A part of Baramati town (Dist.Pune, Maharashtra, India) receives their drinking water supply from Ujani reservoir. This plant of 5.0 mld capacity was constructed by Maharashtra Jeevan Pradhikaran (M.J.P.) The reservoir is located on the downstream side of Pune town. It receives fairly polluted water due to mixing up of partially treated sewage, industrial waste and farmland runoffs. The jack well which supplies the raw water is located in the backwaters of dam. It pumps raw water to a five m.l.d. (million liters/day) water treatment plant located on a hillock, the treated water is supplied to the town by gravity. The treatment consists of aeration, flocculation, tube settling , gravity sand filtration and chlorination. The plant was operated only intermittently for 10-12 hours per day.
In summer of 2006, the citizens complained of yellow-brown tinged, smelly tap water. On investigation , it was found that raw water contained blue-green algae and iron. The raw water had greenish-black tinge and had smell of putrefied fish. The plant walls had turned black. Calcium hypochlorite (Bleaching Powder, CaOCL) which was used for pre-chlorination had very little available chlorine. Since the plant received only intermittent electrical supply, many a times flocculators were not operated. Hence tube settling tank had become ineffective to remove algae and iron. After filtration, the color and residual chlorine were not observed, but again after post chlorination with bleaching powder yellowish-brown tinge appeared to the water (Excessive Ph re-dissolves iron as per the literature) . Bleaching powder dosing was replaced by chlorine gas. Alum was replaced by poly-aluminium chloride. Diesel generators were procured to run flocculators continuously. This mitigated the problem to some extent but not completely . As per AWWRF recommendation the intact cells of algae were tried take out of the system (flocculation-settling), pre-chlorination dose was in fact reduced not bring out the intracellular matter from cells.