Recent news about Municipal Corporation of Greater Mumbai’s (MCGM’s) plan to establish seven massive sewage recycling plants/stations in Mumbai brings hope for changing the city’s sewage treatment situation. The cumulative sewage treatment capacity planned is 2,460 million litres per day (mld). The stringent recycling standards (10 mg/L for BOD) recently issued by the National Green Tribunal (NGT) has put tremendous pressure on the Indian cities to develop the new sewerage infrastructure to meet these standards.

On one side, it may look like a burden; however, it opens the door for many new opportunities. For example, as all sewage needs to be treated to this high discharge standard, municipal governments need to make efforts to utilise this treated water for secondary usages in the city. The figure below shows such a framework proposed by us based on Circular Economy (CE), which will enable cities to help develop strategies for recycling of sewage.

Huge investment

Sewage treatment needs a tremendous amount of investment. To achieve the high effluent water quality standard, the MCGM plans to spend around ₹20,000 crore for its seven new sewage treatment plants (STPs). However, making such a vast investment demands that this must be followed with efforts to fully utilise the huge volume of recycled water that will be generated; else, this will lead to unproductive investment. The good part is that recycling stations will be constructed; however, it is unknown who will consume the treated sewage unless there is a market for it.

The annual operation and maintenance cost of conventional sewage treatment (for 30 mg/L BOD effluent) per m3 is around ₹4, and the cost of wastewater treatment for recycling purposes is around ₹10-12 per m3. This recycling cost excludes capital costs required for separate distribution infrastructure (off-site and on-site) and the pumped distribution system’s operating expenses. In comparison, India’s freshwater tariff is meager ₹3-6 per m3 (with significant variations at a regional level). This shows that recycled sewage water price is not competitive enough.

Although the MCGM has a telescoping billing policy, many connections in the island city are un-metered or most of the meters are dysfunctional, wherever they exist; hence implementing telescoping billing in the current scenario is not possible. The production cost of water for Mumbai is about ₹15 per m3. Therefore, the gap between production cost and the low tariff for residential consumers is expected to be matched by commercial and premium consumers.

However, in the absence of proper metering and billing of all consumers in general and high-value consumers in particular, the revenue demand and collection of the MCGM have been more or less constant for the entire last decade, showing that the gap between production costs and revenue remain un-breached.

The MCGM plans to have 25-50 per cent recycling at each of the seven stations. Even if we assume 10 per cent of recycled water being generated (which is about 400 MLD) in the coming 3-4 years, the big question is who will be ready to use it (even if given free) given the fact that the freshwater price is low and not a concern to most of the consumers.

Locational issue

Another issue is locational. The planned recycling stations are highly centralised, at the fag end of the collection system, and mostly located near the coast or creek, the present discharging points. Hence there is a need to develop a secondary distribution network in mostly concreted roads already cramped with dozens of other utilities, balancing tanks and pumping stations along with modification in storage and internal distribution system in consumer premises. This needs a thorough study and evaluation of cost implications.

Also, to make water recycling operational and successful, existing bye-laws need to be changed, which presently does not anticipate other water sources for non-potable use.

If we add distribution cost to the recycling cost, the total cost will further increase. Hence the whole idea of recycling water will not be feasible unless drastic changes in tariff and bye-laws (making recycled water mandatory for secondary use) are made to create a market for recycled water. The recycling market can be created by working with various stakeholders (and possible consumers) such as institutions, commercial establishments, industrial clusters, railways and metro boards, port trusts, construction sector, big consumers.

There is also a need to rethink the centralised implementation of recycling stations, which are currently planned around 400-500 mld. Decentralised recycling stations (about 50 mld) may be more feasible in Mumbai’s case, as these will create an opportunity for establishing a localised recycling network. Currently, there are about 40 satellite pumping stations, which could be converted into recycling stations after a feasibility check. Buildings can then have a second water connection from such localised recycled water networks.

Comprehensive procedures

There is a need to provide comprehensive procedures/guidelines for the use of recycled water and recovered resources. The level of treatment required, its use after treatment, expenditure, responsibilities of regulating authorities, etc., needs to be clearly defined to actively promote the use of recycled water. Other changes have to go hand in hand.

The building bye-laws and DCRs need to be changed to enable mandatory dual plumbing system for all upcoming and future buildings regardless of use; resizing of all the municipal connection for all residential/commercial/industrial establishments to restrict potable water supply for domestic purpose only (they have to have their own recycling plants or use Municipal recycled water for non-potable use), mandatory usage of efficient water fixtures (also known as demand-side management) and if possible, a rebate in property tax.

Simultaneously, there are other priority action areas such as minimising physical losses in the distribution systems (currently assessed losses of about 30 per cent in the MCGM’s network and more than this in many other cities in India) which need attention. Currently, cities instead are running for centralised infrastructure-driven solutions that are capital costs intensive and do not lead to long-term sustainability.

For example, in the case of Mumbai, immediately opting for extreme solutions such as desalination and creating new sources by building new dams will not be financially and operationally self-sustainable in the water sector.

The MCGM (and for that matter, any other city in India) should be undertaking pilot projects of recycling sewage before investing in large scale high-end recycling stations. Considering that all Indian cities have to follow the recent NGT order to establish sewage treatment infrastructure to achieve 10 mg/L BOD standard, the big question is how cities can leverage this opportunity and establish the market for recycled water simultaneously.

Although the Mumbai’s sewage treatment case is discussed here, the issues and solutions are generic and applicable for all the metros and large cities in India.

The writer is an Assistant Professor at Centre for Urban Science and Engineering, IIT Bombay. The views are personal