A Study of Tannery Effluents and Their Effect on Receiving Waters

Abstract

Four tanneries, two in Nairobi and one each in Thika and Athi River township were identified for this study. Water samples from all the four tanneries were collected, at two different times, from the raw effluent, the treated effluent and either the receiving streams or the oxidation ponds depending on the mode of discharge of each of the tannery. The following quality parameters were determined for each sample collected: (a) Temperature (b) Hydrogen ion concentration (c) Total sulphide (d) Biochemical oxygen demand (e ) Chemical oxygen demand (f) Total non-filtrable residue (suspended solids) (g) Total filtrable residue (dissolved solids) (h) Profile of the elements present with special attention to chromium using X-ray fluorescence spectrometry. The quality parameters analysed indicated that treatment of raw tannery effluents in the selected tanneries was generally inadequate. Where the effluents are discharged into waterways, self purification of the waste waters was found to occur downstream probably through aerial oxidation and sedimentation processes. Holding the effluents in oxidation ponds without aeration was found to result