Wastewater Treatment in a Growing Municipality: Evaluating the Efficiency of the Suneka Plant in Kisii, Kenya

Abstract

Wastewater stabilization ponds (WSPs) are widely used in the tropics for sewage wastewater treatment because they are inexpensive to operate. However, they have been associated as being point sources of pollution to the environment. The purpose of this study was to assess Suneka WSP's wastewater treatment efficiency. Sampling was done from May to August 2021. Dissolved oxygen (DO), pH, temperature, total dissolved solids (TDS) and electrical conductivity (EC) were measured in situ using YSI multi-parameter probe model 35C. Ex situ analyses of nutrients, total suspended solids (TSS), total and fecal coliforms (TC and FC), and chlorophyll-a were conducted in accordance with the standard protocols outlined in APHA, 2014. The effluent's levels of physical, chemical, and biological (coliform) parameters were compared to those set by the National Environment Management Authority (NEMA). The mean EC, DO, TDS, SRP, NO₃-N, NO₂-N, TN and TP differed significantly among the sampling sites (ANOVA; p < 0.05). The means of TC and FC were 37.64 ± 3.3 and 17.94 ± 2.3 counts/100ml. TDS, temperature, pH, and NO₃-N were within NEMA, WHO, and EPA standards while others were above, indicating that the plant did not efficiently polish the wastewater. Moreover, most of the assessed parameters including TP, TN and coliforms had polishing efficiency below 70% in addition to not meeting the required standards. As a result, the poor water quality and eutrophication of Riana River can be attributed to the two nutrients. To further polishing of the effluent from the WSP, this study recommends construction of a wetland.