Assessment of composting potential of screened and decanter-separated pig slurry solids based on oxygen uptake rate

This study was conducted to identify appropriate composting conditions for solids separated during the pretreatment processes of pig slurry treatment system, specifically focusing on primary solid-liquid separation using a screen and secondary solid-liquid separation using a decanter, through the evaluation of oxygen uptake rate (OUR).Seven treatment groups were used to compare primary screened solids (T1), secondary decanter-separated solids (T2), mixtures of primary and secondary solids without bulking agents (T3 and T5), and additional treatments incorporating sawdust as a bulking agent with different mixing ratios (T4, T6, and T7).OUR was evaluated to assess the biodegradability of different solid fractions.Oxygen uptake rates ranged from 7.1 to 14.2 mg O 2 /g VSd.The highest value observed in T2 (secondary decanterseparated solids).Lower oxygen uptake rates were observed in sawdust-amended treatments, indicating reduced microbial activity.This suggests that secondary decanter-separated solids contain more readily biodegradable organic matter and provide a favorable environment for composting.The reduced oxygen uptake rate in sawdust-amended treatments was likely attributable to excessive C/N ratios and the presence of lignin-rich recalcitrant material.Additionally, the increased porosity in sawdust mixtures may have contributed to a substrate dilution effect.Treatments combining both screened and secondary decanter-separated without bulking agents (T3) and (T5) exhibited intermediate OUR 10.3 and 11.5 mg O 2 /g VSd, respectively.Overall, these findings demonstrate that secondary decanter-separated solids (T2) represents the most suitable fraction for composting, whereas sawdust addition requires careful optimization to avoid nitrogen limitation.