Urban wastewater treatment is a major challenge in India, as infrastructural development and regulations have not kept pace with population growth and urbanisation.

To meet growing demand, it is essential to revamp both existing infrastructure along with new capacity additions, which require heavy investments by the municipal sector. Public-private partnerships (PPP) are being encouraged as municipalities are facing various issues related to technical expertise and funds—which private participants can overcome.

Wastewater Reuse Potential in Tamil Nadu

According to the census 2011, the total population of Tamil Nadu is estimated to be approximately 8.3 crores, while the urban population is estimated to be approximately 4 crores. The Ministry of Urban Development has estimated that the per capita demand for water is 135 litres per day, which is expected to create an urban demand of 540 crore litres of water per day.

Of the 540 crore litres of water used by the urban population, 80% becomes sewage water, which amounts to 433 crore litres of sewage water. However, it is observed that only 60% of sewage water is collected in the Sewage Treatment Plants (STPs), which is due to lack of adequate sewage network coverage across different districts. The various steps involved in the wastewater treatment methods in STPs are primary wastewater treatment, secondary wastewater treatment, and tertiary wastewater treatment. The Ministry of Urban Development requires that each state must at least recycle 20% of its sewage water.

Assuming the state is able to recycle a minimum of 20% of the sewage water collected by STPs—as mandated by the Ministry of Urban Development, it will have approximately 5,204 millions of litres per day (MLD) of recycled water available for industrial use. However, the state currently recycles less than 5% of its sewage water, which is mainly due to the poor sewage network in some few districts across the state, operational inefficiencies in the STPs, and lack of modern tertiary water treatment technologies.

The current operational capacity of the state’s STPs is approximately 1160 MLD across the various districts; the capacity of under-construction STPs is 418 MLD, while the capacity of proposed STPs is approximately 214 MLD. These STPs cater to the supply of treated water if developed with appropriate recycling technologies.

The recycled water can be appropriately utilized in industrial estates that are in proximity to the industries. For instance, the Chennai STP with a capacity of 270 MLD located in Kodungaiyur can supply recycled water to industrial estates in the North Chennai, Ponneri, and Ambattur districts.

District-wise Industry Coverage

Currently, Tamil Nadu has approximately 11,750 major industries (State Industries Promotion Corporation of Tamil Nadu Limited (SIPCOT): 2400, large industries: 1850, Micro, Small and Medium Enterprises (MSME) Industries: 7500) which are concentrated in districts such as Chennai, Coimbatore, Kanchipuram, Madurai, Tiruchirapalli, Tiruppur, and Vellore.

Steps to Spearhead the Reuse of Treated Wastewater

Enhancing STP capacity across various districts and increasing sewage network coverage to all households in the district is expected to help the state generate more treated wastewater. Given the context of water scarcity in the state, it is imperative to explore water recycling technologies that consume less space and produce more treated water, which can be provided for industrial purposes.

Districts that are home to automobile, textile, leather, chemical and petrochemical, fertilizer, and cement industries have high potential for wastewater reuse, as treated sewage water can be used in these industries. Hence, the state government should take up proactive policy measures to improve the usability of recycled water in these sectors.

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