Mitigating NH3 emissions via synergistic regulation of ammonification and ammonia assimilation during black soldier fly larvae mediated chicken manure bioconversion.

Bioconversion with black soldier fly larvae (BSFL) is an efficient method for disposing of chicken manure. However, large amounts of ammonia (NH3) are released during bioconversion, resulting in significant nitrogen loss. Previous studies generally neglected the synergistic regulation of ammonification and ammonia assimilation for mitigating NH3 emissions. In this study, a novel biotechnological strategy combining propionic acid, probiotics, and glucose (PPG) was established. Specifically, acidification combined with Bacillus was applied to inhibit ammonification, while glucose was added to regulate substrate carbon to nitrogen ratio (C/N) and promote ammonia assimilation during BSFL mediated chicken manure bioconversion. The results showed that PPG significantly reduced NH3 emissions by 70.98 % compared to the control (CK) (p < 0.05). Metagenomics was used to analyze microbial regulatory mechanisms. PPG treatment resulted in a significantly higher relative abundance of ammonia assimilation gene (glnA) and lower abundance of ammonification associated genes (ureC, glsA, gcvT, gudB) (p < 0.05). These observations could be attributed to microbial community perturbations. Genera including Proteiniphilum and Petrimonas were primary contributors to ammonification and ammonia assimilation in CK, whereas genera such as Limosilactobacillus and Romboutsia dominated these two nitrogen metabolic functions in PPG. Further, the applicability of PPG strategy was effectively verified in high-density BSFL cultivation system. Finally, application of cost-optimized biotechnological strategy using calcium propionate and industrial carbon sources achieved a net profit of 10.81 USD/t. In summary, this study provided a promising biotechnological strategy for NH3 mitigation and elucidated the microbial response mechanism underlying the synergistic regulation of ammonification and ammonia assimilation.