Hydrogen and volatile fatty acids production from marine macroalgae by anaerobic fermentation

Abstract

Hydrogen and volatile fatty acids (VFAs) were coproduced from marine macroalgae by anaerobic fermentation using a microbial community. The hydrogen and VFAs production were characterized based on inoculum heat-treatment, methanogen inhibitor addition, operating temperature, and in-situ extraction of VFAs. Maximum hydrogen of 179 mL/g-VS and VFAs concentration of 9.8 g/L were produced from 35 g/L of S. japonica within 5 days of anaerobic fermentation. Hydrogen and VFAs yields were well-correlated with carbohydrate content of substrate. Inoculum heat-treatment significantly improved hydrogen production while the VFAs productivity was affected adversely. The addition of methanogen inhibitors also enhanced the hydrogen production, but the effect on VFAs production was dependent on the type of inhibitor used. Low temperature (25A degrees C) was found to be favorable for high hydrogen and VFAs yield, while high temperature (40A degrees C) and programmed-temperature (35 45A degrees C) were more favorable for hydrogen and VFAs productivity. Clostridium sp. content was found to be the most abundant at 25A degrees C. An extractive fermentation with anion-exchange resin was tested to recover the VFAs and to control the pH during the anaerobic fermentation.