THE CHEMICAL COMPOSITION OF THE EFFLUENT FROM AWASSA TEXTILE FACTORY AND ITS EFFECTS ON AQUATIC BIOTA

Abstract

The chemical composition of the effluent from the Awassa textile factory was quantified and its effects on chlorophyll-a concentration and fish fry were examined. The effluent contained high concentrations of toxic heavy metals, and concentrations of about 70% of all the elements measured were higher (by 10 to 100 times) in effluent treated in ponds (biological lagoons) than straight from the factory, presumably due to concentration by evaporation. Chlorophyll-a concentration in lake water samples containing 10% and 20% textile effluent from the ponds increased by 5 to 1400% and 7 to 4000%, respectively, whereas the changes in the control were -24% to 433%. About 18% and 53% of the fish fry died within 12 hr in 10% and 20% pond effluent in lake water, respectively. The highest mean mortality level was about 64% in the 20% effluent treatment at 24 hr. It was concluded that the effluent treatment ponds of the factory do not efficiently reduce the chemicals in the discharge. The observed effects of the "treated effluent" on phytoplankton biomass and fish fry indicate the undesirable effects the effluent will have on Lake Awassa. It is recommended that an alternate waste disposal system for the textile factory be set up, with regular monitoring of its effectiveness, so as to avoid undesirable long-term changes to the lake.