Enhancing methane production from cassava starch: The potential of extrusion pretreatment in Single-Stage and Two-Stage anaerobic digestion

The anaerobic digestion (AD) of starch-based feedstocks poses a challenge due to the complex semi-crystalline structure of starch, which could hamper efficient methane (CH4) production. While some pretreatment methods have proven effective, the use of extrusion is still underexplored. Therefore, the effects of extrusion pretreatment on single-stage and two-stage AD were studied. The findings of this study showed that extrusion pretreatment significantly reduced the adaptive phase of single-stage AD from 41 to 23 days and increased CH4 production by 42 % (reaching 3135 ± 322 NmL CH4/Lmedium). The adaptive phase was further reduced to 3 days in the methanogenic stage of two-stage AD, regardless of extrusion pretreatment, reducing the total digestion time by ≥78 % (from 63 days to 14 days) and increasing the overall CH4 production rate by ≥305 %. Notably, introducing a separate first-stage hydrogen (H2) production served as a pretreatment step for the two-stage AD, yielding a high second-stage CH4 production (reaching 2823.76 ± 275.62 NmL CH4/Lmedium), energy potential (≈14 kJ/gCOD), and a purer biogas (≈82 % CH4), at a substantially reduced digestion time. Furthermore, it produced H2, an additional clean energy source, enhancing its overall sustainability. Overall, extrusion mainly enhanced CS hydrolysis, benefiting single-stage AD but not two-stage AD.