Microbial community assembly during aging of food waste-derived hydrochar: key bacterial guilds mediate nutrient dynamics

Hydrochar aging may mitigate the adverse effects of direct application on plant growth. However, little is known about the strategies for accelerating this process and the microbiological mechanisms involved. This study explored the effects of three strategies, including the additions of straw and efficient-degrading microorganisms, on the aging processes of food waste-derived hydrochar, and the key microbial drivers. The bacterial and fungal community compositions in hydrochar were estimated at different aging periods (i.e., day 1, 7, 14 and 35) using 16S and ITS rRNA gene sequencing. The results showed that straw and microbial inoculum addition improved the temperature and shortened the aging time by ~30%. Three bacterial guilds, mainly including Bacillus-like species, were identified that had significant correlations with the nitrogen (N) and phosphorus (P) dynamics during aging. This study demonstrates the feasibility of manipulating key microbial guilds artificially to achieve efficient harmless-treatment of hydrochar.