Comparison of suspended and granular cell anaerobic bioreactors for hydrogen production from acid agave bagasse hydrolyzates

Abstract Acid agave bagasse hydrolyzates have been used as a substrate for hydrogen production, however, bioreactors are unstable and with poor performance. Granular biomass could be more successful in producing hydrogen from acid agave bagasse hydrolyzates in comparison with suspended biomass. Thus, this study aimed to evaluate the effect of increasing concentrations of acid agave hydrolyzates on hydrogen production, to compare the hydrogen productivity and stability of granular biomass in an expanded granular sludge bed (EGSB) reactor and suspended biomass in an anaerobic sequencing batch reactor (AnSBR) fed with acid hydrolyzates, and finally to determine the variation of microbial communities established in both bioreactor configurations. In batch tests, the heat-treated inoculum produced hydrogen from acid agave hydrolyzates without observing inhibition at 6.3 g/L of carbohydrates (CHO). This hydrolyzate concentration was used to start up the AnBSR, which reached a productivity of 226 ± 53 mL H2/L⋅d at organic loading rates (OLR) from 3.2 to 4.5 gCHO/L⋅d. The hydrogen production stability index decreased from 0.8 to 0.6 at increasing OLR, and the AnSBR failed at the highest OLR of 5.7 g/L⋅d. The EGSB reactor reached the highest productivity of 361 ± 130 mL H2/L⋅d at an OLR of 7.4 gCHO/L⋅d, but with a low stability index of 0.6. Independently of the bioreactor configuration, microbial communities associated with the production of acetate/lactate were successfully established in both configurations with the prevalence of Lactobacillus spp. A low abundance of typical H2 producers like Clostridium was always observed over the whole period of operation (