Indian Sludge Has a High Fertiliser Potential, According to a New Study

The article presents the findings of an investigation of sludge found in Indian sewage treatment plants (STP) established under the National Mission for Clean Ganga to treat contaminated Ganga water.

Sludge classification

  • India currently lacks criteria for classifying sludge as A or B.
  • According to the regulations of the United States Environmental Protection Agency, treated sludge can be classed as class A or class B.
  • Class A sludge is suitable for open disposal and can be used as organic fertiliser.
  • Class B sludge: It can be utilised in limited agricultural applications as long as the edible sections of the crop are not exposed to the sludge-mixed soil and animals and people are not in close proximity.

Current sludge disposal methods

  • Those given contracts for establishing and maintaining STPs under the Namami Ganga Mission are being allotted land for sludge disposal.
  • However, the sludge is rarely handled, and it frequently finds its way back into rivers and local water supplies after rainstorms.

The findings of the study

  • The sludge tested after drying was classified as class B.
  • Nitrogen and phosphorus levels in some sludges were higher than those recommended by India’s fertiliser regulations, although potassium levels were lower.
  • The level of pathogens and heavy metal contamination was higher than the prescribed fertiliser standards.
  • Sludge had a calorific value ranging from 1,000 to 3,500 kcal/kg, which was lower than the average calorific value of Indian coal.

Recommendations to improve sludge quality

  • The research recommends keeping the sludge for at least three months to kill infections and combining it with bovine manure and husk or local soil to minimise heavy metals.
  • However, it would still be classified as class B, and turning it to grade A sludge would necessitate significantly more intensive treatment.
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