Water is considered the elixir of life; however, this critical resource has finite availability. It has a quantitative limitation and a qualitative vulnerability. Freshwater availability is decreasing day by day with the rise in population, and the available water is getting increasingly contaminated due to human interference. Over time, many countries, including India, have become water-stressed for this reason. India has only a meagre 4 per cent availability of fresh water but accounts for 16-17 per cent of the world’s population. It also does not meet the standards for per capita water availability set by the United Nations. The government is primarily focused on the provision of fresh water and is tapping the potential use of alternative sources such as treated wastewater. Several sewage treatment plants (STPs) have been constructed in the past 25 years under the Jawaharlal Nehru National Urban Renewal Mission, and subsequently, the Atal Mission for Rejuvenation and Urban Transformation. However, their operability is a concern. Many of these STPs are not functional due to poor operations and maintenance (O&M) or do not meet the requirements of regulatory bodies such as the central and state pollution control boards. In a bid to address these issues and water shortages, the common practice of enhancing water supply projects is undertaken. This approach neglects the potential for recycling and reuse of treated wastewater. To this end, the BMC is making efforts to take advantage of the vast opportunities presented by wastewater treatment projects in Mumbai. It is faced with various challenges but new and emerging technologies are being explored to overcome these issues in the future.
Efficient and effective technology selection needs to be prioritised to reduce operational costs.
Key initiatives
Recycle and reuse of treated wastewater
At present, BMC supplies around 3,850 million litres per day (mld) of water to the residents of Mumbai. This high quantity needs to be facilitated by various sources, including treated wastewater. To enable this, BMC has undertaken the recycling and reuse of 50 per cent of treated wastewater in the city, as against the service-level benchmark of 20 per cent set by the government. Around 1,250 mld of treated wastewater will be made available for non-potable purposes in the city.
One such initiative is the Colaba wastewater treatment facility with a 37 mld capacity. It is a tertiary treatment facility for the recycling and reuse of treated wastewater for non-potable usage. Commissioned in April 2020, it is being further augmented with a pilot project for treating wastewater to potable standards. Out of 37 mld capacity, 12 mld is planned to be added under this project. Seven other similar mega projects are at the construction stage. These include the Worli project with a capacity of 500 mld and the Bandra project with 360 mld. These projects have a 50 per cent wastewater recycling capacity. On commissioning of these projects in the next three to four years, 2,500 mld of wastewater would be treated as per the new regulatory requirements.
Decentralised wastewater treatment
The source of water in most cities is located at a considerable distance from the city centres. In Mumbai, water is transported from almost 100-150 km away from the city, taken to the centralised treatment unit and then distributed to various areas. Similarly, wastewater is currently treated at centralised facilities, which entails a high conveyance cost. Due to this, BMC is adopting decentralised wastewater treatment. Several decentralised STPs have been established to treat water at a reusable level for non-potable purposes such as gardening, firefighting and toilet flushing. These small decentralised wastewater treatment facilities are typically situated on the premises of various sewage pumping stations. This localised practice will help develop the habit of using treated wastewater among citizens over time, while simultaneously solving issues related to the transportation of treated water.
Technological interventions
BMC is actively adopting technologies like desalination to enhance its water supply network. One such project is the Manori desalination plant with a capacity of 200 mld, which can be further expanded to 400 mld. The project has been approved by the Maharashtra Coastal Zone Management Authority and is aimed at enhancing water security in the city.
In the wastewater segment, STPs are being constructed with modern technologies such as membrane bioreactors. Technologies like bio remediation are also being deployed to reduce the pollution load of wastewater entering water bodies. Moreover, they have been successfully implemented in some of the existing wastewater treatment facilities. As a natural and biological technology, it is less energy-intensive and requires minimum infrastructure, lowering the capital cost of the project. Upon achieving successful results, this technology can be integrated with STPs.
Pertinent challenges
There are many environmental issues related to the augmentation of freshwater supply that BMC aims to address. There are also concerns regarding the mindset of the people towards the reuse of treated wastewater, as they are unaware and unfamiliar with its reuse since fresh water is the commonly acceptable source. Another important issue is linked to the water tariff. Water is highly subsidised in all metro cities as governing bodies charge high prices for treated wastewater in order to recover the treatment costs. As a result, the cost of fresh water is much lower than the cost of treated wastewater. This significantly disincentivises the use of treated wastewater among citizens. Therefore, policies are needed to fix the price of treated wastewater at a bare minimum level to facilitate its usage.
Another critical challenge is water network management for potable and non-potable uses. These two uses require distinct water distribution networks. Additionally, once the seven centralised wastewater treatment facilities are commissioned, the tertiary treated water from these facilities would need to be separately distributed to various customers with potable and non-potable requirements. Similarly, the supply of fresh water has to be carried out through a separate network, which requires the setting up of additional infrastructure. Tankers cannot suffice for transporting water to all the areas; they can only be used locally.
Future expectations
There are two key aspects of water and wastewater projects, namely, construction or execution of the projects and their O&M. In the construction of these projects, all players and stakeholders must make necessary changes to adopt technologies that address global warming and climate change. The carbon neutrality targets set by the government must be achieved in both the construction process and the O&M of completed projects. Furthermore, the energy-intensive nature of these projects must be addressed through energy-efficient and smart operations. This can be facilitated by deploying artificial intelligence machine learning, and internet of things-based technologies, which can be further used for predictive maintenance of the plants. Efficient and effective technology selection must be prioritised to reduce operational costs at the beginning of the project itself.
Going forward, the replacement of old water network infrastructure through traditional methods such as the open-cut method would not be acceptable. Instead, rehabilitation work that enhances the life of the network is more suitable. To this end, trenchless and no-dig technologies that last for more than 30 years have been effectively implemented in Mumbai. BMC intends to further use them to improve the life by around 50 years.
Policies are needed to fix the price of treated wastewater at a bare minimum level to facilitate its usage.