Sustainable Reuse: Deploying decentralised wastewater treatment systems

According to the estimates of the Central Pollution Control Board, sewage/wastewater generation in India has grown at a CAGR of 3 per cent from 62,000 million litres per day (mld) in 2015-16 to 72,368 mld in 2020-21, and is estimated to rise to over 74,000 mld in 2022. Of this, less than 50 per cent gets treated. As per the latest updates, the country’s installed sewage treatment ca­pacity stands at 31,841 mld, of which 26,869 mld is operational. The total number of sewage treatment plants (STPs) in India is 1,469, of which 102 STPs are non-operational. The se­wa­ge treat­ment infrastructure is inadequate compared to the sewage generated. The market for recycling/reusing water is yet to gain mo­mentum owing to the lack of networks for channe­lising such water to consumers and the lack of incentives for its use. To bridge the substantial demand-supply gap in water supply, the focus now needs to be on recycling and re­using treated wastewater. The implementation of decentralised methods of treatment is ne­cessary to ensure the sustainable reuse of treated wastewater.

Advantages of DEWATS over traditional methods

Decentralised wastewater treatment systems (DEWATS) are cluster-type facilities that provide wastewater treatment solutions. They use aerobic and anaerobic techniques for wastewater treatment. DEWATS collect, treat reuse and dispose off wastewater at or ne­ar the source. These are cost effective and ma­ke use of in-situ treatment technologies such as constructed wetlands, waste stabilisation ponds and anaerobic digesters. DEWATS eliminate the ne­ed for large-diameter pipelines for transporting wastewater from one part of the city to another for treatment. Instead, small pipes for collecting small volumes of domestic wastewater are installed, and this effectively re­duces the need for a longer sewer network. Further, DEWATS offer the flexibility of adopting multiple techno­logies based on input parameters and can be tailored to unique requirements, which would not be feasible in a typical set-up. Another ad­vantage of decentralised sy­stems is that they require less land and power, and have lower transportation expenses.

Improving water security through DEWATS

According to the Asian Development Bank, DEWATS is the most cost-effective method of wastewater treatment, especially for rural and semi-urban areas. The use of a constructed wetland for decentralised water treatment could be even more beneficial as it aims to achieve se­cu­re wastewater disposal and fulfil the objectives of the Swachh Bharat Mission. This technology can treat both black and grey water and also re­move heavy metals. In addition, it has a low ma­in­tenance cost and requires less energy.

India is working with countries such as Ja­pan to develop an effective system for wastewater treatment, recycling and reuse. Through the use of Johkasou technology, a recent partnership with Japan for decentralised domestic wastewater management is intended to aid in the efficient reuse of treated wastewater. The de­centralised Johkasou system is expected to have a significant impact on the sustainability of freshwater sources as well as the management of grey and black water from towns covered by the Jal Jeevan Mission. It will enable urban local bodies to effectively manage the problem of wa­stewater in their respective cities.

A water circular economy requires the construction of new wastewater treatment facilities, improvements in existing sewage systems, technological advancements in existing wastewater treatment facilities, and a stronger emphasis on commercial viability. Many cities are undertaking initiatives to build DEWATS and achieve efficient wastewater treatment systems.

Applications of DEWATS

Recently, in October 2022, the Delhi governme­nt approved the laying of sewer lines and construction of decentralised sewage treatment plants (DSTPs) in Bawana and Mundka. The objective is to build effective wastewater treatment facilities in order to achieve the target of cleaning the river Yamuna by 2025. The project entails an estimated investment of around Rs 6 billion. It also aims to resolve the sewage issues of unauthorised colonies in Delhi. The government is also planning to set up a water recycling unit at the Bawana water treatment plant. The plant currently lacks a recycling unit, which is leading to acute wastage of water. The government plans to set up a unit with 2 million gallons per day (mgd) capacity at the site.

Hyderabad is working on achieving the target of 100 per cent sewage treatment in the city. Currently, around 2,000 mgd of sewage is being generated by the Hyderabad Urban Agglome­ration, while the Greater Hyderabad Municipal Cor­poration (GHMC) generates 1,650 mgd of sew­age. Of this, 772 mgd is being treated by the existing 25 STPs. To improve the existing gap between generation and treatment of sewage, the Telangana government has planned to develop 31 DSTPs to make the city sewage-free and increase the sewage treatment capacity. Of these, 15 DSTPs with a capacity of over 970 mld are expected to be completed by June 2023, resulting in the treatment of 100 per cent wastewater within GHMC. The remaining DSTPs are scheduled to be completed by December 2023.

On similar lines, the Tiruchirappalli City Mu­nicipal Corporation plans to set up the first DSTP in the city, with a capacity of 1 mld, to pre­vent wastewater from polluting the Kollidam river. The municipal corporation has identified land for the project, which is worth Rs 8.5 million. The goal is to discharge reclaimed water into the river and recycle wastewater as per the guidelines established by the Tamil Nadu Poll­ution Control Board.

Challenges in adoption

To overcome the challenges associated with building significant sewage collection and tr­e­atment infrastructure, several cities across the country have already started to implement de­centralised treatment systems. However, the adoption of DEWATS also faces challenges. The most significant concern is meeting the discharge and reuse standards established by po­ll­ution boards. Since effluent discharge standards are continually evolving in India, DEWATS must adapt to changing discharge standards and new reuse applications. The other challenges include lack of community participation and delays in the adoption of technology-specific regulations for maintenance.

Extending application

India’s water requirement is expected to increase significantly in the coming years. At present, the country lacks effective and efficient wastewater treatment facilities to bridge the demand and supply gap. With the large-scale adoption of DEWATS in India, it is expected that the gap will be filled and a strong water network will be established.

Apart from wastewater treatment, DEWATS can be extended to other applications as well. Through hybrid systems and integration, DEWATS can be used in a variety of growing fields in the future. These include river rejuve­na­tion, fecal sludge management, and other se­condary and tertiary treatment areas.

The central government, along with the sta­tes, is undertaking many advanced digital initiatives in the water and wastewater sector, and en­couraging private sector participation. With these efforts, India is expected to achieve water security in the future and unlock the full potential of wastewater treatment in the country.

Naina Gulati