Indian cities generate an estimated 38354 million litres per day (MLD) of wastewater. However, only 8.5 per cent of it is treated according to the Central Pollution Control Board. This is because the existing sewage infrastructure in cities is woefully inadequate to treat all the wastewater generated. Untreated water, unfortunately, can find its way into our rivers and streams, or much worse, seep into the soil to contaminate underground aquifers forever.
In most industrial and urban centres, infrastructural and basic services are stretched to the seams. Hence, it is difficult or well-nigh impossible to integrate newer sections into the sewerage and other services. Even within cities, slum pockets remain unserved, posing a major danger to health.
This is where DEWATS, or decentralised wastewater treatment systems can help. The Centre for Advanced Solutions (CASS), of the Centre for DEWATS Dissemination (CDD) Society, set up through the collaborative efforts of the Bremen Overseas Research and Development Association (BORDA), and the Rajiv Gandhi Rural Housing Corporation Limited (RGRHCL), has initiated several such projects all over India.
In a general DEWATS design, the wastewater—a combination of grey and black water, enters the settler. The settler could be a conventional settler or a biogas settler. The non utilised biogas is let out from a separate pipe. Sludge accumulates at the bottom of the settler.
Making use of the natural gradient of the land, the water then enters an anaerobic baffled reactor and/or anaerobic filter. The naturally occurring microorganisms in the wastewater break down the organic matter. The partially treated wastewater finds its way to the planted gravel filter (PGF), where a selection of plants such as colocasia ( arvi), cattail reeds, Canna, Nelumbo, Caltha, Eichhornia, and Sagitarria removes the nutrients and re-oxygenates wastewater naturally. An additional polishing pond exposes the effluent to the atmosphere for final treatment. The treated wastewater can now be directly used for gardening and landscaping purposes. In case the water is to be utilised for flushing purposes, carbon and sand filters have to be used, followed by chlorination.
The Bangalore Metro Rail Corporation Limited (BMRCL) has put up toilets adjacent to MG Road Metro station for rail commuters. Prefabricated DEWATS units are implemented at the two public toilets of the metro stations (one near Anil Kumble Circle and other near MG Road Metro station). Wastewater from the Metro Railway toilets is passed through a pre-fabricated settler and anaerobic baffle reactor. The treated wastewater is then sent into the drains of the city sewerage system. Using Dewats has taken care of the space constraints, while preventing uprooting the urban sewerage system to accommodate the Metro Rail toilets.
This kind of system can prove useful for an unserved urban slum pocket too, as has been done in Kolhapur, Maharashtra, and the beedi workers’ resettlement colony in Kengeri satellite town, on the outskirts of Bangalore. Comprising 1600 households resettled in two phases, this colony in Kengeri was too far to be integrated into the Bangalore sewerage system. Hence, connecting the colony would have been a costly affair. DEWATS was put in place. It covered 120 households comprising approximately 700 people. Designed for a capacity of 36 cubic metres of wastewater, it is made up of a biogas settler, anaerobic baffled reactor and a planted gravel filter of cattail reeds and canna.
The black water from the households is collected and treated in the DEWATS unit. The biogas generated as a byproduct from the (biogas) settler here is used as a fuel in the anganwadi to cook food. This win-win situation has not only improved the hygiene of the colony, but done away with waste discharge.
Hill station towns like Shimla are today struggling to cope with huge populations, and resultant waste generation. The CASS is currently working on similar lines to treat the sewage from unserved pockets and improve hygiene in areas under the Shimla Municipal Corporation (SMC) and four other urban local bodies (ULBs) of Himachal Pradesh, namely Mandi, Dharamshala, Nahan and Hamirpur.
As urban agglomerations grow in size, sewerage and water sanitation systems are stretched to their limits. Decentralised sanitation systems use the minimum amount of land, to the maximum advantage. They not only take care of sanitation, but recycle wastewater and contribute to saving precious groundwater resources.