Effect of genus Clostridium abundance on mixed-culture fermentation converting food waste into biohydrogen.

This study examined the effect of various inocula on mixed-culture dark fermentative H production from food waste. Heat-treated and frozen H-producing granular sludge (HPG) grown with monomeric sugars showed a higher H yield, production rate, and acidogenic efficiency along with a shorter lag phase than heat-treated methanogenic sludge. Among three different methods of methanogenic sludge inoculation, inoculation after centrifugation showed better H production performance. Propionic acid production and homoacetogenesis were regarded as major H-consuming pathways when methanogenic sludge was used, whereas only homoacetogenesis was found in HPG-inoculated fermentation. During fermentation, the abundance of Clostridium increased greater than 48-fold for methanogenic sludge and greater than 108-fold for HPG, respectively. The initial abundance of Clostridium showed a linear relationship with the H production rate and lag-phase time. The use of inoculum with a high abundance of Clostridium is essential for H production from food waste.