Precipitating heavy metals in biosludge in a maturation pond: a field experiment at the water hub, Franschhoek, South Africa

Lamont, Camryn

Precipitating heavy metals in biosludge in a maturation pond: a field experiment at the water hub, Franschhoek, South Africa

Thesis / Dissertation

2026

Publisher

Uiversity of Cape Town

Department

Department of Environmental and Geographical Science

Faculty

Faculty of Science

Abstract

Biosludge is a byproduct of wastewater treatment plants. It contains various organics, pathogens and pollutants, including heavy metals. Heavy metals bioaccumulate and are mobile, and therefore pose a risk to human and environmental health. In addition, current practices in biosludge management predominantly involve landfilling, neglecting the potential of biosludge as a valuable resource. This dissertation investigates the bioaccumulation and bioavailability of heavy metals in biosludge in a maturation pond, highlighting the urgent need for effective management strategies for biosludge and maturation ponds. The presence of heavy metals such as cadmium, chromium, and lead in biosludge is due to their bioaccumulative nature, which can lead to human exposure through the food chain in an uncontrolled environment. Existing knowledge gaps regarding the mobility of these contaminants compromises effective risk assessment and management. Therefore, this research emphasises the importance of minimising heavy metal concentrations in biosludge to facilitate safe reuse of biosludge for reuse of the soil media and to reduce landfill dependency. Adopting nature-based solutions (NbS) for biosludge decontamination offers a sustainable alternative to chemical treatments. The study examines the efficacy of lime, a natural calcium containing compound, in mitigating heavy metal toxicity and bioavailability in biosludge. By increasing pH levels, lime enhances heavy metal precipitation, thereby reducing their mobility and potential harm to the environment. Using lime resulted in an increase in biosludge pH, from between 3.35 and 4.85, to between 5.8 and 6.34. The experimental results demonstrate significant reductions in lead concentrations, with removal efficiencies ranging from 42% to 71%, while noting an increase in zinc levels, suggesting complex interactions within the chemistry of the biosludge column. The effects of lime on pH and heavy metal concentrations demonstrate the value of lime as a decontamination method. By implementing effective decontamination methods, including the application of lime, it is possible to transform biosludge from a waste product into a resource. This shift addresses the environmental challenges posed by heavy metal pollution and contributes to sustainable resource management. The findings underscore the need for innovative and sustainable biosludge management strategies that prioritise environmental health and resource recovery, which aligns with the principles of a circular economy

Keywords

Environmental and Geographical Science

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