IMN-04-Biological Waste Water Treatment Systems

7/23/2019 IMN-04-Biological Waste Water Treatment Systems

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Large-scale WW Treatment

Schemes



• Characteristics of wastewater ( domestic)CONSTI TUENT(mg/l)

STRON G Di l uted Tr eated WWf or dischargeto water bodies

Solids : TotalDissolved, Total

FixedVolatile

Suspended, TotalFixedVolatile

120085052532535075

275

72050030020022055

165

100

Settleable solids 20 10

Biochemical oxygendemand(BOD 5 , 20°C) 400 220

30

Total Organiccompound (TOC)

290 160

Chemical oxygendemand (COD) 1000 500

250

Nitrogen (Total as N)

OrganicFree ammonia Nitrites Nitrates

85

355000

40

152500

50 (NH4)

10( NO3)

Phosphorus (Total as P)OrganicInorganic

155

10

835

5

Chlorides 100 50

Alkalinity (as CaCO 3 ) 200 100

Grease 150 100



Wastewater Treatment System • Wastewater treatment system in general comprises of three parts:(i) primary treatment

– The objective of primary treatment is to remove suspended, easily settleableand floating material

(ii) secondary treatment, and –

Secondary treatment systems are mostly biological processes to removecolloidal and dissolved carbonaceous organic matter.(iii) tertiary treatment.

– Tertiary treatment systems are aimed at nitrogen and phosphorus removalprovided for polishing the secondary treated effluent to meet the dischargerequirements

(iv) Quaternary treatment : To bring back waste water to the similar orbetter quality as the freshwater by removing dissolved solids so that it can bereused in industries or recycled back into the water supply



Wastewater Treatment:ReactionsThe aerobic conversion of the organic matter occurs in three steps:1. Oxidation

COHNS + O2 + BACTERIA CO2 + NH3 + END PRODUCTS+ ENERGY(Organic matter)

2. Synthesis of new cellsCOHNS + O2+ BACTERIA + ENERGY C5H7NO2

Organic matter (new cells )3. Endogenous respiration

C5H7NO2 + 5O2 5 CO2+ NH3+ 2H2O + ENERGY(Bacterial cells)

• Tertiary Treatment for nitrogen removal ( Biological)

NH4 + + Nitrifying bacteria NO 3 - + Denitrifying bacteria Nitrogen gas

• Tertiary Treatment for phosporus removal with Alum or Ferric or Lime( Chemical)

Al3+ + PO4 -3 -- AlPO4; Fe3+ + PO4-3 Fe PO4;

Ca(OH)2 + PO4 Ca5OH(PO4)3



Different Biological Systems

Suspended growthActivated Sludge processSBR, Extended Aeration, contact stabilisation

Attached GrowthTricking Filters, Bio towers

Hybrid systemsRotating Biological Contactors ( RBC)Moving Bed Bio reactors( MBBR)

Membrane Bio reactors (MBR)



Sewage Treatment Process Selection

Considerations Consideration Goal Treated Sewage qualitystandards

The technology must consistently meet the standards asrequired.

Power requirement The process choice should consider minimizing power

requirements

Land required Minimize land requirement

Capital Cost of Plant Process should allow optimum utilization of capital

Operation & Maintenancecosts

Process design should be conducive to attaining lowerrunning cost

Maintenance requirement Simplicity and reliability Operator attention Easy to understand procedures

Reliability Deliver the desired quality on a consistent basis

Resource Recovery Ability to minimize operational costs.

Load Fluctuations: Plant can able to withstand organic and hydraulic load

fluctuations



Flow diagram ASP based WWTP



Bar screen - coarse







Oil and Grease removal – SkimmingTank



An empty sedimentation tank.



secondary Sedimentation tank at a ruraltreatment plant.



Suspended Growth Processes

Activated Sludge Process

Designed based on loading

(the amount of organicmatter added relative tothe microorganismsavailable)

Commonly called the food-

to-microorganisms ratio,F/M

F measured as BOD. Mmeasured as volatile

suspended solidsConcentration MLSS



Conventional Activated Sludge Process

• Activated Sludge Process is a suspended growth aerobic process.• About 40% of organic load is removed in primary clarifier• Detention period in aeration tank is maintained between 4-6hours.• A major portion of the sludge is re-circulated and excess sludge is

sent to a digester



Merits and Demerits – Good process flexibility – Reliable operation – Proven track record in all plant sizes – Less land requirement – Low odour emission – Energy production – Ability to withstand nominal changes in water characteristics

Demerits – High energy consumption –

Skilled operators are needed – Uninterrupted power supply is required – Requires elaborate sludge digestion, drying and disposal arrangement – No nutrient removal



Extended Aeration ASP SystemExternal substrate is completely removed.

Auto oxidation (internal substrate is used)

Net growth = 0



Advantages of Extended aeration ASP (IITM plant)

• Sludge production minimal

• Stabilized sludge No digesters are required

• Nutrient requirement minimalDisadvantages of Extended Aeration ASP

• High power requirement

• Large volume of aeration tank

• Suitable for small communities







Aerated lagoon used to treat wastewaterfrom a hogfarm



Fine bubble membrane diffusers in anaeration tank



Sequencing Batch Reactor

• It is a fill-and-draw batch ASP incorporating all the featuresof extended aeration plant.

• Reactor operation takes place in certain sequence in cyclicorder and in each cycle

–

Filling tank – Aeration – Sedimentation/clarification – Decantation – Sludge withdrawal

• A number of large and small scale plants exist with severalyears of continuous operation in India and elsewhere.



System Schematics

C-Tech Basin

DECANTER SELECTOR

INLET

OUTLET

SLUDGE PUMPDIFFUSER BIOMASS



SBR Cycle of operation

Inletstart

Inletend

Outletstart

Outletend

B

BB

B B

Aerobic

Aerobic Anoxic

Anoxic

Anoxic



System Schematics …

3 Hrs

Basin - 1 Settling Decanting

Basin - 2 Settling Decanting

Fill + Aeration

Fill + Aeration

1.5 HrsTime - 0 hrs

Operating sequence of a 2 Basin system



Ammonia converted to Nitrates in the Aeration basin.

Denitrification of recycled effluent occurs in the selector basin

Denitrification occurs concurrently in the aeration tank duringthe settling / decant phase

Nitrogen gas is stripped off during aeration cycle.

Nitrate diffusion rate is 5 times more than Oxygen. So Nitratereaches the center of the flocs faster than Oxygen, therebypromoting denitrification.

Concurrent Nitrification / Denitrification in SBR

Biofloc

De-nitrification occursin the central portionof the floc

Nitrification happensin the periphery ofthe floc



Biological Phosphorous Removal in SBR Anaerobic conditions for short time followed by aerobic phase willincrease the uptake of Phosphorous by biomass

During settlement and decant the biomass oxidation reductionpotential depletes from a positive value of around +50 to +100 mVto a negative value of around –150 to – 200 mV. This aids P removal

d



Over 50% Energy Reduction

Conventional

K W H / K g C O D

Continuous measurement of DO and Temperature in the basin

Predictive calculations of Biological metabolic activity by the PLC

Automatic and dynamic control of aeration time and intensity by the PLCbased on the existing metabolic activity - Oxygen Uptake Rate (OUR).

Recovering the oxygen used for nitrification back in the process bydenitrificationBlower can be switched off during low flow as there is no problem of shortcircuiting like in continuous system like ASP..

Dynamics of OUR and COD-loads

0

200

400

600

800

1.000

1.200

2 5. 6 26. 6 26. 6 26 .6 2 6. 6 27. 6 27. 6 27. 6 27. 6 28. 6 28. 6

[ k g C O D / 2 h r s ]

0

5

10

15

20

25

O U R [ m g / l . h ]

COD

ffc-OUR



Merits and Demerits of SBR – Excellent effluent quality – Smaller footprint because of absence of primary and secondary

clarifiers, and digester – Proven technology –

Biological nutrient (N and P) removal – High degree of coliform removal – Less chlorine dosing required – Can withstand hydraulic and organic shock loads

Demerits – Comparatively higher energy consumption – To achieve high efficiency, complete automation is required – Highly skilled operators are needed – No energy production – Uninterrupted power supply is required



Attached growth processTrickling filter



Attached Growth Systems - Trickling Filters

T.F Reactor in which randomly packed solidsforms provide surface for microbial growth.

- system for wastewater distribution

Specific surface area and porosity

Specific surface area: The amount of surface areaof the media that is available for bio film growth



A typical complete trickling filter system





Trickling Filters

With time, the “slime” layerbecomes thicker and thicker untiloxygen and organic matter can notpenetrate to the organisms on theinside.

The organisms on the inside thendie and become detached from themedia, causing a portion of the“slime” layer to “slough off”.

This means the effluent from atrickling filter will have lots of solids(organisms) in it which must be

removed by sedimentation



Trickling filter- A schematic cross-section of the contact face of the bed of media in a

trickling filter

Trickling Filters Single St ge nd T ost ge



Trickling Filters -Single Stage and Twostage

Single Stage Trickling Filter

Two Stage Trickling Filter



Hybrid systemsRotating Biological contactor





RBCs



Moving Bed Bio film Reactor

• MBBR is an aerobic attached biological growth process• It does not require primary clarifier and sludge

recirculation.• Raw sewage, after screening and de-gritting, is fed to

the biological reactor.• Floating plastic media is provided which remains in

suspension. Biological mass is generated on the surfaceof the media.

•

Excess biological mass leaves the surface of media andis settled in clarifier.• Usually a detention time of 5 to 12 hours are provided

in the reactors.



Aerobic reactor Anoxic reactor

Moving bed biofilm reactor (MBBR)Presence of plastic media of various shapes on which bacteria grows into thick biofilmswhich are always kept suspended thus facilitating attached and suspended conditions



The Moving Bed Biofilm Reactor(MBBR)



The principal moving bedprocesses

The basic MBBR TM processes

The BAS TM processes

The IFAS(HYBAS TM)processes



MAJOR COMPONENTSa) Media

b) Aeration Systemc) Sieve Assemblies

d) Tanke) Blowers

f) Mixers

The components of the MBBRtreatment system

The carriers most commonly



The carriers most commonlyused today

K1

• 500 m 2 /m 3 bulk

• 9,1 mm diameter

• 7,2 mm length

• 335 m 2 /m 3 67 %

• 500 m 2 /m 3 bulk

• 25 mm diameter

• 12,0 mm length

• 335 m 2 /m 3 67 %

K3

Biofilm chip™ -P

• 900 m 2 /m 3 bulk

• 45 mm diameter

• 3 mm thick

• 500 m 2 /m 3 55 % fill



Comparison between systems

Parameter MBBR IFAS (HYBAS) Activatedsludge

Biomass Attached Attached andsuspeded

Suspended

Recycle No Yes Yes

MLSS-conc Low (100 –

300)

High (2000 –

4000)

High (3000 –

5000)Biomassseparation

Any Settling Settling

Design rate r = Q*C/A – kg/m 2*d

Both F/M – kgBOD/kgMLSS*dƟc – kg SS/kgSS d -1 =

H b id S



Hybrid Systems-Membrane Bioreactors (MBR)

• Employ biological reactor and membranefiltration as a unified system for the secondarytreatment of wastewater

• Membranes perform the separation of thefinal effluent from the biomass throughfiltration

• Filtration takes place by the application of apressure gradient



Process Basics

SS

Deni Nitri

SS

SCTdischarge

conventional technologymembrane technology

NDN

effluentUF notSec. Clarif.

http://en.wikipedia.org/wiki/Activated_sludge



Schematic of conventional activated sludge process(top) and membrane bioreactor (bottom)

Hybrid systems Membrane bioreactor





Hybrid systems - Membrane bioreactor

Simple schematic describing the MBR process



Schematic of a submerged MBR



Merits and Demerits of MBR system – Low hydraulic retention time and hence low foot print (area)

requirement – Less sludge production – High quality effluent in terms of low turbidity, TSS, BOD and bacteria – Nutrient Removal is possible –

Stabilized sludge – Ability to absorb shock loadsDemerits

– High construction cost – Very high operation cost – Periodic replacement of membranes is required – High membrane cost – High automation – Fouling of membrane



Anaerobic digestion

Can be done for raw wastewater orsludge from aerobic systems



Stages of anaerobic digestion

Upflow Anaerobic Sludge Blanket



Upflow Anaerobic Sludge BlanketProcess

Promote Anaerobic treatment technologies forenergy generation

Less energy intensive

Can generate alternate energy

So far not very successful due to the lack ofinformation about the process

• Demonstration plants• Operational guidelines• Training in design, maintenance and operation



UASB Reactors• UASB is an anaerobic process

in which influent wastewateris fed from the bottom of thereactor and travels in an up-flow mode through thesludge blanket

• Critical components of UASBdesign are the influentdistribution system, the gas-solids separator and effluentwithdrawal design.

•

Compared to other anaerobicprocesses, UASB allows theuse of high hydraulic loading.

Biogas

HydraulicSeal

Effluent

Settling

PhaseSeparator

element

Screenedand de-grittedsewage

Biogas

Anaerobic Sludge Blanket

Anaerobic digestion and regenerative thermal oxidiser

http://en.wikipedia.org/wiki/Regenerative_thermal_oxidiser




Anaerobic digestion and regenerative thermal oxidiser component of Lübeck mechanical biological treatment plant

in Germany , 2007


http://en.wikipedia.org/wiki/Lubeck_Waste_Treatment_Facility

http://en.wikipedia.org/wiki/Mechanical_biological_treatment

http://en.wikipedia.org/wiki/Germany

http://en.wikipedia.org/wiki/Germany

http://en.wikipedia.org/wiki/Mechanical_biological_treatment

http://en.wikipedia.org/wiki/Lubeck_Waste_Treatment_Facility




Application-Gas street lamp









Tertiary Treatment

Aimed at removing nutrients and make effluent recyclable



Advanced Water Treatment FacilityFlow Diagram

UltravioletDisinfection

(UV)Treated

Sewage

Microfiltration(MF)

Reverse Osmosis(RO)

PurifiedWater





Microfiltration is the First Step• Technology brought to

the U.S. after WW II• Used in computer,

food andpharmaceuticalmanufacturing

• Used to sterilizemedicines that can’tbe heated

• Best pre-treatmentbefore reverse osmosis

Water + contaminantsunder pressure

Porous hollowfiber

MF membranePurified

Water

S

S

S

S

SS

S

SS

SS

S

S

Backwashto OCSD

SS

RO Membrane Is Like a Microscopic



Strainer That Allows Water Moleculesto Pass Through

Protozoa

Bacteria

VirusOrganics

Inorganics

WaterMolecules



IMN-04-Biological Waste Water Treatment Systems

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