Effect of pH on continuous biohydrogen production from liquid swine manure with glucose supplement using an anaerobic sequencing batch reactor

pH is considered as one of the most important factors governing the hydrogen fermentation process. In this project, five pH levels, ranging from 4.4 to 5.6 at 0.3 increments, were tested to evaluate the pH effect on hydrogen production from swine manure supplemented with glucose in an anaerobic sequencing batch reactor system with 16 h of hydraulic retention time (HRT). The optimal hydrogen yield (1.50 mol H₂/mol glucose) was achieved at pH 5.0 when the maximum production rate of 2.25 L/d/L was obtained. Continuous hydrogen production was achieved for over 3 weeks for pH 5.0, 4.7, and 4.4, with no significant methane produced. However, as pH increased to 5.3 and 5.6, methane production was observed in the biogas with concurrent reductions in hydrogen production, indicating that methanogens could become increasingly activated for pH 5.3 or higher. Acetate, propionate, butyrate, valerate, and ethanol were the main aqueous products whose distribution was significantly affected by pH as well.     

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.     

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.     

Effect of hydraulic retention time on hydrogen production and chemical oxygen demand removal from tapioca wastewater using anaerobic mixed cultures in anaerobic baffled reactor (ABR)

This study evaluated hydrogen production and chemical oxygen demand removal (COD removal) from tapioca wastewater using anaerobic mixed cultures in anaerobic baffled reactor (ABR). The ABR was conducted based on the optimum condition obtained from the batch experiment, i.e. 2.25 g/L of FeSO₄ and initial pH of 9.0. The effects of the varying hydraulic retention times (HRT: 24, 18, 12, 6 and 3 h) on hydrogen production and COD removal in a continuous ABR were operated at room temperature (32.3 ± 1.5 °C). Hydrogen production rate (HPR) increased with a reduction in HRT i.e. from 164.45 ± 4.14 mL H₂/L.d (24 h HRT) to 883.19 ± 7.89 mL H₂/L.d (6 h HRT) then decreased to 748.54 ± 13.84 mL H₂/L.d (3 h HRT). COD removal increased with reduction in HRT i.e. from 14.02 ± 0.58% (24 h HRT) to 29.30 ± 0.84% (6 h HRT) then decreased to 21.97 ± 0.94% (3 h HRT). HRT of 6 h was the optimum condition for ABR operation as indicated.     

Biological hydrogen production in an anaerobic sequencing batch reactor: pH and cyclic duration effects

An anaerobic sequencing batch reactor (ASBR) was used to evaluate biological hydrogen production from carbohydrate-rich organic wastes. The goal of the proposed project was to investigate the effects of pH (4.9, 5.5, 6.1, and 6.7), and cyclic duration (4, 6, and 8 h) on hydrogen production. With the ASBR operated at 16-h HRT, 25 g COD/L, and 4-h cyclic duration, the results showed that the maximum hydrogen yield of 2.53 mol H₂/mol sucrose_consumed appeared at pH 4.9. The carbohydrate removal efficiency declined to 56% at pH 4.9, which indirectly resulted in the reduction of total volatile fatty acid production. Acetate fermentation was the dominant metabolic pathway at pH 4.9. The concentration of mixed liquor volatile suspended solid (MLVSS) also showed a decrease from nearly 15,000 mg/L between pHs 6.1 and 6.7 to 6000 mg/L at pH 4.9. Investigation of the effect of cyclic duration found that hydrogen yield reached the maximum of 1.86 mol H₂/mol sucrose_consumed at 4-h cyclic duration while ASBR was operating at 16-h HRT, 15 g COD/L, and pH 4.9. The experimental results showed that MLVSS concentration increased from 6200 mg/L at 4-h cyclic duration to 8500 mg/L at 8-h cyclic duration. However, there was no significant change in effluent volatile suspended solid concentration. The results of butyrate to acetate ratio showed that using this ratio to correlate the performance of hydrogen production is not appropriate due to the growth of homoacetogens. In ASBR, the operation is subject to four different phases of each cycle, and only the complete mix condition can be achieved at react phase. The pH and cyclic duration under the unique operations profoundly impact fermentative hydrogen production.     

Modeling fermentative hydrogen production from sucrose supplemented with dairy manure

Our previous studies had shown that fermentative hydrogen production from sucrose could be improved with dairy manure as a supplement. In addition to contributing to nearly 10% more hydrogen yield at ambient temperature, dairy manure was shown to be capable of providing the required nutritional needs, buffering capacity, and hydrogen-producing organisms, improving the practical viability of fermentative hydrogen production. In this report, we present a kinetic model for fermentative hydrogen production from sucrose supplemented with dairy manure. This model includes hydrogen production from sucrose as well as from the soluble products hydrolyzed from particulate manure. The integrated model was calibrated using experimental data from one batch reactor and validated with dissolved COD, hydrogen, and volatile fatty acid data from four other reactors. Predictions by this model agreed well with the temporal trends in the experimental data, with r² averaging 0.85 for dissolved COD; 0.94 for total COD; 0.84 for hydrogen; 0.84 for acetic acid; and 0.89 for butyric acid; quality of fit in the case of propionic acid was lower with r² averaging 0.57.     

CFD simulation of an expanded granular sludge bed (EGSB) reactor for biohydrogen production

Understanding how a bioreactor functions is a necessary precursor for successful reactor design and operation. This paper describes a two-dimensional computational fluid dynamics simulation of three-phase gas–liquid–solid flow in an expanded granular sludge bed (EGSB) reactor used for biohydrogen production. An Eulerian–Eulerian model was formulated to simulate reaction zone hydrodynamics in an EGSB reactor with various hydraulic retention times (HRT). The three-phase system displayed a very heterogeneous flow pattern especially at long HRTs. The core-annulus structure developed may lead to back-mixing and internal circulation behavior, which in turn gives poor velocity distribution. The force balance between the solid and gas phases is a particular illustration of the importance of the interphase rules in determining the efficiency of biohydrogen production. The nature of gas bubble formation influences velocity distribution and hence sludge particle movement. The model demonstrates a qualitative relationship between hydrodynamics and biohydrogen production, implying that controlling hydraulic retention time is a critical factor in biohydrogen-production.     

Feasibility studies on continuous hydrogen production using photo-fermentative sequencing batch reactor

A novel photo-fermentative sequencing batch reactor (PFSBR) process assisted by activated carbon fibers (ACFs) was used to continuously produce hydrogen gas by Rhodopseudomonas faecalis RLD-53. Feasibility of continuous hydrogen production in PFSBR operation at different hydraulic retention times (HRTs) (48, 96, 144 and 192 h) and influent acetate concentrations (20, 40, 60 and 80 mmol/l) was investigated. The rate and yield of hydrogen production increased with HRTs from 48 to 144 h, and then decreased with the HRTs from 144 to 192 h. Regulation of the proper influent acetate concentration (60 mmol/l) not only increased hydrogen production by PFSBR, but also maintained quality of the effluent with high substrate removal efficiency (97.70%). Free R. faecalis RLD-53 was adsorbed on the surface of ACFs, initially isolated cells, then monolayer, and finally mature biofilm with three dimensional multilayers structures. The PFSBR reached a maximum hydrogen yield (3.12 mol H₂/mol acetate), and achieved a steady state when mature biofilm developed on ACFs. Therefore, photo-fermentative sequencing batch reactor was a promising process for continuous photo-fermentative hydrogen production.     

The effect of HRT on biohydrogen production from acid hydrolyzed waste wheat in a continuously operated packed bed reactor

Biohydrogen production in a continuously operated up flow packed bed reactor was investigated at different hydraulic retention time (HRT) varying between 2 h and 13 h scouring sponge pad. The substrate was sugar solution obtained from hydrolysis of waste wheat at pH = 2 and 90 °C in an autoclave for 15 min. Experimental results indicated that hydrogen production volume and yield increases with decreasing HRT. The highest volumetric hydrogen production rate and yield were obtained as VHPR = 1.75 L H₂/L d and Y_H2 = 1.6 moL H₂/mol TS, respectively, at HRT = 2 h. Yields and rates at HRT = 2 h were almost two times of that obtained at HRT = 13 h. It can be concluded that metal mesh covered plastic scouring sponge pad is a suitable microorganism support particle to obtain high hydrogen yield and rate at short HRTs by dark fermentation.     

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,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.     

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.     

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.     

Influence of Cu concentration on the biohydrogen production of continuous stirred tank reactor

In this paper, the effect of hydraulic retention time (HRT, 16 h–4 h) on fermentative hydrogen production by mixed cultures was firstly investigated in a sucrose-fed anaerobic continuous stirred tank reactor (CSTR) at 35 °C and initial pH 8.79. After stable operations at HRT of 16–6 h, the bioreactor became unstable when the HRT was lowered to 4 h. The maximum hydrogen yield reached 3.28 mol H₂/mol-Sucrose at HRT 4 h. Supplementation of Cu²⁺ at HRT 4 h improved the operation stability through enhancement of substrate degradation efficiency. The effect of Cu²⁺ concentration ranging from 1.28 to 102.4 mg/L on fermentative hydrogen production was studied. The results showed that Cu²⁺ was able to enhance the hydrogen production yield with increasing Cu²⁺ concentration from 1.28 to 6.4 mg/L. The maximum hydrogen yield of 3.31 mol H₂/mol-Sucrose and the maximum hydrogen production rate of 14.44 L H₂/Day/L-Reactor were obtained at 6.4 mg/L Cu²⁺ and HRT 4 h Cu²⁺ at much higher concentration could inhibit the hydrogen production, but it could increase substrate degradation efficiency (12.8 and 25.6 mg/L Cu²⁺). The concentration of Cu²⁺ had effect on the distribution of soluble metabolite.     

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.     

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.     

Continuous hydrogen production from cofermentation of sugarcane vinasse and cheese whey in a thermophilic anaerobic fluidized bed reactor

The co-fermentation of vinasse and cheese whey (CW) was evaluated in this study by using two thermophilic (55° C) anaerobic fluidized bed reactors (AFBRs). In AFBR using vinasse and CW (AFBR-V-CW), the CW was added in increasing proportions (2, 4, 6, 8, and 10 g COD.L^?1) to vinasse (10 g COD.L^?1) to assess the advantage of adding CW to vinasse. By decreasing the hydraulic retention time (HRT) from 8 h to 1 h in AFBR-V, maximum hydrogen yield (HY), production rate (HPR), and H₂ content (H₂%) of 1.01 ± 0.06 mmol H₂.g COD^?1, 2.54 ± 0.39 L H₂.d^?1.L^?1, and 47.3 ± 2.9%, respectively, were observed at an HRT of 6 h. The increase in CW concentration to values over 2 g COD.L^?1 in AFBR-V-CW decreased the HY, PVH, and H₂%, with observed maximum values of 0.82 ± 0.07 mmol H₂.g COD^?1, 1.41 ± 0.24 L H₂.d^?1.L^?1, and 55.5 ± 3.7%, respectively, at an HRT of 8 h. The comparison of AFBR-V-CW and AFBR-V showed that the co-fermentation of vinasse with 2 g COD.L^?1 of CW increased the HPR, H₂%, and HY by 117%, 68%, and 82%, respectively.     

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.     

Enhanced biohydrogen production from leather fleshing waste co-digested with tannery treatment plant sludge using anaerobic hydrogenic batch reactor

Efficient conversion of leather solid waste into bio-hydrogen was evaluated using anaerobic hydrogenic activity in a batch reactor. Major performance indicators such as pH, total solids, volatile solids, chemical oxygen demand, specific hydrogen yield and degradation efficiency of the crude organic matter was investigated for the possibility of optimizing the bio-hydrogen potential. The optimum waste mixing ratio was found to be in LF:S:HS (2:1:1) with a pH of 5.5 at 37°C with a removal rate of 92.3% volatile solids and the cumulative bio-hydrogen yield increased from 41 ml in the control to 323 mL, proving to be 8 times higher. This study proved to increase the efficiency of material and energy, and is definitely more economical for the waste utilization.     

Biohydrogen from molasses with ethanol-type fermentation: Effect of hydraulic retention time

Though ethanol-type fermentation has many advantages for improving hydrogen production rate (HPR) in continuously mode hydrogen producing system, information on this fermentation is very deficient. The effect of hydraulic retention time (HRT) on biohydrogen production and operational stability of ethanol-type fermentation was investigated in a continuous stirred tank reactor (CSTR) using molasses as substrate. Five HRTs were examined, ranging from 4 to 10 h. At HRT 5 h, the highest HPR of 12.27 mmol L⁻¹ h⁻¹ was obtained from ethanol-type fermentation in the pH range of 4.3–4.4. During the whole operation process, ethanol, butyrate and acetate were the predominant metabolites. A total COD concentration of ethanol and acetate accounted for above 73.3% of total soluble microbial products. Linear regression showed that HPR and ethanol production rate were proportionately correlated at all HRTs which could be expressed as y = 0.9821x − 3.5151 (r² = 0.9498). It is meaningful that the proposed recovery of both hydrogen and ethanol from fermentation process can improve energy production rate and economic profit. Results demonstrated that the best energy production rate was 15.50 kJ L⁻¹ h⁻¹, occurred at HRT = 5 h.