Performance enhancement by rumen cultures in anaerobic co-digestion of corn straw with pig manure

Anaerobic co-digestion of corn straw with pig manure by rumen cultures was investigated in this study. Both Box-Behnken design and response surface methodology (RSM) were conducted for parametric optimization in batch tests, and later evaluated the performance enhancement in biogas production for continuous anaerobic digestion test. The optimal pretreatment time and mixing ratio (C/N ratio) were obtained at 3 days and 1:1 (C/N ratio, 19.15:1), corresponding total VFA yield, acetate concentration and VSdegradation at 0.76 g g−1·VSdegraded−1, 4014.43 mg L−1 and 79.44%, respectively. Subsequently, after a start-up time of 23 days, the continuous co-digestion reactor was successfully operated with the rumen microorganisms. The performance of co-digestion was not affected by retention time and dry matter content, resulting in a stable concentration of reducing sugar, TVFA and biogas yield at about 150 mg L−1, 100 mg L−1 and 430 mL g−1·VS−1. The role of rumen microorganisms was confirmed by FPase, CMCase and xylanase activities, up to 0.31 U mL−1·min−1, 0.35 U mL−1·min−1, and 0.45 U mL−1·min−1. A methane content of 60% was found, together with the carbon dioxide and hydrogen content of 40% and 0%. These results demonstrated that there was a remarkable improvement on anaerobic acidification and co-digestion of corn straw with pig manure using rumen microorganisms as inoculum. Co-metabolism maybe play a more important role in this process than pretreatment not only to increase the efficiency of saccharification and acidogenesis but also further provide tremendous potential in biogas production.