Assessment of Faecal Sludge Quality, Heavy Metal Pollution, and Ecological Risk: Implications for Sustainable Agriculture

Abstract Pit latrines represent the predominant form of onsite sanitation in Botswana, posing unique challenges in faecal sludge (FS) management. The key concerns revolve around FS extraction, treatment, and safe disposal. Currently, co-treatment with wastewater is the primary approach, but it strains wastewater treatment plants (WWTPs) and compromises effluent quality. This study comprehensively assesses FS quality from pit latrines and evaluates potential health risks when used in agriculture for soil improvement. Systematic sampling at various depth intervals, approximately 30 cm thick, was conducted, followed by extensive analysis, including heavy metals (copper, iron, lead, cadmium, zinc, manganese, and arsenic). The findings unequivocally demonstrate that FS from VIP latrines poses no significant health risks due to heavy metal content. Specifically, Geo-accumulation Index (Igeo) values for nickel (Ni), chromium (Cr), and arsenic (As) were consistently below zero, indicating negligible risk of environmental contamination. However, copper (Cu) exhibited Igeo values above zero, with a moderate pollution risk but within manageable limits. The high nutrient content, particularly of nitrogen and phosphorus, highlights its agricultural potential, though prudent management is needed to mitigate eutrophication. The study advocates for separate FS treatment, resolving co-treatment operational challenges and enhancing sustainability. Implementing these recommendations promises to address FS management issues, bolster food security, and enhance Botswana's ecological well-being.