ASSESSMENT OF POLLUTION IN NDARUGU RIVER DUE TO AGRICULTURAL WASTEWATER DISPOSAL

Abstract

River Ndarugu is a tributary of Athi River in Kenya and is one of the main sources of fresh water for domestic use to the villages along the river bank and Nairobi City. It traverses Juja Township in Kiambu County, Central Kenya. During its course through the different agricultural and industrial areas of Gatundu, Gachororo and Juja farms, it receives untreated industrial and agricultural waste discharges, effluent from coffee and tea factories, and other agricultural activities in the catchment area. This paper aims at assessing the level of pollution due to these activities. Water samples were collected from eight sampling points during the dry season and analysed at Jomo Kenyatta University Environmental laboratory for eight parameters; pH, temperature, electrical conductivity (EC), Turbidity, Nitrogen, Phosphorous, Biochemical oxygen demand (BOD5) and dissolved oxygen (DO) in order to assess the present water quality of the river. The samples were collected at 15cm depth (to avoid floating materials) and geographical positioning system (GPS) device was used to spatially locate the sampling sites. Samples were taken from upstream and downstream of point sources of pollution. Results indicated that the wastewaters discharged to the river had BOD5 of 350 to 600mg/l and EC of 482 to 620μS/cm. BOD5 of the river water was found to be 20mg/l, while EC ranged from 55 to 85μS/cm. This led to decrease in the river water quality in general and DO content in particular, with DO level reducing from 6.3 to 3.4mg/l. The water is being polluted by the human activities in the catchment. There is need for proper control of wastewater by various techniques, and preliminary treatment of waste discharges prior to effluent disposal. Management of the watershed is necessary so as to protect the river from the adverse impacts of agricultural activities and save it from further deterioration.