The Impact of Waste Water from Kamiti Tanners on River Gatharini (Kasarani) Nairobi- Kenya

Abstract

This study was aimed at establishing the contribution ofKamiti tanners to the pollution of River Gatharaini.Wastewater samples were collected from the tannery for characterization on two different dates while sampling stations G1, G2, G3, G4 and G5 were established along the river. The samples were collected on weekly basis and analyzed for chromium,Cr, lead, Pb, manganese,Mn, cadmium,Cd, magnesium, Mg, calcium, Ca, potassium, K, sodium, Na, iron,Fe, chemical oxygen demand, COD, biochemical oxygen demand,BOD, sulphate, SO/- , fluoride, F- , total dissolved solids,TDS, total suspended solids, TSS, electrical conductivity, EC, nitrates, N0 3- , nitrites, N0 2-,carbonates, C0 3 2- , chloride,c l, dissolved oxygen, DO, temperature, T, and pH. Atomic absorption spectrophotometer, AAS was used to analyze the metals, dichromate refluxing was used to analyze COD while titrations were used for the other parameters. It was found out that as the tannery effluent left thetreatmentpondsatK1,the following parameters had concentrations greater than the permissible limits of either the Ministry of Reclamation, Regional & Water Development or those of WHO, EC, USA and CanadaDO, ci, SO/-, BOD, COD,Cr , Fe , Mnand Pb . The colour and odour of the effluentwere objectionable both to the eye and nose, respectively. For WHO, EC, USA and Canada, the concentrationsalso exceeded the limits for fisheries and aquatic life. At the river sampling stations, most of the parameters listed above also went above the permissible limits. DO, for example varied from 2.3 mg/l at G2 to 5.6 mg/l at G1 which was the control point. The electrical conductivity had mean ranges from 204 ~s/cm at G1 to 997 ~s/cm at G5, showing an increase in the number of ions conducting electrical current in the water. Mean TDS concentrations ranged from 145 mg/l at G1 to682 mg/l at G5. BOD had mean ranges of 79 mg/l at G1 to 373mg/l at G5 while COD had the lowest mean concentration at G1(133 mg/l) and the highest at G3 (424 mg/l).Cr mean concentrations varied from 0.034 mg/l at G1 to 3.6mg/l at G4. Mean Concentrations of Mn also varied from 0.367mg/l at G1 to 2.79 mg/l at G3. It was also observed during the study that geological factors could have contributed to the variations in the concentrations of some of the parameterswhich were being investigated. The change of the gradient orslope between G2 and G3 allowed the total mixing of water, and thereafter the sedimentation of most of the ions. The study also attempted to find out temporal variations with respect to rainfall effects. Several graphs were drawn to represent these temporal variations. It was observed that during the rainy season, the dilution capacity of the river contributed to the low concentrations of the parameters whereas during the dry season like January and February, the concentrations of most parameters were high.