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Effluent Treatment Plants (ETP)

Industrial effluent, treated to meet discharge or reuse norms.

An effluent treatment plant treats the wastewater from an industrial process. Unlike sewage, effluent differs from one factory to the next — so an ETP is designed from the effluent’s own analysis, combining physical, chemical and biological stages.

Effluent Screen &oil trap Equalisation &neutralisation Coagulation &flocculation Primaryclarifier Biologicaltreatment Secondaryclarifier Tertiaryfiltration Discharge or reuse sludge to filter press acid / alkali coagulant

What it means

Effluent can carry almost anything a process uses: oils, dyes, metals, acids or alkalis, high organic loads, fine solids. Each needs a different treatment, which is why there is no standard ETP.

A typical plant works in stages. First the flow is evened out and its pH corrected. Chemicals then gather fine particles into flocs that settle. Biological treatment removes dissolved organics, and tertiary filtration polishes what is left.

The goal is set by the norms the plant must meet — for discharge to a sewer or the environment, or for reuse within the factory.

How it works

Step by step, as drawn in the diagram above.

  1. 1

    Screening and oil removal

    Screens catch solids and an oil and grease trap skims floating oil.

  2. 2

    Equalisation and neutralisation

    A tank evens out flow and strength, and the pH is corrected with acid or alkali dosing.

  3. 3

    Coagulation and flocculation

    Chemicals make fine particles clump into flocs, which settle in the primary clarifier.

  4. 4

    Biological treatment

    An aerated stage removes dissolved organic load, followed by a secondary clarifier.

  5. 5

    Tertiary treatment

    Sand and carbon filtration polish the water for discharge or reuse; sludge is dewatered in a filter press.

Designed from the effluent

Before any design, the effluent is characterised. The key measures:

  1. 1 Flow How much, and how it varies over a shift.
  2. 2 pH Acidic or alkaline, and how much it swings.
  3. 3 COD and BOD The organic load, and how much of it is biodegradable.
  4. 4 Solids, oil and colour Suspended solids, oil and grease, and colour.
  5. 5 Specific contaminants Metals or other substances particular to the process.

What it takes out

  • Suspended solids
  • Oil and grease
  • Organic load (COD and BOD)
  • Colour and many specific contaminants, depending on the stages chosen

What it does not

  • Dissolved salts, unless further stages are added
  • What the chosen stages are not designed for — every ETP is specific

Where it is used

  • Textile and dyeing
  • Food and dairy processing
  • Pharmaceuticals and chemicals
  • Engineering and metal finishing
  • Any process discharging wastewater

What we size it on

  • The effluent analysis — flow, pH, COD, BOD, solids, oil, colour
  • The discharge or reuse norms to meet
  • Shift pattern and peak loads
  • Sludge handling and space on site

Looking after it

  • Keep chemical dosing matched to the effluent
  • Watch pH and the biological stage closely
  • Dewater and dispose of sludge as required
  • Test treated water against the norms

Questions, answered

How is an ETP different from an STP? ＋

An STP treats sewage, which is broadly similar everywhere and mostly organic. An ETP treats industrial effluent, which varies with the process and often needs chemical stages before any biological treatment.

Can effluent be reused? ＋

Often, yes — with enough treatment for the use in mind. Many plants reuse treated water for cooling, washing or gardening; reuse in the process may need further stages such as RO.

What do you need to design an ETP? ＋

An analysis of the effluent, the flow and how it varies, and the norms it must meet. Everything else follows from those.

The rest of the treatment train

Clean water in

Water Softeners

Hardness out. Scale, white spots and failing geysers with it.

Clean water in

Sand & Carbon Filters

Particles out with sand. Chlorine, odour and colour out with carbon.

Clean water in

Ultrafiltration (UF)

Particles and microbes out. Minerals stay in.

Clean water in

Industrial RO Skid Systems

Dissolved salts out — the one thing no filter can touch.

Clean water out

Sewage Treatment Plants (STP)

A building’s sewage, treated well enough to use again.
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