An assessment of the performance of NWSC sewage treatment lagoons in Lira City

Abstract

An assessment of the performance of NWSC Lagoon Sewage Treatment Plants in Lira City was conducted with the aim of establishing their treatment efficiency and their potential to pollute downstream water resources. Permission was requested for and granted by the NWSC Research and Development Department for influent and effluent samples to be taken from the Eastern and Western lagoon systems in Lira City. Sampling was conducted twice in three weeks according to APHA (2005) guidelines, and the two batches of wastewater samples from each plant were subjected to laboratory analysis against seven parameters namely pH, Electro conductivity (EC), Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Chemical Oxygen Demand (COD), and Nitrogen forms (Ammonia-nitrogen and Nitrite nitrogen). Laboratory analysis was conducted in the Makerere University Department of Biochemistry laboratory. Percentage reduction in the physical and chemical parameters of final and secondary effluents from influents was used to gauge performance efficiency of Western and Eastern lagoons respectively. Compliance to the National Environment (Standards for Discharge of Effluent into Water or Land) Regulations, 2020 was used to gauge the potential of final effluent from Western lagoons to pollute downstream water resources and associated health risks to people of Lira, Apac, and Amolatar districts. The Western lagoon system was found to be functioning optimally with respect to reduction of electro-conductivity, TDS, TSS, and COD (with percentage reductions of 39.5%, 51.6%, 95.2%, and 94.0%, respectively) but not ammonia nitrogen and nitrite-nitrogen (with percentage reduction of 89.9% and increment of 99.5% respectively). The final effluent contained higher concentrations of ammonia-nitrogen (21±17mg/L) and nitrite-nitrogen (38.4±11.5mg/L) than the maximum permissible limit of 10mg/L. The temperature and pH in the lagoons supported maximum organic matter removal. The Eastern lagoons were found to be inefficient in removing pollutants from municipal wastewater possibly due to leakage of wastewater from the lagoons since no effluent could be seen from the outlet point of the eastern lagoon system. However, there was observed reduction in electro-conductivity, TSS, and ammonia-nitrogen (with percentage reductions of 21.9%, 56.3%, 29.5%, and 84.0% respectively) indicating reduced loading for maturation ponds. Therefore, the discharge of effluent that does not meet NEMA effluent discharge standards constituted potential health risk to people using downstream water sources as well as ecological disruption to aquatic life in Arocha swamp and Lake Kwania.