Black soldier fly larvae composting as a bioremediation approach for heavy metals and pathogens in fecal sludge cake

Abstract

Black Soldier Fly Larvae (BSFL) composting is increasingly explored as a sustainable strategy to treat organic waste. This study assessed the potential of BSFL to reduce heavy metals and pathogens in fecal sludge cake (FSC) co-composted with fruit and vegetable waste (FVW) or cattle manure (CM). Seven treatments; T1 (100% FSC), T2 (75% FSC:25% CM), T3 (65% FSC:35% CM), T4 (55% FSC:45% CM), T5 (75% FSC:25% FVW), T6 (65% FSC:35% FVW), and T7 (55% FSC:45% FVW),were evaluated for reductions and bioaccumulation of heavy metals (Pb, Cu, Fe, Cr, Zn) as well as Escherichia coli (E.coli) and Staphylococcus aureus (S. aureus). Pb reduction ranged from 33.0% (T5) to 60.9% (T4), with the lowest bioaccumulation (4.4 mg/kg) in T4. Cu decreased by up to 43.1% (T7), while Zn showed the highest decrease (48.2%) in T6. Cr reduction peaked in T7 (32.4%), and Fe in T2 (28.7%). T5 achieved the highest E. coli reduction (99.8%), while T4 exhibited the highest S. aureus decrease (94.9%). Treatments with co-substrates (FVW or CM) consistently outperformed FSC alone, underlining their role in enhancing BSFL composting efficacy. These findings demonstrate the potential of BSFL composting to mitigate environmental and health risks associated with FSC use, offering a scalable solution for organic waste management in low-resource settings.