Economic viability of two-stage biohydrogen and biomethane production from cassava stillage residue focusing on solids content and pretreatment

Abstract

Biohythane (a mixture of hydrogen and methane) may play a significant role in a future decarbonised energy system. The production of biohythane can be achieved by sequential dark hydrogen fermentation and anaerobic digestion. However, the technology readiness level of biohythane can be limited by many process constraints negatively affecting its commercial feasibility. Here, a pilot experiment on fermentative hythane production from cassava stillage residue (CSR) incorporating dilute acid pretreatment and enzymolysis was undertaken. The production of hydrogen and methane was 72.0 ± 10.7 and 295.4 ± 28.5 mL/g volatile solid, respectively. Different scenarios for techno-economic analysis were developed in terms of the dried/wet form of CSR and total solids content during fermentation. Results suggested that hythane from CSR was not economically feasible with a high production cost (1.39–2.33 €/m3). There was a trade-off relationship between the increase in methane yield through pretreatment and the associated cost.