Recovering hydrogen production performance of upflow anaerobic sludge blanket reactor (UASBR) fed with galactose via repeated heat treatment strategy

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.

Improved hydrogen production from pharmaceutical intermediate wastewater in an anaerobic maifanite-immobilized sludge reactor

A novel anaerobic maifanite-immobilized sludge reactor (AMSR) was employed to investigate the feasibility and performance of continuous hydrogen production for the treatment of pharmaceutical intermediate wastewater (PIW) at different organic loading rates (OLR) (from 12 to 96 g COD L-1 d-1) according to changes in the hydraulic retention time (HRT). A reactor without maifanite was also employed as a control. The results indicate that maifanite accelerates granular sludge formation and the AMSR presents more efficient and stable performance than the control in terms of the hydrogen production rate. In the AMSR, the highest hydrogen production rate of 11.2 ± 0.4 mmol L-1 h-1 was achieved at an optimum OLR of 72 g COD L-1 d-1. The main metabolic route for hydrogen production was ethanol-type fermentation, which was reflected in the relative abundance of E. harbinense, which was dominant for all of the OLRs. The maximum energy conversion efficiency in the dual production of hydrogen and ethanol was determined to be 24.5 kJ L-1 h-1 at an OLR of 72 g COD L-1 d-1.

State-of-the-art technologies for continuous high-rate biohydrogen production

Dark fermentation is a technically feasible technology for achieving carbon dioxide-free hydrogen production. This review presents the current findings on continuous hydrogen production using dark fermentation. Several operational strategies and reactor configurations have been suggested. The formation of attached mixed-culture microorganisms is a typical prerequisite for achieving high production rate, hydrogen yield, and resilience. To date, fixed-bed reactors and dynamic membrane bioreactors yielded higher biohydrogen performance than other configurations. The symbiosis between H₂-producing bacteria and biofilm-forming bacteria was essential to avoid washout and maintain the high loading rates and hydrogenic metabolic flux. Recent research has initiated a more in-depth comparison of microbial community changes during dark fermentation, primarily with computational science techniques based on 16S rRNA gene sequencing investigations. Future techno-economic analysis of dark fermentative biohydrogen production and perspectives on unraveling mitigation mechanisms induced by attached microorganisms in dark fermentation processes are further discussed.

Continuous hydrogen and methane production from the treatment of herbal medicines wastewater in the two-phase 'UASBH-ICM' system

A two-phase anaerobic system comprised of upflow anaerobic sludge bed (UASB) reactor for hydrogen production and internal circulation reactor (IC) for methane production was proposed and investigated at laboratory scale and mesophilic temperature (35 °C). Hydrogen was efficiently produced from the UASB with the highest production rate of 3.00 ± 0.04 L · L^-1 _reactor · d^-1 at optimum hydraulic retention time (HRT) of 6 h and in the IC, methane was also produced from residual organic matter and soluble metabolite products (SMP) with a production rate of 2.54 ± 0.04 L · L^-1 _reactor · d^-1 at optimum HRT of 15 h. Finally, system HRT of 21 h was determined to be the optimum HRT at which energy conversion efficiency increased from 9.6 ± 0.1% (hydrogen only production) to 72.4 ± 2.5% (hydrogen and methane coproduction) and system chemical oxygen demand (COD) removal reached up to the high level of 90.1 ± 2.1%.

Biohydrogen production from glucose using submerged dynamic filtration module: Metabolic product distribution and flux-based analysis

A lab scale bioreactor with the submerged polyester mesh of pore size 100 μm, was used for biohydrogen production under mesophilic condition (35 °C). The reactor was continuously fed with glucose (15 g/L) for 90 days with a hydraulic retention time (HRT), ranging from 12 to 1.5 h. Peak hydrogen yield (HY) was achieved at 3 h HRT as 3.22 ± 0.22 mol H₂/mol glucose _added and the hydrogen production rate was achieved at 2 h HRT as 54.07 ± 3.69 L H₂/L-d, respectively. When HRT was reduced to 1.5 h, the hydrogen yield decreased to 1.04 ± 0.44 mol H₂/mol glucose _added. Washout of the hydrogen producing population and metabolic flux shift to non-hydrogen producing at 1.5 h HRT might have attributed to the lower performance of the bioreactor.

Photosynthetic bacteria improved hydrogen yield of combined dark- and photo-fermentation

Integration of dark- and photo-fermentation is a promising strategy to enhance saline wastewater treatment efficiency and biohydrogen production. In this study, dark- and photo-fermentative bacterial consortium was respectively enriched and their communities were analyzed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Both consortia were mainly composed of hydrogen-producing strains. After the first-stage dark-fermentation, the following conditions were applied prior to the second-stage fermentation: fermentative broth pH regulation (the pH group), glucose addition (the glucose group), glucose addition and pH regulation (the glucose + pH group), photosynthetic bacteria addition (the photo group), and photosynthetic bacteria addition and pH regulation (the photo + pH group), respectively. Dark fermentative broth with no pretreatment was used as control (the control group). Then the second stage began. The results showed that pH restriction had more influence than substrate or products restriction on dark-fermentative hydrogen production. Addition of photo-fermentative bacteria after dark-fermentation increased the hydrogen yield (134%) and substrate utilization (67%). These findings indicated syntrophic interactions between dark- and photo-fermentative bacteria during the hydrogen production process.