Contact SMART Radar type Level Transmitter
(LIT 3702), secondary level measurement device –Level Indicator (LI-3702), local and control room indication,
high/low alarms in control room and interlocks to trip the Treated Water Transfer Pumps (601-P-1031 A/B/C) at
low low level and at high level, RO Train (601-RO-1001 A/B/C) in service will proceed to standby.
MBR Feed Tank (601-TK-1034) & MBR Feed Pumps (601-P-1044 A/B/C)
The tank has been provided with Level Transmitter (LIT-2501), local and control room indication, high and low
level alarms in control room and interlocks to trip the MBR Feed Pumps (601-P-1044 A/B/C) at low level in MBR
Feed Tank (601-TK-1034) and also trip pump at high high level in MBR Bioreactor Collector Basin.
Wet Slop Oil Sump (601-TK-1050) & Wet Slop Oil Transfer Pumps (601-P-1014 A/B)
Sump is provided with Non Contact SMART Radar type Level Transmitter (LIT-2608), secondary level
measurement device- Level Indicator (LI-2608), local & control room indication, high/low alarms in control room
and interlock to trip the Wet Slop Oil Transfer Pumps (601-P-1014 A/B) at low level in the Wet Slop Oil Sump (601-
TK-1050).
Slop Oil Storage Tanks (601-TK-1010 A/B) & Dry Slop Oil Transfer Pumps (601-P-1015 A/B)
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Tender 12000123-HD-48002 Annexure-1, Page No.82
Tanks are provided with Non Contact SMART Radar type Level Transmitters (LIT-2609 & LIT-2610), secondary level
measurement device -Level Indicator (LI-2609 & LI-2610), local & control room indication, high/low alarms in
control room and interlocks to trip Dry Slop Oil Transfer Pumps (601-P-1015 A/B) at low level in tank. Interface
(oil-water) Level Indicators (LIT-2611 & LIT-2612) are also provided in the tanks with local & control room
indication and low level alarms. After holding the tank contents for sufficient time, water can be drained from
bottom (through drain valve) and upon receiving the interface low-level alarm, drain valve will be closed and
thereafter dry slop will be pumped to the offsite refinery slop oil tank. Tanks are provided with Temperature
Indicators (TI-2609 & TI-2610) for local & control room indication. High/Low temperatures will also activate
corresponding alarms in the control room. A flow measuring device -Flow Transmitter (FIT-2602) is provided in
the discharge line of the Dry Slop Oil Transfer Pumps (601-P-1015 A/B) with flow indication local and at control
room along with recording cum totalizing facility is provided at Control Room for measuring the dry slop
transferred to offsite slop oil tank at the refinery.
Oily & Chemical Sludge Sump (601-TK-1045), Oily & Chemical Sludge Pumps (601-P-1009 A/B) and Oily & Chemical
Sludge Thickener (601-ST-1001)
Sump is provided with Non Contact SMART Radar type Level Transmitter (LIT-2601), local & control room
indication, high/low alarms in control room and interlocks. Low level in the Oily & Chemical Sludge Sump (601-TK-
1045) will auto trip Oily & Chemical Sludge Pumps (601-P-1009 A/B). A local Temperature Indicator (TI-2601) is
provided in the sludge sump. Oily & Chemical Sludge Thickener (601-ST-1001) is provided with running indication
of the motor in the control room. A Torque Switch (TQSH-2610) is provided with high alarm in control room with
corresponding interlock to trip thickener mechanism at high torque level.
Thickened Oily & Chemical Sludge Sumps (601-TK-1046 A/B), Thickened Oily & Chemical Sludge Pumps (601-P-
1010 A/B) and Dewatering Oily & Chemical Sludge Centrifuge (601-G-1001)
The thickened underflow sludge from Oily & Chemical Sludge Thickener (601-ST-1001) is collected in Thickened
Oily & Chemical Sludge Sumps (601-TK-1046 A/B). The agitator in the sump followed by Pumps (after allowing
sump contents to be agitated) will be started manually. Sumps are provided with Non Contact SMART Radar type
Level Transmitters (LIT-2602 & LIT-2603), secondary level measurement device -Level Indicators (LI-2602 & LI-
2603), local & control room indication, high/low alarms in control room and interlocks. Low level in sump will
auto trip the Thickened Oily & Chemical Sludge Pumps (601-P-1010 A/B) and Agitators (601-AG-1003 A/B) in the
sump. The dewatering centrifuge has instrumentation interconnection with the Thickened Sludge Pumps. In the
event of Thickened Oily & Chemical Sludge Pumps (601-P-1010 A/B) trips, the Dewatering Oily & Chemical Sludge
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Tender 12000123-HD-48002 Annexure-1, Page No.83
Centrifuge (601-G-1001) will also trip simultaneously (after a specified time lag). In case the centrifuge trips, the
thickened sludge pump (centrifuge feed) should trip. Local Temperature Indicators (TI-2602 & TI-2603) are also
provided in the Thickened Oily & Chemical Sludge Sumps (601-TK-1046 A/B).
Bio Sludge Sump (601-TK-1047), Bio Sludge Pumps (601-P-1011 A/B) and Bio Sludge Thickener (601-ST-1002)
Sump is provided with Non Contact SMART Radar type Level Transmitter (LIT-2604), local & control room
indication, high/low alarms in control room and interlocks. Low level in the Bio Sludge Sump (601-TK-1047) will
auto trip Bio Sludge Pumps (601-P-1011 A/B). A local Temperature Indicator (TI-2604) is provided in the sludge
sump.
Thickened Bio Sludge Sumps (601-TK-1048 A/B), Thickened Bio Sludge Pumps (601-P-1012 A/B) and Dewatering
Bio Sludge Centrifuge (601-G-1002)
The thickened bio sludge from Bio Sludge Thickener (601-ST-1002) is collected in Thickened Bio Sludge Sumps
(601-TK-1048 A/B). The agitator in the sump followed by Pumps (after allowing sump contents to be agitated) will
be started manually. Sumps are provided with Non Contact SMART Radar type Level Transmitters (LIT-2605 & LIT-
2606), secondary level measurement device -Level Indicators (LI-2605 & LI-2606), local & control room indication,
high/low alarms in control room and interlocks. Low level in sump will auto trip the Thickened Bio Sludge Pumps
(601-P-1012 A/B) and Agitators (601-AG-1004 A/B) in the sump. The dewatering centrifuge has instrumentation
interconnection with the Thickened Sludge Pumps. In the event of Thickened Bio Sludge Pumps (601-P-1012 A/B)
trips, the Dewatering Bio Sludge Centrifuge (601-G-1002) will also trip simultaneously (after a specified time lag).
In case the centrifuge trips, the thickened sludge pump (centrifuge feed) should trip. Local Temperature
Indicators (TI-2605 & TI-2606) are also provided in the Thickened Bio Sludge Sumps (601-TK-1048 A/B).
Supernatant Sump (601-TK-1049) & Supernatant Transfer Pumps (601-P-1013 A/B)
Sump is provided with Level Transmitter (LIT-2607), secondary level measurement device- Level Indicator (LI-
2607), local & control room indication, high/low alarms in control room and interlock to trip the Supernatant
Transfer Pumps (601-P-1013 A/B) at low level in the Supernatant Sump (601-TK-1049). A Flow Transmitter (FIT-
2601) is provided on the discharge line of these pumps.
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Bulk Chemicals Storage Tanks & Pumps
Liquid chemicals required in bulk quantities such as Hydrogen Peroxide, Con HCL, Caustic Lye are stored in
Storage Tanks. Each tank is provided with Non Contact SMART Radar type Level Transmitter, secondary level
measurement device, local & control room indication, high/low alarms in control room and at low level & high
level in the tank the Unloading/Transfer Pumps will trip in case of Con HCl & Caustic Lye. In case of Hydrogen
Peroxide, at low level in the tank Dosing Pumps will trip and at high level in the tank Unloading Pumps will trip.
The pump discharge is provided with Flow element-transmitter for indication with recording cum totalizing facility
at the control Room. Local flow indicator is also provided. The tag numbers of various instruments are as follows.
Storage Tank Level Transmitter Level Indicator Unloading/Transfer
Pumps
Flow Transmitter
H2O2 Storage Tank (601-
TK-1012 A/B)
LIT-2803 & LIT-
2804
LI-2805 & LI-
2806
601-P-1032 A/B FIT-2801
Con HCl Storage Tank (601-
TK-1013)
LIT-2701 LI-2711 601-P-1018 A/B FT-2714
Caustic Lye Storage Tank
(601-TK-1015)
LIT-2708 LI-2712 601-P-1021 A/B FT-2715
All Chemical Solution Dosing Tanks & Pumps
For chemical solution dosing tanks, two (2) Nos. level measurement instruments is provided for each tank.
Primary level measurement instrument is a Non Contact type SMART Radar type Level Transmitter whereas
secondary level measurement instrument is level gauge. Level transmitter is to be used for local & control room
level indication and for tripping purposes (auto trip of dosing pumps and agitators) including low & high levels
alarms in the control room. Switching will be in PLC. All the dosing pumps have in built pressure safety relief
valves at their respective discharge lines. The tag numbers of various instruments are as follows.
Dosing Tank Level Transmitter Level Indicator Dosing Pumps Flow Indicator
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Tender 12000123-HD-48002 Annexure-1, Page No.85
H2O2 Storage Tanks (601-TK-1012
A/B)
LIT-2803 & LIT-
2804
LI-2805 & LI-
2806
601-P-1017 A/B
601-P-1017 C/D
FI-2802
FI-2803
HCl Dosing Tanks (601-TK-1014
A/B)
LIT-2702 & LIT-
2703
LG-2701 & LG-
2702
601-P-1019 A/B/C
601-P-1020 A/B
FI-2706, FI-2707 &
FI-2708
FI-3702
Caustic Dosing Tanks (601-TK-1016
A/B)
LIT-2709 &
LIT-2710
LG-2707 & LG-
2708
601-P-1022 A/B/C
601-P-1051 A/B
FI-2711, FI-2712 &
FI-2713
FI-3705
DOPE Dosing Tanks (601-TK-1017
A/B)
LIT-2704 &
LIT-2705
LG-2703 & LG-
2704
601-P-1023 A/B FI-2703, FI-2704 &
FI-2705
DWPE (Bio) Dosing Tanks (601-TK-
1020 A/B)
LIT-2706 &
LIT-2707
LG-2705 & LG-
2706
601-P-1026 A/B FI-2701 & FI-2702
DWPE (Oily) Dosing Tanks (601-TK-
1019 A/B)
LIT-2711 &
LIT-2712
LG-2709 & LG-
2710
601-P-1025 A/B FI-2709 & FI-2710
FeCl3 Dosing Tanks (601-TK-1026
A/B)
LIT-2806 &
LIT-2807
LG-2803 & LG-
2804
601-P-1033 A/B FI-2804
Nutrients Dosing Tanks (601-TK-
1018 A/B)
LIT-2801 &
LIT-2802
LG-2801 & LG-
2802
601-P-1024 A/B FI-2801
NaOCl Dosing Tank (601-TK-1021) LIT-3501
LG-3501 601-P-1027 A/B FI-3501
Citric Acid Dosing Tank (601-TK-
1023)
LIT-3502
LG-3502 601-P-1029 A/B FI-3502
Carbon Source Dosing Tank (601-
TK-1035)
LIT-3503
LG-3503 601-P-1041 A/B FI-3503
Antifoam Dosing Tank (601-TK- LIT-3504 LG-3504 601-P-1042 A/B FI-3504
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1036)
Sodium Bisulphite Dosing Tank
(601-TK-1024 A/B)
LIT-3704 & LIT-
3705
LG-3703 & LG-
3704
601-P-1030 A/B FI-3704
Antiscalant Dosing Tank (601-TK-
1024 A/B)
LIT-3706 & LIT-
3707
LG-3705 & LG-
3706
601-P-1028 A/B FI-3703
On-line Analyzers
The following on line analyzers are provided to monitor the pollutant concentrations at various stages of
treatment.
Oil : API Separator Overflow Line to TPI Unit (AE-2408)
: SBR Feed Pump Discharge Line to SBR Tank (AE-2409)
pH : Flash Mixing Tank A outlet (AE-2401)
: Flash Mixing Tank B outlet (AE-2402)
: pH Adjustment Tank outlet (AE-2403)
: Outlet of MBR (AE-3401)
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Tender 12000123-HD-48002 Annexure-1, Page No.87
: Cartridge Feed Pump Discharge Line (AE-3601)
: Discharge Header of Treated Water Transfer Pumps (AE-3701)
TOC (BOD & COD) : pH Adjustment Tank outlet (AE-2410)
: Outlet of MBR (AE-3404)
DO : Each compartments of SBR Aeration Tank (DOE-3001/2/3) : MBR Aeration Tank (AE-3301)
Turbidity : Outlet of MBR (AE-3405)
: Cartridge Feed Pump Discharge Line (AE-3606)
Conductivity : SBR Feed Pump Discharge Line (AE-2404)
: Outlet of MBR (AE-3403)
: Cartridge Feed Pump Discharge Line (AE-3602)
: Outlet of each RO Skid (AE-3608/9/10)
Silica : Outlet of MBR (AE-3402)
: At R O skid -multi channel (AE-3611)
Sulphide : TPI Separator Overflow line to Flash Mixing Tank (AE-2405)
: SBR Feed Pump Discharge line to SBR Tank (AE-2407)
: Spent Caustic Stream Flocculation Tank Outlet (AE-2406)
ORP : Cartridge Feed Pump Discharge Line (AE-3603)
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SDI : Cartridge Feed Pump Discharge Line (AE-3607)
Above analyzers are provided with indication cum recording facility at the control Room along with local
indication.
Gas Detectors
Following gas detectors are provided:
Hydrocarbon (HC) : At Inlet & Outlet of ACF (AE-4101 & AE-4102)
Hydrogen Sulphide (H2S) : Near DAF unit (GDIT-2401& GDIT-2402)
Carbon Monoxide (CO) : Outlet of ACF (AE-4103)
Above gas detector are provided with indication cum recording facility at the control Room along with local
indication with Alarm (both locally & Control Room) for exceeding preset values. The Instruments are selected as
per the specific application and sensors to be suitably located. All specifications provided as recommended by the
respective Instrument manufacturer for the specific model proposed.
GENERAL
All pumps have Pressure Gauge (PG) on their discharge lines. The pressure gauges on all slop oil, sludge and
chemical services are of diaphragm type.
All motors have their running indication in PLC.
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Tender 12000123-HD-48002 Annexure-1, Page No.89
All motors have local start / stop facility. The motors having interlock facility will have local / remote selector
switch , auto/manual switch is located on auxiliary console in control room, start/stop push buttons and selection
of main/standby switch in control room to facilitate remote operation.
All required start/stop push buttons, selector switches, etc. for operation of various equipment is through soft
keys.
In case a motor is already running, there should not be a stoppage due to mode change over from local to remote
and vice-versa. This is equally applicable for mode change over from auto to manual and vice-versa.
For all pumps/blowers acting on interlocks/program, if the running pump/blower fails, the standby pump/blower
will start automatically. However, manual override arrangement for the same is also be available. All
pumps/blowers are interchangeable.
At no point of time both the operating and standby pumps/blowers will run together in auto mode.
In case of more than two pumps, provision of alarm is made only for the highest cut-in level and not for
intermediate cut-in levels, unless otherwise specified. In auto mode removal of high level signal would not cause
stoppage of the running pump. All pumps are interchangeable and start will depend on the liquid level in the
sump, i.e. as the level in the sump rises, pumps to correspondingly get activated.
Effective Liquid Depth of units will be considered between levels corresponding to Lowest Water Level and
Highest Water Level. Flooded suction requires that lowest switch level will not be lower than the elevation of
discharge flange of pump.
All sumps and pumps are provided with appropriate instrumentation for alarms and auto operation (start/stop) of
pumps with respect to preset levels.
No direct level switches are used in the ETP. Instead level transmitters are used for all sumps and other tanks.
These transmitters are connected to PLC system and software switches shall be generated for interlock/alarm.
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No direct process switches are used. Instead level transmitters are used for all sumps and other tanks. These
transmitters are connected to PLC system and alarms will be generated.
Refer attached instrumentation list for details for various instruments and tag numbers.
The instrumentation & control philosophy of SBR, MBR, Bioremediation and VOC system is given in the respective
systems process operating manual.
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PROCESS CONTROL
Once the plant has been stabilized at full load it is important to maintain the operating parameters in a manner
such that the plant produces a treated effluent meeting the desired treated parameters on a consistent basis.
The plant is designed for a load of pollutants as specified in design specifications. However, excess load in terms
of various parameters can affect the performance of the plant. Hence, the values specified in the chapter ‘design
specifications’ should be considered as alarm limit for operating parameters.
Process control involves maintaining all process operating conditions that were stabilized during the stabilization
process. It also involves taking corrective measures as and when the feed conditions change. Further, the
operation and efficiency of the treatment process are best monitored in the laboratory. The analytical data
generated in a laboratory provides data for the evaluation of the incoming waste, performance of the plant and
the course of corrective action for a given problem. Always update and ensure that the spares are available at site
to handle any breakdown at any time. Thus the process control is a two step function involving control based field
observation and those based on laboratory inputs.
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1. Field observations
2. Laboratory control
FIELD OBSERVATIONS
The following important points will need attention during regular plant operation:
API SEPARATOR & TILTED PLATE INTERCEPTOR (TPI)
- Check and control oil levels by regular operation of the oil skimmer.
- Ensure that the oil flows freely through the pipes into the slop oil tank.
- Withdraw sludge at regular intervals so that sludge does not build up in the tank, and at the same time, the
sludge withdrawn is not unnecessarily dilute, leading to a dilute centrifuge feed.
- At least once a day flush the underflow lines with steam, air, service water to prevent clogging of lines.
- If required, flush the plate packs with a water jet to remove any material clogged between the plates. This must
be done very carefully to avoid damage to the Plate Pack sheets.
DISSOLVED AIR FLOTATION
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Check the overflow quality and regulate chemical dosing.
Ensure that saturation line pressure is maintained at 4 -6 Kg / cm2.
Maintain a uniform measured air flow and recycle flow to the Air Saturator.
Regulate the air discharge rate in accordance with the oil and solids load to achieve optimal oil/solids capture.
Periodically check all flow rates, make sure they haven’t significantly varied from the initial set points.
Withdraw the settled sludge at regular intervals to prevent build up in the system.
Check the overflow and regulate chemical dosing as required.
The suction strainers of the FeCl3 and DOPE pumps need to be cleaned regularly to ensure smooth operation of
the pump.
The preparation of FeCl3 and DOPE should be an attended operation to prevent overflow of tanks and waste of
utility.
SECONDARY CLARIFIER (COMPLETREATOR)
Ensure that the return sludge pumps and rake mechanisms are operated continuously.
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Accumulation of the sludge in the clarifier can lead to serious problems such as septicity of the sludge and floating
in the clarifier, high solids in overflow.
Launders should be cleaned regularly to prevent build up of sludge and growth of algae.
THICKENER
Ensure continuous operation of the rake mechanism.
In case of the Bio Sludge Belt Thickener, the speed of the belt should be adjusted to ensure adequate dewatering
of the feed slurry.
Maintain adequate dosing of Dewatering Polyelectrolyte (DWPE) to ensure maximum sludge compaction.
Adequate dosing rate of DWPE is especially essential for the Bio Sludge Belt Thickener to ensure rapid dewatering
of the slurry on the belt.
Ensure regular operation of the underflow sludge pumps.
Accumulation of the excess sludge in the thickeners may lead to serious problems such as overloading of the rake
drive and choking of the underflow pipe, and septicity of the sludge.
Check regularly the underflow solids concentration.
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Launders should be cleaned regularly.
CENTRIFUGE
Check the suspended solids levels in the centrate and moisture content of the centrifuge cake. Improvements
may be possible by varying the dose of polyelectrolyte, and the feed rate to the unit. Periodically conduct
laboratory jar tests to fix the DWPE dosage required.
If centrifuge shows severe vibration when being started or in running condition, it could be due to bearing
problem, improper anti vibration pads or due to accumulation of solids in the unit. In this case stop the feed
immediately and thoroughly flush the centrifuge with water.
Centrifuge should be kept clean by proper flushing with water prior to shutdown.
CHEMICAL DOSING SYSTEM
- Regularly check the stock of dosing chemicals required to ensure availability at all times.
- Make note of the all dosing tank levels regular intervals.
Check all dosing pumps for proper discharge and adjust stroke length according to requirements.
Regularly flush out the dosing tanks .Clean the strainers at pump suction as and when required.
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SPENT CAUSTIC STREAM
- Operation should regularly monitor the level of H2O2 Storage Tank, ensure availability of chemical and to avoid
dry running of pumps.
Operator should keep regular check on operation and dosing rate with respect the sulphide concentration in the
influent and effluent.
In case of emptying of these tanks, operator should follow standard refinery practice.
LABORATORY CONTROL
Sampling
The reliability of the results of wastewater sample depends upon the proper collection of a truly representative
sample from the large volume of wastewater streams. The sample after collection should be transported to the
laboratory in a well preserved condition so that it will represent fairly, accurately the waste in its original state.
The sample may be grab or composite depending upon the requirement and extent of monitoring required.
Grab sample represents the conditions that exist at the time of collection of the sample since they do not indicate
average conditions. This data generally should not be used for final reporting purposes. Grab samples are useful
whenever abnormal discharge is observed or suspected at sampling points. This sampling method is also adopted
for measurement of parameters where the analysis has to be done immediately such as pH, turbidity, dissolved
oxygen, sulphide, etc.
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Composite sample are the average samples collected over specified period and at specified intervals.
Consideration should be given to the duration of the sampling period, which will be dictated by the operating
conditions of the processing units of the main plant.
Method of Sample Collection
Samples are collected for plant operation controls. They should be collected in a suitable sampling bottle with
tight cover.
Interpretation of Laboratory Results
This is one of the most difficult tasks before the plant personnel. Since the main objective of the analysis are
directed towards prevention and control and then proper operation and maintenance of plant. Proper
interpretation of the analytical data should be the prime responsibility of the Plant In-Charge.
Preferably daily, the analytical data in respect of each source of samples has to be examined to determine degree
of conformity or deviation of the prescribed standard for influent and effluent. In case of vast deviation the
corrective action should be initiated by Plant In-Charge.
LABORATORY SAMPLE SCHEDULE
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OM&S Daily Effluent Water Samples:
SN Sample Qty. Time Hrs. Tests
1. API Separator O/L
(FR)
0.5 Lit. 0600,1800 pH, Oi l& Grease, Free Cl2 ppm
2. Mahul Catcher O/L 0.5 Lit. 0600 pH, Oil & Grease, Free Cl2 ppm
3. Oil Catcher
oppositeTk-259
0.5 Lit. 0600 pH, Oil & Grease, Free Cl2 ppm
4. CPP Nallah Outlet 0.5 Lit. 0600 pH, Oil & Grease, Free Cl2 pp
IETP: Daily Samples
SN. Sample Quantity Time Tests
1. API Feed inlet 2 x 1 Lit
0900
pH, O&G, TSS, Sulphide, BOD, COD & Phenol
2. pH tank outlet 2 x 1 Lit 0900
pH,O&G, Sulphide, TSS, BOD, COD & Phenol
3. SBR Outlet 2 x 1 Lit 0900 O&G, TSS, BOD, COD, Sulphide & Phenol
4. SBR Aeration tank 1 Lit 0900 MLSS
5. MBR Aeration tank 1 Lit 0900 MLSS
6. MBR Outlet 2 x 1 Lit 0900 pH, O&G, TSS, BOD, COD & Sulphide
7. RO Outlet (permeate) 2 x 1 Lit
0900 pH, O&G, TSS ,BOD ,COD, Turbidity, Total Silica, TDS
8. Reject 2 x 1 Lit 0900 pH, O&G, TSS ,BOD ,COD, Sulphide, Phenol, TDS
9. Spent Caustic Inlet 0.5 Lit 0900 pH & Sulphide
Note: 1) BOD sample to be collected in 2 BOD bottles only
2) O&G sample to be collected in separate bottle
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IETP: Weekly Samples
SN Sample Qty. Day Tests
1. API Feed inlet 1.0 Lit Monday TDS
2. pH tank outlet 1.0 Lit Monday TDS
3. Spent caustic O/L 2 x 1.0 lit Monday pH,Sulphide
4. SBR Aeration tank 1 x 2.0 lit. Monday MLVSS
5. MBR Aeration tank 1 x 2.0 lit. Wednesday MLVSS
6. Completreater O/L 1 x 2 Lit Tuesday pH, O&G, TSS ,TDS,BOD&COD
TROUBLE SHOOTING
In any process operation system upsets occurred due to various reasons. In ETP, these upsets could be due to
changes in the incoming wastewater or inadequate process controls. Whenever plant upsets occur, the first step
is to identify the cause for the upset. Subsequent, corrective measures then become simpler and meaningful.
Some of the common problems, their causes and possible solutions are discussed below:
API OIL SEPARATOR
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Problem
Slippage of oil or poor performance of unit due to –
- Unit hydraulically overloaded.
- Non uniform overflow of effluent.
Excessive oil in the influent.
Accumulation of excess sludge at the bottom of unit.
Irregular free slop oil withdrawal.
Solution
Hydraulic overloading in the unit will reduce the retention. Maintain an average uniform flow in the specified
range of flow rate.
Check and ensure the overflow weir is not clogged to ensure uniform overflow of effluent throughout the length
of the overflow launder.
Increase oil skimming from upstream unit operations.
Withdraw the settled sludge and floating free slop oil on a regular basis.
TILTED PLATE INTERCEPTOR (TPI)
Problem
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Slippage of oil or poor performance of unit due to –
- Unit hydraulically overloaded.
- Non uniform overflow of effluent.
Accumulation of excess sludge at the bottom of unit.
Plate packs are partly clogged.
Irregular free slop oil withdrawal.
Solution
Hydraulic overloading in the unit will reduce the retention. Maintain an average uniform flow in the specified
range of flow rate.
Check and ensure the overflow weir is not clogged to ensure uniform overflow of effluent throughout the length
of the overflow launder.
Regularly carefully clean the plate packs of adhering oily sludge solids by using a water jet. This would increase
the settling area to the maximum and prevent short-circuiting through the plates.
Check that packing between plate pack and TPI unit wall is intact. Replace packing material wherever required.
Withdraw the settled sludge and floating slop oil on a regular basis.
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DISSOLVED AIR FLOTATION (DAF)
Problem
Turbulence is evident at influent end of flotation basin due to excess undissolved free air with the recycle air
stream.
Solution
Reduce the air flow rate to the saturation vessel or increase the flow rate of the recycle stream. In case the
recycle stream flow rate cannot be increased and the same quantum of dissolved air is required, then the airflow
rate to the saturation vessel may varied by varying the system pressure by means of the Air Filter Regulator (AFR)
so that the solubility of the air increases resulting in consequent a correspondingly larger amount of precipitated
air.
Check and ensure that the set liquid levels are maintained in the saturation vessel. In case the saturator level goes
so low that the saturator is completely empty, then free air from saturator will pass into the DAF unit.
Problem
Insufficient air supply due to -
Clogging of air line.
Malfunction of AFR.
Malfunction of air compressor.
Solution
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Check for malfunctioning of the regulating valve and air compressor. Refer the service manual for air filter
regulating valve and air compressor.
Problem
Excessive oil or solids carry over in overflow.
Causes
Inadequate chemical dosing.
Inadequate quantum of precipitated air.
No uniform overflow of effluent.
Improper operation of skimmer.
Size of air bubbles is not uniform or too large /small.
Saturation system is not working properly.
Excessive sludge accumulation at the bottom.
Solution
Check the dosing system and readjust the dosing as per requirements. Repeat lab jar tests to check/confirm
chemical dosages for FeCl3 /DOPE.
Adjust the air quantity & pressure and recycle pump flow rate to ensure adequate quantity of precipitated air and
ensure air bubble size is proper for effective oil/solids capture at the operated effluent flow rates.
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Regularly check that the liquid levels in the saturator are maintained at the desired range. Too high liquid level
could result in the saturator packing media getting submerged resulting in reduced mass transfer of air into the
effluent. Too low level could result in the saturator vessel getting completely empty cause free air to enter the
DAF resulting in turbulence in the unit.
Improper desludging leads to accumulation of sludge at the tank bottom, which decomposes over a period of
time. The decomposed solids being light in weight and will get carried into the overflow. Regulate the frequency
of underflow withdrawal.
Check the skimmer operation.
Problem
Scum too thick on the surface of DAF Tank.
Solution
Operate the skimmer regularly and remove the scum.
Problem
Air rotameter reading drops.
Causes
- Malfunction of AFR.
- Malfunction of rotameter.
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- Air compressor malfunction.
Solution
Check and correct malfunction of AFR.
Check the performance of the air compressor: Ensure the required pressure is achieved.
Ensure the rotameter is functioning properly.
CENTRIFUGE
Problem
Chokage in centrifuge.
Causes
Feed slurry consistency is high.
Fluctuation in feed flow.
Improper flushing of centrifuge.
Loose ‘V’ belts.
Sudden failure of fluid coupling.
Solution
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The centrifuge feed pump and DWPE dosing pump to be switched off. Check feed solids consistency.
Actuate the flushing system.
The centrifuge to be switched off after getting clear centrate (about 15 minutes).
Ensure the proper cleaning of the centrifuge by getting clear water from solid outlet. If water is not clear, restart
the centrifuge and again flush it with flushing liquid. If required clean the inlet pipes in the centrifuge as per
instructions of centrifuge supplier.
Check belts & fluid coupling.
Problem
Severe vibration.
Causes
Chokage in centrifuge.
Failure of bearings or antivibration pads.
Misalignment of motor and equipment.
Solution
Dechoke the centrifuge by adequate flushing of the centrifuge and clean the inlet pipes in the centrifuge as per
instructions of centrifuge supplier.
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Check bearings and antivibration pads.
Check alignment of motor.
Problem
Output solid consistency is not satisfactory.
Causes
Feed slurry consistency less than specified level.
Feed slurry flow is more.
DWPE dose is not adequate.
DWPE solution strength is not proper
Solution
Check feed slurry solids and increase the concentration to the specified range.
Reduce feed flow.
Check DWPE dose by jar test. Adjust dosing rate based on required dose and solids flow rate.
Check DWPE solution preparation procedure details.
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Problem
High suspended solids in centrate.
Causes
Choking of centrifuge by solids.
High solids consistency in feed slurry.
High feed slurry rate.
DWPE dose is not adequate.
DWPE strength is not proper.
Solution
Flush the centrifuge to remove accumulated solids.
Check feed slurry solids and decrease the concentration to the specified range.
Reduce feed flow rate.
Check DWPE dose by jar test. Adjust dosing rate based on required dose and solids flow rate.
Check DWPE solution preparation procedure details.
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Spent Caustic Treatment
Problem
High sulfide contain in the treated effluent.
Solution
Check sulfide & pH. High pH at inlet could be due to draining of spent caustic in OWS in process units.
Conduct laboratory jar test and adjust the dose of H2O2. As per stoichiometric, 4.25 Kg of H2O2 is required for 1
Kg of sulphide.
COMPLETREATOR
Problem
Poor Organic (BOD/COD) Removals.
Causes
Inadequate biomass (MLVSS) concentration.
Improper recycle of return sludge.
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Organic /Volumetric overloading.
Inadequate air supply – Low Dissolved Oxygen (DO) levels.
Solution
Check the MLSS/MLVSS values at regular intervals and adjust sludge wastage rates to achieve the desired
specified values.
Ensure return sludge is being recycled continuously.
Check the BOD/COD levels and match with specified values. Ensure unit is not highly overloaded volumetrically.
Check dissolved oxygen values in various aerobic compartments are positive (0.5 - 2.0 mg/l DO are normal values
encountered in an aerobic system). Ensure air blowers are functioning properly.
Problem
High suspended solids level in clarifier overflow.
Causes
High volumetric flow rate.
Bulking of bio sludge
Accumulation of bio sludge in clarifier due to inadequate sludge recycle rate.
Solution
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Ensure that system is not grossly overloaded volumetrically.
Bulking of bio sludge can be taken care by bleeding off sludge / chlorination of return sludge.
Adequately desludge the clarifier to remove accumulated sludge.
PLANT SHUTDOWN
Effluent treatment plants are generally not shutdown completely in view of their essentiality from the
environmental angle as under no circumstances effluent can be discharged without treatment. However, at times,
shutdown may be required due to non-availability/ breakdown of equipment for which the following operations
are suggested:
In case of breakdown of API Oil Separators or downstream equipment, by-pass the equipment.
In case of breakdown of the equipment downstream of API Oil Separators or excessive receipt of influent, the
excessive influent may be diverted to guard ponds if provided or release from the refinery. This operation shall
require clearance from Plant In-Charge .
In case of shutdown of Biological systems, keep air blowers running. Biological sludge recirculation pump should
also be kept running for survival of the microbes.
In case of shutdown of Sludge Thickeners, keep sludge scraping mechanism running.
Before shutdown of Centrifuges & Centrifuge Feed Pumps, flushing is must.
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SAFETY SYSTEM
Safe operating practices are an important aspect of plant operation and proper safety instructions must be laid
out and scrupulously followed. This becomes especially significant when handling inflammable and corrosive
materials. Some of the important safety considerations are highlighted below.
The plant area to be kept clean and free of spillage.
Proper precautions must be taken while doing maintenance work of equipments especially equipments handling
oil.
While preparation of chemical solutions, safety gloves & goggles must be worn.
Safety gloves & goggles must be worn while collecting samples.
Safety showers must be checked at regular interval for proper operation.
Chemical splashes must be immediately washed with copious quantity of water. Seek medical aid if necessary.
Contact with the effluent must be avoided as far as possible. However, if contact is unavoidable, ensure that
hands are washed with soap.
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Standard safety procedures to be followed while handling electrical equipments.
EMERGENCY HANDLING
The most likely emergency situations are:
1. Oil spillage
2. Fire
1. Oil spillage - Oil spillage may occur due to accidental overflow/ leakage of equipments.
Action
Isolate the equipment & take action to arrest leakage.
Clean plant area with water.
Oil recovery to be started at Final Oil Traps (‘Effluent Leaving Refinery’) to avoid oil escape from the refinery.
Inform Shift In-Charge & Plant In-charge.
2. Fire
Action
Immediately take action to stop the fire with the fire safety equipments (suitable for type of fire) available at site.
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Inform Fire Station.
Inform Shift In-Charge & Plant In-charge.
GAS EMISSION DETECTION SYSTEM
In the ETP, there are mainly two types of hazardous gases, namely hydrocarbon vapors and hydrogen sulphide
gas.
A gas detection system has been installed for the safety of plant and operating personnel.
Following gas detectors are provided:
Hydrocarbon detector - Near OWS Sump
H2S detectors - Minimum 2 Nos. in the vicinity of DAF unit (Main treatment chain)
Above gas detector are provided with indication cum recording facility at the control Room along with local
indication with Alarm (both locally & Control Room) for exceeding preset values. The Instrument are selected as
per the specific application and sensors to be suitably located. All requirements including (Shed, Environment,
etc.) is provided as recommended by the respective Instrument manufacturer for the specific model proposed.
In case of alarm goes off, the area should be immediately evacuated of all the operating personnel. The cause of
alarm to be investigated and remedial action should be initiated as per standard procedures.
Slop Oil & Sludge Generation- Design basis
The IETP consists of various treatment processes, which yields a number of products as listed below: -
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1. Slop Oil
2. Oily Sludge
3. Chemical Sludge
4. Bio Sludge
5. Treated effluent
The above units are produced in the following units:
1. API separator (601-API-1001 A/B/C)
2. TPI separator (601-TPI-1001 A/B)
3. DAF unit (601-TK-1004 A/B)
4. SBR(601-SBR-1001)
5. MBR(601-MBR-1001)
The quantity of products from the above units is as follows:
A. SLOP OIL
1. From API separator (601-API-1001 A/B/C)
Unit Inlet Outlet
Flow m3/hr 300 300
Free Oil (Nor/Max.) mg/L 800/19500 400/975
Emulsified Oil (Nor/Max) mg/L 200/500 200/500
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Total Oil (Nor /Max.) mg/L 1000/20000 600/1475
Free oil removed at Max. Oil Content = 18525 mg/L (133380 kg/day)
At 20 % consistency, Volume Of
Wet Slop Oil At. Max. oil Content = 133380/ (200)
= 666.9 m3/day
= 27.79 m3/hr.
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Free oil removed at Normal Oil Content = 400 mg/L (2880 kg/day)
At 5% consistency, Volume of
Wet Slop Oil at Normal oil Content = 28800/ (50 )
= 57.6 m3/day
= 2.4 m3/hr.
2. From TPI separator (601-TPI-1001 A/B)
Unit Inlet Outlet
Flow m3/hr 300 300
Free oil (Nor /Max.) mg/L 400/975 15/50
Emulsified Oil (Nor/Max) mg/L 200/500 200/500
Total Oil (Max.) mg/l 600/1475 215/550
Free oil removed at Max. Oil Content = 925 mg/L (6660 kg/day)
At 5% consistency, Volume Of
Wet Slop Oil At. Max. oil Content = 6660/ (0.05 X 1000)
= 133.2 m3/day
= 5.55 m3/hr.
Free oil removed at Nor. Oil Content = 385 mg/L (2772 kg/day)
At 5% consistency, Volume of
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Wet Slop Oil at. Nor. oil Content = 2772/ (50)
= 55.44 m3/day
= 2.31 m3/hr.
3. From DAF flotation tank (601-TK-1004 A/B)
Unit Inlet Outlet
Flow m3/hr 300 300
Free oil mg/L 50 5
Emulsified Oil mg/L 500 5
Total oil mg/L 550 10
Suspended mg/L 20 10
Solids
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Total oil removed at Nor. Oil Content = 540 mg/L (3888 kg/day)
At 3% consistency, Volume Of
Wet Slop Oil At. Nor. oil Content = 3888/ (30)
= 129.6 m3/day
= 5.4 m3/hr.
Total Slop oil Generated at Max. Oil Content = 27.79+5.55+ 5.4
(ISBL) = 38.74 m3/hr
Total Slop oil Generated at Nor. Oil Content = 2.4 + 2.31+ 5.4
(ISBL) = 10.11 m3 / hr
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B. OILY SLUDGE
1. From API separator (601-API-1001 A/B/C)
Unit Inlet Outlet
Flow (Nor.) m3/hr 300 300
Suspended mg/L 200 60
Solids
Suspended Solids removed in API = 140 mg/L (1008 kg/day)
At 1.5% sludge consistency
Sludge generation = 1008/15
= 67.2 m3/day
= 2.8 m3/hr
2. From TPI separator (601-TPI-1001 A/B/C)
Unit Inlet Outlet
Flow (Nor.) m3/h 300 300
Suspended mg/L 60 20
Solids
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Suspended Solids removed in TPI = 40 mg/L (288 kg/day)
At 1.5% sludge consistency
Sludge generation = 288/15
= 19.2 m3/day
= 0.8 m3/h
Total oily sludge @ 1.5 % consistency = 2.8 + 0.8
= 3.6 m3/h
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C. CHEMICAL SLUDGE
From DAF tank (601 -TK-1004 A/B)
Unit Inlet Outlet
Flow (Nor.) m3/hr 300 300
Suspended mg/L 20 10
Solids
Suspended Solids removed in DAF = 10 mg/L (72 kg/day)
At 1.5% sludge consistency
Sludge generation = 72/15
= 4.8 m3/day
= 0.2 m3/h
Sludge due to precipitation of Fe(OH)3
FeCl3 dosing = 30 mg/L
Chemical mass balance:
FeCl3 + 3NaOH Fe (OH) 3 + 3NaCl
1. 107
FeCl3 dose per day = 30/1000 x 300x24
= 216 kg/day
Fe (OH) 3 sludge generated = 107/162.5 x 216
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= 142.23 kg/day
Sludge flow rate @ 1.5 % consistency = 9.48 m3/day
= 0.4 m3/hr.
Total Chemical sludge = 0.2 + 0.4 m3/h
= 0.6 m3/h
Total Oily and Chemical sludge generated = 3.6 + 0.6
(ISBL) = 4.2 m3/h
Total oily & chemical sludge dry solids : 1008 + 288 + 72 + 142.23
(ISBL) : 1510.23 Say 1511 kg/d
Total oily & chemical sludge generated
(ISBL + OSBL) : 8.4 m3/h
Total oily & chemical sludge dry solids : 3023 kg / day
(ISBL + OSBL)
Thickened Oily & chemical Sludge from : 3023/ (50 x 1.05)
the thickener as 5 % solids & Sp. Gr. Of 1.05 = 57.58 m3/ day = 2.4 m3 / h
(Feed to Centrifuge)
Solids in Thickener supernatant (0.1%) : (8.4-2.4) x 1000/1000
= 6 kg/hr = 144 kg/day
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Actual solid loading to Centrifuge : 3023 – 144 = 2879 kg/day
Solid capture in centrifuge (97%) : 2792.63 kg/day
De watered sludge from centrifuge as 20 % : 2792.63 / (200 x 1.1)
Solids and Sp. Gr. Of 1.1 = 12.69 m3/day =0.53 m3 / h
Supernatant from Oily and Chemical sludge thickener = 201.6– 57.58
= 144.02 m3/day
Supernatant from Oily and Chemical sludge Centrifuge = 57.58 – 12.69
= 44.89 m3/day
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D. BIO SLUDGE
Bio sludge from SBR
Bio sludge generated in SBR = 1872 kg/day based on BOD load of 7200 kg/day
However, the SBR is followed by MBR where the inlet BOD concentration will be 100 mg/l viz. BOD
load of 720 kg/day.
Hence, the biological sludge generated in SBR considering BOD removal of 6480 kg/day:
BOD removed from SBR : 1000 – 100 = 900 mg/l
Considering sludge wasting rate of
0.26 kg/kg of BOD removed,
Bio sludge wasted : (900/1000) x 300 x 24 x 0.26
=1684.8 kg/day
At 0.8 % consistency,
Sludge generation rate : 1684.8 / 8 = 210.6 m3/day
= 8.78 m3/hr
Bio sludge from MBR
BOD removed from MBR : 100 – 5 = 95 mg/l
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As per BEP of MBR(R2)
Bio sludge wasted : 341.2 kg/day
At 0.8 % consistency,
Sludge generation rate : 341.2 / 8
= 42.6 m3/day
= 1.78 m3/h
Bio sludge from Sanitary Treatment
Sludge generated from sanitary treatment
Package @ 0.8 % consistency : 3.75 m3/d (30 kg/day)
= 0.16 m3/h
Total Bio-Sludge generation rate = 8.78 +1.78+ 0.16
( At 0.8 % consistency) = 10.72 m3 / h
(2058 kg /d)
Solid capture rate in GBT (96%) : 1975.9 kg/d
Thickened Bio Sludge from : 1975.9/50/1.05 = 37.63 m3/ day
GBT as 5 % solids & Sp. Gr. Of 1.05 =1.57 m3 / hr
(Feed to Centrifuge)
Solid capture in centrifuge (97%) : 1916.62 kg/day
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De watered sludge from centrifuge at 20 % : 1916.62/1.1/200 = 8.71 m3/day
Solids and Sp. Gr. Of 1.1 = 0.36 m3 /h
Supernatant from Bio-sludge thickener = 257.28–37.63 = 219.65
m3/day
minuscule
Supernatant from Bio-sludge Centrifuge = 37.63 – 8.71
= 28.92 m3/day
Total Supernatant quantity from Bio sludge and Chemical sludge de-water
= ( 144.02+44.89+219.65+28.92)
= 437.48 m3/day
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Chemical Consumption at IETP
Chemicals used and their application
Sr No
Chemical & concentration for rated feed
Pumps Application/Purpose
1 Acid (HCL) 10%
601-P-1019 A/B/C & 601-P-1020 A/B.
Used for neutralization/Flash Mixing Tank/PH adjustment Tank & RO permeate dosing.
2 Alkali (NaOH) 10%
601-P-1022 A/B/C
Used for Neutralization/Flash Mixing Tank/PH adjustment Tank & permeate water PH adjustment.
3 Hydrogen Peroxide (H2O2) 50%
601-P-1019 A/B/C
Used for oxidation of sulphides to sulphates in flash mixing tank of oily and spent Caustic treatment.
4 FeCl3
601-P-1033 A/B
Used as flocculant in flash mixing tank of oily effluent chain.
5 DOPE 0.5%
601-P-1023 A/B
Used as de-emulsifier in flocculant tank for emulsified oil removal.
6 UREA & DAP 0.1%
601-P-1024 A/B
Used in PH adjustment tank for nutrients.
7 DWPE (Oily + Bio) 0.5%
601-P-1025 A/B 601-P-1026 A/B
For Dosing in Chemical/& Oily & Bio sludge thickener and dewatering centrifuge.
8 Methanol 10%
601-P-1041 A/B
Used in MBR as a carbon Source for growth of Microbes.
9 Anti-form 10%
601-P-1042 A/B
Used in MBR for Foam Control
10 Citric Acid 50%
601-P-1029 A/B
Used for Cleaning of MBR Membranes.
11 Sodium hypochlorite (NaOCL) 11%
601-P-1027 A/B
Used for Cleaning of MBR Membranes.
12 Antiscalant 6%
601-P-1028 A/B
Used for RO Scale Controls.
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13 Sodium Bi-sulphite 5%
601-P-1030 A/B
Used in RO to remove free chlorine.
Chemical dosage at IETP
Sr No
Chemical Dosage Consumption Unit Purity of chemical available
% of solution prepared
1 DOPE 5ppm 36 Kg/day 100 0.5
2 DWPE (Oily) 2.0 kg/T of dry solids
6.046 Kg/Day 100 0.5
3 DWPE (Bio) 2.5 kg/T of dry solids
4.940 Kg/day 100 0.5
4 DAP (Note-1) BOD:P(100:1) 384 Kg/day 80 10
5 Sodium Bisulphite 5 ppm 36 Kg/day 80 5
6 Urea (Note-1) BOD:N(100:5) 631 Kg/day 100 10
7 Citric Acid Note 2 3784 Litres/Year
50 ---
8 Sodium Hypo-chloride
Note 3 3242 Litres/Year
10.8 ----
9 Anti-Foam 2 ppm 15.16 Litres/Day
100 10
10 Anti-Scalant 5.55 ppm 40 Litres/Day
100 6
11 H2O2 Sulphides:H2O2 (1:4.25)
16014 Litres/Day
50 __
12 HCL 35 788 Litres/day
100 10
13 NaOH 25 418 Litres/Day
100 10
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14 Methanol 20 ppm 180 Litres/Day
100 10
15 FeCl3(anhydrous) 30ppm 216 Kg/day 100 10
Notes:
I. Sufficient Quantity of N&P are available in the raw effluent and hence normally
nutrient dosing will not be required. A dosage of 100:5:1 of BOD:N:P has been
considered to calculate the DAP and urea consumption during startup of the plant.
For Stabilized plant a dosage of 350:5:1 of BOD:N:P has been considered for DAP &
urea consumption.
II. For maintenance cleanning of Citric acid dosa is 2000ppm and for recovery clean
citric acid soaking concentration is 200ppm.
III. For maintenance cleanning of NaOCL dose is 200ppm and for recovery clean citric
acid soaking concentration is 1000 ppm.