Worli, India: compact and efficient solutions for the new wastewater treatment plant

The new Worli wastewater treatment plant (WWTP) reflects a different approach to urban infrastructure design. By transforming wastewater into valuable resources and minimising its land footprint, the facility contributes to a more sustainable wastewater management system for Mumbai. Developed in close collaboration with the metropolitan authorities and adapted to local conditions, it combines operational performance with a reduced environmental impact.

In Mumbai, as in many rapidly growing metropolitan areas, wastewater treatment relied on energy-intensive infrastructure operating continuously to support treatment processes and sludge management. This significant energy demand, combined with emissions associated with sludge treatment and disposal, contributed to a substantial carbon footprint that was increasingly at odds with the city’s climate ambitions and growing expectations regarding energy efficiency.

The need expressed by the territory was clear: a reliable and sustainable wastewater treatment solution capable of reducing greenhouse gas emissions while maintaining operational performance, controlling operating costs and adapting to future challenges.

To address this challenge, SUEZ helped implement a low-carbon wastewater management model. The potential of wastewater, previously underutilised, is now fully harnessed through its conversion into local renewable energy. As a result, the wastewater treatment plant can cover part of its own energy needs, strengthening both its environmental performance and operational resilience.

At Worli, wastewater treatment is designed to support resource recovery. Sewage sludge generated during the treatment process is converted into biogas, enabling the production of 40 GWh of renewable electricity per year directly on site. This energy covers approximately 75% of the plant’s electricity demand, increasing its energy self-sufficiency and reducing its reliance on external energy sources. The on-site use of this locally generated renewable electricity reduces the plant’s annual carbon emissions by around 40,000 tons of CO₂.

In addition, the implementation of anaerobic sludge digestion significantly reduces the volume of residual sludge requiring disposal, with up to 30% less sludge being sent to landfill.

For many years, insufficiently treated wastewater discharges affected the marine ecosystem of the Arabian Sea, impacting both biodiversity and coastal activities, including fishing and recreation. In response, the city adopted a new approach aimed at better protecting its coastline and marine environment while treating increasing volumes of wastewater. Improving the quality of wastewater treatment became a key requirement to support the long-term preservation and restoration of aquatic ecosystems.

In line with circular economy principles, wastewater and the by-products generated during its treatment, such as sewage sludge, can be recovered and reused. Treated wastewater may be reused for certain urban or industrial applications, helping to reduce pressure on water resources in a context where water availability is an increasing concern.

On a dense and constrained site, particular attention was given to the environmental integration of the facility. An eco-design approach guided the project in order to limit land use and preserve existing vegetation, contributing to the protection of local natural habitats. As part of this approach, 800 trees were preserved or transplanted.

The use of a compact membrane treatment process made it possible to maximise treatment capacity while reducing the space required for the installation. This approach resulted in a 20% reduction in the footprint of the sludge treatment facilities. At the same time, the plant treats and recycles up to 250,000 m³ of effluent per day for non-potable uses such as landscape irrigation and street cleaning.

Mumbai is a dense and highly populated city where infrastructure exists alongside residential and tourist areas. The city faces increasing pressure on its wastewater system, with direct impacts on residents’ quality of life. Modernising wastewater treatment was therefore necessary to improve sanitary conditions while limiting disturbances in a very constrained urban environment.

Like many large cities, the municipality faced a common challenge: upgrading essential infrastructure without disrupting the surrounding environment or interrupting essential services. The choice of processes, equipment and construction methods was therefore guided by the need to balance technical performance with respect for local living conditions.

The project was designed to integrate as seamlessly as possible into its urban surroundings, with particular attention given to reducing visual and noise impacts and enhancing the landscape integration of the site. The compact design of the facilities, combined with measures to preserve existing vegetation, helps limit the footprint of the infrastructure within a dense urban environment while contributing to a more pleasant setting for residents. In addition, reducing the volume of sludge produced significantly decreases transportation requirements, a key consideration in a city already affected by heavy traffic congestion and high levels of air pollution. This optimisation helps reduce logistics flows, associated emissions and disturbances for nearby communities.

SUEZ has also committed to supporting the city’s greening strategy through the planting of 10,000 trees. This initiative contributes to the development of green spaces that can help cool the local urban environment and mitigate urban heat island effects, a particularly important challenge in a dense and highly exposed metropolis such as Mumbai. As a result, the project not only modernises an essential public service but also contributes to improving urban livability and supporting the well-being of local communities. The construction phase represented approximately 122,500 working days and relied extensively on local expertise and labour. Over the longer term, operation of the facility is also expected to support the creation of skilled jobs over an estimated 15-year period, further strengthening the project’s economic and social contribution to the local area and its long-term integration into the community.