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How Effluent Treatment Plant (ETP) works?

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What is Effluent Treatment?

Effluent Treatment is the process of removing solid, chemical, and organic substances from the wastewater produced by industries as an outcome of the production process and recycle the water for industrial use or discharge it into the environment safely.

Why is Effluent Treatment important for industries?

Industries use water in their production processes. For example, Pulp & Paper mills, water, cooling system, food & beverages, etc. Every industry needs to adhere to the government guidelines when they discharge the treated wastewater into the environment.

How does Effluent Treatment Plant work?

Effluent Treatment Plant (ETP) has many stages in treating the wastewater produced by the factories. The influent water has acid, oil, grease, and other solid substances like plastic, paper. The Effluent water is recycled back for industry use or discharged to the environment.

ETP Process Stages:


Screening is the first stage where influent water enters. Oil skimmer, Bar Screens, and Grit chambers are used in this stage. An oil skimmer is a type of machine that removes the oil and grease floating on the water. Bar Screen is another piece of equipment that is used as a filter to remove large solid substances like plastic, paper, etc. Grit chambers are another mechanical equipment that filters small solid substances like stone, sand.

After screening, the wastewater goes to Collection Tank and then pumped into Equalization Tank.

Coagulation and flocculation

It's a chemical process. Lime, Aluminum Sulfate are mixed with wastewater to destabilize the suspended solid particles in the water. As Alum is mixed with the water, it helps quicker bonding between solid particles and forms large solid particles. Lime is helping to reduce the pH value. So that it is easy to remove or separate from the wastewater.


A clarifier is a process by which solids are sedimented in a tank at the bottom. This can be achieved naturally by gravity force or using mechanical force. The velocity of the influent is slowed down in the tank so that the sedimentation of the solid will be faster.

Clarifiers are of two types: Primary and Secondary

Primary Clarifier is used to remove large solid particles. Secondary Clarified is used to remove smaller solid particles. The secondary Clarifier tank is bigger in size, has a longer detention time for influent.

The Suspended Solid that is settled at the bottom of the tank is called sludge. Floatable solids are called Scum.

Finally, Sludge is removed from the tank using a sludge plate through a Pit.

Two parameters are mainly measured in Primary & Secondary Clarifiers are :

Surface Over Flow Rate = influent flow rate per second/surface area of the tank

Weir Flow Rate = influent flow rate /length of the weir


Aeration is the next stage to remove Carbon Dioxide(CO2) from wastewater. Oxygen is pumped into wastewater as tiny bubbles. This process will help remove unwanted air like carbon dioxide, hydrogen sulfide, iron, and manganese. As a result, the water will be less corrosive.

After Aeration tank, sometimes the wastewater sent to secondary clarifier.


The filtration process consists of multiple stages. Multi-Grade Filtration, Activated Carbon Filtration, and Ultra Violet Filtration.

Multi-Grade Filtration

Wastewater is sent to the filter tank. The MGF filter tank consists of sand, pebbles that filter the dust and solids, allow the water to pass through, and finally, the water goes to the outlet.

Activated Carbon Filtration

In the ACF filter tank, carbon molecules are used to filter out the chemicals from the water.

Ultra Violet Filtration

UV light is used to disinfect the bacteria, viruses in the wastewater.

Reverse Osmosis

Finally, wastewater is passed through a membrane that will allow only the water and blocks the waste tiny particles and chemicals.

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