Can sewage waste be used as fertilizer?

Researchers at IIT-Roorkee have conducted a study on sludge produced from different sewage treatment plants (STPs) and found out that sludge, if used correctly can be reused in various ways, including organic fertilisers, bricks, and even biofuel.

What is sludge?

Sludge is a thick residue filtered out of Sewage Treatment Plants (STP).  Sludge contains high concentration of organic chemicals, heavy metals, industrial effluents and bacterial contaminants. This sludge needs to be managed in a proper way to ensure environment sustainability.

The ‘Arth Ganga’ initiative, launched under the National Mission for Clean Ganga, aims to monetize and reuse treated wastewater and sludge. This will also enable livelihood opportunities from the river rejuvenation programme.

However, the contaminants in sludge make it crucial to treat it before use to avoid potential hazards to human health and the environment.

Treated sludge is classified as Class A or Class B, with Class A being safe for disposal in the open and useful as organic fertilizer, while Class B sludge can be used only in “restricted” agricultural applications. However, India does not yet have any standards classifying sludge as Class A or B.

What does the study say?

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 — the basic soil nutrients — were higher than those recommended by India’s fertilizer standards (FCO, 2009).

-Potassium levels of some sludges were less than recommended.

-The total organic carbon was more than 16 percent. This is also higher than FCO recommendations.

-The degree of pathogens as well as heavy metal contamination was above the recommended fertilizer standards.

-The calorific value of sludge ranged from 1,000-3,500 kcal/kg. This is lower than the average calorific value of Indian coal.

The potential uses of sludge

A first of its kind analysis of the sludge found in Indian sewage treatment plants (STP), set up to treat polluted water from the Ganga, found that most of it had “high potential” for use as fertilizer, but required treatment before it could be used unrestricted in farms, or as a potential biofuel.

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.

Challenges

Although the uses of sludge looks promising. There are several roadblocks when it comes to actually putting it to use. India doesn’t yet have standards classifying sludge as class A or B. There is a lack of proper processing of the sludge. The contractors responsible for the development and maintenance of STPs under the Namami Ganga Mission are allotted land for sludge disposal. However, this sludge is often left untreated, leading to its release into rivers and local water sources during rainy periods.

Even after the sludge is stored and blended with cattle manure and husk or local soil to reduce the heavy metal. It would still put it in class B, and converting it into grade A sludge would require far more extensive treatment.

What are your thoughts on this study? And do you think it has potential to be something grand? Drop a comment to share your views with us.

Picture credits: Netsol Water

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