Field-scale application of constructed wetlands for treating surface water contaminated by an informal settlement

Abstract

The rapid expansion of informal settlements near South African water bodies has led to a significant decline in water quality. Runoff from inadequate sanitation and drainage systems contaminates rivers, wetlands and groundwater, posing risks to aquatic ecosystems and human health. Addressing these challenges requires innovative, low-cost solutions such as nature-based infrastructure (NBI), which can be implemented in a decentralised manner. Among these, constructed wetlands (CWs) stand out as potentially effective NBI solutions, providing a sustainable approach for water treatment without relying on additional chemicals or energy. They can remove pollutants such as total suspended solids (TSS), organic matter, nutrients and heavy metals, although their efficacy depends on site-specific conditions and water quality characteristics. Despite their potential, research on field-scale CWs for treating surface water polluted by informal settlements remains limited. This study evaluates the performance of a field-scale CW, incorporating vegetated and non-vegetated cells, to treat surface water from an informal settlement. Rigorous monitoring and operational protocols were implemented to optimise CW efficiency and enhance water quality for irrigation and environmental discharge. The CW effectively reduced ammonia nitrogen (NH₃-N), orthophosphate (PO₄³⁻) and Escherichia coli (E. coli) concentrations by up to 84%, 75% and 100%, respectively. The treated water met standards for irrigation reuse, although additional disinfection was required in some cases. While the findings highlight CWs' potential, uncertainties persist about their sustained performance under fluctuating water quality and pollutant loads typical of informal settlement runoff. Further research is therefore needed to understand temporal water quality variations, optimise CW operation under peak pollutant loadings, and address emerging contaminants in surface waters affected by informal settlements.