Hydrogen and methane production via a two-stage processes (H2-SBR + CH4-UASB) using tequila vinasses

The feasibility of producing hydrogen and methane via a two-stage fermentation of tequila vinasses was evaluated in sequencing batch (SBR) and up-flow anaerobic sludge blanket (UASB) reactors. Different vinasses concentrations ranging from 500 mg COD/L to 16 g COD/L were studied in SBR by using thermally pre-treated anaerobic sludge as inoculum for hydrogen production. Peak volumetric hydrogen production rate and specific hydrogen production were attained as 57.4 ± 4.0 mL H₂/L-h and 918 ± 63 mL H₂/gVSS-d, at the substrate concentration of 16 g COD/L and 6 h of hydraulic retention time (HRT). Increasing substrate concentration has no effect on the specific hydrogen production rate. The fermentation effluent was used for methane production in an UASB reactor. The higher methane composition in the biogas was achieved as 68% at an influent concentration of 1636 mg COD/L. Peak methane volumetric, specific production rates and yield were attained as 11.7 ± 0.7 mL CH₄/L-h, 7.2 ± 0.4 mL CH₄/g COD-h and 257.9 ± 13.8 mL CH₄/g COD at 24 h-HRT and a substrate concentration of 1636 mg COD/L. An overall organic matter removal (SBR + UASB) in this two-stage process of 73–75% was achieved.     

Application of immobilized upflow anaerobic sludge blanket reactor using Clostridium LS2 for enhanced biohydrogen production and treatment efficiency of palm oil mill effluent

Polyethylene glycol (PEG) gel was used to immobilize hydrogen producing Clostridium LS2 bacteria for hydrogen production in an upflow anaerobic sludge blanket (UASB) reactor. The UASB reactor with a PEG-immobilized cell packing ratio of 10% weight to volume ratio (w/v) was optimal for dark hydrogen production. The performance of the UASB reactor fed with palm oil mill effluent (POME) as a carbon source was examined under various hydraulic retention time (HRT) and POME concentration. The best volumetric hydrogen production rate of 365 mL H₂/L/h (or 16.2 mmol/L/h) with a hydrogen yield of 0.38 L H₂/g COD_added was obtained at POME concentration of 30 g COD/L and HRT of 16 h. The average hydrogen content of biogas and COD reduction were 68% and 65%, respectively. The primary soluble metabolites were butyric acid and acetic acid with smaller quantities of other volatile fatty acid and alcohols formed during hydrogen fermentation. More importantly, the feasibility of PEG-immobilized cell UASB reactor for the enhancement of the dark-hydrogen production and treatment of wastewater is demonstrated.     

Thermophilic hydrogen and methane production from sugarcane stillage in two-stage anaerobic fluidized bed reactors

This study evaluated the feasibility of H₂ and CH₄ production in two-stage thermophilic (55 °C) anaerobic digestion of sugarcane stillage (5,000 to 10,000 mg COD.L⁻¹) using an acidogenic anaerobic fluidized bed reactor (AFBR-A) with a hydraulic retention time (HRT) of 4 h and a methanogenic AFBR (AFBR-S) with HRTs of 24 h–10 h. To compare two-stage digestion with single-stage digestion, a third methanogenic reactor (AFBR-M) with a HRT of 24 h was fed with increasing stillage concentrations (5,000 to 10,000 mg COD.L⁻¹). The AFBR-M produced a methane content of 68.4 ± 7.2%, a maximum yield of 0.30 ± 0.04 L CH₄.g COD⁻¹, a production rate of 3.78 ± 0.40 L CH₄.day⁻¹.L⁻¹ and a COD removal of 73.2 ± 5.0% at an organic loading rate (OLR) of 7.5 kg COD.m⁻³.day⁻¹. In contrast, the two-stage AFBR-A system produced a hydrogen content of 23.9 ± 5.6%, a production rate of 1.30 ± 0.16 L H₂.day⁻¹.L⁻¹ and a yield of 0.34 ± 0.08 mmol H₂.g CODap⁻¹. Additionally, the decrease in the HRT from 18 h to 10 h in the AFBR-S favored a higher methane production, improving the maximum methane content (74.5 ± 6.0%), production rate (5.57 ± 0.38 L CH₄.day⁻¹.L⁻¹) and yield (0.26 ± 0.06 L CH₄.g COD⁻¹) at an OLR of 21.6 kg COD.m⁻³.day⁻¹ (HRT of 10 h) with a total COD removal of 70.1 ± 7.1%. Under the applied COD of 10,000 mg L⁻¹, the two-stage system showed a 52.8% higher energy yield than the single-stage anaerobic digestion system. These results show that, relative to a single-stage system, two-stage anaerobic digestion systems produce more hydrogen and methane while achieving similar treatment efficiencies.     

Hydrogen and methane production in a bio-electrochemical system assisted anaerobic baffled reactor

In this study, a new process was proposed to enhance the stability and efficiency of an anaerobic baffled reactor (ABR). The process was examined in a four equal compartments ABR with total volume of 3.46 L. The first compartment was operated for fermentative hydrogen production and the last three compartments were used as continuous singer chamber microbial electrolysis cells (MECs) for methanogenesis. The system was operated at 35 ± 1 °C and hydraulic retention time (HRT) of 24 h with influent chemical oxygen demand (COD) concentration of 3500 mg/L–4000 mg/L. The results indicated that the proportion of hydrogen in the first compartment was 20.7% and proportions of methane in the last three compartments were 98.0%, 93.6% and 70.1%, respectively. A total of 98.0% of COD removal rate was achieved as well. Hence, this new system has following advantages: hydrogen production with cleaner effluent, high COD removal rate, and net methane production for practical use.     

Continuous hydrogen production from tofu processing waste using anaerobic mixed microflora under thermophilic conditions

We carried out continuous fermentative H₂ production from tofu (soybean curd)-processing waste (TPW) using anaerobic mixed microflora under thermophilic (60 °C) conditions and compared the rates and yields of H₂ production in a continuous stirred-tank reactor (CSTR) and a membrane bioreactor (MBR), wherein the membrane filtration unit was coupled to the CSTR. The TPW was diluted with tap water and then hydrolyzed by blending for 5 min in the presence of 0.5% HCl, and it was found that this protocol significantly increased the amount of soluble material in the mixture. The soluble chemical oxygen demand (SCOD)-to-total COD (TCOD) ratio jumped from 14% to 60%, and the soluble carbohydrate concentration was increased threefold, from 2.4 g/L to 7.2 g/L. Accordingly, H₂ production potential was increased 2.8-fold. In a CSTR operation using pretreated TPW as the substrate, a stable volumetric H₂ production rate (VHPR) of 8.17 ± 0.32 L H₂/L/d and a H₂ yield of 1.20 ± 0.05 mol H₂/mol hexose_added at 8-h HRT were achieved. Substantial increases in the VHPR and H₂ yield over those obtained with the CSTR were observed in the MBR operation. The role of the MBR was to increase the retention time of the solid substrate and the concentration of microorganisms, thereby enhancing the substrate utilization rate for H₂ production. Acetic and butyric acids were the main liquid-state metabolites produced during the fermentation process, thus indicating that the thermophilic operation provided favorable conditions for H₂ production from TPW. A maximum H₂ yield of 1.87 mol H₂/mol hexose_added was achieved at 8-h HRT and then gradually decreased to 1.00 mol H₂/mol hexose-equivalent at 2-h HRT. Meanwhile, the VHPR continuously increased to a maximum of 19.86 L H₂/L/d at 4-h HRT and then decreased with a high dilution rate as the HRT was lowered to 2 h (minimum). At 2-h HRT, the degradation of soluble carbohydrate was limited.     

Effects of substrate concentration and hydraulic retention time on hydrogen production from common reed by enriched mixed culture in continuous anaerobic bioreactor

This study aims to investigate the effect of substrate concentration and hydraulic retention time (HRT) on hydrogen production in a continuous anaerobic bioreactor from unhydrolyzed common reed (Phragmites australis) an invasive wetland and perennial grass. The bioreactor has capacity of 1 L and working volume of 600 mL. It was operated at pH 5.5, temperature at 37 °C, hydraulic retention time (HRT) 12 h, and variation of substrate concentration from 40, 50, and 60 g COD/L, respectively. Afterward, the HRT was then varied from 12, 8, to 4 h for checking the optimal biohydrogen production. Each condition was run until reach steady state on hydrogen production rate (HPR) which based on hydrogen percentage and daily volume. The results were obtained the peak of substrate concentration was at the 50 g COD/L with HRT 12 h, average HPR and H₂ concentration were 28.71 mL/L/h and 36.29%, respectively. The hydrogen yield was achieved at 106.23 mL H₂/g CODre. The substrate concentration was controlled at 50 g COD/L for the optimal HRT experiments. It was found that the maximum of average HPR and H₂ concentration were 43.28 mL/L/h and 36.96%, respectively peak at HRT 8 h with the corresponding hydrogen yield of 144.35 mL H₂/g CODre. Finally, this study successful produce hydrogen from unhydrolyzed common reed by enriched mixed culture in continuous anaerobic bioreactor.     

Non-sterile bio-hydrogen fermentation from food waste in a continuous stirred tank reactor (CSTR): Performance and population analysis

Bio-hydrogen production from food waste by anaerobic mixed cultures was conducted in a continuous stirred tank reactor (CSTR). The hydraulic retention time (HRT) was optimized in order to maximize hydrogen yield (HY) and hydrogen production rate (HPR). The maximum hydrogen content (38.6%), HPR (379 mL H₂/L. d) and HY (261 mL H₂/g-VS_added) were achieved at the optimum HRT of 60 h. The major soluble metabolite products were butyric and acetic acids which indicated a butyrate-acetate type fermentation. Operation of CSTR at HRT 60 h could select hydrogen producing bacteria and eliminate lactic acid bacteria and acetogenic bacteria. The microbial community analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) revealed that the predominant hydrogen producer was Clostridium sp.     

Continuous production of hydrogen from oat straw hydrolysate in a biotrickling filter

Hydrogen was produced in a biotrickling filter (BF) packed with perlite and fed with oat straw acid hydrolysate at 30 °C. Inlet chemical oxygen demand (COD) from 1.2 to 35 g/L and hydraulic retention time (HRT) between 24 h and 6 h were assayed. With increasing inlet COD or decreasing HRT, H₂ production rate (HPR) increased but H₂ production yield (HY) decreased. Maximum HPR of 81.4 mL H₂/L_reactor h (3.3 mmol H₂/L_reactor h) and HY of 2.9 mol H₂/mol_{hexose consumed} were found at an inlet COD of 0.05 g_COD/L h (HRT 24 h) and 2.9 g_COD/L h (HRT 12 h), respectively. Maximum hydrogen composition in gas was 45 ± 4% (v/v) with CO₂ as balance. Methane was not detected. Maximum HPR and inlet COD used in this work were higher than others reported for reactors with suspended or fixed biomass. However, implementation of strategies for biomass control to avoid reactor clogging is needed.     

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.     

An approach of auxiliary carbohydrate source on stabilized biohythane production and energy recovery by two-stage anaerobic process from swine manure

In this study, a two-stage biohythane production system was used to treat swine manure to solve the high Chemical Oxygen Demand (COD) concentration and verify the total energy recovery between the two-stage and a traditional single-stage system. Experiments were carried out in single-stage methane production, two-stage biohythane production in long Hydraulic Retention Time (HRT), and short HRT. The COD removal efficiency and energy recovery were finally compared between single-stage (CH₄ fermenter) and two-stage (H₂+ CH₄ fermenter) systems. The results showed that the methane production rate of 53.2 ± 2.7 mL/d.L, the COD removal efficiency of 29.6 ± 5.8%, and total energy recovery of 2.9 ± 0.1 kJ/L.d was obtained in the single-stage of methane production system with HRT 11.08 d, pH 7, and temperature 55 °C, respectively. In the two-stage of hydrogen and methane productions system, the hydrogen production rate of 1.8 ± 0.7 mL/d.L, the methane production rate of 65.7 ± 2.5 mL/d.L, the COD removal rate was 97.8 ± 1.7%, and the total energy recovery of 3.6 ± 0.1 kJ/L.d was obtained and stabilized when the sugary wastewater content gradually reduced to 0%. This study shows that the methane production rate increases 20%, COD removal efficiency increases to 97.8 ± 1.7%, and total energy recovery increases 30%. At the same time, the single-stage (CH₄ fermenter) switched to a two-stage (H₂+ CH₄ fermenter) system. The two-stage anaerobic biohythane production system successfully treated the high organic swine manure and obtained a higher energy recovery against the traditional single-stage of the biomethane production system.     

The use of acidified palm oil mill effluent for thermophilic biomethane production by changing the hydraulic retention time in anaerobic sequencing batch reactor

The feasibility of thermophilic biomethane production from acidified palm oil mill effluent (POME) was assessed in a 5 L anaerobic sequencing batch reactor (ASBR). The effects of various hydraulic retention time (HRT) (10-1 d) on methane production performance and the stability of ASBR in treating acidified POME were evaluated herein. It was found that the highest methane productivity of 5.65 L CH₄/L/d could be attained at HRT of 2 d. However, the removal of chemical oxygen demand (COD) and volatile fatty acid (VFA) at this HRT is rather low (65-62%) hence making it inefficient to operate at HRT 2 d since most of the contaminants remained in the liquid streams. Thus the most recommended HRT was 3 d with maximum methane productivity of 3.96 L CH₄/L/d with corresponding methane yield of 260.3 L CH₄/kgCOD_removed. The COD removal efficiency at 3 d HRT was 71%, and the VFA consumption was more than 80%. The correlation of total VFA: total alkalinity (TVFA: TA) at HRT of 3 d was found to be 0.1. This recommended HRT of 3 is equally shorter than any previously reported application of POME as a substrate for thermophilic biomethane.     

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.     

Optimizing hydrogen production from a switchgrass steam exploded liquor using a mixed anaerobic culture in an upflow anaerobic sludge blanket reactor

In this study, the operation of an upflow anaerobic sludge blanket reactor (UASBR) producing hydrogen (H₂) from a steam-exploded switchgrass (SWG) liquor was statistically optimized. The factors consider included pH, hydraulic retention time (HRT) and linoleic acid (LA) concentration. Under optimal operational conditions (pH 5.0, 10 h HRT and 1.75 g L⁻¹ LA), which were close to the predicted conditions using the D-optimality index, the maximum H₂ and methane yield observed were 99.86 ± 5.6 mL g⁻¹ TVS and 0.5 ± 0.1 mL g⁻¹ TVS, respectively. Under maximum H₂-producing conditions, high levels of acetate plus butyrate were observed with low levels of ethanol and lactate. A principal component analysis revealed that clustering of the samples was based on the operating conditions and fermentation metabolites. The microbial profiles revealed that by lowering the HRT from 16 to 8 h or decreasing the pH from 7.0 to 5.0 in the controls caused a 50% reduction in the relative abundance of the terminal restriction fragments belonging to the methanogenic population (Methanobacteria, Methanomicrobia, Methanococci). With LA treatment, H₂ producers (Ruminococcaceae and Clostridiaceae) were dominant and methanogens were inhibited and/or washed-out from the UASBR.     

Optimization of hydrogen production from pretreated rice straw waste in a mesophilic up‐flow anaerobic staged reactor

This study was carried out to assess the efficiency of a mesophilic up‐flow anaerobic staged reactor for continuous H₂ production from pretreated rice straw waste. The reactor was operated at different hydraulic retention times (HRTs) of 20, 16, 12, 8 and 4 h. The organic loading rate and sludge residence time were kept constant at 30 g chemical oxygen demand (COD)/L/day, and 1.9 days, respectively. The results showed that increasing the HRT from 4 to 20 h increased the H₂ production from 0.4 ± 0.1 to 3.6 ± 0.3 L H₂/day, respectively. This corresponds to a H₂ yield of 2.1 ± 0.2 mol H₂/g COD_removed at an HRT of 20 h and 0.03 ± 0.002 mol H₂/g COD_removed at an HRT of 4 h. Likewise, carbohydrate and COD removal efficiency was strongly dependant on HRT. The removal efficiency decreased from 76.5 ± 3.4% to 40 ± 2.2% for carbohydrate and from 77.7 ± 4.3% to 12.2 ± 2.1% for COD when the HRT is reduced from 20 to 4 h, respectively. The addition of presettled sewage sludge to pretreated rice straw at a mixing ratio of 1:4 (v/v) increased the volumetric H₂ production from 3.6 ± 0.3 to 8.2 ± 2.5 L/day and the H₂ yield from 2.1 ± 0.2 to 2.8 ± 0.3 mol H₂/g COD_removed. Moreover, the removal efficiency of COD, volatile solids and carbohydrate was significantly improved. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Effect of hydraulic retention time on the hydrogen production in a horizontal and vertical continuous stirred-tank reactor

Hydraulic retention time (HRT) is the main process parameter for biohydrogen production by anaerobic fermentation. This paper investigated the effect of the different HRT on the hydrogen production of the ethanol-type fermentation process in two kinds of CSTR reactors (horizontal continuous stirred-tank reactor and vertical continuous stirred-tank reactor) with molasses as a substrate. Two kinds of CSTR reactors operated with the organic loading rates (OLR) of 12kgCOD/m3•d under the initial HRT of the 8 h condition, and then OLR was adjusted as 6kgCOD/m3•d when the pH drops rapidly. The VCSTR and HCSTR have reached the stable ethanol-type fermentation process within 21 days and 24 days respectively. Among the five HRTs settled in the range of 2–8 h, the maximum hydrogen production rate of 3.7LH₂/Ld and 5.1LH₂/Ld were investigated respectively in the VCSTR and HCSTR. At that time the COD concentration and HRT were 8000 mg/L and 5 h for VCSTR, while 10000 mg/L and 4 h for HCSTR respectively.Through the analysis on the composition of the liquid fermentation product and biomass under the different HRT condition in the two kinds of CSTR, it can found that the ethanol-type fermentation process in the HCSTR is more stable than VCSTR due to enhancing biomass retention of HCSTR at the short HTR.     

Biohydrogen production from diluted-acid hydrolysate of rice straw in a continuous anaerobic packed bed biofilm reactor

Bio-hydrogen production in a continuously operated anaerobic packed bed biofilm reactor (APBR) using acid-hydrolysate of rice straw as feedstock and inoculated with an anaerobic mesophilic sludge from a municipal wastewater treatment plant was investigated at three different HRTs (17, 8.2 and 2 h). Fermentable sugars solution achieved from a two-stage diluted acid hydrolysis of rice straw was used as the feedstock. First, rice straw was treated with 1% w v^?1 sulfuric acid at 120 °C for 30 min with a yield of 58.5% xylose. Higher temperature of 180 °C for 10 min at 0.5% w v^?1 sulfuric acid was applied in the second stage in which cellulosic crystalline structure was partially depolymerized to glucose with a yield of 19.3% glucose. Hydrogen production rate and yield were enhanced as the hydraulic retention time was decreased with a maximum production rate of 252 mL L^?1 h^?1 and yield of 1 mol H₂ mol^?1 sugar consumed at 2 h HRT. Experimental results illustrated the increase of COD conversion from 44% to 47% by shortening the HRT from 17 to 2 h. Furthermore, acetic acid and butyric acid production were reduced slower than other soluble metabolites like ethanol.     

Effect of acid,heat and combined acid-heat pretreatments of anaerobic sludge on hydrogen production by anaerobic mixed cultures

Activated sludge (AS) from wastewater treatment plant of brewery industry was used as substrate for hydrogen production by anaerobic mixed cultures in batch fermentation process. The AS (10% TS) was pretreated by acid, heat and combined acid and heat. Combined acid- heat treatment (0.5% (w/v) HCl, 110 °C, 60 min) gave the highest soluble COD (sCOD) of 1785.6 ± 27.1 mg/L with the highest soluble protein and carbohydrate of 8.1 ± 0.1 and 38.5 ± 0.8 mg/L, respectively. After the pretreatment, the pretreated sludge was used to produce hydrogen by heat treated upflow anaerobic sludge blanket (UASB) granules. A maximum hydrogen production potential of 481 mL H₂/L was achieved from the AS pretreated with acid (0.5% (w/v) HCl) for 6 h.     

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.     

Evaluation of feeding strategies in upflow anaerobic sludge bed reactor for hydrogenogenesis at psychrophilic temperature

The present work evaluated the biohydrogen production from a 0.4 L upflow anaerobic sludge blanket reactor type (UASB) operating at psychrophilic temperature (21 ± 2 °C) at different feeding strategies varying hydraulic retention times (HRT) and sucrose concentration in the feeding. First strategy (24 h/31c) fed semi-continuously 31 g_sucrose L⁻¹ at 24 h HRT; second strategy (12 h/19c) fed semi-continuously 19 g_sucrose L⁻¹ at 12 h HRT; third strategy (4 h/8c) fed continuously 8.3 g_sucrose L⁻¹ at 4 h HRT.After 70 days of operation, the UASB accumulated 65.44 L H₂. The average HY for the whole operation during the three strategies was 62.6 NmL H₂ g_sucrose⁻¹, and average hydrogen content was 69.04%. In general terms, the best operation strategy was 12 h/19c since it presented good set of results, the best HY (70.6 NmL H₂ g_sucrose⁻¹) and a comparable hydrogen production rate (2.6 L (L d)⁻¹) to that obtained in 4 h/8c strategy (3.17 L (L d)⁻¹). The average gross energy potential rate from the 12 h/19c strategy was 46.21 kJ (L d)⁻¹, whereas energy heating losses were circumvented due to operation at psychrophilic regime. Indeed, psychrophilic or room temperatures should be broadly regarded as an effective alternative towards net energy gains in biohydrogen production.