Optimizing hydrogen production from organic wastewater treatment in batch reactors through experimental and kinetic analysis

Anaerobic hydrogen production from organic wastewater, an emerging biotechnology to generate clean energy resources from wastewater treatment, is critical for environmental and energy sustainability. In this study, hydrogen production, biomass growth and organic substrate degradation were comprehensively examined at different levels of two critical parameters (chemical oxygen demand (COD) and pH). Hydrogen yields had a reverse correlation with COD concentrations. The highest specific hydrogen yield (SHY) of 2.1 mole H₂/mole glucose was achieved at the lowest COD of 1 g/L and decreased to 0.7 mole H₂/mole glucose at the highest COD of 20 g/L. The pH of 5.5–6.0 was optimal for hydrogen production with the SHY of 1.6 mole H₂/mole glucose, whereas the acidic pH (4.5) and neutral pH (6.0–7.0) lowered the hydrogen yields. Under all operational conditions, acetate and butyrate were the main components in the liquid fermentation products. Additionally, a comprehensive kinetic analysis of biomass growth, substrate degradation and hydrogen production was performed. The maximum rates of microbial growth (μ_m) and substrate utilization (R_su) were 0.03 g biomass/g biomass/day and 0.25 g glucose/g biomass/day, respectively. The optimum pH for the rate of hydrogen production (RH₂$R_{{\text{H}}_2}$) and SHY were 5.89 and 5.74 respectively. Based on the kinetic analysis, the highest RH₂$R_{{\text{H}}_2}$ and SHY for batch-mode anaerobic hydrogen production systems were projected to be 13.7 mL/h and 2.32 mole H₂/mole glucose.     

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.     

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.     

Continuous biohydrogen production from liquid swine manure supplemented with glucose using an anaerobic sequencing batch reactor

Liquid swine manure supplemented with glucose (10 g/L) was used as substrate for hydrogen production using an anaerobic sequencing batch reactor at 37 ± 1 °C and pH 5.0 under different hydraulic retention times (HRTs). Decreasing HRT from 24 to 8 h caused an increasing hydrogen production rate from 0.05 to 0.15 L/h/L. Production rates of both total biogas and hydrogen were linearly correlated to HRT with R² being 0.993 and 0.997, respectively. The hydrogen yield ranged between 1.18 and 1.63 mol-H₂/mol glucose and the 12 h HRT was preferred for high production rate and efficient yield. For all the five HRTs examined, the glucose utilization efficiency was over 98%. The biogas mainly consisted of carbon dioxide and hydrogen (up to 43%) with no methane detected throughout the experiment. Ethanol and organic acids were the major aqueous metabolites produced during fermentation, with acetic acid accounting for 56–58%. The hydrogen yield was found to be related to the acetate/butyrate ratio.     

Evolution of methane and hydrogen from ethanol wastewater with maximization of energy yield by three-stage anaerobic sequencing batch reactor system

A new anaerobic sequencing batch reactor (ASBR) unit with three stage concept was proposed and tested for spontaneous generation of hydrogen (H₂) and methane (CH₄) from ethanol wastewater with maximum energy yield. The system was controlled at 37 °C, a fixed pH of 5.5 in the first bioreactor and a recycle ratio of unity from the third bioreactor to the first bioreactor to lower the amount of sodium hydroxide for pH regulation in the first bioreactor and to increase total alkalinity and process stability. Under the optimum organic loading rate of 15 kg COD/m³d (based on the total liquid holding volume), it exhibited the highest yields and specific generation rates of both gases, resulting in the uppermost overall energy yield which was much higher than those of all other anaerobic systems. The lactic acid was found to be about 4–8 times more toxic than acetic acid to methanogens. The higher the solution pH in any anaerobic system, the greater the reduction of micronutrients.     

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.     

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.     

Biohydrogen and biomethane production from cassava wastewater in a two-stage anaerobic sequencing batch biofilm reactor

The objective of the present study was to determine the energetic potential from cassava starch wastewater in a two-stage system (BioH₂ + BioCH₄) composed by anaerobic sequencing batch biofilm reactors (AnSBBR). Included in this general objective, the behavior of the methanogenic AnSBBR regarding organic matter removal and biomethane production will be investigated. The acidogenic AnSBBR was operated with organic loading rate (OLR) of 14 gCarb.L⁻¹.d⁻¹, influent concentration of 5 gCarb.L⁻¹ and cycle time of 4 h. The methanogenic AnSBBR was submitted to OLR increase (3.7–12 gCOD.L⁻¹.d⁻¹), provided by arrangements between influent concentration (2.8; 4.0 and 6.0 gCOD.L⁻¹) and cycle time (6; 8 and 12 h). For the evaluated condition, the acidogenic reactor presented productivity of 0.7 LH₂.L⁻¹.d⁻¹ and yield of 1.1 molH₂.kg⁻¹Carb. The methanogenic reactor presented stable methane production (%CH₄ > 78) during the 260-days operating period. The maximum methane productivity (2.71 LCH₄.L⁻¹.d⁻¹) and yield (0.263 LCH₄.g⁻¹COD) were obtained at OLR of 12 gCOD.L⁻¹.d⁻¹ and cycle time of 6 h. The estimated energy production rate in the two-stage system (BioH₂ + BioCH₄) was 105.2 kJ.L⁻¹.d⁻¹.     

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.     

On-site hydrogen production from transportation fuels: An overview and techno-economic assessment

Hydrogen production for future transportation applications have received increased interest due to its inherent environmental and efficiency benefits. Currently, hydrogen is produced from natural gas and naphtha for its use in refineries for clean fuel production along with its use in ammonia production. The hydrogen demand will grow in future for hydrogen based fuel cell vehicles. Significant research is underway to produce hydrogen from renewable and fossil fuel sources. However, on-site hydrogen production using existing fuel and gas station infrastructure to support future hydrogen based fuel cell vehicles has advantages over other approaches. In this context, this study is focused on a techno-economic assessment of hydrogen production from transportation fuels using different conversion technologies. In addition, detailed economics with higher capacity and volume of the hydrogen stations are also discussed. Finally, a detailed roadmap is presented to produce on-site hydrogen at commercial scale.     

Membrane reactors for green hydrogen production from biogas and biomethane: A techno-economic assessment

This work investigates the performance of a fluidized-bed membrane reactor for pure hydrogen production. A techno-economic assessment of a plant with the production capacity of 100 kg_H2/day was carried out, evaluating the optimum design of the system in terms of reactor size (diameter and number of membranes) and operating pressures. Starting from a biomass source, hydrogen production through autothermal reforming of two different feedstock, biogas and biomethane, is compared.Results in terms of efficiency indicates that biomethane outperforms biogas as feedstock for the system, both from the reactor (97.4% vs 97.0%) and the overall system efficiency (63.7% vs 62.7%) point of views. Nevertheless, looking at the final LCOH, the additional cost of biomethane leads to a higher cost of the hydrogen produced (4.62 €/kg_H2@20 bar vs 4.39 €/kg_H2@20 bar), indicating that at the current price biogas is the more convenient choice.     

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.     

Fixed bed membrane reactors for WGSR-based hydrogen production: Optimisation of modelling approaches and reactor performance

The production of high-purity hydrogen using the water–gas-shift reaction in both conventional fixed bed reactor and hydrogen perm-selective membrane reactor at low to medium scale is studied in this work by developing and comparing models with different complexity levels. A two-dimensional rigorous reactor model considering radial and axial variations of properties (including bed porosity), setting mass, energy and momentum differential balances, and nesting a rigorous model for mass transfer within the porous catalyst was considered as reference for comparison. Different simplifications of this model for taking into account mass-transfer effects within the catalyst pellet (Thiele modulus, evaluation of apparent kinetic constants, empirical correlation for effectiveness factors or just neglecting these effects) were tested, being observed that these effects are not negligible and that the first two approaches are accurate enough for taking into account mass transfer within catalyst pellets. Regarding to the reactor model, it was observed that one-dimensional models are not adequate, especially for the membrane reactor. Analogously, neglecting the momentum balances in the reactor (as made is most simulations reported in the literature) leads to important misspredictions in the behaviour of the membrane reactor performance. Finally, the influence of the main operation parameters (inlet temperature, pressure, space velocity, etc.) was studied using the detailed reactor model, concluding that space velocity and pressure are the most important parameters affecting reactor performance for membrane reactors.     

A technical and economical assessment of hydrogen production potential from solar energy in Morocco

In this study, a techno-economic analysis of the capacity of Morocco to produce hydrogen from solar energy has been conducted. For this reason, a Photovoltaic-electrolyze system was selected and the electricity and hydrogen production were simulated for 76 sites scattered all over the country. The Global Horizontal Irradiation (GHI) data used for the simulation were extracted from the CAMS-Rad satellite database and meteorological stations at ground level.Before simulations, the accuracy of the GHI values from the satellite dataset has been checked, and their uncertainties was calculated against accurate data measured in-situ. After that, the simulated values of the hydrogen mass were interpolated using a GIS software to create a Hydrogen production map of Morocco. Finally, an economical investigation of electricity and hydrogen production costs has been conducted by calculating the $LCOE$ and $LC{O}_{H_2}$.Results show that the satellite dataset has a mean average deviation of 6.8% which is a very acceptable error rang. Also, it was found that Morocco have a high potential for hydrogen production, with a daily annual production that varies between 6489 and 8308 Tons/km². Moreover, the cost of electricity and hydrogen production in the country are in the range of 0.077–0.099 $/kWh and 5.79–4.64 $/Kg respectively.The findings of this study are with high importance as they provide an overall perspective of the country potential of hydrogen production for policy makers and investors, and it was motivated by the lack of information on the subject in the literature since it's, at the best of our knowledge, the first study assessing the hydrogen production from solar for the whole country.     

Assessing techno-economic uncertainties in nuclear power-to-X processes: The case of nuclear hydrogen production via water electrolysis

Nuclear assisted low carbon hydrogen production by water electrolysis represents a potential application of nuclear cogeneration towards deep decarbonization of several fossil fuel-dependent industrial sectors. This work builds a probabilistic techno-commercial model of a water electrolysis plant coupled to an existing nuclear reactor for base load operations. The objective is to perform discounted cash flow (DCF) calculations for levelized nuclear hydrogen production cost under input parameter uncertainty. The probability distributions of inputs are used with the Monte Carlo-Latin Hypercube (MC-LH) sampling technique to generate 10⁵ input scenarios and corresponding distribution of the levelized or life cycle hydrogen production cost instead of deterministic point values. Based on current techno-economic conditions, the levelized production costs of electrolytic hydrogen using electricity from large water-cooled nuclear reactors are determined to be US $ 12.205 ± 1.342, 8.384 ± 1.148 and 6.385 ± 1.051/kg H₂ respectively at rated alkaline water electrolyser capacities of 1.25 MW(e), 2.5 MW(e) and 5 MW(e). The corresponding values for PEM water electrolysers are US $ 13.162 ± 1.356, 8.891 ± 1.141 and 6.663 ± 1.057/kg H₂. The potential for flexible nuclear reactor operation and management of power demand uncertainties through nuclear hydrogen cogeneration is also examined through a case study.     

Hydrogen production from cassava wastewater using an anaerobic sequencing batch reactor: Effects of operational parameters,COD:N ratio,and organic acid composition

In this work, hydrogen production from cassava wastewater using anaerobic sequencing batch reactors (ASBR) was investigated to determine the optimum number of cycles per day, chemical oxygen demand (COD) loading rate, and COD:N ratio. The system operated at a COD loading rate of 30 kg/m³d and 6 cycles per day provided maximum hydrogen production performance in terms of specific hydrogen production rate (SHPR) (388 ml H₂/g VSS d or 3800 ml H₂/l d) and hydrogen yield (186 ml H₂/g COD removed). The effect of nitrogen supplementation was also studied by adding NH₄HCO₃ into the system at the COD:N ratios of 100:2.2, 100:3.3, and 100:4.4 under the COD loading rate of 30 kg/m³d and 6 cycles per day. The maximum SHPR and hydrogen yield of 524 ml H₂/g VSS d (5680 ml H₂/l d) and 438 ml H₂/g COD removed, respectively, were obtained at the stoichiometric COD:N ratio of 100:2.2. An excess nitrogen was found to promote the productions of higher organic acids and ethanol, resulting in lowering hydrogen production efficiency.     

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.     

Performance assessment and evaluation of catalytic membrane reactor for pure hydrogen production via steam reforming of methanol

The steam reforming of methanol was investigated in a catalytic Pd–Ag membrane reactor at different operating conditions on a commercial Cu/ZnO/Al₂O₃ catalyst. A comprehensive two-dimensional non-isothermal stationary mathematical model has been developed. The present model takes into account the main chemical reactions, heat and mass transfer phenomena in the membrane reactor with hydrogen permeation across the PdAg membrane in radial direction. Model validation revealed that the predicted results satisfy the experimental data reasonably well under the different operating conditions. Also the impact of different operating parameters including temperature, pressure, sweep ratio and steam ratio on the performance of reactor has been examined in terms of methanol conversion and hydrogen recovery. The modeling results have indicated the high performance of the membrane reactor which is related to continuous removal of hydrogen from retentate side through the membrane to shift the reaction equilibrium towards formation of hydrogen. The obtained results have confirmed that increasing the temperature improves the kinetic properties of the catalyst and increase in the membrane's H₂ permeance, which results in higher methanol conversion and hydrogen production. Also it is inferred that the hydrogen recovery is favored at higher temperature, pressure, sweep ratio and steam ratio. The model prediction revealed that at 573 K, 2 bar and sweep ratio of 1, the maximum hydrogen recovery improves from 64% to 100% with increasing the steam ratio from 1 to 4.     

Hydrogen production from acid and enzymatic oat straw hydrolysates in an anaerobic sequencing batch reactor: Performance and microbial population analysis

Feasibility of hydrogen production from acid and enzymatic oat straw hydrolysates was evaluated in an anaerobic sequencing batch reactor at 35 °C and constant substrate concentration (5 g chemical oxygen demand/L). In a first experiment, hydrogen production was replaced by methane production. Selective pressures applied in a second experiment successfully prevented methane production. During this experiment, initial feeding with glucose/xylose, as model substrates, promoted biomass granulation. Also, the highest hydrogen molar yield (HMY, 2 mol H₂/mol sugar consumed) and hydrogen production rate (HPR, 278 mL H₂/L-h) were obtained with these model substrates. Gradual substitution of glucose/xylose by acid hydrolysate led to disaggregation of granules and lower HPR and HMY. When the model substrates were completely substituted by enzymatic hydrolysate, the HMY and HPR were 0.81 mol H₂/mol sugar consumed and 29.6 mL H₂/L-h, respectively. Molecular analysis revealed a low bacterial diversity in the stages with high hydrogen production and vice versa. Furthermore, Clostridium pasteurianum was identified as the most abundant species in stages with a high hydrogen production. Despite that feasibility of hydrogen production from hydrolysates was demonstrated, lower performance from hydrolysates than from model substrates was obtained.