Nallahs, the blackish and smelly drains, frothing and slithering through human settlements have an unwelcome but inevitable presence. The nallahs, wide or narrow, shallow or deep, are a man-made necessity that channelize domestic or industrial wastewater. And because it is a drain, more waste is dumped into it along the way making it even further polluted.
Aesthetic spoiler and the stink aside, drains can be hazardous breeding grounds for mosquitos, and they can also be toxic—the contaminants in the drain-water leech into the soil. Many drains find their way into freshwater bodies like lakes and rivers, thus polluting them too. There are sewage management systems, but these do not address even 30% of the domestic wastewater generated in our country.
In 2014, the Government of India launched the Swacch Bharat Abhiyan. There have been many initiatives under this especially important clean-India mission. One of them was to look at scientific solutions to manage the sewage. A cost-effective, ecologically sustainable, long-lasting, easy to use, maintenance-free and efficient technology that meets pollution control norms on water quality was needed. Restoring polluting nallahs into clean water channels was not the most straightforward task.
The Council of Scientific and Industrial Research’s National Environmental Engineering Research Institute (CSIR-NEERI) took upon the challenge and designed and developed RENEU (Restoration of Nallah with Ecological Units)— a combination of engineering and biological tools to renew the nallahs.
To prevent the percolation of the wastewater into the soil, along the way, water-proof base using brick and mortar is constructed for the sewage to flow. Provisions are made for placing RENEU’s ecological units in different segments of the sewage canal. The first is a physical segment that has the simple but important filtration gates. The gates act as sieves to filter the floating matter. From the filtration zone, the sewage water enters the sedimentation zone. In the sedimentation zone, the grit and other suspended solids settle down. The effluent which is now devoid of the solid matter moves from the physical segment to the biological segment.
The biological segment begins with the anoxic zone—a zone in the nallah with low oxygen. Here heterotrophic bacteria—the microbes that feast on organic matter munch away the nitrogenous, phosphorous, and carbonaceous content in the water. Clearly, the aim is to have cleaner water at the other end. But we are not there yet.
There are still other organic chemicals in the sewage which passes through bio-curtains and bio-mats where different microbes degrade more organic content present in the sewage. The more adamant organic and inorganic content that continue to remain in the sewage are broken down in the florafts treatment units. At this zone, the nallah begins to look beautiful with floating plants but underneath, the plants breakdown more organic and inorganic chemicals.
The effluent is in now in its final leg in the chemical segment. Here the water is treated with chemicals to kill any disease causing microbes. Though still not potable, the water is fit for irrigation, horticulture or can be safely discharged into water bodies.
The originally blackish and smelly sewage, after its passage through the different RENEU stations is odour free and sparkling. RENEU was successfully implemented at Jhunsi, Prayag Raj, in readiness for the Kumbh Mela of 2019, being part of the National Mission to keep the Ganges clean for the pilgrims during the holy festival.