FPJ Special: Is Mumbai's 130-year-old sewage disposal system enough to handle waste generated by 12.91 million people?

04:33 PM Aug 02, 2021 | Dipti Singh

Mumbai: With a population of 12.91 million people, Mumbai’s population has been exploding through its seams and projections. By NEERI’s estimates, it will reach 13.35 million in 2034. But can the city support the kind of population it has is an egging question that many would like to dodge.

One of the major concerns for Mumbai, according to environmentalists, is its 130 year-old sewage disposal system, which at the moment is close to being non-existent, considering that the development of Mumbai’s sewage system dates back to the British era when the first section of the sewage system was constructed between Colaba and Worli in 1867.


Post-independence, it took 32 years for the civic body to create a master plan for its sewage disposal system, which would have sustained for 25 years. The master plan, which was envisaged in1979, when the city’s population was just above 71 lakh, was completed in 2003 with the help of the World Bank. It saw Mumbai being demarcated into seven sewage zones defined largely as Colaba,Worli, Bandra, Versova, Malad, Bhandup and Ghatkopar with an 1830 kilometre long sewage network. But what strangely remained elusive through the master plan of the sewage disposal system were the Sewage Treatment Plants in these seven zones.


Waste water

According to the National Green Tribunal’s (NGT) latest order, there is only one state-of-the-art sewage treatment plant in Mumbai at Colaba, which treats sewage to the required standards before allowing the water to be released into the nearest water source. The remaining sewage plants essentially have been pumping out close to 1,842 million litres of waste water per day directly into the rivers, streams, or the sea without it being treated. In its order dated July 16, 2021, NGT stated: "There is no treatment mechanism for sludge or grit at any sewage treatment facility (except Colaba STP). Mumbai is surrounded by creeks and sea. The net result is the separation ofsludge and grit at the sewage treatment facility. It ultimately pollutes water bodies through potential seepage.

It ultimately pollutes water bodies through potential seepage and leachate from the grit disposal location, keeping in mind the rainfall Mumbai receives. This fact can be easily experienced at the sewage treatment facilities in Mumbai as the grits emit a bad smell. In general, about 10 kg to 20 kg of grits per million litres may be available in sewage, which needs proper treatment. "More than 2,700 million litres of raw or partially treated sewage is directly discharged into nullahs, sea or creek per day. Also, the treated sewage from primary level STPs is far behind the standard discharge norms. The island city has proper sewerage connections. However, the suburbs have grown rapidly.

Unfortunately, it has very few sewerage networks as well as treatment facilities,” said a BMC official. Moreover, western suburbs (Bandra to Dahisar), which has seen a prominent surge in population in the last few years, does not have a proper sewerage network and no treatment facility either. With a population of 33 lakh, raw sewage from these suburbs enters the creeks directly. The reasons attributed for the slowdown of the implementation of the Mumbai Sewage Disposal Project(MSDP) and the up-gradation of sewage treatment plants are land acquisition, environment clearance and non-compliance of effluent discharge norms, amongst others.DM Sukhthankar, former IAS officer and BMC commissioner (1981-1984), said that the issue of proper disposal of wastewater and augmentation of sewer lines always took a back seat and it continues to be neglected even today. "I would like to confess that, in the '80s, there was less consciousness or awareness about the issue of sewage treatment and waste water disposal.

Waste in creek

The STPs and sewer lines planned during 1979 were keeping in mind the population density of that time. Things are totally different now. The focal point in those times remained the augmentation of the water supply. Availability of resources and capital was also limited and rates of interest were very high, which forced us to prioritise projects. This was exactly a time when the World Bank loans had started coming in and it was a big deal. The population then was rising by 5 to 6 per cent every year as compared to now when it has stabilized.

Now, the supply of capital has increased and the cost of capital has decreased. There is no constraint on resources. Hence, it is relatively easier for the administration to address the issue of augmenting sewage treatment plants. Sukhthankar added, "Allocating the budget every year is not the only thing that will help make the sewage treatment facilities better. Resources need to be mobilised. The administration will also have to learn and achieve the global standards of sewer disposal. This needs to be done urgently before the ecology is harmed and is irreparable.


BMC’s Mumbai Sewage Disposal Project was an ambitious project to overhaul the drainage system. The civic body aimed to construct seven treatment plants to treat raw sewage.

However, the civic body failed to implement the project in compliance with the norms stipulated by the Central Pollution Control Board (CPCB).BMC’s plan to upgrade/rebuild completely the STPs at a cost of Rs 15,000crore has been moving at a snail’s pace for more than 15 years. In 2018, Nitin S Deshpande, a Pune-based activist, approached the NGT against a Ministry of Environment, Forest and Climate Change (MoEF) notification issued on October 13, 2017, for required standards for biochemical oxygen demand (BOD) and total solid suspended (TSS) for sewage treatment plants (STPs). As per Deshpande’s case, in its 2015 draft notification, the MoEF had laid down effluent discharge norms of 10mg/l of BOD and 20 mg/l of TSS as optimal for the health of water bodies but later relaxed the norms in the 2017 notification. The discharge norms changed to 20 mg/l for BOD and 50 mg/l for TSS. Following this, the NGT ordered a stay on the notification on December 21, 2018, and asked experts from the CPCB, NEERI and IIT to prepare a report and submit it before March 31, 2019.

The stay by NGT in 2018 put on hold BMC's plan of awarding contracts for construction and upgradation of five Sewage Treatment Plants at Worli, Bandra, Versova, Ghatkopar and Bhandup. Work on the up-gradation of the Colaba STP had begun then. However, the proposed STP at Malad did not get environmental clearance, as it would require the destruction of mangroves.

Cement slurry being dumped into creek

On August 31, 2020, BMC floated fresh tenders with new discharge norms, which stated that BOD or dissolved oxygen level should be at 10 mg/L and total suspended solids (TSS) at 20 mg/l for the STPs to be constructed on a Design, Build, and Operate (DBO) basis. BOD and TSS are important factors to maintain water quality. Elaborating on the situation P Velarasu, BMC's additional municipal commissioner (projects), said that the civic body floated tenders for all STPs, except salad. The project will take at least five more years to complete with the revised effluent discharge norms and revised cost. "As per the instructions of the NGT, we have already floated the tenders. The revised tenders are in conformity with the effluent discharge norms. However, we still have many hurdles before we actually start implementing or constructing these STPs,” said Velarasu.

Velarasu added, “However, financial packages have been opened. We are inthe final process of awarding the work to appropriate contractors. The offers from bidders are on a slightly higherside i.e. about 30 to 35 per cent higher. Hence, we are in the process of negotiating with the companies to bring down the cost. This process will at least take a month or two. Once finalised, the revised proposal will be tabled before thecivic standing committee for its approval, following which work order will be given.

"The existing STPs do only a primary treatment before discharging effluent or waste water into the sea. Once the new STP's are built, it will carry out tertiary treatment of the water, said Velarasu."As per the norms stipulated by the CPCB, secondary treatment of sewage water is sufficient. However, our system will be advanced and will carry out tertiary treatment," said Velarasu.


Environmentalists say this will not address the sewerage needs of nearly a third of the city’s population that lives in about 250 slums clusters. The sewerage requirement for these areas runs into an estimated 143 km. BMC has clarified that it will be laid ‘as and when’ slum rehabilitation schemes are effectively implemented across the city.

Sewage Treatment Plant

To prevent the flow of untreated sewage in creeks and rivers, Mumbai urgently needs a well-connected system of sewer lines. Stalin D, green activist and director of NGO Vanashakti said, "Even after the upgradation of STPs, the civic body will be able to service only 68 per cent of the city’s population,that too the BMC said it would need another ‘four to five years’. However, the city will still have 32 per cent of population/households, whose sewer lines will continue to the storm waterdrainwater drainspal Jhaveri, co-founder of River March (an organisation that works towards rejuvenating the city’s rivers) said, "This has become a chain, which BMC does not seem to be wanting to break.

Until they organise the sewer lines from slums, which will discharge sewage into the SWD, the problem will continue to persist. The gutters and nullahs that exist across Mumbai were originally meant to be functional only during monsoon to carry rainwater. However, they carry sewer water all year round. This is because the sewage from slums does not have a connection to enter the SWD. Then, it flows into the tributaries, creeks and mangroves and finally into the sea.

"Due to these shortcomings, there are still more than 90 openings across the city that continue to discharge untreated sewage directly into creeks. Explaining its stand, BMC in its recent submission to MPCB stated: “Sewerage infrastructure development to provide 100 per cent sewer connectivity is being implemented under the Mumbai Sewerage Improvement Program (MISP). It will require four to five years’ time for completion.

"As a quick solution, the activists demanded nets across outlets discharge from entering the mangroves. “Installing nets is a simple, cost-effective way to reduce some of the burdens on our creeks and coastline. This is a quick solution that can make a huge difference. It is baffling that the corporation has taken no steps toward getting it done. They are more interested in implementing costlier options and spending a huge amount in court cases,” said Stalin.

Besides, MPCB had also directed the civic body to install nets in the stormwater drains to prevent sewage from en-tering entering long with solid waste. It is an inexpensive stop-gap measure, the pollution body stated. "I feel sad when I see tourists bathing in the water at Juhu Beach or Chowpatty. These tourists enjoy it, not knowing that the water they are soaking themselves into is nothing but sea water mixed with sewer," added Stalin.


The NGT, in its order dated July 16, 2021, levied a penalty of Rs 2.1 crore on BMC as environmental compensation for discharging inadequately treated effluents into the drains from six different STPs.

The tribunal has also directed Municipal Commissioner Iqbal Singh Chahal to remain present in person during the next hearing to be held on August 28. In October 2020, in response to a petition by Vanashakti, NGT had rapped the civic body over the surging pollution levels of the creeks and water bodies and had imposed an environmental compensation of Rs 34 crore, which BMC is yet to pay to the CPCB.

The total penalty to be paid by the civic body now stands at Rs 36 crore. BMC appealed against the NGT’s October 2020, order before the Supreme Court, which will decide on the legitimacy of the penalty imposed by the tribunal. "It is surprising that BMC has money and time to expedite projects like the Coastal Road, which are threatening Mumbai's coastline.

However, it does not have enough to pay for or to fix the pollution it is causing knowingly,” said Stalin. Dr YB Sontakke, MPCB Joint director(water quality), " BMC is the local body. We have to accept the reason they submit to us for the delay in resolving the issue of STPs and discharge of effluents into water bodies and then investigate accordingly.

Besides, they need to recognise their responsibilities. Corporations should spend more on constructing STPs systematically along all marine and river outfalls. About compliance to sewage treatment, even if the MoEF notification on levels of BOD and TSS is on record, we have sought another clarification on it."


BOD stands for the amount of oxygen needed by microorganisms in the water to break down organic matter for their own food. A high BOD points to the presence of a high amount of sewage and other organic matter in the water.

Consequently, a drop in oxygen levels makes it completely unsustainable for fish and other aquatic life. TSS is the portion of organic material that does not dissolve, but remain suspended in the water. It provides hiding space for disease-causing microorganisms, which silt in water bodies and deteriorate the water quality.

Another important factor is faecal coliform (FC) that causes disease and epidemics, such as diarrhoea, dysentery, cholera, gastroenteritis and hepatitis B, amongst others. As per norms set by the CPCB, a BODlevel above 60 mg/l is harmful to aquatic life. An MPCB official said: “Sewage mainly contains human excreta. Raw sewage and primary treatment sewage contain extremely high bacteria and dangerous e-coli.

They go untreated into the sea. They can spread various diseases like stomach upset and loose motion. Besides, bacterial infections can cause skin infections. Untreated sewage also contains extremely high levels of organic material. And this organic material provides food for all the bacteria. These bacteria consume the dissolved oxygen in the sea. So obviously the sea around the city has less oxygen.” Sontakke added that creeks are more polluted than the sea. “The major problem is untreated or primary level treated sewage discharged in creeks. Recent studies show there is no major impact on the sea. Any pollution in any waterbody is definitely affecting it,” he added.

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