Influence of culture age,ammonium and organic carbon in hydrogen production and nutrient removal by Anabaena sp. in nitrogen-limited cultures

Hydrogen can be generated from cyanobacteria cultivation with light and organic carbon as an energy source. The aim of this study was to investigate the influence of ammonium and glucose concentration, and the culture age on the production of hydrogen and other products, and phosphate and organic carbon removal by Anabaena sp. (UTEX 1448) in batch anaerobic photobioreactors. Our results demonstrated an effect of culture age and ammonium concentration in hydrogen production, an average increase of 4.1 times (90.4 μmol H₂ mg Chl a⁻¹ h⁻¹ and 13.2 mmol mg Chl a⁻¹) in the conditions with younger biomass and without ammonium. Culture age also had an effect in phosphate removal, with 92% of removal efficiency, and ethanol production (an average increase of 2.9 times–97 mg L⁻¹), however the optimum conditions were obtained with older biomass. This study demonstrates efficient hydrogen production by this strain of Anabaena sp. fewer researched.     

Treatment with moderate concentrations of NaHSO3 enhances photobiological H2 production in the cyanobacterium Anabaena sp. strain PCC 7120

In cyanobacteria, treatment with low concentrations of NaHSO₃ can enhance photosynthetic efficiency, whereas NaHSO₃ in high amounts often inhibits cell growth and photosynthesis may even cause death. In the present study, our results showed that treatment with moderate concentrations of NaHSO₃ considerably improved the yield of photobiological H₂ production in the filamentous N₂-fixing cyanobacterium Anabaena sp. strain PCC 7120. Under steady state conditions, the accumulated H₂ levels in cells treated with 1 mM NaHSO₃ were approximately 10 times higher than that in untreated cells. Such improvement occurred in heterocysts and was most likely caused by increases in the expression and activity of nitrogenase. The effects of treatment with low, moderate, and high concentrations of NaHSO₃ in cyanobacteria were proposed on the basis of the results obtained in the present study and from previous knowledge.     

Biohydrogen production by Anabaena sp. PCC 7120 wild-type and mutants under different conditions: Light, nickel, propane, carbon dioxide and nitrogen

Increasing awareness of environmental problems caused by the current use of fossil fuel-based energy, has led to the search for alternatives. Hydrogen is a good alternative and the cyanobacterium Anabaena sp. PCC 7120 is naturally able to produce molecular hydrogen, photosynthetically from water and light. However, this H₂ is rapidly consumed by the uptake hydrogenase.This study evaluated the hydrogen production of Anabaena sp. PCC 7120 wild-type and mutants: hupL⁻ (deficient in the uptake hydrogenase), hoxH⁻ (deficient in the bidirectional hydrogenase) and hupL⁻/hoxH⁻ (deficient in both hydrogenases) on several experimental conditions, such as gas atmosphere (argon and propane with or without N₂ and/or CO₂ addition), light intensity (54 and 152 ??Em⁻²s⁻¹), light regime (continuous and light/dark cycles 16 h/8 h) and nickel concentrations in the culture medium.In every assay, the hupL⁻ and hupL⁻/hoxH⁻ mutants stood out over wild-type cells and the hoxH⁻ mutant. Nevertheless, the hupL⁻ mutant showed the best hydrogen production except in an argon atmosphere under 16 h light/8 h dark cycles at 54 ??Em⁻²s⁻¹ in the light period, with 1 ??M of NiCl₂ supplementation in the culture medium, and under a propane atmosphere.In all strains, higher light intensity leads to higher hydrogen production and if there is a daily 1% of CO₂ addition in the gas atmosphere, hydrogen production could increase 5.8 times, related to the great increase in heterocysts differentiation (5 times more, approximately), whereas nickel supplementation in the culture medium was not shown to increase hydrogen production. The daily incorporation of 1% of CO₂ plus 1% of N₂ did not affect positively hydrogen production rate.     

Fermentative hydrogen production by Clostridium butyricum CGS5 using carbohydrate-rich microalgal biomass as feedstock

In this work, a carbohydrate-rich microalga, Chlorella vulgaris ESP6, was grown photoautotrophically to fix the CO₂. The resulting microalgal biomass was hydrolyzed by acid or alkaline/enzymatic treatment and was then used for biohydrogen production with Clostridium butyricum CGS5. The C. vulgaris biomass could be effectively hydrolyzed by acid pretreatment while similar hydrolysis efficiency was achieved by combination of alkaline pretreatment and enzymatic hydrolysis. The biomass of C. vulgaris ESP6 containing a carbohydrate content of 57% (dry weight basis) was efficiently hydrolyzed by acid treatment with 1.5% HCl, giving a reducing sugars (RS) yield of nearly 100%. C. butyricum CGS5 could utilize RS from C. vulgaris ESP6 biomass to produce hydrogen without any additional organic carbon sources. The optimal conditions for hydrogen production were 37 °C and a microalgal hydrolysate loading of 9 g RS/L with pH-controlled at 5.5. Under the optimal conditions, the cumulative H₂ production, H₂ production rate, and H₂ yield were 1476 ml/L, 246 ml/L/h, and 1.15 mol/mol RS, respectively. The results demonstrate that the C. vulgaris biomass has the potential to serve as effective feedstock for dark fermentative H₂ production.     

Effect of CaO on tar reforming to hydrogen-enriched gas with in-process CO2 capture in a bubbling fluidized bed biomass steam gasifier

Previous studies showed that calcium oxide (CaO), when added to a biomass steam gasifier, could play the role of both CO₂ sorbent and tar reforming catalyst, and thereby produce more hydrogen. However, most of these works focused on the former role with little attention to tar reforming aspect of CaO. Therefore, this work aims primarily at studying the tar reforming effect of in-bed CaO. To this end, an in-depth analysis of the effect of CaO on tar yield and composition is presented. The present work also studies the role of CaO as a CO₂ sorbent to enhance hydrogen production from steam gasification of biomass in a bubbling fluidized bed. The influence of different operating parameters, temperature (T) and steam to biomass (S/B) ratio, as well as the effect of using in-bed CaO on gas and tar production is investigated. Results show that the maximum H₂ and minimum CO₂ concentration of 63.07% and 18.68%, respectively are obtained at T = 650 °C and S/B = 3.41. The maximum H₂ yield of 256.81 ml g⁻¹-biomass was obtained at T = 700 °C and S/B = 3.41, at which the minimum tar content of 6.45 g N m⁻³ was also received. Compared to a bed of sand alone, a 20% higher H₂ concentration, an almost double H₂ yield and a 67% reduction in tar content were obtained when a bed of CaO was used. Moreover, shifting the tar species from higher to fewer ring structures as a result of in-bed CaO can reduce tar dew point by 11 °C and tar carcinogenic potential by almost 60%.     

New cyanobacterial strains for biohydrogen production

Under certain conditions, cyanobacteria can switch from photosynthesis to hydrogen production, which is a good energy carrier. However, the biological diversity of hydrogen-releasing cyanobacteria has a great unexplored potential. This study is aimed to investigate the ability of new strains of cyanobacteria Cyanobacterium sp. IPPAS B-1200, Dolichospermum sp. IPPAS B-1213, and Sodalinema gerasimenkoae IPPAS B-353 to release H₂ and to evaluate the effects of photosystem II inhibitor 3-(3,4-dichlorphenyl)-1,1-dimethylurea (DCMU) on H₂ production under light and dark conditions. The results showed that cultures treated with DCMU produced several times more H₂ than untreated cells. The highest rate of H₂ photoproduction of 4.24 μmol H₂ (mg Chl a h)^?1 was found in a Dolichospermum sp. IPPAS B-1213 culture treated with 20 μM DCMU.     

The production of biohydrogen by a novel strain Clostridium sp. YM1 in dark fermentation process

In view of increasing attempts for the production of renewable energy, the production of biohydrogen energy by a new mesophilic bacterium Clostridium sp. YM1 was performed for the first time in the dark fermentation. Experimental results showed that the fermentative hydrogen was successfully produced by Clostridium sp. YM1 with the highest cumulative hydrogen volume of 3821 ml/L with a hydrogen yield of 1.7 mol H₂/mol glucose consumed. Similar results revealed that optimum incubation temperature and pH value of culture medium were 37 °C and 6.5, respectively. The study of hydrogen production from glucose and xylose revealed that this strain was able to generate higher hydrogen from glucose compared to that from xylose. The profile of volatile fatty acids produced showed that hydrogen generation by Clostridium sp. YM1 was butyrate-type fermentation. Moreover, the findings of this study indicated that an increase in head space of fermentation culture positively enhanced hydrogen production.     

Enhanced H2 fermentation of organic waste by CO2 sparging

This study aimed to improve the productivity of dark fermentative hydrogen production from organic waste. An anaerobic sequencing batch reactor was used for hydrogen fermentation and it was fed with food waste (VS 4.4 ± 0.2% containing 27 g carbohydrate-COD/L) at various CO₂ sparging rates (40–120 L/L/d), hydraulic retention times (HRTs; 18–42 h), and solid retention times (SRTs; 18–160 h). CO₂ sparging increased the H₂ productivity by 5–36% at all the examined conditions, confirming the benefit of the replacement of headspace gas by CO₂. The maximum H₂ production was obtained by CO₂ sparging at 80 L/L/d, resulting in the H₂ productivity of 3.18 L H₂/L/d and the H₂ yield of 97.3 mL H₂/g VS_added. Increase of n-butyrate and isopropanol yields were concurrent with the enhanced H₂ yield by CO₂ sparging. Acidogenic efficiency, the sum of H₂, organic acid, and alcohol, in the CO₂-sparged reactor ranged from 47.9 to 56.0%, which was comparable to conventional acidogenesis. Thermodynamic analysis confirmed that both CO₂ sparging and CO₂ removal were beneficial for H₂-producing reactions, but CO₂ sparing has more profound effect than CO₂ removal on inhibiting H₂-consuming reactions.     

Cost analysis of wind-electrolyzer-fuel cell system for energy demand in Pınarbaşı-Kayseri

In this study, the hydrogen production potential and costs by using wind/electrolysis system in P?narba??-Kayseri were considered. In order to evaluate costs and quantities of produced hydrogen, for three different hub heights (50 m, 80 m and 100 m) and two different electrolyzer cases, such as one electrolyzer with rated power of 120 kW (Case-I) and three electrolyzers with rated power of 40 kW (Case-II) were investigated. Levelised cost of electricity method was used in order to determine the cost analysis of wind energy and hydrogen production. The results of calculations brought out that the electricity costs of the wind turbines and hydrogen production costs of the electrolyzers are decreased with the increase of turbine hub height. The maximum hydrogen production quantity was obtained 14192 kgH₂/year and minimum hydrogen cost was obtained 8.5 $/kgH₂ at 100 m hub height in the Case-II.     

High cell density culture of Anabaena variabilis using repeated injections of carbon dioxide for the production of hydrogen

Cyanobacteria have the unique characteristic of using CO₂ in the air as a carbon source and solar energy as an energy source. Reducing equivalents from the fermentation of carbohydrates are used as the primary electron donors in cyanobacteria for the hydrogen producing enzymes. The cells take up CO₂ first to produce cellular substances, which are subsequently used for H₂ production. Since the optimal operating conditions for the CO₂ uptake and H₂ production are different, a two-stage system can be effectively employed to separate these two phases. In this study, for the efficient production of H₂ in the second stage, the conditions for the effective CO₂ uptake and cell growth in the first stage were characterized, and high cell density culture was carried out using repeated injections of CO₂. The specific growth rate and growth yield based on CO₂ decreased with an increase in light intensity or CO₂ concentration. However, the effect of CO₂ concentration on the growth yield was much smaller than that of a light intensity. A CO₂ uptake rate per unit cell decreased linearly with the initial CO₂ concentration in the gas phase. With repeated injections of CO₂, the CO₂ was continuously consumed and the cell concentration reached 3.7 g dry cell/l in 20 days, which is 6.7 times higher than that in a batch culture without further supply of CO₂. The CO₂ injection in the cell growth phase increased not only the cell concentration but also the hydrogen production per gram cell.     

Experimental and modeling kinetic study of the CO2 absorption by Li4SiO4

Nowadays, research aims to produce H₂ efficiently through modifying conventional processes by removing CO₂ at high temperature (T ≥ 500 °C). The sorption enhanced reforming (SER) is an example of such a process where CO₂ capture offers significant energy savings (≈23%). Besides, feedstock to this process may include different sources of biofuels. An essential part of this new reaction system is the use of a solid CO₂ absorbent. Among absorbents stands lithium orthosilicate (Li₄SiO₄) for its high absorption capacity and thermal stability. Therefore, the present research aims to study and model the kinetics of CO₂ absorption by Li₄SiO₄ in a temperature range of 550–650 °C. Results were consistent with a first order reaction dependence with respect to CO₂ concentration. Apparent activation energy of the gas–solid reaction (22.5 kcal/mol) is approximately equal the intrinsic activation energy (28.6 kcal/mol), suggesting that the surface reaction resistance determines the overall reaction rate.     

Enhanced ethanol steam reforming by CO2 absorption using CaO,CaO*MgO or Na2ZrO3

This paper presents results of thermodynamic analysis and experimental evaluation of hydrogen production by steam reforming of ethanol (SRE) combined with CO₂ absorption using a mixture of a solid absorbent (CaO, CaO*MgO and Na₂ZrO₃) and a Ni/Al₂O₃ catalyst. Thermodynamic analysis results indicate that a maximum of 69.5% H₂ (dry basis) is feasible at 1 atm, H₂O/C₂H₅OH = 6 (molar ratio) and T = 600 °C. whereas, the addition of a CO₂ absorbent at 1 atm, T = 600 °C and H₂O/C₂H₅OH/Absorbent = 6:1:2.5, produced a H₂ concentration of 96.6, 94.1, and 92.2% using CaO, CaO*MgO, and Na₂ZrO₃, respectively. SRE experimental evaluation achieved a maximum of 60% H₂. While combining SRE and a CO₂ absorbent exhibited a concentration of 96, 94, and 90% employing CaO, CaO*MgO, and Na₂ZrO₃, respectively at 1 atm, T = 600 °C, SV = 414 h⁻¹ and H₂O/C₂H₅OH/absorbent = 6:1:2.5 (molar ratio).     

A review on wind energy and wind–hydrogen production in Turkey: A case study of hydrogen production via electrolysis system supplied by wind energy conversion system in Central Anatolian Turkey

Studies about investigation of hydrogen production from wind energy and hydrogen production costs for a specific region were reviewed in this study and it was shown that these studies were rare in the world, especially in Turkey. Therefore, the costs of hydrogen, hydrogen production quantities using a wind energy conversion system were considered as a case study for 5 different locations of Nigde, Kirsehir, Develi, Sinop and Pinarbasi located in the Central Anatolia in Turkey. Annual wind energy productions and costs for different wind energy conversion systems were calculated for 50 m, 80 m and 100 m hub heights. According to wind energy costs calculations, the amounts and costs of hydrogen production were computed. Furthermore, three different scenarios were taken into account to produce much hydrogen. The results showed that the hydrogen production using a wind energy conversion system with 1300 kW rated power had a range from 1665.24 kgH₂/year in Nigde at 50 m hub height to 6288.59 kgH₂/year in Pinarbasi at 100 m hub height. Consequently, Pinarbasi and Sinop have remarkable wind potential and potential of hydrogen production using a wind–electrolyzer energy system.     

Curtailed electricity and hydrogen in Association of Southeast Asian Nations and East Asia Summit: Perspectives form an economic and environmental analysis

This study examines how well producing hydrogen via electrolysis from curtailed electricity from renewables could fulfil environmental benefits against the cost of producing hydrogen via electrolysis in the context of the Association of Southeast Asian Nations (ASEAN) and the East Asia Summit (EAS). The cost of producing hydrogen via electrolysis ranges from less than USD² per kgH₂ when the electrolyser load factor is 1500 h or above to USD10 per kgH₂ or even higher when the electrolyser load factor is 500 h or lower. The amount of CO₂ emissions abated by hydrogen produced from curtailed electricity from renewables ranges from about 130 million tonnes to about 150 million tonnes for ASEAN and from about 18,000 million tonnes to about 19,000 million tonnes for EAS. Applying prevailing carbon prices to the CO₂ emissions abated, the possible monetised benefits of hydrogen produced via electrolysis from curtailed electricity from renewables range from about USD0.25 per kgH₂ to about USD9.00 per kg H₂ for ASEAN and from about USD0.50 per kgH₂ to about USD15.00 per kg H₂ for EAS. The results of the cost-benefit analysis suggest that the price of carbon needs to be about USD15 per tonne of CO₂ to justify hydrogen produced via electrolysis from curtailed electricity from renewables for both ASEAN and EAS. The results also suggest that high electrolyser load factors make hydrogen produced via electrolysis from curtailed electricity from renewables cost-competitive even under low carbon prices.     

Solar syngas production from CO2 and H2O in a two-step thermochemical cycle via Zn/ZnO redox reactions: Thermodynamic cycle analysis

Solar syngas production from CO₂ and H₂O is considered in a two-step thermochemical cycle via Zn/ZnO redox reactions, encompassing: 1) the ZnO thermolysis to Zn and O₂ using concentrated solar radiation as the source of process heat, and 2) Zn reacting with mixtures of H₂O and CO₂ yielding high-quality syngas (mainly H₂ and CO) and ZnO; the ZnO is recycled to the first, solar step, resulting in net reaction βCO₂ + (1 − β)H₂O → βCO + (1 − β)H₂. Syngas is further processed to liquid hydrocarbon fuels via Fischer-Tropsch or other catalytic processes. Second-law thermodynamic analysis is applied to determine the cycle efficiencies attainable with and without heat recuperation for varying molar fractions of CO₂:H₂O and solar reactor temperatures in the range 1900-2300 K. Considered is the energy penalty of using Ar dilution in the solar step below 2235 K for shifting the equilibrium to favor Zn production.     

Co-digestion of cassava starch wastewater with buffalo dung for bio-hydrogen production

Batch and continuous modes for bio-hydrogen production by co-digesting cassava starch wastewater with buffalo dung were investigated. Response surface methodology with central composite design was used to optimize the bio-hydrogen production conditions. A hydrogen production potential of 1787 mL H₂/L was achieved under optimal conditions of 2.84 g/L of NaHCO₃, an initial pH of 6.77 and a total chemical oxygen demand (tCOD)/total nitrogen ratio of 42.36. A continuous stirred tank reactor was operated under the optimum conditions from batch mode to investigate the effects of hydraulic retention time (HRT) of 72, 60 and 48 h on hydrogen production. The highest hydrogen content, hydrogen production rate and hydrogen yield of 33%, 839 mL H₂/L.d and 16.90 mL H₂/g-COD_added, respectively, were achieved at a HRT of 60 h. The predominant hydrogen producer under the optimal conditions in batch mode was Clostridium sp. while Clostridium sp., Megasphaera sp. and Chloroflexi sp. were observed in the continuous hydrogen production mode at an optimal HRT.     

Biohydrogen production from algal biomass (Anabaena sp. PCC 7120) cultivated in airlift photobioreactor

The present study deals with the optimization of pretreatment conditions followed by thermophilic dark fermentative hydrogen production using Anabaena PCC 7120 as substrate by mixed microflora. Different airlift photobioreactors with ratio of area of downcomer and riser (A_d/A_r) in range of 0.4–3.2 were considered. Maximum biomass concentration of 1.63 g L⁻¹ in 9 d under light intensity of 120 μE m⁻² s⁻¹ was observed at A_d/A_r of 1.6. The mixing time of the reactors was inversely proportional to A_d/A_r. Maximal H₂ production was found to be 1600 mL L⁻¹ upon pretreatment with amylase followed by thermophilic fermentation for 24 h compared to other methods like sonication (200 mL L⁻¹), autoclave (600 mL L⁻¹) and HCl treatment (1230 mL L⁻¹). The decrease of pH from 6.5 to 5.0 during fermentation was due to the accumulation of volatile fatty acids. Amylase pretreatment gave higher reducible sugar content of 7.6 g L⁻¹ as compare to other pretreatments. Thermophilic fermentation of pretreated Anabaena biomass by mixed bacterial culture was found suitable for H₂ production.     

Carbon dioxide reforming of methane in a SrCe0.7Zr0.2Eu0.1O3−δ proton conducting membrane reactor

Utilizing CO₂ for fuel production holds the promise for reduced carbon energy cycles. In this paper we demonstrate a membrane reactor, integrating catalytic CO₂ reforming of methane with in-situ H₂ separation, that results in increased CO₂ and CH₄ conversion and H₂ production compared to a Ni catalyst alone. The tubular proton-conducting SrCe_0.7Zr_0.2Eu_0.1O_3−δ membrane reactor demonstrates that the addition of the membrane improves CO₂ conversion, due to in-situ H₂ removal, by 10% and 30% at 900 °C for CH₄/CO₂ = 1/1 and CH₄/CO₂/H₂O = 2/1/1 feed ratios, respectively. It also improves total H₂ production at 900 °C by 15% and 18% for CH₄/CO₂ = 1/1 and CH₄/CO₂/H₂O = 2/1/1, respectively. Further, the H₂/CO in the reactor side effluent can be adjusted for subsequent desired Fischer-Tropsch products by combining CO₂ reforming and steam reforming of methane.     

Hydrogen production via steam reforming of methanol over Cu/(Ce,Gd)O2−x catalysts

Hydrogen production via steam reforming of methanol is carried out over Cu/(Ce,Gd)O_2−x catalysts at 210–600 °C. The CO content in reformate is about 1% at 210–270 °C, which are the typical temperature for hydrogen production via steam reforming of methanol. Largest H₂ yield and CO₂ selectivity and smallest CO content are obtained at 240 °C. The formation rate of CO increases with increasing temperature. The average formation rate of CO becomes larger than that of CO₂ at about 450 °C. The H₂ yield, the CO₂ selectivity and the CO content become constant at about 550 °C. At 240 °C, the smallest CO content is obtained with a catalyst weight of 0.5 g and a Cu content of 3 wt%. The H₂ yield, defined as H₂/(CO + CO₂) in formation rates, at 240 °C is always 3 and not affected by the variations of either the catalyst weight or the Cu content.     

Catalytic performance of steam reforming of ethanol at low temperature over LaNiO3 perovskite

A LaNiO₃ perovskite catalyst was prepared using the coprecipitation–oxidation hydrothermal method, followed by calcination at 600 °C for 2 h. The as-prepared sample was composed of La(OH)₃ in nanorod structures and was covered with poorly crystalline Ni(OH)₂. The mixed metal hydroxides were converted into cubic LaNiO₃ perovskite after calcination at 600 °C. A catalytic steam reforming of ethanol (SRE) reaction for hydrogen production was performed in a fixed-bed reactor. The catalyst was reduced in situ in hydrogen at 400 °C prior to the reaction. The ethanol conversion reached 100% at 300 °C with 70% hydrogen selectivity. The highly catalytic activity of the reduced catalyst was due to the well-dispersion of Ni particles on the surface of active catalyst was formed in the in situ reduced catalyst. After a 80 h time-on-stream test at 350 °C, the used catalyst presented a La₂O₂CO₃ component that was formed owing to the reaction of the CO₂ product with La₂O₃. La₂O₂CO₃ acted as a carbon reservoir to eliminate the deposited carbon and further stabilized the Ni particles on the La₂O₃ surface, which resulted in the highly catalytic activity during the entire reaction period. The deposited carbon after the SRE reaction was further examined by TGA, TPR, elemental analysis, and TEM.