Mesophilic fermentative hydrogen production from sago starch-processing wastewater using enriched mixed cultures

Biohydrogen (bioH₂) production from starch-containing wastewater is an energy intensive process as it involves thermophilic temperatures for hydrolysis prior to dark fermentation. Here we report a low energy consumption bioH₂ production process with sago starch powder and wastewater at 30 °C using enriched anaerobic mixed cultures. The effect of various inoculum pretreatment methods like heat (80 °C, 2 h), acid (pH 4, 2.5 N HCl, 24 h) and chemical (0.2 g L⁻¹ bromoethanesulphonic acid, 24 h) on bioH₂ production from starch powder (1% w/v) showed highest yield (323.4 mL g⁻¹ starch) in heat-treatment and peak production rate (144.5 mL L⁻¹ h⁻¹) in acid-treatment. Acetate (1.07 g L⁻¹) and butyrate (1.21 g L⁻¹) were major soluble metabolites of heat-treatment. Heat-treated inoculum was used to develop mixed cultures on sago starch (1% w/v) in minimal medium with 0.1% peptone-yeast extract (PY) at initial pH 7 and 30 °C. The effect of sago starch concentration, pH, inoculum size and nutrients (PY and Fe ions) on batch bioH₂ production showed 0.5% substrate, pH 7, 10% inoculum size and 0.1% PY as the best H₂ yielding conditions. Peak H₂ yield and production rate were 412.6 mL g⁻¹ starch and 78.6 mL L⁻¹ h⁻¹, respectively at the optimal conditions. Batch experiment results using sago-processing wastewater under similar conditions showed bioH₂ yield of 126.5 mL g⁻¹ COD and 456 mL g⁻¹ starch. The net energy was calculated to be +2.97 kJ g⁻¹ COD and +0.57 kJ g⁻¹ COD for sago starch powder and wastewater, respectively. Finally, the estimated net energy value of +2.85 × 10¹³ kJ from worldwide sago-processing wastewater production indicates that this wastewater can serve as a promising feedstock for bioH₂ production with low energy input.