High-solid dark fermentation of cassava pulp and cassava processing wastewater for hydrogen production

Dark fermentation (DF) is a promising biological process for hydrogen production from biomass. However, low hydrogen yield (HY) is a major hurdle impeding its use at large-scale operation. A potential way to mitigate this problem is to increase the concentration of substrate in the process to increase hydrogen production. The present study investigated the possibility of using high-solid DF to produce hydrogen from cassava processing wastes, i.e., cassava pulp (CP) and cassava processing wastewater (CPW). CP was suspended in CPW and hydrolyzed enzymatically under optimum conditions of 150 g-CP/L, 29 U/g of α-amylase, 47 U/g of glucoamylase, and 60 FPU/g of cellulase. The hydrolysis performed at 50 °C for 24 h yielded a reducing sugar concentration of 117.7 ± 1.8 g/L, equivalent to 0.78 g-reducing-sugar/g-CP. Subsequent DF of CP-CPW enzymatic slurry, which contained 12.1% water insoluble solids, resulted in a cumulative production of 13.72 ± 0.22 L-H₂, equivalent to 225.2 ± 3.7 mL-H₂/g-VS. This was 83.1% of a maximum stoichiometric HY, based on carbohydrate content of CP and soluble metabolites production. The present study shows clearly the applicability of high-solid DF in the production of hydrogen from cassava processing wastes.