Determination of pollutant loads from selected urban streams and Nakivubo Channel, Kampala.

Abstract

The study was carried out in Kampala City from November 2010 to May 2012 to determine pollutant loads of selected urban streams and the Nakivubo channel so that an effective monitoring program may be designed. The streams namely Kayunga, Kitante, City Abattoir and the Nakivubo channel had the following discharge values in order: 0.033±0.008, 0.035±0.006, 0.009±0.005 and 0.492±0.038m3/s in the dry and 0.148±0.178, 0.212±0.246, 0.010±0.012 and 1.970±0.838m3/s in the wet season. Water samples from streams and the Nakivubo channel had the following physico-chemical qualities: pH (ranged from 6.6 to 8.4 in the dry and 6.3 to 7.6 in wet season; DO (from 0.0 to 2.2±1.2mg/L in the dry and 0.0 to 3.0±0.1mg/L in wet season); EC (from 252±60 to 2028±897µS/cm in the dry and 215±100 to 1597±523µS/cm in the wet season); TSS (from 25±10 to 514±44mg/L in the dry and 61±12 to 877±350mg/L in the wet season); Temperature (from 24.9±0.3 to 28.9±0.9 oC in the dry and 23.0±1.0 to 25.5±0.9oC in the wet season); TN (from 3.49±0.84 to 173.93±34.10mg/L in the dry and 2.28±0.31 to 164.07±22.85 mg/L in wet season); TP (from 0.94±0.51 to 38.18±9.71mg/L in the dry and 0.77±0.24 to 23.33±11.55mg/L in wet season); COD (from 96.19±31.44 to 1352.48±880.00mg/L in the dry and 100.70±5.58 to 1480.50±582.40mg/L in the rain season); BOD (from 69.31±34.01 to 1108.05±333.16mg/L in the dry and 82.28±18.36 to 839.40±372.40mg/L in the wet season); Fecal coliform (from 2.6x106±1.5x106 to 5.4x107±4.8x107 Cfu/100mL in the dry and (3.8x106±3.5x105 to 2.1x107±1.3x107Cfu/100mL) in the wet season. Pollutant concentrations were compared with effluent discharge standards set by NEMA and most pollutant concentrations in streams did not meet standards. The pollutant loads of streams and the Nakivubo channel were determined as a function of discharge and concentration, and had the following values: TN (10.66±1.92 to 646.23±186.83Kg/day in the dry and 40.39±21.61 to 1860.86±1161.71 Kg/day in the wet season); TP (2.69±0.85 to 84.29±26.78Kg/day in the dry and 7.93±5.00 to 246.48±118.25Kg/day in the wet season). Other pollutant loads include BOD, COD and TSS. City Abattoir was the most and Kitante the least polluted among streams. Nakivubo carried the highest pollutant loads of all streams under study. Regular monitoring of pollutant levels in urban streams and the Nakivubo channel should be carried out. Other recommendations on reduction of pollution in streams were made.