Simulating the impact of suppression of methanogenesis in continuous flow biohydrogen reactors

A calibrated model of the patent-pending integrated biohydrogen reactor clarifier system (IBRCS) using BioWin was used to evaluate the impact of sludge and/or feedstock pre-treatment for methanogens inhibition in a dynamic simulation for 90 days with and without methanogens suppression. Dynamic simulations at four different OLRs ranging from 6.5 to 103 gCOD/L-d have shown that without any pre-treatment, the system was capable of washing out methanogens and enriching hydrogen producers. The average methane gas content in the reactor’s headspace was 4% after 7 days of continuous operation, decreasing sharply to less than 0.5%, while the maximum reduction in hydrogen gas was <10%. The hydrogen gas content in the headspace ranged from 65% to 72%. Simulating the impact of extended SRT ranging from 3 days to 20 days on the performance of the IBRCS revealed that up to an SRT of 5 days hydrogen production was predominant with a reasonable deterioration in the production rate by 20%. Biomass distribution showed that at SRTs up to 20 days, acetoclastic methanogens were naturally eliminated. However, hydrogenotrophic methanogens had a significant impact on the overall hydrogen production rate where most of the hydrogen gas produced was consumed at SRTs of 10 days and 20 days.     

One-dimensional dynamic modeling of a high-pressure water electrolysis system for hydrogen production

Research on high-pressure water electrolyzers is under way worldwide as the economic production of hydrogen from renewable energy sources becomes more important. With increases in operating pressures, new safety issues have emerged, for which a reliable dynamic model of the electrolyzers is important for predicting their behavior. In this paper, a one-dimensional dynamic model of a high-pressure proton exchange membrane water electrolyzer is proposed. The model integrates various important physico-chemical phenomena inside the electrochemical cell that have been investigated individually into a dynamic model framework. Water transport, gas permeation, gas volume variation in anode/cathode channels, gas compressibility, and water vaporization are considered to formulate the model. Numerical procedures to handle and solve the model and the model performance for the prediction of steady and dynamic state behaviors are also presented.     

An integrated system for hydrogen and methane production during landfill leachate treatment

The patent-pending integrated waste-to-energy system comprises both a novel biohydrogen reactor with a gravity settler (Biohydrogenator), followed by a second stage conventional anaerobic digester for the production of methane gas. This chemical-free process has been tested with a synthetic wastewater/leachate solution, and was operated at 37 °C for 45 d. The biohydrogenator (system (A), stage 1) steadily produced hydrogen with no methane during the experimental period. The maximum hydrogen yield was 400 mL H₂/g glucose with an average of 345 mL H₂/g glucose, as compared to 141 and 118 mL H₂/g glucose for two consecutive runs done in parallel using a conventional continuously stirred tank reactor (CSTR, System (B)). Decoupling of the solids retention time (SRT) from the hydraulic retention time (HRT) using the gravity settler showed a marked improvement in performance, with the maximum and average hydrogen production rates in system (A) of 22 and 19 L H₂/d, as compared with 2–7 L H₂/d in the CSTR resulting in a maximum yield of 2.8 mol H₂/mol glucose much higher than the 1.1–1.3 mol H₂/mol glucose observed in the CSTR. Furthermore, while the CSTR collapsed in 10–15 d due to biomass washout, the biohydrogenator continued stable operation for the 45 d reported here and beyond. The methane yield for the second stage in system (A) approached a maximum value of 426 mL CH₄/gCOD removed, while an overall chemical oxygen demand (COD) removal efficiency of 94% was achieved in system (A).     

Wake effect in wind farm performance: Steady-state and dynamic behavior

The aim of this paper is to evaluate the impact of the wake effect on both the steady-state operation and dynamic performance of a wind farm and provide conclusions that can be used as thumb rules in generic assessments where the full details of the wind farms are unknown. A simplified explicit model of the wake effect is presented, which includes: the cumulative impact of multiple shadowing, the effects of wind direction and the wind speed time delay. The model is implemented in MATLAB^® and then integrated into a power system simulation package to describe the wake effect and its impact on a wind farm, particularly in terms of the wake coefficient and overall active power losses. Results for two wind farm layouts are presented to illustrate the importance of wind turbine spacing and the directionality of wind speeds when assessing the wake effect during steady-state operation and dynamic behavior.     

Modeling microbial growth of dynamic membrane in a biohydrogen production bioreactor

Biohydrogen is renewable and has a huge potential to replace fossil fuels. Understanding mechanisms of controlling microbial processes of the dynamic membrane is critical for effective dark fermentative biohydrogen production in a dynamic membrane bioreactor (DMBR). This paper aims to develop a sophisticated model of biofilm growth, dynamic membrane formation, and dark fermentative hydrogen production within a platform of coupled lattice Boltzmann and cellular automata. The model was validated against the experimental data available and then was applied for the investigation of biohydrogen production in bioreactors under different membrane structures and inlet velocities. The results showed that porous twisted channels in the dynamic membrane could significantly affect biohydrogen extraction and biofilm patterns. In all cases, the dynamic membrane formation has three phases: the initial bacteria deposit, stable biofilm growth, and stable maximum biofilm biomass. The biohydrogen production could increase by 16.4% by optimizing the porous structure and increase 30%–40% of the hydrogen extraction. Inlet velocity also affects biohydrogen extraction in a range of ?28.3%–71.2%. Both porous structure and inlet velocity would be critical operational parameters for continuous biohydrogen production. The present model demonstrated its capability to investigate dark fermentative hydrogen production and its potential applications to porous bioreactors.     

Preliminary results of the integrated hydrolysis reactor in the Cu-Cl hydrogen production cycle

This paper presents preliminary results of an integrated hydrolysis reactor at the Clean Energy Research Laboratory (CERL), University of Ontario Institute of Technology. Initial tests have demonstrated a successful reactor design allowing for effective recovery of liquid products. Using our best available performance metrics, the conversion rate of reagents to products ranged from 7% to 10%. Initial experimental runs demonstrated that the reactor was successfully operational with combined H₂O and reagent injection in a configuration suitable for integration with the electrolysis step of the Copper-Chlorine loop. In this paper, we discuss the updated hydrolysis reactor design and present data from a number of recent experiments in which our research team recovered solids and chemical products not previously collected in prior studies. Comparisons were made with earlier XRD data taken at the Argonne National Laboratory. The comparisons showed promising results in the chemical composition of the solids produced. We conclude this paper with a discussion of future experiments to increase the conversion rate of reaction based on the observed trends.     

环境低负荷制氢技术及集成制氢系统

讨论了各种环境低负荷的制氢技术。SPE电解水制氢技术成熟,将成为未来主要制氢方法之一。生物化学制氢和半导体光解水制氢仅以太阳能为能源,前景广阔。生物质制氢清洁、节能,值得推广。环境低负荷集成制氢系统综合多种技术,是制氢技术发展的一个趋势。     

Comparison of biohydrogen production processes

For hydrogen to be a viable energy carrier, it is important to develop hydrogen generation routes that are renewable like biohydrogen. Hydrogen can be produced biologically by biophotolysis (direct and indirect), photo-fermentation and dark-fermentation or by combination of these processes (such as integration of dark- and photo-fermentation (two-stage process), or biocatalyzed electrolysis, etc.). However, production of hydrogen by these methods at commercial level is not reported in the literature and challenges regarding the process scale up remain. In this scenario net energy analysis (NEA) can provide a tool for establishing the viability of different methods before scaling up. The analysis can also be used to set targets for various process and design parameters for bio-hydrogen production.     

Multiscale kinetic modeling for biohydrogen production: A study on membrane bioreactors

Hydrogen can be a capable alternative to fossil fuels due to its carbon-free characteristics, in this content, biological hydrogen production is considered a practical approach because technology is green. Due to parameters affecting biohydrogen production, such as operating conditions, it is crucial to predict the process to see the proper yield. There are several conventional and unconventional models used in biohydrogen production prediction. This paper derived a triple first-order prediction model from a previously presented multi-scale kinetic model polynomial built upon the multi-stage growth hypothesis for bio-hydrogen production prediction. The original model was applied to batch and continuous stirred tank reactor studies for their model evaluation, this study evaluated the newly derived model for studies of membrane bioreactors. Due to their increased production yield, membrane bioreactors are an emerging field in biohydrogen production. Although the previous study was mainly applied for batch dark fermentations consisting of various microorganisms, the results presented in this study indicate that it is also applicable for continuous and photo fermentation systems. The original model results reported significant fitness accuracy among different datasheets compared to conventional models like the modified Gompertz model, considering essential factors impacting biohydrogen production suggested in the original model, this paper investigated eleven case studies of dynamic membrane bioreactors with modeling fitness of 99% for most cases. This study reports even higher fitness accuracy compared to the original model, even with different operating conditions.     

Bio-hydrogen production from organic wastes in a pilot plant reactor and its use in a SOFC

The aim of this study is to investigate dark anaerobic fermentation in a pilot scale reactor (V = 35 l) under batch conditions for the production of bio-H₂ as a clean and sustainable vector of energy. The inoculum of the reactor was an anaerobic wastewater sludge, previously treated with HCl 1N for 24 h at pH 3 in order to inhibit the methanogenic bioactivity. The sludge was inoculated in the reactor and fed with a solution containing organic wastes (fruit and vegetables unsold stock) at an initial sugar concentration of 53 g/l. The experiments were conducted at room temperature (24 °C) under anaerobic conditions; temperature, pH and ORP were monitored online.The process led to a total gas production of 240 l containing H₂ (49%) and CO₂ (51%), whereas no CH₄ was detected in the gas.An experiment, where the bio-hydrogen produced has been used as a fuel for an anode-supported SOFC, is presented.     

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.     

A review on process modeling and design of biohydrogen

The current energy supply depends on fossil fuels which have increased carbon dioxide emissions leading to global warming and depleted non-renewable fossil fuels resources. Hydrogen (H₂) fuel could be an eco-friendly alternative since H₂ consumption only produces water. However, the overall impacts of the H₂ economy depend on feedstock types, production technologies, and process routes. The existing process technologies for H₂ production used fossil fuels encounter the escalation of fossil fuel prices and long-term sustainability challenges. Therefore, biohydrogen production from renewable resources like biomass wastes and wastewaters has become the focal development of a sustainable global energy supply. Different from other biohydrogen production studies, this paper emphasizes biohydrogen fermentation processes using different renewable sources and microorganisms. Moreover, it gives an overview of the latest advancing research in different biohydrogen process designs, modeling, and optimization. It also presents the biohydrogen production routes and kinetic modeling for biohydrogenation.     

Biological hydrogen production in suspended and attached growth anaerobic reactor systems

Biological production of hydrogen gas has received increasing interest from the international community during the last decade. Most studies on biological fermentative hydrogen production from carbohydrates using mixed cultures have been conducted in conventional continuous stirred tank reactors (CSTR) under mesophilic conditions. Investigations on hydrogen production in reactor systems with attached microbial growth have recently come up as well as investigations on hydrogen production in the thermophilic temperature range. The present study examines and compares the biological fermentative production of hydrogen from glucose in a continuous stirred tank type bioreactor (CSTR) and an upflow anaerobic sludge blanket bioreactor (UASB) at various hydraulic retention times (2–12 h HRT) under mesophilic conditions (35 °C). Also the biohydrogen production from glucose in the CSTR at mesophilic and thermophilic (55 °C) temperature range was studied and compared. From the CSTR experiments it was found that thermophilic conditions combine high hydrogen production rate with low production of microbial mass, thus giving a specific hydrogen production rate as high as 104 mmole _H2/h/l/g${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}/\mathrm{g}$ VSS at 6 h retention time compared to a specific hydrogen production rate of 12 mmole _H2/h/l/g${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}/\mathrm{g}$ VSS under mesophilic conditions. On the other hand, the UASB reactor configuration is more stable than the CSTR regarding hydrogen production, pH, glucose consumption and microbial by-products (e.g. volatile fatty acids, alcohols etc.) at the HRTs tested. Moreover, the hydrogen production rate in the UASB reactor was significantly higher compared to that of the CSTR at low retention times (19.05 and 8.42 mmole _H2/h/l${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}$, respectively at 2 h HRT) while hydrogen yield (mmole _H2/mmole${\mathrm{H}}_2/\mathrm{mmole}$ glucose consumed) was higher in the CSTR reactor at all HRT tested. This implies that there is a trade-off between technical efficiency (based on hydrogen yield) and economic efficiency (based on hydrogen production rate) when the attached (UASB) and suspended (CSTR) growth configurations are compared.     

An evaluative report and challenges for fermentative biohydrogen production

Hydrogen, the most abundant and lightest element in the universe, has enormous potential as a future energy. High conversion efficiency, recyclability and nonpolluting nature of hydrogen make it the fuel of future. Various microorganisms are explored for producing hydrogen by exploiting variety of biological organic substrates. The target is the genetic improvement of the organism or the biochemical pathway required for biohydrogen production and devising path even better in comparison to the other production methods.The present review discusses different methods of biohydrogen production specifically by the fermentative route, physical factors affecting its production and other aspects for enhancement in the yield of hydrogen production. Metabolic engineering strategies for enhancement in hydrogen production to overcome different limitation have been also summarized.     

Multiscale mixing analysis and modeling of biohydrogen production by dark fermentation

Hydrogen production by dark fermentation (DF) from wastewater, food waste, and agro-industrial waste combines the advantages to be renewable, sustainable and environmentally friendly. But this attractive process involves a three-phase gas-liquid-solid system highly sensitive to mixing conditions. However, mixing is usually disregarded in the conventional strategies for enhancing biohydrogen productivity, even though H₂ production can be doubled, e.g. versus of reactor design (0.6–1.5 mol H₂/mol hexose). The objective of this review paper is, therefore, to highlight the key effects of mixing on biohydrogen production among the abiotic parameters of DF. First, the pros and cons of the different modes of mixing in anaerobic digesters are described. Then, the influence of mixing on DF is discussed using recent data from the literature and theoretical analysis, focusing on the multiphase and multiscale aspects of DF. The methods and tools available to quantify experimentally the role of mixing both at the local and global scales are summarized. The 0-D to 3-D strategies able to implement mixing in fermentation modeling and scale-up procedures are examined. Finally, the perspectives in terms of process intensification and scale-up tools using mixing optimization are discussed with the issues that are still to be solved.     

有机废水生物制氢的连续流发酵工艺

对生物制氢的工程实践应用的研究进行了评论性的回顾。讨论了发酵法生物制氢系统的特点，重点讨论了厌氧发酵生物制氢系统的工艺流程与设计、工程控制参数与发酵调控、产氢速率与产量的提高技术对策等许多技术问题。     

A study on the dynamic behavior of a sulfur trioxide decomposer for a nuclear hydrogen production

The sulfur–iodine thermochemical water-splitting cycle (S–I cycle) is one of the most promising technologies for mass H₂ production. The S–I cycle is generally divided into three sections, one of which involves a H₂SO₄ concentration and decomposition. In the sulfuric acid processing section (Section 2), H₂SO₄ is decomposed into H₂O and SO₃, and then the produced SO₃ is further decomposed into SO₂ and O₂, which takes place in a H₂SO₄ decomposer and a SO₃ decomposer, respectively. The SO₃ decomposition requires heat of a high temperature and this suggests a heat-exchanger type reactor. To understand the temperature profiles and chemical reactions through a SO₃ decomposer, a dynamic model was developed by considering the heat and material balances in partial differential forms. A model was used to size the decomposer to a proposed design basis and it was also applied to simulate the responses corresponding to the changes of the operation conditions such as increased or decreased flow rates.     

Transient thermodynamic analysis of a novel integrated ammonia production,storage and hydrogen production system

A transient thermodynamic analysis is reported of a novel chemical hydrogen storage system using energy and exergy approaches. The hydrogen is stored chemically in ammonia using the proposed hydrogen storage system and recovered via the electrochemical decomposition of ammonia through an ammonia electrolyzer. The proposed hydrogen storage system is based on a novel subzero ammonia production reactor. A single stage refrigeration system maintains the ammonia production reactor at a temperature of −10 °C. The energy and exergy efficiencies of the proposed system are 85.6% and 85.3% respectively. The proposed system consumes 34.0 kJ of work through the process of storing 1 mol of hydrogen and recovering it using the ammonia electrolyzer. The system is simulated for filling 30,000 L of ammonia at a pressure of 5 bar, and the system was able to store 7500 kg of ammonia in a liquid state (1% vapor) in 1500 s. The system consumes nearly 45.3 GJ of energy to store the 7500 kg of ammonia and to decompose it to reproduce the stored hydrogen during the discharge phase.     

Enhancement of simultaneous hydrogen production and methanol synthesis in thermally coupled double-membrane reactor

Coupling the methanol synthesis with the dehydrogenation of cyclohexane to benzene in a co-current flow, catalytic fixed-bed double-membrane reactor configuration in order to simultaneous pure hydrogen and methanol production was considered theoretically. The thermally coupled double-membrane reactor (TCDMR) consists of two Pd/Ag membranes, one for separation of pure hydrogen from endothermic side and another one for permeation of hydrogen from feed synthesis gas side (inner tube) into exothermic side. A steady-state heterogeneous model is developed to analyze the operation of the coupled methanol synthesis. The proposed model has been used to compare the performance of a TCDMR with conventional reactor (CR) and thermally coupled membrane reactor (TCMR) at identical process conditions. This comparison shows that TCDMR in addition to possessing advantages of a TCMR has a more favorable profile of temperature and increased productivity compared with other reactors. The influence of some operating variables is investigated on hydrogen and methanol yields. The results suggest that utilizing of this reactor could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the recuperative reactor.     

Dynamic system modeling of thermally-integrated concentrated PV-electrolysis

Understanding the dynamic response of a solar fuel processing system utilizing concentrated solar radiation and made of a thermally-integrated photovoltaic (PV) and water electrolyzer (EC) is important for the design, development and implementation of this technology. A detailed dynamic non-linear process model is introduced for the fundamental system components (i.e. PV, EC, pump etc.) in order to investigate the coupled system behavior and performance synergy notably arising from the thermal integration. The nominal hydrogen production power is ～2 kW at a hydrogen system efficiency of 16–21% considering a high performance triple junction III-V PV module and a proton exchange membrane EC. The device operating point relative to the maximum power point of the PV was shown to have a differing influence on the system performance when subject to temperature changes. The non-linear coupled behavior was characterised in response to step changes in water flowrate and solar irradiance and hysteresis of the current-voltage operating point was demonstrated. Whilst the system responds thermally to changes in operating conditions in the range of 0.5–2 min which leads to advantageously short start-up times, a number of control challenges are identified such as the impact of pump failure, electrical PV-EC disconnection, and the potentially damaging accentuated temperature rise at lower water flowrates. Finally, the simulation of co-generation of heat and hydrogen for various operating conditions demonstrates the significant potential for system efficiency enhancements and the required development of control strategies for demand matching is discussed.