The toilet-to-tap project of the Delhi Jal Board (DJB), which aims at purifying sewage to meet drinking water standards, is the first of its kind in India. It has been implemented on a pilot basis under the banner Sujala Dhara at the Keshopur sewage treatment plant. Under the pilot project, a decentralised recycling facility with a capacity to treat 5,000 litres of sewage per hour was commissioned in July 2015. The facility presents an example of a cost-effective model for recycling.
The project has been implemented in collabor-ation with a Delhi-based NGO, Social Awareness Newer Alternatives. Currently, about 4,000 litres is being treated to meet drinking water standards at the facility. Delhi-based Absolute Water has set up the facility at a cost of Rs 5.5 million. The company is responsible for the plant’s functioning till December 2015 after which DJB is expected to take over the operations and main-tenance (O&M) of the plant.
In order to treat wastewater to drinking quality, the recycling facility uses the biofiltration nanomembrane technology. The process involves the pumping of raw sewage into a five-layered biofilter comprising earthworms, cotton extracts, bacteria, organic sand, pebbles and stones. The technology works on the principle of vermi-filter and is capable of treating 85 per cent of the sewage at the facility. The vermi-filter technology uses specially bred worm species and a mix of bacteria to act on the suspended and dissolved solids in the raw sewage.
Next, the treated sewage undergoes membrane treatment. The nanomembrane technology has a high recovery rate of 85 per cent. The membranes are designed to remove impurities as small as 0.001 microns. After membrane treatment, the treated sewage undergoes chlorination, which makes it fit for drinking purposes.
The treatment process deployed at the facility results in minimal wastage with 95 per cent of the wastewater treated and utilised for various non-potable purposes. The reject water produced during the process has a high nutrient content that could be used as liquid fertiliser. Besides, the facility has an added advantage in the form of no sludge generation. This is a huge respite as sludge disposal involves high costs.
The treated water meets the drinking water standards prescribed by the World Health Organization and the Bureau of Indian Standards. The treated water has a biochemical oxygen demand level of less than 3 mg per litre, pH in the range of 6.5 to 8.5, dissolved solids of less than 500 in 1 mg per litre and the absence of thermotolerant coliform bacteria in any 100 ml sample.
Benefits of the plant
The recycling facility has several advantages that make it more cost-effective as compared to a conventional sewage treatment system. It uses advanced biofiltration nanomembrane technology, which offers reduced costs, lower power requirements and greater applicability. Further, owing to its compact design, the facility can be set up near the source of sewage generation. This results in significant cost savings in the form of reduced capital investments for the construction of sewage collection and transmission infrastructure, and lower O&M costs.
To further enhance operational efficiency and optimise production costs, the facility is being run on solar power, which reduces O&M costs. Highlighting the advantages of the facility, Rahul Jha, project head, Absolute Water, says, “The capacity of these decentralised recycling units can be altered according to the need of the locality and can be as low as 4 million litres per day. In addition, the O&M costs of these plants are at least 30 per cent lower in comparison with those of conventional plants.”
The cost savings accruing from the facility will be utilised for capacity expansion and the development of new facilities. In fact, plans are afoot to increase the capacity of the Keshopur recycling facility to 66,000 litres.
The commissioning of the Keshopur recycling facility has added Delhi to the list of the few cities that have taken the initiative to adopt technologies for purifying sewage to levels that make it potable. Meanwhile, to ensure the utilisation of water produced from the plant, DJB is planning to supply it to the Delhi Secretariat. Although this technology offers many benefits in the form of reduced costs, increased water availability and environmental sustainability, the major impediment to its success is hesitation amongst the general public regarding the water quality. A lot of effort is needed to overcome this hurdle and bring about a change in mindset.
Going forward, the Sujala Dhara initiative can prove to be a game changer for Delhi by redu-cing the city’s dependence on water imported from other states. DJB has plans to supply the water generated at the plant for drinking purposes. However, it remains to be seen to what extent the utility will succeed.