Colaba STP, Mumbai - Case Study
Extensive tertiary treatment with DynaDisc® microscreens at the Colaba STP contributes to improved local environment status and guarantees fresh water supply to the citizens of Mumbai.
Colaba is located at the outermost tip of Mumbai and is one of the seven islands that used to make up the old city of Mumbai. The Colaba region is appreciated by tourists for its seaside golf club, beaches and public parks. During the last years the Colaba Sewage Treatment Plant (STP) has gone through an extensive modernization and upgrade. The latest one is tertiary treatment using DynaDisc® microscreens. The microscreens remove residual suspended solids containing nutrients, such as phosphate and nitrogen, as well as biological oxygen-consuming material. The upgraded STP, commissioned in mid-2019, now meets the new higher effluent requirements while minimising energy usage and contributing to improved environmental quality. The microfiltration process from Nordic Water was found to be the most compatible solution.
The Municipal Corporation of Greater Mumbai (MCGM) has seen a rapid growth of the population, which is now more than 15 million. This has put the public water & wastewater utilities under pressure. Increased water demand in combination with future regional water scarcity and more sewage water led to the decision to upgrade the Colaba STP. In 2016 Suez won the contract to upgrade and operate the STP for 15 years. To meet the demands until 2025, MCGM is following the Mumbai Sewage Disposal Project (MSDP) Stage-II Master Plan. The Colaba STP upgrade is part of that plan. The DynaDisc® microscreens allow for potential reuse of treated wastewater, which will help secure future high-quality fresh water to Mumbai.
The aim of the design concept, using Nordic Water’s discfilters for tertiary treatment, is to achieve effective separation of Suspended Solids (SS), in order to provide a high level of treatment, while reducing energy usage and decreasing the footprint of the plant as well as the overall carbon footprint. This brings MCGM and Nordic Water closer to their common motivations, the United Nations Sustainable Development Goals (SDGs).
The design also enables future expansion to treat higher flows or loads. This is possible by increasing the number of discs installed on the existing machines or by adding chemically enhanced coagulation/flocculation, as new demands arise. At Colaba, the wastewater is treated biologically by Sequential Batch Reactors (SBRs) which is an upg
rade compared to conventional activated sludge systems. The SBRs also minimise the footprint by incorporating several treatment functions within a single treatment stage. The effluent residual suspended solids from the SBRs are separated by the DynaDisc®microscreens, chlorinated and finally discharged into the Arabian Sea.
The result The installation meets the new demands of effluent SS (< 5 mg/l) and also reduces the overall maintenance. Some of the most important factors in the evaluation of the process equipment at the Colaba STP were energy efficiency, a high separation degree and the overall most economical solution. The low head loss and the low height of all of the treatment equipment has made it possible to gravitate the flow through the complete treatment plant. The upgraded treatment plant far exceeds the regulatory requirements, with an average removal rate of about 75 % of SS, which corresponds to a reduced load of 131 tonnes of fertile nutrients to the sea per year, without any use of coagulation or flocculation chemicals.