Inhibition of hydrogen production by endogenous microorganisms from food waste

Food waste can be used as substrate in the dark fermentation to produce value-added products such as hydrogen, a future renewable energy supply. However, biological reactor unstable conditions might affect its potential use as green energy by low production rates. This study examined the instability of hydrogen production by dark fermentation of food waste in an anaerobic sequential biological reactor through a microbial community analysis. Hydrogen production varied significantly with a maximum of 25.74 mL H-2/g VSadded to low production as 1.29-3.18 mL H-2/g VSadded until the end of the experiment. Microbial community analysis showed that the unstable stage was related to the displacement of hydrogen-producing bacteria as Clostridium, Prevotella, Caloramator, and Bacteroides by a predominant abundance of Bifidobacterium, a lactic-acid bacteria. Furthermore, microbial analysis of food waste revealed the endogenous abundance of lactic-acid bacteria as Latilactobacillus (43.73%), Leuconostoc (12.1%), Lactiplantibacillus (1.84%), Lactococcus (1.37%), Lactobacillus (0.43%), Streptococcus (0.39%) and Bifidobacterium (0.19%). Thus, the inhibition of hydrogen production could be caused by the incoming of Bifidobacterium from food waste, which could compete for the substrate changing the acetic/butyric fermentation to a possible lactic acid fermentation.