Effects of microbial inoculation on mitigating odor release, curtailing nitrogen and sulfur losses, and accelerating the maturation during food-waste composting

A thermotolerant, odor-suppressing microbial agent was inoculated into food-waste (FW) composting to systematically evaluate its influence on odorants, volatile organic compounds (VOCs), microbial community structure, extracellular enzyme activities, and the transcriptional profile of nitrogen- and sulfur-cycle genes. Compared with the uninoculated control, cumulative emissions of NH₃, H₂S, ethanol, and acetaldehyde declined by 73.45%, 65.30%, 40.22%, and 37.20%, respectively, in the bio-augmented reactor. NH₃ High-throughput 16S rRNA sequencing revealed that the inoculation enhanced the microbial richness and diversity, while increasing the abundance of thermophilic strains that promote compost maturation and reduce nitrogen loss. Concomitantly, the relative abundances of acid-producing and skatole-generating populations were suppressed. Quantitative PCR showed that the expression of narG, norB, nif, nrfA, nirB, aprA, and sat genes was down-regulated. This consequently reduced the production of NH₄⁺-N and inhibited the sulfate reduction process, thereby coordinating nitrogen and sulfur metabolic transformations and significantly lowering NH₃ and H₂S emissions. Overall, this study demonstrates the feasibility of microbial inoculation for mitigating odor emissions, retaining nutrients, and accelerating compost maturation, while providing mechanistic insights into how microbial formulations regulate enzyme activities and the expression of functional genes during composting.