Degradation and transformation of furfural derivatives from hydrothermal pre-treated algae and lignocellulosic biomass during hydrogen fermentation

The inhibitory effects of typical intermediate degradation products of furfural including furfuralcohol and furoic acid, as well as the transformation characteristics and the corresponding rate-limiting step, were analysed during hydrogen fermentation in this study. The results showed that furfural inhibition on hydrogen production were much higher than its derivatives, resulting in a maximum inhibition coefficient in the range of 7.1%–99.8%. Furfural at the concentrations ranging from 1 to 4 g/L was completely degraded after 48 h of fermentation, whereas 49%–70% of furfuralcohol remained unconverted after 96 h of fermentation. The degradation of furfural was actually an aldehyde-alcohol transformation process. Although adding furfuralcohol prolonged the lag-phase time and reduced the hydrogen production peak rate, it had slightly negative impacts on the accumulative hydrogen yield. Additionally, furoic acid exhibited a higher degradation rate than that of furfural and furfuralcohol, which was completely degraded after 24 h of fermentation. The typical metabolic product was acetic acid, and this process may simultaneously produce hydrogen. However, the transformation of furfuralcohol to furoic acid was still a rate-limiting step. Compared with the control group, the energy conversion efficiencies with the addition of furfural derivatives could decrease by 12.7%–91.7%. A high concentration (above than 2 g/L) of furfural and its derivatives would also significantly decrease the species richness and diversity.