Inhibitory effect of 5-hydroxymethylfurfural on continuous hydrogen fermentation by mixed culture in a fixed bed reactor

The authors explored the inhibitory effect of 5-hydroxymethylfurfural (5-HMF) on continuous hydrogen fermentation using a mixed microbial population. A lab-scale fixed bed reactor (FBR) with a 3.0-L working volume was fed with 15 g/L of glucose as sole carbon source at 6 h HRT, while the 5-HMF concentration in feedstock was increased stepwise from 1.2 to 2.7 g/L. 5-HMF gradually decreased hydrogen production. At 2.7 g 5-HMF/L, hydrogen yield, and hydrogen production rate were 0.86 ± 0.08 mol H2/mol glucoseadded and 7.4 L H2/L-d, respectively, which were 15% of the yield and production rate observed without 5-HMF. Quantitative polymerase chain reaction (qPCR) analysis showed that 5-HMF changed the dominant bacteria from Clostridium sp. to Lactobacillus sp. Scanning electronic microscope (SEM) showed the biofilm structure of mixed culture was also damaged by 5-HMF. However, the inhibition was milder than that on batch fermentation reported earlier. Furthermore, the H2-producing performance, bacterial population, and granular morphology were partially recovered when 5-HMF was removed. The resistance to 5-HMF inhibition would result from the acclimation during continuous operation and attached growth microorganism by immobilization and entrapment.