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The management of sludge

It comes as no surprise that India has probably the world’s largest number of pit toilets and septic tanks. The census data of 2011 revealed more than 115 million such structures in India. In Bengaluru alone there may be over 500,000 such pit toilets and septic tanks.

Though ill designed and made large, taking years to fill, they still fill up eventually and have to be emptied. Thanks to the growth of the mechanical vacuum sucking devices the horrendous practice of manual scavenging is coming to an end. These ‘honeysuckers’ are able to empty the pits quite quickly and with least smell. There are of course problems in not being able to reach houses in small, narrow roads and densely populated areas. There are also problems in full removal of the sludge if it thickens up.

On-plot sanitation as a sector has tremendous scope for improvement.

There is a need for building bye-laws to insist on a range of on-plot sanitation as mandatory depending on the location and the groundwater table. Commencement and completion certificates should only be provided when the disposal or at least containment of toilet waste is clearly established. This is necessary in non-sewered areas.

There is a need for better design of the receptacles of waste from toilets. The twin leach pit was a system evolved but has yet to be taken up at large scale. One of the two pits built for the purpose is used at a time for one-and-a-half years. This had the advantage of safely confining solid waste from toilets and allowing dessication for a year-and-a-half, therefore permitting easier removal without harmful health effect, and the sludge sanitised to a great extent.

Single pits, if permitted, should be easily accessible and have a pipe slot for easy removal of sludge.

Septic tanks should have design standards and be as per BIS code.

Better alternatives to septic tanks such as the DEWATS system should be preferred. The DEWATS system has better sludge digestion capacity and sanitises waste water upto higher standards of release.

Faecal sludge treatment plants (FSTP)

All of the towns currently un-sewered or partially sewered must have a FSTP. Ideally this must be together with the solid waste management plant. Devanahalli town near Bengaluru has just started operation of its FSTP. Designed and built by CDD-BORDA , a Bengaluru-based group, this is the one of the first in India. Kochi too is reported to have its first FSTP operational recently.

These FSTPs receive raw sludge from pit toilets and septic tanks, safely contain, digest and sanitise it. In the process energy may be recovered as bio-gas and finally the sanitised sludge will be a good soil amendment nutrient.

Each State needs to work out a Faecal Sludge Management Policy, set up FSTPs where necessary and ensure that on-plot and decentralised sanitation systems are integrated with the larger sewer-based sanitation systems. As the nation with the largest number of people defecating in the open, safe sanitation will see on-plot systems as the first part up the sanitation ladder. Putting knowledge and design to enable better management and reuse of the waste is an opportunity as much as open defecation is a threat.

Having a faecal sludge management plan, building FSTPs and reusing the nutrients in the waste after hygienising it would be water- and waste-water wisdom.


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Printable version | May 14, 2021 7:57:53 PM | https://www.thehindu.com/features/homes-and-gardens/the-management-of-sludge/article8004903.ece

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