General Studies Paper 3

Context: A recent analysis found that sludge found in Indian sewage treatment plants (STP)has high potential for use as fertilizer but required treatment before it could be used unrestrictedly in farms, or as a potential biofuel.

About Sludge 

  • It is the thick residue filtered out of sewage treatment plants
  • It is rich in organic chemicals and is also a repository of heavy metals, industrial effluents, and bacterial contaminants.

Classification of Treated sludge

  • Treated sludge can be classified as class A or class B as per the standards of the United States Environmental Protection Agency with class A being safe to be disposed of in the open and useful as organic fertilizer.
  • Class B means that the sludge can be used in “restricted” agricultural applications, the edible parts of the crop not be exposed to the sludge-mixed soil, and animals and people have not come into extensive contact.

Efforts of India 

  • Arth Ganga is a sustainable viable economic model conceptualized under the “Namami-Gange” program to integrate people in the basin with Ganga Rejuvenation.
    • One of the measures, under this ‘Arth Ganga’ (economic value from Ganga), is to “monetize” and reuse treated wastewater and sludge.
      • This means converting sludge into usable products such as manure and bricks.


  • India doesn’t yet have standards classifying sludge as class A or B.
    • Currently, those awarded contracts for developing and maintaining STPs under the Namami Ganga Mission are also apportioned land for disposing of the sludge.
    • However, this is rarely treated, and during rains, such sludge — with its accompanying chemical and metallic constituents — often makes its way back into rivers and local water sources.
  • A study by the Indian Institute of Technology (IIT)-Roorkee found that most of the sludge analysed after drying fell into the class B category.
  • Nitrogen and phosphorous levels were higher than those recommended by India’s fertilizer standards (FCO, 2009).
    • However, the potassium levels of some sludges were less than recommended.


  • To improve the quality of sludge, the report recommends the sludge needs to be stored for at least three months to kill pathogens, and blended with cattle manure and husk or local soil to reduce the heavy metal.
  • This, however, would still put it in class B and converting it into grade A sludge would require far more extensive treatment.

Before standards were made, it was necessary to understand the characteristics of the sludge from these STPs before ways could be devised to incentivize private players to treat and dispose of sludge.

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