Bacterial dynamics and functions driven by bulking agents to enhance organic degradation in food waste in-situ rapid biological reduction (IRBR).

This study investigated the effects of different bulking agents (i.e., sawdust, wheat straw, rice straw, and corncob) on bacterial structure and functions for organic degradation during food waste in-situ rapid biological reduction (IRBR) inoculated with microbial agent. Results showed that the highest organic degradation (409.5 g/kg total solid) and volatile solids removal efficiency (41.0%) were achieved when wheat straw was used, largely because the degradation of readily degradable substrates and cellulose was promoted by this bulking agent. Compared with other three bulking agents, the utilization of wheat straw was conducive to construct a more suitable environmental condition (moisture content of 18.0-28.2%, pH of 4.91-5.87) for organic degradation during IRBR process, by virtue of its excellent structural and physiochemical properties. Microbial community analysis suggested that the high-moisture environment in rice straw treatment promoted the growth of Staphylococcus and inhibited the activity of the inoculum. By contrast, lowest bacterial richness was observed in corncob treatment due to the faster water loss. Compared with these two bulking agents, sawdust and wheat straw treatment led to a more stable bacterial community structure, and the inoculated Bacillus gradually became the dominant genus (36.6-57.8%) in wheat straw treatment. Predicted metagenomics analysis showed that wheat straw treatment exhibited the highest carbohydrate metabolism activity which improved the pyruvate, amino sugar and nucleotide sugar metabolism, and thereby promoted the organic degradation and humic substrate production. These results indicated that wheat straw was a more desirable bulking agent, and revealed the potential microbial organics degradation mechanism in IRBR process.