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Dark Fermentative Hydrogen Production from Xylose in Different Bioreactors Using Sewage Sludge Microflora†
Abstract
In this study, the H2-producing activity of the sewage sludge microflora using xylose as the sole carbon substrate was investigated in three bioreactor systems, including a suspended continuously stirred tank reactor (CSTR), an immobilized-cell continuously stirred anaerobic bioreactor (IC-CSABR), and a powder activated carbon-assisted agitated granular sludge bed (AGSB). For suspended-culture CSTR operations, fermentative H2 production was conducted at different hydraulic retention times (HRT = 4–12 h). The H2 production rate (HPR) was 183 mmol/L/d at HRT = 12 h, but the H2 production rate and yield decreased significantly when the HRT was shortened to 4 h due primarily to the washout of cells. To improve the operational stability of short HRTs, silicone-immobilized cells (IC-CSABR system) and powder activated carbon carriers (AGSB system) were adopted for the reactor systems to either maintain stable biomass concentration in the reactor or enhance biomass content by stimulating sludge granulation. Both IC-CSABR and AGSB showed improved biomass retention while operating at a HRT of 4 h. In particular, the biomass content in the IC-CSABR system (HRT = 2 h) went up to 8.03 g of VSS/L, leading to a drastic enhancement in the H2 production rate (1.06 mol/L/d). Bacterial community analysis by denatured gradient gel electrophoresis (DGGE) indicates a transition in bacterial composition in the CSTR under different HRT conditions. Moreover, under the same HRT (4 h), the major bacterial populations in the AGSB and IC-CSABR reactors were very different from those observed in the CSTR, indicating that the performance of H2 production seemed to be in close connection with the bacterial community structure. Several H2-producing bacterial strains (e.g., Clostridium butyricum and Klebsiella pneumoniae) were also detected in the sludge samples by DGGE and 16S rDNA sequence matching, revealing the effectiveness of the H2-producing sludge used in this study.
... These compounds are of special interest because of their high market value [21,22], especially butyric and lactic acid, which are used as precursors of industrial thermoplastics [23] and biodegradable polymers [24,25]. Although only a few studies have addressed hydrogen and organic acid production using sugarcane bagasse (SCB) hydrolysate [26][27][28][29][30], several studies have used pure xylose as a substrate for the production of biohydrogen [31][32][33][34][35][36][37][38][39], indicating a gap for exploitation within the context of dark fermentation studies. Furthermore, most researchers have used batch reactors in contrast with the few studies conducted in continuous bioreactors. ...
... According to Table 3, the production of the main volatile organic acids was comparable to other studies reported in the literature, while H 2 production was significantly lower. In the studies by Wu et al. [36] and Lin et al. [34], 20 g·L −1 of xylose was used as the initial substrate concentration, which was more than ten-fold higher than the sugar concentrations used to feed the packed-bed reactor in this study. The effect of the temperature should also be considered because other studies with an equivalent substrate concentration reported hydrogen yields higher than those obtained in this study [26,32,34,36]. ...
... In the studies by Wu et al. [36] and Lin et al. [34], 20 g·L −1 of xylose was used as the initial substrate concentration, which was more than ten-fold higher than the sugar concentrations used to feed the packed-bed reactor in this study. The effect of the temperature should also be considered because other studies with an equivalent substrate concentration reported hydrogen yields higher than those obtained in this study [26,32,34,36]. Lin et al. [34] demonstrated that increasing temperatures (from 30 to 50 • C) promoted higher hydrogen yields and production rates. ...
Second-generation (2G) ethanol production has been increasingly evaluated, and the use of sugarcane bagasse as feedstock has enabled the integration of this process with first-generation (1G) ethanol production from sugarcane. The pretreatment of bagasse generates pentose liquor as a by-product, which can be anaerobically processed to recover energy and value-added chemicals. The potential to produce biohydrogen and organic acids from pentose liquor was assessed using a mesophilic (25 °C) upflow anaerobic packed-bed bioreactor in this study. An average organic loading rate of 11.1 g COD·L−1·d−1 was applied in the reactor, resulting in a low biohydrogen production rate of 120 mL·L−1 d−1. Meanwhile, high lactate (38.6 g·d−1), acetate (31.4 g·d−1), propionate (50.1 g·d−1), and butyrate (50.3 g·d−1) production rates were concomitantly obtained. Preliminary analyses indicated that the full-scale application of this anaerobic acidogenic technology for hydrogen production in a medium-sized 2G ethanol distillery would have the potential to completely fuel 56 hydrogen-powered vehicles per day. An increase of 24.3% was estimated over the economic potential by means of chemical production, whereas an 8.1% increase was calculated if organic acids were converted into methane for cogeneration (806.73 MWh). In addition, 62.7 and 74.7% of excess organic matter from the 2G ethanol waste stream could be removed with the extraction of organic acid as chemical commodities or their utilization as a substrate for biomethane generation, respectively.
... In recent years, the immobilized cell systems have become popular alternatives over freecell systems because they are capable of maintaining higher biomass concentrations and operating at higher dilution rates without biomass washout [27]. However, the H 2 production based on immobilized-cell systems has mainly focused on using mesophilic bacteria such as porous glass beads-immobilized growing cells of Clostridium butyricum [28, 29a], agar gels-immobilized cells of Rhodospirillum rubrum [30], agar gels/porous glass beads-immobilized cells of aciduric Enterobacter aerogenes HO-39 [29b], lignocellulosic materialssupported Enterobacter cloacae IIT-BT08 [27], immobilized sewage sludge [31,32], polydimethylsiloxane-immobilized microbial consortia [33], and so on. To the best of our knowledge, until now, there has been no research on enhanced H 2 production using immobilized cells of T. neapolitana on porous glass bead. ...
... Hexose (glucose) and pentose (xylose) are the hydrolyzed products of lignocellulosic materials and they respectively account for 55-65 % and 35-45 % in the total mass [32]. These substrates were used for H 2 production by T. neapolitana [4,5,9,15,23,34]. ...
... The substrate utilization was observed to be faster in the immobilized cells compared to the suspended cells (Figure 1). A similar result was obtained from previous report [27][28][29][30][31][32][33][34][35][36][37][38]. found that H 2 production and substrate consumption with immobilized cells of Clostridium butyricum on porous glass beads were higher than the corresponding values with free cells. ...
... Fermentative hydrogen production from hexose, glucose and sucrose is well studied [11e15]. In contrast, fermentative hydrogen production of xylose (i.e., pentose) is less studied [14,16,17]. Several authors [16,18,19] have obtained high yields of biological hydrogen production from xylose, though such testing have been performed with high concentrations (10e20 g xylose/L) with additions of nutrient rich media (yeast extract, peptone, among others). ...
... Several compounds such as glucose, hexose isomers and polymers as starch or cellulose, give different hydrogen yields per mole of organic substrate, depending on the fermentative pathway and on the end products formed. Diverse wastewater from agriculture, wood processing and the paper industry may contain xylose [14,16]. Waste containing simple compounds such as sugar is readily degradable, requiring low hydraulic retention time, whereas complex wastes, for example, chlorinated organic compounds, are slowly degradable and need longer hydraulic retention time for their metabolism [8]. ...
... The major components of lignocellulosic hydrolysate include hexose (glucose) and pentose (xylose and trace amount of arabinose) [19]. The lignin cellulosic materials may contain 35e45% of xylose in their composition [14]. Glucose and sucrose are excellent substrates for fermentative hydrogen production and they have been well studied using pure cultures and consortia of anaerobic bacteria as hydrogen producers. ...
Environmental from tropical climate countries as sediments in standing waters are complex habitats which are able to provide favorable living conditions for manifold microbial species. The aim of this study was to evaluate the diversity of the anaerobic bacteria present in the sediment of the reservoir and its application in biological production of hydrogen gas. The anaerobic batch reactors showed a xylose consumption of 63.5% at 72 h of operation with yield of H2 production of 0.3 (mol H2/mol xylose) at 37 °C, pH 5.5. Molecular biology techniques used for genomic DNA extraction, cloning, sequencing and phylogenetic analyses of the sediment sampling revealed clones similar to the phyla Proteobacteria, Chloroflexi, Firmicutes, Deferribacteres, Fusobacteria, Cyanobacteria and uncultured bacteria. The analysis of DGGE revealed changes in microbial populations from the sediment and the anaerobic consortia of bacteria from the reactors fed with xylose. Anaerobic bacteria coming from the sediment, mainly rods forming endospores from Phylum Firmicutes were favored by the experimental conditions imposed and they were probably involved in the biologic process of the H2 production.
... In recent years, the immobilized cell systems have become popular alternatives over freecell systems because they are capable of maintaining higher biomass concentrations and operating at higher dilution rates without biomass washout [27]. However, the H 2 production based on immobilized-cell systems has mainly focused on using mesophilic bacteria such as porous glass beads-immobilized growing cells of Clostridium butyricum [28, 29a], agar gels-immobilized cells of Rhodospirillum rubrum [30], agar gels/porous glass beads-immobilized cells of aciduric Enterobacter aerogenes HO-39 [29b], lignocellulosic materialssupported Enterobacter cloacae IIT-BT08 [27], immobilized sewage sludge [31,32], polydimethylsiloxane-immobilized microbial consortia [33], and so on. To the best of our knowledge, until now, there has been no research on enhanced H 2 production using immobilized cells of T. neapolitana on porous glass bead. ...
... Hexose (glucose) and pentose (xylose) are the hydrolyzed products of lignocellulosic materials and they respectively account for 55-65 % and 35-45 % in the total mass [32]. These substrates were used for H 2 production by T. neapolitana [4,5,9,15,23,34]. ...
... The substrate utilization was observed to be faster in the immobilized cells compared to the suspended cells (Figure 1). A similar result was obtained from previous report [27][28][29][30][31][32][33][34][35][36][37][38]. found that H 2 production and substrate consumption with immobilized cells of Clostridium butyricum on porous glass beads were higher than the corresponding values with free cells. ...
... Although only a few studies have addressed hydrogen production with sugarcane bagasse hidrolisate (Pattra et al., 2008 and Kongjan et al., 2009), several studies have used xylose as a substrate for the production of biohydrogen (Fangkum and Reungsang, 2011; Maintinguer et al., 2011; Lin and Cheng, 2006; Lin et al., 2008; Zhao et al., 2010; Wu et al., 2008). Furthermore, most ...
... The substrate concentration and temperature likely played fundamental roles in the packed-bed reactor performance in this study. In some studies conducted (Wu et al., 2008 and Lin et al., 2008), 20 g O 2 L -1 of xylose was used as the substrate, which was more than ten-fold higher than the sugar concentrations used to feed the packed-bed reactors in the present study. The effect of temperature was probably more important than the initial substrate concentration. ...
... This phenomenon is also observed when comparing the volatile organic acid production results in this study to the reported by another works (Maintinguer et al., 2011 and Patra et al., 2008). Furthermore, the volatile organic acid production resulting from the use of sugarcane bagasse hydrolysate in experimental condition II was higher than that obtained in studies utilizing other reactor configurations, even when higher temperatures and substrate concentrations were used (Lin et al., 2008 and Wu et al., 2008). ...
Xylose and sugarcane bagasse hydrolysate as carbon source for a continuous anaerobic acidogenic bioreactor with fixed-bed --Manuscript Draft--Manuscript Number: IWA-10805 Full Title: Xylose and sugarcane bagasse hydrolysate as carbon source for a continuous anaerobic acidogenic bioreactor with fixed-bed Article Type: Outline Paper for Oral Presentation Abstract: This study assesses an upflow anaerobic packed-bed bioreactor that processes sugarcane bagasse hydrolysate to obtain biohydrogen and organic acids. In addition, a control containing only xylose as the carbon source was assessed. The bioreactor was operated with a hydraulic retention time of 2 hours at 25 ºC. The total carbohydrate influent concentrations were 1,459 and 1,495 mg L-1 in the sugarcane bagasse hydrolysate and the control treatment, respectively. In addition, 54 and 42% of the carbohydrate was converted at pH 4.8 and 4.6, respectively. The mean hydrogen production resulting from the sugarcane hydrolysate treatment was 0.004 L H2 h-1 L-1, and the hydrogen yield was 20 mmol H2 mol-1 xylose. However, more interesting results were obtained regarding volatile organic acid production. The hydrolysate yielded 15,206, 5,388 and 4,607 mg h-1 of acetic, propionic and n-butyric acid, respectively. In contrast, the xylose yielded 2,749, 2,108 and 1,524 mg h-1 of acetic, propionic and n-butyric acid, respectively. Comparisons between the control and hydrolysate operations showed that H2 production was affected by the presence of high sulfate concentrations during the hydrolysis process. These high sulfate concentrations alter the metabolic pathway toward sulfate reduction, which consumes hydrogen from the system. Overall, this system was suitable for producing H2 and organic acids. In addition, these results suggest that increased hydrogen production may be possible under certain conditions. Manuscript Classifications: 59.1: AD as a core technology. Biorefinery; 59.14: Sewage and Industrial wastewater Powered by Editorial Manager® and Preprint Manager® from Aries Systems Corporation
... During the last two decades, mixed culture dark anaerobic fermentation of carbohydrates to produce H 2 has been studied extensively and has been shown to be economical, immediately potential and industrially feasible [2]. It could combine waste reduction with high H 2 production rate and use the same hardware of the industrial methane (CH 4 ) fermentation [3,4]. Almost all of the studies reported on H 2 production via the dark fermentation focused on characterizing and optimizing substrates, reactor designs, culture pre-treatments, and operational parameters. ...
... In anaerobic digestion, reduced organic substrates are degraded and converted into CH 4 and carbon dioxide (CO 2 ) by a series of biochemical reactions through the metabolic interactions of physiologically unique groups of anaerobic microorganisms (Fig. 1). The major stages of degradation are hydrolysis, acidogenesis, acetogenesis, and methanogenesis; they occur synergistically in a successive fashion such that a product of one reaction becomes a substrate for the next reaction. ...
... Mixed culture dark fermentation is a natural process evolved to maximize the cell growth but not the H 2 yield [22]. The byproducts (H 2 , VFAs and alcohols) are ultimately converted into CH 4 . In balanced mixed culture fermentation, H 2 is produced through hydrogenases activity as an intermediate by-product accompanying acetate and butyrate formation ( Fig. 2) [22]. ...
This paper is a comprehensive review of H2 consumption during anaerobic mixed culture
H2 dark fermentation with a focus on homoacetogenesis. Homoacetogenesis consumed
from 11% to 43% of the H2 yield in single and repeated batch fermentations, respectively.
However, its quantification and extent during continuous fermentation are still not well
understood. Models incorporating thermodynamic and kinetic controls are required to
provide insight into the dynamic of homoacetogenesis during H2 dark fermentation.
Currently, no adequate method exists to eliminate homoacetogenesis because it does not
depend on the culture’s source, pre-treatment, substrate, type of reactor, or operation
conditions. Controlling CO2 concentrations during dark fermentation needs further
investigation as a potential strategy towards controlling homoacetogenesis. Incorporating
radioactive labeling technique in H2 fermentation research could provide information on
simultaneous production and consumption of H2 during dark fermentation. Genetic
studies investigating blocking H2 consuming pathways and enhancing H2 evolving hydrogenases
are suggested towards controlling homoacetogenesis during dark
fermentation.
... In recent years, the immobilized cell systems have become popular alternatives over freecell systems because they are capable of maintaining higher biomass concentrations and operating at higher dilution rates without biomass washout [27]. However, the H 2 production based on immobilized-cell systems has mainly focused on using mesophilic bacteria such as porous glass beads-immobilized growing cells of Clostridium butyricum [28, 29a], agar gels-immobilized cells of Rhodospirillum rubrum [30], agar gels/porous glass beads-immobilized cells of aciduric Enterobacter aerogenes HO-39 [29b], lignocellulosic materialssupported Enterobacter cloacae IIT-BT08 [27], immobilized sewage sludge [31,32], polydimethylsiloxane-immobilized microbial consortia [33], and so on. To the best of our knowledge, until now, there has been no research on enhanced H 2 production using immobilized cells of T. neapolitana on porous glass bead. ...
... Hexose (glucose) and pentose (xylose) are the hydrolyzed products of lignocellulosic materials and they respectively account for 55-65 % and 35-45 % in the total mass [32]. These substrates were used for H 2 production by T. neapolitana [4,5,9,15,23,34]. ...
... The substrate utilization was observed to be faster in the immobilized cells compared to the suspended cells (Figure 1). A similar result was obtained from previous report [27][28][29][30][31][32][33][34][35][36][37][38]. found that H 2 production and substrate consumption with immobilized cells of Clostridium butyricum on porous glass beads were higher than the corresponding values with free cells. ...
Biohydrogen fermentation using immobilized cells of Thermotoga neapolitana on porous glass beads was successfully performed in a continuously stirring anaerobic bioreactor (CSABR) system operated under the conditions of temperature 75 oC, pH 7.0 and 5.0 g/L pentose (xylose) and/or hexose (glucose). The results showed that both batch and fed-batch cultivations of the immobilized cells were effective for high-rate and high-yield H2 production compared with those from the free cells. In the batch cultivation, the H2 production rate and H2 production yield of the immobilized cells, respectively achieved the highest values of 5.64 ± 0.19 mmol-H2L-1h-1 and 1.84 ± 0.1 mol H2/mol xylose, which were almost 1.7-fold and 1.3-fold higher than those with free cells. The maximum H2 production rate (6.91 mmol L-1h-1) in this proposed method was 1.5-fold higher than that of free cells in the fed-batch cultivation.
... Reactors are considered to be practical and economical for industrial H 2 production, particularly via mixed culture fermentation [70,100]. The two main bioreactor conigurations: suspended and atached, or immobilized, growth types have been applied to optimize fermentation process for H 2 production through advancements in active biomass concentration and substrate conversion eiciency [101,115]. Most studies on H 2 production from carbohydrate rich substrates have been conducted in suspended CSTRs, which are simple to construct, easy to regulate both acidity and temperature, and give complete homogeneous mixing for direct contact between the substrate and active biomass [1,70,72]. ...
... In addition, cell density retained in CSTR is limited, since the active biomass has the same retention time as HRT, resulting in process instability caused by the luctuation of environmental parameters, including acidity and then having the consequence of limiting substrate degradation and H 2 production. To overcome the above mention problem, a new coniguration of a continuous low reactor is required to decouple the cell mass retention from HRT and subsequently retain higher cell densities in the reactor, such as UASB and ASBR, which can be achieved through granules and bioilm [47,91,115,116]. Cells immobilization can be employed successfully by using a diluted waste stream with relatively small reactor volumes in ASBR, SAB, and UASB reactors. ...
... Substrate Xylose solution at various concentrations was used as carbon source. Sufficient inorganics were prepared in the substrate to provide the essential nutrients and trace elements for H 2 producing consortia: 382.1 mg/L NH 4 Cl, 87.7 mg/L KH 2 PO 4 , 260.0 mg/L CaCl 2 Á2H 2 O, 320.0 mg/L MgSO 4 Á7H 2 O, 125.0 mg/L FeSO 4 Á7H 2 O, 0.3397 mg/L Zn 2? , 0.3365 mg/L Ni 2? , 1.5747 mg/L Co 2? , 0.2661 mg/L B 3? , 2.8646 mg/L Mn 2? , 5.7380 mg/L I -, 0.1920 mg/L Cu 2? , 0.5950 mg/L Mo 6? (Wu et al. 2008). ...
... Previous studies have reported that conditions with initial pH of 6.0-8.0 and final pH ranged from 5.8 to 7.1 were appropriate for hydrogen under extreme thermophilic condition (Liu et al. 2008;Zhao et al. 2013). The metabolic pathways for fermentative hydrogen production from xylose under anaerobic conditions were acetate-type and butyrate-type fermentation (Wu et al. 2008;Kongjan et al. 2009). Butyrate-type fermentation may be the dominant hydrogen producing metabolic pathways at pH 6.0-8.0. ...
Biohydrogen is considered as one of the most promising energy alternatives considering the climate and energy crisis. The dark fermentative hydrogen production from xylose at extreme thermophilic condition (70 °C) using mixed culture was conducted in this study. The effects of initial pH values (ranged from 5.0 to 10.0) and substrate concentrations (ranged from 2.5 to 15.0 g/L) on the hydrogen production, substrate degradation and metabolite distributions were investigated using batch-mode operations. Results showed that initial substrate pH values in the neutral region (6.0–7.0) were beneficial for hydrogen production. The fermentation at initial pH 7.0 and 7.5 g/L xylose reached an optimal hydrogen yield of 1.29 mol-H2/mol-xyloseconsumed. Ethanol, butyrate, and propionate were the major liquid metabolites. The xylose biodegradation efficiency of the mixed culture decreased sharply at high initial culture pH values. The increase of xylose concentration resulted in the accumulation of propionate and an obvious decrease in the final pH value, as well as a low hydrogen yield. Polymerase chain reaction–denaturing gradient gel electrophoresis analysis indicated that hydrogen producing bacteria were enriched by repeated culture under extreme thermophilic conditions. Also, the mixed culture was dominated with bacterial species related to Clostridium and Thermoanaerobacterium.
... Although only a few studies have addressed hydrogen production with sugarcane bagasse hidrolisate Kongjan et al., 2009), several studies have used xylose as a substrate for the production of biohydrogen (Fangkum and Reungsang, 2011;Maintinguer et al., 2011;Lin and Cheng, 2006;Lin et al., 2008;Zhao et al., 2010;Wu et al., 2008). Furthermore, most of these studies employed batch reactors, in contrast with the few studies that used continuous bioreactors. ...
... This phenomenon is also observed when comparing the volatile organic acid production results in this study to the reported by another works Patra et al., 2008). Furthermore, the volatile organic acid production resulting from the use of sugarcane bagasse hydrolysate in experimental condition II was higher than that obtained in studies utilizing other reactor configurations, even when higher temperatures and substrate concentrations were used Wu et al., 2008). ...
This study assesses an upflow anaerobic packed-bed bioreactor that processes sugarcane bagasse hydrolysate to obtain biohydrogen and organic acids. In addition, a control containing only xylose as the carbon source was assessed. The bioreactor was operated with a hydraulic retention time of 2 hours at 25 ºC. The total carbohydrate influent concentrations were 1,459 and 1,495 mg L-1 in the sugarcane bagasse hydrolysate and the control treatment, respectively. In addition, 54 and 42% of the carbohydrate was converted at pH 4.8 and 4.6, respectively. The mean hydrogen production resulting from the sugarcane hydrolysate treatment was 0.004 L H2 h-1 L-1, and the hydrogen yield was 20 mmol H2 mol-1 xylose. However, more interesting results were obtained regarding volatile organic acid production. The hydrolysate yielded 15,206, 5,388 and 4,607 mg h-1 of acetic, propionic and n-butyric acid, respectively. In contrast, the xylose yielded 2,749, 2,108 and 1,524 mg h-1 of acetic, propionic and n-butyric acid, respectively. Comparisons between the control and hydrolysate operations showed that H2 production was affected by the presence of high sulfate concentrations during the hydrolysis process. These high sulfate concentrations alter the metabolic pathway toward sulfate reduction, which consumes hydrogen from the system. Overall, this system was suitable for producing H2 and organic acids. In addition, these results suggest that increased hydrogen production may be possible under certain conditions.
... Continuous reactors are considered to be practical and economical for industrial hydrogen production, particularly via mixed culture fermentation (van Groenestijn et al., 2002;Hawkes et al., 2007). The two main bio-reactor configurations: suspended and attached, or immobilized, growth types have been applied to optimize mixed culture fermentation process for bio-hydrogen production through advancements in active biomass concentration and substrate conversion efficiency (Gavala et al., 2006;Wu et al., 2008). Most studies on hydrogen production from carbohydrate rich substrates have been conducted in suspended CSTRs, which are simple to construct, easy to regulate both acidity and temperature, and give complete homogeneous mixing for direct contact between the substrate and active biomass (Li and Fang, 2007;Hawkes et al., 2007;). ...
... To overcome the above mentioned problem, a new configuration of a continuous flow reactor is required to decouple the cell mass retention from HRT and subsequently retain higher cell densities in the reactor, such as cell immobilization, which can be achieved through granules and bio-film, (Kotsopoulos et al., 2006;O-Thong et al., 2008;Wu et al., 2008;Zhang et al., 2008). Culture immobilization can be employed successfully by using a diluted waste stream with relatively small reactor volumes in CSTRs, AF reactors, fluidized bed reactors, and UASB reactors. ...
... However, to the best of our knowledge, up to now, there have been no studies reporting the inhibitory effects of added ethanol or propionic acid (propionate) on fermentative hydrogen production. However, in some cases, ethanol can be dominant in the soluble metabolites [9][10][11][12][13][14], and in other cases, propionic acid can be dominant in the soluble metabolites [12,15,16]. At a high concentration, ethanol and propionic acid can also inhibit hydrogen-producing bacteria growth and then inhibit the fermentative hydrogen production accordingly. ...
... However, to the best of our knowledge, up to now, there have been no studies reporting the inhibitory effects of added ethanol or propionic acid (propionate) on fermentative hydrogen production. However, in some cases, ethanol can be dominant in the soluble metabolites [9][10][11][12][13][14], and in other cases, propionic acid can be dominant in the soluble metabolites [12,15,16]. At a high concentration, ethanol and propionic acid can also inhibit hydrogen-producing bacteria growth and then inhibit the fermentative hydrogen production accordingly. ...
The inhibitory effect of added ethanol, acetic acid, propionic acid and butyric acid on fermentative hydrogen production by mixed cultures was investigated in batch tests using glucose as substrate. The experimental results showed that, at 35°C and initial pH 7.0, during the fermentative hydrogen production, the substrate degradation efficiency, hydrogen production potential, hydrogen yield and hydrogen production rate all trended to decrease with increasing added ethanol, acetic acid, propionic acid and butyric acid concentration from 0 to 300mmol/L. The inhibitory effect of added ethanol on fermentative hydrogen production was smaller than those of added acetic acid, propionic acid and butyric acid. The modified Han–Levenspiel model could describe the inhibitory effects of added ethanol, acetic acid, propionic acid and butyric acid on fermentative hydrogen production rate in this study successfully. The modified Logistic model could describe the progress of cumulative hydrogen production.
... The observed similarity in utilization of these carbon sources for biohydrogen production does suggest that the inoculum either may contain microbial strains which catabolize glucose and xylose in similar potential though glucose and xylose metabolism deviate at initial steps of glycolysis or some strains use glucose and other strains use xylose preferentially. This data is in contrast with the reported biohydrogen production values observed municipal sewage sludge as inoculum under identical environments where more than 50% variation depending on the reactor configuration and nature of inoculum i.e., free or immobilized [35,36], substrate type [35,37]. However, Wang and Wan [5] and van Ginkel et al., [38] reviewing the fermentative hydrogen production reported that the noticed variations in these studies may be attributed to differences among these studies at fermentation parameters. ...
... Biohydrogen yields with xylose as carbon source were followed similar pattern to that glucose indicating xylose also can be used as efficient substrate for H 2 production with buffalo dung anaerobic inoculum. Though xylose as carbon source for fermentative biohydrogen production was reported [5,25,28,31,32,45,46] however, most of these studies are associated with pure culture as inoculum and a few with municipal sewage sludge [31,36,46]. Thus the present study assumes importance in view of inoculum developed from buffalo dung for biohydrogen production. ...
Glucose Xylose Glucose to Xylose ratio Mixed anaerobic consortia a b s t r a c t Glucose and xylose are the dominant monomeric carbohydrates present in agricultural materials which can be used as potential building blocks for various biotechnological products including biofuels production. Hence, the imperative role of glucose to xylose ratio on fermentative biohydrogen production by mixed anaerobic consortia was investi-gated. Microbial catabolic H 2 and VFA production studies revealed that xylose is a preferred carbon source compared to glucose when used individually. A maximum of 1550 and 1650 ml of cumulative H 2 production was observed with supplementation of glucose and xylose at a concentration of 5.5 and 5.0 g L À1 , respectively. A triphasic pattern of H 2 production was observed only with studied xylose concentration range. pH impact data revealed effective H 2 production at pH 6.0 and 6.5 with xylose and glucose as carbon sources, respectively. Co-substrate related biohydrogen fermentation studies indicated that glucose to xylose ratio influence H 2 and as well as VFA production. An optimum cumulative H 2 production of 1900 ml for 5 g L À1 substrate was noticed with fermentation medium supplemented with glucose to xylose ratio of 2:3 at pH 6. Overall, biohydrogen producing microbial consortia developed from buffalo dung could be more effective for H 2 production from lignocellulosic hydrolysates however; maintenance of glucose to xylose ratio, inoculum concentration and medium pH would be essential requirements.
... Glucose is easily biodegraded during hydrogen production by fermentation [2] . Conversely, fermentative hydrogen production from xylose is generally inefficient345678. Hydrogen fermentation at high temperatures using thermophilic bacteria has garnered considerable attention due to the high hydrogen production rate, suppression of H 2 consuming bacteria, and ability to utilize numerous substrates [9,10]. ...
... Thermophiles typically generate higher hydrogen yield from xylose (1.7–2.5 mol H 2 mol À1 xylose) than mesophiles (commonly <1 mol H 2 mol À1 xylose). Conversely, with a novel reactor design and cell immobilization technology, the hydrogen production rate from xylose can achieve a high level [8]. Hence, optimizing reactor design should enhance the hydrogen production rate for thermophiles from xylose. ...
Hydrolyzed sugars from lignocellulosic biomass are primarily glucose and xylose. Efficient dark fermentation of isolated strains of both glucose and xylose to generate hydrogen is of considerable practical and academic importance. This study utilized a newly isolated, moderately thermophilic bacterium, W16, to produce hydrogen from xylose, glucose, and mixed xylose and glucose. The strain W16 was identified and designated as Thermoanaerobacterium thermosaccharolyticum W16. Physiology of strain W16 strain with numerous carbon sources and at pH of 4–7.5 and temperature of 30–70 °C was demonstrated. The maximum cumulative H2 yield and H2 production rate obtained using the W16 strain in pure glucose and pure xylose tests were 2.42 mol H2 mol−1 glucose and 12.9 mmol H2 L−1 h−1, and 2.19 mol H2 mol−1 xylose and 10.7 mmol H2 L−1 h−1, respectively. The strain W16 also uptakes mixed xylose and glucose at comparable rates of individual pure sugar tests to produce biohydrogen via an acetate–butyrate-type fermentation. The isolated strain W16 was noted to effectively degrade reducing sugars in hydrolysate of corn stover collected in field.
... The acetates are then decarboxylated by acetoclastic methanogens, resulting in the end products of methane and carbon dioxide. Simultaneously, BioH 2 gas is consumed as an electron donor by hydrogen-utilizing methanogens in the reduction of carbon dioxide to methane (Kapdan and Kargi, 2006;Wu et al., 2008). ...
Biohydrogen (BioH2) is considered as one of the most environmentally friendly fuels and a strong candidate to meet the future demand for a sustainable source of energy. Presently, the production of BioH2 from photosynthetic organisms has raised a lot of hopes in the fuel industry. Moreover, microalgal-based BioH2 synthesis not only helps to combat current global warming by capturing greenhouse gases but also plays a key role in wastewater treatment. Hence, this manuscript provides a state-of-the-art review of the upstream and downstream BioH2 production processes. Different metabolic routes such as direct and indirect photolysis, dark fermentation, photofermentation, and microbial electrolysis are covered in detail. Upstream processes (e.g. growth techniques, growth media) also have a great impact on BioH2 productivity and economics, which is also explored. Technical and scientific obstacles of microalgae BioH2 systems are finally addressed, allowing the technology to become more innovative and commercial.
... Anaerobic fermentation is receiving increasing attention because of its high H 2 yield, simple equipment, easy operation, raw material availability, and low cost. 6 This biogas production is often divided into three stages: hydrolysis, acidogenesis/acetogenesis, and methanogenesis. Thermophilic fermentation is a more popular process for generating H 2 , because this technique can shorten the evolution time and produce more H 2 , although its stability and inhibition problems require further improvement. ...
This study investigated the roles of calcium lignosulfonate (CL) and its derived biochar (BC) in biohydrogen production. CL was pyrolyzed at 250°C to produce BC, and the main characteristics of the two materials were compared. A series of anaerobic processes were carried out at 54±1°C, and the results suggested that CL remarkably lowered the H2 yield compared with that obtained with CL-derived BC. The highest H2 yield (262 mL/g glucose) was obtained at 20 g/L, corresponding to an increase of 50.9%, while the lowest H2 yield (110 mL/g glucose) occurred at 20 g/L and was 36.4% lower than that in the control group (173 mL/g glucose, without CL and BC). The CL-derived BC exhibited more pore structures than CL, providing more attachment sites for anaerobes. In addition, the high potassium, calcium and magnesium contents and low sulfur dosage enhanced the microbial activity and process stability.
... At present, most of the studies on bio-hydrogen production were confined to pure carbohydrates and carbohydrate-rich waste water as substrates (Fan et al., 2004;Wu et al., 2008;Lo et al., 2008a;Lin et al., 2008). Bio-hydrogen production from cellulosic biomass seems to be a better option due to the abundant availability of cellulosic biomass in the earth (Xing et al., 2009). ...
A new hydrogen producing strain with potent cellulose degrading ability was isolated from soil sample collected from sugarcane bagasse (SCB) storage yard. Among the colonies screened, the newly identified strain, Bacillus subtilis AuChE413 has shown better performance in terms of hydrogen yield and cellulose degradation. Morphological, physiological, and biochemical traits of the isolated strain were studied. And its molecular characterization was studied by analyzing the sequence of 16S rRNA gene. The sequence of Bacillus subtilis AuChE413 was compared with other GenBank sequences using BLASTn to study its homology with other species. Phylogenetic tree was constructed using the neighbor joining method. The hydrogen production capacity of Bacillus subtilis AUChE413 was tested by employing the pretreated SCB and sweet sorghum stalk biomass (SSB) as substrates. In comparison, the substrate sorghum stalk has produced the highest hydrogen yield of 55.2 l H2 /kg SSB at pH 7 and 37 °C.
... Enriching H 2producing pure and mixed microbial cultures from anaerobic substrates, mostly sludge are described in several studies [12][13][14]. Usually microbial cultures are used for biodegradation experiments with defined and relatively simple model substrates, for example starch [15], xylose [16] or sewage sludge [8]. Nevertheless, microbiologists are still seeking ideal cultures. ...
Bacteria produce hydrogen during anaerobic dark digestion of carbon rich natural resources including renewable cellulosic materials. The purpose of this work was to study the impact of maize silage pretreatment with Trichoderma fungi, bioaugmentation with defined bacterial inocula and/ or biostimulation with humic acids and an additional inorganic nitrogen source on the fermentative hydrogen production in laboratory batch assay. Experiments were carried out with and without Trichoderma asperellum pretreated silage. The selected bacterial inocula consisted of Clostridium, Enterobacter and Tissierella species, with or without Bacillus mycoides. Headspace gas composition, the amount of dry particulate matter, chemical oxygen demand and concentration of volatile fatty acids in liquid were determined. Bacterial communities were studied with fluorescence in situ hibridization. The predominant cultivable microbial species were isolated and identified. The study demonstrated a significant increase of hydrogen production from maize silage by indigenous bacteria after pretreatment with Trichoderma in comparison with silage untreated with Trichoderma. From tested factors, pretreatment, biostimulation with additional nutrients (ammonium nitrate and/ or humic acids) and bioaugmentation with defined bacterial inocula, pretreatment demonstrated significant improvement of hydrogen production from maize silage. Thereby, aerobic treatment with Trichoderma could be recommended for the pretreatment of silage for the purpose of fermentative production of hydrogen.
... (1)). Alternatively, only 1.67 mol of hydrogen are obtained when butyrate is produced, as shown in Eq. (2) [28]. ...
Xylose was used to produce hydrogen by anaerobic mixed cultures in elephant dung. The elephant dung was subjected to heat shock (90 ºC for 3 h) and acid (pH 3.0 - 4.0 for 24 h followed by neutralization) pretreatments before using it as a seed inoculum. The results showed that the seed inoculum pretreatment by heat shock produced higher hydrogen gas than acid seed inoculum pretreatment, while untreated seed inoculum gave the lowest hydrogen production. Therefore, seed inoculum by heat shock was suitable for hydrogen production from xylose, arabinose and glucose. It was found that xylose was a preferred pentose sugar for hydrogen production, in which the results were comparable to those of glucose. The initial pH of 8.0 was found to be optimal for hydrogen production from xylose, in which a maximum hydrogen production of 371 mL H2/g VSS and a yield of 1.62 mol H2/mol xylose were obtained. Microbial community analysis by denaturing gradient gel electrophoresis (DGGE) revealed that, under the optimum initial pH of 8.0, the predominant hydrogen producers were Clostridium acetobutylicum and Ethanoligenens sp. In addition, lactic acid bacteria i.e. Bifidobacterium minimum and Bifidobacterium sp. were observed, which coincided with the small amount of lactic acid detected at this optimum initial pH.
... Chen et al. (2006) relataram que a produção de hidrogênio por K. pneumoniae através da fermentação de glicose estava associada com a atividade da nitrogenase. Por meio de análises de comunidade bacterianas por DGGE, foi observada presença de Klebsiella pneumoniae durante operação de agitated granular sludge bed (AGSB) reactor usado na produção de H 2 sob TDH de 12, 2, 1 e 0,5 h (Wu et al., 2008). Em RALF de produção de H 2 , alta produção de EtOH ocorreu provavelmente devido a dominância de Klebsiella sp. ...
... could result in a low hydrogen production in which the activity of hydrogenase could be inhibited [33]. Our results revealed that pH range 7.0e8.0 lowered the level of hydrogen production (120e160 ml) (Fig 2), which was in agreement with the findings that increasing pH causes a decrease in hydrogen production owing to a switch in the metabolism of sugar [20,25,52,55] and the cell growth at a higher pH was more efficient than the hydrogen production [54]. Thus an increase in initial pH led to a decrease in HPR, HP and hydrogen yield. ...
The potential use of cassava pulp hydrolysate for fermentative hydrogen production by anaerobic mixed cultures was investigated in laboratory batch fermentation. Cassava was hydrolyzed in autoclave at 121 °C using H2SO4 at different concentrations and reaction times. The optimal conditions obtained were 0.5% H2SO4 at the ratio of 1:15 (dry wt.: volume) for 30 min, which gave the maximum yield of 27.4 g L−1 of total sugar. A series of batch fermentation were investigated for the effects of (1) sources of mixed culture, (2) initial pH, (3) initial substrate concentrations and (4) initial biomass concentrations. The tests were carried out in 100 ml serum bottles to determine the optimal operating conditions for hydrogen production using acid- hydrolyzed cassava pulp as raw material. The results indicated that the UASB granules from the local brewery company yielded the highest bio-hydrogen production at the optimal initial total sugar concentration of 25 g COD L−1 with a biomass concentration of 3.0 g L−1 and the initial medium pH of 5.5 with the peak values of hydrogen yield (HY) of 342 ml H2 g-1CODreduced and the hydrogen production rate (HPR) of 3381 ml H2 L−1 d−1. The optimum substrate/biomass ratio (S0/X0) maximizing the hydrogen yield and formation rate was determined to be 8.33. The results revealed the possibility of using cassava pulp hydrolysate as a fermentation substrate for hydrogen production by the selected mixed culture.
... The model provided a useful approach for predicting optimum conditions for maximum H 2 production by inhibiting the H 2 consumers in the mixed anaerobic cultures. [8] Sewage sludge Continuous 40 6.5 0.8 [51] Hydrogen producing sludge Continuous 50 7.0 1.4 [52] Compost Fed-batch 55 5.0 1.7 [52] Thermoanaerobacterium thermosaccharolyticum W16 Batch 60 6.5 2.19 [3] T. thermosaccharolyticum W16 Batch 60 6.8 2.37 [28] Caldicellulosiruptor saccharolyticus Batch 70 7.2 2.24 [53] Mixed anaerobic micro flora Batch 75 7.3 0.54 [54] Industrial wastewater mixed culture Batch 37 6.7 2.64 This study i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y3 7 ( 2 0 1 2 ) 1 1 7 1 0 e1 1 7 1 8 ...
The role of different chemical and physical factors in enhancing biohydrogen production from xylose using a mixed anaerobic culture was examined under mesophilic conditions. A fractional factorial design (FFD) 3(k–p) was used to optimize pH, the oleic acid (OA) concentration and the biomass concentration. The FFD analysis indicated that the hydrogen (H2) yield was affected by 3 single factors as well as by 2 factor interactions. Under optimum conditions (1600 mg L−1 of oleic acid (OA) and 1900 mg L−1 VSS and pH 6.7), the H2 yield reached 2.64 ± 0.12 mol mol−1 of xylose (80% of the theoretical yield). Based on the ANOVA and Pareto chart analysis, the linear and quadratic OA and pH terms were significant and the linear and quadratic VSS terms were insignificant. Normally distribution of the residuals was confirmed from the Anderson-Darling (AD) plot. The studentized residuals versus the predicted values plot clearly demonstrated that the data points were randomly scattered.
... Table 5 summarizes a lot of studies using continuous reactors for fermentative hydrogen production. As is shown in Table 5, the continuous stirred tank reactor (CSTR) was widely used for continuous fermentative hydrogen production [67][68][69][70][71][72][73][74][75]. ...
... Klebsiella pneumonia (bands 1, 2 and 10) which has been observed in all of the reactors is a facultative anaerobic bacterium that is frequently used for hydrogen production as a pure culture [33,34] or detected as one of the active microorganisms in mixed cultures of hydrogen production systems [35]. Band 3 in CSTR-2 is also a Klebsiella sp. ...
a b s t r a c t This study compared biological hydrogen production from glucose in two continuously stirred tank reactors (CSTRs) and two integrated biohydrogen reactor clarifier systems (IBRCSs) comprising CSTRs with gravity settlers to decouple the hydraulic retention time (HRT) from solids retention time (SRT). The four systems were operated at organic loading rates of 6.5–42.8 gCOD/L-d, and HRTs of 8–12 h. The SRT was maintained at 2 days in the two IBRCSs. The decoupling of SRT from HRT not only increased glucose conversion from 29–50% in the CSTR to 99.9% in the IBRCSs, but also the volumetric hydrogen production from 0.55–1.8 in the CSTRs to 2.4–9.6 L/L-d. Biomass yields in the two IBRCSs were 0.09 and 0.13 g VSS/g glucose converted, about 50% lower than the CSTR yields of 0.19 and 0.29 g VSS/g glucose converted. Hydrogen yield increased from 0.5–1.0 mol H 2 /mol glucose con-verted in the CSTR to 2.8 mol H 2 /mol glucose converted in the IBRCSs. The inverse rela-tionship between hydrogen yield and biomass yield observed in this study implies that the hydrogen yield is maximized with the minimization of biomass yield, thus necessitating decoupling of SRT from HRT to ensure sufficient reactor biomass. DGGE analysis confirmed the specificity of the microbial culture in the IBRCSs with the high-hydrogen producing Clostridium species, as compared to the more diverse cultures in the CSTR.
... Table 5 summarizes a lot of studies using continuous reactors for fermentative hydrogen production. As is shown in Table 5, the continuous stirred tank reactor (CSTR) was widely used for continuous fermentative hydrogen production [67][68][69][70][71][72][73][74][75]. ...
This review summarized several main factors influencing fermentative hydrogen production. The reviewed factors included inoculum, substrate, reactor type, nitrogen, phosphate, metal ion, temperature and pH. In this review, the effect of each factor on fermentative hydrogen production and the advance in the research of the effect were briefly introduced and discussed, followed by some suggestions for the future work of fermentative hydrogen production. This review showed that there usually existed some disagreements on the optimal condition of a given factor for fermentative hydrogen production, thus more researches in this respect are recommended. Furthermore, most of the studies on fermentative hydrogen production were conducted in batch mode using glucose and sucrose as substrate, thus more studies on fermentative hydrogen production in continuous mode using organic wastes as substrate are recommended.
... Xylose is the major constitute of hemicellulose and is thus an abundant organic compound in nature [33]. Further, very few reports available in the literature describing utilization of xylose for fermentative hydrogen production especially with pure isolates [34,35,37]. ...
Present study investigated fermentative hydrogen production of two novel isolates of Enterobacter aerogenes HGN-2 and HT 34 isolated from oil water mixtures. The two isolates were identified as novel strains of E. aerogenes based on 16S rRNA gene. The batch fermentations of two strains from glucose and xylose were carried out using economical culture medium under various conditions such as temperature, initial pH, NaCl, Ni+/Fe++, substrate concentrations for enhanced fermentation process. Both the strains favoured wide range of pH (6.5–8.0) at 37 °C for optimum production (2.20–2.23 mol H2/mol-glucose), which occurred through acetate/butyrate pathway. At 55 °C, both strains favoured 6.0–6.5 and acetate type fermentation was predominant in HT 34. Hydrogen production by HT 34 from xylose was highly pH dependant and optimum production was at pH 6.5 (circa 1.98 mol-H2/mol-xylose) through acetate pathway. The efficiency of the strain HGN-2 at pH 6.5 was 1.92–1.94 mol-H2/mol-xylose, and displayed both acetate and butyrate pathways. At 55 °C, very low hydrogen production was detected (less than 0.5 m mol/mol-xylose).
... Results from Table 4 also indicated that acetate is the second abundant soluble metabolite. Therefore, the hydrogen production by C. butyricum was essentially butyrate-type fermentation and can be described by Eq. (3) [11,31]. Our finding was in accordance with previous report [32][33][34]. ...
Sugarcane bagasse (SCB) used in hydrogen production by Clostridium butyricum was hydrolyzed using H2SO4 at various concentrations (0.25–7.0% volume) and reaction times (15–240 min) at 121 °C, 1.5 kg/cm2 in autoclave. Optimal conditions obtained were 0.5% H2SO4 and 60 min which yielded 24.5 g-COD/L of total sugar. At these conditions, 11 g glucose/L; 11.29 g xylose/L; 2.22 g arabinose/L; 2.48 g acetic acid/L and 0.12 g/L furfural were obtained. Effects of initial pH and substrate concentration on the bio-hydrogen production from SCB hemicellulose hydrolysate by C. butyricum were then investigated. The best hydrogen yield of 1.73 mol H2/mol total sugar and the hydrogen production rate of 1611 mL H2/L/day were obtained at the initial pH 5.5 and initial sugar concentration 20 g-COD/L and compared very favorably with those reported in literature. Results suggested the possibility of using SCB hemicellulose hydrolysate as a fermentation media for hydrogen production by C. butyricum.
As an important raw material for chemical synthesis, hydrogen has been studied in China since the early 1960s. During this stage, hydrogen primarily served as an industrial product. With domestic energy structure transformation and social environmental protection consciousness enhancement, hydrogen energy property gets more attention. Hydrogen as a clean and efficient energy has become the hotspot in research of energy, at the same time in the downstream technologies such as electric cars and fuel-cell progress, also leading to the rapid development of the hydrogen industry. Therefore, the hydrogen energy industry in China will stride into a period of sustained and rapid development, and the role of hydrogen energy in promoting economic and social development will become more and more obvious.
With increasing interest in biohydrogen as an alternative fuel to petroleum, it is essential to identify a hyper biohydrogen producer. In the present study, Clostridium sp. YD09 was isolated from a brewery wastewater upflow anaerobic sludge blanket digestion reactor; its 16 S ribosomal RNA sequencing analysis showed 96% similarity to Clostridium beijerinckii. Clostridium sp. YD09 produced the highest cumulative volume of hydrogen using xylose as the substrate (optimal concentration of 10 g/L) to obtain 1.21 mol H2/mol xylose. Furthermore, Clostridium sp. YD09 tolerates various inhibitors from pre-treated lignocellulosic biomass up to a 0.1% concentration. A maximum yield of 1.62 mol H2/mol xylose and 1.98 mL H2/mL media with 38- to 48-fold increase was recorded in ligno-hemicellulose xylose treated with biochar and activated carbon. The newly isolated Clostridium sp. YD09 can therefore be used for efficient biohydrogen production from xylose-based substrates.
This study represents an integrated and sustainable approach to mine fullest potential of sugarcane bagasse (SCB) for the production of bio-H2 and bioethanol along with organic farming. Experiments were designed in three phases, where feasibility of bio-H2 production was initially evaluated with pure xylose and further validated with real field feedstock (i.e, SCB). Acid pretreatment of SCB with 2% H2SO4 (v/v) yielded xylose rich hydrolysate (21.8g xylose/100g SCB) which was subjected to dark fermentation for bio-H2 and VFA production. Heat pretreated inoculum at pH 7.0 showed maximum bio-H2 fraction of 34.2% (v/v) with corresponding volumetric yield of 204.5 mL H2/g xylose. 5200.6 mg/L of VFA was noted with butyrate and acetate as the major fermentative metabolites. Further, the unhydrolysed biomass recovered after acid hydrolysis of SCB was subjected to simultaneous saccharification and fermentation (SSF) for bioethanol production. SSF of cellulose rich recovered biomass with cellulase enzyme showed 86.56% (w/w) depolymerization of cellulose into glucose and production of 241.25 mg ethanol/g treated SCB by Saccharomyces cerevisiae. Lastly acidogenic effluent (AE) from the bio-H2 process was utilized as phosphate solubilizing organic fertilizer for cultivation of chick pea (Cicer arietinum). Regular supplementation of AE showed beneficial effect on phosphate solubilization in soil and uptake by plant. The obtained results confirm the feasible utilization of segregated streams of SCB for bio-H2 and bioethanol production with integrated organic farming by closing the loop approach. This integrated strategy would extract maximum potential of the agir-biomass feedstock with net-zero waste discharge.
The environmental impacts associated with fossil fuels and depletion of their resources motivated the development of alternate fuels. Hydrogen is an attractive alternate fuel with high heating value and no environmental impact. Although hydrogen is majorly produced by steam reforming, biochemical production especially from carbohydrate rich wastes is of great interest. Hydrogen production from these wastes is carried out by indirect/direct biophotolysis, dark fermentation, two‐stage fermentation and photofermentation. The major constraints of these processes are low hydrogen evolution rate and less yield at large scale. However, effective pretreatment of substrates and inoculum maximize the yield of hydrogen. The factors influence the hydrogen production include nature of microorganism, biochemical process/reactor, temperature, pH, ionic strength, hydraulic retention time, hydrogen and carbon dioxide partial pressure, organic acid concentration, and C/N ratio. The commercial exploitation of biohydrogen production is hindered by lack of high potential microorganism and bioreactor. Hence, it demands multidisciplinary research to understand the fundamental underlying principles besides the development of microbial strains for industrial applications.
Clean fuels are the critical requirement for industrialized world to combat emission of greenhouse gas. Hydrogen is one of the cleanest fuels that generates water as a result of combustion. Production of hydrogen from renewable and nonpolluting resources is an imperative task for sustainable clean fuel production. Biological processes provide an opportunity to produce hydrogen from renewable and economical bio-resources like biomass and solar energy through various processes such as direct/indirect photolysis, photo-fermentation, dark-fermentation, and CO gas-fermentation. This paper provides a comprehensive review on biological hydrogen production including organisms, type of substrates and their concentrations, role of chemical addition, operation conditions such as temperature, pH, and agitation, as well as illumination systems in case of light dependent processes. Further discussions in this work comprise various configuration of integrated biological processes of photolysis, dark, and photo-fermentation such as two component and three-component systems.
This study aims to investigate the effect of solid substrates composition on hydrogen production performances, metabolic pathways and microbial community changes in batch reactor and their dynamics in continuous reactors (CSTR). Hydrogen is an ideal energy carrier which has gained scientific interest over the past decade. Biological H2, so-called biohydrogen, can especially be produced by dark fermentation processes concomitantly with value-added molecules (i.e. metabolic end-products), while organic waste is treated. However, the effect of solid organic waste composition on biohydrogen production in dark fermentation has not yet been clearly elucidated. In this study, a bibliographic review was made on hydrogen production from agricultural waste. This survey on literature showed that diverse performances were reported on hydrogen production due to the variability in substrate compositions and experimental conditions. After having optimized a protocol of biohydrogen potential test (BHP), a wide variety of organic solid substrates aiming to covering a large range of solid waste was tested to provide a comparable data analysis. The results of a PLS regression showed that only soluble carbohydrates or easily available carbohydrates correlated with hydrogen production. Furthermore, hydrogen yields correlated as well with butyrate H2-producing pathway which is consistent with the literature knowledge. A predictive model of hydrogen yield according to carbohydrate content was proposed. Then, experiments were carried out in CSTR with Jerusalem artichoke tubers as a case study. It was shown that low organic loading rate favored continuous hydrogen production while higher organic loading introduced hydrogen competition pathways and decreased the overall hydrogen yields. Moereover, 16S rRNA gene based CE-SSCP profiles showed that increasing OLR had a significant effect on the microbial diversity by favoring the implementation of microorganisms not producing hydrogen, i.e. lactic acid bacteria
There are several main factors influencing fermentative hydrogen production, including inoculum, substrate, reactor type, nitrogen, phosphate, trace heavy metal ion, temperature, and pH. In this chapter, the effect of each factor on fermentative hydrogen production and the advance in the research on the effect were introduced and discussed, followed by some suggestions for the future study of fermentative hydrogen production. There usually existed some disagreements on the optimal condition of a given factor for fermentative hydrogen production, thus more researches in this respect are suggested. Furthermore, most of the studies on fermentative hydrogen production were conducted in batch mode using glucose and sucrose as substrate, thus more studies on fermentative hydrogen production in continuous mode using various organic wastes as substrate are recommended.
Mesophilic hydrogen production from acid pretreated hydrolysate (biomass concentration of 100 g/L and 2% hydrochloric acid) of de-oiled jatropha waste was carried out in continuous system using immobilized microorganisms at various hydraulic retention times (HRTs) ranging from 48-12h. The experimental results of the reusability of immobilized microorganisms showed their stability up to 10 cycles with an average cumulative hydrogen production of 770 mL/L. The peak hydrogen production rate and hydrogen yield were 0.9 L/L∗d and 86 mL/g reducing sugars added, respectively at 16h HRT, with butyrate as the predominant volatile fatty acid. The microbial community analysis revealed that majority of the PCR-DGGE bands were assigned to genus Clostridium and were perhaps the key drivers of the higher hydrogen production.
BACKGROUND
Hydrogen production through anaerobic dark fermentation is considered to be a potential biological process for xylose utilization. Temperature is one of the most important environmental factors. However, most of the studies were carried out under small temperature range. Batch tests were carried out to investigate the temperature effect on hydrogen production from xylose using mixed culture under wide temperature range (35–65 °C). Hydrogen production, metabolite distribution and dynamics of microbial communities were investigated.
RESULTS
Hydrogen-producing cultures were successfully enriched at each tested temperature. Two peaks of fermentation temperatures for hydrogen production were observed at 35 and 55 °C (1.11 and 1.30 mol-H2/mol-xyloseconsumed, respectively). Butyrate and acetate were the major liquid metabolites at 35–60 °C. While at 65 °C the main by-product was ethanol. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis indicated that Clostridium species were dominant at 35–40 °C, while Thermoanaerobacterium was dominated at 45–60 °C. Both species were found at 65 °C, but with lowest microbial community diversity.
CONCLUSION
Hydrogen production efficiency was mainly affected by the liquid metabolite distributions, which depended mainly upon the temperature. Several microbial community structures were formed at mesophilic, transition, thermophilic and extreme-thermophilic conditions, resulting in different metabolic pathways of xylose and hydrogen production capacity.
Anaerobic dark fermentation biohydrogen production from xylose was investigated under mesophilic (35 oC) and thermophilic (55 oC) conditions at various initial pH (5.0-10.0) and substrate concentrations (2.5-12.5 g/L). In addition, the microbial community structures variation under different temperatures were analyzed. It was demonstrated that the maximum hydrogen yield (1.24 mol-H2/mol-xylose) was obtained with substrate concentration of 7.5 g/L and initial cultivation pH 7.0 at 35 oC, with butyrate, acetate, and ethanol as the major by-products. The increase of substrate concentration resulted in accumulation of volatile fatty acids (VFAs), especially propionate, and decrease in final pH under mesophilic condition. However, the hydrogen yield increased along with the increase of substrate concentration at 55 oC with butyrate and ethanol as the main metabolite. Stable pH of the system could be maintained even at high xylose concentration up to 12.5 g/L due to low level of VFAs accumulation. A lower hydrogen yield of 1.14 mol-H2/mol-xylose was obtained at thermophilic condition, while stable operation condition could be achieved and maintained more easily. PCR-DGGE analysis showed that microbial community structures of both systems were dominated with bacterial species related to Clostridium, while thermophilic system had fewer hydrogen-producing microbial species than that at mesothermal condition.
This study investigated the effects of sugar composition and hydraulic retention time (HRT) on continuous hydrogen fermentation. Continuously-stirred tank reactors (CSTRs) were inoculated with heat-treated digester sludge and fed with 15 g/L of glucose, galactose and galactose: glucose mixture (8:2 ratio-simulating the hydrolysate composition of macroalgae) at HRTs of 6-24 h. Peak hydrogen production rate (HPR) and hydrogen yield (HY) of 4.49 L/L/d and 1.62 mol/mol glucoseadded were attained while using glucose as feedstock at HRTs of 6 and 18 h, respectively. Meanwhile, galactose provided a peak HPR and HY of 2.35 L/L/d and 1.00 mol/mol galactoseadded during the HRTs of 12 and 24 h, respectively. In case of mixed sugars (galactose 8: glucose 2) the production performances were inferior to the sole sugar conditions due to the low substrate utilization of less than 65%, which showed a maximal HPR and HY of 2.75 L/L/d and 0.48 mol/mol carbohydrateadded at the HRTs of 6 and 18 h, respectively.
This study evaluated the effects of the organic loading rate (OLR) and pH buffer addition on hydrogen production in two anaerobic fluidized bed reactors (AFBRs) operated simultaneously. The AFBRs were fed with glucose, and expanded clay was used as support material. The reactors were operated at a temperature of 30 °C, without the addition of a buffer (AFBR1) and with the addition of a pH buffer (AFBR2, sodium bicarbonate) for OLRs ranging from 19.0 to 140.6 kg COD m−3 d−1 (COD: chemical oxygen demand). The maximum hydrogen yields for AFBR1 and AFBR2 were 2.45 and 1.90 mol H2 mol−1 glucose (OLR of 84.3 kg COD m−3 d−1), respectively. The highest hydrogen production rates were 0.95 and 0.76 L h−1 L−1 for AFBR1 and AFBR2 (OLR of 140.6 kg COD m−3 d−1), respectively. The operating conditions in AFBR1 favored the presence of such bacteria as Clostridium, while the bacteria in AFBR2 included Clostridium, Enterobacter, Klebsiella, Veillonellaceae, Chryseobacterium, Sporolactobacillus, and Burkholderiaceae.
Dark fermentative hydrogen production by a hot spring culture was studied from different sugars in batch assays and from xylose in continuous stirred tank reactor (CSTR) with on-line pH control. Batch assays yielded hydrogen in following order: xylose > arabinose > ribose > glucose. The highest hydrogen yield in batch assays was 0.71 mol H2/mol xylose. In CSTR the highest H2 yield and production rate at 45 °C were 1.97 mol H2/mol xylose and 7.3 mmol H2/h/L, respectively, and at 37 °C, 1.18 mol H2/mol xylose and 1.7 mmol H2/h/L, respectively. At 45 °C, microbial community consisted of only two bacterial strains affiliated to Clostridium acetobutulyticum and Citrobacter freundii, whereas at 37 °C six Clostridial species were detected. In summary hydrogen yield by hot spring culture was higher with pentoses than hexoses. The highest H2 production rate and yield and thus, the most efficient hydrogen producing bacteria were obtained at suboptimal temperature of 45 °C for both mesophiles and thermophiles.
The rapid development of hydrogen-producing granule (HPG) technologies in recent years has significantly lifted the productivity and stability of anaerobic hydrogen-producing systems and is driving biohydrogen production to a near-practical level. However, the various HPG processes so far are still in infancy, and there exist many barriers to its application. Moreover, our understanding in this area is rather limited. This review introduces the recent advances of HPG technologies in terms of high-rate bioreactor, microbes, process control and characterization techniques, highlights the major remaining challenges toward practical implementation, and discusses the future possibilities and directions for a solution.
Hydrogen production was obtained from low concentrations of xylose metabolized by heat treated inoculum obtained from the slaughterhouse wastewater treatment UASB reactor installed in Brazil. The molecular biological analysis Clostridium and Klebsiella species, recognized as H2 and volatile acid producers, in addition to Burkholderia species and uncultivated bacteria. The assays were carried out in batch reactors: (1) 630.0 mg xylose/L, (2) 1341.0 mg xylose/L, (3) 1848.0 mg xylose/L and (4) 3588.0 mg xylose/L. The following yields were obtained: 3% (0.2 mol H2/mol xylose), 8% (0.5 mol H2/mol xylose), 10% (0.6 mol H2/mol xylose) and 14% (0.8 mol H2/mol xylose), respectively. The end products obtained were acetic acid, butyric acid, methanol and ethanol in all of the anaerobic reactors. The concentrations of xylose did not inhibit microbial growth and hydrogen production. This suggested that low concentrations of xylose should be added to wastewater to produce hydrogen.
Biohydrogen production by batch fermentation of mixed xylose/arabinose at thermophilic temperature using anaerobic mixed cultures in elephant dung as the seed inoculums was investigated. Elephant dung was heat-treated in boiling water for 2h before used as the seed inoculum in order to inhibit methanogenic activity. Biohydrogen was successfully produced from mixed xylose/arabinose. The optimum conditions for hydrogen production were the initial concentration of mixed xylose/arabinose 5g/L each, initial cultivation pH 5.5 and temperature 55°C. Under the optimum conditions, a maximum hydrogen yield of 2.49mol-H2/mol-sugar consumed was obtained. The optimum conditions were then used to produce hydrogen from sugar derived from acid-hydrolysed sugarcane bagasse (SCB) at a reducing sugar concentration of 10g/L in which a lower hydrogen yield of 1.48mol-H2/mol-sugar consumed was achieved. Main soluble product was acetate suggesting the hydrogen fermentation from mixed xylose/arabinose is the acetate type. The dominant hydrogen producers found in both fermentation broth were Thermoanaerobacterium thermosaccharolyticum and Clostridium sp. Lower hydrogen yield in the SCB hydrolysate fermentation broth may be due to the present of Clostridium ragsdalei and microorganisms in the class Bacilli viz. Lactococus lactis subsp., Lactobacillus delbrueckii, and Sporolactobacillus sp. as well as the inhibitors (acetic acid and furfural) contained in the SCB hydrolysate.
Pretreatment and saccharification of lignocellulosic materials is the key technology affecting the efficiency of cellulosic biohydrogen production. In this work, two pure cellulosic materials (i.e., carboxymethyl-cellulose (CMC) and xylan) were directly hydrolyzed (without pretreatment) by a cellulolytic isolate Cellulomonas uda E3-01 able to release extracellular cellulolytic enzymes. Natural cellulosic feedstock (i.e., sugarcane bagasse) was chemically pretreated prior to the bacterial hydrolysis.A temperature-shift strategy (35 °C for cellulolytic enzymes production and 45 °C for hydrolysis reaction) was used to increase the production of reducing sugars during the bacterial hydrolysis. The hydrolysates of CMC, xylan, and bagasse were efficiently converted to H2 via dark fermentation with Clostridium butyricum CGS5. The maximum hydrogen yield was 8.80 mmol H2/g reducing sugar (i.e., 1.58 mol H2/mol hexose) for CMC, 6.03 mmol H2/g reducing sugar (i.e., 0.91 mol H2/mol pentose) for xylan, and 6.01 mmol H2/g reducing sugar for bagasse.
a b s t r a c t Efficient biohydrogen production from lignocellulosic hydrolysate assumes considerable practical and academic importance. The impact of glucose to xylose ratio, medium pH, inoculum size and age on bio-hydrogen production indicated that glucose to xylose ratio is the critical parameter for effective H 2 pro-duction compared to either pure glucose or xylose as carbon source. Inoculum size and its age contributed more than 70% to overall H 2 production and revealed significance at individual as well as interactive level. Maximum interaction of 39% and 32% was noticed with inoculum size and its age vs. glucose to xylose ratio (2:3), respectively. The H 2 production yield enhanced from 140 to 357 ml/g sub-strate upon statistical optimization revealing >240% improvement.
Let enzymes work! H2 was produced from xylose and water in one reactor containing 13 enzymes (red). By using a novel polyphosphate xylulokinase (XK), xylose was converted into H2 and CO2 with approaching 100 % of the theoretical yield. The findings suggest that cell-free biosystems could produce H2 from biomass xylose at low cost. Xu5P=xylulose 5-phosphate, G6P=glucose 6-phosphate.
The interactions of Clostridium sp. and other non-hydrogen producing bacteria directly influence anaerobic hydrogen production. In this study, bacteria in a sucrose-feeding hydrogen-producing bioreactor were investigated via 16S rDNA-based analysis. Results showed that Clostridium pasteurianum, Klebsiella sp., and Streptococcus sp. were the predominant microorganisms. The Streptococcus sp. cells were found to localize inside hydrogen-producing granular sludge and were surrounded by clostridia. Significant oxygen consumption was found in the Klebsiella sp. pure culture experiment, in which oxidation reduction potential (ORP) dropped from 100 to −500 mV during the log phase within 2 h. Oxygen consumption by Streptococcus sp. was not significant, and it accumulated EPS under anaerobic conditions. Results suggest that Klebsiella sp. first utilized the oxygen to form anaerobic conditions in this system. Streptococcus sp., on the other hand, produced EPS complexes to strengthen the sludge granule followed by the mass growth of Clostridium sp.
Non-sterile operation of continuous stirred tank reactor (CSTR) augmented with Clostridium butyricum and fed with sugarcane juice was studied at various hydraulic retention time (HRT). The maximum hydrogen production rate and yield of 3.38 mmol H2/L/h and 1.0 mol H2/mol hexose consumed, respectively, were achieved at HRT 4 h. The relationship of the augmented microorganism and normal flora in the fermentation system under non-sterile condition were analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Initially, at HRT 36 h, other species related to Lactobacillus harbinensis and Klebseilla pneumoniae were present as a major group in the reactor. When HRT was decreased to 12, 6 and 4 h, C. butyricum was present with a competition between L. harbinensis and K. pneumoniae. Results indicated that augmented C. butyricum could compete with contaminated microorganisms during non-sterile operation at low HRT (12–4 h) with the support of normal flora (K. pneumoniae).
The present study summarizes the observations on various nutrient and seed formulation methods using sewage sludge that have been aimed at ameliorating the biohydrogen production potential. Pretreatment methods viz., acid/base treatment, heat treatment, sterilization, freezing–thawing, microwave, ultrasonication and chemical supplementation were attempted on sludge. It was observed that pretreatment was essential not only to reduce the needless, competitive microbial load but also to improve the nutrient solublization of sludge. Heat treatment at 121 °C for 20 min was found to be most effective in reducing the microbial load by 98% and hydrolyzing the organic fraction of sludge. However, this pretreatment alone was either not sufficient or inconsistent in developing a suitable microbial consortium for hydrogen production. Hydrogen yield was found to improve 1.5–4 times upon inoculation with H2-producing microorganisms. A defined microbial consortium was developed consisting of three established bacteria viz., Enterobacter cloacae IIT-BT 08, Citrobacter freundii IIT-BT L139 and Bacillus coagulans IIT-BT S1. Following pretreatments soluble proteins and lipids (the major component of the sludge) were also found to be consumed besides carbohydrates. This laid out the concurrent proteolytic/lipolytic ability of the developed H2-producing consortium. 1:1:1 v/v ratio of these bacteria in consortium was found to give the maximum yield of H2 from sludge, 39.15 ml H2/g CODreduced. 15%v/v dilution and supplementation with 0.5%w/v cane molasses prior to heat treatment was found to further improve the yield to 41.23 ml H2/g CODreduced.
Exogenous H2/CO2 and glucose were consumed simultaneously by Butyribacterium methylotrophicum when grown under glucose-limited conditions. CO2 reduction to acetate was coupled to H2 consumption. The addition of either H2 or CO2 to glucose batch fermentation resulted in an increase in cell density, hydrogenase (H2-consuming and -producing) activities and fatty acid production by B. methylotrophicum as compared to when N2 was the feed gas. Hydrogenase activities appeared to be tightly regulated and were produced at higher rates during the exponential
phase when CO2 was the feed gas as compared to H2 or N2. The increase in H2-consuming activity and decrease in H2-producing activity was correlated with an increase in butyrate synthesis. H2-consuming and ferredoxin (Fd)–NAD reductase activities increased while H2-producing and NADH–Fd reductase activities decreased in cells grown at pH 5.5 compared to those at pH 7.0. The molar ratio
of butyrate/acetate was shifted from 0.35 at pH 7.0 to 1.22 at pH 5.5. The addition of exogenous H2 did not decrease the butyrate/acetate ratio at pH 7.0 nor at pH 5.5. The results indicated that growth pH values regulated
both hydrogenase and Fd–NAD oxidoreductase activities such that, at acid pH, more intermediary electron flow was directed
towards butyrate synthesis than H2 production.
This paper reviews information from continuous laboratory studies of fermentative hydrogen production useful when considering practical applications of the technology. Data from reactors operating with pure cultures and mixed microflora enriched from natural sources are considered. Inocula have been derived from heat-treated anaerobically digested sludge, activated sludge, aerobic compost and soil, and non-heat-treated aerobically composted activated sludge. Most studies are on soluble defined substrates, and there are few reports of continuous operation on complex substrates with mixed microflora to produce H2. Methanogenesis which consumes H2 may be prevented by operation at short hydraulic retention times (around 8– on simple substrates) and/or pH below 6. Although the reactor technology for anaerobic digestion and biohydrogen production from complex substrates may be similar, there are important microbiological differences, including the need to manage spore germination and oxygen toxicity on start-up and control sporulation in adverse circumstances during reactor operation.
This study addressed the utilization of an industrial waste stream, paper sludge, as a renewable cheap feedstock for the fermentative production of hydrogen by the extreme thermophile Caldicellulosiruptor saccharolyticus. Hydrogen, acetate, and lactate were produced in medium in which paper sludge hydrolysate was added as the sole carbon and energy source and in control medium with the same concentration of analytical grade glucose and xylose. The hydrogen yield was dependent on lactate formation and varied between 50 and 94% of the theoretical maximum. The carbon balance in the medium with glucose and xylose was virtually 100%. The carbon balance was not complete in the paper sludge medium because the measurement of biomass was impaired owing to interfering components in the paper sludge hydrolysate. Nevertheless, >85% of the carbon could be accounted for in the products acetate and lactate. The maximal volumetric hydrogen production rate was 5 to 6 mmol/(L x h), which was lower than the production rate in media with glucose, xylose, or a combination of these sugars (9-11 mmol/[L x h]). The reduced hydrogen production rate suggests the presence of inhibiting components in paper sludge hydrolysate.
Identifying and building a sustainable energy system are perhaps two of the most critical issues that today's society must
address. Replacing our current energy carrier mix with a sustainable fuel is one of the key pieces in that system. Hydrogen
as an energy carrier, primarily derived from water, can address issues of sustainability, environmental emissions, and energy
security. Issues relating to hydrogen production pathways are addressed here. Future energy systems require money and energy
to build. Given that the United States has a finite supply of both, hard decisions must be made about the path forward, and
this path must be followed with a sustained and focused effort.
Clostridium beijerinckii ("Clostridium butylicum") NRRL B592 and NRRL B593 were grown in batch cultures without pH control. The use of more sensitive and accurate procedures for the determination of solvents in cultures led to the recognition of the onset of solvent production about 2 h earlier than the previously assigned point and at a higher culture pH for both strains. Reliable assays for solvent-forming enzyme activities in cell extracts have also been developed. The results showed that activities of solvent-forming enzymes in strain NRRL B592 started to increase about 1 h before the measured onset of solvent production and that the increase in activities of solvent-forming enzymes was not simultaneous. The degree of increase of these enzyme activities for both strains ranged from 2- to 165-fold, with acetoacetate decarboxylase and butanol-isopropanol dehydrogenase showing the largest activity increases. However, the pattern of increase of enzyme activities differed significantly in the two strains of C. beijerinckii. When an increase in solvent-forming enzyme activities was first detected in strain NRRL B592, the culture pH was at 5.7 and the concentrations of total acetic and butyric acids were 5.2 and 3.6 mM, respectively. For strain NRRL B593, the corresponding pH was 5.5. Thus, the culture conditions immediately preceding the expression of solvent-forming enzyme activities differed significantly from those that have been correlated with the production of solvents at later stages of growth.
The microbial diversity of a deteriorated biological phosphorus removal reactor was investigated by methods not requiring direct cultivation. The reactor was fed with media containing acetate and high levels of phosphate (P/C weight ratio, 8:100) but failed to completely remove phosphate in the effluent and showed very limited biological phosphorus removal activity. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S ribosomal DNA was used to investigate the bacterial diversity. Up to 11 DGGE bands representing at least 11 different sequence types were observed; DNA from the 6 most dominant of these bands was further isolated and sequenced. Comparative phylogenetic analysis of the partial 16S rRNA sequences suggested that one sequence type was affiliated with the alpha subclass of the Proteobacteria, one was associated with the Legionella group of the gamma subclass of the Proteobacteria, and the remaining four formed a novel group of the gamma subclass of the Proteobacteria with no close relationship to any previously described species. The novel group represented approximately 75% of the PCR-amplified DNA, based on the DGGE band intensities. Two oligonucleotide rRNA probes for this novel group were designed and used in a whole-cell hybridization analysis to investigate the abundance of this novel group in situ,The bacteria were coccoid and 3 to 4 mu m in diameter and represented approximately 35% of the total population, suggesting a relatively close agreement with the results obtained by the PCR-based DGGE method. Further, based on electron microscopy and standard staining microscopic analysis, this novel group was able to accumulate granule inclusions, possibly consisting of polyhydroxyalkanoate, inside the cells.
Hydrogen is the fuel of the future mainly due to its high conversion efficiency, recyclability and nonpolluting nature. Biological hydrogen production processes are found to be more environment friendly and less energy intensive as compared to thermochemical and electrochemical processes. They are mostly controlled by either photosynthetic or fermentative organisms. Till today, more emphasis has been given on the former processes. Nitrogenase and hydrogenase play very important role. Genetic manipulation of cyanobacteria (hydrogenase negative gene) improves the hydrogen generation. The paper presents a survey of biological hydrogen production processes. The microorganisms and biochemical pathways involved in hydrogen generation processes are presented in some detail. Several developmental works are discussed. Immobilized system is found suitable for the continuous hydrogen production. About 28% of energy can be recovered in the form of hydrogen using sucrose as substrate. Fermentative hydrogen production processes have some edge over the other biological processes.
Temperature effects on H2 production performance of a novel carrier-induced granular sludge bed (CIGSB) reactor were investigated. Using sucrose-based synthetic wastewater as the feed, the CIGSB system was operated at 30– to identify the optimal working temperature. It was found that H2 production was the most efficient at , especially when it was operated at a low hydraulic retention time (HRT) of 0.5 h. The overall maximal hydrogen production rate and yield were 7.66 l/h/l and 3.88 mol H2/mol sucrose, respectively, both of them occurred at . The biomass content tended to decrease as the temperature was increased, suggesting that granular sludge formation may be inhibited at high temperatures. However, increasing temperature gave better specific H2 production rate, signifying that the average cellular activity for H2 production may be enhanced as the temperature was increased. The H2 yield and gas phase H2 content did not vary considerably regardless of changes in temperature and HRT. This reflects that the CIGSB was a relatively stable H2-producing system. The major soluble products from hydrogen fermentation were butyric acid and acetic acid, accounting for 46±3% and 28±2% of total soluble microbial products (SMP), respectively. Thus, the dominant H2 producers in the mixed culture belonged to acidogenic bacteria that underwent butyrate-type fermentation.
Sewage sludge microflora were anaerobically cultivated in a chemostat-type anaerobic bioreactor at a temperature of , pH of 7.1 and hydraulic retention time of 12 h to determine the hydrogen production efficiency from xylose (20 g-COD/L). This enriched microflora was used as a seed in batch experiments to investigate the pH and substrate concentration effects on hydrogen-producing bioactivity. It is demonstrated that the enriched mesophilic sewage sludge microflora with a continuous feeding can produce hydrogen from xylose with hydrogen content of 32% (v/v) in the biogas. Each mole of xylose yields 0.7 moles of hydrogen and each gram of biomass produces 0.038 moles of hydrogen per day. According to the batch test results, changes in pH and xylose concentration could enhance the microflora hydrogen production activity. Batch cultivation of this mixed microflora at pH values of 6–7 and xylose concentrations of 20 g-COD/L resulted in high hydrogen production with a yield of 1.92–2.25 mol-H2/mol-xylose. This value is comparable to that from an enrichment culture. Strategies based on pH and xylose concentration controls for optimal hydrogen production from xylose using sewage sludge microflora are proposed.
Organic municipal solid waste (OFMSW) and two seed microorganisms, namely heat-pretreated digested sludge and hydrogen-producing bacteria enriched from soybean-meal silo, were varied according to a full factorial central composite experimental design with the aim of assessing the feasibility of hydrogen production from OFMSW. A simple model developed from the Gompertz equation was suitable for estimating the hydrogen production potential and rate. Through response surface methodology, empirical equations for specific hydrogen production potential and rate were fitted and plotted as contour diagrams in order to facilitate examination of experimental results. The contour plots showed that high hydrogen production potentials of 140 and 180 ml H2·g TVS−1 occurred when the pretreated digested sludge and the hydrogen-producing bacteria consumed OFMSW, respectively. A high hydrogenic activity for the pretreated digested sludge (45 ml·g VSS−1·h−1) was obtained at a high food-to-microorganism (F/M) ratio; however, that for the hydrogen-producing bacteria (36 ml·g VSS−1·h−1) was found at a low F/M ratio. The experimental results showed that the hydrogen composition of the biogas was greater than 60% except for initial incubation and no significant methane was found throughout this study. Further experiments confirmed that the results of this study were highly reliable and the OFMSW had a considerable potential on biological hydrogen production. Metabolic responses confirmed that characteristics of the heat-pretreated digested sludge converting the OFMSW into hydrogen were similar to that of anaerobic spore-forming bacteria of the genus Clostridium.
Our newly developed carrier-induced granular sludge bed (CIGSB) bioreactor was shown to be very effective in hydrogen production. However, since mechanical agitation was not employed to enable sludge granulation, the CIGSB system might encounter problems with poor mass transfer efficiency during prolonged operations. This work was undertaken to improve mixing efficiency of CIGSB for better biomass-substrate contact by adjusting the height to diameter (H/D) ratios of the reactor and by implementing appropriate agitation device. Three H/D ratios (4, 8, and 12) resulting in liquid upflow velocities (vup) of 0.057–1.32 m/h were examined as the CIGSB reactor was carried out at a descending hydraulic retention time (HRT) from 4 to 0.5 h. The results show that decreasing HRT resulted in increases in the H2 production rate, regardless of the H/D ratios. Reactors with a H/D ratio of 8 gave better H2 production performance with a H2 production rate of 6.87 l/h/l and a H2 yield of 3.88 mol H2/mol sucrose, suggesting that the effectiveness of H2 production in the CIGSB system can be enhanced by using a proper vup and physical configuration of the reactor. Supply of additional mechanical agitation for CIGSB reactor (H/D=12) alleviated the phenomena of sludge piston floatation, leading to further increases in the H2 production rate and H2 yield to 9.31 l/h/l and 4.02 mol H2/mol sucrose, respectively. The major soluble metabolite was butyric acid, followed by acetic acid, propionic acid, and ethanol. The former two accounted for nearly 67–76% of total soluble microbial products, indicating the presence of favorable pathways in the CIGSB culture from the aspect of H2-producing metabolism.
Hydrogen may be produced by a number of processes, including electrolysis of water, thermocatalytic reformation of hydrogen-rich organic compounds, and biological processes. Currently, hydrogen is produced, almost exclusively, by electrolysis of water or by steam reformation of methane. Biological production of hydrogen (Biohydrogen) technologies provide a wide range of approaches to generate hydrogen, including direct biophotolysis, indirect biophotolysis, photo-fermentations, and dark-fermentation. The practical application of these technologies to every day energy problems, however, is unclear. In this paper, hydrogen production rates of various biohydrogen systems are compared by first standardizing the units of hydrogen production and then by calculating the size of biohydrogen systems that would be required to power proton exchange membrane (PEM) fuel cells of various sizes.
The effects of hydraulic retention time (HRT) on biohydrogen production and its mixed anaerobic microbial community grown with glucose were investigated in a continuous stirred tank reactor culture. Starting from a HRT of 50 h the culture was acclimated by stepwise HRT reduction until a steady-state was reached at a HRT of 8 h after 19 days. After that the culture was run with HRTs of 6 h, 8 h, 10 h and 12 h, each lasting 9–15 days. Hydrogen, CO2 and dissolved products were daily measured. The species composition of the culture was ascertained using 16S rDNA genes separated by denaturing gradient gel electrophoresis (DGGE). While a hydrogen yield of 1.6 mol/mol glucose was found during the first steady-state at 8 h HRT it stabilized at 1.9 in the following steady-states. The predominant dissolved products were butyrate and acetate in a ratio of about 2.1:1 and amounted to 82–94% of the total products. In the first 8 h HRT period also propionate was found in an amount of 9%. It is concluded that the increase of the hydrogen yield after transition from 8 h to 6 h HRT is caused by a washout of the propionate producing population during the 6 h HRT period. In fact the fading of two 16S rDNA gene fragments was noticed in the DGGE profiles at the same time.
A novel synthetic polymer (ethylene-vinyl acetate copolymer; EVA) was used to immobilize acclimated sewage sludge for H2 production under anaerobic conditions. Using sucrose as the sole carbon substrate, the resulting EVA-immobilized cells achieved an optimal H2 production rate (vH2) of 488 ml H2/g VSS and the best substrate-based yield (YH2/sucrose) of 1.74 mol H2/mol sucrose. Operation at a temperature of 40 °C resulted in the most efficient H2 production. Acclimation of the sewage sludge allowed up to 3-fold enhancement on the performance of H2 production. Kinetic studies show that a Monod-type model is able to describe the dependence of specific H2 production rate on sucrose concentration. The immobilized cells maintained stable and efficient H2 production during 15 repeated runs, indicating excellent durability and stability of the immobilized-cell system. The composition of soluble metabolites was found to be a reliable indicator for the efficiency of biohydrogenation.
An investigation on anaerobic hydrogen production was conducted in fixed-bed bioreactors containing hydrogen-producing bacteria originated from domestic sewage sludge. Three porous materials, loofah sponge (LS), expanded clay (EC) and activated carbon (AC), were used as the support matrix to allow retention of the hydrogen-producing bacteria within the fixed-bed bioreactors. The carriers were assessed for their effectiveness in biofilm formation and hydrogen production in batch and continuous modes. It was found that LS was inefficient for biomass immobilization, while EC and AC exhibited better biomass yields. The fixed-bed reactors packed with EC or AC (denote as EC or AC reactors) were thus used for continuous hydrogen fermentation at a hydraulic retention time (HRT) of 0.5–. Sucrose was utilized as the major carbon source. With a sucrose concentration of ca. COD/l in the feed, the EC reactor () was able to produce H2 at an optimal rate of at . In contrast, the AC reactor ( in volume) exhibited a better hydrogen production rate of , which occurred at . When the AC reactor was scaled up to , the hydrogen production rate was nearly 0.53– for HRT=1–, but after a short thermal treatment (75°C, ) the rate rose to ca. at . The biogas produced with EC and AC reactors typically contained 25–35% of H2 and the rest was mainly CO2, while production of methane was negligible (less than 0.1%). During the efficient hydrogen production stage, the major soluble metabolite was butyric acid, followed by propionic acid, acetic acid, and ethanol.
Batch experiment results showed that hydrogen production from rice slurry was found most effective at pH 4.5, 37 °C treating a slurry containing 5.5 g-carbohydrate/L. An anaerobic digester sludge was used as seed after a 100 °C heat treatment for 30 min. After a 36 h acclimation period, the sludge had a maximum specific hydrogen production rate of 2.1 L/(g-VSS d) and a hydrogen yield of 346 mL/g-carbohydrate, corresponding to 62.6% of stoichiometric yield. The effluent was composed mostly of acetate (28.3–43.0%) and butyrate (51.4–70.9%). Based on the 16S rDNA analysis, the 28 clones developed from this acidophilic hydrogen-producing sludge may be classified into nine OTUs, all of which are affiliated with the genus Clostridium. Phylogenetic analysis shows that eight OTUs (96.4% of population) form a distinct group with Clostridium sp. 44a-T5zd. Results indicate the acidophilic hydrogen-producing bacteria found in this study are unknown, and warrant further studies.
Long-term operation for biohydrogen production with an efficient carrier-induced granular sludge bed (CIGSB) bioreactor had encountered problems with poor biomass retention at a low hydraulic retention (HRT) as well as poor mass-transfer efficiency at a high HRT or under a prolonged operation period. This work was undertaken to develop strategies enabling better biomass retention and mass-transfer efficiency of the CIGSB reactors. Supplementation of calcium ion was found to enhance mechanical strength of the granular sludge. Addition of 5.4–27.2 mg/l of Ca2+ also led to an over three-fold increase in biomass concentration and a nearly five-fold increase in the H2 production rate (up to 5.1 l H2/h/l). Two reflux strategies were utilized to enhance the mass-transfer efficiency of the CIGSB system. The liquid reflux (LR) strategy enhanced the H2 production rate by 2.2-fold at an optimal liquid upflow velocity of 1.09 m/h, which also gave a maximal biomass concentration of ca. 22 g VSS/l. Similar optimal H2 production rate was also obtained with the gas reflux (GR) strategy at a rate of 1.0–1.49 m/h, whereas the biomass concentration decreased to 2–7 g VSS/l and thereby the specific H2 production rate was higher than that with LR. The operation strategies applied in this work were effective to allow stable and efficient H2 production for nearly 100 days.
It has been found, in this study, that a new ethanol-type fermentation can be obtained in a continuous flow, high-rate acidogenic reactor receiving molasses as the feed. The operating pH must be maintained at about 4.5 to avoid onset of propionic fermentation. The acidogenic reactor had a VSS level of 20 g/L and its organic loading was as high as 80 to 90 kg COD/m(3) d. The operating ORP was around -250 mV. The ethanol-type fermentation was characterized by a simultaneous production of acetic acid and ethanol, while the yield of propionic was minimal even at a high organic loading rate of 80 to 90 kg COD/m(3) d, and also, the hydrogen partial pressure was as high as 50 kPa. Thus, this study has shown that the production of propionic acid is not always related to high hydrogen partial pressure. When the operating pH was increased to 5.5, the yield of propionic acid became significant.
HYVOLUTION is the acronym of an Integrated Project ¿Non-thermal production of pure hydrogen from biomass¿ which is under negotiation for granting in the 6th EU Framework Programme on Research, Technological Development and Demonstration, Priority 6.1.ii, Sustainable Energy Systems. The aim of HYVOLUTION: ¿Development of a blue-print for an industrial bioprocess for decentral hydrogen production from locally produced biomass¿ adds to the number and diversity of H2 production routes giving greater security of supply at the local and regional level. Moreover, this IP contributes a complementary strategy to fulfil the increased demand for renewable hydrogen expected in the transition to the Hydrogen Economy. The novel approach in HYVOLUTION is based on a combined bioprocess employing thermophilic and phototrophic bacteria, to provide the highest hydrogen production efficiency in small-scale, cost effective industries. The process starts with the conversion of biomass to make a suitable feedstock for the bioprocess. The subsequent bioprocess is optimized in terms of yield and rate of hydrogen production through integrating fundamental and technological approaches. Dedicated gas upgrading is developed for efficiency at small-scale production units. Production costs will be reduced by system integration combining mass and energy balances. The impact of small-scale hydrogen production plants is addressed in socio-economic analyses. In HYVOLUTION, 11 EU countries, Turkey and Russia are represented to assemble the critical mass needed to make a breakthrough in cost-effectiveness. This multinational and multidisciplinary consortium reinforces the European Research Area in sustainable energy issues. The participation of prominent specialists from academia and industries and the 7 SMEs warrants high quality and commercial exploitation of project results. The participants in this Integrated Project have a complementary value in being biomass suppliers, end-users or stakeholders for developing specialist enterprises and stimulating new agro-industrial development, which will be needed to make the objectives of HYVOLUTION:
The concentrations of methyl glycosides, oligosaccharides, glycopeptides, and glycoproteins can be accurately determined by using calibration curves composed of the appropriate monosaccharide(s) obtained with a modified version of the colorimetric phenol-sulfuric acid method. Calibration curves of micrograms sugar vs. 490 nm for Man, Glc, or Gal are shown to provide reliable determinations (typically +/- 3-4%) of corresponding methyl glycosides and linear and branched-chain oligosaccharides containing the corresponding reactive hexose residue. For complex oligosaccharides containing a known mixture of reactive hexose units, the appropriate mixture of monosaccharides are shown to provide equally accurate calibration curves for concentration determinations. In the case of the soybean agglutinin, which is a tetramer possessing one Man9 oligomannose-type chain per subunit, the protein concentration was determined from the Man calibration curve which agreed with that obtained from the molar extinction coefficient of the protein.
In this study, local sewage sludge was acclimated to establish H2-producing enrichment cultures, which were used to convert sucrose to H2 with continuously stirred anaerobic bioreactors. The steady-state behaviors of cell growth, substrate utilization, and product formation were closely monitored. Kinetic models were developed to describe and predict the experimental results from the H2-producing cultures. Operation at dilution rates (D) of 0.075–0.167 h–1 was preferable for H2 production, resulting in a H2 concentration of nearly 0.02 mol/l. The optimal hydrogen production rate was 0.105 mol/h occurring at D=0.125 h–1. The major volatile fatty acid produced was butyric acid (HBu), while acetic acid and propionic acid were also produced in lesser quantities. The major solvent product was ethanol, whose concentration was only 15% of that of HBu, indicating that the metabolic flow favors H2 production. The proposed model was able to interpret the trends of the experimental data. The maximum specific growth rate (µ
max), Monod constant (K
s
), and yield coefficient for cell growth (Y
x/s
) were estimated as 0.172 h–1, 68 mg COD/l, and 0.1 g/g, respectively. The model study also suggests that product formation in the continuous hydrogen-producing cultures was essentially a linear function of biomass concentration.
The conversion of organics in wastewaters into hydrogen gas could serve the dual role of renewable energy production and waste reduction. The chemical energy in a sucrose rich synthetic wastewater was recovered as hydrogen gas in this study. Using fractional factorial design batch experiments, the effect of varying pH (4.5-7.5) and substrate concentration (1.5-44.8 g COD/L) and their interaction on hydrogen gas production were tested. Mixed bacterial cultures obtained from a compost pile, a potato field, and a soybean field were heated to inhibit hydrogen-consuming methanogens and to enrich sporeforming, hydrogen-producing acidogens. It was determined that the highest rate (74.7 mL H2/(L*h)) of hydrogen production occurred at a pH of 5.5 and a substrate concentration of 7.5 g COD/Lwith a conversion efficiency of 38.9 mL H2/(g COD/L). The highest conversion efficiency was 46.6 mL H2/(g COD/L).
The effect of pH on the conversion of glucose to hydrogen by a mixed culture of fermentative bacteria was evaluated. At 36 degrees C, six hours hydraulic retention, over 90% of glucose was degraded at pH ranging 4.0-7.0, producing biogas and an effluent comprising mostly fatty acids. At the optimal pH of 5.5, the biogas comprised 64 +/- 2% of hydrogen with a yield of 2.1 +/- 0.1 mol-H2/mol-glucose and a specific production rate of 4.6 +/- 0.4 l-H2/(g-VSS day). The effluent was composed of acetate (15.3-34.1%) and butyrate (31.2-45.6%), plus smaller quantities of other volatile fatty acids and alcohols. The diversity of microbial communities increased with pH, based on 16S rDNA analysis by denaturing gradient gel electrophoresis (DGGE).
The selective production of organic acids by anaerobic acidogenesis with pH control was examined using a chemostat culture. The results showed that the product spectrum in the acid reactor strongly depended on the culture pH. Under acidic and neutral conditions, the main products were butyric acid, while acetic and propionic acids were the main products under the basic condition. This phenomenon was reversible between the acidic and basic conditions, and was not affected by the dilution rate. The change in the main products was caused by the change in the dominant microbial populations, from butyric acid-producing bacteria to propionic acid-producing bacteria in the acid reactor due to the pH shift. The control of culture pH was considered to be a useful way for controlling the product spectrum in the anaerobic acid reactor.
Municipal sewage sludge was immobilized to produce hydrogen gas under anaerobic conditions. Cell immobilization was essentially achieved by gel entrapment approaches, which were physically or chemically modified by addition of activated carbon (AC), polyurethane (PU), and acrylic latex plus silicone (ALSC). The performance of hydrogen fermentation with a variety of immobilized-cell systems was assessed to identify the optimal type of immobilized cells for practical uses. With sucrose as the limiting carbon source, hydrogen production was more efficient with the immobilized-cell system than with the suspended-cell system, and in both cases the predominant soluble metabolites were butyric acid and acetic acid. Addition of activated carbon into alginate gel (denoted as CA/AC cells) enhanced the hydrogen production rate (v(H2)) and substrate-based yield (Y((H2)/sucrose)) by 70% and 52%, respectively, over the conventional alginate-immobilized cells. Further supplementation of polyurethane or acrylic latex/silicone increased the mechanical strength and operation stability of the immobilized cells but caused a decrease in the hydrogen production rate. Kinetic studies show that the dependence of specific hydrogen production rates on the concentration of limiting substrate (sucrose) can be described by Michaelis-Menten model with good agreement. The kinetic analysis suggests that CA/AC cells may contain higher concentration of active biocatalysts for hydrogen production, while PU and ALSC cells had better affinity to the substrate. Acclimation of the immobilized cells led to a remarkable enhancement in v(H2) with a 25-fold increase for CA/AC and ca. 10- to 15-fold increases for PU and ALSC cells. However, the ALSC cells were found to have better durability than PU and CA/AC cells as they allowed stable hydrogen production for over 24 repeated runs.
Experiments were conducted to study the acidogenesis of a dairy wastewater in batch reactors at pH 5.5 and 55 degrees C. There was a biased fermentation sequence for carbohydrate and protein, and the protein fermentation was delayed by carbohydrate. The production of hydrogen was exclusively from the fermentation of carbohydrate. Acetate and butyrate concentrations both increased rapidly at the beginning and peaked at some points, then declined in the reactors fed with 8 g-COD (chemical oxygen demand)/l, or higher concentrations. Butanol and propanol fractions increased with the substrate concentration. The metabolism shifted from the volatile fatty acid-producing pathways to the alcohol-producing pathways when the substrate concentration increased beyond 8 g-COD/l. The acidogenic biomass yield was in the range 0.19-0.25 mg-VSS/mg-COD.
Municipal sewage sludge was immobilized with a modified alginate gel entrapment method, and the immobilized cells were used to produce hydrogen gas in a three-phase fluidized bed. The hydrogen-producing fluidized beds were operated at different liquid velocity (U(0)) and hydraulic retention time (HRT). The results show that in response to operating liquid velocities, the fluidized-bed system had three flow regimes, namely, plug flow, slug flow, and free bubbling. Pressure fluctuation analysis was used to analyze the hydrodynamic properties in this three-phase fluidized bed when it was under a steady-state production of biogas. With a steady-state biogas production rate (U(g)) of 0.196 mL/s/L, a transition state occurred at a liquid velocity (U(0)) of 0.85 cm/s. As U(0) < 0.85 cm/s, the system was basically a nonhomogeneous fluidized bed, whereas the bed became homogeneous when U(0) was higher than 0.85 cm/s. The fluidized bed can be stably carried out at high loading rates (HRT as low as 2 h). Hydrogen fermentation results show that the maximal hydrogen production rate was 0.93 L/h/L and the best yield (Y(H)2(/sucrose)) was 2.67 mol H(2)/mol sucrose.
A novel bioreactor containing self-flocculated anaerobic granular sludge was developed for high-performance hydrogen production from sucrose-based synthetic wastewater. The reactor achieved an optimal volumetric hydrogen production rate of approximately 7.3 L/h/L (7,150 mmol/d/L) and a maximal hydrogen yield of 3.03 mol H2/mol sucrose when it was operated at a hydraulic retention time (HRT) of 0.5 h with an influent sucrose concentration of 20 g COD/L. The gas-phase hydrogen content and substrate conversion also exceeded 40 and 90%, respectively, under optimal conditions. Packing of a small quantity of carrier matrices on the bottom of the upflow reactor significantly stimulated sludge granulation that can be accomplished within 100 h. Among the four carriers examined, spherical activated carbon was the most effective inducer for granular sludge formation. The carrier-induced granular sludge bed (CIGSB) bioreactor was started up with a low HRT of 4-8 h (corresponding to an organic loading rate of 2.5-5 g COD/h/L) and enabled stable operations at an extremely low HRT (up to 0.5 h) without washout of biomass. The granular sludge was rapidly formed in CIGSB supported with activated carbon and reached a maximal concentration of 26 g/L at HRT = 0.5 h. The ability to maintain high biomass concentration at low HRT (i.e., high organic loading rate) highlights the key factor for the remarkable hydrogen production efficiency of the CIGSB processes.
In this study batch experiments were conducted to investigate the inhibitory effects of butyrate addition on hydrogen production from glucose by using anaerobic mixed cultures. Experimental results showed that addition of butyrate at 4.18 and 6.27 g/l only slightly inhibited hydrogen production, and addition of butyrate at 8.36-12.54 g/l imposed a moderate inhibitory effect on hydrogen production. At addition of 25.08 g/l, butyrate had a strong inhibitory influence on substrate degradation and hydrogen production. The distribution of the volatile fatty acids produced from the acidogeneisis of glucose was significantly influenced by the addition of butyrate. The inhibition of butyrate addition on hydrogen production was described well by a non-competitive and non-linear inhibition model, with the maximum hydrogen production rate of 59.3 ml/g-SS/h, critical added butyrate concentration of 25.08 g/l, and inhibition degree of 0.323, respectively. The C(I,50) values (the butyrate concentration at which bioactivity is reduced by 50%) for hydrogen production rate and yield were estimated as 19.39 and 20.78 g/l of added butyrate, respectively.
A novel continuously stirred anaerobic bioreactor (CSABR) seeded with silicone-immobilized sludge was developed for high-rate fermentative H2 production using sucrose as the limiting substrate. The CSABR system was operated at a hydraulic retention time (HRT) of 0.5-6 h and an influent sucrose concentration of 10-40 g COD/L. With a high feeding sucrose concentration (i.e., 30-40 g COD/L) and a short HRT (0.5 h), the CSABR reactor produced H2 more efficiently with the highest volumetric rate (VH2) of 15 L/h/L (i.e., 14.7 mol/d/L) and an optimal yield of ca. 3.5 mol H2/mol sucrose. The maximum VH2 value obtained from this work is much higher than any other VH2 values ever documented. Formation of self-flocculated granular sludge occurred during operation at a short HRT. The granule formation is thought to play a pivotal role in the dramatic enhancement of H2 production rate, because it led to more efficient biomass retention. A high biomass concentration of up to 35.4 g VSS/L was achieved even though the reactor was operated at an extremely low HRT (i.e., 0.5 h). In addition to gaining high biomass concentrations, formation of granular sludge also triggered a transition in bacterial community structure, resulting in a nearly twofold increase in the specific H2 production rate. According to denatured-gradient-gel-electrophoresis analysis, operations at a progressively decreasing HRT resulted in a decrease in bacterial population diversity. The culture with the best H2 production performance (at HRT = 0.5 h and sucrose concentration = 30 g COD/L) was eventually dominated by a presumably excellent H2-producing bacterial species identified as Clostridium pasteurianum.
EnVironmental biotechnology: principle and applications; McGraw-Hill Anaerobic acidification of a synthetic wastewater in batch reactors at 55 °C
- B E Rittmann
- P L Mccarty
Rittmann, B. E.; McCarty, P. L. EnVironmental biotechnology: principle and applications; McGraw-Hill: New York, 2001. (28) Yu, H. Q.; Fang, H. H. P. Anaerobic acidification of a synthetic wastewater in batch reactors at 55 °C. Water Sci. Technol. 2002, 46, 153– 157.
Ethanol-type fermentation from carbohydrate in high rate acidogenic reactor Feasibility of biological hydrogen production from organic fraction of municipal solid waste Effect of hydraulic retention time on biohydrogen production and anaerobic microbial community
- N Q Ren
- B Z Wang
- J C Huang
- J J Lay
- Y J Lee
- T Noike
Ren, N. Q.; Wang, B. Z.; Huang, J. C. Ethanol-type fermentation from carbohydrate in high rate acidogenic reactor. Biotechnol. Bioeng. 1997, 54, 428–433. (33) Lay, J. J.; Lee, Y. J.; Noike, T. Feasibility of biological hydrogen production from organic fraction of municipal solid waste. Water Res. 1999, 33, 2579–2586. (34) Zhang, Z. P.; Show, K. Y.; Tay, J. H.; Liang, D. T.; Lee, D. J.; Jiang, W. J. Effect of hydraulic retention time on biohydrogen production and anaerobic microbial community. Process Biochem. 2006, 41, 2118– 2123.
Bio-methane & Bio-hydrogen
- R H Wijffels
- H Barten
Wijffels, R. H.; Barten, H. Bio-methane & Bio-hydrogen;