Optimization of combined (acid + thermal) pretreatment for fermentative hydrogen production from Laminaria japonica using response surface methodology (RSM)

In the present work, a combined (acid + thermal) pretreatment was applied for the enhanced fermentative H₂ production (FHP) from Laminaria japonica. Various pretreatment conditions including HCl concentrations, heating temperatures, and reaction times were optimized via response surface methodology (RSM) with a Box-Behnken design (BBD). Through regression analysis, it was found that H₂ yield was well fitted by a quadratic polynomial equation (R² = 0.97), and the HCl concentration was the most significant factor influencing FHP. The desirable pretreatment conditions found were HCl concentration of 4.8%, temperature of 93 °C, and reaction time of 23 min, under which H₂ yield reached to 159.6 mL H₂/g dry cell weight (dcw). The main organic acids produced were acetic and butyric acids that related closely with H₂ production. The concentration of hydroxymethylfurfural (HMF), a byproduct formed during the pretreatment process, showed an inverse relationship with H₂ yield, indicating that pretreatment conditions for the H₂ production from L. japonica were successfully optimized, by increasing the hydrolysis rate of the feedstock and also reducing the formation of HMF.