Effect of ethanol distillery effluent on the water quality of the receiving waters of Lake Malawi during the rainy season

Abstract

A study was carried out in Dwangwa area of Nkhotakota d i str i ct in Malawi to determine the effect of ethanol distillery effluent from the Ethanol Company on the water quality of the receiving waters of Lake Malawi. Water samples were collected from six sites located along Dwangwa River , in the effluent ponds and in the lake at week intervals for 8 weeks. The samples were analysed for BOD, COD, DO, pH, alkalinity, acidity, turbidity, a mm onia, nitrate, phosphorous, potassium, calcium and chlorophyll. Concentration levels of pollutants, BOD, COD, DO and alkalinity generally decreased from the source downstream to the lake with a few exceptions. This was attributed to the dilution factor and evaporation of some components. Concentration levels in the receiving waters were found to be within the tolerable limits except for ammonia. On average the levels of DO, BOD, pH, Chlorophyll, Nitrate, Phosphorous and Ammonia were 6.24 ppm, 30.54 mg/l, 7.48, 5 . 05 ppm, 0.29 ppm, 0.22 ppm and 2.1 ppm respectively. The levels detected for ammonia were generally ranging between the suggested toxic concentration of 0.6 and 2 mg/l, for most of the species in water (Smith and Piper, 1975). However, concentration of pollutants in the effluent was found to be higher than the acceptable limits. It was therefore concluded that the ethanol effluent from the factory was potentially hazardous to the aquatic life in the receiving waters