So far, researches about two–stage process have been focused on improvement of wastewater treatment efficiency, not energy recovery and profits. And despite many advantages of two-stage process, 90% of full-scale biogas plants in Europe were operated one-stage process because of the lower cost compared with two-stage process because this system requires complexity and increasing initial investment. Little information is available in literature concerning the evaluation of two stage process using cost-effective substrate as economic and environmental aspects and makes to be difficult to apply into practical case broadly. Therefore two-stage system for hydrogen and methane production is necessity to be evaluated in terms of energy recovery and profits in this study.
To achieve this objective, molasses, a byproduct of sugar refining process, was used as cost-effective substrate and packed bed reactor system, in which could maintain high cell density, was applied for maximizing hydrogen and methane production.