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.
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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.
Source: https://th-i.thgim.com/public/incoming/ldmidp/article66832121.ece/alternates/LANDSCAPE_1200/Vartur%20lake_02.jpg