[Commentary] Decentralised waste water treatment systems to improve water security

  • The decentralised wastewater treatment systems (DEWATS) approach is considered a cost-effective method of wastewater treatment in rural and semi-urban India.
  • DEWATS in India face challenges over a time, as they are unable to meet the effluent standards. The lack of community participation and the delay in adoption of technology-specific regulations for maintenance are some of the challenges.
  • The decentralised wastewater treatment and reuse system may gain traction with the proper combination of higher water tariffs, stronger enforcement and rewards for early adopters, write the authors of this commentary.
  • The views in the commentary are that of the authors.

India’s water requirement is expected to be 1.5 trillion cubic metres by 2030. The country only treats 16.8% of the total estimated sewage generated. There is a huge gap between demand and supply that could only be bridged by recycling and reusing treated wastewater. The domestic wastewater reuse data from the Central Pollution Control Board indicates that less than five percent of the treated wastewater is being reused.

In India, 95.2% of the rural population uses individual toilets, as per the National Annual Rural Sanitation Survey (NARSS) report of 2019-20. While there has been progress in reducing open defecation habits, an indication of the achievement under the Swachh Bharat Mission, the common wastewater disposal methods used in semi-urban and rural areas of India continue to be that of open drainage, water bodies and soak pits.

Soak pits are vertical with low-depth, porous-walled chambers that hold biosolids and percolate water slowly, which gets into the subsurface soil. Improper soak pit management due to lack of timely removal of biosolids leads to overflow of sewage water during the rainy season. This causes groundwater contamination and increases the probability of waterborne diseases. The soak pit technique for wastewater management interrupts safe solid-liquid disposal if not managed properly.

Further, wastewater recovery for reuse is limited in these cases. A recommended solution would be an integrated decentralised wastewater treatment systems (DEWATS) approach in rural and semi-urban areas which would increase the generation of treated wastewater that could be reused locally and further reduce the demand for fresh water.

According to the data from Central Pollution Control Board, less than five percent of the treated wastewater is being reused in India. Photo by McKay Savage/Flickr.

The DEWATS approach

According to the Asian Development Bank’s report in 2020 Decentralized Wastewater and Faecal Sludge Management: Case Studies from India, it is suggested that DEWATS is the most cost-effective method of treatment in rural and semi-urban areas of India. There are several technological systems available under DEWATS that could be implemented in accordance with the local needs.

Some common methods, widely used as DEWATS technology in India, are constructed wetlands, activated sludge processes, waste stabilisation ponds, and USAB (anaerobic digesters), along with the extended aeration process, moving bed bio-film reactors, sequential batch reactors, membrane bioreactors, bio-towers and anaerobic baffled wall reactors.

A representative image of a DEWATS system. The method is a cost effective way of treatment in rural and semi-urban areas of India. Photo by SuSanA Secretariat/Flickr.

The decentralised wastewater treatment through a constructed wetland could be more beneficial as it aims for safe wastewater disposal methods and satisfies the aim of the Swachh Bharat Mission. This is a technology that can treat both black and grey water and remove heavy metals. It consumes less energy, has low cost of maintenance, and is socially acceptable and sustainable. The results were confirmed by a study conducted by the School of Water Resources Engineering, Jadavpur University in West Bengal focusing on decentralised constructed wetland with a 1200 litres/day treatment capacity. The project was implemented as a pilot in Murshidabad District, West Bengal and designed for grey water.

The wastewater collected from kitchens, bathing, cloth washing, and toilet flushing was passed through an oil and grease separator and mixed with black water in a holding tank. This constructed wetland system was made to mimic and improve the process of phytoremediation wastewater treatment using artificially created aerobic, anoxic, and anaerobic zones. The outcome of this depicts an overall removal efficiency of 85-90% of contaminants and heavy metals from wastewater. These experimental results showed that constructed wetlands will play a very significant role as a decentralised wastewater treatment solution in rural India.

Present challenges

There is a need to focus on wastewater reuse to address water scarcity. This is an appropriate situation for the introduction of decentralised wastewater treatment systems (DEWATS) wastewater treatment, especially in rural and peri-urban areas. Although there is political motivation to enhance the efficiency of DEWATS in India, there is a need to develop an integrated strategy that strikes a balance between socioeconomic and physical infrastructure.

The DEWATS constructed in rural and semi-urban areas of India face challenges over a period of time, as they are not able to meet the effluent standards. The underlying causes of such situations are the lack of community participation and the adoption of technology specific regulations for maintenance.

While India has in place national-level legislation and programmes that offer important guidelines and incentives, a strong legal and policy framework is urgently required for better management of DEWATS. It is also essential to develop a key centralised governance model that focusses on market governance mechanism, coordination amongst government agencies and active participation from all significant stakeholders.

Building new wastewater treatment systems, sewer system upgrades, enhancing existing wastewater treatment systems technology and stronger focus on economic viability is imperative for water circular economy. The vision of the ‘Swachh Bharat’ or ‘Clean India’ campaign would be more successful if there is a focus on water reuse from built-in toilets and resource recovery of the generated wastewater. Think tanks could play a key role in solution development and effective implementation on ground level.

Therefore, there is a pragmatic need to develop a robust mechanism to monitor, innovate and manage these systems. The decentralised wastewater treatment and reuse system may gain traction with the proper combination of higher water tariffs, stronger enforcement and rewards for early adopters.

The authors are Research Associates with The Energy and Resources Institute (TERI) in New Delhi.

Read more: [Commentary] Water tariff could be a tool to improve water use efficiency in domestic sector


Banner image: It is expected that by 2030, India’s water requirement will be 1.5 trillion cubic metres. Photo by Vyacheslav Argenberg/Wikimedia Commons.

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