Effect of starch addition on the biological conversion and microbial community in a methanol-fed UASB reactor during long-term continuous operation

The effect of starch addition on the microbial composition and the biological conversion was investigated using two upflow anaerobic sludge bracket (UASB) reactors treating methanolic wastewater: one reactor was operated with starch addition, and another reactor was operated without starch addition. Approximately 300 days of operation were performed at 30 kg COD/m3/d, and then, the organic load of the reactors was gradually increased to 120 kg COD/m3/d. Successful operation was achieved at 30 kg COD/m3/d in both reactors; however, the methanol-fed reactor did not perform well at 120 kg COD/m3/d while the methanol–starch-fed reactor did. The granule analysis revealed the granule developed further only in the methanol–starch-fed reactor. The results of the microbial community analysis revealed more Methanosaeta cells were present in the methanol–starch-fed reactor, suggesting the degradation of starch produced acetate as an intermediate, which stimulated the growth of Methanosaeta cells responsible for the extension of granules.