Impact of waste water discharge on the bacteriological quality and physico-chemical properties of Thome River, Nairobi
Karanja, AnnCarol Waruguru
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Water pollution is one of the major problems facing many countries of the world. It may result from the discharge of various substances into water bodies in their catchment areas. Consequently the world experiences a number of water related problems including water scarcity and waterborne diseases. The city of Nairobi has experienced rapid industrialization and growth in population in the last 100 years. However, these have not been matched by development of infrastructure to deal with waste disposal. The unplanned disposal of garbage, human and industrial waste has resulted in increased pollution of water bodies. Against this background, a study aimed at determining the water quality of a section of Thome River passing through the city, was carried out between December 2004 and January 2006. The section of the river studied is located about 10 km from Nairobi city along Nairobi-Thika highway. It receives wastewater discharge from various sources. The purpose of this study was to determine whether the river water meets the recommended standards for watering livestock, recreational and irrigation of crops eaten raw. The study focused at determining the bacterial (faecal) status of the river water and measurement of selected physicochemical properties. Water samples for physico-chemical and bacteriological analyses were collected from five stations; Safari Park, Kasarani, Icipe, Sportsview and Warren along the stretch of the river and analyzed. The range in levels of the physico-chemical properties at all sites during the study period were as follows: water temperature, 18.1 to 27.3 °C; pH, 6.6 to 8.1; DO, 0 to 10.8 mg L-1; total alkalinity, 25.0 to 298.0; BOD, 0.1 to 118.9 mg 02 L"1; and electrical conductivity, 160.0 to 496.0 p S cm-1. One way AN() VA tests revealed significant differences in levels of total alkalinity, electrical conductivity, and DO at different sampling sites (P<0.05, n=20). The water was found to be contaminated with faecal bacteria such as total coliforms, heterotrophic bacteria, Escherichia coli, Salmonella, Shigella, Vibrio cholera and faecal Streptococcus. There were significant differences in mean total coliform counts at different samplin sites (P<0.05, n=12). E. coli counts recorded during the study (6.7 x 10 3 to 4.9 x 10 ) were higher than WHO standards (0/ 100 ml). Vibrio cholera was present in 50.0 % of all water samples analyzed.. Salmonella spp were detected in 29.0 % of all the water samples analyzed with Safari Park sampling site recording the lowest occurrence frequency (10.0 %). The highest frequency of occurrence for Shigella spp (35.0 %) was obtained during the dry season. Icipe sampling site had the highest E. coli counts (2.8 x 105 MPN/ 100 ml). The highest faecal Streptococcus density (4.0 x 10 MPN/ 100 ml) was recorded at Kasarani and Sportsview sampling sites several times during the study period. Based on the levels of bacterial indicators of faecal pollution, BOD concentration and DO levels, the river water at Kasarani, Icipe and Sportsview sampling sites is unfit for drinking, watering animals and irrigation of crops eaten raw. The water at Safari Park and Warren was less impacted. The results indicate that the Thome River water is polluted with domestic and , agricultural and /or surface run off effluents. Corrective measures must be taken to stop the pollution of the river.