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Wastewater Quality
Wide variations in the quality of wastewaters are quite common. Beside the
nature of the manufacturing process, the variations are also beingcontributed by the rate of hydraulic flow, which can affect the concentration
of the untreated effluent to be discharged.
An industrial WWTP is required to handle varying inputs, but is expected to
give an output of effluent fit for discharge to the environment at all times.
This is possible to achieve in a well designed, operated and maintained
plant.
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Effective Wastewater Treatment Operation
In order to be able to bring about effective treatment of the effluent, it is
necessary to know more about:
• Characteristics of wastewater to be treated
• Requirement of treated wastewater quality
• Types of treatment alternatives available
• Techniques of wastewater sampling and analysis
These are the additions to the preventive and corrective maintenance of the
treatment machinery, knowledge of repairs to and replacement of various parts of equipment, record keeping, report preparation, aspects of safety in
treatment plants.
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WWTP Aims
Ultimate aims for the WWTP operation is to remove the unwanted
constitutions in the wastewater to a level where they can be safelydischarged into the environment.
Malaysian Standard for industrial effluent discharged is listed in EQA 1974.
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General Description of EQA
Regulations and Orders under EQA:
- Control of Agro based Water pollution
- Control of Municipal and Industrial Waste water pollution
- Control of Industrial Emissions
- Control of Motor Vehicle Emissions- Control of Toxic and Hazardous Wastes
- Integration of Environment and Development
- Control of Substances That Deplete the Ozone Layer
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Control of Municipal and Industrial Waste water pollutionControl of Municipal and Industrial Waste water pollution
• Environmental Quality (Sewage and Industrial Effluents): Regulations 1979
• Environment Quality (Prohibition on the used of control substance in soap,synthetic detergent and other cleaning agent): Order 1995
• Control the discharged of wastewater from domestic (sewage) and
industrial premises
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WWTP Design
Suitable combination of various available unit operations and unit processes
constitutes a flow scheme. It is to be noted that WWTP is like an assembly line in
a factory, where the various steps in purification are arranged in such a sequence
that the quality of output of one step is acceptable in the next step.
Explanation and illustration
Unit of operations include screening, sedimentation, filtration, adsorption, heating,drying, incineration, i.e. those steps involving physical forces.
Unit of processes include chemical and biological agents which bring about
purification and include pH correction, coagulation, aerobic and anaerobic
treatment.
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Integrated Wastewater Treatment OperationIntegrated Wastewater Treatment Operation
• Generally, the coarsest material is removed first such as floating objects by
screenings.
• Inorganic grit particles are removed next.; Thereafter, the organic material is
handled. The larger organic particles which are big enough to settle by themselves
are removed in settling tanks and enter the sludge phase.
• A part of the finer organic particles may also settle in these settling (or
sedimentation) tanks.
• Further, settling of very fine particles needs the addition of chemicals.
• Finally the dissolved organic can be treated in biological processes (i.e. activated
sludge or trickling filter).
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Sewage Treatment Plant (STP)Sewage Treatment Plant (STP)
P u m p
h o u s e
P r i m a
r y C l a
f i e r
A e r a t
i o n P o
n d
S l u d
g e T h
i c k e n i
n g
D i s i n f
e c t i o n
P u m p H
o u s e a n d
F i l t r a t
i o n
S l u d g e P
r o c e s s i n g
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Conveyance System: CollectionConveyance System: Collection
SystemSystem
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Preliminary Treatment:Preliminary Treatment:
ScreeningScreening
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Conveyance System:Conveyance System:Pumping SystemPumping System
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Primary Treatment System: SettlingPrimary Treatment System: Settling
Tank Tank
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Secondary Treatment: AerationSecondary Treatment: Aeration
Tank Tank
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Secondary Treatment: Clarifier Secondary Treatment: Clarifier
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Secondary Treatment: SolidSecondary Treatment: Solid
ThickeningThickening
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Tertiary Treatment: DisinfectionTertiary Treatment: Disinfection
ChlorinationChlorination
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Tertiary Treatment: DisinfectionTertiary Treatment: Disinfection
UltravioletUltraviolet
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Tertiary Treatment:Tertiary Treatment:
FiltrationFiltration
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Solid Processing: AnaerobicSolid Processing: Anaerobic
DigestionDigestion
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Sludge DewateringSludge Dewatering
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BiosolidBiosolid RecyclingRecycling
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WWTP House KeepingWWTP House Keeping
In a WWTP, it is always necessary to check the volume and quality of raw
and treated wastewater and also to keep A FAITHFUL RECORD OF THERESULTS OF THESE ANALYSES.
In addition, close watch over the quality and quantity of chemical added for
treatment is required to ensure economy. It may be even necessary to
conduct treatability studies in the plant laboratory to decide if anymodifications are required to the existing treatment processes.
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CharacterisationCharacterisation of Wastewater of Wastewater
The characterisation involves determination of physical, chemical and
biological characteristics of the samples of wastewater using laboratorytechniques such as gravimetry, colorimetry and titrimetry.
Knowledge of the characteristics help the plant operators to provide the
information on:
• the strength of the raw and treated wastewater
• the efficiency of the plant operation as a whole and each of the treatment
processes
• the nature of treatment required in the case of the given wastewater to meet thequality standard
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Introduction to Wastewater Constituents and its GenerationIntroduction to Wastewater Constituents and its Generation
Industrial activity results in the generation of a number of pollutants which
can be broadly grouped as•O2 demanding substances
• Suspended solids
• Nutrients• Disease producing organisms
• Salts
• Toxic metals
• Toxic organic chemical
• Heat
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Categories of Water PollutantsCategories of Water Pollutants
Pollutants can be classified into several groups.:
The first are the nutrients, i.e. dissolved inorganics i.e. nitrate, and phosphate.
A second group included heavy metals, such as chromium, lead, and arsenic.
The third and largest group is the organics substances, which included pesticide,
industrial by-products, and solvents. Organic substances can be divided into twosubclasses based on solubility or lipid partitioning. These are hydrophobic
compounds, which dissolve in lipids (fats), and hydrophilic compounds, which
dissolve in water.
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Categories of Water Pollutants IICategories of Water Pollutants II
Other than chemical characteristic, water pollutant also can be categorised based
on the physical analysis which include the temperature, colour, solids contents, pH, dissolved oxygen.
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Wastewater from RefineryWastewater from Refinery
The process-intensive petrochemical industry has demanding environmentalmanagement challenges to protect water, soil and atmosphere of the refinery
pollution.
Petroleum refineries use relatively large volumes of water, especially forcooling systems. In fact, wastewater from the petrochemical industry usuallycontains hazardous chemicals, as hydrocarbons, phenol or ammoniacalnitrogen among others.
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General Description
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General Issues in Refinery Plant
- Cooling system produced 3.5-5 m3 of wastewater generated per ton of crude
- Polluted wastewater contains
BOD 150-250 mg/l COD 300-600 mg/l
phenol 20-200 mg/l
oil 100-300 mg/l (desalter water)
oil 5000 mg/l in tank bottom
benzene 1-100 mg/l
heavy metals 0.1-100 mg/l
- Solid waste and sludge
- VOC emissions- Others emissions
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General Issues in Refinery Plant 2
• Salts in the feedstock (corrosion and fouling problems) and aromatics
(source of VOC)• Aromatics, oil, grease and organic removal
• Phenol and ammoniacal nitrogen removal with a biological treatment
• The organic and inorganic contaminants from refinery wastewater
• Oily water separation
• Oily rain water
• Process water
• Petroleum refineries and heavy metals
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Oxygen demanding substancesOxygen demanding substances
Basically, O2 demanding substances originated from organic matters. Thesematter can be measured by four ways :
a. Theoretical Oxygen Demand (ThOD)
b. Biochemical Oxygen Demand (BOD)
c. Chemical Oxygen Demand (COD)
d. Total organic carbon analyser (TOC)
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Theoretical Oxygen Demand (Theoretical Oxygen Demand (ThODThOD))
ThOD is the amount of oxygen to oxidise a known compound completely to CO2 andH2O.
It can also be used to calculate the amount of oxygen required to oxidise the ammonia present in the water of wastewater, which is known as Nitrogenous Oxygen Demand
(NOD) which is not able to be determined by BOD analysis.
Example 1
Acetic acid (CH3COOH); molecular weight = 60 g/mol
CH3COOH + Y O2 2CO2 + 2H2O
complete oxidation requires Y O2 which is equal to 260 g acetic acid requires 64 g O2
if 1000 mg/L acetic acid, then the oxygenrequirement will be
60g CH3COOH = 1000 mg CH3COOH
64g O2 Y O2Y = 1000mg x 64g / 60g = 1067 mg O2
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Biochemical Oxygen Demand (BOD)Biochemical Oxygen Demand (BOD)
BOD measurement is the most widely used parameter of organic pollutant applied to bothwastewater and surface water. This determination involves the measurement of thedissolved oxygen used by microorganism in the biochemical oxidation of organic matter.
Calculation: BODt = DOi – DOf x dilution factor
Example
Time Dissolved O2
T0 25 mgl-1
T1 22 mgl-1
T2 19 mgl-1
T3 18 mgl-1
T4 16 mgl-1
T5 15 mgl-1
BOD5 = (T0 - T5) x dilution factor
BOD5 = 25 - 15 = 20 mgl-1 x 10 = 200 mg.l-1
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BOD AnalysisBOD Analysis
δTt/δt = - k.t
integration ( from 0 to t) δTt/t = - δt.k
ln Tt - l n T0 = - k.t
ln [Tt / To ] = - k.t Tt = T0 . exp - k.t
BOD5 = T0 - T5
= T0 - T0 . exp - k.5
= T0 ( 1- exp - k.5 )
T0 = BOD5 / ( 1- exp - k.5 )
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BOD Analysis 2BOD Analysis 2
Example (Dilution 100 times)
DO measurement (mg/L)
Day Sample 1 Sample 2
0 18.0 20.0
1 12.0 15.0
2 9.5 13.0
3 6.0 10.0
4 5.0 8.0
5 4.0 6.0
Both samples give BOD5 = 140 mg.l-1
The differences is based on the degradation rate which can be determined based on thegraph plot.
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BOD Degradation Rate (BOD Degradation Rate (k k ))
Determination of coefficient k can be obtained based on
ln [Tt / To ] = - k.t
Convert the equation as a linearequation:
y = mx + c; where
y = ln [Ti/T0]
k = m
x = time
Dissolved Oxygen Depletion
0
5
10
15
20
25
0 1 2 3 4 5 6
Time (d)
O x y g e n C o n c ( m g / L ) Sample 1
Sample 2
Thus another set of data is required for the linearation of the equation. This set of data can be
used for the plot of Ln [Ti/To] against time where the cut off value point is ZERO.
O A l i 2BOD A l i 2
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BOD Analysis 2BOD Analysis 2
Linear Equation for BOD analysis
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 1 2 3 4 5 6
Time (d)
L n [ T i / T o ]
Sample 1
Sample 2
Linearisation of BOD curveLn [Ti/T0]
Day Sample 1 Sample 2
0 0 0
1 0.36 0.22
2 0.51 0.363 0.92 0.62
4 1.1 0.91
5 1.21 1.21
k 1 = 0.26
k 2 = 0.23
Sample 1 has higher
degradation rate
more biodegradable
Oxygen ConsumptionOxygen Consumption
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Oxygen ConsumptionOxygen Consumption
Sometimes the amount of O2 consumption plays important roles.
Dissolved Oxygen Consumption
0
2
4
6
8
10
12
1416
0 1 2 3 4 5 6
Time (d)
O x y g e n C o n c ( m g / L )
Sample 1
Sample 2
DO consumption
Day Sample 1 Sample 2
0 0 0
1 6 52 8.5 7
3 12 10
4 13 12
5 14 14
It can be used to determine ultimate
BOD which indicate the final fate of
the organic constituent in the
wastewater
BOD ultimateBOD ultimate
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BOD ultimateBOD ultimate
Determination of BOD ultimate can be done based on the BOD rate (k ) whichhas been previously determined.
lnln [ [ T T t t / T / T oo ] = ] = -- k.tk.t T T t t = T = T oo expexp--kt kt
Oxygen consumption
Y t = T o - T i
Y t = T o – (T oexp-kt ) T o (1-exp-kt )
T o = Y t / (1-exp-kt)
Based on BOD5
T o for both samples Sample 1: 140 / (1-exp-0.26 x 5) = 192 mg/L
Sample 2: 140 / (1-exp-0.23 x 5) = 205 mg/L
Application
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Chemical Oxygen Demand (COD)Chemical Oxygen Demand (COD)
COD is the test that measure the oxygen requirement to oxidise the organicmatter by a strong oxidising agent in an acidic medium. Its able to determineorganics which both biodegradable and non biodegradable. Some inorganicmatter may interfere with the measurement such as chlorine.
6Cl- + Cr 2O72- + 14H+ 3Cl2 + 2Cr 3+ + 7H2O
A few "preservative" reagents can be used to eliminate interference.Hg2+ + 2Cl- HgCl2
Measurement is based on the unreacted Cr 2O72- , thus high salinity or
conductivity sample interfere with COD analysis.
COD analysis can be used after correlation with sources of organic matter has been established.
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COD analysisCOD analysis
For many type of wastes, COD is correlated to BOD. This can be useful to
estimate the BOD measurement in the next analysis. COD takes 3 hours for
the result, while BOD takes 5 days for the result, which is going to be too late
if the discharge is already entering the external system. Once the correlation
has been established, COD measurement can be used to good advantage fortreatment-plant control and operation.
Ratio of BOD:COD analysis indicates biodegradable content for the organic
constituent. Example BOD:COD < 0.7; chemical processes are required ratherthan solely depending on biological processes.
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COD analysis 2COD analysis 2
Many costly mistakes in wastewater plant design and operational strategies
can be traced to a lack of knowledge and measurement data on these COD
constituents, by both plant designers and operations staff.
The common use of BOD5 as the only carbonaceous load plant parameter
monitored, has further acerbated the situation - although BOD5 has been
known within the industry for many years as an inferior parameter forcharacterizing the biological processes within a wastewater plant.
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COD analysis 3COD analysis 3
The four primary carbon components of influent wastewater above, play a
fundamental role in activated sludge plant design and operation. These are
commonly referred to as:
a. Biodegradable COD (BCOD) components:
• Readily Biodegradable COD (RBCOD), and
• Slowly Biodegradable COD (SBCOD)
b. Unbiodegradable COD (UCOD) components:
• Unbiodegradable Soluble COD (USCOD), and
• Unbiodegradable Particulate COD (UPCOD).
Relationship between COD and BODRelationship between COD and BOD
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pp
9001100
680930
500700
450750
550800
240500
730950
8501000
BOD ultimateCOD
Correlation Between BOD ultimate and COD
y = 1.13x - 336.19
R2 = 0.97
0
200
400
600
800
1000
0 200 400 600 800 1000 1200
COD
B O D u l t i m a t e
BODultimate = 1.13 COD – 337
Correlation andCorrelation and LinearisationLinearisation of COD and BODof COD and BOD
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Using MS – Excel:• Plot scattered data for BOD
vs COD
• Add trend line with specificcommand to linear line
• Add equation andcorrelation values
COD l i 3COD l i 3
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COD analysis 3COD analysis 3
http://www.scitrav.com/wwater/sasspro/fraccalc.asp (Scientific Traveller)
http://www.scitrav.com/wwater/sasspro/fraccalc.asp (Science Traveller)
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Sampling TechniquesSampling Techniques
Characterisation is greatly affected by the sampling techniques, and follwed by prompt
conveyance of the samples to the laboratory and preservation of the samples, if required.
Correct sampling techniques yields a sample which is truly representative of the nature of
the wastewater. If the flow of wastewater comes to the sampling point in batches, one grab
sample during the flow period may suffice. But if the flow in known to be fluctuated in
quantity and quality, collecting small samples at regular time intervals and mixing them
will be more representative of the actual condition than one grab samples. Mixing up thegrab samples is known as composite samples.
Sampling can be done manually or with the help of autosampler. When sampling program
extends over a long time, it is necessary to preserve either by storing or using suitable
preservatives.
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Wastewater flow fluctuationWastewater flow fluctuation
Every industrial WWTP is designed to handle a certain volume of wastewater per
unit time.
The hydraulic loading varies with time; magnitude of this variation depends on:
•diversity of products manufactured
•process operations contributing to waste
•batch or continuous operation
Difficulties caused by the fluctuation are overcome by providing equalisation
tanks which ensure a more uniform wastewater to the downstream treatment unit
in terms of quality and flowrate.
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Flow measurementFlow measurement
Flow measurement at a treatment plant can be done by:
•Use of stopwatch and bucket
•Area velocity method
•Use of overflow weirs
•Use of Parshall flume
Each method has its own limitations.
Area velocity method
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Area velocity method
Flow can be measured without a hydraulic structure such as a
weir or flume. In the area velocity method, the mean velocity of
the flow is calculated at a cross-section, and this value is
multiplied by the flow area. Flow rate Q is determined according
to the continuity equation:
Q = V x A
The area velocity method is used when it is not practical to use a weir or flume, andfor temporary flow measurements.
The velocity measurement is made using a variety of technologies, including:
Doppler Transit time Electromagnetic Radar
http://www.marsh-mcbirney.com/Articles/yoder-open_channel_flow-3.htm
Overflow weirs
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Overflow weirs
Weirs are structures consisting of an obstruction such as a dam or bulkhead
placed across the open channel with a specially shaped opening or notch. The
weir results an increase in the water level, or head, which is measured
upstream of the structure. The flow rate over a weir is a function of the headon the weir.
http://www.engineeringtoolbox.com/49_592.html
O fl W i 2
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Over-flow Weirs 2
Common weir constructions are the rectangular weir, the triangular or v-
notch weir, and the broad-crested weir. Weirs are called sharp-crested if their
crests are constructed of thin metal plates, and broad-crested if they are made
of wide timber or concrete.
Water level-discharge relationships can be applied and meet accuracy
requirements for sharp-crested weirs if the installation is designed and
installed consistent with established ASTM and ISO standards .
http://www.engineeringtoolbox.com/49_592.html
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V or Rectangular Notch
The basic principle is that discharge is directly related to the water depth above the crotch
(bottom) of the V; this distance is called head (h). The V-notch design causes small changes
in discharge to have a large change in depth allowing more accurate head measurement than
with a rectangular weir.
http://www.engineeringtoolbox.com/49_524qframed.html
http://www.dwaf.gov.za/HydroMpumalanga/structure_types.htm
VV-- Notch Equation Notch Equation
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qq
V-notch weir equations have become somewhat standardized. ISO (1980) and ASTM (1993)
all suggest using the Kindsvater-Shen equation, which is presented below from USBR (1997)
for Q in m3
s and heights in m units. All of the references show similar curves for C and k vs.angle, but none of them provide equations for the curves.
C i T bl f V N h (90 C)
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Conversion Table for V Notch (90oC)
68.0300
57.3280
47.6260
38.9240
31.3220
24.7200
18.9180
14.1160
10.2140
6.911204.36100
2.4980
1.2160
0.44140Flow (l/s)Head (mm)
http://www.fao.org/docrep/T0848E/t08
48e-09.htm
Rectangular Weirs
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The flow rate measurement in a rectangular weir is based on the Bernoulli
Equation principles and can be expressed as:
where
Q = flow rate
h = head on the weir
b = width of the weir
g = gravity
C d = discharge constant for the weir - must be determined
C d must be determined by analysis and calibration tests. For standard weirs - C d - is well
defined or constant for measuring within specified head ranges.
3
2
232 h g C Q d .=
http://www.engineeringtoolbox.com/49_592.html
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Parshall FlumesA Parshall flume is a specially shaped structure which
can be installed in a channel to measure the water flow
rate. The flume was developed and calibrated by Ralph
Parshall at Colorado State University early in this
century and has been used extensively. AlthoughParshall flumes are difficult devices to set and build,
they are an accepted and widely used measuring device.
where:
ha = measuring head (m)
Q = discharge (m3/s)
C and n for each size are given
http://waterknowledge.colostate.edu/parshall.htm
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Flow rateFlow rate
Unit of measurement of flowrate which is often used is meter cubic per second
(m3.s-1) or also known as cumec.
Example
A rectangular channel 3 m wide contains water 2m deep and flowing at a velocity
of 1.5 m/s. What is the flow rate in cumec?
Q = V.A: 1.5m/s x 3m x 2m = 9 cumec.
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Selection of formulaSelection of formula
Most problems involving mathematics in WWTP can be solved by selecting the
proper formula, inserting the known information and calculating the unknown.
Example: Hydraulic Retention Time (HRT) in the processing tank. Q = 6,360
m3/d and the dimension for volume (V) = 18m x 9m x 2.4m (388.8 m3).
HRT = V/Q 388.8 / 6360 = 0.061 d = 1.47 hours
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Selection of formula: Mass Loading RateSelection of formula: Mass Loading Rate
Most of the regulation include the emission standard, but not on the
environmental standard. Environmental standard consider the mass loading rate.
Example:
Plant A emits discharge BOD5 at 100 mg.l-1 with Q: 0.1 cumec
Plant B emits discharge BOD5 at 10 mg.l-1 with Q: 1 cumec
Which plant pollutes more?
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Mass Loading Rate (Answer)Mass Loading Rate (Answer)
MLR = Q x Concentration (mass/time)
Q = m3.s-1 (60 s.min-1 x 60 min.h-1 x 24 h.day-1)
= 86400 m3/d
Concentration = mg.L-1 = g.m-3
Unit for MLR = m3.d-1 x g.m-3 = g.d-1
Plant A: (0.1 x 86 400 x 100) g.d-1 = 864 kg.d-1
Plant B: (1.0 x 86 400 x 10) g.d-1 = 864 kg.d-1