The water people use in their homes and factories gets dirty. Sewers carry much of the domestic waste water away. Many factories get rid of their waste water in a similar way. Most of this waste water ends up in natural water bodies,such as rivers, lakes and oceans. If it is not cleaned first, it can pollute the water and cause harmful effects.

• This waste water contains large amounts of organic waste from food and other materials and includes Carbohydrates, Fats, Proteins and micro organisms

Now lets ask some questions to ourselves...

  • Why should we purify the waste water?
  • Studying the adverse effects of discharging large amount of waste water into natural water bodies may make you realize the answer...
  1. 1. Dis semination of pathogenic micro organisms
  2. 2.Water pollution due to accumulation of biodegradable material and their decomposition products
  3. 3.Decomposition which may consume large amounts of oxygen in water affecting aquatic organisms (high BOD – biological oxygen demand)
  4. 4.Anaerobic decomposition leading to bad smells
  5. 5.Natural water bodies are polluted and become useless for human needs.
  6. 6.When the nutrients in the waste water reach the natural water bodies, it may result in eutrophication and large algal blooms, which may result in serious damage to animal and plant life.

• It is a legal requirement in most countries that such waste waters are properly treated to a required standard before being discharged into natural waters



Now lets see the principles and main steps in purification of industrial waste water.

  • The purification process contains two steps:

            1.Primary treatment

            2.Secondary treatment

 Primary treatment


  • ™ Large floating materials screened out
  • Sand removed
  • Oil and grease removed
  • Solid matter settles out in sedimentation tanks
  • Sludge collected and removed (see diagram)
  • No biological activity is used here
  • Primary treatment removes 25-35% organic matter


 Secondary treatment


™ The liquid flowing out of primary treatment enters the secondary treatment stage


  • During this treatment waste water is aerated to facilitate growth of aerobic bacteria and rapid microbial oxidation.
  • One of two systems used are:
  1. 1.Activated sludge
  2. 2.Trickling filter.


  • ™ In activated sludge vigorous aeration is done mechanically.

  secondary treatment in purification of industrial waste water

  • The terms trickle filter, trickling biofilter, biofilter, biological filter and biological trickling filter are often used to refer to a trickling filter. These systems have also been described as roughing filters, intermittent filters, packed media bed filters, alternative septic systems, percolating filters, attached growth processes, and fixed film processes.
  • In trickling filters waste water is slowly sprinkled or sprayed over a bed of rocky material and allowed to trickle.
  • In this process micro organisms grow on the filter bed and oxidize organic matter.

 secondary treatment in purification of industrial waste water


™ In secondary treatment 75-95 % of organic material is oxidized.



™ The liquid flowing through these systems are then disinfected using Chlorine or Ozone and allowed to flow into natural waters

™ Sludge remaining from both treatments is sent to an anaerobic sludge digester where anaerobic decomposition convert the organic material in the sludge finally to methane and CO2 ( bio-gas)

Typical bio-gas contains CH4, CO2, H2S, N2, H2

™ Digested sludge can be used as fertilizer


A mind map for this section will make it easy for sure!!

 purification of industrial waste water



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