1 Centre for Sustainable Technologies, 2 Centre for infrastructure, Sustainable Transportation and Urban Planning,
3 Energy and Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560 012, India
Many lakes in India receive sewage and are eutrophied. The functioning of sewage fed Varthur Lake, Bangalore, where the sewage flows into the lake through storm water courses creating natural anaerobic-aerobic lagoons with some wetland zones is described. The lake receives about 500 MLD sewage at BOD 120-200 mg/l and undergoes anaerobic digestion in the upper reaches. Subsequently, with time, as the BOD falls below a threshold, the water becomes oxic to facilitate algae driven oxidative BOD reduction to finally reach levels c.30mg/l. This understanding is corroborated by sludge characteristics studied at various points in the water body. It was observed that anaerobic sludge (mostly organic) is formed in the upper reaches. As water towards the outlet begins to become aerated a matured and improved sludge settles closer to the outlets. The study also brings out that such natural phenomena of the water body could be harnessed and engineered to create a sustainable mode of sewage treatment, nutrients and energy capture with water recycling in developing country cities, especially in tier-2 cities that will need to wait a long time to become capable of using conventional wastewater treatment systems.