Black soldier fly larvae bioconversion and subsequent composting promote larval frass quality during pig and chicken manure transformation process

This research systematically assessed the changes in carbon, nitrogen and microbial profiling during pig and chicken manure transformation by black soldier fly larvae (BSFL) and subsequent composting process. BSFL had higher conversion efficiency for chicken manure. The pH, phosphorus and potassium contents in fresh BSFL frass increased than raw manure, but conductivity, total-/nitrate-/ammonium-nitrogen decreased. After BSFL conversion, pig manure had a larger nitrogen loss (25 %) while chicken manure had a larger carbon loss (32 %). During subsequent composting, the indicator changes (e.g. humus, ammonium nitrogen) in frass composts basically remained stable after 20-30 days. Compared to natural composts, frass composts had higher humification degree, cellulase activities, and more cellulose-degrading bacteria. Subsequent composting further reduced potential pathogens (reduced by 98.9 %-99.7 % than raw manure), and elevated the aromaticity and humification of frass. The findings gave an insight into the maturation management of manure-sourced insect frass.