India's Original Direct Potable Reuse Project

Modern-day Mumbai has seen large population growth driven by commercial activities. The current population of Mumbai is approximately 14.08 million. BrihanMumbai Municipal Corporation (BMC) is the municipal authority responsible for supplying water within the municipal limits. Mumbai's existing water supply sources are shown in Table 1. Due to growing demand, a scarcity of water supply is anticipated. The projected water demand for years 2031 and 2041 is approximately 5,320 and 6,424 MLD, respectively, as shown in Figure 1. BMC has been planning to meet the ever-growing demand for potable water by looking into various options. Initiatives undertaken by BMC include:

*Source Augmentation: Create new sources or augment existing sources to draw more water.

*Demand-side Management: Metering, telescopic rates, pre-paid water

*Supply-side Management: Water distribution management, non-revenue water (NRW) reduction Because the above initiatives are long-term, used water (domestic wastewater) treatment and reuse has become an option in minimizing the demand-supply gap. At Colaba WWTF, BMC is developing this pilot project to produce potable grade water. In the conventional wastewater treatment plant, the treated wastewater is discharged into water bodies. For indirect potable or direct potable reuse, the high-quality treated used water (wastewater) is further treated by advanced processes and is passed through a natural or engineered buffer to ensure additional safeguards before its distribution/consumption as shown in Figure 2. Colaba Advanced Tertiary Treatment Plant (ATTP) The Colaba WWTF in South Mumbai is a 37 MLD capacity municipal sewage treatment plant consisting of a sequential batch reactor (SBR) process that is followed by disk filtration as a tertiary treatment. The proposed Colaba ATTP will take the tertiary treated water from the outlet of the disk filter and further treat it to make potable water for potential supply to the nearby 'A ward' area of Mumbai. The primary objective of this first-of-its-kind project in India is to establish a 12 MLD full-scale advanced tertiary treatment plant (ATTP) as well as a 0.1 MLD pilot ATTP facility mounted inside a trailer. The 0.1 MLD pilot facility could be moved to various other wastewater treatment plant locations in Mumbai to ensure the same or slightly modified treatment process can be adopted for developing potable water at these locations. The Colaba ATTP aims to generate water that will be of equal or higher quality than the quality of water that BMC currently supplies. Table 2 provides details of Mumbai's present water quality results. The direct potable reuse (DPR) project will have a treatment process based on worldwide (see Figure 3) practices and will consist of ozone, GAC/BAC, ultrafiltration, reverse osmosis, ultraviolet disinfection with or without advance oxidation process (AOP), and a remineralization facility with chlorine for distribution residual management. The entire process in the proposed ATTP is being considered to get a multiple barrier approach in mitigating risks associated with physical, chemical and biological contaminants while producing water of drinkable quality. Proposed Treatment At present, an extensive sampling exercise is being carried out to assess the quality of wastewater that will be taken further for the advance treatment process. The results of the initial analysis and the historical data are presented in Table 3. Based on the analysis and global trends in the ATTP processes, a tentative treatment process train customized for the local conditions and allied constraints has been developed and is provided in Figures 4 and 5. The process for the 0.1 MLD pilot plant is being developed so sequences can be altered to determine the most optimum treatment process train. The data generated during the operation of the 0.1 MLD prototype will be useful for fine-tuning the process and developing an effective public outreach program. Public Outreach Public outreach is essential for the success of the ATTP concept. The project team has planned an extensive Information Education and Communication (IEC) program to be disseminated over the next several years. The IEC program will be based on the proven guidelines that include, but are not limited to:

*Build on lessons learned from existing potable reuse projects

*Start outreach early and engage the public throughout the lifetime of the project

*Engage the media

*Increase awareness of the value of potable reuse and build confidence in the quality of ATWT

*Create messages that are consistent and communicated to the entire community, including different audiences

*Build relationships with influential community members

*Create transparency in all aspects of the project, including costs, water quality, and safety

*Prepare for tough questions and address misinformation Summary To evaluate the efficacy of treatment trains within an ATTP, the following must be considered:

*Water meets published guidelines or health advisory levels

*A large dynamic range of constituents

*Diversity of constituents that cause health concerns

*Constituents with different properties that affect their removal by various unit processes

*Real-time online monitoring for maintaining standards and getting real data