Evaluation of Point Source Pollutants impact on Water Quality and Self-purification Capacity of Abay River in Ethiopia

摘要

This study was conducted to evaluate influence of point source pollutants on self-purification capacity of Abay River within 8 kms from Lake Tana to Sebatamit. For assessment of the overall water quality level, the water quality index was used. The river's self-cleaning potential was assessed based on physicochemical parameters as indicators and using the modified Streteer-Phelps model after selecting the best reaeration coefficient through velocity and depth measurements. The outcome of the study showed that TDS, EC, BOD5, Ammonia, temperature, pH, and salinity were found within the permissible limits of EPA. The turbidity was higher than the WHO limit at sampling point two and DO value was below the WHO and EPA limit at sampling points two, three, four, five and six. The result shows that the critical distance and time in which the river attains its self-purification capacity is at 1.3, 2.8 and 0.3 kms from Bahirdar Textile, Bahir Dar municipal and Habesha Tannery Effluent mixing points for 1.68, 0.82 and 0.48 hour, respectively. This showed that the river have good purification capacity at a moment even though the point sources are discharging an effluent which is not properly treated.