wastewater treatment 01-02-12

7/31/2019 Wastewater Treatment 01-02-12

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Wastewater Treatment

M.M. Ghangrekar

Department of Civil EngineeringIndian Institute of Technology

Kharagpur


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EFFECT OF UNTREATED WASTEWATERDISPOSAL

The organic matter present in the wastewater will undergo decomposition withproduction of large quantities ofmalodorous gases.

Untreated wastewater will result in the depletion of Dissolved Oxygen (DO)from the water bodies.

Due to depletion of DO, the survival of aquatic life will become difficult, finally

leading to anaerobic conditions in the receiving waters. The nutrients present in the wastewater can stimulate the growth of aquaticplants, leading to problems like eutrophication.

Untreated domestic wastewater usually contains numerous pathogenic ordisease causing microorganisms, that dwell in the human intestinal tract orwhich may be present in certain industrial wastewaters.

The continuous deposition ofinorganic material may reduce the capacity ofwater body considerably over a period.

Even untreated wastewater will have adverse effect when used for irrigation,such as altering salts in the soil, alteration in granulation characteristics of soil,etc.


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SEWAGE CHARACTERISTICS

Temperature: under Indian condition the temperature of the rawsewage was observed to be between 20 to 300C at various places. The pH: Generally the pH of raw sewage is in the range 5.5 to 8.0. Colour and Odour: slightly soapy and cloudy appearance depending

upon its concentration. Solids: sewage contains only 0.1 percent solids, the rest being water,

still the nuisance caused by the solids cannot be overlooked, as thesesolids are highly putrescible and therefore need proper disposal.

Nitrogen and Phosphorus: About 25 40 mg/L N, and 5 to 10 mg/L P Organic Material: BOD 100 to 400 mg/L, COD 200 to 700 mg/L. Toxic Metals and Compounds: Generally these materials are not

present in toxic limits for biological wastewater treatment in domesticsewage, but in municipal wastewater some of them may be present inhigher concentration due to industrial discharges.


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EFFLUENT DISPOSAL & UTILISATION

The sewage after treatment may be disposed either intoa water body such as lake, stream, river, estuary, andocean or on to land.

Treated sewage can be used forIndustrial reuse orreclaimed sewage effluent cooling system, boiler feed,

process water, etc., Reuse in agriculture and horticulture, watering of

lawns, golf courses and similar purpose, and Ground water recharge for augmenting ground water

resources for downstream users or for preventing salinewater intrusion in coastal areas.


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IS tolerance limits for sewage & industrial effluents

These standards are withdrawn and modified by CPCB now


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What is Sewage Treatment Plant ?

Sewage Treatment Plant is a facility designed to receive thewaste from domestic, commercial and industrial sources and toremove materials that damage water quality and compromisepublic health and safety when discharged into water receivingsystems.

Objective: - The Principal objective of wastewater treatment isgenerally to allow human and industrial effluents to be disposed ofwithout danger to human health or unacceptable damage to thenatural environment.

Conventional wastewater treatment consists of a combination ofPhysical, chemical, and biological processes and operations toremove solids, organic matter and, sometimes, nutrients fromwastewater.


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Sewage treatment

Preliminary treatment:

It is the removal of coarse solids and other large materials often found in raw wastewater. Removal of these materials is necessary to enhance the operation and maintenance ofsubsequent treatment units.

Preliminary treatment operations typically include coarse screening, grit removal and, in somecases, shredding of large objects.

Primary treatment is the removal of settleable organic and inorganic solids bysedimentation, and the removal of materials that will float (scum) by skimming.

Secondary treatment: In most cases, secondary treatment follows primary treatment andinvolves the removal of biodegradable dissolved and colloidal organic matter usingaerobic biological treatment processes.

Aerobic biological treatment is performed in the presence of oxygen by aerobic microorganisms

(principally bacteria) that metabolize the organic matter in the wastewater, thereby producing moremicroorganisms and inorganic end-products (principally CO

2, NH

3, and H

2O). Several aerobic and

anaerobic biological processes are used for secondary treatment.

Common high-rate aerobic processes include the activated sludge processes, trickling filters or biofilters, oxidation ditches, and rotating biological contractors (RBC).

Anaerobic high rate processes such as upflow anaerobic sludge blanket (UASB) reactor and anaerobic

filters are also used. A combination of two of these processes in series (e.g. UASB followed by activated sludge or oxidation


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SEWAGE TREATMENT FLOW SHEET

(a) Process Flow sheet Incorporating Oxidation Ditch

(b) Process Flow sheet Employing Aerated Lagoon


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(c) Process Flow sheet Employing Waste Stabilization Pond

(d) Process flow sheet employing anaerobic treatment devices


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(e) Process Flow-sheet of Conventional Domestic Wastewater Treatment


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Wastewater Treatment ProcessPretreatmentinvolves:

Screening Grit Removal

Oil separation Flow equalization

Disinfectioncan use: Chlorine

compounds Bromine Chloride Ozone UV Radiation

Chemical Treatmentisused in conjunction withthe physical and

chemical processes: Chemical

precipitation Adsorption

Sludge Treatment andDisposal involves:grinding, degritting, blending,thickening, stabilization,conditioning, disinfection,dewatering, heat drying, thermal

reduction, ultimate disposal


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Screens


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Grit chamber

Horizontal flow grit chamber

Aerated Grit chamber


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Primary Sedimentation Tank

Baffle placed ahead of effluent channelfor removal of oil & grease


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Biological Treatment

In the case of domestic wastewater treatment, theobjective of biological treatment is:

To stabilize the organic content To remove nutrients such as nitrogen and phosphorus

Types:

Aerobic Processes Anoxic Processes Anaerobic Processes Combined Aerobic-Anoxic-

Anaerobic Processes

Pond Processes

Attached Growth Suspended Growth

Combined Systems

Aerobic Maturation Facultative

Anaerobic


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Major Aerobic Biological Processes

Type ofGrowth

Common Name Use

SuspendedGrowth

Activated Sludge (AS) Carbonaceous BOD removal (nitrification)

Aerated Lagoons Carbonaceous BOD removal (nitrification)

Attached

Growth

Trickling Filters Carbonaceous BOD removal. nitrification

Roughing Filters (tricklingfilters with high hydraulicloading rates)

Carbonaceous BOD removal

Rotating BiologicalContactors

Carbonaceous BOD removal (nitrification)

Packed-bed reactors Carbonaceous BOD removal (nitrification)CombinedSuspended &AttachedGrowth

Activated BiofilterProcess

Trickling filter-solidscontact process

Biofilter-AS process Series trickling filter-AS

process

Carbonaceous BOD removal (nitrification)


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Activated Sludge Process

The aeration tank contains a suspension of the wastewater andmicroorganisms, the mixed liquor. The liquor is mixed by aerationdevices (supplying also oxygen)

A portion of the biological sludge separated from the secondary

effluent by sedimentation is recycled to the aeration tank

Types of AS Systems: Conventional, Complete-Mix, SequencingBatch Reactor, Extended Aeration, Deep Tank, Deep Shaft


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Advantages/Disadvantages of ASP

Advantages

Flexible, can adapt tominor pH, organic andtemperature changes

Small area required Degree of nitrification is

controllable Relatively minor odor

problems

Disadvantages

High operating costs(skilled labor, electricity,

etc.) Generates solidsrequiring sludge disposal

Some processalternatives are sensitive

to shock loads andmetallic or other poisons

Requires continuous airsupply


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Trickling Filters

The trickling filter or biofilter consists of a bed of permeablemedium of either rock or plastic

Microorganisms become attached to the media and form abiological layer or fixed film. Organic matter in the

wastewater diffuses into the film, where it is metabolized.Periodically, portions of the film slough off the media


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Advantages/Disadvantages of Trickling Filter

Advantages

Good quality (80-90%BOD

5removal) for 2-

stage efficiency couldreach 95%

Moderate operatingcosts (lower thanactivated sludge)

Withstands shock loadsbetter than otherbiological processes

Disadvantages

High capital costs Clogging of distributors

or beds Snail, mosquito andinsect problems


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Major Anaerobic BiologicalProcesses

Type ofGrowth

Common Name Use

SuspendedGrowth

Anaerobic Contact Process Carbonaceous BOD removal

Upflow Anaerobic Sludge-Blanket (UASB)

Carbonaceous BOD removal

AttachedGrowth

Anaerobic Filter Process Carbonaceous BOD removal,waste stabilization(denitrification)

Expanded Bed Carbonaceous BOD removal,waste stabilization


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Upflow Anaerobic Sludge Blanket

Wastewater flowsupward through a sludgeblanket composed ofbiological granules that

decompose organicmatter

Some of the generatedgas attaches to granules

that rise and strikedegassing bafflesreleasing the gas

Free gas is collected by

special domes


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Advantages/Disadvantages of UASB

Advantages

Low energy demand Low land requirement

Methane as valuablebyproduct Low sludge production Less expensive than

other anaerobic

processes High organic removal

efficiency

Disadvantages

Long start-up period Requires sufficient

amount of granular seedsludge for faster start-up Significant wash out of

sludge during initialphase of process

Required skilledoperator.


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Pond Treatment Processes

CommonName Comments Use

AerobicStabilizationPonds

Treatment with aerobic bacteria;oxygen is supplied by algalphotosynthesis and natural surfacereaeration; depth of 0.15 to 1.5 m

Carbonaceous BODremoval

Maturation(tertiary) Ponds

Use aerobic treatment; appliedloadings are low to preserve aerobicconditions

Secondary effluentpolishing and seasonalnitrification

FacultativePonds

Treatment with aerobic, anaerobicand facultative bacteria; the pondhas 3 zones: a surface aerobiczone, a bottom anaerobic zone, andan intermediate zone partly aerobic-anaerobic

Carbonaceous BODremoval

AnaerobicPonds

Treatment with anaerobic bacteria;depths of up to 9.1 m to conserveanaerobic conditions

Carbonaceous BODremoval (wastestabilization)


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Anaerobic digester for sludge treatment

wastewater treatment 01-02-12

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