Hydrogen Photoproduction Research Articles

Optimization of photo-hydrogen production based on cheese whey spent medium

Cheese whey wastewater diluted to 10 g lactose/L was initially subjected to dark-fermentation by Enterobacter aerogenes MTCC 2822, and the VFAs-rich spent medium (acetic acid 1900 mg/L, butyric acid 537 mg/L, and traces of propionic acid) was subjected to photo-fermentation through enrichment by Ni2+ (0–8 μmol/L), Fe2+ (0–100 μmol/L) or Mg2+ (0–15 mmol/L) in batch mode by Rhodopseudomonas BHU 01 strain. The maximum cumulative H2 production (144 ml) and yield (58 mmol) was obtained at 4 μmol Ni2+/L. Likewise, Fe2+ (60 μmol/L) resulted in maximum cumulative H2 production (139 ml) and yield (56 mmol). Nevertheless, 6 mmol of Mg2+ did not significantly affect H2 production (110 ml) or yield (44 mmol); the latter value in close proximity with the control (37 mmol). The concomitant reduction in COD was maximum (15.61%) for 4 μmol Ni2+/L, followed by 15.33% for 60 μmol Fe2+/L, and the least for 6 mmol Mg2+/L (14.5%). The observations suggest the role of Fe2+ and Ni2+ in regulation of nitrogenase and hydrogenase, while that of Mg2+ mainly in the biosynthesis of photopigment bacteriochlorophyll (Bchl).

Photo-fermentative bacteria aggregation triggered by L-cysteine during hydrogen production

BackgroundHydrogen recovered from organic wastes and solar energy by photo-fermentative bacteria (PFB) has been suggested as a promising bioenergy strategy. However, the use of PFB for hydrogen production generally suffers from a serious biomass washout from photobioreactor, due to poor flocculation of PFB. In the continuous operation, PFB cells cannot be efficiently separated from supernatant and rush out with effluent from reactor continuously, which increased the effluent turbidity, meanwhile led to increases in pollutants. Moreover, to replenish the biomass washout, substrate was continuously utilized for cell growth rather than hydrogen production. Consequently, the poor flocculability not only deteriorated the effluent quality, but also decreased the potential yield of hydrogen from substrate. Therefore, enhancing the flocculability of PFB is urgent necessary to further develop photo-fermentative process.ResultsHere, we demonstrated that L-cysteine could improve hydrogen production of Rhodopseudomonas faecalis RLD-53, and more importantly, simultaneously trigger remarkable aggregation of PFB. Experiments showed that L-cysteine greatly promoted the production of extracellular polymeric substances, especially secretion of protein containing more disulfide bonds, and help for enhancement stability of floc of PFB. Through formation of disulfide bonds, L-cysteine not only promoted production of EPS, in particular the secretion of protein, but also stabilized the final confirmation of protein in EPS. In addition, the cell surface elements and functional groups, especially surface charged groups, have also been changed by L-cysteine. Consequently, absolute zeta potential reached a minimum value at 1.0 g/l of L-cysteine, which obviously decreased electrostatic repulsion interaction energy based on DLVO theory. Total interaction energy barrier decreased from 389.77 KT at 0.0 g/l of L-cysteine to 127.21 kT at 1.0 g/l.ConclusionsThus, the strain RLD-53 overcame the total energy barrier and flocculated effectively. After a short settlement, the biomass rush out will be significantly reduced and the effluent quality will be greatly improved in the continuous operation. Furthermore, aggregation of PFB could enable high biomass hold-up of photobioreactor, which allows the photobioreactor to operate at low hydraulic retention time and high organic loading rate. Therefore, the described flocculation behaviour during photo-hydrogen production is potentially suitable for practicable application.

Effect of AI crude extract on PHB accumulation and hydrogen photoproduction in Rhodobacter sphaeroides

Poly-β-hydroxy butyric acid (PHB) accumulation and gaseous H2 release are regarded as alternatives for expending reducing power. Some researchers suggested that quorum-sensing system affects PHB accumulation in Rhodobacter sphaeroides, but whether the system plays regulation role between hydrogen producing and PHB synthesis is still unknown. By adding autoinducer of R. sphaeroides into its culture solutions, measuring its total hydrogen production, PHB content and PHB synthase activity, the function of quorum-sensing on PHB accumulation and hydrogen production was preliminarily investigated. Compared with the control, the total gas productions in experimental groups increased accompanying slight decrease of PHB contents, which was partially caused by the reduction of PHB synthase activities. Biolog tests indicated the carbon source utilization profiles, especially those involving fatty acids and butanoate metabolism, had partly changed after exogenous signal molecules added. These results suggest that quorum-sensing is involved in signal regulation between PHB accumulation and hydrogen production in R. sphaeroides.

Algal biofuels

The world is facing energy crisis and environmental issues due to the depletion of fossil fuels and increasing CO2 concentration in the atmosphere. Growing microalgae can contribute to practical solutions for these global problems because they can harvest solar energy and capture CO2 by converting it into biofuel using photosynthesis. Microalgae are robust organisms capable of rapid growth under a variety of conditions including in open ponds or closed photobioreactors. Their reduced biomass compounds can be used as the feedstock for mass production of a variety of biofuels. As another advantage, their ability to accumulate or secrete biofuels can be controlled by changing their growth conditions or metabolic engineering. This review is aimed to highlight different forms of biofuels produced by microalgae and the approaches taken to improve their biofuel productivity. The costs for industrial-scale production of algal biofuels in open ponds or closed photobioreactors are analyzed. Different strategies for photoproduction of hydrogen by the hydrogenase enzyme of green algae are discussed. Algae are also good sources of biodiesel since some species can make large quantities of lipids as their biomass. The lipid contents for some of the best oil-producing strains of algae in optimized growth conditions are reviewed. The potential of microalgae for producing petroleum related chemicals or ready-make fuels such as bioethanol, triterpenic hydrocarbons, isobutyraldehyde, isobutanol, and isoprene from their biomass are also presented.

Photoelectrochemical properties of doped polyaniline: Application to hydrogen photoproduction

The semi conducting properties of doped polyaniline (emeraldine-salt, PANI) elaborated by chemical route are investigated by the photo-electrochemical technique. The band gap is found to be 1.48 eV and the transition is directly allowed. The electrical conduction obeys to an exponential law with activation energy of 0.13 eV. p-type conductivity is evidenced from the cathodic photocurrent. The energy band diagram clearly shows the spontaneous hydrogen photo evolution. The potential of the conduction band of PANI (−0.93 VSCE) determined from the capacitance measurements is suitably positioned with respect to H2O/H2 level (−0.66 VSCE). Therefore, the photocatalytic properties of this material has been evaluated according to the hydrogen generation. The best performance is achieved at pH ∼7 with a liberation rate of 0.113 mL h−1 (mg catalyst)−1 and a quantum efficiency of 0.18% under visible light (29 mW cm−2). An increase of 56% is obtained on the hetero-system PANI/TiO2.

Carrier modification and its application in continuous photo‐hydrogen production using anaerobic fluidized bed photo‐reactor

AbstractPoor hydrogen production performance and low biomass limit the practical application of photo‐fermentation. To improve the immobilization capability of bacteria and hydrogen production performance, activated carbon fibers (ACFs) were modified by acidic, alkaline, and neutral solutions. The modified ACFs were further used in the anaerobic fluidized bed photo‐reactor (AFBPR) to explore its continuous operation characteristics. Results showed that among the three reagents, nitric acid was the most efficient for ACF modification, and the maximum yield and production rate of hydrogen increased between about 33.6% and 65.8% compared to the control. Furthermore, with the optimal influent glutamate concentration (10 mmol L−1) and light intensity (4000 lux), the AFBPR gave efficient and stable performance with hydrogen yield of 2.26 mol H2 mol−1 acetate and hydrogen production rate of 25.8 mL L−1 h−1. The results showed the potential of using the AFBPR with HNO3‐modified ACF carriers for the large‐scale production of bio‐hydrogen.

Dephenolization of stored olive-mill wastewater, using four different adsorbing matrices to attain a low-cost feedstock for hydrogen photo-production

This investigation deals with the conversion of olive-mill wastewater (OMW) into several feedstocks suitable for hydrogen photo-production. The goal was reached by means of two sequential steps: (i) a pre-treatment process of stored-OMW for the removal of polyphenols, which made it possible to obtain several effluents, and (ii) a photo-fermentative process for hydrogen production by means of Rhodopseudomonas palustris sp. Four different adsorbent matrices (Azolla, granular active carbon, resin, and zeolite) were used to dephenolize stored-OMW. The four liquid fractions attained by using the above process created the same number of effluents, and these were diluted with water and then used for hydrogen photo-production. The maximum hydrogen production rate (14.31 mL/L/h) was attained with the photo-fermenter containing 25% of the effluent, which came from the pre-treatment of stored-OMW using granular active carbon. Using the carbon effluent as feedstock, the greatest light conversion efficiency of 2.29% was achieved.

Influence of sulfate-reducing bacteria, sulfide and molybdate on hydrogen photoproduction by purple nonsulfur bacteria

The interaction between bacterial species is of great importance for H2 production using microbial consortia or non-sterile conditions. Sulfate reducing bacteria were found in anaerobic starch-hydrolyzing consortium and their inhibitory effect on the following H2 photoproduction by purple nonsulfur bacteria was shown. This inhibition was clearly demonstrated in the mixed culture of Rhodobacter sphaeroides and Desulfomicrobium baculatum using the synthetic medium. This effect was conditioned by sulfide production rather than H2 consumption or competition for organic substrate. Actually, the addition of equivalent sulfide concentration brought about the similar effects: inhibition of H2 production without growth inhibition, cells aggregation, and the increase of carbohydrate content as an alternative way of expenditure of organic acids. In the long-term experiments the average sulfide concentration of about 0.3 mM was detrimental while in short-terms the H2 production was not inhibited even at 3.2 mM. The protective effect of molybdates against sulfate reducers and sulfide was discussed.

The effect of Pt characteristics on the photoactivity of Pt/TiO2 for hydrogen production from ethanol

Pt/TiO2 photo-catalysts prepared by different methodologies (deposition–precipitation and wet impregnation using various Pt precursors) are investigated for the photo-production of hydrogen from aqueous solutions of ethanol. Textural, structural and surface catalyst properties are determined by N2 adsorption isotherms, UV–vis spectroscopy, XRD and XPS and related to the photo-activity results. Physicochemical characterization of Pt/TiO2 samples revealed differences in the electronic state and surface concentration of Pt nanoparticles depending on the method of preparation. Stronger interaction of Pt nanoparticles with TiO2 support that leads to some partially charged Pt particles was observed in the samples prepared by the deposition–precipitation (Ptδ−) and by impregnation (Ptδ+) using neutral Pt acetylacetonate precursor. It is found that H2 production rates on Pt/TiO2 photo-catalysts depend on the characteristics of Pt particles showing the partially charged Pt particles (Ptδ−and Ptδ+) better intrinsic photoactivity than that observed for metallic Pt counterpart. The improvement in the intrinsic activity observed for the partially charged Pt particles is attributed to a better e-conductivity (in the case of Ptδ− particles) and an increase in the adsorption of surface molecules (in the case of Ptδ+) extending the e-/hole carrier separation of TiO2 photo-catalyst.

Self-assembly of CdS quantum dots with polyoxometalate encapsulated gold nanoparticles: enhanced photocatalytic activities

The molecular self-assembled nanohybrids CdS QDs–POM–Au NPs can be synthesized by a convenient, efficient and environmentally friendly strategy. The POMs, which function as the reducing, encapsulating molecules and bridging molecules, not only successfully realize the strong coupling of the different nanoparticles, but also enhance the electron transfer among the components of the nanohybrids. More importantly, the present nanohybrids can effectively harvest visible light and show synergistic photocatalytic activity both in photoproduction of hydrogen and degradation of organic pollutants. This synthesis method is versatile and promising for the design and development of other new solar energy hybrid systems.

Nanostructured N-doped TiO2 marigold flowers for an efficient solar hydrogen production from H2S

Nitrogen-doped TiO₂ nanostructures in the form of marigold flowers have been synthesized for the first time using a facile solvothermal method. The structural analysis has shown that such an N-doped TiO₂ system crystallizes in the anatase structure. The optical absorption spectra have clearly shown the shift in the absorption edge towards the visible-light range, which indicates successful nitrogen doping. The nitrogen doping has been further confirmed by photoluminescence and photoemission spectroscopy. Microscopy studies have shown the thin nanosheets (petals) of N-TiO₂ with a thickness of ∼2-3 nm, assembled in the form of the marigold flower with a high surface area (224 m(2) g(-1)). The N-TiO₂ nanostructure with marigold flowers is an efficient photocatalyst for the decomposition of H₂S and production of hydrogen under solar light. The maximum hydrogen evolution obtained is higher than other known N-TiO₂ systems. It is noteworthy that photohydrogen production using the unique marigold flowers of N-TiO₂ from abundant H2S under solar light is hitherto unattempted. The proposed synthesis method can also be utilized to design other hierarchical nanostructured N-doped metal oxides.

Genome-wide transcriptome analysis of hydrogen production in the cyanobacterium Synechocystis: Towards the identification of new players

We report the development of new tools and methods for facile integration and meaningful representation of high throughput data generated by genome-wide analyses of the model cyanobacterium Synechocystis PCC6803, for future genetic engineering aiming at increasing its level of hydrogen photoproduction. These robust tools comprise new oligonucleotide DNA microarrays to monitor the transcriptomic responses of all 3725 genes of Synechocystis, and the SVGMapping method and custom-made templates to represent the metabolic reprogramming for improved hydrogen production. We show, for the first time, that the AbrB2 repressor of the hydrogenase-encoding operon, also regulates metal transport and protection against oxidative stress, as well as numerous plasmid genes, which have been overlooked so far. This report will stimulate the construction and global analysis of hydrogen production mutants with the prospect of developing powerful cell factories for the sustainable production of hydrogen, as well as investigations of the probable role of plasmids in this process.

Fresh olive mill waste deprived of polyphenols as feedstock for hydrogen photo-production by means of Rhodopseudomonas palustris 42OL

In the present study, fresh olive mill waste (OMWF) was processed using an innovative pre-treatment based on the adsorption capacity of two natural matrices. The liquid fraction coming from the pre-treatment is an inexpensive feedstock for hydrogen photo-production by means of purple non-sulphur photosynthetic bacteria (PNSB). The culture broth, which contained OMWF (30%) and distilled water (70%) was tested for hydrogen photo-production using Rhodopseudomonas palustris 42OL. The photo-fermentative process was studied under batch growth conditions, at three different irradiances (18.5, 37 and 74 W/m2). The lowest cumulative amount of hydrogen (439 ml-H2/L-broth) was attained at the irradiance of 18.5 W/m2, while the highest one (1030 ml-H2/L-broth) was obtained at the irradiance of 74 W/m2. The resulting average hydrogen evolution rates (HPRavg), which were based on the culture volume and were attained at the three different irradiances (i.e. 18.5, 37 and 74 W/m2), were 1.40, 3.17 and 5.28 ml-H2/L-broth/h respectively. The culture age at which the hydrogen photo-evolution ceased showed an inverse proportionality as compared to the irradiance: i.e. the higher the irradiance, the lower the culture age. On the contrary, the COD removal efficiency (CODRE) increased depending on the irradiance. The maximal light conversion efficiency (1.07%) was attained at the irradiance of 37 W/m2, and decreased at both lower and higher irradiances.

The enhancement of hydrogen photoproduction in Chlorella protothecoides exposed to nitrogen limitation and sulfur deprivation

H-2 photoproduction, hydrogenase activities and PSII photochemical activities in Chlorella protothecoides under sulfur (S-) or nitrogen (N-) deprivation or simultaneous N-limitation and S-deprivation were studied. C. protothecoides pre-cultured in full nutrient TAP medium containing 7 mM NH4Cl was found to produce a detectable but low level of H-2, once the cells were inoculated either in S-free or N-free medium. However, cells pre-grown in a low concentration of NH4Cl (0.35 and 0.7 mM) generated a large amount of H-2 after transfer to N-limited and S-free medium. The maximal H-2 outputs of similar to 233.7 and similar to 129.1 ml/l were obtained within 100 h in the cultures exposed to S-deprived medium containing 0.35 mM and 0.7 mM NH4Cl, with the average H-2 production rates being similar to 2.19 and similar to 1.37 ml/l/h, respectively. Our studies further indicated that N-limitation resulted in considerable starch accumulation, chlorophyll synthesis reduction, photosynthetic electron transfer block and oxygen evolving complex (OEC) injury, as well as attenuation in PSII oxygenic activity. Significant starch degradation was not observed during the H-2 photoevolution process. Attenuation of PSII O-2 evolution favored a rapid establishment of anaerobiosis for hydrogenase induction. Meanwhile, a constant high level of hydrogenase activities in C. protothecoides exposed to simultaneous N-limitation and S-deprivation were measured. Based on the above results, a possible mechanism of high H-2 photoproduction in C. protothecoides exposed to N-limitation and S-deprivation was discussed. Low net photosynthetic oxygenic rates, together with high hydrogenase activities were thought to contribute to the enhancement of H-2 photoproduction by C. protothecoides. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The [4Fe–4S]-cluster coordination of [FeFe]-hydrogenase maturation protein HydF as revealed by EPR and HYSCORE spectroscopies

[FeFe] hydrogenases are key enzymes for bio(photo)production of molecular hydrogen, and several efforts are underway to understand how their complex active site is assembled. This site contains a [4Fe–4S]-2Fe cluster and three conserved maturation proteins are required for its biosynthesis. Among them, HydF has a double task of scaffold, in which the dinuclear iron precursor is chemically modified by the two other maturases, and carrier to transfer this unit to a hydrogenase containing a preformed [4Fe–4S]-cluster. This dual role is associated with the capability of HydF to bind and dissociate an iron–sulfur center, due to the presence of the conserved FeS-cluster binding sequence CxHx46–53HCxxC. The recently solved three-dimensional structure of HydF from Thermotoga neapolitana described the domain containing the three cysteines which are supposed to bind the FeS cluster, and identified the position of two conserved histidines which could provide the fourth iron ligand. The functional role of two of these cysteines in the activation of [FeFe]-hydrogenases has been confirmed by site-specific mutagenesis. On the other hand, the contribution of the three cysteines to the FeS cluster coordination sphere is still to be demonstrated. Furthermore, the potential role of the two histidines in [FeFe]-hydrogenase maturation has never been addressed, and their involvement as fourth ligand for the cluster coordination is controversial. In this work we combined site-specific mutagenesis with EPR (electron paramagnetic resonance) and HYSCORE (hyperfine sublevel correlation spectroscopy) to assign a role to these conserved residues, in both cluster coordination and hydrogenase maturation/activation, in HydF proteins from different microorganisms.

The Rhodobacter sphaeroides F0F1-ATPase activity: Effects of heavy metal ions and relationship with hydrogen photoproduction

The important aspect in regulation of hydrogen (H2) photoproduction by purple bacteria and its energetics is the requirement of the F0F1-ATPase, the main membrane mechanism generating proton motive force [1,2]. Previously the relationship between H2 production, proton transport and the F0F1-ATPase activity was shown by purple bacteria Rhodobacter sphaeroides [2]. It is well known that H2 production varies depending on the different factors: anaerobic conditions, light intensity, pH, carbon and nitrogen sources, and heavy metals ions [3,4]. Fe, Ni and Mo ions are the components of enzymes, which are responsible for H2 production by photosynthetic bacteria, such as hydrogenase and nitrogenase. Bacterial photosynthetic pigments such as bacteriochlorophyll contain Mg. R. sphaeroides MDC 6521 (isolated from Arzni mineral springs in Armenia) is able to grow and produce H2 in anaerobic conditions under illumination in the presence of various heavy metal ions [4]. In this study in order to examine the mediatory role of the F0F1-ATPase in H2 production, the effects of metal ions (Ni, Mg, Mo, and Fe) on DCCD inhibited ATPase activity of R. sphaeroides membrane vesicles were investigated. These metal ions in appropriate concentrations considerably enhanced H2 production by R. sphaeroides. But H2 production was not observed in the absence of Fe, indicating that Fe is required for H2 production. As was shown in our previous study [2] the R. sphaeroides membrane vesicles demonstrated significant ATPase activity. The absence of Fe caused to marked inhibition (~80%) in ATPase activity. After treatment of membrane vesicles with Ni (0.004 mM) and Mg (10 mM) the ATPase activity stimulation was observed: the activity was increased by 15 and 30%, respectively. The Fe (0.08 mM) and Mo (0.016 mM) added gave a stimulated (~2.5 fold) ATPase activity. These results indicate a relationship between the F0F1-ATPase activity and H2 photoproduction. This provides novel evidence on the role of the F0F1-ATPase in H2 production by this bacterium.

PCR Designing and Amplification of Partial Hydrogenase Gene from Selected Hydrogen Producing Microorganisms

Hydrogen production involves the use of hydrogenase (H2ase) enzyme, especially for photohydrogen production. Specific detection of fermentative hydrogen producing bacteria from the microbial communities is achieved based on the universal Iron-hydA primers. In the present study, the primers for the H2ase gene were designed, followed by the isolation of the DNA from the selected hydrogen producing microorganisms. Amplification of the genome by the designed primers were carried out by the polymerase chain reaction. The PCR primers designed were HyF, Hyff, HyR and Hyrr. The primers were analyzed and best fitted by the computer aided program. The resulted primers were amplified (400 bps) from the genome of the selected hydrogen producing microorganisms. This work was carried out as a preliminary assay in molecular cloning of hydrogenase genes by primer designing from the selected strains for the improvement of hydrogen production process. Keywords: Hydrogen production, hydrogenase gene, nitrogenase gene, DNA isolation, PCR primers, primer designing, HyF, Hyff, HyR and Hyrr, gene amplification, Hydrogen uptake, autotrophic, thermophilic, oxidizing bacterium, H-cluster

Design of new strategy for green algal photo-hydrogen production: Spectral-selective photosystem I activation and photosystem II deactivation

A new strategy in photosynthetic hydrogen (photo-H2) production from green algae was developed based on theory and successfully demonstrated. The new strategy applied a spectral-selective photosystem I (PSI) activating/photosystem II (PSII) deactivating radiation (or PSI light) that would drive a steady flow of electrons in the electron transport chain for delivery to hydrogenase for photo-H2 production, but would reduce oxygen production through water photolysis below the respiratory oxygen consumption so that an anoxic condition would be maintained as required by hydrogenase. Implementing the strategy by using a PSI light (692nm peak, 680–700nm) on Chlamydomonas reinhardtii cells resulted in relatively sustained photo-H2 production (total of 0.108mLH2mg−1Chl, exceeding 0.066mLH2mg−1Chl under white light). The strategy also proved successful and convenient in allowing cells to alternately switch between photo-H2 production and a recovery period by simply turning on or off the PSI light.

Enhanced photo-fermentative hydrogen production by Rhodobacter capsulatus with pigment content manipulation

High content of pigment in purple nonsulfur photosynthetic bacteria hinders its photo-hydrogen production rate under intense light irradiation. In order to alleviate the light shielding effect and improve its photo-fermentative hydrogen production performance, pufQ, which is the regulatory gene of bacteriochlorophyll biosynthesis in Rhodobacter capsulatus, was cloned and relocated in the genome under cbb3 promoter by homologous recombination. The UV–vis spectra indicated that the light absorption of the mutant between 300 and 900nm was reduced. Photo-hydrogen production experiments by the recombinant and wild type strain were carried out in 350mL photo bioreactors using acetic and butyric acid as substrate. The results showed that the hydrogen production of recombinant with reduced pigment was 27% higher than that of its parental strain, indicating that it is effective on enhancing photo-fermentative hydrogen production by manipulating pigment biosynthesis in purple nonsulfur photosynthetic bacteria.

A feasibility study on unsaturated flow bioreactor using optical fiber illumination for photo-hydrogen production

An unsaturated flow bioreactor with Rhodopseudomonas palustris CQK 01 was developed for photo-hydrogen production. The bioreactor developed in this work consisted of a reaction bed packed with spherical glass beads and internal optical fiber that provided uniform light distribution and achieved high light transmission efficiency. Unsaturated conditions were obtained by filling both argon and nutrient solution into the bioreactor. Experimental results demonstrated the feasibility of the biofilm formation in an unsaturated environment. With the formed biofilm, parametric studies on the photo-hydrogen production performance under different liquid flow rates and initial substrate concentrations were conducted. It was found that the performance of the bioreactor came to the optimal state at the liquid flow rate of 500 mL/h. Moreover, such a design enabled the bioreactor to be operated at relatively high glucose concentration without the substrate inhibition, yielding a good biohydrogen production performance.