Treating and reusing polluted runoff from an informal settlement, South Africa

Abstract

Biofiltration holds one of the most promising options for removing environmental pollutants from water by reducing inorganic matter, and nutrient concentrations and removing pathogens. This study evaluates the performance of six large field-scale biofiltration cells and assesses the risk of reusing this treated water for irrigating food gardens. The study took place at an abandoned wastewater treatment work (WWTW) in Franschhoek, South Africa. A batch operation was used to measure physical water properties and nutrient concentrations. Large stone cells performed best in reducing ammonia nitrogen (NH3) and orthophosphate () by 98 and 95%, respectively, however, an overall increase in nitrate () and nitrites () was also observed in these and other cells. Phytoremediation made a marginal contribution to reducing contamination. The extent to which biofiltration can be used to clean and reuse contaminated surface water runoff from an informal settlement to safely reuse the water for irrigation purposes is poorly understood. Laboratory analyses revealed that the water quality from four successive harvests broadly met South African guidelines for irrigation and compared favourably with the quality of vegetables from local supermarkets. HIGHLIGHTS Biofiltration treatment of contaminated runoff from informal settlements holds considerable promise in reducing nutrient concentrations.; Large stone filter media performed best in reducing nutrient concentrations by 95%.; Treated water for vegetable irrigation complied with South African water quality standards.; The quality of vegetables compared favourably with similar vegetables sold in local supermarkets.;

Keywords

• informal settlements
• nature-based treatment
• nutrient loading
• risk assessment