Co-production of hydrogen and methane from herbal medicine wastewater by a combined UASB system with immobilized sludge (H₂ production) and UASB system with suspended sludge (CH₄ production)

An upflow anaerobic sludge bed (UASB) system with sludge immobilized on granular activated carbon was developed for fermentative hydrogen production continuously from herbal medicine wastewater at various organic loading rates (8–40 g chemical oxygen demand (COD) L⁻¹ d⁻¹). The maximum hydrogen production rate reached 10.0 (±0.17) mmol L⁻¹ hr⁻¹ at organic loading rate of 24 g COD L⁻¹ d⁻¹, which was 19.9% higher than that of suspended sludge system. The effluents of hydrogen fermentation were used for continuous methane production in the subsequent UASB system. At hydraulic retention time of 15 h, the maximum methane production rate of 5.49 (±0.03) mmol L⁻¹ hr⁻¹ was obtained. The total energy recovery rate by co-production of hydrogen and methane was evaluated to be 7.26 kJ L⁻¹ hr⁻¹.