An assessment of the pollution of Kabuthi river by wastewater from Dagoretti slaughterhouses complex in Kiambu district of Kenya

Abstract

Wastewater is an important source of environmental pollution. Both ground and surface water is polluted by wastewater from abattoirs, domestic, agricultural and industrial effluent. Wastewater from slaughterhouses contains both organic waste and micro-organisms. Organic waste results in reduction in oxygen demand of receiving water thus affecting the aquatic eco-system. Presence of micro-organisms may pose a public health risk to users of the receiving water body. The current study sought to assess the quality of effluent from the Dagoretti slaughterhouses and its level of pollution in the receiving stream, the Kabuthi River. Water samples were taken from taps in the slaughterhouses, effluent near the slaughterhouses, at the point of discharge into the river, 200 metres upstream from the point of discharge and 200 metres downstream from the point of discharge. Samples were taken at weekly intervals for a period of nine weeks. There was no weather change during the sampling period. The samples were analysed for total coliform, faecal coliform, faecal streptococci, presence or absence of faecal Escherichia coli, presence or absence of Salmonella, and for antibiotic resistance patterns of the isolated E. coli. The water samples taken inside the slaughterhouse had insignificant counts of bacteria. Samples collected at the point of discharge and downstream from the point of discharge had very high counts of all micro-organisms considered. The total bacterial count was an average of 1.5x 105 for samples taken 200 metres upstream from the point of discharge, 6.7x 108 200 metres downstream from the point of discharge, and 4.Ox1OSat the point of discharge into the river. There was a significant difference (p>0.05) between bacterial count of samples collected upstream from the point of discharge and those at the point of discharge and downstream from the point of discharge but there was no significant difference in counts from other sample collection sites. Faecal streptococci counts were 3.3x 103 for samples taken upstream from the point of discharge, 1.3x107 downstream to the point of discharge, 2Ax107 at the point of discharge into the stream during peak operation; 1.1x 107 where effluent from Nyongara, Thiani and Mumu slaughterhouses meet and lAx 105 for the point of discharge into the stream before start of operations in the slaughterhouses. Fifteen (15) samples (28.8%) were positive for faecal E. coli. Of the E. coli isolates, 13(65%) were resistant to one or two of the 12 antimicrobials tested while 4(25%) were resistant to five or more antimicrobials. The isolates were resistant to ampicilin (25%), sulphamethoxazole (25%), streptomycin (20%), tetracycline (20%), chloramphenicol (10%), amoxyllinlclavulanic acid (10%) and nalidixic acid (5%). There was no significant difference (p>0.05) in 5-day Biochemical Oxygen Demand (BODs) between samples taken from the different sites except for samples collected upstream from the point of discharge where the BODs level was below detectable level as compared to BODs at the point of discharge (2944 mgll). Salmonella was isolated from the site downstream to the point of discharge and one isolate was identified as Salmonella typhimurium.