River water treatment for water supply in Dhaka city

Abstract

The city of Dhaka, Capital of Bangladesh, is suffering from an acute shortage of domestic water supply. Present water supply system, which is solely dependent on groundwater, can meet 60% the demand of its total population. The aquifer beneath Dhaka City is unable to produce more water in a sustainable manner to meet the growing demand of the city. Jt was felt that the use of water of the rivers around Dhaka city by installation of small treatment plants could be advantageous for domestic water supply. This work represents an attempt to evaluate the quality of these five rivers watef)and the degree of treatment required to make the water from these rivers suitable for domestic water supply. The physical, chemical and some of the biological characteristics of the river water were determined through extensive laboratory tests. The river waters were highly turbid in the wet season. But BOD and fecal Coliform concentration were higher in the dry season .. This indicated that the bacteriological pollution load as compared to flow was very high in the dry season. Physico-chemical treatment methods namely, sedimentation, and sedimentationfiltration with coagulation were used to treat the river waters. Effectiveness of each of the methods is improving quality of river waters was determined. Turbidity, Color, BOD and Fecal Coliform was taken as indicator parameters in the assessment of water quality improvement. Waters of the rivers around Dhaka City are highly contaminated and unfit for any domestic uses. Plain sedimentation improves quality of river water to some extent but unable to make water safe for any domestic use. Alum dosage was found effective for reduction turbidity and fecal Coliform. With increasing alum dosage Turbidity, Color, BOD and fecal Colifonn removal rate were found increasing. Fecal Coliform can be removed completely by high dosage of alum. Sand filter was effective for removing Turbidity, Total solids and BOD from river waters. But coagulation with low dosage of alum and filtration with sand filter was very much effective for river waters treatment.