Unexpected heroes: invasive macrophytes boost performance of faltering waste stabilization ponds

Waste stabilization ponds (WSPs) are a widely used technology for removing organic matter and pathogens from wastewater. However, their effectiveness is often hindered by hydraulic overload, sludge accumulation, and the proliferation of invasive macrophytes–the impacts of these challenges are not fully understood. In this study, standard methods were used to assess WSPs under these operational challenges for the removal efficiency of physical, nutrient, and organic pollutants, as well as faecal indicator bacteria (FIB); the extent of macrophyte occupancy; and the level of FIB colonizing invasive macrophyte roots. Results indicated high removal efficiencies (73.38–99.67%) for turbidity, total nitrogen, NO3−, NO2−, NH3, PO43−, BOD5, total coliforms, Escherichia coli, enterococci, and Clostridium perfringens, whereas total dissolved solids, electrical conductivity, and total phosphorus showed considerably lower removal (33.5–45.2%). Significant correlations (r = 0.47–0.96, P < 0.05) were found between the removal efficiencies of physical, nutrient, and organic pollutants, as well as FIB, and macrophyte occupancy. Furthermore, high densities of FIB colonizing the macrophyte roots suggest that these roots may have positively contributed to the performance of the WSPs. The final effluent complied with East African standards for all pollutants except turbidity, BOD5, and FIB. This study reveals that ignoring WSP maintenance significantly compromises treatment performance, with potential implications for public health, and underscores the role of macrophytes in enhancing the performance of faltering WSPs.