STUDY OF DISSOLVED OXYGEN SAG ALONG KABUTHI RIVER IN DAGORETTI

Abstract
Rivers are sources of life providing water for domestic use, irrigation, and a source of food for fish. Rivers are also the habitats for aquatic plants and animals. However, rivers also provide an easy conduit for discharge of various domestic, industrial and agricultural effluents. With the rapid increase in population and urbanisation, pollution of rivers in urban centres has been on the rise thereby overstressing river systems and decreasing the aesthetic value of aquatic ecosystems. It is
therefore necessary to study the levels of pollution of rivers into which various effluents are discharged. The importance of this study was to provide data on the levels and trends of pollution of Kabuthi River into which slaughterhouse effluent is discharged. The main objective of this project was to study the dissolved oxygen sag of Kabuthi River which flows through Dagoretti Town. Five samples of water were collected along the river. The sampling stations were located at intervals of 300 m starting at S1 upstream from the point of discharge of slaughterhouse effluent,to station S5 900 m downstream from the discharge point. The samples were tested in the laboratory to determine the levels of Dissolved Oxygen (DO), 5-day Biological Oxygen Demand(BOD) and Chemical Oxygen Demand (COD). There was a sag in the DO profile observed after
the discharge of slaughterhouse waste into the river. The DO decreased from a concentration of 8.2 mg/l upstream to a critical minimum of 5.1 mg/l 300 m downstream from the discharge point of slaughterhouse effluent. Although the DO levels along Kabuthi River were above the
recommended minimum limit of 5.0 mg/l (WHO) required for the survival of aquatic life, the margin was too small thereby suggesting a risk to aquatic life. The DO concentration increased from the minimum value of 5.1 mg/l to a value of 7.1 mg/l at a distance of 900 m from the point
of discharge of slaughterhouse waste into Kabuthi River. This recovery of DO demonstrated the self-purification process of the river. The BOD values obtained at the five sampling stations along
the river, S1 to S5, were 16, 82.5, 110, 60 and 25 mg/l respectively. These values exceeded the recommended maximum limit of 2 mg/l for drinking water suggesting that the river water is not
safe for drinking. The COD values obtained at stations S1 to S5 along the river were 16, 96, 114, 71 and 32 mg/l respectively. The maximum allowable limit of 30 mg/l set by NEMA for water for
domestic use was exceeded along River Kabuthi suggesting that the water is not safe for domestic use.