Nature-based solutions can offer low-energy answer to Tamil Nadu’s wastewater gap: Experts

CHENNAI: Although Tamil Nadu has made notable progress in wastewater treatment, there still are gaps in sewage collection and treatment across urban and rural local bodies, which call for innovative, context-specific solutions, said Simranjeet Singh Kahlon, managing director, Chennai Rivers Transformation Company Limited (CRTCL).

“Nature-based approaches hold promise for decentralised treatment, while cities need systems that handle higher, fluctuating volumes. Collaboration among government, industry and technical institutions will be essential to scale these solutions," he said, while addressing the session on Innovative Nature-Based Wastewater Treatment Solutions organised by the CII’s Indian Green Building Council (IGBC) here on Thursday.

Kahlon also stressed the importance of linking sustainable wastewater management with river restoration and urban waterbody conservation.

Bakan Jagdish Sudhakar, chief executive officer, Tamil Nadu Green Climate Company (TNGCC), said nature-based solutions have the potential to address challenges at multiple scales, from restoring coastal ecosystems to enabling sustainable wastewater treatment, and also advance climate-responsive and environmentally sustainable infrastructure.

He added that Tamil Nadu has shown leadership in ecosystem restoration and already implements such solutions in schools across the Greater Chennai Corporation.

According to the report, Nature-Based Solutions for Treating Wastewater in Tamil Nadu, released during the event, India is among the world's top five emitters, and that rapid economic growth has strained water resources and increased pollution. Cities are shifting from climate-vulnerable to climate-resilient infrastructure, reconnecting with nature and upgrading urban common spaces ecologically.

According to the Central Pollution Control Board's National Inventory of sewage treatment plants (March 2021), about 80 per cent of water supplied for domestic use becomes wastewater. However, sewage treatment plant capacity has not grown with urban populations, the report said.

“Nature-based solutions, defined by the International Union for Conservation of Nature (2017) as actions to protect, sustainably manage and restore ecosystems to address societal challenges, rely on plants, soil and microorganisms, offering a low-energy alternative to costly mechanised plants, particularly for decentralised treatment and reuse,” it said.

The report suggested technical and cost-effective plans for urban local bodies, engineers, contractors and consultants. All designs were of 1 MLD plant serving around 8,300 to 9,300 people. The choice of technology depends on a city's population tier under the National Green Tribunal's 2019 norms, which cap biochemical oxygen demand (BOD) at 10 mg/L in mega and metro cities, 20 mg/L in Class I cities, and 30 mg/L elsewhere.

The report stressed seven constructed wetland options such as free-water surface wetlands, which serve only as a polishing stage and need the most land; horizontal flow systems, which can withstand shock loads; vertical flow systems, which have the smallest space among passive types; French vertical flow, which accepts raw sewage directly; and aerated wetlands, which need the least land but require continuous power.

The hybrid design is the only one that meets the stricter nitrogen limits for large cities, while the willow system is not recommended for tropical Tamil Nadu. The cost of these plants range from about Rs 1.14 crore to Rs 3.69 crore per MLD.

CONSTRUCTED WETLAND OPTIONS

• Free-water surface wetlands: Need the most land

• Horizontal flow systems: Can withstand shock loads

• Vertical flow systems: Need smallest space among passive types

• French vertical flow: Accepts raw sewage directly

• Aerated wetlands, Need the least land but require continuous power