High-solid anaerobic acidification of cassava pulp in leach-bed reactors-inoculated with Clostridium butyricum-rich microbial consortiums and its prospective for biogas

The leach-bed reactor (LBR) is known for its leachate-separation, avoiding the inhibition of anaerobic digestion (AD) caused by volatile fatty acids (VFAs) accumulation. Cassava pulp (CP) contains starch, leading to VFAs accumulation in high-solid AD. This study evaluates the performance of reactor-inoculated with original inoculum (Ro) and reactor-inoculated with improved enriched hydrolytic and acidogenic (EHA) (Ri) containing 19.37% and 45.50% Clostridium butyricum, in the AD of CP using LBRs and its leachate for biogas production. The Ri performed better than the Ro, degraded up to 78.61% VS of CP, and produced acetic, propionic, and butyric acids up to 5.14, 1.85, and 5.17 g. The key genus responsible for anaerobic acidification, Clostridium butyricum, can be maintained during fermentation. The VFAs-rich leachate from Ri was used as the feed to start-up the methanogenic reactor seeded with a syntrophic-methanogenic microbial consortium. The organic loading rate (OLR) was set from 0.5 to 3.0 gCOD/L/d. A high methane yield of 339 NmL/gCOD_removed was obtained during the steady state. The microbial community in the methanogenic reactor revealed Methanosarcina dominancy over Methanosaeta as the acetoclastic methanogens at the highest OLR. As for hydrogenotrophic methanogen, Methanobacterium was dominating, suggesting symbiosis with syntrophic Syntrophomonadaceae, Synergistaceae, and Anaerolineaceae. This is a promising strategy for future biogas development.

Graphical Abstract