Impact of Partially Treated Wastewater on Downstream Water Quality of Notwane River in Botswana
Gilbert K. Gaboutloeloe
Department of Agricultural Engineering and Land Planning, Botswana University of Agriculture and Natural Resources, Private Bag 0027, Gaborone, Botswana
Gugu Molokwe
Department of Agricultural Engineering and Land Planning, Botswana University of Agriculture and Natural Resources, Private Bag 0027, Gaborone, Botswana
Benedict Kayombo *
Department of Agricultural Engineering and Land Planning, Botswana University of Agriculture and Natural Resources, Private Bag 0027, Gaborone, Botswana
*Author to whom correspondence should be addressed.
Abstract
The impact of partially treated wastewater on the water quality of Notwane river stretch in the Gaborone region of Botswana was investigated. Water samples collected at effluent discharge point and three other sampling sites downstream were analyzed for pH, temperature, Biological Oxygen Demand (BOD5), Ammonia-nitrogen (Ammonia-N) and Nitrate-nitrogen (Nitrate-N). Sampling was conducted bi-weekly between February 2013 and April 2013. The ranges of measured parameters were: pH (7.6-8.5), temperature (22-23ºC), BOD5 (11.2-27.0 mg/l), Ammonia-N (2.4-60.5 mg/l), Nitrate-N (20.6-28.6 mg/l). Analysis of variance, Games-Howel multiple comparisons and Pearson correlation were used to separate variable means. The results signal river non-point pollution due to runoff inflow of organics mainly from land use and domestic waste dumping by nearby dwellings. Temperature, BOD5, and pH range values were all within the Botswana Bureau of Standards (BOBS) limit while the maximum Ammonia-N and Nitrate-N were above BOBS limit by 50.5 mg/l and 6.6 mg/l, respectively. Regulations on indiscriminate waste dumping and discharge standards adherence should be enforced.
Keywords: Wastewater discharge, notwane river, non-point pollution, waste dumping, Botswana Bureau of Standards