Effect of oxygen deficiency on organic matter decomposition during the early stage of composting

This study aimed to elucidate the recovery of organic matter decomposition after oxygen deficiency in the early stage was replaced by aerobic conditions during composting. Oxygen deficiency at the early stage was created by supplying nitrogen gas into the composting for 3 days (LN3dA) and 5 days (LN5dA). Subsequently, air was introduced until the end of composting instead of nitrogen gas. Runs LN3dA and LN5dA had lower organic matter decomposition by 10% and 19%, respectively, compared with fully aerobic composting (LA) after oxygen deficiency was changed to aerobic conditions. Compared with fully aerobic composting, composting with oxygen deficiency at the early thermophilic stage had a different bacterial community, as analyzed by high-throughput sequencing. During vigorous organic matter decomposition, Bacillus was dominant in Run LA, whereas Caldibacillus proliferated in Runs LN3dA and LN5dA. Bacillus thermoamylovorans, Bacillus arbutinivorans, and Bacillus kokeshiiformis were hypothesized to be inhibited by Caldibacillus. Moreover, dissimilarity analysis indicated that different bacterial communities remained until the end of composting, which could be a reason for the incomplete recovery of organic matter decomposition. As analyzed by the API-ZYM kit, the enzymatic activities were also different between all composting runs. One of the characterized enzymes, α-galactosidase, displayed low activity during oxygen deficiency and could not achieve high activity with sufficient oxygen until composting was completed. Overall, our study showed that oxygen deficiency at the early thermophilic stage caused incomplete recovery of organic matter decomposition.