Partnering with our environment to manage our wastes: land application of drinking water treatment and wastewater treatment sludges in sandy soils

The application of sewage sludge to agriculture is particularly risky in sandy soils, due to pollutant mobility. However, these nutrients are most needed in these soils, which are widely distributed in Southern Africa. This perspective piece investigates the co-amendment of water treatment residuals (WTR) to promote soil integrity, analogous to the sorptive properties of clay, fortifying nutrient-poor sandy soils to receive sewage sludge. Ecological motivations like biomimicry, environmental carrying capacity and evolutionary adaptation were explored. Land application was compared to other sludge re-use options, focusing on practical considerations. The local distribution of sandy soils and their agricultural consequences were mapped, with an exploration of the high-value crops ideal for this strategy – harnessing crop growth for pollutant remediation and minimizing downstream market risks. The economic benefits and challenges were explored in the ‘sandbox’ of the Philippi Horticultural Area, where a co-diversion strategy was modelled using simple cost analyses. Public participation was explored through the vehicle of eco-conscious markets and certification. Finally, a relatively consistent WTR and sewage sludge production ratio was shown across provincial, national and international urban development, a golden thread facilitating this waste management strategy.