Composting Performance and Microbial Community Responses Under Different Treatment Modes During Food Waste Digestate–Straw Composting

Food waste digestate is a high-moisture organic residue that requires effective stabilization before resource recovery or land application. This engineering-scale study compared high aeration (HA, 0.30 L·min−1·kg−1 dry matter), low aeration (LA, 0.15 L·min−1·kg−1 dry matter), and turning without forced bottom aeration (TG) during a 30-day food waste digestate–corn straw co-composting experiment. One engineering-scale pile was operated for each treatment. Physicochemical trajectories, bacterial succession, predicted functional potential, and microbial co-occurrence patterns were evaluated. All treatments rapidly entered the thermophilic phase. HA reached the highest temperature (63.70 °C) and remained above 55 °C for 340.8 h, but it also had the lowest final moisture reading (18.62%). LA achieved the greatest organic matter (OM) reduction (17.47%), compared with 13.47% in HA and 7.44% in TG, while retaining more moisture than HA at day 30. Bacillota became dominant in all treatments, although the intensity of thermophilic filtering and the pattern of late-stage succession differed among treatments. Functional predictions indicated the highest late-stage ureolysis potential in LA, whereas TG showed greater predicted representation of several nitrogen-transformation-related groups and the densest co-occurrence network. These findings suggest that engineering-scale composting performance depends on the balance among oxygen supply, heat accumulation, moisture conservation, and microbial organization rather than on thermophilic intensity alone. Under the tested conditions, LA provided the most favorable balance, particularly in terms of OM reduction and moisture retention.