Continuous Hydrogen Production Research Articles

Comparison of ASBR and CSTR reactor for hydrogen production from palm oil mill effluent under thermophilic condition

Hydrogen production from palm oil mill effluent (POME) by Thermoanaerobacterium thermosaccharolyticum PSU-2 was investigated both in batch and continuous reactors using anaerobic sequencing batch reactor (ASBR) and continuous stirred tank reactor (CSTR). The hydrogen production determined from batch experiment of POME at an inoculum size of 0%, 10%, 20% and 30% (v/v) was 161, 201, 246 and 296 mL H2/g-COD with COD removal efficiency of 21%, 23%, 23% and 23%, respectively. Continuous hydrogen production was start-up with 30% (v/v) inoculum in both ASBR and CSTR reactors and more than 30% COD removal could be obtained at HRT of 4 days, corresponding to OLR of 11.3 g COD/ L·day. Similar hydrogen production rates of 2.05 and2.16 LH2/L. day were obtained from ASBR and CSTR, respectively. COD removal efficiency of ASBR was 37.7%, while it was 44.8% for CSTR. However, ASBR was stable in term of alkalinity, while the CSTR was stable in term of hydrogen production, soluble metabolites concentration and alkalinity. Therefore, the CSTR was found to be more stable in hydrogen production than ASBR under the same OLR.

Effect of Mass Transfer on Performance of Substrate Degradation within Annular Fiber-illuminating Biofilm Reactor for Continuous Hydrogen Production

To promote hydrogen production of immobilized photosynthetic bacteria, an annular fiber-illuminating bioreactor (AFIBR) for biofilm formation on the surface of side-glowing optical fiber was developed. Mathematical model on coupled mass transport processes of substrate transport and biodegradation within biofilm with substrate diffusion and convection within bulk flow region during continuous hydrogen production was proposed. Effects of mass transfer on performance of substrate bio-degradation were investigated. 10 g/L inlet substrate concentration and 100 mL/h flow rate were identified to be Optimum conditions for maximal substrate degradation in the bioreator.

Properties of Anaerobic Activated Sludge in Biohydrogen Production Reactor

For the properties of activated sludge studies, three kinds of activated sludge were obtained from continuous hydrogen production reactor. Activated sludge was got under organic loading rate (OLR) of 3, 7 and 25 kgCOD/m3·d condition, respectively. Sedimentation performance and activities of sludge were investigated. When OLR was 3 kgCOD/m3·d, activated sludge showed good sedimentation performance. After 30 minutes sedimentation, the volume of activated sludge in total mixture volume was about 39%. When OLR was 7 and 25kgCOD/m3·d, after 30 minutes sedimentation, the volume of activated sludge in total mixture volume was 80% and 83%, respectively. The increase of biomass is the main reason for increase of sedimentation performance. MLVSS/MLSS of activated sludge was 37.7% and 79.6% under OLR of 3 and 25kgCOD/m3·d condition, therefore, activities of activated sludge was high under high OLR condition. Since sedimentation performance of sludge is high under high OLR condition, hydraulic retention time should controlled carefully in engineering operation.

Review of hydrogen-enriched gas production from steam gasification of biomass: The prospect of CaO-based chemical looping gasification

Abstract Global warming, climate change and energy security issues are the forces driving the fossil fuel based energy system towards renewable and sustainable energy. Hydrogen as a clean energy carrier is believed to be the most promising source to replace fossil fuel. Biomass gasification with the presence of steam offers a feasible, sustainable, and environment-friendly option as well as a favorable alternative for higher hydrogen yields and for large-scale hydrogen production which can satisfy the need of hydrogen in the future. However, the process suffers from the problem of undesirable CO 2 and tar formation. Calcium oxide (CaO) has been acknowledged as a catalyst to produce hydrogen-rich gas and has currently gained broad attention due to its cheapness and abundance. Nevertheless, the deactivation of CaO after carbonation reaction is challenging for continuous hydrogen production and economical perspective. To conquer such challenge, the concept of CaO-based chemical looping gasification (CaO-based CLG) has emerged recently. Additionally, due to its energy-efficient and environment-friendly aspects, the CaO-based CLG using biomass as feedstock is gaining more attention in recent years. This study first presents a review on conventional steam gasification of biomass without catalysts for producing hydrogen-rich product gas. The effects of key variables, such as biomass characteristics, gasifier temperature, steam-to-biomass ratio (S/B) and equivalence ratio (ER), on hydrogen-enriched gas production are discussed based on recent researches and developments. Then the use of CaO in biomass steam gasification for hydrogen production with in situ CO 2 capture and tar reduction is described. The prospect of CaO-based CLG using biomass fuel is also discussed as a promising process for renewable, sustainable and environment-friendly hydrogen production.

Fe/TiO2: A Visible Light Active Photocatalyst for the Continuous Production of Hydrogen from Water Splitting Under Solar Irradiation

A series of Fe/TiO2 catalysts with varying amounts of Fe (0.2–2.0 wt%) were prepared by doping of Fe on the surface of nano TiO2. The XPS results revealed that Fe exists in Fe3+ state in a strong interaction with TiO2. The strong absorption band for Fe/TiO2 in the range of 440–575 nm infers the modification of TiO2 surface with Fe dopant. N2 adsorption, TEM and SEM studies proved that the catalysts are mesoporous with high surface area and nanosized particle in size (≈5 nm). Photocatalytic activity of the catalysts was evaluated for the generation of H2 from water splitting under solar irradiation. Optimisation of Fe3+ ion doped over the surface of TiO2 was studied, it is observed that 0.5 wt% Fe/TiO2 catalyst exhibited enhanced hydrogen yield of 270 μmol-H2/h activity, while un doped TiO2 shows 2.8 μmol-H2/h.The improved photocatalytic activity of Fe/TiO2 can be attributed to synergistic effects such as band gap in the visible region and minimum electron hole recombination over the surface by the formation of electron trapping centres. Fe/TiO2, a nano and mesporous visible light active photocatalyst shows highly enhanced hydrogen production under solar irradiation. Surface doping of metal ions seems to be more suitable than the lattice doping for the enhanced photocatalytic activity.

Research of Anaerobic Fermentation Hydrogen Production Process by Continuous Flow from Contained Sugar Wastewater

The basal fermentation time and hydraulic retention time were systemically investigated about anaerobic fermentation production hydrogen process by continuous flow which is based on activated sludge for a basic strain and simulating sucrose wastewater for a substrate in a continuous stirred tank reactor. The highest hydrogen production rate was got at the fermentation time of 15h for and 6h for hydraulic retention time. The optimum run acidity (pH = 4.5 5.0) was kept through their own system circulation to hold the system state of high-speed and continuous hydrogen production. The results can really laid the groundwork for the anaerobic fermentation production hydrogen process by continuous flow from contained sugar wastewater from the laboratory research towards industrialization.

Effect of Substrate Concentration on Hydrogen Production from Fermentation of Sugar Wastewater

The biological hydrogen production by the sugar wastewater is an effective way to achieve the reclamation. In this paper, the effect of substrate concentration on the hydrogen production is discussed through employing the self-made continuous flow anaerobic fermentation hydrogen production reactor, taking the sludge in urban sewage treatment plant as the inoculated sludge and the simulated sugar wastewater as the substrate. The experimental results show that the best hydrogen production effect can be obtained when the temperature is (37±1) °C, HRT is 7h, the water alkalinity is around 530mg/L and the substrate concentration is 5000mg/L, namely the organic load is 60kgCOD/(m3·d). The volumes of gas production and hydrogen production both reach the maximum. The average values are respectively 36.2L/d and 21.8L/d. The obtained hydrogen production rate is 0.93kgCOD/(m3·d). During the whole process, the proportion of volatile acid composition remains stable, which is the butyric acid-type fermentation. When the concentration of COD is increased to 6000-8000mg/L, the ability of hydrogen production of system will be significantly dropped due to the increase of pH of system. The hydrogen production performance can be restored through artificially and timely lowering the water alkalinity. However, the hydrogen production rate will be decreased compared to the previous situation.

Hydrogen production in a light-driven photoelectrochemical cell

Conversion of organic matter to hydrogen in a microbial electrolysis cell (MEC) is one of promising ways for hydrogen generation. However, the lack of efficient and cost-effective cathode catalysts and the need of additional electricity input make it less attractive. To resolve these problems, in this work a light-driven microbial photoelectrochemical cell (MPC) system, which consists of a TiO2 photocathode and a microbial anode, was constructed to utilize light energy and harvest electrons respectively. In this MPC system, continuous hydrogen production was achieved without external applied voltage under UV irradiation, and it had worked well continuously over 200h in a batch-fed mode under light illumination. An average hydrogen production rate of 3.5μmol/h was obtained. The results are useful for designing new hydrogen-harvesting systems.

Effect of temperature on continuous fermentative hydrogen production from Laminaria japonica by anaerobic mixed cultures.

The temperature effect on continuous dark fermentative hydrogen production from non-pretreated Laminaria japonica was investigated in the present study. In a preliminary step, the fermentors were continuously operated as an inoculation process at three different temperatures, 35, 50 and 65°C, to respectively represent mesophilic, thermophilic, and hyperthermophilic conditions. An optimization process was subsequently conducted with a range of organic loading rate (OLR) and cultivation pH. Among the various operation conditions, the maximum H2 yield, 61.3±2.0 mL H2/g TS, was observed under a mesophilic condition at OLR of 3.4 g COD/L/d and pH 5.5. From a PCR-DGGE analysis, it was found that an increase of temperature can reduce the microbial diversity and change the predominant species. Finally, total cellulase activity was measured, to investigate the effect of temperature on hydrolysis of L. japonica. The highest cellulase activity was 0.19±0.02 FPU/mL, observed at 35°C, coinciding with the maximum H2 yield.

Cobalt doped TiO2: A stable and efficient photocatalyst for continuous hydrogen production from glycerol: Water mixtures under solar light irradiation

Glycerol is the main by-product during the trans-esterification of vegetable oils to biodiesel. In this study, we investigate the process of photocatalytic hydrogen production from glycerol aqueous solution, with the use of cobalt doped TiO2 photocatalyst under solar light irradiation. Cobalt doped TiO2 photocatalysts are prepared by impregnation method and these catalysts are characterized by XRD, EDAX, DRS, TEM, EPR and XPS techniques. DRS studies clearly show the expanded photo response of TiO2 into visible region on impregnation of Co2+ ions on surface of TiO2. XPS studies also show change in the binding energy values of O1s, Ti 2p and Co 2p, indicating that Co2+ ions are in interaction with TiO2. Maximum hydrogen production of 220 μ mol h−1 g−1 is observed on 2 wt% cobalt doped TiO2 catalysts in pure water under solar irradiation. A significant improvement in hydrogen production is observed in glycerol: water mixtures; and maximum hydrogen production of 11,021 μ mol h−1 g−1 is obtained over 1 wt% cobalt doped TiO2 in 5% glycerol aqueous solutions. Furthermore, to evaluate some reaction parameters such as cobalt wt% on TiO2, glycerol concentration, substrate effect (alcohols) and pH of the solution on the hydrogen production activity are systematically investigated. When the catalysts are examined under UV irradiation, a 3–4 fold increase in activity is observed where this activity seems to decrease with time; however, a continuous activity is observed under solar irradiation on these catalysts. The decreased activity could be ascribed the loss of cobalt ions under UV irradiation, as evidenced by EDAX and TEM analysis. A possible explanation for the stable and continuous activity of cobalt doped TiO2 photocatalysts under solar irradiation is proposed.

A two-dimensional mass transfer model for an annular bioreactor using immobilized photosynthetic bacteria for hydrogen production

A two-dimensional model for substrate transfer and biodegradation in a novel, annular fiber-illuminating bioreactor (AFIBR) is proposed in which photosynthetic bacteria are immobilized on the surface of a side-glowing optical fiber to form a stable biofilm. When excited by light, the desired intensity and uniform light distribution can be obtained within the biofilm zone in bioreactor and then realize continuous hydrogen production. Substrate transfer and biodegradation within the biofilm zone, as well as substrate diffusion and convection within bulk fluid regions are considered simultaneously in this model. The validity of the model is verified experimentally. Based on the model analysis, influences of flow rate and light intensity on the substrate consumption rate and substrate degradation efficiency were investigated. The simulation results show that the optimum operational conditions for the substrate degradation within the AFIBR are: flow rate 100 ml h(-1) and light intensity 14.6 μmol photons m(-2 )s(-1).

Continuous hydrogen production by biomass gasification in supercritical water heated by molten salt flow: System development and reactor assessment

Hydrogen production by biomass gasification using solar energy is a promising approach for overcoming the drawbacks of fossil fuel utilization, but the storage of discontinuous solar flux is a critical issue for continuous solar hydrogen production. A continuous hydrogen production system by biomass gasification in supercritical water using molten-salts-stored solar energy was proposed and constructed. A novel double tube helical heat exchanger was designed to be molten salts reactor for hydrogen production. Model compounds (glycerol/glucose) and real biomass (corn cob) were successfully gasified in this molten salts reactor for producing hydrogen-rich gas. The unique temperature profiles of biomass slurry in the reactor were observed and compared with that of conventional electrical heating and direct solar heating approaches. Product gases yield, gasification efficiency and exergy conversion efficiency of the reactor were analyzed. The results showed that the performances of reactor were determined by feedstock style, biomass concentration, residence time and biomass slurry temperature profiles.

Bioflocculation of photo-fermentative bacteria induced by calcium ion for enhancing hydrogen production

The applications of photo-fermentative bacteria (PFB) for continuous hydrogen production are generally subjected to a serious biomass washout from photobioreactor, resulting from poor flocculation of PFB. In this study, through reducing the absolute ζ-potentials of PFB, Ca2+ greatly decreased total interaction energy barrier of PFB based on DLVO theory, thus promoted the bioflocculation of Rhodopseudomonas faecalis RLD-53. Average floc size of PFB increased with the Ca2+ concentration, and reached maximum 30.07 μm at 4 mmol/l. Consequently, biomass retention capacity of photobioreactor significantly enhanced after 30 min settling with half working volume discharge. In the continuous photo-fermentative sequencing batch reactor, compared with the free cell culture, bioflocculation reached a higher steady-state hydrogen production rate of 879 ml H2/l/d and hydrogen yield of 2.64 mol H2/mol acetate, respectively. Therefore, bioflocculation promoted by calcium ion was an effective strategy for retaining PFB in photobioreactor to produce hydrogen continuously.

The Effect of Biomass Immobilization Support Material and Bed Porosity on Hydrogen Production in an Upflow Anaerobic Packed-Bed Bioreactor

The aim of this study was to investigate the effect of the support material used for biomass attachment and bed porosity on the potential generation of hydrogen gas in an anaerobic bioreactor treating low-strength wastewater. For this purpose, an upflow anaerobic packed-bed (UAPB) reactor fed with sucrose-based synthetic wastewater was used. Three reactors with various support materials (expanded clay, vegetal coal, and low-density polyethylene) were operated for hydraulic retention time (HRT) of 0.5 and 2 h. Based on the results obtained, three further reactors were operated with low-density polyethylene as a material support using various bed porosities (91, 75, and 50 %) for an HRT of 0.5 h. The UAPB reactor was found to be a feasible technology for hydrogen production, reaching a maximum substrate-based hydrogen yield of 7 mol H₂ mol(-1) sucrose for an HRT of 0.5 h. The type of support material used did not affect hydrogen production or the microbial population inside the reactor. Increasing the bed porosity to 91 % provided a continuous and cyclic production of hydrogen, whereas the lower bed porosities resulted in a reduced time of hydrogen production due to biomass accumulation, which resulted in a decreasing working volume.

연속 혐기성 수소발효 공정에서 성공적인 start-up 방법

The variations of performance and metabolites at an early stage were investigated for the successful start-up technology in continuous fermentative hydrogen production. Unsuccessful start-up was observed when the operation mode was changed from batch to continuous mode after the yield was reached to 0.5 mol <TEX>$H_2$</TEX>/mol <TEX>$hexose_{added}$</TEX> by batch mode. <TEX>$H_2$</TEX> production continued till 12 hours accompanied by butyrate production, but did not last with propionate production increase. It was suspected that the failure was due to the regrowth of propionic acid bacteria during batch mode which were inhibited by heat-shock but not completely killed. Thus, successful start-up was tried by early switchover from batch to continuous operation; continuous operation was started after the <TEX>$H_2$</TEX> yield was reached to 0.2 mol <TEX>$H_2$</TEX>/mol <TEX>$hexose_{added}$</TEX> by batch mode. Although <TEX>$H_2$</TEX> production rate decreased at an early stage, stable <TEX>$H_2$</TEX> yield of 0.8 mol <TEX>$H_2$</TEX>/mol <TEX>$hexose_{added}$</TEX> was achieved after 10 days by lowering down propionate production. And it was also concluded that the reason for <TEX>$H_2$</TEX> production decrease at an early stage was due to alcohol production by self detoxification mechanism against VFAs accumulation.

Optimization of continuous hydrogen production from co-fermenting molasses with liquid swine manure in an anaerobic sequencing batch reactor

This study investigated and optimized the operational conditions for continuous hydrogen production from sugar beet molasses, co-fermented with liquid swine manure in an anaerobic sequencing batch reactor. Results indicated that pH, HRT and total solids content in the swine manure (TS) had significant impact on all the responses such as biogas production rate (BPR), hydrogen content (HC), hydrogen production rate (HPR), and hydrogen yield (HY), although the highest level of each response was achieved at different combination of the three variables. The maximum BPR, HC, HPR and HY of 32.21L/d, 30.51%, 2.23L/d/L and 1.57mol-H2/mol-sugar were estimated at the optimal pH, HRT, and TS of 5.55, 15.78h, and 0.71% for BPR; 5.22, 12.04, and 0.69 for HC; 5.32, 15.62, and 0.78% for HPR; and 5.36, 17.56, and 0.74% for HY, respectively. Good linear relationships of the predicted and tested results for all the parameters were observed.

Characterization by length heterogeneity (LH)-PCR of a hydrogen-producing community obtained in dark fermentation using coastal lake sediment as an inoculum

Sustainable biohydrogen production can be achieved by dark fermentation of organic wastes, and studies were carried out using a range of substrates and inocula. The bacterial populations involved were mainly identified as facultative anaerobes (Enterobacteriaceae) and strictly anaerobes (Clostridiales), and their dynamics in relation to H2 and metabolite production depends on the physical and environmental conditions of the bioreactor. This study has evaluated the use of length heterogeneity (LH)-PCR fingerprinting to detect changes in the microbial community during continuous hydrogen production under dark fermentation. A mesophilic continuous dark fermentation was established using coastal lake sediment as an inoculum in a synthetic medium with glucose as a substrate. The LH-PCR profiling associated to the sequencing of 16S rRNA genes was used for the characterization of the bacterial community and identification of species during a continuous production of H2. The resulting dominant units of the communities present at both 24 h (batch) and 210 h (continuous culture) were affiliated to species of the genus Clostridium. Fluctuations based on their relative abundance over time were observed. At 24 h, a higher ratio was detected for the group Clostridium butyricum - Clostridium tertium followed by Clostridium bifermentans and Clostridium perfringens, while at 210 h, the group Clostridium aurantibutyricum - Clostridium acetobutylicum was the most abundant. The LH-PCR profiling has proven to be a sensitive and rapid method for the evaluation of the dynamics of a functional consortium formed by species of the genus Clostridium and has a potential for studies aimed at the optimization of biohydrogen production.

Demonstration of the HI decomposition section embedded with electrodialysis stack in the sulfur–iodine thermochemical cycle for hydrogen production

Demonstration of the HI decomposition section (SEC3) embedded with electrodialysis stack in the SI (sulfur–iodine) process for hydrogen production was conducted in the pressurized conditions. The goal of the experiments was to verify that the SEC3 composed of the electrodialysis (ED), distillation and HI decomposition reactor can be operated properly and show the continuous hydrogen production. The ED embedded SEC3 operation at a pressurized condition was not yet disclosed. The automated process control and commercially available engineered components were used for constructing SEC3 prior to building fully integrated skids which will be composed of the Bunsen Section (SEC1), the H2SO4 decomposition section (SEC2) and SEC3. An electrodialysis stack was installed to concentrate HI in HIx solution and overcome the H2O–HI azeotrope. A packed distillation column was used to obtain the concentrated HI gas. A Pt/SiO2 catalyst was used to decompose the HI gas. The electrodialysis stack was able to concentrate HI over azeotrope composition effectively. The H2O/HI molar ratio of the exit stream of the electrodialysis stack was approximately 4.2, which overcome the azeotropic composition of 5.2. These experiments demonstrated that hydrogen can be produced from a pressurized SEC3 of SI process, using an electrodialysis stack and engineered components. The hydrogen production rate was approximately 10L/h at approximately 4.0bar(g).

Continuous photo-fermentative hydrogen production from lactate and lactate-rich acidified food waste

In the present work, a continuous photo-fermentative hydrogen (H2) production from lactate was attempted at various hydraulic retention times (HRTs) (48–120 h). Electron balance was made at each operating conditions to elucidate different performances. At 120 h HRT, H2 production was negligible, while 42% and 52% of substrate electrons diverted towards cell growth and soluble microbial products (SMPs), respectively. After changing HRT to 96 h, H2 yield jumped to 2.3 mol-H2/mol-lactateadded with less SMPs production and minimal cell growth. The highest H2 production rate of 260 mL-H2/L-fermenter/d was also achieved at 96 h HRT. When HRT was further shortened to 72 and 48 h, H2 yield dropped to 1.4 and 0.2 mol-H2/mol-lactateadded, respectively. While almost all of the lactate was degraded at <72 h HRT, only 65% of the lactate was consumed at 48 h HRT. From 200th day, the feedstock was changed to lactate-rich acidified food waste, which was obtained via one-day fermentation of food waste and subsequent centrifugation. At 2 g chemical oxygen demand/L, substrate conversion efficiency reached 35%, which was slightly lower than that of feeding pure lactate. SMPs were found to be mainly consisted of low molecular weight compounds (<500 Da), and the majority of organic matters were aromatic proteins at 120 h HRT and it was shifted to humic-like region in 96 h HRT.

Mathematical model for a continuous hydrogen production system: Stirred fermenter connected to a biocatalyzed electrolysis cell

This paper presents a mathematical model applied to a continuous hydrogen production system, composed of a stirred fermenter connected to a biocatalyzed electrolysis cell (BEC). The model contemplates two differential equation systems which describe the adaptation (start-up) and continuous phases between the fermenter and the BEC. The proposed model describes the dynamics of hydrogen and volatile fatty acid (VFA) production and substrate consumption (glucose for the stirred fermenter and acetate in the BEC), based on a Tessier-type bacterial kinetic which simulates the lag phase in the bacteria. A hybrid evolutionary algorithm and least squares method were used to estimate the parameters. Model validation and simulation were achieved by obtaining the volumes of hydrogen and VFAs produced and the statistical bacterial density via the most probable number (MPN) method.