Utilization of gibberellin fermentation residues with swine manure by two-step composting mediated by housefly maggot bioconversion

[Display omitted] •Two-step composting was used to dispose of gibberellin fermentation residues (GFRs).•GFR substitution improved maggot production during maggot bioconversion.•GFR substitution at a ratio of 20% accelerated the maturity of composting.•No gibberellin residue was detected in the T20% treatment after two-step composting. The ecological disposal of gibberellin fermentation residues (GFRs) is urgently needed. This study explored a new method of direct GFR utilization with swine manure at different substitution proportions (0%, 20%, 40%, and 60%) using two-step composting mediated by housefly maggot bioconversion. Regarding maggot bioconversion, substitution of GFRs accelerated the temperature increase and water content decrease, slowed the pH increase, and enhanced the maggot conversion rate. Among the proportions, 20% GFR substitution had the highest maggot conversion rate of 15.15%. During the composting stage, GFR substitution promoted the initial temperature increase and the water content decrease and maintained a relatively low pH. However, only 20% substitution promoted the maturity of compost. The degradation rates of the gibberellin residue were all higher than 97% in the treatments with GFRs after two-step composting. High-throughput sequencing analysis showed that GFR substitution had significant effects on the microbial community structure during the whole process. However, the change in the microbial community was similar to that of conventional composting. Therefore, this innovative approach is feasible for GFR resource utilization, and substitution below 20% for swine manure is recommended.