Industrial waste water ( Effluent ) treatment describes the process used for treating waste water produced by industries as an undesirable by-product. After treatment, the treated waste water may be reused or released to a Sanitary sewer or to a surface water in the environment.


  • To remove all inorganic & organic through physical, chemical and biological process
  • To clean industry effluent and recycle it for further use.
  • To reduced the usage of fresh/potable water in industries.
  • To cut expenditure on water procurement.
  • To meet the standards for emission or discharge of environmental pollutants from various industries set by the government and avoid hefty penalties.
  • To safeguard environment against pollution and contribute in sustainable development

Design of ETP:-

The design and size of the ETP depends upon:

  • Quality and quality of the industries discharge effluent.
  • Land availability.
  • Monetary consideration for construction, operation & maintenance.

Treatment Levels & Mechanisms of ETP:–

Treatment Levels:

  • Preliminary
  • Primary
  • Secondary
  • Tertiary ( or advanced )

Treatment Mechanisms:

  • Physical
  • Chemical
  • Biological

Preliminary Treatment Level:

Purpose: Physical separation of big sized impurities like cloth, plastics, wood logs, paper, etc.Common physical unit operations at Preliminary level are:

Screening : A screen with openings of uniform size is used to remove large solids such as plastics, cloths etc. Generally maximum 10mm is used.

Sedimentation: Physical water treatment process using gravity to remove suspended solids from water.

Clarification: Used for separation of solids from fluids.

Tertiary / Advanced Treatment:

Purpose :-  Final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment.

Mechanism:-  Removes remaining inorganic compounds, and substances, such as the nitrogen and phosphorus. Bacteria, viruses and parasites, which are harmful to public health, are also removed at this stage.


  • Alum : Used to help remove additional phosphorus particles and group the remaining solids together for easy removal in the filters.
  • Chlorine contact tank disinfects the tertiary treated waste water by removing microorganisms in treated waste water including bacteria, viruses and parasites.
  • Remaining chlorine is removed by adding sodium bisulphate just before it’s discharged.

Primary Treatment Level:

Purpose: Removal of floating and settleable materials such as suspended solids and organic matter.

Method: Both physical and chemical methods are used in this treatment level.

Chemical unit process:

  • Chemical unit processes are always used with physical operations and may also be used with biological treatment process.
  • Chemical processes use the addition of chemicals to the waste water to bring about changes in its quality.
  • Example: pH control, coagulation, chemical precipitation and oxidation.

pH Control:

  • To adjust the pH in the treatment process to make wastewater pH neutral.
  • For acidic wastes ( low pH ): NaOH, Na2Co3, CaCO3 or Ca(OH)2.
  • For alkali wastes ( high pH): H2SO4, HCL.

Chemical coagulation and Flocculation:

  • Coagulation refer to collecting the minute solid particles dispersed in a liquid into a larger mass.
  • Chemical coagulants like AL(SO4)3 { also called alum } or Fe2(SO4)3 are added to wastewater to improve the attraction among fine particles so that they come together and form larger particles called flocks.
  • A chemical flocculent ( usually a polyelectrolyte ) enhances the flocculation process by bringing together particles to form larger flocks, which settle out more quickly.
  • Flocculation is aided by gentle mixing which causes the particles to collide.

Secondary Treatment Level:

Methods: Biological and chemical processes are involved in this level.

Biological unit process:

  • To remove, or reduce the concentration of organic and inorganic compounds.
  • Biological treatment process can take many forms but all are based around microorganisms, mainly bacteria.

Aerobic Processes:

  • Aerobic treatment processes take place in the presence of air ( OXYGEN ).
  • Utilizes those microorganisms ( aerobes ), which use molecular/free oxygen to assimilate organic impurities i.e. convert them into carbon dioxide, water and biomass.

Anaerobic Processes:

  • The anaerobic treatment processes take place in the absence
  • Utilizes microorganisms (anaerobes) which do not require air (molecular/ free oxygen ) to assimilate organic impurities.
  • The final products are methane and biomass.

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