Optimization of zero-waste hydrogen peroxide - Acetic acid pretreatment for sequential ethanol and methane production

In this study, the development of an environmentally friendly version of hydrogen peroxide – acetic acid (HPAC) pretreatment was investigated and optimized with two different approaches as maximum biofuel production optimization and cost optimization. Central composite design and response surface method were used for the experimental design and data analysis, respectively. In the experimental design, investigated HPAC pretreatment parameters were 50–100 °C reaction temperature, 6–24 h reaction time, 0–2 wt% HAc and 0–2 wt% H2O2. Significant ethanol production enhancement was observed only for the samples pretreated at 100 °C. This increase was due to the enhanced enzyme accessibility by the surface area increment and delignification, which were also revealed in SEM imaging and FTIR analysis. Maximum ethanol production was observed in 2% H2O2, 0% HAc, 24 h, and 100 °C pretreatment conditions as 81.65 mg EtOH/g total solid (TS) (103.49 L EtOH/tonne TS), corresponding 49.55% of the theoretical ethanol yield. Maximum methane production, on the other hand, was observed in 2% HAc, 0% H2O2, 100 °C, 6 h conditions as 363.82 mL CH4/g VS. In terms of net energy production, cost optimum pretreatment (1.87% HAc, 0% H2O2, 50 °C, and 6 h) was found be the most beneficial condition with 67.5% energy recovery.