Current Status in Quality of Treated Wastewater for Potential Reuse Scheme in Ruai, Nairobi County, Kenya

Abstract

The study examined the current status in quality of the treated wastewater (TWW) discharged at Dandora Estate Sewage Treatment Works (DESTW) in Ruai with a view to assessing its reuse potential and conformity to the national standards recommended for safe use. The DESTW discharges approximately 80,000m³/day of TWW through its three outlets into the adjacent Nairobi River without any planned use option. However, some people use it directly or indirectly for their livelihoods oblivious of its quality status, putting at risk their own health, public health and the environment. Understandably, with freshwater becoming increasingly scarce, thus limiting livelihood options, water planners and users are forced to reconsider other water resources such as wastewater which can be used both economically and effectively. Samples of TWW were collected from the three outlets (sampling sites) at DESTW, prepared and analysed for heavy metals [lead (Pb), zinc (Zn), copper (Cu), cadmium (Cd), chromium (Cr), manganese (Mn), nickel (Ni) and iron (Fe)]; macronutrients [nitrogen (N) as nitrate, phosphorous (P) as phosphate and potassium (K)] and environmental characteristics [microbes; faecal coliforms (FC) and total coliforms (TC), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total solid (TS), pH and chlorides]. Raw data were analysed with the help of Statistical Package for Social Sciences [SPSS] software version 20 for both descriptive statistics (means and standard deviations) and inferential statistics (ANOVA’s F and post hoc procedures by Tukey and Games-Howell test where applicable & Kruskal-Wallis H test. All inferential statistical tests were conducted at a 0.05 level of significance. Results showed that the content of Cd, Cr, Fe, Mn, phosphate, TS, chlorides, and pH were lower than their safe limits for reuse but that of lead, BOD, COD, nitrates and TC exceeded the recommended threshold limits. Results of one-way ANOVA performed on the data suggested that the levels of all the measured parameters of the study except Fe, Pb, pH, BOD and FC varied significantly among the three sites. Overall, the results show that the TWW is not entirely safe for use in its current quality state. There is need for an improved optimal wastewater treatment configuration at DESTW aimed at rendering suitable effluent for reuse schemes in Ruai.

Key Terms: treated wastewater, quality, water resource, livelihoods, reuse

DOI: 10.7176/JEES/10-7-07

Publication date:July 31^st 2020