Investigating the effect of compaction on the anaerobic digestion process of rice straw

This study aims to evaluate the effects of compaction on the anaerobic biodegradability of straw. In the study, compaction tests were carried out at different applied pressures, i.e., 0 (CK), 277 (T1), 555 (T2), and 1109 Pa (T3), respectively. The results showed that the maximum gain in biogas production was 298.35 mL·g−1 TS for the T2 reactor, significantly higher than CK (228.51 mL·g−1 TS) and T3 (249.14 mL·g−1 TS) reactors. The concentration of COD and TVFA of the T3 reactor was the highest throughout the anaerobic digestion (AD) process, the same thing for DHA, with maximum values of 39.12 g/L, 11.62 g/L, and 31.97 ug TPF/(h mL), respectively. However, the effect of compaction on the physical and chemical indicators of digestive fluid was not significant during the batch-type AD process. The factor analysis results suggested that the major factors affecting biogas production were influenced by the compaction and varied based on the different stages of digestion. Scanning electron microscopy (SEM) showed that the straw surface was damaged as the compaction increases. The degradation of TS in the AD did correlate to biogas yield, the best performance of TS loss rate was T2 (44.79%), and the lowest was CK (37.64%). This research concluded that compaction on gas production via changing the environment during the bath AD process and proper compaction could positively affect biogas yield, while excessive compaction will inhibit gas production. The impacts of compaction on the physicochemical indexes of the liquid digestate, structural and compositional changes of solid digestate, and biogas yield