59. Advanced Treatment of Municipal Secondary Effluents and Reuse of the High-Quality Reclaimed Water in Various Industries, Chennai, India

Chennai, the capital city of Tamil Nadu, is a very water-stressed, highly industrialized conurbation with a population of more than 11 million. Owing to its water problems, reclamation and reuse require urgent expansion. Accordingly, following the start-up of the Koyambedu and Kodungaiyur water reclamation plants in Q3 of 2019, the total reclaimed water supply to industry amounts to approximately 126,000 m³/d, which represents roughly 17% of the total quantity of sewage (municipal used water) generated. This percentage is set to increase substantially as it is now mandatory for all industries in Chennai to use treated, municipal secondary effluents. In this chapter, the process design and operational results of the Koyambedu water reclamation plant are presented and discussed. It is a 45,000 m³/d multi-barrier system, which via a 60-km-long pipeline provides high-grade water (ultrafiltration [UF] and reverse osmosis [RO] are the core process steps) to various industries such as the large automotive production facilities at Irungattukottai, Sriperumbudur, and Oragadam southwest of Chennai. The process consists of pretreatment with chlorine dioxide dosing (for pre-disinfection and pre-oxidation in the equalization tank) and dual media (sand and hydro-anthracite) rapid gravity filtration (for the removal of turbidity and biodegradable substances), basket strainers (200 μm) as a protective measure for ultrafiltration (UF), pressure-driven UF for the removal of residual turbidity and colloidal matter, cartridge filtration (5 μm), reverse osmosis (with brackish water membranes), and ozone (O₃) disinfection of the RO permeate. The major design parameters/contractual standards consist of the total dissolved solids and silica concentrations in the source water amounting to 1500 mg/L and 40 mg/L, respectively (secondary effluent from the Koyambedu Sewage Treatment Plant), and 70 mg/L and 5 mg/L, respectively, in the RO permeate (reclaimed product water). The typical actual reclaimed water values for total dissolved solids and silica are 40 and 0.5 mg/L, respectively. The operational results show that every contractual standard is met at all times.