Treatment of faecal sludge with eco-friendly and pilot-scale plant for sustainable pollution control of water resources

The study was conducted to assess the characteristics of faecal sludge and septage collected from domestic septic tanks and latrine pits, and to develop a suitable eco-friendly treatment technology for mitigation of pollution caused by human excreta. A pilot scale model of integrated faecal sludge treatment plant of capacity, at the daily influent rate of 60 litres, was established at Sonarpur, Kolkata, India. The plant composed of the treatment units - Bar Screen Chamber, Anaerobic Pond, Sludge Drying Beds, Aerobic Pond, Constructed Wetland, Polishing Pond and Stand-alone Filter, arranged in series. Nine complete cycles of treatment operations were completed from September, 2024 to August, 2025 across four climatic seasons. Performance evaluation of individual treatment units and the model plant was undertaken through laboratory examination and analysis of nine water quality parameters. Results showed that Anaerobic Pond and Sludge Drying Beds collectively removed major portion of contaminants. Total ‘average removal efficiency’ of these two units and that of the entire plant reached to: Total Suspended Solids - 94.53% / 98.44%, Chemical Oxygen Demand - 89.14% / 94.78%, Biochemical Oxygen Demand (BOD 3 ) - 89.48% / 96.00%, Total Phosphorus – 72.88% / 95.12%, Total Nitrogen - 53.61% / 83.44%, Faecal Coliform - 96.10% / 99.69% and Total Coliform - 92.62% / 98.84%. The effluent water met the required discharge standard of government regulatory bodies (CPCB, India and EPA) in respect of the parameters - pH, TSS, COD and FC. However, further treatment and disinfection are needed to reduce the concentration of BOD 3 , TP, TN and TC to conform acceptable discharge standard and pathogen control.