Assessment of the combined response of heavy metals and human pathogens to different additives during composting of black soldier fly manure.

The bioconversion of black soldier fly (BSF) is a new model of livestock manure resourcing. However, the biochemical properties of BSF manure are unstable and direct application can be harmful to crops. Therefore, the effect of additives (biochar, humic acid and tea residue) on the removal of heavy metals and pathogens from BSF compost was investigated. Biochar inhibited the availability of Zn (58.9 %) and As (51.7 %) more significantly. Humic acid and tea residue significantly reduced the availability of Zn (60.8 %) and As (42.5 %) respectively. Humic acid and tea residue inhibited the bioavailability index of heavy metals more than biochar. At the end of composting, the total number of pathogenic bacteria was reduced by 80.1-96.0 % and pathogenic fungi by 41.4-99.9 %. Humic acid and biochar are more helpful in inhibiting the growth of pathogens. The abundance of dominant pathogenic genera was reduced by additive modulation. OM, EC, and temperature were the most key factors affecting the pathogenic bacteria. OM, pH, EC, Cu, Zn, and Cr also responded significantly to the pathogenic fungi. This study promotes the efficient conversion of livestock manure via BSF and provided theoretical guidance for the removal of pollutants in compost.