Effect of different oxygen supply rate on microbial communities and enzymatic activities during composting of model food waste in a laboratory-scale reactor

Effects of oxygen supply rate (OSR) on the composting were elucidated by using a mini-scale reactor with frequent turning for keeping homogenous composting conditions, and by controlling the temperature and the moisture content of the composting material. The OSR was varied for 4 different levels, 96.2, 24.2, 13.7, and 3.45 mL-O2/min/kg-WS (wet solid), and the severe oxygen deficiency was observed in the composting with 3.45 mL-O2/min/kg-WS; the O2 concentration in the exhaust gas from the reactor became zero, the organic matter degradation rate was small and constant, and the degree of organic matter degradation at the end of composting was far smaller than those of the other composting runs. The enzymatic activity analysis revealed that all of the enzymes measured, i.e., phosphatase, esterase/lipase, protease, and sugar degrading enzymes in the composting with 3.45 mL-O2/min/kg-WS tended to be lower than those of the other composting runs. Furthermore, high-throughput sequencing of microbial DNA clarified the microbial community was considerably different between the oxygen deficiency run and the other runs, and Caldibacillus and Ureibacillus became dominant in the later stages of oxygen deficiency run, while Geobacillus were the most dominant microorganisms throughout the composting of other runs.