Industrial effluents contain various materials, depending on the industry. Some effluents contain oils and grease, and some contain toxic materials (e.g., cyanide). Effluents from food and beverage factories contain degradable organic pollutants. Since industrial wastewater contains a diversity of impurities and therefore specific treatment technology called ETP is required.

Effluent Treatment Plant (ETP) is one type of wastewater treatment method which is particularly designed to purify industrial wastewater for its reuse and its aim is to release safe water to environment from the harmful effect caused by the effluent. The plant works at various levels and involves various physical, chemical, biological and membrane processes to treat wastewater from different industrial sectors like chemicals, drugs, pharmaceutical, tannery, refineries, dairy, ready mix plants & textile, etc.

Treatment of industrial wastewater using ETP

Wastewater enters the effluent or sewage treatment plant and goes through several processes before effluent goes into the environment. Industrial effluent treatment plant process includes the following stages:
  • Preliminary treatment
  • Primary treatment
  • Secondary/Biological treatment
  • Tertiary/Advanced treatment
Preliminary treatment involves physical separation of large-sized contaminants. For example cloth, paper, plastics, wood logs etc. There are 4 levels of treatment at this stage:
  1. Screening: Carried out using a screen with uniform openings and its purpose is to remove large floating solids.
  2. Sedimentation: A physical water treatment process using gravity to remove suspended solids from water.
  3. Grit chambers: Removal of the dense inorganic solids such as gravel, metal fragments and sand which have made their way into the sewers. Removal of grit can prevent damaging of pumps & operational difficulties.
  4. Clarifiers: Tanks built with mechanical means for continuous removal of solids being deposited by sedimentation before biological treatment.
Effluent water after preliminary treatment is then forwarded for primary treatment.
Primary treatment involves removal of floating and settleable materials such as suspended solids and organic matter. In this treatment, both physical and chemical methods like Flocculation, Coagulation, and neutralization are used.
  • Flocculation is a physical process and does not involve the neutralization of charge. It involves the addition of destabilized particles together into large aggregates so that they can be easily separated from the water.
  • Coagulation involves the use of coagulants that are added for the purpose of rapid settlement of minute solid particles in a liquid into a larger mass. It permits particle removal by sedimentation and for filtration.
  • Neutralization helps in maintaining the pH range of 6-9 to meet the requirements of different processing units in ETP system.
  • Primary clarifiers are used to slow the velocity of the water to a point where organic solids will settle to the bottom of the tank and it contains an equipment that is used to remove floating solids and greases from the surface.
Secondary/Biological treatment involves further treatment of the effluent from primary treatment to remove the suspended solids and residual organics using Activated sludge, Aerated lagoons, Trickling filters, and more.
  • Activated Sludge process

This process is for treating industrial wastewater using air and a biological floc composed of bacteria. Here air or oxygen is blown into raw, unsettled sewage to smash the solids and develop a biological ‘floc’ which digests the organic content and pollutants in the sewage. After being discharged into a clarification chamber where live bacteria settle to the bottom, dead bacteria rise to the top and form a crust with a clear liquid in the middle. This clean water is then discharged into either a watercourse or a soak away. The live bacteria, called activated bacterial sludge, are returned to the digestion chamber to re-seed the new raw sewage entering the tank. 

  • Aerated lagoons

These are treatment ponds provided with artificial aeration to promote the biological oxidation of wastewater. The objective of the lagoon is, therefore, to act as a biologically assisted flocculator which converts the soluble biodegradable organics in the influent to biomass which is able to settle as sludge. Usually, the effluent is then put in a second pond where the sludge can settle. The effluent can then be removed from the top, while the sludge accumulates on the floor and undergoes anaerobic stabilization.

  • Trickling filters or sprinkling filters

These are commonly used for the biological treatment of domestic sewage and industrial wastewater. It consists of a fixed bed of rocks, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced-air flowing through the bed or natural convection of air if the filter medium is porous.

  • Rotating Biological Contractor

This process allows the wastewater to come in contact with a biological medium in order to remove pollutants in the wastewater before the discharge of the treated wastewater to the environment. It consists of a series of closely spaced, parallel discs mounted on a rotating shaft which is supported just above the surface of the wastewater. Microorganisms grow on the surface of the discs where biological degradation of the wastewater pollutants takes place.

Tertiary/Advanced treatment involves a final treatment stage to raise the effluent quality to the desired level before it is reused, recycled or discharged to the environment. Processes used at this stage are:
  • Chemical coagulation and sedimentation to increase the removal of solids from effluent after primary and secondary treatment.
  • Filtration plants contain large filter blocks through which the clarified water is passed to ensure high-quality water.
  • Reverse Osmosis is used to force effluent through a membrane that retains contaminants on one side and allows the clean water to pass to the other side.
  • UV disinfection is used as an ideal disinfectant for industrial wastewater. It leaves no residual disinfectant in the water by ensuring the water quality. It does not produce any disinfection by-products.

Benefits of ETP

There are several benefits associated with using ETPs for treating industrial wastewater.

  • To clean industry effluent and recycle it for further use
  • To reduce the usage of fresh water in industries
  • To preserve the natural environment against pollution
  • To meet the standards for emission of pollutants set by the Government & avoid heavy penalty
  • To reduce expenditure on water acquisition

Common Effluent Treatment Plant (CETP)

The design of ETP depends on quality and quantity of wastewater discharged from the different industries and land availability. If the availability of land in your industry is less, then Common Effluent Treatment Plant (CETP) is preferred over Effluent Treatment Plant (ETP).

Debarassi CETP case study

In January 2018, following efforts put in by the Punjab Pollution Control Board (PPCB), major pharmaceutical companies having their manufacturing plants in and around Derabassi in Mohali district have decided to come up with an Rs. 80-crore common effluent treatment plant (CETP). The Derabassi municipal committee had already given a piece of land on lease for the setting up of a CETP.
In an official public statement, it was said in addition to the effluent from the units, the CETP would also treat sewage water from ponds of adjoining villages as a part of the corporate social responsibility.