Investigation of light transfer procedure and photobiological hydrogen production of microalgae in photobioreactors at different locations of China

In this study, the light transfer procedure and photobiological hydrogen production of microalgae in the photobioreactors (PBRs) at different locations of China are investigated thoroughly. Firstly, the solar irradiation projected on the ground of four different regions (Harbin, Beijing, Shanghai and Sanya) at the same moment and that of Harbin at four different moments are calculated by the SMART model. Based on the finite volume method and the photobiological hydrogen production dynamic model, the effects of different irradiance on the photobiological hydrogen production rate in the PBRs are analyzed. In addition, the effect of microalgae cell concentration and the scattering and absorbing of gas bubbles on the hydrogen production have also been studied. All the results elucidate these two factors play a significant role in the light transfer and hydrogen production rate in the PBRs. Meanwhile, the light intensity and microalgae cell density both have the saturation inhibition effect on the hydrogen production process. The distribution of the highly efficient hydrogen production region in the reactor varies with different bubbles concentration.     

Hydrogenases and photobiological hydrogen production utilizing nitrogenase system in cyanobacteria

We constructed three hydrogenase mutants from Anabaena sp. PCC 7120: ΔhupL (deficient in uptake hydrogenase), ΔhoxH (deficient in bidirectional hydrogenase), and ΔhupL/ΔhoxH (deficient in both genes), and showed that the Δhup and ΔhupL/ΔhoxH produced H₂ at a rate 4–7 times that of wild-type under optimal conditions (Appl. Microbiol. Biotechnol. 58 (2002) 618). We have studied H₂ producing activity of Δhup in more detail. H₂ producing activity of Δhup cells was moderately improved in older cultures when 1% CO₂ was added to the bubbling air. The efficiency of light energy conversion to H₂ by the ΔhupL mutant at its highest H₂ production stage was 1.0–1.6% at an actinic visible light intensity of lower than 50 W/m² under argon atmosphere, and the activity lasted for at least 35 min. At 250 W/m², H₂ producing activity gradually decreased with illumination time.     

Performance of a groove-type photobioreactor for hydrogen production by immobilized photosynthetic bacteria

The biofilm technique has been proved to be an effective cell immobilization method for wastewater biodegradation but it has had restricted use in the field of photobiological H₂ production. In the present study, a groove-type photobioreactor was developed and it was shown that a groove structure with large specific surface area was beneficial to cell immobilization and biofilm formation of the photosynthetic bacteria on photobioreactor surface as well as light penetration. A series of experiments was carried out on continuous hydrogen production in the groove-type photobioreactor illuminated by monochromatic LED lights and the performance was investigated. The effects of light wavelength, light intensity, inlet glucose concentration, flow rate and initial substrate pH were studied and the results were compared with those obtained in a flat panel photobioreactor. The experimental results show that the optimum operational conditions for hydrogen production in the groove-type photobioreactor were: inlet glucose concentration 10 g/L, flow rate 60 mL/h, light intensity 6.75 W/m², light wavelength 590 nm and initial substrate pH 7.0. The maximum hydrogen production rate, H₂ yield and light conversion efficiency in the groove-type photobioreactor were 3.816 mmol/m²/h, 0.75 molH₂/molglucose and 3.8%, respectively, which were about 75% higher than those in the flat panel photobioreactor.     

Improving conversion efficiency of solar energy to electricity in cyanobacterial PEMFC by high levels of photo-H2 production

In this study, we described an efficient electrical power generating system containing cyanobacterial photo-H₂ production and custom-built proton exchange membrane fuel cell (PEMFC). The filamentous N₂-fixing cyanobacterium Anabaena cylindrica was used as the photo-H₂ producer. A photosynthesis inhibitor-diuron (DCMU) was used for the enhancement of photo-H₂ production in the culture under argon gas. For the first time, a total of 1.0 μM DCMU was found to be the most effective treatment, as this produced 3.6 fold higher levels of H₂ in microalgae. By measuring polarization curve, the gas mixture collected from the culture was proven to be an effective fuel for electrical generation through a custom-built PEMFC. When the PEMFC was directly combined with the culture tube, the cells generated as much as 843 mV during a 5-day incubation due to the efficient conversion of solar energy to H₂ by A. cylindrica. Light energy conversion efficiency (LCE) for both solar energy to H₂ and solar energy to electricity were also determined. The LCE for the cyanobacterial conversion of solar energy to H₂ reached a peak at four days with a maximal value of 2.05% and an average value of 1.70% ± 0.17. The corresponding LCE for the conversion of solar energy to electricity in this system was 1.13% at peak and 0.94% ± 0.09 on average.     

微藻生物制氢技术

介绍了微藻光合制氢技术的生物原理及固氮酶和可逆产氢酶的产氢机制.讨论了基于微藻的硫缺乏生理调控而发展起来的一步法与两步法光解制氢的方式,其中微藻可逆产氢酶两步法间接光解制氢是最具发展潜力的制氢方式.分析了实现微藻光合制氢的限制因子及要解决的问题,指出高效光合产氢藻株的筛选及高效光反应器的实现是该技术获得成功的关键,使微藻大规模光合产氢成为可能.     

Characterization of cell growth and photobiological H2 production of Chlamydomonas reinhardtii in ASSF industry wastewater

Photobiological H₂ production in microalgae is a promising approach for the development of alternative clean and renewable energy. As a unicellular green alga, Chlamydomonas reinhardtii is regarded as an ideal candidate for sustainable photo-H₂ production. However, growth and photo-H₂ producing are still expensive and energy extensive. Wastewater has been suggested as an economical resource for microalgae growth and biofuels production. In this study, we characterized the cell growth and photo-H₂ production of C. reinhardtii CC503 cultured in waste water from pressing process of fermented sweet sorghum stalks during Advanced Solid State Fermentation (ASSF). The maximal cells concentration reached 8.9 × 10⁶ cells/mL in ASSF wastewater medium (AWM) with the fastest growth rate of 0.19 × 10⁶ cells/h, compared to 18.2 × 10⁶ cells/mL and 0.36 × 10⁶ cells/h in TAP medium and to 1.3 × 10⁶ cells/mL and 0.02 × 10⁶ cells/h in BGII medium respectively. The optimized concentration of wastewater for algae cells growth was determined to be 13.3% (7.5 folds dilution), under which, surprisingly the photosynthetic H₂ evolution was increased by more than 700% compared to the cells grown in TAP medium. This system appears to be a good strategy for the development of an economical microalgal photobiological H₂ production scheme. Finally, the possible mechanism for such an H₂ enhancement was identified as the reduction of PSII activity in AWM grown cells.     

Photobiological hydrogen production: photochemical efficiency and bioreactor design

Biological production of hydrogen can be carried out by photoautotrophic or photoheterotrophic organisms. Here, the photosystems of both processes are described.The main drawback of the photoautotrophic hydrogen production process is oxygen inhibition. The few efficiencies reported on the conversion of light energy into hydrogen energy are low, less than 1.5% on a solar spectrum basis. However, these can be increased to 3–10%, by the immediate removal of produced oxygen.The photochemical efficiency of hydrogen production can be calculated theoretically, and is estimated to be 10% (on solar spectrum basis) for the photoheterotrophic process. With use of the theoretical photochemical efficiency, and the climatic data on sunlight irradiance at a certain location at a certain moment of the year, the theoretical maximum hydrogen production can be estimated.Data on H₂ yields and photochemical efficiency from experiments reported in the literature are summarized. Photochemical efficiencies, essentially based on artificial light, can reach 10% or even more, but only at low light intensities, with associated low-H₂ production rates.Some reflections on possible photobioreactors lead to two types of (modified) photobioreactors that might be successful for a large-scale biological hydrogen production.     

Improving hydrogen production from cassava starch by combination of dark and photo fermentation

The combination of dark and photo fermentation was studied with cassava starch as the substrate to increase the hydrogen yield and alleviate the environmental pollution. The different raw cassava starch concentrations of 10–25 g/l give different hydrogen yields in the dark fermentation inoculated with the mixed hydrogen-producing bacteria derived from the preheated activated sludge. The maximum hydrogen yield (HY) of 240.4 ml H₂/g starch is obtained at the starch concentration of 10 g/l and the maximum hydrogen production rate (HPR) of 84.4 ml H₂/l/h is obtained at the starch concentration of 25 g/l. When the cassava starch, which is gelatinized by heating or hydrolyzed with α-amylase and glucoamylase, is used as the substrate to produce hydrogen, the maximum HY respectively increases to 258.5 and 276.1 ml H₂/g starch, and the maximum HPR respectively increases to 172 and 262.4 ml H₂/l/h. Meanwhile, the lag time (λ) for hydrogen production decreases from 11 h to 8 h and 5 h respectively, and the fermentation duration decreases from 75–110 h to 44–68 h. The metabolite byproducts in the dark fermentation, which are mainly acetate and butyrate, are reused as the substrates in the photo fermentation inoculated with the Rhodopseudomonas palustris bacteria. The maximum HY and HPR are respectively 131.9 ml H₂/g starch and 16.4 ml H₂/l/h in the photo fermentation, and the highest utilization ratios of acetate and butyrate are respectively 89.3% and 98.5%. The maximum HY dramatically increases from 240.4 ml H₂/g starch only in the dark fermentation to 402.3 ml H₂/g starch in the combined dark and photo fermentation, while the energy conversion efficiency increases from 17.5–18.6% to 26.4–27.1% if only the heat value of cassava starch is considered as the input energy. When the input light energy in the photo fermentation is also taken into account, the whole energy conversion efficiency is 4.46–6.04%.     

Effect of light intensity and initial pH during hydrogen production by an integrated dark and photofermentation process

Photofermentation was carried out with the spent fermentation broth obtained from the anaerobic dark fermentation in a two-stage process. For the first stage, i.e. dark fermentation Enterobacter cloacae DM 11 was used as hydrogen producing microorganism. For photofermentation Rhodobacter sphaeroides O.U. 001, a photo-heterotrophic purple non-sulfur bacterium, was used. pH study revealed that cumulative hydrogen production was maximum at initial medium pH of 7.0 ± 0.2. Biomass yield was also high at the vicinity of pH 7.0 and it decreased as the pH increased from 7.0 to 8.0. Increased light intensity resulted in an increase in the total volume of hydrogen evolved and also hydrogen production rate. However, light conversion efficiency decreased by increasing light intensity. A four-fold increase in light intensity resulted in a three-fold decrease in light conversion efficiency although the cumulative volume of hydrogen gas production increased. It was observed that only a maximum of 0.51% light conversion efficiency could be achieved but at the expense of very low light intensity of 2500 lux (3.75 W m⁻²).     

Parameters affecting the growth and hydrogen production of the green alga Chlamydomonas reinhardtii

The green alga Chlamydomonas reinhardtii has the ability to photosynthetically produce molecular hydrogen (H₂) under anaerobic conditions. It offers a biological route to renewable H₂ production from sunlight and water. Algal growth and H₂ production kinetics must be understood in order to determine appropriate system parameters and develop photobioreactors. Algal biomass should be grown efficiently and economically to attain the high cell densities necessary for H₂ production. The nutrient requirements and process conditions that encourage the growth of dense and healthy algal cultures were explored. Anaerobic conditions were imposed by sulphur deprivation, which requires an exchange of the algal growth medium by centrifugation or dilution. A tubular flow photobioreactor featuring a large surface-to-volume ratio was used to monitor and control the key parameters in the H₂ production process, including pH, dissolved oxygen, optical density, temperature, agitation and light intensity. A cumulative H₂ yield of 3.1 ± 0.3 ml/l of culture was measured.     

Study of hydrogen production by three strains of Chlorella isolated from the soil in the Algerian Sahara

In this study, the photosynthetic hydrogen production rates by some strains of green microalgae were investigated. Three strains of Chlorella isolated from arid soil and foggaras's water in the Algerian Sahara were used. Chlorella sorokiniana strain Ce, Chlorella salina strain Mt and Chlorella sp strain Pt6 produced hydrogen gas under sulphur-deprived conditions, but its rate was dependent on strain type and oxygen partial pressure in medium. In C. sorokiniana strain Ce, the maximum value of hydrogen accumulated was 147 ml at 222 h at 2% of O₂ pressure. Compared to C. sorokiniana strain Ce, C. salina strain Mt and Chlorella sp strain Pt6 produced less amount of hydrogen, but they were able to sustain with an O₂ partial pressure of up to 11–15.4%. Our data were compared with hydrogen production by Chlamydomonas reinhardtii. In this communication, the relationship between physiological behaviour, biochemical characteristic (starch and protein) and rates gas production (O₂ and H₂) was also specified.     

Experimental measurements of the radiation characteristics of Anabaena variabilis ATCC 29413-U and Rhodobacter sphaeroides ATCC 49419

The objective of this study is to experimentally measure the radiation characteristics of hydrogen producing microorganisms. Special attention is paid to the filamentous cyanobacteria Anabaena variabilis ATCC 29413-U and the unicellular purple bacteria Rhodobacter sphaeroides ATCC 49419 two of the widely studied photobiological hydrogen producers. The extinction and absorption coefficients are measured in the spectral range from 300 to 1300 nm using a spectrophotometer with and without an integrating sphere. Moreover, a nephelometer has been constructed to measure the scattering phase function of the microorganisms at 632.8 nm. The data are used to recover the mass specific absorption, scattering, and extinction cross-sections, the single scattering albedo, and the scattering phase function of the microorganisms. The scattering phase functions of both microorganisms were peaked strongly in the forward direction as expected from their size parameter and shape. The results reported in this study can be used with the radiative transport equation (RTE) to accurately predict and optimize light transport in photobioreactors for photobiological hydrogen production. Finally, the results show that absorption cross-sections of A. variabilis and R. sphaeroides have peaks that do not overlap but rather enlarge the spectral width of the absorption cross-section of a potential symbiotic culture promising more efficient utilization of solar radiation from light transfer point of view.     

Characterization of hydrogen production by Platymonas Subcordiformis in torus photobioreactor

Platymonas subcordiformis, a marine green alga, was demonstrated to photo-biologically produce hydrogen when regulated by a kind of proton uncoupler CCCP (Carbonyl Cyanide m-Chlorophenylhydrazone). In this paper, hydrogen production experiments by P. subcordiformis were carried out in a torus photobioreactor equipped with a mass spectrometer and other necessary sensors so that instantaneous gas components could be measured and other successive physiological states could be well recorded.     

链霉素对蛋白核小球藻Chlorella pyrenoidosa产氢及其生长的影响

以蛋白核小球藻Chlorella pyrenoidosa为材料,研究不同链霉素浓度对其生长及其产氢过程的影响。结果表明,添加600 mg/L的链霉素对蛋白核小球藻的产氢具有最大促进作用,产氢时间可持续8 d,比对照组延长近6 d,总产氢量为354.54μL/mg,分别是对照组、200 mg/L和1 000 mg/L试验组的18.44,5.85和1.35倍;通过比较不同条件下蛋白核小球藻的光合及生长状况,证实链霉素明显抑制了蛋白核小球藻的光合放氧,对藻细胞产氢后期的生长也有一定抑制作用。     

Long-term stable hydrogen production from acetate using immobilized Rhodobacter capsulatus in a panel photobioreactor

Biological hydrogen production is attractive since renewable resources are utilized for hydrogen production. In this study, a novel panel photobioreactor (1.4 L) was constructed from Plexiglas with a network of nylon fabric support for agar immobilized bacteria complex. Two strains of Rhodobacter capsulatus DSM 1710 wild-type strain and Rhodobacter capsulatus YO3 (hup⁻, uptake hydrogenase deleted mutant) with cell concentrations of 2.5 and 5.0 mg dcw/mL agar, respectively were entrapped by 4% (w/v) of agar. The system was operated for 72–82 days in a sequential batch mode utilizing acetate as substrate at 30 °C under continuous illumination. Immobilization increased the stability of the photobioreactors by reducing the fluctuations in pH. The pH remained between 6.7 and 8.0 during the process. Both hydrogen yield and productivity were higher in immobilized photobioreactors compared to suspended culture. The highest hydrogen productivities of 0.75 mmol H₂/L/h and 1.3 mmol H₂/L/h were obtained by R. capsulatus DSM1710 and R. capsulatus YO3 respectively.     

Growth and hydrogen production by three Chlamydomonas strains cultivated in a commercial fertilizer

In the present investigation, we report the growth and hydrogen production of two wild type Chlamydomonas reinhardtii strains isolated from a tropical oxidation pond in Costa Rica. The performance of these two new isolates was compared to that of Chlamydomonas reinhardtii CC124. All the strains were grown both in conventional Tris-Acetate-Phosphate medium (TAP) and in a commercial fertilizer medium (NPK 20-20-20). The growth of the new two isolates in medium formulated with fertilizer was higher than that attained with the reference strain (CC124). However, the hydrogen production performance of the strain CC124 in TAP-S and fertilizer were comparable, while the two new strains performed better in fertilizer, although the total hydrogen production was lower than that achieved with CC124. By using fertilizer it is possible to reduce the cost of chemical reagents by about 63% compared to TAP. Another advantage of the fertilizer is that it does not contain sulfur, therefore it can be directly used for hydrogen production using the Melis protocol.     

太阳能制氢技术及其进展

阐述了光解水制氢的原理,介绍了光解水制氢技术的现状,分析了目前光解水制氢技术存在的问题以及提高光解水效率的有效途径,指出了利用光热化学循环进行光解水制氢的新途径.     

Photoautotrophic hydrogen production by nitrogen-deprived Chlamydomonas reinhardtii cultures

In this study we have demonstrated the possibility of phototrophic hydrogen production in C. reinhardtii under N-deprived conditions. When tested under air + CO₂, and Ar + CO₂ N-deprived C. reinhardtii demonstrated decrease in PSII activity mainly due to over reduction of PQ, in addition no ascorbate accumulation was observed in cells. Under air + CO₂ atmosphere cells accumulated excessive amounts of starch. When incubated under Ar + CO₂ atmosphere cells accumulated starch as nitrogen replete cultures and no hydrogen production was observed. Hydrogen production (86 ml H₂ per one l of culture) occurred under Ar + CO₂ atmosphere when particular two-step illumination protocol was implicated. In oxygen producing and early oxygen consuming stage cells were illuminated under light intensity 169 μE m^?2 s^?1. When light was switched to 30 μE m^?2 s^?1, cultures quickly respired all oxygen and transient to anaerobic conditions with subsequent hydrogen production 2 h later. Actual quantum yield of C. reinhardtii cultures was measured in photobioreactor and maximal quantum efficiency of PSII of dark adapted cells together with JIP test were studied.     

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.     

Dye-sensitized photocatalytic hydrogen evolution by using copper-based ternary refractory metal chalcogenides

The exploration of photocatalytic transformation of solar energy into H₂ through water splitting is an important direction towards sustainable and non-polluting energy in order to cover energy necessity partially. Ternary transition metal chalcogenides have been attracted attention among the other chalcogenides due to their potential applications in the photocatalytic and electrocatalytic hydrogen evolution. Herein, Cu₂WS₄ nanocubes and Cu₂WSe₄ nanosheets have been synthesized through a facile hot-injection method to benefit from the advantages such as minimizing the required pressure and reaction time by this technique. The photocatalytic hydrogen evolution activities of Cu₂WS₄ and Cu₂WSe₄ have been investigated under the visible light irradiation by using eosin-Y (EY) dye and triethanolamine (TEOA) as a photosensitizer and an electron donor, respectively. Cu₂WS₄ nanocubes have exhibited higher photocatalytic activity and stability than Cu₂WSe₄ nanosheets. The photocatalytic HER rates of Cu₂WS₄ and Cu₂WSe₄ have been determined as 1260 μmol g⁻¹ h⁻¹ and 861 μmol g⁻¹ h⁻¹, respectively. Photocatalytic HER activities were figured out in the order of Cu₂WS₄ > Cu₂WSe₄ which could be attributed to differences between proton reduction potential and the conduction band energy levels.