Mumbai coastline crisis: How to save a city: Treat its waste well
Stopping his car a few metres from the Guzdhar Bandh in Santacruz (west), activist Zoru Bathena talks about how the structure was built in the early 1900s to prevent the sea from entering the city. To get to it, we must cross the slum built next to the outlet of the estuary, and piles of garbage. Finally, a large nullah that drains out into the sea comes into view.
“This is a storm water drain,” Bathena said, emphasising that a nullah in Mumbai is another term for a storm water drain and not a sewage pipeline. This one is lined with all kinds of garbage, and sewage water flows into it from the houses on its flanks.
Bathena pointed to the sluice gates, further down where the nullah drains into the sea, that clap down when the tide is high and when the intensity of rain during the monsoon increases. The sluice gates are supposed to help save the area from flooding. A water treatment plant adjacent to the gates has floating booms that form a barrier and intercept debris and trash preventing them from entering the sea.
Of course, when the sluice gates open, the water from the nullah flows out freely. There are no nets here to catch the plastic, because in theory, storm water drains should not be carrying any plastic at all.
And this is where the city’s sewage problem lies.
Sewage pipes are meant to carry the wastewater from buildings and connect these to a larger network. In Mumbai, all sewage pipes are connected to one of eight sewage treatment plants (STPs). A storm water drain, however, collects run-off water from the streets during rains and drains it into the sea.
The storm water drainage system of the city, in fact, comprises a hierarchal network of roadside surface drains, underground drains, and laterals, major and minor nullahs and outfalls which discharge all the surface run-off into the rivers (Mithi, Dahisar, Poisar and Oshiwara and their tributaries) and the Arabian sea.
A warren of pipelines
Mumbai’s sewage network has had a patchy evolution over the history of the city’s urban development, said historian Shekhar Krishnan, who is an advisor to the Brihanmumbai Municipal Corporation (BMC) heritage conservation cell.
“Up until the start of the 20th century, there was never any adequate sewage disposal system. What existed was skewed towards the rich and elite areas. It was also built to cater to the industrial areas where cotton mills had a good sewage system because the textile industry was water intensive. In fact, Mahatma Gandhi too had commented upon Mumbai’s poor sanitation system during his first visit to the city,” he said.
It was in the 1920s, when the flushing technology was added to toilets, increasing water to sewage pipelines that Mumbai had to upgrade its system. This was also improved upon when local self-governance took charge of civic infrastructure in the same decade.
Even so, development has only followed population expansion, and our sewage system is constantly playing catch-up.
When a storm water drain carries sewage, plastic and other chemical pollutants from human activity, it chokes the life in the water bodies it drains into.
“Untreated sewage reduces oxygen in the creeks. It’s a gas chamber for the organisms in the water bodies. The only reason sardines and Bombay duck can still be seen in our waters in because their tolerance to sewage is high. Treating sewage involves aerating it with chemicals and adding natural enzymes to this to breathe life into the sewage,” said Stalin D, the director of Mumbai-based non-profit Vanashakti.
As things stand now, the total area under the Municipal Corporation of Greater Mumbai (MCGM) is 454.40 km sq out of which 322.81 km sq falls under what is demarcated as the Development Zone, while the remaining 131.59 km sq comes under what is called the non-development zone, which comprises forests, mangroves, salt pans etc, where no regular development is permitted.
Since 2016, the corporation has been expanding the sewerage network. But the problem of raw sewage entering the sea remains.
Treating our waste
In October 2020, the National Green Tribunal (NGT) ordered the BMC to pay ₹34 crore as environmental compensation for discharging raw sewage into city drains following Vanashakti’s 2017 public interest litigation (PIL).
Following the order, the Maharashtra Pollution Control Board (MPCB) drew up a set of compliances that the BMC was required to put into effect from January 1, 2021. The MPCB carried out an audit between December 2020 and June 2021, which revealed that none of the compliances had been adhered to.
“The BMC has plans to upgrade their existing STPs [Sewage Treatment Plants], and one new STP will be installed at Dharavi. At present, tendering process for modification and expansion of the existing and new STPs are completed. It will take four to five years for completion of these STPs,” the BMC submitted in a written response to MPCB. Speaking to Hindustan Times at the time, Atul Rao, chief engineer, BMC had attributed the delay to the Covid-19 pandemic.
Currently, Mumbai has eight STPs, and the BMC is upgrading them to increase the quantum of sewage that they can treat, but the deadlines are at least five years away. Apart from this, the BMC also plans to build 19 STPs for the four river rejuvenation projects, which includes one that can treat up to 418 Mega Litres (one million) per Day (MLD) in Dharavi.
Even so, this isn’t going to be enough.
According to data made available by the MCGM to a Central Pollution Control Board (CPCB) progress report, the eight treatment plants service 322.81 km sq — which covers the area of the city’s seven sewerage zones — but the accompanying sewerage network is only 269.39 km sq. Simply put, the existing network only covers 83.5% of the area it should service, with most of the shortfall (53.43 km sq) in areas like Malad, Charkop and Ghatkopar.
Work on 6.89 km sq of unserviced sewerage area has been ongoing since 2016 (in Colaba and Worli, the existing sewer network of 230mm / 450mm/600 mm diametres is also being upsized to 800mm /1200mm) and it is expected to be completed by 2024.
“For the remaining unsewered area (44.06 km sq) (…) and also to prevent discharge of untreated sewage/dry weather flow from storm water drain/nallas directly into water bodies (rivers/creeks/sea) which causes water pollution, MCGM has undertaken major projects which include either diversion of dry weather flow (DWF) to MCGM sewerage system or by providing on-site treatment through decentralized STPs under various package works of Mithi River and other rivers rejuvenation project. MCGM has various proposals of installing various sewerage network/tunnel,” the report stated.
A problem of volume
Let’s reassess. A little over 68% of the population in Greater Mumbai has access to a sewerage network. One of the reasons why the rest of the population doesn’t have access could be attributed to a rule that buildings need an occupation certificate before being allowed access to the sewage pipe. This rule immediately excludes the city’s slums. “Buildings that don’t have a connection link their sewage outflow to the storm water drains instead, illegally,” Bathena said.
A starting point, said Himanshu Thakkar, coordinator for South Asia Network on Dams, Rivers and People (SANDRP), would be to conduct surveys at the ward level to understand how much sewage is being generated, what is the capacity of the current system.
Treatment plants are advisable not just at the ward level but also within each building complex. In fact, it’s a rule in Mumbai according to an urban development department resolution.
“If buildings treat the sewage sufficiently, it would allow for this water to be used locally, for gardening, washing cars or even floor. If treated very well, the water can be used to recharge ground water and local water bodies,” Thakkar said.
According to P Velrasu, additional municipal commissioner of BMC, “The long term plan is to have localised mini STP’s in the city with the help of our river rejuvenation plans. By this plan say we aim to have 15-20 mini STPs that will handle the problem in a localised manner. But the eight STPs are in a strategic location, and they should solve the problem.”
Velrasu said that another major factor that would ease the city’s sewage problem is to turn informal housing into formal housing. “This will help the city in solving its problem related to sewage in the city.”
Anuradha Parmar, executive director of the Urban Design Research Institute, provided a bird’s eye view of the issue. The problem, she said, is that often there is inadequate coordination between waste segregation and collection, transportation, and disposal.
“The governing body needs to have an eye on the larger picture and ensure these processes don’t work is silos. If we take the issue of slums, while there might be well intentioned CSR projects that build toilets there, their monitoring and impact is often incomplete. Details of how they fit into the larger sewage network and if the trunk has the capacity to handle this inflow is often overlooked,” she said.
P. Velrasu , Additional municipal commissioner (Projects)
“The long term plan is to have localised mini Sewage Treatment Plants in the city with the help of our river rejuvenation plans. By this plan say we aim to have 15-20 mini STPs at a localised level that will handle the problem in a more localised manner. But the eight STPs are in a strategic location and they should solve the problem. ”
With inputs from Mehul Thakkar and Prayag Arora-Desai