Hydrochemical Characteristics and Self-Purification Potential of Iyiechu Stream in Okigwe Area, Southeastern Nigeria

Abstract

Iyiechu stream is a small tropical urban stream that receives both domestic and industrial wastes. The self-purification potential of the stream was determined by evaluating its deoxygenation and reaeration rate coefficients. The methods of study used include dissolved oxygen (DO) measurements, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) tests as well as measurements of hydrological parameters. Deoxygenation rate of 0.20 to 0.42/day were obtained indicating very swift depletion of oxygen in the stream probably as a result of domestic sewage input. The reaeration rate coefficients ranged from 0.01 to 0.84 day and these values suggest deep and slow moving streams. The measured DO values are quite low, indicating high deoxygenation reaction in the stream and minimal dissolved oxygen contribution from other sources such as algal photosynthesis. Spatially, about 66.66% of the stream is dominated by deoxygenation reaction. The chemical oxygen demand ranged from 20 to 40 mg/l. These values are relatively high and show that the process may be partly responsible for the low dissolved oxygen levels in the stream. However, the stream is capable of re-attaining its optimum dissolved oxygen level within a flow time of 0.84 day (20hrs 16minutes) in the rainy season. Thus, a flow time much greater than 0.84 day (20hrs 16minutes) would be required during the dry season. These flow times suggest that the stream has poor self-purification potential.