Treated sewage water for non-potable use: BMC’s ambitious plans for Mumbai explained

BMC's planned treatment of sewage water will improve the state of water bodies and also meet some of the demand for non-potable water.

The Brihanmumbai Municipal Corporation (BMC) is trying to commercially sell sewage treated water. As of now, the city generates about 2190 million litres per day (MLD) of sewage or black water, of which it manages to recycle 22.65 MLD of water fit for reuse for non-potable use.

Citizen Matters examines the status of this project and how it could help the city with its water requirements.

What is the BMC doing with its sewage waste treated water?

In December 2023, the Brihanmumbai Municipal Corporation (BMC) invited bids for commercial use of 15.8 MLD of treated sewage wastewater generated from its four Sewage Treatment Plants (STP) for industrial or non-potable use.

It floated an expression of interest inviting various bodies from the government, semi-government, public sector organisations, private firms or service provider sector to use its treated water for commercial use.

The BMC has generated 15.8 MLD of recycled sewage water including one crore litres or 10 MLD from the STP in Colaba, 1 MLD from Banganga, 4.5 MLD from Charkop and 0.3 MLD Videocon STP at Chembur, for commercial sale.

Mumbai generates 22.65 MLD of tertiary recycled sewage water fit for reuse, of which 15.8 MLD is provided for commercial use and rest is used for BMC’s own internal use such as water for its gardens and road-cleaning.

How can this help the drinking water shortfall?

Till recently, most industries or those requiring bulk water supply, used drinking water or tanker water for industrial purposes, since that is the only water the BMC provided. However, now that the BMC is making sewage treated water available for non-potable use, the city could save its precious drinking water and reduce the huge demand gap.

Currently, the city supplies 3850 MLD of water as against the demand of 4505 MLD. This shortfall is aggravated by use of drinking water for secondary purposes such as flushing, gardening, car washing and so on.

Are there any other benefits of providing treated water?

Instead of spending money in treating sewage water and then dumping in to the sea through Marine Outfalls, the BMC hopes to rake in money from selling this recycled water, says deputy chief engineer (Sewerage Operations) Ajit Salvi.

The civic body wishes to develop treated water as an alternative, secondary source of water.

There is a need for developing a strategic master plan for reusing treated water on a large scale. “We hope to introduce a paradigm shift from sewage treatment to reuse and recycle of waste water. Waste water is a resource, in terms of being used as nutrients for agricultural use. Effective management of waste water is essential for water security,” says Salvi.

This is over and above the benefits of treatment of sewage water resulting in cleaner water bodies and improved quality of marine aquatic life. This would eventually lead to a healthier city.

How much recycled sewage water the BMC hopes to generate in the future?

As mentioned above, the BMC has put out expression of interest for 22.65 MLD. By 2026, it hopes to make 1234 MLD of tertiary treated recycled water available, which will be fit for non-potable use. They will achieve this by treating about 2464 MLD of sewage water, according to the BMC’s Environment Status Report 2021-22.

STP at ghatkopar
Sewage Treatment Plant at Ghatkopar which was inaugurated in 2023. Several such projects are underway to make more water available through sewage treatment. Pic: Twitter (MLA Ashish Shelar)

This will be possible after the completion of eight Sewage Treatment Plants (STP) as part of the Mumbai Sewage Disposal Project (Stage -II), which is meant to overhaul the entire sewerage network operations of Mumbai.

“The 1234 MLD of sewage treated water (once all the STPs are fully functional) will be a huge quantity, almost equivalent to the water supply needs of Chennai or Bangalore city,” says Salvi. However, at present, the project is in a nascent stage with only 10 MLD of recycled sewage treated water being generated from the Colaba STP.

Currently, how is the recycled sewage water utilised?

As of now, the sewage treated water is used for gardening particularly at the lush green gardens of Raj Bhavan (about 0.5 MLD), the Willingdon Club and also the Love Grove Project (LGP) premises.

Such water is also being used for road cleaning and for cleaning machinery. Beyond this, the BMC also provides 6 MLD (another 4.3 MLD will be added soon) to HPCL for industrial use. Atharva College is also likely to take 10,000 liters or 0.01 MLD from the BMC. 

The defense establishment at Colaba will also be taking 3.5 MLD of recycled water soon.

What is the rate for sewage treated water?

The tariff is nominal and variable subject to factors like the costs incurred in providing water, the distance from the STP’s and various other allied costs involved. The BMC provides recycled sewage water to Raj Bhavan at Rs 3.27 per 1000 liters. The recycled water is provided free to its gardens like the 0.3 MLD to the Pramod Mahajan Park at Dadar.

The BMC supplies Sewage treated water to the defence forces from the Colaba STP at the nominal rate of Rs 1 per 1000 litres of water to encourage buyers. This is also because the defence establishment set up its own network of underground pipelines to receive this water.

Read more: Explainer: How to get a green sewage treatment plant (STP) for your housing society

How is sewage wastewater treated?

There are three levels of sewage water treatment, namely primary, secondary and tertiary based on the extent of purification. So, primary level treated water is barely good enough to be discharged, secondary level of treated water is deemed fit for discharge, while tertiary level treated water is good enough for being re-used. The wastewater can be recycled and reused for non-potable purposes, and the slush waste can be used as nutrients in agricultural fields.

Which technology does the BMC use to treat sewage water?

Different technologies are used at different STP’s since they were set up at different points of time. Currently, the BMC uses the Sequential Bio-Reactor (SBR), Rotating Media Bio-Reactor (RMBR), Submerged Aerated Fixed Film (SAFF), Moving Bed Bio-Film Reactor (MBBFR)  technology to treat the water.

In an interview to WaterDigest, former additional municipal commissioner P Velarasu said, “The latest Sequential Batch Reactor (SBR) Technology and Membrane Bioreactor (MBR) is used for secondary treatment, which were selected on the basis of lowest whole life-cycle costs. The latest technology from South Korea, Constant Level Continuous Flow Sequential Batch Reactor (CSBR) will be implemented for the Bhandup STP plant.”

MLA Ashish Shelar
MLA Ashish Shelar examines the treated water after inauguration of the STP at Ghatkopar. Pic: Twitter (X)

The BMC claims that its technology is comparable to the best in the world. “The technological standards of the proposed STP’s are world-class with 50% of water being treated at tertiary level. The marine pollution will come down drastically and Mumbai as an international city will get what it deserves,” Velarasu said in the same interview.

Mumbai’s has a 130- year-old sewage network developed by the British, which is only being maintained and used by the BMC.

What is the current status of sewage treatment?

As of now, the BMC’s initiative to recycle the sewage wastewater is still at an nascent stage – the city generates 22.65 MLD, just 0.01% of recycled water from the total 2190 MLD after tertiary treatment. The rest is disposed of in the sea through marine outfalls at Colaba, Worli and Bandra and at creeks through the Lagoons at Versova, Bhandup and Ghatkopar after primary treatment. The sewage collected at Malad is disposed off in the Malad Creek after preliminary treatment.

The civic body also developed the marine outfalls at Bandra and Worli, but it has now been asked to gradually phase out this practice following an order from the National Green Tribunal (NGT). The NGT insisted that the BMC follow the effluent discharge standards determined by the National Green Tribunal in its order in 2020.

And what is the status of waste water recycling?

Under MSDP-II, the BMC is undertaking the construction and upgrading of seven sewage treatment plants (STPs) at Worli, Bandra, Dharavi, Versova, Malad, Ghatkopar, and Bhandup to treat 2,464 million litres of sewage daily. The project is expected to cost upwards of Rs 26,000 crore.

Currently, Mumbai generates sewage of about 2190 MLD from its network of 2026 km of sewer lines spread across seven sewerage zones that are managed by 46 satellite pumping stations and seven terminal stations with treatment facilities.

While sewage waste is also discharged at Thane and Malad creeks, it also disposes about 3.7 km into the Arabian Sea from the  Worli and Bandra sewerage zones through marine outfalls.

Are there any challenges in using the sewage treated water?

There is resistance attached to the idea of using sewage treated water. “The main challenges facing the selling of treated water is maintenance of tertiary treatment facilities, provision of  distribution and its network, assurance of quality of recycled water as also tariff gap between freshwater and recycled water. “We can’t have a take flush and forget attitude towards sewage waste,” he says.

Is it possible to provide treated water as potable water?

The BMC is planning for further treatment of tertiary water so that it can be blended and treated for use as drinking water as a sustainable solution. In this regard, BMC has proposed a pilot project of 12 MLD capacity in the premises of Colaba STP.

The BMC has also decided to construct a 12 MLD Advanced Tertiary Treatment Plant (ATTP) on a pilot basis for converting tertiary water into potable water. The captioned project will provide direct potable water becoming the first of its kind project in India.

Internationally, sewerage treated water is already being used in various ways. Switzerland, for instance, has produced beer from such water, informs Salvi. “Future plans is to encourage reuse of sewage treated water. We are trying to sell subsidised water at cheaper rates and have infrastructure in place to distribute treated sewage waste water for commercial use,” he says.

The BMC is also proposing to manage sludge in a sustainable manner. A public and private partnership in the field of treated water and sludge for production, distribution and sale would effectively make the projects sustainable for all stakeholders. They are also welcoming private players with a proposal to play a role in sustainability.

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