Photofermentation Research Articles

Exploring the potential of biohydrogen as a sustainable energy solution for Pakistan: A review of production processes and policy challenges

Due to growing carbon dioxide emissions and the depletion of fossil-based energy sources, international studies have been focusing more intensely on developing hydrogen as a source of renewable energy. Biohydrogen is an exciting and green alternative energy source with various different benefits. Unlike traditional energy sources, biohydrogen production does not emit pollutants, making it a more environmentally friendly option. Biohydrogen generation, particularly from microalgae and other low-cost biomass feedstocks, so offers the dual benefit of delivering clean electricity while absorbing Carbon Dioxide. This research investigates the possibility of biohydrogen as a sustainable energy solution for Pakistan's climate issue. We examine the current state of biohydrogen generation technologies, such as dark fermentation, photo fermentation, bio photolysis, with a focus on their potential application in Pakistan. The study investigates global advances in biohydrogen research and their significance in Pakistan, demonstrating biohydrogen's potential contribution to Pakistan's energy independence and environmental targets, as well as the practical and policy-related challenges that must be addressed to advance biohydrogen energy generation and wider adoption.

Environmental impact assessment of biohydrogen production from orange peel waste by lab-scale dark and photofermentation processes

Orange peel waste (OPW), as a relevant and recoverable residue, is composed of peel, internal tissue, pulp, and seeds. This organic residue is rich in carbohydrates useful for biofuel production processes. Biohydrogen is obtained from dark fermentation (DF) and photofermentation (PF), which are complementary in the bioprocessing chain. The objective of this work was to compare the environmental impact assessment of a sequential dark–photofermentation process (Scenario DF-PF) and the individual fermentation processes: dark fermentation (Scenario DF) and photofermentation (Scenario PF). The assessment was performed at a laboratory scale, and the functional unit (FU) was defined as the production of 1 kg H2. Scenario DF showed the lowest environmental impacts regarding global warming and fossil resource scarcity indicators, with 375.5 kg CO2-eq/FU and 108.8 kg oil-eq/FU, respectively, followed by Scenario DF-PF and Scenario PF. Scenario DF-PF presented the lowest impact regarding the water consumption indicator (7.6 m3/FU), followed by Scenario DF, which had 46.6% more impact. Additionally, Scenario DF-PF required 3.3 times less substrate than Scenario DF due to more efficient substrate conversion. The high share of fossil fuels in the Mexican electricity mix directly impacts the processes that require electric energy, such as the PF process. Therefore, eco-friendly light sources should be used to minimize effects. Valorization of OPW could follow two routes depending on whether the aim is to reduce a specific environmental impact indicator or biowaste conversion efficiency.

Ammonia-dependent reducing power redistribution for purple phototrophic bacteria culture-based biohydrogen production

The global energy crisis has intensified the search for sustainable and clean alternatives, with biohydrogen emerging as a promising solution to address environmental challenges. Leveraging photo fermentation (PF) process, purple phototrophic bacteria (PPB) can harness reducing power derived from organic substrates to facilitate hydrogen production. However, existing studies report much lower H2 yields than theoretical value when using acetate as carbon source and ammonia as nitrogen source, primarily attributed to the widely employed pulse-feeding mode which suffers from ammonia inhibition effect on nitrogenase. To address this issue, a continuous feeding mode was applied to avoid ammonia accumulation in this study. On the other hand, other pathways like carbon fixation and polyhydroxyalkanoate (PHA) formation could compete reducing power with H2 production. However, the reducing power allocation under continuous feeding mode is not yet clear. In this study, the reducing power allocation and hydrogen production performance were evaluated under various ammonia loading, using acetate as carbon source and infrared LED at around 50 W·m−2 as light source. The results show that (a) The absence of ammonia resulted in the best performance for hydrogen production, with 44 % of the reducing power distributed to H2 and the highest H2 volumetric productivity, while the allocation of reducing power to hydrogen production stopped when ammonia loading was above 7.6 mg NH4-N·L−1·d−1; (b) when PPB required to eliminate reducing power under ammonia limited conditions, PHA production was the preferred pathway followed by the hydrogen production pathway, but once PHA accumulation reached saturation, hydrogen generation pathway dominated; (c) under ammonia limited conditions, the TCA cycle was more activated rendering higher NADH (i.e. reducing power) production compared with that under ammonia sufficient conditions which was verified by metagenomics analysis, and all the hydrogen production, PHA accumulation and carbon fixation pathways were highly active to dissipate reducing power. This work provides the insight of reducing power distribution and PPB biohydrogen production variated by ammonia loading under continuous feeding mode.

Valorization of Purple Phototrophic Bacteria Biomass Resulting from Photo Fermentation Aimed at Biohydrogen Production.

This study evaluated the feasibility of contextually producing hydrogen, microbial proteins, and polyhydroxybutyrate (PHB) using a mixed culture of purple phototrophic bacteria biomass under photo fermentative conditions. To this end, three consecutive batch tests were conducted to analyze the biomass growth curve and to explore the potential for optimizing the production process. Experimental findings indicated that inoculating reactors with microorganisms from the exponential growth phase reduced the duration of the process. Furthermore, the most effective approach for simultaneous hydrogen production and the valorization of microbial biomass was found when conducting the process during the exponential growth phase of the biomass. At this stage, achieved after 3 days of fermentation, the productivities of hydrogen, PHB, and microbial proteins were measured at 63.63 L/m3 d, 0.049 kg/m3 d, and 0.045 kg/m3 d, respectively. The biomass composition comprised a total intracellular compound percentage of 56%, with 27% representing PHB and 29% representing proteins. Under these conditions, the estimated daily revenue was maximized, amounting to 0.6 $/m3 d.

Combining pretreatments and co-fermentation as successful approach to improve biohydrogen production from dairy cow manure

The present paper is focused on enhancing the production of biohydrogen (bioH2) from dairy cow manure (DCM) through dark fermentation (DF). Two enhancement production strategies have been tested: i) the combination of H2O2 with sonification as pretreatment and ii) the co-fermentation with cheese whey as co-substrate. Concerning the pretreatment, the best combination was investigated according to the response surface methodology (RSM) by varying H2O2 dosage between 0.0015 and 0.06 g/gTS and ultrasonic specific energy input (USEI) between 35.48 and 1419.36 J/gTS. The increase of carbohydrates concentration was used as target parameter. Results showed that the combination of 0.06 g/gTS of H2O2 with 1419.36 J/gTS of USEI maximized the concentration of carbohydrates. The optimized conditions were used to pretreat the substrate prior conducting DF tests. The use of pretreatment resulted in obtaining a cumulative bioH2 volume of 51.25 mL/L and enhanced the bioH2 production by 125% compared to the control test conducted using raw DCM. Moreover, the second strategy, i.e. co-fermentation with cheese whey (20% v/v) as co-substrate ended up to enhancing the DF performance as the bioH2 production reached a value of 334.90 mL/L with an increase of 1372% compared to the control DF test. To further improve the process, dark fermentation effluents (DFEs) were valorized via photo fermentation (PF), obtaining an additional hydrogen production aliquot.

Photofermentative Biohydrogen Production Enhancement with Nanoparticle

This study will explore the use of a biological pathway known as photo fermentation for the production of biohydrogen under anoxic and nitrogen deficient conditions due to its high hydrogen production, and to emphasize the role of a dominating enzyme, the nitrogenase enzyme, in catalyzing the process of hydrogen evolution from a medium composed of Purple Non-Sulfur Bacteria (Rhodopseudomonas Palustris) with glycerol as the substrate. For Purple Non-Sulphur Bacteria, the optimal H2 production temperature ranges between 30 °C to 36 °C. Simultaneously, illumination is applied by LED lights and is varied from no string LED illumination, to single string illumination (240 W/m2), and double string illumination (480 W/m2) to simulate and examine performance in outdoor conditions and achieved a maximum of 428% increase in hydrogen productivity compared to previous studies. Consequently, this suggests that it is economically appealing to use the non-growing R. palustris bacterium as the chosen biocatalyst for continuous hydrogen production. These preliminary results constitute the development of continuous H2 production which evolves into the green fuel of the future production.

Enrichment of a Mixed Culture of Purple Non-Sulfur Bacteria for Hydrogen Production from Organic Acids

Hydrogen (H2) as a clean fuel holds global potential and can be produced through bio-processes. To enhance bioH2 yields, integrated systems have been proposed, combining dark fermentation (DF) of wastewater with a subsequent photofermentation (PF) stage involving purple non-sulfur (PNS) bacteria. Mixed cultures of PNS bacteria and their microbial ecology have been relatively understudied despite the known benefits of mixed cultures in industrial applications. The aim of this study was to obtain various mixed cultures of PNS bacteria under different environmental conditions during the enrichment stage. Four different mixed cultures were obtained (A, B, C, and D). However, in the H2 production phase, only Consortium A, which had been enriched with malic acid as the carbon source, exposed to 32 W m−2 of irradiance, and subjected to intermittent agitation, produced H2 with a yield of 9.37 mmol H2 g−1 COD. The consortia enriched were a hybrid of PF and DF bacteria. Especially in Consortium A, Rhodopseudomonas palustris was the dominant organism, and various DF bacteria were positively associated with H2 production, with their dominance comparable to that of PNS bacteria. Despite the reported low yields, optimizing environmental conditions for this culture could potentially enhance hydrogen production from DF effluents.

Nanotechnology based technological development in biofuel production: Current status and future prospects

Depleting fossil fuels and net carbon emissions associated with their burning have driven the need to find alternative energy sources. Biofuels are near-perfect candidates for alternative energy sources as they are renewable and account for no net CO2 emissions. However, biofuel production must overcome various challenges to compete with conventional fuels. Conventional methods for bioconversion of biomass to biofuel include chemical, thermochemical, and biological processes. Substrate selection and processing, low yield, and total cost of production are some of the main issues associated with biofuel generation. Recently, the uses of nanotechnology and nanoparticles have been explored to improve the biofuel production processes because of their high adsorption, high reactivity, and catalytic properties. The role of these nanoscale particles and nanocatalysts in biomass conversion and their effect on biofuel production processes and yield are discussed in the present article. The applicability of nanotechnology in production processes of biobutanol, bioethanol, biodiesel, biohydrogen, and biogas under biorefinery approach are presented. Different types of nanoparticles, and their function in the bioprocess, such as electron transfer, pretreatment, hydrolysis, microalgae cultivation, lipid extraction, dark and photo fermentation, immobilization, and suppression of inhibitory compounds, are also highlighted. Finally, the current and potential applications of nanotechnology in biorefineries are also discussed.

Illumination and fluid flow effects on bioplastic production and biohydrogen generation in microbioreactors with different geometries

The utilization of photofermentative processes to create biohydrogen and bioplastic has significant environmental and economic benefits. In this study, a mechanistic model of photo fermentation of acetic acid to investigate simultaneous bioplastic and biohydrogen production was developed. Two distinct bioreactors: one with a porous structure generated by X-ray CT and another one with an array of solid blocks were simulated to examine the effects of varied velocities and light intensities on biohydrogen and bioplastic production. The results revealed that biohydrogen production depends on not only bioplastic accumulation in biofilms but also illumination intensities and fluid velocities. Illumination intensity affected the bioplastic generation and decreased the time to reach the highest normalized bioplastic concentration. Higher bioplastic productions were achieved at lower illumination intensity. The base illumination (6000lx) had the lowest bioplastic formation while the lowest illumination intensity (3000lx) could increase it by 30%. Changing velocity could increase +48.1% of the bioplastic normalized concentration at the highest velocity and decrease −38.1% at the lowest. Biofilm growth could significantly reduce biohydrogen extraction at low velocities due to bioclogging. The CT-bioreactor outperformed the block-bioreactor in terms of bioplastic concentration, while the block-bioreactor exceeded the CT-bioreactor in terms of biohydrogen generation.

Influence of titanate photocatalyst in biohydrogen yield via photo fermentation from corn stover

The effects of three common titanate photocatalysts (TPC) on the photo fermentation biohydrogen production (PFHP) from corn stover were studied in this paper. Compared with CaTiO3 and BaTiO3, the experimental group with the addition of MgTiO3 showed stronger potential for PFHP, the maximum hydrogen yield of 344 mL (68.8 mL/g TS) was obtained at 3 g/L MgTiO3, increased by 48.3%. For CaTiO3, BaTiO3, the optimal amount of addition was 8 and 7 g/L, respectively, in which, the hydrogen yield was 308 and 288 mL (61.6 and 57.6 mL/g TS). TPC addition could shorten the delay period of hydrogen production lower the Oxidation-Reduction Potential (ORP) of fermentation broth, especially MgTiO3 addition, the delayed hydrogen production could be shortened by 33.2% compared with control group, and the ORP could reach the lowest value of −371 mV.

Biological Hydrogen Production from Urban and Industrial Wastewater

Biological hydrogen production is a process in which microorganisms convert organic matter into hydrogen gas. This renewable energy production method is of great interest as an environmentally friendly and sustainable energy source. Biological hydrogen production can be accomplished using different methods. The dark fermentation method is a process in which organic substances are converted into hydrogen gas by microorganisms in anaerobic (oxygen-free) environments. In this method, organic materials are subjected to the fermentation process and hydrogen gas is released. This process also offers a solution for waste management. Photo fermentation is a process in which photosynthetic organisms convert organic materials into hydrogen gas using light energy. The light is absorbed by the photosynthetic pigments and provides the necessary energy for hydrogen gas production. In this method, clean hydrogen gas can be produced using solar energy. Biological hydrogen production methods have several advantages. These include the use of renewable resources, low greenhouse gas emissions, waste management and low energy consumption. However, there are also some disadvantages depending on the methods, for example limited light access or the difficulty of obtaining the purity of hydrogen gas. Biological hydrogen production is a promising method to meet clean and sustainable energy needs. Continuous research and development studies continue to increase the efficiency of these methods and eliminate their disadvantages. In the future, with the more widespread use of biological hydrogen production methods, the diversity of clean energy sources will increase and environmental sustainability will be ensured.

From Microalgae to Bioenergy: Recent Advances in Biochemical Conversion Processes

Concerns about rising energy demand, fossil fuel depletion, and global warming have increased interest in developing and utilizing alternate renewable energy sources. Among the available renewable resources, microalgae biomass, a third-generation feedstock, is promising for energy production due to its rich biochemical composition, metabolic elasticity, and ability to produce numerous bioenergy products, including biomethane, biohydrogen, and bioethanol. However, the true potential of microalgae biomass in the future bioenergy economy is yet to be realized. This review provides a comprehensive overview of various biochemical conversion processes (anaerobic digestion, direct biophotolysis, indirect biophotolysis, photo fermentation, dark fermentation, microalgae-catalyzed photo fermentation, microalgae-catalyzed dark fermentation, and traditional alcoholic fermentation by ethanologenic microorganisms) that could be adapted to transform microalgae biomass into different bioenergy products. Recent advances in biochemical conversion processes are compiled and critically analyzed, and their limitations in terms of process viability, efficacy, scalability, and economic and environmental sustainability are highlighted. Based on the current research stage and technological development, biomethane production from anaerobic digestion and bioethanol production from traditional fermentation are identified as promising methods for the future commercialization of microalgae-based bioenergy. However, significant challenges to these technologies’ commercialization remain, including the high microalgae production costs and low energy recovery efficiency. Future research should focus on reducing microalgae production costs, developing an integrated biorefinery approach, and effectively utilizing artificial intelligence tools for process optimization and scale-up to solve the current challenges and accelerate the development of microalgae-based bioenergy.

Biohydrogen production from lignocellulosic feedstock: Abiotic and biotic methods

Bioenergy is known as green energy produced from organic biomass, such as food leftovers, non-edible agri-residues, and municipal wastes through biotic and abiotic methods. Globally, generation of the most common renewable fuels including biohydrogen (bioH2), biogas, bioethanol, biofertilizers and bio plastics as fossil fuel substitutes by means of circular bioeconomy is gaining tremendous focus in support of environmental concerns. Carbon free bioH2 is considered as deemed fuel due to its multifaceted applications and potent ecological features. As the present commercial energy manufacturing methods tap on non-renewable fuels and associated high cost, there is an immediate need for full scale sustainable bioH2 production systems in accordance with regional demand through domestic innovations. Though, research on hydrogen production is not less common via conventional thermo chemical methods, it is essential to understand much regarding biological methods to achieve feasible transition from depleting fossil fuels to eco-friendly renewable energy. Thus, this review primarily focuses on different sustainable approaches for lignocellulosic biomass valorization towards bioH2 production along with potential thermo chemical approaches. In particular, bioH2 production from lignocellulosic biomass in the presence and absence of light by photo fermentation and dark fermentation, respectively, reactor configuration, importance of biocatalyst pretreatment and potential methods, and natural and mutant microalgal bioH2 evolution have been discussed in detail to address their industrial level applicability.

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.

Biological Hydrogen Energy Production by Novel Strains Bacillus paramycoides and Cereibacter azotoformans through Dark and Photo Fermentation

In daily life, energy plays a critical role. Hydrogen energy is widely recognized as one of the cleanest energy carriers available today. However, hydrogen must be produced as it does not exist freely in nature. Various methods are available for hydrogen production, including electrolysis, thermochemical technology, and biological methods. This study explores the production of biological hydrogen through the degradation of organic substrates by anaerobic microorganisms. Bacillus paramycoides and Cereibacter azotoformans strains were selected as they have not yet been studied for biological hydrogen fermentation. This study investigates the ability of these microorganisms to produce biological hydrogen. Initially, the cells were identified using cell morphology study, gram staining procedure, and 16S ribosomal RNA (rRNA) gene polymerase chain reaction. The cells were revealed as Bacillus paramycoides (MCCC 1A04098) and Cereibacter azotoformans (JCM 9340). Moreover, the growth behaviour and biological hydrogen production of the dark and photo fermentative cells were studied. The inoculum concentrations experimented with were 1% and 10% inoculum size. This study found that Bacillus paramycoides and Cereibacter azotoformans are promising strains for hydrogen production, but further optimization processes should be performed to obtain the highest hydrogen yield.

Bioreactors and biophoton-driven biohydrogen production strategies

Given the current issues with global warming and rising greenhouse gas emissions, biohydrogen is a viable alternative fuel option. Technologies to produce biohydrogen include photo fermentation, dark fermentation, direct and indirect bio-photolysis, and two-stage fermentation. Biological hydrogen generation is a green and promising technique with mild reaction conditions and low energy consumption compared to thermochemical and electrochemical hydrogen generation. To optimize hydrogen gas output using this method, the activity of hydrogen-consuming bacteria should be restricted during the production stages of hydrogen and acetate to prevent or limit hydrogen consumption. Raw material costs, poor hydrogen evolution rates, and large-scale output are the main limitations in biological hydrogen generation systems. Organic wastes would be the most preferred target feedstock for hydrogen fermentation, aside from biodegradable wastes, due to their high amount and simultaneous waste treatment advantage. This study examined the three primary methods for converting waste into bio-hydrogen: microbial electrolysis cell, thermochemical gasification, and biological fermentation, from both a technological and environmental standpoint. The effectiveness and applicability of these bioprocesses in terms of aspects influencing processes and their constraints are discussed. Alternative options for improving process efficiency, like microbial electrolysis, bio-augmentation, and multiple process integration, are also considered for industrial-level applications. Biohydrogen generation might be further enhanced by optimization of operating conditions and adding vital nutrients and nanoparticles. Cost reduction and durability enhancement are the most significant hindrances to fuel-cell commercialization. This review summarizes the biohydrogen production pathways, the impact of used organic waste sources, and bacteria. The work also addresses the essential factors, benefits, and challenges.

Ascorbic acid-mediated zero-valent iron enhanced hydrogen production potential of bean dregs and corn stover by photo fermentation

Ascorbic acid was introduced to enhance the performance of zero-valent iron (Fe(0)) in hydrogen production by photo fermentation of bean dregs and corn stover. The highest hydrogen production of 664.0 ± 5.3 mL and hydrogen production rate of 34.6 ± 0.1 mL/h was achieved at 150 mg/L ascorbic acid, which was 10.1% and 11.5% higher than that of 400 mg/L Fe(0) alone. The supplement of ascorbic acid to Fe(0) system accelerated the formation of Fe(Ⅱ) in solution due to its reducing and chelating ability. Hydrogen production of Fe(0) and ascorbic acid-Fe(0) (AA-Fe(0)) systems at different initial pH (5, 6, 7, 8 and 9) was studied. Result showed that hydrogen produced from AA-Fe(0) system was improved by 2.7–27.5% compared with Fe(0) system. The maximum hydrogen production of 767.5 ± 2.8 mL was achieved with initial pH 9 in the AA-Fe(0) system. This study provided a strategy for enhancing biohydrogen production.

A mechanistic mathematical model for photo fermentative hydrogen and polyhydroxybutyrate production.

An original mathematical model describing the photo fermentation process is proposed. The model represents the first attempt to describe the photo fermentative hydrogen production and polyhydroxybutyrate accumulation, simultaneously. The mathematical model is derived from mass balance principles and consists of a system of ordinary differential equations describing the biomass growth, the nitrogen and the substrate degradation, the hydrogen and other catabolites production, and the polyhydroxybutyrate accumulation in photo fermentation systems. Moreover, the model takes into account important inhibiting phenomena, such as the self-shading and the substrate inhibition, which can occur during the evolution of the process. The calibration was performed using a real experimental data set and it was supported by the results of a sensitivity analysis study. The results showed that the most sensitive parameters for both hydrogen and PHB production were the hydrogen yield on substrate, the catabolites yield on substrate, and the biomass yield. Successively, a different experimental data set was used to validate the model. Performance indicators showed that the model could efficiently be used to simulate the photo fermentative hydrogen and polyhydroxybutyrate production by Rhodopseudomonas palustris. For instance, the index of agreement of 0.95 was observed for the validated hydrogen production trend. Moreover, the model well predicted the maximum PHB accumulation in bacterial cells. Indeed, the predicted and observed accumulated PHB were 4.5 and 4.8%, respectively. Further numerical simulations demonstrated the model consistency in describing process inhibiting phenomena. Numerical simulations showed that the acetate and nitrogen inhibition phenomena take place when concentrations are higher than 12.44 g L-1 and lower than 4.76 mg L-1, respectively. Finally, the potential long term hydrogen production from accumulated polyhydroxybutyrate in bacterial cells was studied via a fast-slow analysis technique.

Clean technology selection of hydrogen production on an industrial scale in Morocco

Sustainable hydrogen production is a priority for Morocco, and it's part of the country's national energy strategy, which is currently being developed. Many processes can be used for its production. However, it's necessary to select the appropriate one for Morocco's case. In this study, a multi-criteria analysis was followed to select the best clean and renewable catalytic process for hydrogen production on an industrial scale. Ten routes were evaluated using the AHP method coupled with the Fuzzy Vikor method for criteria weighting and ranking of alternatives, respectively. The results showed that alkaline water electrolysis coupled with renewable energy sources is the most suitable for industrial production in Morocco. The processes that are not well ranked and require further study and development before deployment on an industrial scale are biophotolysis, photo fermentation, photolysis, and thermolysis. The parametric sensitivity analysis performed validated the result obtained. Then, the potential for hydrogen production using solar energy is investigated. It was found that Morocco can produce 1057.26 million tons of green hydrogen, showing how attractive the selected catalytic process is. This study enables investors and decision-makers to make an informed decision about whether to develop a green hydrogen production industrial installation in Morocco.

Enhancing biohydrogen yield from corn stover by photo fermentation via adjusting photobioreactor headspace pressure

In this study, the effect of bioreactor headspace pressure regulation on photo-fermentative hydrogen production (PFHP) from corn stover (CS) was investigated. The results showed that the headspace pressure could significantly affect the performance of PFHP. With the decrease in the reactor headspace pressure (100 kPa–10 kPa), cumulative biohydrogen production firstincreased and then decreased, the maximum hydrogen yield of 546.57 mL was obtained at the headspace pressure of 30 kPa. The parameters of Gompertz model showed a lower hydrogen partial pressure was beneficial to speed up the reaction process and shorten the hydrogen production delay time of the system, however, too low pressure would inhibit the metabolism of microorganisms in the PFHP process, resulting lower hydrogen yield obtained.