High-rate biohydrogen production from xylose using a dynamic membrane bioreactor.

This study aimed a high-rate dark fermentative H2 production from xylose using a dynamic membrane module bioreactor (DMBR) with a 444-µm pore polyester mesh. 20 g xylose/L was fed continuously to the DMBR at different hydraulic retention times (HRTs) from 12 to 3 h at 37 °C. The maximum average H2 yield (HY) and H2 production rate (HPR) at 3 h HRT were found to be 1.40 ± 0.07 mol H2/mol xyloseconsumed and 30.26 ± 1.19 L H2/L-d, respectively. The short HRT resulted in the maximum suspended biomass concentration (8.92 ± 0.40 g VSS/L) along with significant attached biomass retention (7.88 ± 0.22 g VSS/L). H2 was produced by both butyric and acetic acid pathways. Low HY was concurrent with lactic acid production. The bacterial population shifted from non-H2 producers, such as Lactobacillus and Sporolactobacillus spp., to Clostridium sp., when HY increased. Thus, xylose from lignocellulose is a feasible substrate for dark fermentative H2 production using DMBR.

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 H2 production from food waste. Heat-treated and frozen H2-producing granular sludge (HPG) grown with monomeric sugars showed a higher H2 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 H2 production performance. Propionic acid production and homoacetogenesis were regarded as major H2-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 H2 production rate and lag-phase time. The use of inoculum with a high abundance of Clostridium is essential for H2 production from food waste.

Dynamic membrane bioreactor for high rate continuous biohydrogen production from algal biomass.

This study aimed to achieve continuous biohydrogen production from red algal biomass using a dynamic membrane bioreactor (DMBR). The DMBR was continuously fed with pretreated Echeuma spinosum containing 20 g/L hexose. The highest average hydrogen production rate (HPR) of 21.58 ± 1.59 L/L-d was observed at HRT 3 h, which was higher than previous reports for continuous H2 production from biomass feedstock. Metabolic flux analysis revealed that butyric acid and propionic acid were the major by-products of the H2-producing and H2-consuming pathways, respectively, of the algal biomass fermentation. Hydrogen consumption by propionic acid pathway could not be prevented completely by heat treatment. PICRUSt2 analysis predicted that Clostridium sp., Anaerostipes sp., and Caproiciproducens sp. might significantly contribute to the expression of both ferredoxin hydrogenase and propionate CoA-transferase. This study would provide the design and operational information on high-rate bioreactor for continuous hydrogen production using biomass.

High-rate mesophilic hydrogen production from food waste using hybrid immobilized microbiome.

This study examined the feasibility of dark fermentative biohydrogen production from food waste using hybrid immobilization in mesophilic condition. Among four different organic loading rates (OLRs), the highest average hydrogen production rate (HPR) of 9.82 ± 0.30 L/L-d was found at an OLR of 74.7 g hexose/L-d, which was higher than reported values from particulate feedstock in mesophilic condition. The average hydrogen yield (HY) at the condition was 1.25 ± 0.04 mol H2/mol hexoseconsumed. Whereas the average HPR and HY at an OLR 80 g hexose/L-d were 5.82 ± 0.12 L/L-d and 0.64 ± 0.02 mol H2/mol hexoseconsumed, respectively. Metabolic flux analysis showed the low HY was concurrent with the highest propionic acid and homoacetogenis. Bacterial population was shift from Clostridium sp. to non-hydrogen producers including Bifidobacterium, Bacteriodes, Olsenella, Dysgonomonas, and Dialister sp.