Chennai’s Security Tied to Cleaning Up Its Water

Chennai Can Learn From Other Cities

These water conflicts damage Tamil Nadu’s reputation and economy. To help avoid them, city leaders can start by addressing fecal waste, floating trash, and chemical contamination of Chennai’s three wretched rivers.

River restoration projects in cities as different as Oakland, Seoul, Shenzhen, Kuala Lumpur, and San Antonio could serve as models for Chennai.

These cities, and many others, invested considerable public and private funds to build or expand sewage treatment plants, construct floodwater storage basins and wetlands, move residents of informal settlements to new homes, and develop shoreline parks and promenades. Rivers that were essentially urban sewers became gardens of recreation that provide flood protection and attract real estate and business investment that covered the costs of restoration.

Tamil Nadu’s big cities, and especially Chennai, have a lot of work to do. The view from the bridges across any of Chennai’s three big rivers is a geography of hydrological ruin. Garbage lies in thick, moist mounds along the river banks. In the heat of the day, the warm waters are dimpled with bubbles that erupt amid a slow current colored by a rainbow of sickly greens and decayed red and orange.

A primary reason for the mire is that Chennai treats just a portion of its wastewater. The Chennai Metropolitan Water Supply and Sewerage Board operates 12 plants that are capable of treating 190 million gallons of wastewater daily. The city’s drinking water plants produce 400 million gallons of fresh water daily, 80 percent of which becomes wastewater. Tens of millions of gallons more water is supplied daily by private water companies and from groundwater. Altogether well under half of the sewage produced each day by residents and industries in Chennai is untreated and flows as raw waste into the city’s rivers and wetlands, according to state data. The rest of Tamil Nadu’s big cities fare no better: more than 40 percent of urban sewage is untreated. Although Tamil Nadu plans to build new treatment capacity, it is not nearly enough to meet the rising demand. Chennai, population 10.1 million this year, has added an average of 244,000 new residents annually since 2010.

It’s not that Chennai is ignorant of the challenge. It’s more a matter of scale, speed, and complexity. In October this year Chennai Metrowater announced an ambitious 2019 infrastructure initiative to update and expand the capacity of the 12 sewage plants. But expanding plants also will raise the energy and electrical costs of treating more wastewater and managing larger quantities of sludge.

The two new factors — more power and sludge — are a challenge everywhere. Cleaning up sewage and processing sludge are typically the two largest municipal energy consumers. In the United States half of the country’s large and medium wastewater treatment plants have addressed the higher costs. They installed anaerobic digesters (AD) to dewater and sanitize the sludge, and capture methane emissions. The energy-rich gas is then used to generate electricity for their plants. Excess power is either fed to the local grid or sold as compressed natural gas for vehicles.

Any residual sludge not consumed by the bugs can be sold as soil-enriching ground cover for landscaping. The energy generating wastewater plants — now being rebranded within the industry as “resource recovery facilities” — greatly lower costs for cities and water ratepayers.

Should it adopt large AD technology, Chennai Metrowater could go a step further and follow the model of Oakland and the Los Angeles County Joint Water Pollution Control Plant(JWPCP), and add food waste into the process. The Los Angeles installation is the largest sludge-to-energy plant in North America. Since adding food waste to its digesters in 2014 the plant has generated enough methane to supply all of its electricity. Oakland’s big wastewater treatment plant has achieved similar results.

As California moves to limit all food waste from landfills, JWPCP and other wastewater plants in the state are expanding their capacity to co-digest dinner scraps and potentially become major electrical and gas suppliers for their cities.