Effect of hydraulic retention time on a continuous biohydrogen production in a packed bed biofilm reactor with recirculation flow of the liquid phase

The present paper reports on results obtained from experiments carried out in a laboratory-scale anaerobic packed bed biofilm reactor (APBR), with recirculation of the liquid phase, for continuously biohydrogen production via dark fermentation. The reactor was filled with Kaldnes^® biofilm carrier and inoculated with an anaerobic mesophilic sludge from a urban wastewater treatment plant (WWTP). The APBR was operated at a temperature of 37 °C, without pH buffering. The effect of theoretical hydraulic retention time (HRT) from 1 to 5 h on hydrogen yield (HY), hydrogen production rate (HPR), substrate conversion and metabolic pathways was investigated. This study indicates the possibility of enhancing hydrogen production by using APBR with recirculation flow. Among respondents values of HRT the highest average values of HY (2.35 mol H₂/mol substrate) and HPR (0.085 L h^?1L^?1) have been obtained at HRT equal to 2 h.     

Biohydrogen production from organic solid waste in a sequencing batch reactor: An optimization of the hydraulic and solids retention time

Hydrogen production from organic solids waste was evaluated using a sequencing batch reactor (SBR) under mesophilic conditions, to investigate the effect of the hydraulic retention time (HRT) and solids retention time (SRT) on hydrogen production. The examined HRT and SRT values were from 4.6 to 27 h and 17–102 h, respectively. The results showed high hydrogen production rates (1.86 LH₂/L·d) and a yield of 127.26 mLH₂/gCOD_removed for an SRT of 60 h and an HRT of 16 h. The highest chemical oxygen demand (COD) removal (38.6 ± 6.9%) was also obtained under those conditions. The highest substrate hydrolysis percentage (73.0 ± 11.4%) was obtained at an HRT of 16 h and an SRT of 102 h. A short SRT of 20 h affected hydrogen production, which decreased up to 90%. With an SRT of 20 h and an HRT of 16 h, acetic acid-like fatty acids were mainly obtained. In experiments with a long SRT (60 h), the obtained fatty acid was butyrate. The conversion efficiencies for converting particulate material into fatty acids were 51–47% using a long SRT; a short HRT resulted in percentages of 37–40%. A 3D surface analysis was performed using the maximum hydrogen yield conditions as the central point, showing that the optimal hydrogen production can be obtained with an HRT of 16 h and an SRT of 55 h. Microbial analysis showed the predominance of the Olsenella genus at an HRT< 8 h and the presence of Clostridium at an HRT of 16 h. The HRT is the main parameter leading the community composition in the process.     

Hydrogen and methane production in extreme thermophilic conditions in two-stage (upflow anaerobic sludge bed) UASB reactor system

Two-stage hydrogen and methane production in extreme thermophilic (70 °C) conditions was demonstrated for the first time in UASB-reactor system. Inoculum used in hydrogen and methane reactors was granular sludge from mesophilic internal circulation reactor and was first acclimated for extreme thermophilic conditions. In hydrogen reactor, operated with hydraulic retention time (HRT) of 5 h and organic loading rate (OLR) of 25.1 kg COD/m³/d, hydrogen yield was 0.73 mol/mol glucose_added. Methane was produced in second stage from hydrogen reactor effluent. In methane reactor operated with HRT of 13 h and OLR of 7.8 kg COD/m³/d, methane yield was 117.5 ml/g COD_added. These results prove that hydrogen and methane can be produced in extreme thermophilic temperatures, but as batch experiments confirmed, for methane production lower temperature would be more efficient.     

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.     

Thermophilic hydrogen production from starch wastewater using two-phase sequencing batch fermentation coupled with UASB methanogenic effluent recycling

The aim of this study was to evaluate the performance of thermophilic hydrogenesis coupled with mesophilic methanogenesis in which the effluent was recycled to the hydrogen reactor for starch wastewater treatment. With this system, the hydrogen production rate and yield were 3.45 ± 0.25 L H₂/(L·d) and 5.79 ± 0.41 mmol H₂/g COD_added respectively, and thus higher than the values of the control group without methanogenic effluent recycling. In addition, relatively higher contents of acetate and butyrate were obtained in the hydrogen reactor with recirculation. The methane reactors were operated with the effluent from the hydrogen reactor, and methane yield was stabilized at 0.21–0.23 L/g COD_removal in both. Analysis of the microbial communities further showed that methanogenic effluent recirculation enriched microbial communities in the hydrogen reactor. Two species of bacteria effective in hydrogenesis, Thermoanaerobacterium thermosaccharolyticum and Clostridium thermosaccharolyticum, dominated during hydrogen production, whereas archaea belonging to Euryarchaeota were detected and cultured in the methane reactor. The recycled effluent supplied alkaline substrates for the hydrogen producing bacteria. Alkali balance calculations showed that the amount of added alkali was reduced by 88%. This amount, required for hydrogen production from starch wastewater, was contributed by alkali in the methanogenic effluent, (2225 ± 140 mg CaCO₃/L), resulting in lower operational costs.     

Effects of process,operational and environmental variables on biohydrogen production using palm oil mill effluent (POME)

A batch study for biohydrogen production was conducted using raw palm oil mill effluent (POME) and POME sludge as a feed and inoculum respectively. Response Surface Methodology (RSM) was used to design the experiments. Experiments were conducted at different reaction temperatures (30–50 °C), inoculum size to substrate ratios (I:S) and reaction times (8–24 h). An optimum condition of biohydrogen production was achieved with COD removal efficiency of 21.95% with hydrogen yield of 28.47 ml H₂ g^?1 COD removed. The I:S ratio was 40:60, with reaction temperature of 50 °C at 8 h of reaction time. The study showed that a lower substrate concentration (less than 20 g L^?1) for biohydrogen production using pre-settled POME was achievable, with optimum HRT of 8 h under thermophilic condition (50 °C). This study also found that pre-settled POME is feasible to be used as a substrate for biohydrogen production under thermophilic condition.     

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.     

Biohydrogen production,sludge granulation,and microbial community in an anaerobic inner cycle biohydrogen production (AICHP) reactor at different hydraulic retention times

This study investigated the continuous biohydrogen production in an anaerobic inner cycle biohydrogen production (AICHP) reactor fed with synthetic molasses wastewater as the model substrate under mesophilic conditions (37 ± 1 °C). The hydraulic retention times (HRTs) were set as 6.12, 4.90, 4.08, 3.50, and 3.06 h. Both maximum hydrogen production rate (HPR) (8.08 ± 0.48 L/L/d) and maximum granule formation were achieved at the HRT of 3.50 h. Acetic acid and butyric acid were the dominant metabolites in all tested HRTs throughout the experiment. Microbial community analysis showed that shortening the HRT promoted hydrogen production. This was mainly achieved by enhancing the growth of acetogenic bacteria in the AICHP reactor, rather than the growth of hydrogen-producing bacteria.     

Performance optimization of microbial electrolysis cell (MEC) for palm oil mill effluent (POME) wastewater treatment and sustainable Bio-H2 production using response surface methodology (RSM)

Microbial electrolysis cells (MECs) are a new bio-electrochemical method for converting organic matter to hydrogen gas (H₂). Palm oil mill effluent (POME) is hazardous wastewater that is mostly formed during the crude oil extraction process in the palm oil industry. In the present study, POME was used in the MEC system for hydrogen generation as a feasible treatment technology. To enhance biohydrogen generation from POME in the MEC, an empirical model was generated using response surface methodology (RSM). A central composite design (CCD) was utilized to perform twenty experimental runs of MEC given three important variables, namely incubation temperature, initial pH, and influent dilution rate. Experimental results from CCD showed that an average value of 1.16 m³ H₂/m³ d for maximum hydrogen production rate (HPR) was produced. A second-order polynomial model was adjusted to the experimental results from CCD. The regression model showed that the quadratic term of all variables tested had a highly significant effect (P < 0.01) on maximum HPR as a defined response. The analysis of the empirical model revealed that the optimal conditions for maximum HPR were incubation temperature, initial pH, and influent dilution rate of 30.23 ^°C, 6.63, and 50.71%, respectively. Generated regression model predicted a maximum HPR of 1.1659 m³ H₂/m³ d could be generated under optimum conditions. Confirmation experimentation was conducted in the optimal conditions determined. Experimental results of the validation test showed that a maximum HPR of 1.1747 m³ H₂/m³ d was produced.     

An anaerobic sequential batch reactor for enhanced continuous hydrogen production from fungal pretreated cornstalk hydrolysate

Anaerobic sequencing batch reactor (ASBR) process offers great potential for H₂ production from wastewaters. In this study, an ASBR was used at first time for enhanced continuous H₂ production from fungal pretreated cornstalk hydrolysate by Thermoanaerobacterium thermosaccharolyticum W16. The reactor was operated at different hydraulic retention times (HRTs) of 6, 12, 18, and 24 h by keeping the influent hydrolysate constant at 65 mmol sugars L⁻¹. Results showed that increasing the HRT from 6 to 12 h led to the H₂ production rate increased from 6.7 to the maximum of 9.6 mmol H₂ L⁻¹ h⁻¹ and the substrate conversion reached 90.3%, although the H₂ yield remained at the same level of 1.7 mol H₂ mol⁻¹ substrate. Taking into account both H₂ production and substrate utilization efficiencies, the optimum HRT for continuous H₂ production via an ASBR was determined at 12 h. Compared with other continuous H₂ production processes, ASBR yield higher H₂ production at relatively lower HRT. ASBR is shown to be another promising process for continuous fermentative H₂ production from lignocellulosic biomass.     

Continuous biohydrogen production in immobilized biofilm system versus suspended cell culture

In this study, the performance of a new cell immobilization material, namely ceramic ball, was examined for continuous biohydrogen production in comparison to suspended cell culture system (CSTR). Production of biohydrogen in both systems was assessed under thermophilic conditions. Both systems were operated at varying hydraulic retention times (HRT) by shortening HRT values from 24 to 1.5 h at an influent sucrose concentration of 10 g/l. The immobilized bioreactor configuration outcompeted the CSTR bioreactor in terms of both volumetric hydrogen production (2.7 l H₂/l/day for immobilized system @ HRT = 3 h and 0.5 l H₂/l/day for CSTR @ HRT = 24 h) and resistance to cell-washout (CSTR reactor lost significant amount of biomass at short HRT values). It was concluded that immobilized bioreactor configuration is much more robust than CSTR against high organic loading rates and 5 fold more volumetric hydrogen production was achieved in 8 fold smaller immobilized bioreactor.     

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.     

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.     

Two-stage UASB reactor converting coffee drink manufacturing wastewater to hydrogen and methane

In this study, the feasibility of a continuous two-stage up-flow anaerobic sludge blanket (UASB) reactor system, consisted of thermophilic (55 °C) dark fermentative H₂ production and mesophilic (35 °C) CH₄ production from coffee drink manufacturing wastewater (CDMW), was tested. A recently proposed operational strategy was used to overcome a major drawback of the long start-up period of the UASB reactor. Firstly, a completely stirred tank reactor (CSTR) was operated for 8 days to prepare seeding. The seed was then directly transferred to the UASB reactor. Microbial aggregation took place in the initial period, and the floc size was gradually increased over time. In UASB reactor, the maximum H₂ yield of 2.57 mol H₂/mol hexose_added and a stable H₂ production rate of 4.24 L H₂/L/h were observed at a hydraulic retention time (HRT) of 6 h and substrate concentration of 20 g Carbo. COD/L. In this novel method using CDMW, thermophilic H₂-producing granules with an average particle size of 1.3 mm was successfully developed after 100 days. The more bioenergy recovery was attempted in a post-treatment process using a mesophilic UASB reactor for CH₄ production from the H₂ fermented effluent. The maximum CH₄ yield of 325 mL of CH₄/g COD was achieved with removing 93% of the COD at an organic loading rate of 3.5 g COD/L/d. The developed two-stage UASB reactor system achieved biogas conversion by 88.2% (H₂ 15.2% and CH₄ 73%) and COD removal by 98%.     

Hydrogen production from alcohol wastewater by an anaerobic sequencing batch reactor under thermophilic operation: Nitrogen and phosphorous uptakes and transformation

The objective of this study was to investigate hydrogen production from alcohol wastewater using an anaerobic sequencing batch reactor (ASBR) under thermophilic operation and at a constant pH of 5.5. Under the optimum COD loading rate of 68 kg/m³d, the produced gas contained 43% H₂ without methane and the system provided a hydrogen yield and specific hydrogen production rate of 130 ml H₂/g COD removed and 2100 ml H₂/l d, respectively, which were much higher than those obtained under the mesophilic operation. Under thermophilic operation, both nitrogen and phosphate uptakes were minimal at the optimum COD loading rate for hydrogen production and most nitrogen uptake was derived from organic nitrogen. Under the thermophilic operation for hydrogen production, the nutrient requirement in terms of COD:N:P was found to be 100:6:0.5, which was much higher than that for the methenogenic step for methane production under both thermophilic and mesophilic operations and for the acidogenic step for hydrogen production under mesophilic operation.     

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.     

Biohydrogen production from crude glycerol by immobilized Klebsiella sp. TR17 in a UASB reactor and bacterial quantification under non-sterile conditions

Biohydrogen production from crude glycerol by immobilized Klebsiella sp. TR17 was investigated in an up-flow anaerobic sludge blanket (UASB) reactor. The reactor was operated under non-sterile conditions at 40^○C and initial pH 8.0 at different hydraulic retention times (HRTs) (2–12 h) and glycerol concentrations (10–30 g/L). Decreasing the HRT led to an increase in hydrogen production rate (HPR) and hydrogen yield (HY). The highest HPR of 242.15 mmol H₂/L/d and HY of 44.27 mmol H₂/g glycerol consumed were achieved at 4 h HRT and glycerol concentrations of 30 and 10 g/L, respectively. The main soluble metabolite was 1,3-propanediol, which implies that Klebsiella sp. was dominant among other microorganisms. Fluorescence in situ hybridization (FISH) revealed that the microbial community was dominated by Klebsiella sp. with 56.96, 59.45, and 63.47% of total DAPI binding cells, at glycerol concentrations of 10, 20, and 30 g/L, respectively.     

Steady-state and dynamic modeling of biohydrogen production in an integrated biohydrogen reactor clarifier system

Steady-state operational data from the integrated biohydrogen reactor clarifier system (IBRCS) during anaerobic treatment of glucose-based synthetic wastewater at HRT of 8 h and SRT ranging from 26 to 50 h and organic loading rates of 6.5–206 gCOD/L-d were used to calibrate and verify a process model of the system developed using BioWin. The model accurately predicted biomass concentrations in both the bioreactor and the clarifier supernatant with average percentage errors (APEs) of 4.6% and 10%, respectively. Hydrogen production rates and hydrogen yields predicted by the model were in close agreement with the observed experimental results as reflected by an APE of less than 4%, while the hydrogen content was well correlated with an APE of 10%. The successful modeling culminated in the accurate prediction of soluble metabolites, i.e. volatile fatty acids in the reactor with an APE of 14%. The calibrated model confirmed the advantages of decoupling of the solids retention time (SRT) from the hydraulic retention time (HRT) in biohydrogen production, with the average hydrogen yield decreasing from 3.0 mol H₂/mol glucose to 0.8 mol H₂/mol glucose upon elimination of the clarifier. Dynamic modeling showed that the system responds favorably to short-term hydraulic and organic surges, recovering back to the original condition. Furthermore, the dynamic simulation revealed that with a prolonged startup periods of 10 and 30 days, the IBRCS can be operated at an HRT of 4 h and OLR as high as 206 gCOD/L-d without inhibition and/or marked performance deterioration.     

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).     

Hydrogen production from alcohol wastewater with added fermentation residue by an anaerobic sequencing batch reactor (ASBR) under thermophilic operation

The objective of this study was to investigate the enhancement of hydrogen production from alcohol wastewater by adding fermentation residue using an anaerobic sequencing batch reactor (ASBR) under thermophillic operation (55 °C) and at a constant pH of 5.5. The digestibility of the added fermentation residue was also evaluated. For a first set of previous experiments, the ASBR system was operated to obtain an optimum COD loading rate of 50.6 kg/m³ d of alcohol wastewater without added fermentation residue and the produced gas contained 31% H₂ and 69% CO₂. In this experiment, the effect of added fermentation residue (100–1200 mg/l) on hydrogen production performance was investigated under a COD loading rate of 50.6 kg/m³ d of the alcohol wastewater. At a fermentation residue concentration of 1000 mg/l, the produced gas contained 40% H₂ and 60% CO₂ without methane and the system gave the highest hydrogen yield and specific hydrogen production rate of 128 ml/g COD removed and 2880 ml/l d, respectively. Under thermophilic operation with a high total COD loading rate (51.8 kg/m³ d) and a short HRT (21 h) at pH 5.5, the ASBR system could only break down cellulose (41.6%) and hemicellulose (21.8%), not decompose lignin.