Producing hydrogen from the fermentation of cheese whey and glycerol as cosubstrates in an anaerobic fluidized bed reactor

This study aimed to evaluate the effect of the organic loading rate (OLR) (60, 90, and 120 g Chemical Oxygen Demand (COD). L^?1. d^?1) on hydrogen production from cheese whey and glycerol fermentation as cosubstrates (50% cheese whey and 50% glycerol on a COD basis) in a thermophilic fluidized bed reactor (55 °C). The increase in the OLR to 90 gCOD.L^?1. d^?1 favored the hydrogen production rate (HPR) (3.9 L H₂. L^?1. d^?1) and hydrogen yield (HY) (1.7 mmol H₂. gCOD^?1_app) concomitant with the production of butyric and acetic acids. Employing 16S rRNA gene sequencing, the highest hydrogen production was related to the detection of Thermoanaerobacterium (34.9%), Pseudomonas (14.5%), and Clostridium (4.7%). Conversely, at 120 gCOD.L^?1. d^?1, HPR and HY decreased to 2.5 L H₂. L^?1. d^?1 and 0.8 mmol H₂. gCOD^?1_app, respectively, due to lactic acid production that was related to the genera Thermoanaerobacterium (50.91%) and Tumebacillus (23.56%). Cofermentation favored hydrogen production at higher OLRs than cheese whey single fermentation.     

Pilot-scale of biohythane production from palm oil mill effluent by two-stage thermophilic anaerobic fermentation

The pilot-scale of two-stage thermophilic (55 °C) for biohythane production from palm oil mill effluent (POME) was operated at hydraulic retention time (HRT) of 2 days and organic loading rate (OLR) of 27.5 gCOD/L⋅d) for first stage and HRT of 10 days and OLR of 5.5 gCOD/L⋅d for second stage. Biohythane production rate was 1.93 L-gas/L⋅d with biogas containing 11% H₂, 37% CO₂, and 52% CH₄. Recirculation of methane effluent mixed with POME at a ratio of 1:1 can control pH in the first stage at an optimal range of 5.0–6.5. Microbial community in hydrogen stage dominated by Thermoanaerobacterium sp., while methane stage dominated by Methanosarcina sp. The H₂/CH₄ ratio of biohythane was 0.13–0.18 which suitable for vehicle fuel. Biohythane production from POME could be promising cleaner biofuel with flexible and controllable H₂/CH₄ ratio.     

Comparison of suspended and granular cell anaerobic bioreactors for hydrogen production from acid agave bagasse hydrolyzates

Acid agave bagasse hydrolyzates have been used as a substrate for hydrogen production, however, bioreactors are unstable and with poor performance. Granular biomass could be more successful in producing hydrogen from acid agave bagasse hydrolyzates in comparison with suspended biomass. Thus, this study aimed to evaluate the effect of increasing concentrations of acid agave hydrolyzates on hydrogen production, to compare the hydrogen productivity and stability of granular biomass in an expanded granular sludge bed (EGSB) reactor and suspended biomass in an anaerobic sequencing batch reactor (AnSBR) fed with acid hydrolyzates, and finally to determine the variation of microbial communities established in both bioreactor configurations. In batch tests, the heat-treated inoculum produced hydrogen from acid agave hydrolyzates without observing inhibition at 6.3 g/L of carbohydrates (_CHO). This hydrolyzate concentration was used to start up the AnBSR, which reached a productivity of 226 ± 53 mL H₂/L⋅d at organic loading rates (OLR) from 3.2 to 4.5 g_CHO/L⋅d. The hydrogen production stability index decreased from 0.8 to 0.6 at increasing OLR, and the AnSBR failed at the highest OLR of 5.7 g/L⋅d. The EGSB reactor reached the highest productivity of 361 ± 130 mL H₂/L⋅d at an OLR of 7.4 g_CHO/L⋅d, but with a low stability index of 0.6. Independently of the bioreactor configuration, microbial communities associated with the production of acetate/lactate were successfully established in both configurations with the prevalence of Lactobacillus spp. A low abundance of typical H₂ producers like Clostridium was always observed over the whole period of operation (<10% of the total abundance). In sum, the hydrogen productivity from acid agave hydrolyzates was higher for the EGSB reactor than for the AnSBR, but with much lower stability. The evidence provided by this study suggests the establishment of metabolic pathways for hydrogen production from organic acids.     

Effect of organic loading on a novel hydrogen bioreactor

This study investigated the impact of six organic loading rates (OLR) ranging from 6.5 gCOD/L-d to 206 gCOD/L-d on the performance of a novel integrated biohydrogen reactor clarifier systems (IBRCSs) comprised a continuously stirred reactor (CSTR) for biological hydrogen production, followed by an uncovered gravity settler for decoupling of solids retention time (SRT) from hydraulic retention time (HRT). The system was able to maintain a high molar hydrogen yield of 2.8 mol H₂/mol glucose at OLR ranging from 6.5 to 103 gCOD/L-d, but dropped precipitously to approximately 1.2 and 1.1 mol H₂/mol glucose for the OLRs of 154 and 206 gCOD/L-d, respectively. The optimum OLR at HRT of 8 h for maximizing both hydrogen molar yield and volumetric hydrogen production was 103 gCOD/L-d. A positive statistical correlation was observed between the molar hydrogen production and the molar acetate-to-butyrate ratio. Biomass yield correlated negatively with hydrogen yield, although not linearly. Analyzing the food-to-microorganisms (F/M) data in this study and others revealed that, both molar hydrogen yields and biomass specific hydrogen rates peaked at 2.8 mol H₂/mol glucose and 2.3 L/gVSS-d at F/M ratios ranging from 4.4 to 6.4 gCOD/gVSS-d. Microbial community analysis for OLRs of 6.5 and 25.7 gCOD/L-d showed the predominance of hydrogen producers such as Clostridium acetobutyricum, Klebsiella pneumonia, Clostridium butyricum, Clostridium pasteurianum. While at extremely high OLRs of 154 and 206 gCOD/L-d, a microbial shift was clearly evident due to the coexistence of the non-hydrogen producers such as Lactococcus sp. and Pseudomonas sp.     

Hydrogen fermentation of different galactose–glucose compositions during various hydraulic retention times (HRTs)

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 glucose_added 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 galactose_added 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 carbohydrate_added at the HRTs of 6 and 18 h, respectively.     

The effect of hydraulic retention time on thermophilic dark fermentative biohydrogen production in the continuously operated packed bed bioreactor

The main objective of the study is to investigate the effect of hydraulic retention times on continuous dark fermentative biohydrogen production in an up-flow packed bed reactor (UPBR) containing a novel microorganism immobilization material namely polyester fiber beads. The hydrogen producing dark fermentative microorganisms were obtained by heat-pretreatment of anaerobic sludge from the acidogenic phase of an anaerobic wastewater treatment plant. Glucose was the sole carbon source and the initial concentration was 15 ± 1 g/L throughout the continuous feeding. UPBR was operated under the thermophilic condition at T = 48 ± 2 °C and at varying HRTs between 2 h and 6 h. The hydrogen productivity of continuously operated UPBR increased with increasing HRT. Hydrogen production volume varied between 4331 and 6624 ml/d, volumetric hydrogen production rates (VHPR) were obtained as 3.09–4.73 L H₂/L day, and hydrogen production yields (HY) were 0.49 mol/mol glucose-0.89 mol/mol glucose depending on HRT. Maximum daily hydrogen volume (6624 ml/d), the yield (0.89 mol/mol glucose) and VHPR (4.73 L H₂/L day) were obtained at HRT = 6 h. The production rate and the yield decreased with increasing organic loading rate due to substrate inhibition.     

Evaluation of hidden H2-consuming pathways using metabolic flux-based analysis for a fermentative side-stream dynamic membrane bioreactor using untreated seed sludge

This study investigates the performance and hidden hydrogen consuming metabolic pathways of a fermentative side stream dynamic membrane (DM) bioreactor using flux balance analysis (FBA). The bioreactor was inoculated with untreated methanogenic seed sludge. It was found that fouling rate aggravated with increasing COD concentration (10–30 g/L) and was positively correlated to it rather than to the applied solid flux on the DM module. Due to increased fouling rate the hydraulic retention time (HRT) could not be reduced less than 0.82 ± 0.02 d. An increase in the organic loading rate (OLR) led to an increase in H₂ yield from 0.01 to 0.76 mol H₂/mol of sucrose. FBA revealed that homoacetogenesis was the main H₂-consuming pathway at lower OLRs (corresponding to 10 and 15 g COD/L), while for the OLR corresponding to 30 g COD/L, homoacetogens were suppressed. More importantly, caproic acid production pathway was identified for the first time as another H₂-consuming pathway at high OLR which was not significant at lower OLRs during fermentative dynamic membrane bioreactor operations.     

High-solid dark fermentation of cassava pulp and cassava processing wastewater for hydrogen production

Dark fermentation (DF) is a promising biological process for hydrogen production from biomass. However, low hydrogen yield (HY) is a major hurdle impeding its use at large-scale operation. A potential way to mitigate this problem is to increase the concentration of substrate in the process to increase hydrogen production. The present study investigated the possibility of using high-solid DF to produce hydrogen from cassava processing wastes, i.e., cassava pulp (CP) and cassava processing wastewater (CPW). CP was suspended in CPW and hydrolyzed enzymatically under optimum conditions of 150 g-CP/L, 29 U/g of α-amylase, 47 U/g of glucoamylase, and 60 FPU/g of cellulase. The hydrolysis performed at 50 °C for 24 h yielded a reducing sugar concentration of 117.7 ± 1.8 g/L, equivalent to 0.78 g-reducing-sugar/g-CP. Subsequent DF of CP-CPW enzymatic slurry, which contained 12.1% water insoluble solids, resulted in a cumulative production of 13.72 ± 0.22 L-H₂, equivalent to 225.2 ± 3.7 mL-H₂/g-VS. This was 83.1% of a maximum stoichiometric HY, based on carbohydrate content of CP and soluble metabolites production. The present study shows clearly the applicability of high-solid DF in the production of hydrogen from cassava processing wastes.     

Effect of hydraulic retention time on biohydrogen production from palm oil mill effluent in anaerobic sequencing batch reactor

The feasibility of hydrogen generation from palm oil mill effluent (POME), a high strength wastewater with high solid content, was evaluated in an anaerobic sequencing batch reactor (ASBR) using enriched mixed microflora, under mesophilic digestion process at 37 °C. Four different hydraulic retention times (HRT), ranging from 96 h to 36 h at constant cycle length of 24 h and various organic loading rate (OLR) concentrations were tested to evaluate hydrogen productivity and operational stability of ASBR. The results showed higher system efficiency was achieved at HRT of 72 h with maximum hydrogen production rate of 6.7 LH₂/L/d and hydrogen yield of 0.34 LH₂/g COD_feeding, while in longer and shorter HRTs, hydrogen productivity decreased. Organic matter removal efficiency was affected by HRT; accordingly, total and soluble COD removal reached more than 37% and 50%, respectively. Solid retention time (SRT) of 4-19 days was achieved at these wide ranges of HRTs. Butyrate was found to be the dominant metabolite in all HRTs. Low concentration of volatile fatty acid (VFA) confirmed the state of stability and efficiency of sequential batch mode operation was achieved in ASBR. Results also suggest that ASBR has the potential to offer high digestion rate and good stability of operation for POME treatment.     

Optimizing energy harvest in wastewater treatment by combining anaerobic hydrogen producing biofermentor (HPB) and microbial fuel cell (MFC)

This study focused on the optimization of energy harvest from wastewater treatment by integrating two novel biotechnologies: anaerobic hydrogen production and microbial fuel cell (MFC). The simultaneous production of hydrogen and electricity from wastewater was examined at continuous flow at different organic loading rates (OLR) by changing chemical oxygen demand (COD) and hydraulic retention time (HRT). The experimental results showed that the specific hydrogen yield (SHY, mole H₂/mole glucose) increased with the decrease in OLR, and reached at the maximum value of 2.72 mol H₂/mole glucose at the lowest OLR of 4 g/L.d. The effluent from hydrogen producing biofermentor (HPB) was fed to a single chamber MFC (SCMFC), obtaining the highest power density and coulombic efficiency (CE) of 4200 mW/m³ and 5.3%, respectively. The energy conversion efficiency (ECE) increased with OLR and reached the peak value of 4.24% at the OLR of 2.35 g/L.d, but decreased with higher OLR. It was demonstrated that the combination of HPB and MFC improved the ECE and COD removal with the maximum total ECE of 29% and COD removal of 71%. The kinetic analysis was conducted for the HPB-MFC hybrid system. The maximum hydrogen production was projected to be 2.85 mol H₂/mole glucose. The maximum energy recovery and COD removal efficiency from MFC were projected to be 559 J/L and 97%, respectively.     

Optimization and microbial community analysis for production of biohydrogen from palm oil mill effluent by thermophilic fermentative process

The optimum values of hydraulic retention time (HRT) and organic loading rate (OLR) of an anaerobic sequencing batch reactor (ASBR) for biohydrogen production from palm oil mill effluent (POME) under thermophilic conditions (60 °C) were investigated in order to achieve the maximum process stability. Microbial community structure dynamics in the ASBR was studied by denaturing gradient gel electrophoresis (DGGE) aiming at improved insight into the hydrogen fermentation microorganisms. The optimum values of 2-d HRT with an OLR of 60 gCOD l⁻¹ d⁻¹ gave a maximum hydrogen yield of 0.27 l H₂ g COD⁻¹ with a volumetric hydrogen production rate of 9.1 l H₂ l⁻¹ d⁻¹ (16.9 mmol l⁻¹ h⁻¹). The hydrogen content, total carbohydrate consumption, COD (chemical oxygen demand) removal and suspended solids removal were 55 ± 3.5%, 92 ± 3%, 57 ± 2.5% and 78 ± 2%, respectively. Acetic acid and butyric acid were the major soluble end-products. The microbial community structure was strongly dependent on the HRT and OLR. DGGE profiling illustrated that Thermoanaerobacterium spp., such as Thermoanaerobacterium thermosaccharolyticum and Thermoanaerobacterium bryantii, were dominant and probably played an important role in hydrogen production under the optimum conditions. The shift in the microbial community from a dominance of T. thermosaccharolyticum to a community where also Caloramator proteoclasticus constituted a major component occurred at suboptimal HRT (1 d) and OLR (80 gCOD l⁻¹ d⁻¹) conditions. The results showed that the hydrogen production performance was closely correlated with the bacterial community structure. This is the first report of a successful ASBR operation achieving a high hydrogen production rate from real wastewater (POME).     

Optimal operational conditions for biohydrogen production from sugar refinery wastewater in an ASBR

The performance of biohydrogen production in an anaerobic sequencing batch reactor (ASBR) was evaluated with respect to variations in the key operational parameters – pH, hydraulic retention time HRT, and organic loading rate OLR using sugar refinery wastewater as substrate. Analysis of variance (ANOVA) indicated HRT had less significant influence on hydrogen content and yield in comparison to pH and OLR, whereas OLR has much impact on hydrogen production rate. Taxonomic analysis results showed that diverse bacterial species contributed to hydrogen production and the dominant species in the bioreactor were governed by all operational parameters. Even without pretreatment of the seed sludge, a high proportion of Clostridium spp. over the other bacterial species was observed at pH 5.5, and this is compatible with the high hydrogen productivity. Consequently, pH 5.5, HRT 10 h, and OLR 15 kg/m³ d were delineated as the optimal operational conditions for an ASBR fed with sugar refinery wastewater.     

Intensification of hydrogen production by B. licheniformis using kitchen waste as substrate

Bacillus licheniformis AP1 isolated from dairy waste cheese whey water possess pyruvate formate lyase (PFL) and formate hydrogen lyase (FHL) enzyme gene which can hydrolyze pyruvate and formate to produce hydrogen under anaerobic conditions. Molecular characterization of this strain was done using 16rRNA gene sequencing. Phylogenetic tree was formed on the basis of neighbor-joining method using MEGA5 which showed that no significant change occurred in 16s rRNA during the course of evolution. Biohydrogen production using this laboratory isolate was performed using pre-treated kitchen waste as substrate at optimized pH 6.5 with yield of 12.29 ± 1.2 mmolH₂/gCOD reduced. Effect of macronutrients and micronutrients were studied by varying concentrations on the hydrogen production. Hydrogen production substantially increased from 14.10 ± 1.4 mmolH₂/gCOD, 17.027 ± 1.7 mmolH₂/gCOD, 17.029 ± 1.7 mmolH₂/gCOD to 17.62 ± 1.8 mmol/gCOD reduced kitchen waste by B. licheniformis at optimized concentrations of –different metals like magnesium (MgCl₂) 0.59 g/L, nitrogen (NH₄Cl) 7 g/L, nickel (NiCl₂) 180 μg/L, and iron (II) (FeSO₄) 67 μg/L respectively. The optimized temperature for this process was found to be 34 ± 2 °C with the maximal hydrogen yield of 17.62 ± 1.8 mmol/g COD reduced kitchen waste. The end fermentation metabolites detected were acetic acid, isobutyl acid, butyric acid, and pyruvic acid in the proportion of 3.75:1:1:1 under the optimized conditions in batch experiment (30 ml MGY media broth). These are the products of pyruvate-formate lyase enzyme complex that indicates the major electron flux towards formate during hydrogen production by B. licheniformis in hydrolyzed kitchen waste.     

Biological hydrogen production from sweet sorghum syrup by mixed cultures using an anaerobic sequencing batch reactor (ASBR)

Continuous biological hydrogen production from sweet sorghum syrup by mixed cultures was investigated by using anaerobic sequencing batch reactor (ASBR). The ASBR was conducted based on the optimum condition obtained from batch experiment i.e. 25 g/L of total sugar concentration, 1.45 g/L of FeSO₄ and pH of 5.0. Feasibility of continuous hydrogen fermentation in ASBR operation at room temperature (30 ± 3 °C) with different hydraulic retention time (HRT) of 96, 48, 24 and 12 hr and cycle periods consisting of filling (20 min), settling (20 min), and decanting (20 min) phases was analyzed. Results showed that hydrogen content decreased with a reduction in HRT i.e. from 42.93% (96 hr HRT) to 21.06% (12 hr HRT). Decrease in HRT resulted in a decrease of solvents produced which was from 10.77 to 2.67 mg/L for acetone and 78.25 mg/L to zero for butanol at HRT of 96 hr-12 hr, respectively. HRT of 24 hr was the optimum condition for ASBR operation indicated by the maximum hydrogen yield of 0.68 mol H₂/mol hexose. The microbial determination in DGGE analysis indicated that the well-known hydrogen producers Clostridia species were dominant in the reacting step. The presence of Sporolactobacillus sp. which could excrete the bacteriocins causing the adverse effect on hydrogen-producing bacteria might responsible for the low hydrogen content obtained.     

Upgrading continuous H2 gas recovery from rice straw hydrolysate via fermentation process amended with magnetite nanoparticles

Continuous H₂ production from alkali‐hydrolyzed rice straw in two mesophillic anaerobic baffled reactors (ABRs) was investigated in parallel. ABR₁ was inoculated with thermally pretreated sludge while the sludge in ABR₂ was amended with magnetite nanoparticles (MNPs). Both reactors were operated at organic loading rates (OLRs) ranged from 0.8 to 4.8 g_COD/L/day. The addition of MNPs significantly improved the H₂ production and yield, ie, maximum H₂ yield was 21.4 ± 3.2 and 60.6 ± 5.7 mL/g COD_removed for both ABR₁ and ABR₂, respectively, at OLR of 1.6 g_COD/L/day. Likewise, substrate degradation efficiency (SDE) was augmented from 48.4 ± 3.9% (ABR₁) to 55.8 ± 4.2% (ABR₂). The enhancement effect of MNPs can be emphasized by hydrogenase enzyme activity increase from 0.097 ± 0.013 to 0.205 ± 0.019 mg MB_reduced/min at ABR₁ and ABR₂, respectively. Besides, ABR₂ witnessed higher concentrations of acetate (HAc) and butyrate (HBu) coupled with lower values of propionate (HPr). Additionally, HAc/HBu ratio for ABR₂ (3.03 ± 0.31) was higher than that for ABR₁ (1.95 ± 0.29). Microbial analysis indicated that Bacillus and Clostridium species became dominant in mixed culture bacteria supplemented with MNPs. Furthermore, economic analysis revealed that the minimum payback period of 10.5 years at OLR of 3.2 g_COD/L/day was recorded for ABR₂ compared with 14.6 years at OLR of 4.8 g_COD/L/day for ABR₁.     

Direct fermentation of Laminaria japonica for biohydrogen production by anaerobic mixed cultures

A few studies have been made on fermentative hydrogen production from marine algae, despite of their advantages compared with other biomass substrates. In this study, fermentative hydrogen production from Laminaria japonica (one brown algae species) was investigated under mesophilic condition (35 ± 1 °C) without any pretreatment method. A feasibility test was first conducted through a series of batch cultivations, and 0.92 mol H₂/mol hexose_added, or 71.4 ml H₂/g TS of hydrogen yield was achieved at a substrate concentration of 20 g COD/L (based on carbohydrate), initial pH of 7.5, and cultivation pH of 5.5. Continuous operation for a period of 80 days was then carried out using anaerobic sequencing batch reactor (ASBR) with a hydraulic retention time (HRT) of 6 days. After operation for approximately 30 days, a stable hydrogen yield of 0.79 ± 0.03 mol H₂/mol hexose_added was obtained. To optimize bioenergy recovery from L. japonica, an up-flow anaerobic sludge blanket reactor (UASBr) was applied to treat hydrogen fermentation effluent (HFE) for methane production. A maximum methane yield of 309 ± 12 ml CH₄/g COD was achieved during the 90 days operation period, where the organic loading rate (OLR) was 3.5 g COD/L/d.     

Enhanced bio-hydrogen production from sugarcane juice by immobilized Clostridium butyricum on sugarcane bagasse

Immobilized Clostridium butyricum TISTR 1032 on sugarcane bagasse improved hydrogen production rate (HPR) approximately 1.2 times in comparison to free cells. The optimum conditions for hydrogen production by immobilized C. butyricum were initial pH 6.5 and initial sucrose concentration of 25 g COD/L. The maximum HPR and hydrogen yield (HY) of 3.11 L H₂/L substrate·d and 1.34 mol H₂/mol hexose consumed, respectively, were obtained. Results from repeated batch fermentation indicated that the highest HPR of 3.5 L H₂/L substrate·d and the highest HY of 1.52 mol H₂/mol hexose consumed were obtained at the medium replacement ratio of 75% and 50% respectively. The major soluble metabolites in both batch and repeated batch fermentation were butyric and acetic acids.     

Hydrogen production from alcohol distillery wastewater containing high potassium and sulfate using an anaerobic sequencing batch reactor

In this study, the feasibility of hydrogen production from alcohol distillery wastewater containing high potassium and sulfate was investigated using an anaerobic sequencing batch reactor (ASBR). The seed sludge taken from an anaerobic tank treating the distillery wastewater was boiled for 15 min before being fed to the ASBR. The ASBR system was operated under different feed chemical oxygen demand (COD) values and different COD loading rates at a mesophilic temperature of 37 °C, a controlled pH at 5.5, and a cycle time of 6 cycles per day. When the studied ASBR was operated under the best conditions (providing a maximum hydrogen production efficiency) of a feed COD of 40,000 mg/l, a COD loading rate of 60 kg/m³ d, and a hydraulic retention time of 16 h, the produced gas was found to contain 34.7% H₂ and 65.3% CO_2, without any methane being detected. Under these best conditions, the specific hydrogen production rate (SHPR) of 270 ml H₂/g MLVSS d (or 3310 ml H₂/l d), and hydrogen yield of 172 ml H₂/g COD removed, were obtained. When the feed COD exceeded 40,000 mg/l, the process performance in terms of hydrogen production decreased because of the potassium and sulfate toxicity.     

Evaluation of process performance on biohydrogen production in continuous fixed bed reactor (C-FBR) using acid algae hydrolysate (AAH) as feedstock

In this study, a novel inoculation method to mitigate the inhibition of 5-hydroxymethylfurfural (5-HMF) is proposed. Acid algae hydrolysate containing 1.5 g 5-HMF/L and 15 g hexose/L hexose was fed to a continuous fixed bed reactor (C-FBR) partially packed with hybrid-immobilized beads. The inoculation method enabled a high rate of H₂ production, due to the reduction of 5-HMF inhibition and enhanced biofilm formation. Maximum hydrogen production was achieved at a hydraulic retention time of 6 h with a hydrogen production rate (HPR) of 20.0 ± 3.3 L H₂/L-d and a hydrogen yield (HY) of 2.3 ± 0.4 mol H₂/mol hexose _added. Butyrate and acetate were the major soluble metabolic products released during fermentation. Quantitative real-time polymerase chain reaction analysis revealed that Clostridium butyricum comprised 94.3% of the total bacteria, which was attributed to the high rate of biohydrogen production.     

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

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