Efficient Sludge Management

Best practices by Devanahalli and Leh municipalities

In India, cities are working towards achieving open defecation free (ODF) status by constructing toilets in rural and urban areas. While this is a much-needed step for ensuring sanitation in the country, another major aspect that needs attention is faecal sludge management. Today, several small villages and towns lack a sewerage network to transport faecal sludge safely. As a result, the sludge gets discharged into waterbodies and pollutes underground water. To ensure safe storage of faecal sludge, the construction of underground pits and septic tanks is needed. It is also necessary to undertake desludging to avoid contamination of groundwater. In addition, treatment of faecal sludge is critical to prevent it entering the ecosystem.

Two civic agencies – the Devanahalli Town Municipal Council in Karnataka and the Municipal Committee Leh (MCL) in Jammu & Kashmir – have set precedents by implementing environment-friendly faecal sludge treatment plants (FSTPs) using biological technologies. While the Devanahalli Town Municipal Council was the first to implement a town-scale FSTP in November 2015 using biogas digester and stabilisation plants, MCL took up a similar initiative in August 2017 using the first-of-its-kind planted drying bed technology. Both the plants are aesthetically pleasing, safe for sanitation workers, odourless, low cost, and offer reuse of treated sludge in the form of compost (fertiliser for agriculture) and for irrigation. With this, the plants are not only reducing the burden of human waste but also adding value by providing safer fertilisers and enabling the reuse of water.

Devanahalli faecal sludge management case study

Devanahalli, a small town in Karnataka, lacked an underground sewerage system and was confronted with the issue of untreated faecal sludge. People used on-site collection systems such as pits and septic tanks, which once filled were cleaned through desludging vehicles. To make the treatment process sustainable, the Devanahalli Town Municipal Council successfully developed a low-cost FSTP in the town in association with Bengaluru-based Consortium for DEWATS Dissemination (CDD) Society and German NGO Bremen Overseas Research and Development Association (BORDA).

Treatment technology: The plant uses biological treatment technology instead of chemicals to treat human waste. The process involves a number of steps beginning with desludging of tanks/pits using vehicles, transferring the human waste into a feeding tank for screening and separation of solids and liquids. The solid sludge gets pushed into a biogas digester whereas the liquid sludge percolates into the integrated settler equipped with anaerobic baffle reactor.

From the biogas digester, the solid sludge is transferred to a stabilisation tank for dewatering. Pathogens are removed by shifting the residue onto a sludge drying bed thereby completing the faecal sludge treatment process. With this, a by-product in the form of compost is generated which can be used as fertiliser for agricultural activities. Meanwhile, the liquid residue is treated by filtering all the gravel using planted filter bed technology and used as irrigation water. Finally, it gets collected in a percolating pit. Spread over a 615 square metre area, the plant can treat up to 6,000 litres of sludge every day. It was commissioned in November 2015 and has been instrumental in achieving the ODF status for the town.

Benefits: The first-of-its-kind town-scale facility successfully handles 100 per cent faecal sludge generated in the town without sanitary workers coming into direct contact with the sludge. This odourless mechanism allows for safe operations as no chemicals are used in the treatment process. Apart from this, low-cost electromechanical equipment is deployed, thereby making the technology an affordable option for civic agencies. The plant is built on the existing collection and conveyance system, thereby eliminating the need for investments on transportation infrastructure. Through the biological treatment, safe fertilisers are delivered to farmers and the risk of contamination of open lands due to illegal dumping of faecal sludge is minimised. The plant has a low operations and maintenance cost, as it runs on gravity and does not use electricity.

Sludge management in Leh

MCL, too, faced the issue of FSM due to the increasing influx of tourists and the rapidly growing commercial establishments. While local population continues to rely on conventional dry composting toilets, the tourism industry has instead opted for flush toilets and underground septic tanks, which has damaged the ecology of the city. At times, the faecal sludge overflows from septic tanks and seeps into underground water used for drinking purposes without filtration.

To tackle the problem, MCL replicated the approach of the Devanahalli Town Municipal Council and developed a similar FSTP in the region. To this end, MCL approached CDD and BORDA in May 2017 to design the plant. An agreement was signed among MCL, CDD and BORDA in June 2017. To implement the project, MCL awarded a five-year contract to Blue Water Company on a public-private partnership basis under the design-, build-, operate-transfer model.

Treatment technology: Given the high altitude and extreme weather conditions in Leh, BORDA and CDD designed the plant based on planted drying bed technology. This technology is environment-friendly as it does not involve the use of chemicals or electricity for FST. It consists of three primary modules. The first is the planted drying beds. About 10 units of such beds with each having a capacity of 12 cubic metre per day have been constructed across a 48 square metre area. Every day, one bed is filled with faecal sludge to enable the separation of solids and liquids besides the removal of solid fractions. The solid sludge is allowed to dry (as excess water percolates) and can be used as fertiliser. The excess water is treated using two horizontal plants (second module) having graded gravel or sand filters. Finally, the treated water is collected in a polishing pond (third module) where it is disinfected through ultraviolet rays.

Benefits: The technology deployed under the plant is robust and flexible to work in extreme weather conditions of Leh. It also takes care of the safety aspect as sanitation workers do not have to work in hazardous conditions. Besides, by-products such as compost and tertiary water can be used for farming activities.

Conclusion

The two plants at Devanahalli and Leh are shining examples of how small towns and cities can ensure complete sanitation. It highlights the fact that the construction of toilets is not enough to get ODF status. Technology undoubtedly plays a key part in this and its wider adoption is necessary to make the country swachh.

The success of these plants is driving other towns such as Gowribidanur, Kalaburagi and Madikeri in Karnataka to build town-scale plants. However, a survey of the town, and an inspection of the existing transportation infrastructure is a precursor to the construction of such plants as it will save a lot of unnecessary investments. Apart from this, new technology solutions that have the potential to reduce the burden of human waste and treat it scientifically as per international standards need to be adopted. Co-composting of slurry together with municipal solid waste, co-treatment of sludge in waste stabilisation ponds, deep row entrenchment, sludge incineration, mechanical sludge drying processes such as centrifugation, and chemical treatment through lime addition are some of the globally used techniques. Pilot projects based on these technologies can be tested before large-scale enrolment of a particular sludge management technique.

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