Role of Lignocellulosic Biomass Composition to Regulate Microbial Mutualism for Organic Mineralization and Humification during Digestate Composting

This study investigated the performance of lignocellulosic wastes to regulate microbial interactions to improve the composting of digestate from the anaerobic digestion of food waste regarding organic mineralization and humification. Garden waste, rice husk, and cornstalks with diverse lignocellulosic biomass compositions and structures were representatively selected for comparison. High-throughput sequencing was integrated with a modular network analysis to decipher microbial community structures and their interactions. Results showed that mixing 15% of cornstalks and garden waste with digestate (wet weight) was more effective than rice husk to enrich functional microbes (e.g., Tepidimicrobium and Mortierella) to promote the microbial interkingdom for lignocellulosic degradation and humus formation. In particular, a stronger bacterial intrakingdom mutualism was observed with cornstalk addition to facilitate the progressive succession of bacteria in digestate from anaerobic to aerobic and thus inhibit the activities of anaerobic and denitrifying microbes to reduce the emissions of methane and nitrous oxide by 14.2–49.1%. Furthermore, garden waste with more lignin could effectively strengthen intrakingdom mutualism within fungi and their interkingdom interaction with bacteria to mitigate organic carbon mineralization and reduce carbon dioxide emission by 39.8–42.7%. By contrast, rice husk weakened microbial interkingdom mutualisms to retard organic biodegradation and humification during digestate composting. Results from this study provided fundamental understanding on selecting lignocellulosic wastes to regulate organic biotransformation and to improve humification and simultaneously mitigate gaseous emissions in digestate composting.