Clean Initiatives: Constructing sludge treatment plants to maintain basic sanitation

Constructing sludge treatment plants to maintain basic sanitation

India faces a severe lack of adequate sanitary infrastructure. There are not enough community and household toilets in the country, while the existing ones are poorly maintained. Open defecation still accounts for almost 50 per cent of the total faecal discharge in the country. Moreover, the fact that most of the discharge does not undergo any treatment and is directly dumped in the open adds to the overall dismal scenario. This untreated faecal waste is disposed of in the domestic environment, agricultural fields and waterbodies.

At present, there are almost no facilities for faecal waste treatment in India and very few sewage treatment plants allow sludge dumping. Only about 7 per cent of the total faecal waste discharged is effectively treated. Since most of the sludge remains untreated, there is minimal reuse.

Therefore, there is an urgent need to formulate a faecal sludge management (FSM) plan for the country. Dedicated sludge treatment facilities need to be constructed, with a special focus on the reuse of treated sludge and wastewater. To this end, some states have taken a few initiatives. For instance, Karnataka and Tamil Nadu have implemented FSM practices and are undertaking construction works of faecal sludge treatment plants (FSTPs). The FSTP at Devanahalli, in Karnataka, is one of the first operational sludge treatment plants in India. However, overall investment in the sector still remains very low.

Sludge management in Devanahalli

Devanahalli town, near Bengaluru in Karnataka, has 6,400 households, of which around 5,780 households (almost 90 per cent) are equipped with latrine facilities. The remaining 620 households (10 per cent) practise open defecation.

Even households that have functioning toilets are not linked to any sewerage network. The town does not have an underground drainage system and the urban local body (ULB) lacks funds to construct a viable sewerage network. There is also no sewage treatment facility in the town. Therefore, most households collect septage in on-site facilities such as storage pits, septic tanks, twin pits and open drains. About 78 per cent of the households use a single storage pit to contain faecal waste. The majority of these collection facilities are unlined and are 5-10 years old. Besides, only 3 per cent households discharge the grey water collected from their bathrooms and kitchen into these collection systems.

The desludging of septic tanks is undertaken by the Devanahalli Town Municipal Council (TMC), along with five independent private players operating in the town. However, the majority of the households in the town do not undertake timely desludging of their collection systems. In fact, according to reports, about 44 per cent of the households in Devanahalli have never undertaken any desludging activity. On the other hand, the Swachh Bharat Mission Guidelines, 2014 recommend a two- to three-year desludging interval.

Due to such irregular desludging and the lack of construction standards for sludge container facilities, most of the sewage stored in collection systems seeps underground or is simply discharged into stormwater drains.

Devanahalli FSTP

To systematically manage the faecal sludge generated in the town, a decentralised FSTP was set up in January 2016. The plant is equipped to treat about 6,000 litres of sludge a day.

The FSTP was executed by TMC, the Consortium for DEWATS Dissemination (CDD) Society and the Bremen Overseas Research and Development Association (BORDA). The CDD and BORDA were responsible for its design and building. The CDD is also tasked with the implementation and operations and maintenance (O&M) of the plant till November 2016.

Project financing

The FSTP has been built with an investment of Rs 6 million. In addition, the plant requires Rs 240,000-Rs 400,000 per year for O&M. While the plant’s civil construction work was funded by the Bill and Melinda Gates Foundation, the O&M expenses are being borne by TMC. The plant has a low O&M expenditure outlay since it does not depend on electricity or skilled labour for its operations.

Technology focus

The FSTP consists of an underground facility with a land requirement of around 550 square metres. It deploys a gravity-based biological approach to treat faecal matter.

At the first stage of treatment, a screening chamber separates the solid waste from the faecal sludge, before discharging the sludge into further modules. Solid waste at the facility typically constitutes plastic and medicinal waste, daily household consumables, etc.

After the screening chamber, the faecal sludge is stored in a feeding tank for three to four hours. This separates the solids from the liquids, both of which are conveyed for further treatment through the operation of valves.

The solids from the feeding tank are further retained in two biogas digesters. These are air-tight prefabricated tanks, where the solid waste is stored for a span of three to four days. This leads to anaerobic digestion of the solids. The process also produces biogas as a by-product.

The partially processed solids from biogas digesters are then treated in two stabilisation tanks. These tanks consist of three chambers each, where the solids are processed for five to six days. The treated sludge is then discharged into a sludge drying bed for dewatering and the removal of pathogens. While the percolate from the bed is further connected to a percolation pit to ensure its safe disposal, the sludge is dried for 15-20 days.

Meanwhile, the water separated from the stabilisation tanks is conveyed to an integrated settler anaerobic baffle reactor for further treatment. The liquid undergoes treatment in two chambers of the settler, four chambers of the ABR and two chambers of the anaerobic filter. Dissolved solids in the water are also treated through anaerobic digestion.

Further, effluents from the anaerobic filter are conveyed to a planted gravel filter and are treated aerobically for the removal of odour, colour and nutrients. The process uses gravel of different sizes and Cana indica and papyrus plants. The treated wastewater from the PGF is stored in a collection tank for reuse at the facility.

Progress so far

The FSTP at Devanahalli caters to about 30,000 people. As of September 20, 2016, the plant’s capacity utilisation stood at 33 per cent. It has treated about 524,300 litres of faecal sludge and produced 30 tonnes of treated dry sludge.

The dry sludge produced is being used as a soil conditioner for several crops. While most of it is distributed free of cost, some of it is sold by CDD to farming communities, at Re 0.50-Re 0.70 per kg. However, these estimates are subject to change since the project is still at the pilot stage.

Besides, the plant has generated an estimated 200,000 litres of treated sewage. It is currently being used for landscaping on the FSTP’s premises. The amount of treated sewage produced in the process largely depends on the liquid fraction in the faecal sludge disposed of at the plant. The treatment process also generates other by-products such as biogas, which is used for cooking.

The way forward

By 2020, on-site containment facilities will store about 60 per cent of India’s urban faecal discharge. However, sewerage connections will be able to cater to only 26 per cent of the discharge. Against this backdrop, the Devanahalli FSTP should be replicated by other ULBs for efficient faecal management.

In fact, ULBs in Tiruchirappalli and Gulbarga have successfully initiated the adoption of similar innovative and cost-effective faecal management practices. In August 2016, the Tiruchirappalli City Municipal Corporation in Tamil Nadu proposed a Rs 32 million project involving the construction of an FSTP at Kasi Vilangi. Gulbarga in Karnataka is also planning to undertake similar measures to effectively manage its faecal discharge.

Going forward, an integrated national-level FSM policy is required to streamline faecal management in the country. In addition, ULBs need to be incentivised to undertake faecal treatment practices. However, given the lack of available funds with these civic agencies, private player participation will also have to be encouraged.