Enhanced Biomethanation in Co-Digestion of Cassava Pulp and Pig Manure Using A Two-Phase Anaerobic System

In this study, the co-digestion of cassava pulp (CP) and pig manure (PM) in a two-phase continuously stirred tank reactor (CSTR) was examined to find the optimum CP-to-PM mixture ratio (w/w volatile solids; VS) and to evaluate the effect of phase separation on the efficiencies of solid destruction and methane production. The results showed that the highest VS removal (29%) and the greatest production of intermediates, such as volatile fatty acids and ethanol (24%) in the hydrolysis/acidification reactor were obtained using a 50:50 CP:PM ratio. Using feedstock that had a higher CP ratio, the activity of the hydrolytic/acidogenic bacteria was inhibited at approximately pH 4. In addition, the distribution of the VFA produced was shifted at approximately pH 4.5. The removal of solids and the production of methane increased in the two-phase CSTR with increasing cassava pulp ratio, up to 60% of the feedstock. The highest reduction in solids (68%) and the greatest methane yield (370 mL g-1VSadded) were obtained using a 60:40 CP:PM ratio. Co-digestion in a two-phase CSTR reduced the solids by 14% and increased the production of methane by 36% over those obtained using a single-phase CSTR.