Hydrogen Molar Yield Research Articles

Performance and mechanism of different pretreatment methods for inoculated sludge in biohydrogen production

A comparison was conducted between pre-culture bacteria (PCB) and heat treatment anaerobic granular sludge (HTAGS) for hydrogen production, and it was found that hydrogen molar yield (HMY) of PCB was 21–35% higher than that of HTAGS. The addition of biochar increased hydrogen production in both cultivation methods by acting as an electron shuttle to enhance extracellular electron transfers of Clostridium and Enterobacter. On the other hand, Fe3O4 did not promote hydrogen production in PCB experiments but had a positive effect on HTAGS experiments. This was due to the fact that PCB was mainly composed of Clostridium butyricum, which could not reduce extracellular iron oxide, resulting in a lack of respiratory driving force. In contrast, HTAGS retained a significant amount of Enterobacter, which possess the ability of extracellular anaerobic respiration. Different pretreatment methods of inoculum resulted in significant changes in the sludge community, thus exerting a noticeable impact on biohydrogen production.

Study on Hydrogen Production by Supercritical Water Gasification of Unsymmetrical Dimethylhydrazine under Multi-Parameters

Unsymmetrical dimethylhydrazine (UDMH) is very toxic and hard to decompose in traditional ways. In this paper, the gasification of unsymmetrical dimethylhydrazine (UDMH) in supercritical water was studied in a batch reactor under different conditions. The hydrogen production process of supercritical water gasification of UDMH in metal containers is a multiphase reaction process. The effects of reaction temperature, alkaline catalysts, residence time, and oxidation on gasification were systematically studied. COD and ammonia nitrogen of the residual liquid were tested. Results showed that the maximum molar fraction and yield of hydrogen were 87.0% and 97.9 mol/kg, respectively, with KOH at 600 °C, 23 MPa. The COD removal efficiency in relation to alkaline catalysts was in the following order: NaOH > Na2CO3 > KOH > K2CO3. The highest COD removal efficiency (up to 95%) can be obtained at the temperature of 600 °C, 23 MPa with NaOH as the catalyst, and a residence time of 20 min. Ammonia nitrogen can be decreased by adding an oxidant. The COD and ammonia nitrogen of the residual liquid can meet the requirement of the Chinese emission standard of water pollution for space propellants. In addition, the organic compounds formed under different conditions were also identified.

The role of anthraquinone-2-sulfonate on biohydrogen production by Klebsiella strain and mixed culture

The role of anthraquinone-2-sulfonate (AQS) on biohydrogen production was explored in this study. The hydrogen molar yield (HMY) of the batch experiment with 0.2 mM AQS was not significantly improved comparing to that without AQS, but the acetate and ethanol yields were increased by 12.1% and 9.82%, respectively. According to the metabolites flux analysis, e- balance calculations and stoichiometry results, the biogenic anthrahydroquinone-2,6,-disulfonate (AH2QS) preferred to improve the H2 generation that catalyzed by hydrogenase, but not likely affect the H2 generation that through formate cleavage pathway (FCP). However, comparing to the mix culture without AQS, the hydrogen production rate and hydrogen yield were increased by 20.97% of 1.96%, respectively, in the presence of AQS. The results of this study provided better understanding of the role of AQS on biohydrogen production by the strain that follows FCP, and the synergistic biohydrogen production by the co-culture that follows FCP and butyrate/acetate pathway.

Hydrogen production and phosphorus recovery via supercritical water gasification of sewage sludge in a batch reactor

In this study, gasification of sewage sludge in supercritical water using a batch reactor was investigated. The effects of temperature, retention time, and the oxidation coefficient on gas composition, gas yield, total organic carbon removal efficiency (XTOC), gasification efficiency (GE), carbon gasification efficiency (CE), and phosphorus release rate (Xp) were investigated. The experimental results indicated that the yields for hydrogen, methane, and carbon dioxide increased with the increase in temperature from 380 °C to 460 °C. A maximum hydrogen molar fraction of 55.72% and a yield of 19.86 mol/kg were obtained at 460 °C and 27 MPa after 6 min. The GE, CE, XTOC, and Xp also increased with the increase in temperature. An extension of the retention time promoted the gasification of sludge, thereby resulting in an increase in the hydrogen and methane molar fraction, yield, GE, CE, XTOC, and Xp. Under the conditions of 420 °C and 27 MPa after 6 min, with an increase in the oxidation coefficient from 1.5 to 2.5, the oxidation reaction became dominant in the supercritical water. Hydrogen and methane were converted to carbon dioxide and water with an excess of hydrogen peroxide, which resulted in a lower hydrogen yield. However, the decomposition of organic compounds in the sludge was promoted with the addition of hydrogen peroxide, thereby resulting in an increase in the GE, CE, XTOC, and Xp. When the oxidation coefficient reached 2.5, a maximum GE of 131.6% and Xp of 98.74% were obtained.

Understanding the NaCl-dependent behavior of hydrogen production of a marine bacterium, Vibrio tritonius.

Biohydrogen is one of the most suitable clean energy sources for sustaining a fossil fuel independent society. The use of both land and ocean bioresources as feedstocks show great potential in maximizing biohydrogen production, but sodium ion is one of the main obstacles in efficient bacterial biohydrogen production. Vibrio tritonius strain AM2 can perform efficient hydrogen production with a molar yield of 1.7 mol H2/mol mannitol, which corresponds to 85% theoretical molar yield of H2 production, under saline conditions. With a view to maximizing the hydrogen production using marine biomass, it is important to accumulate knowledge on the effects of salts on the hydrogen production kinetics. Here, we show the kinetics in batch hydrogen production of V. tritonius strain AM2 to investigate the response to various NaCl concentrations. The modified Han–Levenspiel model reveals that salt inhibition in hydrogen production using V. tritonius starts precisely at the point where 10.2 g/L of NaCl is added, and is critically inhibited at 46 g/L. NaCl concentration greatly affects the substrate consumption which in turn affects both growth and hydrogen production. The NaCl-dependent behavior of fermentative hydrogen production of V. tritonius compared to that of Escherichia coli JCM 1649 reveals the marine-adapted fermentative hydrogen production system in V. tritonius. V. tritonius AM2 is capable of producing hydrogen from seaweed carbohydrate under a wide range of NaCl concentrations (5 to 46 g/L). The optimal salt concentration producing the highest levels of hydrogen, optimal substrate consumption and highest molar hydrogen yield is at 10 g/L NaCl (1.0% (w/v)).

Evaluation of semi-continuous hydrogen production from enzymatic hydrolysates of Agave tequilana bagasse: Insight into the enzymatic cocktail effect over the co-production of methane

This work addresses the hydrogen production from enzymatic hydrolysates of Agave tequilana bagasse and the valorization of the acidogenic effluent for methane production in anaerobic sequencing batch reactors (ASBRs). Regarding hydrogen production, the ASBR was operated at four organic loading rates (OLRs), which were modified by decreasing the cycle time (from 24 to 12 h) and increasing the COD concentration (from 8 to 12 and 16 g L−1). Results showed that the highest OLR promoted the highest hydrogen production rate of 25.2 ± 2.1 NmL L−1 h−1. Conversely, the hydrogen molar yield remained constant, obtaining similar values to the highest reported for lignocellulosic hydrolysates in continuous reactors (1.6H2-mol molconsumed sugar−1). Regarding methane production from the acidogenic effluent, an unexpected methane suppression was observed during the first 5 cycles of the ASBR operation. Such event was attributed to the disaggregation of the granular sludge due to the remaining hydrolytic activity of the enzymatic cocktail used for the hydrolysates production. This was corroborated by feeding acetate to an ASBR (positive control) and supplying the enzymatic cocktail. Overall, even though the ASBR configuration demonstrated its suitability for hydrogen production, further studies are needed to coupling the methanogenic phase in different reactor configurations.

Feasibility of biohydrogen production by co-digestion of vinasse (sugarcane stillage) and molasses in an AnSBBR

Abstract This work studied the feasibility of biohydrogen production by co-digestion of vinasse/molasses in an AnSBBR operated with mechanical stirring (30°C and 200 rpm). Hydrogen production by co-digestion of vinasse/sucrose was also studied to verify the performance of the process with a known co-substrate with easy degradation. The effects of influent composition (vinasse/sucrose and vinasse/molasses), influent concentration (3000 and 4000 mgCOD.L-1) and cycle time (3 and 4 h) on performance indicators were evaluated using stability, organic matter removal efficiency, molar hydrogen yield, productivity and biogas composition. The condition with vinasse/molasses in the influent that showed the best results was obtained with a 3-hour cycle time, influent concentration of 3000 mgCOD.L-1 and composition of 33% vinasse and 67% molasses. The molar productivity in this condition was 3.8 molH2.m-3.d-1 with a hydrogen molar fraction of 16% (and a methane molar fraction of 14%). A first order kinetic model was fitted efficiently to the best conditions.

Simultaneous Decolorization and Biohydrogen Production from Xylose by Klebsiella oxytoca GS-4-08 in the Presence of Azo Dyes with Sulfonate and Carboxyl Groups.

Biohydrogen production from the pulp and paper effluent containing rich lignocellulosic material could be achieved by the fermentation process. Xylose, an important hemicellulose hydrolysis product, is used less efficiently as a substrate for biohydrogen production. Moreover, azo dyes are usually added to fabricate anticounterfeiting paper, which further increases the complexity of wastewater. This study reports that xylose could serve as the sole carbon source for a pure culture of Klebsiella oxytoca GS-4-08 to achieve simultaneous decolorization and biohydrogen production. With 2 g liter-1 of xylose as the substrate, a maximum xylose utilization rate (URxyl) and a hydrogen molar yield (HMY) of 93.99% and 0.259 mol of H2 mol of xylose-1, respectively, were obtained. Biohydrogen kinetics and electron equivalent (e- equiv) balance calculations indicated that methyl red (MR) penetrates and intracellularly inhibits both the pentose phosphate pathway and pyruvate fermentation pathway, while methyl orange (MO) acted independently of the glycolysis and biohydrogen pathway. The data demonstrate that biohydrogen pathways in the presence of azo dyes with sulfonate and carboxyl groups were different, but the azo dyes could be completely reduced during the biohydrogen production period in the presence of MO or MR. The feasibility of hydrogen production from industrial pulp and paper effluent by the strain if the xylose is sufficient was also proved and was not affected by toxic substances which usually exist in such wastewater, except for chlorophenol. This study offers a promising energy-recycling strategy for treating pulp and paper wastewaters, especially for those containing azo dyes.IMPORTANCE The pulp and paper industry is a major industry in many developing countries, and the global market of pulp and paper wastewater treatment is expected to increase by 60% between 2012 and 2020. Such wastewater contains large amounts of refractory contaminants, such as lignin, whose reclamation is considered economically crucial and environmentally friendly. Furthermore, azo dyes are usually added in order to fabricate anticounterfeiting paper, which further increases the complexity of the pulp and paper wastewater. This work may offer a better understanding of biohydrogen production from xylose in the presence of azo dyes and provide a promising energy-recycling method for treating pulp and paper wastewater, especially for those containing azo dyes.

Continuous hydrogen production from enzymatic hydrolysate of Agave tequilana bagasse: Effect of the organic loading rate and reactor configuration

Lignocellulosic biomass is a promising alternative energy source, which after pretreatment can be efficiently used as feedstock for biological production of second generation biofuels. Hydrogen is considered an ideal biofuel and its production through dark fermentation has been recognized as a sustainable process. However, more studies with continuous systems are needed for its application at industrial scale. In this study, enzymatic hydrolysate of Agave tequilana bagasse was used for long-term continuous hydrogen production in both, a continuous stirred tank reactor (CSTR) and a trickling bed reactor (TBR), which were operated up to 87days under different organic loading rates (OLR) ranging from 17 to 60gCOD/L-d. Volumetric hydrogen production rate (VHPR) and hydrogen molar yield (HMY) in CSTR displayed an inverse correlation with maximum values of 2.53LH2/L-d and 1.35molH2/mol substrate, attained at OLR 52.2 and 40.2gCOD/L-d, respectively. In contrast, increasing OLR up to 52.9gCOD/L-d simultaneously enhanced VHPR and HMY in TBR, attaining values of 3.45LH2/L-d and 1.53molH2/molsubstrate, respectively. Acetate and butyrate were the main metabolites in both reactors, while lactate and propionate were detected in minor concentrations. Metabolites distribution, electron balances and hydrogen production trends obtained from both reactors suggest that CSTR may be more susceptible to inhibition by hydrogen accumulation than TBR. Apparent hydrogen consumption and susceptibility to high solids load were found to limit further OLR increments in CSTR and TBR, respectively.

Optimization, metabolic pathways modeling and scale-up estimative of an AnSBBR applied to biohydrogen production by co-digestion of vinasse and molasses

This study investigated the application of an AnSBBR in biohydrogen production process from the co-digestion of vinasse and molasses. Process performance indicators were evaluated using the organic matter removal efficiency, molar hydrogen yield, productivity and composition of the biogas. The influence of influent composition and concentration, feeding mode (batch/fed batch), need for micronutrient supplementation and inoculum pretreatment were evaluated. Kinetic modeling of the metabolic pathways of the conditions with the highest hydrogen productivity was performed. The results showed that the system was stable under all conditions. The best results were obtained with an influent concentration of 6000 mgCOD L−1, composition of 67–33% vinasse-molasses, without micronutrient supplementation, with inoculum heat shock pretreatment, and batch mode (13.5 molH2 m−3 d−1 with 39% H2). Increasing the percentage of the vinasse in the influent was unfavorable, but increasing the influent concentration, refraining from micronutrient supplementation and performing the inoculum heat shock pretreatment favored the performance indicators. The fitted kinetic model aided the understanding of the metabolic pathways: hydrogen is produced via acetic, butyric and valeric acids routes. Scale up estimation (performed with data of best condition) resulted in a system with 6 discontinuous reactors configured in parallel, each one with a volume of 27,297 m3.

Stoichiometry evaluation of biohydrogen production from various carbohydrates.

In this paper, biochemical hydrogen potential (BHP) tests were conducted to investigate H2 production from different substrate with acid-treated anaerobic digested sludge at the mesophilic range. The sludge was collected from an anaerobic digester and was subjected to sulfuric acid pretreatments at pH 3 for 24h. The effects of substrate type (glucose, fructose, and sucrose as carbon source) were investigated in batch experiments. Results showed that substrate degradation rate for all of the substrates was up 95% and the electron equivalent balance showed good closure for glucose and sucrose. Batch experiments showed that the maximum molar hydrogen yield with glucose, fructose, and sucrose was 3.27, 3.16, and 6.46mol H2/mol of substrate. The maximum cumulative biohydrogen production was 1552, 1487, and 1366mL and maximum hydrogen production rate was 308, 279, and 275mL/h for glucose, sucrose, and fructose, respectively. The experimental results suggest that the formation of hydrogen associates with the main aqueous products, i.e., acetate butyrate.

Cell wash-out enrichment increases the stability and performance of biohydrogen producing packed-bed reactors and the community transition along the operation time

Most of the fermentative hydrogen production studies based on mixed cultures have shown enrichment of the microbial community by means of a heat treatment. This heat treatment enrichment strategy selects for Clostridum spp., an efficient hydrogen producer; however, other bacteria that may contribute to the systems performance could be excluded. Another enrichment strategy based on high dilution rates selects different taxonomic groups, which may affect hydrogen production and the system stability. In this work, two enrichment strategies were evaluated, heat shock and cell wash-out, for hydrogen production and the system stability in continuous stirred reactors. The enriched communities were then inoculated in packed bed reactors and operated up to 70 days. Both strategies selected hydrogen producing bacteria, mainly Clostridium spp. The highest hydrogen production rate (6.01 L H2/L-d), molar yield (1.29 mol H2/mol glucoseconsumed), and stability were achieved by the wash-out procedure; this high performance was attributed to facultative bacteria like Lactobacillus and Lactococcus. Furthermore, there was a transition within the community (along the operation time in the reactor with cell wash-out inoculum) and a selection for methanogenic activity (due to the long solids retention time).

Enhanced biohydrogen production from corn stover by the combination of Clostridium cellulolyticum and hydrogen fermentation bacteria

Hydrogen was produced from steam-exploded corn stover by using a combination of the cellulolytic bacterium Clostridium cellulolyticum and non-cellulolytic hydrogen-producing bacteria. The highest hydrogen yield of the co-culture system with C. cellulolyticum and Citrobacter amalonaticus reached 51.9L H2/kg total solid (TS). The metabolites from the co-culture system were significantly different from those of the mono-culture systems. Formate, which inhibits the growth of C.cellulolyticum, could be consumed by the hydrogen-evolving bacteria, and transformed into hydrogen. Glucose and xylose were released from corn stover via hydrolysis by C.cellulolyticum and were quickly utilized in dark fermentation with the co-cultured hydrogen-producing bacteria. Because the hydrolysis of corn stover by C.cellulolyticum was much slower than the utilization of glucose and xylose by the hydrogen-evolving bacteria, the sugar concentrations were always maintained at low levels, which favored a high hydrogen molar yield.

Enhanced H2 Production and Redirected Metabolic Flux via Overexpression of fhlA and pncB in Klebsiella HQ-3 Strain.

Genetic modifications are considered as one of the most important technologies for improving fermentative hydrogen yield. Herein, we overexpress fhlA and pncB genes from Klebsiella HQ-3 independently to enhance hydrogen molar yield. HQ-3-fhlA/pncB strain is developed by manipulation of pET28-Pkan/fhlA Kan(r) and pBBR1-MCS5/pncB Gm(r) as expression vectors to examine the synchronous effects of fhlA and pncB. Optimization of anaerobic batch fermentations is achieved and the maximum yield of biohydrogen (1.42 mol H2/mol of glucose) is produced in the range of pH 6.5-7.0 at 33-37 °C. Whole cell H2 yield is increased up to 40 % from HQ-3-fhlA/pncB, as compared with HQ-3-fhlA 20 % and HQ-3-pncB 12 % keeping HQ-3-C as a control. Mechanism of improved H2 yield is studied in combination with metabolic flux analysis by measuring glucose consumption and other metabolites including formate, succinate, 2,3 butanediol, lactate, acetate, ethanol, and hydrogen. The results suggest that under transient conditions, the increase in the total level of NAD by NAPRTase can enhance the rate of NADH-dependent pathways, and therefore, final distribution of metabolites is changed. Combined overexpression of fhlA and pncB eventually modifies the energy and carbon balance leading to enhanced H2 production from FHL as well as by NADH pathway.

(Invited) Fermentative Hydrogen Production from Biomass in the Cellulose-Degrading Bacterium Clostridium Thermocellum

Hydrogen can be produced from diverse energy sources, using a variety of process technologies. One promising route for biological hydrogen production is via the fermentation of renewable lignocellulosic biomass. However, due to its crystallinity, biomass has to undergo a thermochemical pretreatment step in order for microbes to ferment its cellulose and hemicellulose constituents. Clostridium thermocellum is a thermophilic (55 – 60oC) and anaerobic bacterium which displays one of the highest growth rates on cellulose. C. thermocellum is capable of simultaneous biomass hydrolysis and fermentation in one integrated step, which could be a potential cost saver. During cellulose fermentation, the bacterium produces hydrogen, ethanol, formate, lactate, acetate, and CO2. To reduce the cost of hydrogen production, we aim to overcome several technical barriers identified by the DOE Fuel Cell Technologies Office. To reduce the feedstock cost barrier, we optimized cellulose fermentation in bioreactors, operating in either batch or fed-batch mode. In the latter mode we tested parameters including hydraulic retention time, and amount and frequency of liquid replacement. To circumvent the low hydrogen molar yield barrier (mol H2/mol hexose), we conducted genetic engineering by redirecting metabolic pathways toward maximal hydrogen production lieu of reduced carbon byproducts. Lastly, a techno-economic analysis is underway to set the targets and to guide future research direction to deliver low cost hydrogen. This effort would rely on standardization of metrics in the fermentation technology to assess more accurately as to its economic viability.

Inoculum pretreatment promotes differences in hydrogen production performance in EGSB reactors

Hydrogen production by dark fermentation is one of the most promising methods for obtaining clean energy. Inoculum pretreatments allow the selection of bacteria that have better performance in hydrogen production, because the selection of pretreatment limits the presence of some species while favoring others. In order to elucidate the inoculum pretreatment influence during the operation of two EGSB reactors, two pretreatments were assayed: heat shock and cell wash-out. Different organic loading rates (24–60 g glucose/L d) and hydraulic retention times (10–4 h) were applied to both reactors to determine population dynamics along 100 days of operation. Reactors exhibited differences in both volumetric hydrogen production rate and molar yield but with cell wash-out pretreatment showing better performance than heat shock pretreatment. Maximum molar yield (0.92 mol H2/mol hexose) and volumetric hydrogen production rate (4.23 L H2/L d) were obtained with organic loading rates of 36 g glucose/L d at HRT of 10 h in EGSB reactor inoculated with cell wash-out pretreated sludge. The microbial community of the reactors samples was analyzed by 16S rRNA genes profiles and the predominant bands were excised and their DNA sequence determined. Clostridium and representatives of Enterobacteriaceae were dominant, with a strong presence of Lactobacillus genus. The whole result indicates that the inoculum pretreatment has a strong initial effect during early stages of fermentation, after which the operating conditions have a greater impact on reactor performance.

Biohydrogen production from rice straw hydrolyzate in a continuously external circulating bioreactor

The biohydrogen production from rice straw hydrolyzate in a continuously external circulating bioreactor (CECBR) was carried out in this study. The rice straw hydrolyzate was obtained by a concentrated sulphuric acid pretreatment. The original hydrolyzate concentration was 40–50 g total sugar/L. The feeding concentration of hydrolyzate was adjusted to 20 g total sugar/L by tap water. The working volume of CECBR was 300 mL with a height of 22.5 and a width of 7.5 cm respectively. The positions of external circulating ports were 13 and 5 cm high of CECBR with volumetric circulating rate of 9.6 L/min.The average hydrogen production rates (HPR) of 5.52 L/L/d (hydrogen molar yield: 0.72 mol H2/mol hexose) and 16.32 L/L/d (hydrogen molar yield: 1.02 mol H2/mol hexose) were obtained at hydraulic retention time (HRT) 8 and 4 h respectively. The value of hydrogen production rate at HRT 4 h was three times more than that at HRT 8 h. The presence of bacteria Clostridium favors the hydrogen production from the acetic acid and butyric acid metabolic pathways which were determined by DGGE analysis. The biomass could not be maintained in the CECBR by washing out of the bacteria when the feeding rate was lowered to HRT 2 h. This phenomenon resulted in less hydrogen production and ineffective degradation of hydrolyzate. But the continuously external circulating bioreactor could be steady operated at HRT 4 h with an impressive hydrogen production rate by a rice straw hydrolyzate.

Continuous hydrogen production in a trickling bed reactor by using triticale silage as inoculum: effect of simple and complex substrates

AbstractBACKGROUNDPrevious studies have reported that complexity of the substrate, type of inoculum and reactor configuration strongly affect fermentative hydrogen production. Therefore, the aim of this study was to evaluate the effect of simple (glucose, xylose and sucrose) and complex (acid and enzymatic oat straw hydrolysates) substrates on the continuous hydrogen production in a trickling bed reactor. Novel inoculum (triticale silage) and biofilm support configuration (vertically organized PET tubing) were tested.RESULTSThe enzymatic hydrolysate was a suitable substrate for hydrogen production, since its hydrogen molar yield was similar to that obtained with glucose, mean values of 1.6 and 1.7 mol H2 mol−1 sugar consumed were obtained, respectively. In contrast, hydrogen was not produced from the acid hydrolysate. The highest hydrogen production rate (840 mL H2 L−1 h−1) was obtained with glucose at an organic loading rate of 160 g COD L−1 d−1. In spite of the high organic loading rate applied, clogging due to excessive biomass growth was not observed. Finally, PCR‐DGGE analysis revealed that bacteria from Clostridium genus were the putative responsible for hydrogen production.CONCLUSIONThis work demonstrates that continuous hydrogen production is affected by complexity of the substrate. Furthermore, it also shows the feasibility of using triticale silage as inoculum in hydrogen production systems. © 2014 Society of Chemical Industry

Enhanced hydrogen production by a newly described heterotrophic marine bacterium, Vibrio tritonius strain AM2, using seaweed as the feedstock

To achieve more stable bio-hydrogen (bioH2) production from non-food feedstocks, stable feedstock preparations of marine biomass and an efficient bioH2 system using marine bacteria under saline conditions are two important key technologies that needed to be developed. Vibrio tritonius strain AM2, which was isolated from the gut of a marine invertebrate, was cultured under various conditions in marine broth (at initial 2.25% (w/v) NaCl) supplemented with mannitol, a seaweed carbohydrate, to evaluate its hydrogen production. The maximum molar yield of bioH2 was recorded as 1.7 mol H2/mol mannitol at pH 6 and 37 °C. The mannitol-grown cells had higher yields of bioH2 than the glucose-grown cells in the pH range 5.5–7.5. Compared to glucose, mannitol might be a better substrate for bioH2 production using strain AM2. Fermentation product profiling revealed that strain AM2 might be utilising the formate-hydrogen pathway for bioH2 production. Furthermore, strain AM2 was able to produce hydrogen from powdered brown macroalgae containing 31.1% dry weight of mannitol. The molar yield of hydrogen reached 1.6 mol H2/mol mannitol contained in the seaweed feedstock. In conclusion, strain AM2 has the ability to produce hydrogen from mannitol with high yields even under saline conditions.

Optimization of biohydrogen inoculum development via a hybrid pH and microwave treatment technique – Semi pilot scale production assessment

The interactive effect of a hybrid pH and microwave pre-treatment on a mixed inoculum for biohydrogen production was investigated. Response surface methodology (RSM) was employed to obtain the optimum pre-treatment conditions of pH, microwave duration and microwave intensity for maximum hydrogen yield. The obtained model had a coefficient of correlation (R2) of 0.87. The optimum inoculum pre-treatment conditions predicted were pH 11 and 2 min microwave treatment at 860 W and the validation experiments demonstrated a 32.41% increase on hydrogen yield.Two semi pilot scale-up processes were carried out in a 10 L bioreactor initiated in batch mode with 7 L working volume using the optimally pre-treated inoculum. In the absence of pH control, 46% of glucose was utilized corresponding to a molar hydrogen yield of 1.78 mol H2/mol glucose and a maximum hydrogen fraction of 49.3% whereas under controlled pH environment, a twofold increase in glucose utilization was obtained which corresponds to a molar hydrogen yield of 2.07 mol H2/mol glucose and a maximum hydrogen concentration of 56.4%.The controlled fermentation significantly improved biohydrogen production in the scale-up process and methane production was completely suppressed suggesting the effectiveness of the combined pre-treatment to enrich hydrogen producing bacteria. Viable counts and microscopical analysis indicated the presence of hydrogen producing endospore forming presumptive Clostridum species.