Abstract
Egerton University (EU) uses Wastewater Stabilization Ponds (WSPs) for wastewater treatment. An adjoining wetland with gravel bed substrate and freesurface flow meant to polish discharge before releasing into River Njoro is currently non-operational. The current study aimed at establishing the performance of WSPs in terms of concentration and reduction efficiencies of Faecal Indicator Bacteria (FIB); Total Coliforms (TC) and Escherichia coli (E. coli). Wastewater samples were collected weekly for one month from mid- November to mid-December 2017. Total Coliforms and E. coli were isolated using selective and differential media following Membrane Filtration (MF) method. Colonies were cultured on Chromocult Coliform Agar (CCA) and enumerated using standard procedures for examination of water and wastewater. The results were expressed as Colony Forming Units (CFUs) per 100 ml of the original sample. The inlet showed highest concentration of FIB which reduced along the treatment pathway. Total Coliforms and E. coli ranged between 2.5 × 108 - 2.9 × 1011 and 5.9 × 105 - 1.8 × 1010 CFUs/100 ml respectively with cumulative reduction efficiencies between 2 to 4 log units for E. coli and 2 to 3 log units for TC in the two maturation ponds. Although concentration of FIB in EU WSPs reduces along the treatment pathway, the effluent quality is above recommended international standards for discharge into surface waters. The trend is attributed to lack of frequent monitoring, insufficient maintenance, together with short- circuiting effect due to by-passing of wastewater in the design of the new pond system.
Highlights
Wastewater management is still a challenge in many developing countries, and untreated or partially treated wastewater finds its way into aquatic systems (Drechsel et al, 2015)
Higher temperature of 22.1 °C ± 0.5 was recorded in the Second Facultative Pond (SFP) as compared to other ponds whose mean temperature ranged between 21.3-21.9 °C
Dissolved Oxygen was very low at the inlet, 1.8mg/l while super saturation was observed in the First Maturation Pond (FMP) and First Facultative Pond (FFP), with measured values of 10.9 mg/l and 14.6 mg/l respectively
Summary
Wastewater management is still a challenge in many developing countries, and untreated or partially treated wastewater finds its way into aquatic systems (Drechsel et al, 2015). The most common technologies for wastewater treatment in developing countries are Wastewater Stabilization Ponds (WSPs) and Constructed Wetlands (CWs), Kivaisi (2001). Wastewater stabilization ponds are shallow basins that naturally treat wastewater using decomposition and autotrophic activities of aerobic and anaerobic micro-organisms. WSPs require large tracts of land for their construction, which was a promoting factor in EU that stands on about 1600 hectares of land, providing enough space for construction of a WSPs system. Lukhabi et al / Afr.J.Bio.Sc. 3(2) (2021) 16-26
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