J. Bio. Env. Sci.11(1), 123-133, July 2017
Ground water depletion in Dhaka indicates that shifting to a surface water source is now inevitable to continue Dhaka’s public water supply. But indiscriminate pollution of the rivers of Dhaka has made them difficult to treat. Hence study on the evolution of some of the critical quality parameter is carried to understand the occasional problems of odour and aesthetic in the treated surface water in Dhaka. The Sitalakhya River water & Saidabad water treatment plant (SWTP) at Dhaka is the concern of this study. Water samples were collected & tested for a period of four years from 2002 to 2006 mostly in the laboratory of SWTP following standard methods and analyzed. Ammonia levels are found generally below 0.5 mg NH4-N/l in the wet season but rise up to 10 mg NH4-N/l (sometimes more) during the dry season. Other parameters such as BOD, COD, phosphate, hardness, TDS, and conductivity show the same general pattern of variation. BOD reaches levels of 20 mg/l & BOD to COD ratio is between 1.5 and 2.Colour exists in treated water from around 2 TCU to around 15 TCU respectively in dry & wet seasons. Sulfide presence is negligible. The average and max values, both increasing around three mg NH4-N/l every year with a trend signifying that it will continue further. Compared to design criteria of SWTP of max 4 mg NH4-N per litre the increases are substantial. This needs attention both in terms of regulatory measures and of proactive strategies on how to handle the resulting future treatment challenges.
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