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INDUSTRIAL EFFLUENT

TREATMENT

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Wastewater treatment is a series of steps.

The major categories of treatment steps are :

Preliminary treatment - Removes materials that could

damage plant equipment or would occupy treatment

capacity without being treated.

Primary treatment - Removes settleable and floatable solids

( may not be present in all treatment plants).

Secondary treatment - Removes BOD, dissolved andsuspended organic matter by biological action.

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PRELIMINARY TREATMENT

It is the initial stage in the wastewater treatment

process.

The purpose of preliminary treatment is to protect

plant equipment by removing those materials that

could cause clogs, jams, or excessive wear to plant

machinery .

Preliminary treatment may include many different

processes

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Screening

The purpose of screening is to remove large solids,

such as cans , rocks etc., from the flow before the flow

moves on to downstream processes .

Shredding

shredding can be used to reduce solids to a size that can

enter the plant without causing mechanical problems or

clogging.

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Grit Removal

The purpose of grit removal is to remove the heavy

inorganic solidsthat cause excessive mechanical wear.

accomplished in grit chambers or by the centrifugalseparation of sludge .

Pre-aeration

wastewater is aerated to achieve and maintain: aerobic state

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PRIMARY TREATMENT

The purpose of primary treatment is to remove settleable

organic and floatable solids .

Primary treatment reduces the organic load on downstream

treatment processesby removing a large amount of

settleable, suspended, and floatable materials .

In this treatment, speed of the wastewater through a

clarifier is reduced approximately 1 to 2 ft /min , so thatsettling and floatation can take place.

Slowing the flow, enhances removal of suspended solids in

wastewater

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SECONDARY TREATMENT

The main purpose of secondary treatment/biological

treatment is to provide BOD removal beyond what is

achievable by primary treatment .

There are two commonly used approaches

the trickling filter

the activated sludge Process

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Trickling Filter Tank is filled with solid media

Rocks

Plastic

Bacteria allowed grow on surface of media

Wastewater is trickled over media, at top of the tank

As water trickles through media, bacteria degrade BOD

Bacteria eventually die, fall off of media surface

Filter is open to atmosphere, air flows naturally through

media

Treated water leaves bottom of the tank, flows into

secondary clarifier

Bacterial cells settle, removed from clarifier as sludge

Some water is recycled to the filter, to maintain moistconditions

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Trickling Filter System

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Trickling Filter Process

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Bacteria Removal

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Activated Sludge

Wastewater is aerated in a tank ( Adequate oxygen is fed)

Bacteria are encouraged to grow by providing Oxygen

Food (BOD)

Nutrients

Correct temperature

Time

As bacteria consume BOD, they grow and multiply ( flocculate)

Treated wastewater flows into secondary clarifier

Flocculated cells are readily settle, removed from clarifier assludge

Part of sludge is recycled back to activated sludge tank, tomaintain bacteria population

Remainder of sludge is wasted

Treated water is discharged in to the environment or furtherprocessed for disinfection

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