ASSESSSMENT OF DOWNSTREAM POLLUTION PROFILE OF HAWASSA CITY MUNICIPAL WASTEWATER AND ITS INFLUENCE ON LAKE HAWASSA

Abstract

Lake Hawassa is used for a variety of purposes like fishing, recreation, swimming, drinking water supply by the communities surrounding it and cultivation of vegetables. However, it is exposed to wastewater discharge from the city and polluting the aquatic ecosystem. The objective of this study was characterization of municipal wastewater of Hawassa city and its impact on the receiving lake water quality. Five sites were selected from Wastewater channel and on the lake. A total of 20 grab samples were collected on two week basis for physio-chemical analysis. Samples were examined using standard procedure over the duration of May 2013 to July 2013. The significant pollution parameters for these effluents include a COD mean concentration ranged from (13.28±2.00mg/l -75.48±3.48), BOD5 concentration of (6.03±1.74 mg/l -26.97±3.56mg/l). Chloride and total hardness concentrations with mean values ranged from (12.44±4.14-18.58±14.88) and (292.75±438.21mg/l- 49.50±14.46) respectively. Ammonia and total nitrogen concentrations were with mean values of ranged (0.52±0.25mg/l -4.39±0.99 mg/l) and (10.00±1.63-32.75±2.75mg/l) respectively. The mean phosphorus, nitrate and nitrite content of the effluent were also found to be 0.34±0.06mg/l -4.20±0.14, 0.41±0.25mg/l 3.77±0.34 and 0.11±0.15mg/l- 0.27±0.17 mg/l respectively. The concentration of nitrite was negligible when the value compared with other parameters investigated. The pH values were 7.36±0.52-8.31±0.28 indicating alkalinity of the wastewater. Total Dissolved solids, electrical conductivity and Total Suspended Solids of the effluent wastewaters were (513.00±45.77-755.25±162.70) mg/l, (865.00±66.73-1287.75±297.23) (μS/cm) and (21.75±23.89 - 276.75±109.76) mg/l, respectively. The investigation of temperature and turbidity ranged from 21.50±2.69 - 23.00 +2.7 OC. and 23.28±21.10NTU -226.00±35.56 NTU respectively. The values of most parameters were significantly different among sites, at 0.05 significant level of post Hoc ANOVA.