INDUSTRIAL WASTEWATER TREATMENT

Department of Environmental EngineeringSCHOOL OF ENGINEERING

The principal objective of industrial wastewatertreatment is generally to allow industrial effluents tobe disposed of without danger to human health orunacceptable damage to the natural environment.

To manage water discharged from homes,businesses, and industries to reduce the threat ofwater pollution.

OBJECTIVE

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Sources of Wastewater

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Preliminary treatment

Primary treatment

Secondary treatment

Tertiary treatment

Disposal

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Wastewater Treatment Processes

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• The purpose of preliminary treatment is to protect theoperation of the wastewater treatment plant. This is achievedby removing from the wastewater any constituents which canclog or damage pumps, or interfere with subsequenttreatment processes.

• They are designed to:

1) Remove or to reduce in size the large, entrained,

suspended or floating solids.

2) Remove heavy inorganic solids such as sand and gravel as

well as metal or glass.

3) Remove excessive amounts of oils or greases.

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Preliminary Treatment Processes

Preliminary treatment process consists of following process-

• Screening

• Grit chamber

• Floatation units

• Skimming tanks

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• These consist of bars usually spaced three-quarter inches to sixinches. Those most commonly used provide clear openings of oneto two inches.

• They are usually set at an angle of 45 to 60 degrees with thevertical.

• The racks or screens may be cleaned either manually or by meansof automatically operated rakes.

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Screening

• Wastewater usually contains a relatively large amount of inorganicsolids such as sand, cinders and gravel which are collectively calledgrit

• Grit chambers are usually located ahead of pumps or comminutingdevices, and if mechanically cleaned, should be preceded by coarsebar rack screens. The detention period is usually between 20seconds to 1.0 minute.

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Grit Chamber

• A skimming tank is a chamber so arranged that the floating matterlike oil, fat, grease etc., rise and remain on the surface of the wastewater.

• The chamber is a long trough shaped structure divided up into twoor three lateral compartments by vertical baffle walls.

• A theoretical detention period of 3 minutes is enough. The floatingmatter can be either hand or mechanically removed.

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Skimming Tanks

• The objective of primary treatment is the removal of settle-able organic and

inorganic solids.

• Approximately 25 to 50% of the incoming biochemical oxygen demand (BOD5),

50 to 70% of the total suspended solids (SS).

• It may be considered sufficient treatment if the wastewater is used to irrigate

crops that are not consumed by humans or to irrigate orchards, vineyards, and

some processed food crops.

• Primary sedimentation tanks or clarifiers may be round or rectangular basins,

typically 3 to 5 m deep, with hydraulic retention time between 2 and 3 hours.

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Primary Treatment

• Primary treatment process consists of –

a. Sedimentation tank-primary settling tank

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b. Coagulation-secondary settling tank

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c. Flocculation

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Working of Primary Processo Sludge from the primary sedimentation tanks is pumped to the

sludge thickener. More settling occurs to concentrate the sludgeprior to disposal.

o Primary treatment reduces the suspended solids and the B.O.D. ofthe wastewater.

o Measurement and sampling at the inlet structure

- a flow meter continuously records the volume of water enteringthe treatment plant

- water samples are taken for determination of suspended solidsand B.O.D.

o From the primary treatment tanks water is pumped to the tricklingfilter for secondary treatment.

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Important Concepts in Primary Treatment

• Suspended Solids – the quantity of solid materials floating inthe water column

• B.O.D. (Biochemical Oxygen Demand) - a measure of theamount of oxygen required to aerobically decompose organicmatter in the water

• C.O.D (Chemical Oxygen Demand) - value indicates theamount of oxygen which is needed for the oxidation of allorganic substances in water.

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• The objective of secondary treatment is the further treatment ofthe effluent from primary treatment to remove the residualorganics and suspended solids.

• secondary treatment follows primary treatment and involves theremoval of biodegradable dissolved and colloidal organic matterusing aerobic biological treatment processes.

• High-rate biological processes are characterized by relatively smallreactor volumes and high concentrations of microorganismscompared with low rate processes.

• The biological solids removed during secondary sedimentation,called secondary or biological sludge, are normally combined withprimary sludge for sludge processing.

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Secondary Treatment

Common high-rate processes includes -

• Trickling filters or bio filters

• Rotating biological contactors (RBC).

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Trickling Filters• A trickling filter or bio filter consists of a basin or tower filled with

support media such as stones, plastic shapes, or wooden slats.

• Wastewater is applied intermittently, or sometimes continuously,over the media. Microorganisms become attached to the media andform a biological layer or fixed film.

• Wastewater is applied intermittently, or sometimes continuously,over the media. Microorganisms become attached to the media andform a biological layer or fixed film.

• Forced air can also be supplied by blowers but this is rarelynecessary. The thickness of the biofilm increases as new organismsgrow. Periodically, portions of the film 'slough off the media.

• The sloughed material is separated from the liquid in a secondaryclarifier and discharged to sludge processing.

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Rotating biological contactors (RBC)• Rotating biological contactors (RBCs) are fixed-film reactors similar

to bio filters in that organisms are attached to support media.

• In the case of the RBC, the support media are slowly rotating discsthat are partially submerged in flowing wastewater in the reactor.Oxygen is supplied to the attached biofilm from the air when thefilm is out of the water.

• Sloughed pieces of biofilm are removed in the same mannerdescribed for bio filters.

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• Tertiary and/or advanced wastewater treatment is employed whenspecific wastewater constituents which cannot be removed bysecondary treatment must be removed.

• Individual treatment processes are necessary to remove nitrogen,phosphorus, additional suspended solids, refractory organics, heavymetals and dissolved solids.

• Tertiary Treatment Process are-

- De-chlorination and disinfection

- Reverse Osmosis

- Ion Exchange

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Tertiary Treatment (Optional)

Disposal of wastewater and storm-water should preferably beconsidered only when reuse options are not feasible. Ultimatedisposal of wastewater is either onto land or water (river, lake,ocean).

The general problem areas that are of concern in final disposal arepathogenic microorganisms (viruses, etc.), heavy metals and thepresence of biologically resistant organic compounds, such aspesticides or insecticides which can find their way into watersupplies.

There are three methods by which final disposal of wastewater -Surface Disposal, Subsurface Disposal, Disposal by Dilution

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Sewage Disposal

Surface Disposal• Generally this is disposal by irrigation. This involves spreading the

wastewater over the surface of the ground, generally by irrigationditches.

• This method is largely restricted to small volumes of wastewaterfrom a relatively small population where land area is available andwhere nuisance problems will not be created.

• It has its best use in arid or semi-arid areas where the moistureadded to the soil is of special value.

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Subsurface Disposal• By this method wastewater is introduced into the ground below its

surface through pits or tile fields.

• It is commonly used for disposal of settled wastewater fromresidences or institutions where there is only a limited volume ofwastewater.

• Little application for large scale use in municipalities.

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Disposal by Dilution• Disposal by dilution is the simple method of discharging wastewater

into a surface water such as a river, lake, ocean, estuaries orwetlands.

• The degree of pollution depends on the dilution, volume andcomposition of the wastewater as compared to the volume andquality of the water with which it is mixed.

• However, in spite of the continued aerobic status of the receivingwater, microbial pollution remains a health menace and floatingsolids in the wastewater, if not previously removed, are visibleevidence of the pollution.

• The presence of excessive amounts of nutrients can stimulate plantand algae growth in the receiving waters. This is of special concernin inland, enclosed waters such as lakes and ponds

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THANK YOUNitin Yadav