A city known to have a strong olfactory connect with its people, Mumbai, is really an exercise in sensory overload. Exhaust fumes on traffic-jammed roads, the smell of stagnant water rising from the gutters, malodour of overflowing sewage, salty sea air, piles of rotting vegetables, the collective body odour of citizens in the tropical heat, the bazaars, the jumbled mayhem – the smell is at once both intoxicating, and repellent. The fact that India’s largest city is home to one of the largest slums in Asia – Dharavi – only adds to the olfactory cocktail! This teeming mass of humanity generates, on a daily basis, 7,500 tonnes of solid waste and 2,100 million litres of sewage, or waste water. In addition, there is daily waste of about 1,000 tonnes from construction and demolition work. To dispose of all this scientifically continues to be challenging for the city.
It hasn’t helped that the state’s regulator for waste disposal – the Maharashtra Pollution Control Board (MPCB) – goes by standards that are pretty lax. Not surprising, therefore, that the levels of biological oxygen demand (BOD), i.e. the amount of oxygen consumed by bacteria in oxidising (stabilising) the sewage, and total suspended solids (TSS), i.e. solids content in the sewage, in the sea off the coast are five to 10 times higher than in developed countries. In Europe, mostly, the levels of BOD and TSS are 10 and 20. In Sweden, it is 5 BOD and 10 TSS. In contrast, the MPCB allows BOD and TSS levels of 100 each.
While the Municipal Corporation of Greater Mumbai (MCGM) has allocated Rs 1,611.16 crore in its 2018 budget for water supply and sewage, it is waiting for the Centre to finalise the standards for sewage treatment. The Centre has issued a draft notification proposing international standards of 10 BOD and 20 TSS for coastal cities and 5 BOD and 10 TSS for inland cities. MCGM’s additional commissioner Sanjay Mukherjee tells FE the municipal body would invite bids for sewage treatment plants once the standards come into effect. “The new sewage treatment facilities will be built according to the new norms set by the Central Pollution Control Board,” he says.
Currently, there are seven waste water treatment plants, six of which are engaged in primary treatment, to the level of 100 BOD and 100 TSS. One of the plants – at Malad – is equipped to only do preliminary treatment. All this sewage is carried via undersea tunnels and released into the sea, 3.7 km from the coastline.
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With respect to municipal solid waste (MSW), the dumping and treatment is carried out at three sites – Kanjur, Mulund and Deonar – with the Mulund dumping ground in the process of being closed down as the bio-reactor plant at Kanjur is upgraded from 3,500 tonnes to 4,500 tonnes per day. For the site at Deonar, MCGM is inviting bids to set up a waste-to-energy plant with a capacity of 3,000 tonnes per day. Mukherjee says MCGM has more spaces to increase capacities for treatment of solid waste. It is in discussions with the state government to take possession of 52 hectares of land at Airoli in Navi Mumbai.
It already has 38 hectares at Taloja in Thane district and may acquire another 32 hectares at the same location. Once the new plants are set up, MCGM will be able to process 8,500 tonnes of MSW per day. Will that be enough to deal with future population growth? Only time will tell.