Electric field mitigates NH3 and N2O emissions during bioconversion of dairy manure by black soldier fly

Abstract

As a potential strategy for the disposal of various organic wastes, bioconversion with black soldier fly larvae (BSFL) emits large amounts of ammonia (NH3) and nitrous oxide (N2O), especially at the late stage. Recently, application of electric field has been proposed as an effective strategy to mitigate NH3 and N2O emissions in the composting progress, but its effect remains to be explored in BSFL-based bioconversion. Here, this study firstly evaluated the effect of 1, 3, and 5 V direct-current voltage on the bioconversion of dairy manure by BSFL. The results showed that 3 V treatment significantly enhanced the growth and survival rate of BSFL and significantly reduced the emissions of NH3 and N2O by 24.55 % and 66.71 %, respectively. Consistently, 3 V treatment significantly reduced the contents of NH4+-N, NO3–-N, and NO2–-N, as well as the relative abundance of key genes (amoA, narG, nirS, and norB) for microbial nitrification and denitrification in the substrate relative to CK at day 6. Hence, electric field can stimulate BSFL growth and mitigate NH3 and N2O emissions, which might be ascribed to the effect of current on the activity of BSFL, and the suppression of microbial nitrogen transformation while promoting the degradation of organic matter. This study novelly demonstrates that electric field is a novel and environment-friendly strategy to facilitate bioconversion of organic wastes by BSFL with higher biomass production and lower nitrogen loss.