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. 

Key words: Biochemical oxygen demand, dissolved oxygen, electrical conductivity, pollution