Assessment of Selected Physico-Chemical Properties of Leachate at Kenkombe Dumping Site, Mbarara City and Modelling of Surface Water Quality of Rwentondo Stream

Abstract

The leachate from municipal solid waste landfills is a highly concentrated "chemical soup" – so concentrated that small amounts of leachate can pollute large amounts of ground and surface waters leaving it unsuitable for domestic use. The people of Rwentondo, a small village neighboring Kenkombe dumping site, have always raised complaints about the leachate making its way to the stream of Rwentondo, whose water they consume. This work was aimed at quantifying selected physicochemical parameters in both the leachate and surface water samples, and later compare their levels to the threshold values for leachate and surface water monitoring as stated by NEMA. Using a multiparameter photometric technique, the concentrations of lead, copper, iron, phosphates, sulphates, nitrates, and the electrolytic conductivity of both the leachate and surface water samples were assessed. Specified standardized meters were used to measure pH, total dissolved solids, and temperature. The saturation indices (SI) and chemical ion species in surface water were predicted using PHREEQC software in order to reveal the interaction and distribution of the aquatic ion species. In the leachate samples, the mean levels of each of the parameters were higher than the corresponding values recorded in surface waters. On comparison of the obtained results with the NEMA threshold limits for each of the parameters, most of the values from surface water analysis, except for pH, TDS, and Cu, lie outside the acceptable ranges. All the results from leachate analysis surpassed the threshold levels. It was observed that Rwentondo stream had SI>0 for metal complexes: hematite, vivianite, goethite, iron (III) hydroxide, anglesite. Speciation modelling predicted that the dominant species of iron was FeSO₄ with a molality of 1.846 e^-01 m. The dominant species of lead was PbSO₄ with a molality of 1.586e-⁰² m while that of copper was CuSO₄ with a molality of 3.120e^-3 m. The higher levels of each of the analyzed parameters in the samples pose a strong threat to the environment, people and animals of Kenkombe that consume the surface water of Rwentondo stream.