No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A critical review on limitations and enhancement strategies associated with biohydrogen production
Abstract
The potential to operate energy efficient and less expensive production methods are important in biohydrogen production. Biological hydrogen production is often constrained by less productivity. However, to obtain industrial level implementation, greater productivity is essential. Researches on various bioreactors configurations and influencing factors were deeply investigated in this regard. The bioreactors operated in batch mode are appropriate for preliminary optimization whereas industrial level execution needs continuous mode. The main objective of this review is to recap the limitations and constraints associated with bioreactor operation and to list out the enhancement approaches that are currently investigated for improved biohydrogen generation. Recent approaches designed towards biohydrogen production enhancement such as substrate pre-treatments, inhibitors removal, bioaugmentation, immobilization, effluent recycling, buffering capacity maintenance, exploitation of by-products etc., are reviewed thoroughly.
... The design and configuration of the reactor, which influence both the circumstances for the microorganism's development and operation, have a substantial impact on hydrogen generation. The optimal bioreactor should be able to prevent biomass washing that might happen due to a decreased hydraulic retention time (HRT) to maximise biohydrogen production [123]. ...
... Numerous studies have used food industrial waste as a substrate for manufacturing biofuels, such as sugarcane bagasse, sugar beetroot waste, rice straw, potato and sweet potato waste, etc. By reducing human dependence on forest trash and shortening the time needed to gather field waste, the use of agricultural residues reduces deforestation [123]. Numerous researchers have suggested utilising lignocellulosic materials and other agrarian leftovers to produce biofuel, namely bioethanol. ...
... One can use LCA and/or multi-criteria analysis (MFA) tools to help you find problem areas and work on the environmentally friendly parts of the process that can be fed back into the system or rebuilt [122]. Throughout the life cycle, chemistry must play a key role, especially during endof-life activities, in moving the material that has the most potential for use in industry and in a way that is beneficial to both parties in the setting of industrial ecology [123]. New business models, rules, and funding [121] also significantly impact the adoption of circularity. ...
Attempts are made to utilise waste organic biomass to produce fuels, chemicals, energy, power, and by-products for many mercantile applications. Hydrogen is a demanding fuel with the highest calorific value, and conventional chemical processes have raised specific environmental concerns. Alternatively, such biodegradable organic waste can be managed better with fermentation technologies and also for producing hydrogen, which is more environmentally friendly and cost-effective. Given environmental concerns, retrofitting the current chemical industry 3.0 with sustainable product management is vital. This review communication provides crucial information about the chemical industry’s restructuring within the scope of using the circular economy principle in circular chemistry in the burgeoning industry 4.0 scenario. It also focuses on recovering energy from waste materials, a potential strategy for mitigating environmental effects. More case studies utilising organic waste as feedstock in bio-refinery processes will be of interest in future to attain environmental sustainability, which is also highlighted in parallel.
... The generation of H2 from biomass and/or organic wastes through biological and chemical processes is a well-defined, commercially applied process [20][21][22]. The energy required for biochemical reactions that generate H2 can be provided by solar power or by converting fluid carbon sources, or by a combination of both. ...
... The generation of H 2 from biomass and/or organic wastes through biological and chemical processes is a well-defined, commercially applied process [20][21][22]. The energy required for biochemical reactions that generate H 2 can be provided by solar power or by converting fluid carbon sources, or by a combination of both. ...
... 2024, 14, 6217 5 of 24 media, and inhibitory factors. The authors also provided a summary of the principal biochemical reactions that lead to bio-H 2 generation, and they presented the H 2 yield resulting from this mechanism, as reported in various studies [20,25,27,28,31,36]. Table 2 presents the results of selected experimental works including the H 2 yield per type of carbohydrate used, the microorganisms involved, and the experimental conditions. ...
In today’s industry, H2 is mostly produced from fossil fuels such as natural gas (NG), oil, and coal through various processes. However, all these processes produce both carbon dioxide (CO2) as well as H2, making them questionable in terms of climate change mitigation efforts. In addition to efforts to increase the conversion efficiency of green H2 technologies, work is also underway to make H2 production from fossil fuels more environmentally friendly by reducing/avoiding CO2 emissions. In this framework, these technologies are combined with geologic carbon storage. In a further step, the use of depleted hydrocarbon reservoirs for in situ H2 production is being investigated, with the co-generated CO2 remaining permanently in the reservoir. The objective of this paper is to provide a brief overview of the technologies that can be used to produce H2 from depleted and depleting hydrocarbon reservoirs (DHRs) in various ways. We evaluate the required processes from a reservoir engineering perspective, highlighting their potential for H2 generation and their technology readiness level (TRL) for applications. We also investigate the possibility of permanently storing the co-produced CO2 in the reservoir as a means of mitigating emissions. In addition, we provide a preliminary cost analysis to compare these methods with conventional hydrogen production techniques, as well as an assessment of operational risks and associated cost estimates.
... The generation of H2 from biomass and/or organic wastes through biological and chemical processes is a well-defined, commercially applied process [20][21][22]. The energy required for biochemical reactions that generate H2 can be provided by solar power or by converting fluid carbon sources, or by a combination of both. ...
... The generation of H 2 from biomass and/or organic wastes through biological and chemical processes is a well-defined, commercially applied process [20][21][22]. The energy required for biochemical reactions that generate H 2 can be provided by solar power or by converting fluid carbon sources, or by a combination of both. ...
... 2024, 14, 6217 5 of 24 media, and inhibitory factors. The authors also provided a summary of the principal biochemical reactions that lead to bio-H 2 generation, and they presented the H 2 yield resulting from this mechanism, as reported in various studies [20,25,27,28,31,36]. Table 2 presents the results of selected experimental works including the H 2 yield per type of carbohydrate used, the microorganisms involved, and the experimental conditions. ...
Renewable hydrogen (H2) plays a crucial role in the energy transition as it can replace fossil fuels in industries and transportation that are difficult to decarbonize. In today’s industry, H2 is mostly produced from fossil fuels such as natural gas (NG), oil, and coal; however used processes produce carbon dioxide
(CO2) in addition to H2. These technologies are combined with geologic carbon storage to make them more environmentally friendly. In a further step, the use of depleted/depleting hydrocarbon reservoirs (DHRs) for in-situ H2 production is being investigated, with the co-generated CO2 remaining permanently in the reservoir. The objective of this study is to provide a brief overview of the technologies that can be used to produce H2 from DHRs in various ways. We evaluate the required processes from a reservoir engineering perspective, highlighting their potential for H2 generation and their technology readiness level (TRL) for applications. We also investigate the possibility of storing
the co-produced CO2 in the reservoir permanently to reduce emissions. We provide a preliminary cost analysis to compare these methods with conventional hydrogen production techniques, as well as an assessment of operational risks and associated cost estimates.
... Continuous automated bioprocess operation is a critical aspect in maximising the efficiency and productivity of bioprocesses, which are inherently characterised by limited profitability [33][34][35][36]. Specifically, while continuous bioreactors (chemostats) serve as the primary source of revenue generation for bioprocesses, by utilising microorganisms to generate high-value products, their operational sensitivity poses a fundamental challenge [33,[37][38][39]. Among the various obstacles encountered in continuous bioreactor operation, one of the most significant is the occurrence of wash-out -an operational failure which abruptly disrupts the performance of the bioreactor [37,38,40]. ...
... However, these changes often incur extra costs or adversely affect productivity. Alternatively, better control algorithms which attempt to introduce additional robustness tend to overly-complicate an already complex control strategy for bioreactors and are thus impractical [37,39,42,46]. All of these challenges force industrial practitioners to rely on rule-of-thumb approaches (such as a naive back-off from the optimum). ...
... All of these challenges force industrial practitioners to rely on rule-of-thumb approaches (such as a naive back-off from the optimum). These approaches have to be employed on an ad-hoc basis due to significant variations in the depicted curves ( Figure 13) across systems, often more complex than the ideal conditions assumed [37][38][39]46]. Instead, the ARRTOC algorithm precisely addresses processes needing a fine-tuned balance between optimality and operability by finding set-points which are inherently robust to the level of perturbations expected at the control layers. ...
Real-Time Optimization (RTO) plays a crucial role in the process operation hierarchy by determining optimal set-points for the lower-level controllers. However, these optimal set-points can become inoperable due to implementation errors, such as disturbances and noise, at the control layers. To address this challenge, in this paper, we present the Adversarially Robust Real-Time Optimization and Control (ARRTOC) algorithm. ARRTOC draws inspiration from adversarial machine learning, offering an online constrained Adversarially Robust Optimization (ARO) solution applied to the RTO layer. This approach identifies set-points that are both optimal and inherently robust to control layer perturbations. By integrating controller design with RTO, ARRTOC enhances overall system performance and robustness. Importantly, ARRTOC maintains versatility through a loose coupling between the RTO and control layers, ensuring compatibility with various controller architectures and RTO algorithms. To validate our claims, we present three case studies: an illustrative example, a bioreactor case study, and a multi-loop evaporator process. Our results demonstrate the effectiveness of ARRTOC in achieving the delicate balance between optimality and operability in RTO and control.
... Table 3 outlines the influences of bioreactor type and operating conditions on biohydrogen production in continuous mode. According to Banu et al. [161], the production of hydrogen is significantly influenced by the reactor's design and configuration, which affects both the conditions for growth and operation of the microbes. In order to optimize biohydrogen production, the ideal bioreactor should have a lower hydraulic retention time (HRT) and the ability to prevent biomass washout that can result from a lower HRT. ...
... In CSTRs, the mixing pattern completely mixes and suspends hydrogen-producing microbes in the reactor liquor resulting in an efficient mass transfer through a good substrate-microbes contact. However, the hydrogen production rate is limited in CSTR due to biomass washout that occurs at short hydraulic retention times [161]. Also, high-level fermentation cannot be maintained due to the rapid mixing. ...
... The AFBR is widely used in biohydrogen production since it can maintain stable operation under short HRT and high organic loading rates and has a high mass transfer rate. The two essential factors that affect the hydrogen production rate (HPR) and hydrogen yield (HY) in the AFBR are HRT and organic loading rate (OLR) [161]. Although AFBRs can handle high loading rates and low HRT without washing out the biomass, they face limitations in terms of biomass washout due to the low HRT. ...
Biofuel generated from different organic waste substrates has been described as a sustainable option to the rapidly exhausting fossil fuels. To worsen the dependence on fossil fuels, the price is skyrocketing daily attributable to high demand for it. The high demand and usage of fossil has therefore led to increased atmospheric CO2, which is a major greenhouse gas. Thus, the dire need to explore the production of biofuel, of which biohydrogen is one. In spite of the several benefits linked to the application of biohydrogen as fuel, its production is currently facing some levels of practical challenges, some of which include inadequate conversion of biomass and low rate of production. In order to enhance the production of biohydrogen, some influencing factors for production need to be optimized. In view of this, this review critically discusses fundamental factors that affect biohydrogen production, like substrate composition, pretreatment of substrates, physico-chemical parameters, etc. It was found that the key constituents in fermentative biohydrogen generation are carbohydrates while proteins are not that efficient. In addition, amongst metal ions like (Ni, Fe, Cu, Mg, Zn, and Na), Mg has been found to be one of the essential cofactors that activates more than ten enzymes involved in hydrogen fermentation. Biological pretreatment method for substrate has more advantages than others in terms of low-toxicity, mild reaction and low-cost. Reduction of partial pressure to an optimum level could enhance the yield of biohydrogen production. The integration of nanoparticles into the substrate to refill the biohydrogen (H2) production is well-thought-out as a robust approach. Finally, this paper comprehensively discusses the effects of various nanoparticles on biohydrogen fuel production while it concludes by highlighting the future prospects.
... Moreover, the steam reforming process does not produce hydrogen in a pure state but generates a mixture of gasses including CO 2 , CH 4 , etc. [11]. Although the hydrogenase enzyme can produce hydrogen using earth-abundant metals such as iron and nickel, its commercial application is limited due to the low stability of the enzymes outside their native environment and the complex preparation of the catalysts [12]. Two other alternative techniques for generating hydrogen in a highly pure state are photochemical and electrochemical water-splitting reactions [13][14][15]. ...
... From the slope of Figure 10b, the C dl value with respect to the Au/GCE electrode was determined to be 2.55 µF cm −2 . By comparing the C dl value (0.65 µFcm −2 ) obtained for a pure GCE surface in 0.1 M KCl with respect to its area of 0.0314 cm 2 , the active area of the modified electrode (Au/GCE) was determined to be approximately 0.12 cm 2 using Equation (12). ...
A hydrogen fuel cell is a highly promising alternative to fossil fuel sources owing to the emission of harmless byproducts. However, the operation of hydrogen fuel cells requires a constant supply of highly pure hydrogen gas. The scarcity of sustainable methods of producing such clean hydrogen hinders its global availability. In this work, a noble Au-atom-decorated glassy carbon electrode (Au/GCE) was prepared via a conventional electrodeposition technique and used to investigate the generation of hydrogen from acetic acid (AA) in a neutral electrolyte using 0.1 M KCl as the supporting electrolyte. Electrochemical impedance spectroscopy (EIS), open circuit potential measurement, cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE) were performed for the characterization and investigation of the catalytic properties. The constructed catalyst was able to produce hydrogen from acetic acid at a potential of approximately −0.2 V vs. RHE, which is much lower than a bare GCE surface. According to estimates, the Tafel slope and exchange current density are 178 mV dec−1 and 7.90×10−6 A cm−2, respectively. Furthermore, it was revealed that the hydrogen evolution reaction from acetic acid has a turnover frequency (TOF) of approximately 0.11 s−1.
... The current technology for dark fermentation is not yet efficient enough to be implemented on an industrial scale, and there are still several challenges to overcome, such as the instability of the process and the presence of inhibitors. Researchers are exploring different reactor designs and operation conditions to improve the efficiency and stability of the process, such as pH control, temperature control, hydraulic retention time, and inoculum concentration [11,12]. Overall, ongoing research is aimed at developing a stable, efficient, and cost-effective process for hydrogen production through dark fermentation. ...
... These nanoparticles have been shown to promote the growth and activity of hydrogen-producing microorganisms by providing a suitable microenvironment for microbial attachment and growth [30,31]. They also improve mass transfer of substrates and products, facilitate the removal of inhibitory compounds that can limit biohydrogen production [12], as well as drastically enhanced the thermal properties of the media where they are added [32]. Also, relationship between the nanoparticles shape and their magnetic and photocatalytic properties has been suggested [33]. ...
Dark fermentation holds great promise as a game-changing strategy in the field of biological hydrogen generation. With its ability to utilize a diverse range of organic feedstocks as a starting material, it offers the added advantage of waste valorization. Despite this, it has long been plagued by a low yield of hydrogen production when compared to traditional thermochemical processes. Recently, researchers have explored the use of nanoparticles as a means of intensifying the fermentation process. In this paper, the latest research on the use of metallic additives in dark fermentation, with a specific focus on naturally magnetic additives such as iron, nickel, and cobalt, is critically reviewed. The influence of these additives on the hydrogen generation process and the mechanisms that make it all happen are evaluated in detail. Optimal dosages for each additive type are also explored based on previous research. Finally, insightful suggestions for future research in this field are put forth. The conclusion is drawn that metal nanoparticles with natural magnetism, such as Fe, Ni, and Co, can improve hydrogen production, process stability, system start-up, and substrate utilization in dark fermentation. However, further research is needed to address various issues, including optimal dosage, operating conditions, microbial population dynamics, use of unconventional substrates, metal toxicity, morphology of metal additives, and potential risks generated by metals that remain in the system after fermentation. The exploration of combining several additives with complementary characteristics or properties is also proposed as an interesting line of research.
... This type of bioreactor is mostly used bioreactor for the continuous production of biohydrogen with a simple design, easier maintenance of parameters, and effectivity for continuous and uniform stirring. Although parameters like temperature, pH, and HRT affect the efficiency, the configuration of the stirrer and the speed used for mixing actually control the biohydrogen production [65]. Hasty mixing operation and washout biomass at low HRTs cause upholding lower fermenting microbes with lower biohydrogen generation. ...
... They discussed the experimental works of these emerging technologies and evaluated the potential of each technology. Banu J et al. (2021) evaluated the bioreactor configurations and the challenges associated with large-scale biohydrogen production. The authors stressed using optimized process configurations for efficient biohydrogen utilization. ...
... Nanoparticle technology is a potential solution to issues such as low bioconversion, enzyme inactivity and many other bottlenecks of biohydrogen production. Specifically inorganic nanomaterials may be used to enhance hydrogen production owing to their structural and chemical nature which allows them to maintain stable conditions during biohydrogen production [35]. They can act as oxygen scavengers preventing oxygen inhibition. ...
The usage of fossil fuel dominates the global energy landscape, leading to drastic environmental consequences such as climate change. In this context, the shift towards green hydrogen production is becoming a pressing need. This transition from carbon-based fuels to renewable energy is crucial to mitigate environmental challenges. Hydrogen, an energy carrier based on renewable energy resources, offers several technological production routes. Among them is biohydrogen, a biological pathway that produces sustainable energy from natural resources like biomass and wastewater. This study reviews various biological production technologies, their operational and design parameters, enhancement techniques and prospects. Furthermore, the development of nanomaterials and their significance in enhancing microbial growth for biohydrogen production is also emphasized. This study then underscores the prospects of biohydrogen production as a promising and remarkable technology for sustainable future energy carriers such as hydrogen. Therefore, exploring the performance indicators will bridge the gap between laboratory-scale and large-scale applications.
... Substrate pre-treatment has been suggested to improve biohydrogen production other than other enhancements such as nutrient addition, bioreactor design modifications, and inoculum genetic modification (Banu J et al., 2021). Substrate pre-treatment could also be categorised into chemical, physicochemical or biological treatments. ...
... Table 1 is an overview on the methods of hydrogen production in terms of the hydrogen color, by product, resources, efficiency, and cost. Moreover, biohydrogen is typically obtained from renewable feedstocks such as biomasses, and biological wastes and municipal sludge [33]. Biochemical methods, microbial electrolysis, and thermochemical routes are three main bio-approaches of hydrogen production from the mentioned feeds. ...
Fuel cells (FCs) are considered as the next generation of energy power sources with various feedstocks like hydrogen. Hydrogen FCs, with the combined advantages of hydrogen, are one of the promising renewable sources of energy with zero carbon dioxide emissions and high-power value. Hydrogen for FCs can be produced via water splitting and biobased approaches with their sub-techniques. Although there are many approaches to hydrogen, not all the methods result in green hydrogen. Green materials in FCs can be applied to different components of the membrane electrode assemblies. They are either incorporated within existing commercial grades of electrolytes and electrodes or as substitutes for non-environmentally materials in the form of single matrices or composites. This article presents the various methods for the production of green hydrogen, including water splitting with triggers of electricity, light, biological, and temperature, as well as biochemical and bio thermochemical routes. It also reviews the green materials employed in the various types of FCs, with the possibility of use for hydrogen FCs.
... The limitations and restraints associated with bioreactor operation are investigated, and discrete approaches for improved biohydrogen production are explored. These approaches include substrate pre-situations, inhibitor expulsion, bio-augmentation, immobilization, effluent reusing, buffering capacity, maintenance, and outgrowth utilization (Tiang et al. 2020;Banu et al. 2021). All conventional fuel reserves have their own limitations. ...
The global transition towards clean and sustainable energy sources has led to an increasing interest in green hydrogen production. The present work focuses on the development and assessment of a solar-assisted green hydrogen production system. The basic objective of this work is to investigate the influence of solar radiation to drive the electrolysis process for green hydrogen production. The system design includes photovoltaic solar panel to capture solar radiation and convert it into electrical energy. This energy is further utilized to operate an electrolyzer with zinc electrodes that facilitates the water-splitting reaction resulting in the production of hydrogen gas. The solar panel outputs along with global radiation and other relevant climatic conditions are monitored. The hydrogen production is analyzed at three different voltages, i.e., 11 V, 12 V, and 13 V. After 60 min of operations, the maximum amount of hydrogen (2952 mL) is produced at 13 V. The fabricated electrolyzer has been found suitable and economically feasible.
... HRT denotes the duration during which microorganisms can utilize and decompose the organic substrate in the reactor [50]. Operating at a short HRT with increased flow rates can lead to insufficient time for microorganisms to degrade organic substrates or substrate inhibition, ultimately reducing hydrogen production [51,52]. Reducing the HRT below optimal levels can cause microorganisms to be washed out of the AD process, resulting in decreased production of hydrogen and metabolic products [53]. ...
... The effectiveness of biohydrogen production process relies on reactor design, configuration, and operational conditions. Bioreactor's performance measurement can be assessed by its ability to function at lower hydraulic retention time (HRT) and reduced cell washout to achieve high production rate (Banu et al. 2021). Batch systems for biohydrogen production are majorly suitable for experimental studies or research purposes at laboratory scale to test effects of different substrate, inoculum, environmental conditions, etc., or in reactions with slow kinetics. ...
There is a global attention toward production of clean and green energy to reduce the dependency on fossil fuel-derived sources and its subsequent environmental impact. Biohydrogen, thus offers an attractive potential source of energy with both economic and environmental advantages. Hydrogen is produced biologically through light-driven and light-independent pathways. At present, light-independent process of dark fermentation appears more favorable due to low operational costs and high hydrogen yield, and thus, is advancing in research. Production involves a complex interplay of genetically and functionally diverse mixed microbial cultures with a multitude of organic substrates. The dominant types of microorganisms involved in these metabolic reactions function in mesophilic range and are both facultative and strict anaerobes, belonging to genera Clostridium and Enterobacter. However, with varying environmental and operational conditions, a shift occurs in the microbial community structure that further affects the yield of hydrogen produced. By understanding the syntrophic co-metabolism of hydrogen-producers and hydrogen-consumers, the bioreactor performance can be modified for scaling-up biohydrogen production in continuous systems. With modern molecular techniques and metagenomic studies, it is now becoming possible to study these reactor microbiomes to extract information about essential enzymes and respective microorganisms that may increase the hydrogen yield.
... Mu et al. investigated the H 2 yield with varying temperatures and found 33-39 • C as the most favorable temperature range for H 2 production by hydrogenproducing bacteria in an anaerobic fermentation process (Mu et al., 2006). On the other hand, increasing the temperature in an anaerobic fermentation process enhances H 2 productivity owing to the decreasing H 2 solubility in the liquid phase (Banu et al., 2021). However, additional thermal energy is needed to increase temperature, which subsequently impacts the economic feasibility of the process. ...
... Mixed culture systems and pure cultures of hydrogen-producing bacteria have been used in biohydrogen production studies [24]. The selection of appropriate microbial strains, optimization of operational parameters, and development of efficient bioreactor configurations are crucial for enhancing the biohydrogen production process [24,26]. Despite progress in this field, achieving high hydrogen yields and understanding the complex interactions between microbial consortia and operational parameters require further investigation. ...
Upper mesophilic temperature acclimation of halophilic, hydrogen-producing bacteria from salt fields was investigated in this study, along with the changes in microbial abundance during an-aerobic digestion (AD) process. Genomic approaches such as PCR-denaturing gradient gel elec-trophoresis (DGGE) and next-generation sequencing (NGS) were performed to profile the mi-crobial communities. During AD, there was a significant abundance of Halanaerobacter lacunarum at 48°C followed by the increase in hydrogen yield, signifying potential contribution from the halophile in the hydrogen production. A decrease in the dominance of H. lacunarum and Halan-aerobium fermentans at 42°C, likely due to an increase in other bacterial species, was noted but their dominance significantly increased at temperatures of 45°C and 48°C. This investigation provides valuable insights in highlighting the potential of Halanaerobium sp. and the other halo-philic bacteria to adapt under upper mesophilic temperature conditions and synthesizing hy-drogen. The findings in the present study also underscore the importance of optimizing temper-ature and pH conditions to maximize hydrogen yield during high-salt anaerobic digestion.
... Por su parte, Clostridium butyricum es una importante especie productora de solventes e hidrógeno [237][238][239] que ha sido ampliamente estudiada por su capacidad para consumir glicerol crudo, pero no ha sido utilizada en el proceso de electrofermentación catódica [9,12,39,40]. ...
Sugars and glycerol can serve as low-cost substrates in biotechnological applications to
obtain various chemical intermediates with high added value. Electrofermentation is a
recent technology with which it is possible to improve and control microbial fermentation,
especially with strains of the Clostridium genus, increasing the specificity of metabolic
pathways. In this context, bacterial strains isolated from Colombian soils, and closely
related to Clostridium butyricum. These strains have been efficient producers of solvents
and acids, including acetic acid, butyric acid, ethanol, butanol, acetone, and hydrogen from
glucose or 1,3-propanediol from glycerol. In this work, the production of commercial interest
metabolites is assessed using an electron external supply with a metabolic network of C.
butyricum. The simulation results show that the interaction with the cathode electrode
improves the reduced product rates. Specifically, using glycerol as a substrate, the average
yield of the product increases with 1,3-propanediol (23%) and hydrogen (45%). Finally, it
was established experimentally that the native strain IBUN 158B is electroactive and has
the capacity to increase the product/substrate yield values of 1,3-PD (7-9%) when it is
submitted to the feeding of small amounts of electrons from a cathode in a cathodic
electrofermentation process and that the use of electron carriers such as Neutral Red
increases the effects of electrofermentation, reaching higher yield values when it is present
in the culture medium. In conclusion, the electrofermentation of Clostridium butyricum as a
bioelectrochemical culture technique has potential as an alternative production process to
traditional fermentation to control the redox state during the synthesis of biochemicals and
increase the production of metabolites of commercial interest. More basic and applied
research is necessary to elucidate the mechanisms of electron transfer and reveal the
underlying regulatory mechanisms.
... For commercial-scale application, microalgaebased hydrogen generation utilizes dark bioreactors such as membrane bioreactor, anaerobic fluidized bed reactor, continuous stirred tank reactor, and flow anaerobic sludge blanket reactor rather than conventional photobioreactors Limongi et al. 2021;Li et al. 2022b;Sahrin et al. 2022). Moreover, to avoid the limitation of low residence time of continuous stirred tank reactor for biohydrogen production, modified reactors with immobilized microalgal biomass have been proposed (Usman et al. 2021). ...
Global warming is induced partly by rising atmospheric carbon dioxide levels, calling for sustainable methods to sequester carbon. Here we review carbon capture, usage, and storage with microalgae, with focus on methods to improve carbon
dioxide uptake, systems combining wastewater and flue gases, machine learning for strain identification, artificial intelligence and automation, and the circular bioeconomy. Carbon dioxide uptake by microalgae can be improved by using modified photobioreactors, membranes, chemical methods, solvents, adapted strains, genetically engineered strains, omics, and nanotechnology. We also discuss the economic viability of microalgae-based carbon capture and bioenergy generation. On an average, microalgal farming on 13 million acres area can sequester approximately 0.5 gigatons of CO2 to generate more than 300 tons of biomass.
... This is because it affects the contact between the microorganisms (the hydrogen producers) and their substrates, which subsequently affects substrate utilization rate, biomass dilution rate, among other factors. The design and configuration of the reactor could increase the production and efficiency for long-term operation, as well as its ability to withstand shock loads and operational circumstances (Ren et al. 2011;Jung et al. 2011;Bakonyi et al. 2015;Banu et al. 2021). It also serves as a crucial parameter since it influences the environment for microbial growth . ...
The growing acceptance of hydrogen as a suitable substitute for fossil fuel makes it a resource that can be completely utilized in decarbonizing the environment. It is recognized as the cleanest and best fuel that can expedite the mitigation of the presence of anthropogenic greenhouse gas emissions in the environment because of its high energy density, good calorific value, and significant environmental benefits. It is distinct from other fuels in that it may be created through biological, thermochemical, and electrochemical processes and in that wastes can be used as a feedstock for its production. This paper focuses on reviewing biohydrogen production from wastewater. It discusses techniques that could be harnessed to produce biohydrogen from wastewater, factors that can be improved to enhance the performance of this gaseous fuel, an overview of bioreactors, and the technical challenges associated with the use of biohydrogen produced from wastewater. It also provides an economic overview of biohydrogen production from wastewater and the prospects of using this waste-to-fuel technique to address both energy and environmental concerns in developing areas such as Africa. This work established that using wastewater for biohy-drogen production is economically friendly and also gives considerable hydrogen yield. The cost-to-benefit analysis varies depending on the type of wastewater used, the biological process involved, and the amount of hydrogen produced. The average investment cost varies around a range of 0.4-18.5 USD/m 3 of biohydrogen. The revenue obtained by using wastewater for biohydrogen production can be as high as 4.2 million USD on an annual basis for a reactor volume of 500 m 3 , which produces about 448,000 kg of H 2 yearly. Deploying low-cost and effective bioreactors, optimizing available hydrogen production techniques, and addressing the storage issues scourging biohydrogen are suggested ways of improving its potential.
The global shift towards sustainable energy sources, necessitated by climate change concerns, has led to a critical review of biohydrogen production (BHP) processes and their potential as a solution to environmental challenges. This review evaluates the efficiency of various reactors used in BHP, focusing on operational parameters such as substrate type, pH, temperature, hydraulic retention time (HRT), and organic loading rate (OLR). The highest yield reported in batch, continuous, and membrane reactors was in the range of 29–40 L H2/L per day at an OLR of 22–120 g/L per day, HRT of 2–3 h and acidic range of 4–6, with the temperature maintained at 37 °C. The highest yield achieved was 208.3 L H2/L per day when sugar beet molasses was used as a substrate with Clostridium at an OLR of 850 g COD/L per day, pH of 4.4, and at 8 h HRT. The integration of artificial intelligence (AI) tools, such as artificial neural networks and support vector machines has emerged as a novel approach for optimizing reactor performance and predicting outcomes. These AI models help in identifying key operational parameters and their optimal ranges, thus enhancing the efficiency and reliability of BHP processes. The review also draws attention to the importance of life cycle and techno-economic analyses in assessing the environmental impact and economic viability of BHP, addressing potential challenges like high operating costs and energy demands during scale-up. Future research should focus on developing more efficient and cost-effective BHP systems, integrating advanced AI techniques for real-time optimization, and conducting comprehensive LCA and TEA to ensure sustainable and economically viable biohydrogen production. By addressing these areas, BHP can become a key component of the transition to sustainable energy sources, contributing to the reduction of greenhouse gas emissions and the mitigation of environmental impacts associated with fossil fuel use.
The process of hydrogen production interacts highly with gas–liquid mass transfer and bubble behaviors as well as the gaseous pressures. In this chapter, basic mathematical models for analysis of liquid–gas mass transfer kinetics, the relationship between gas solubility and mass transfer, and liquid product composition will be discussed. Then, basic information of system pressure and effects of headspace composition and gas partial pressures on biohydrogen production will be summarized. The routes to enhance hydrogen production metabolic pathway through regulating the gas composition and partial pressure in the system will also be proposed. The information of gas mass transfer and system pressure will certainly pose insight for possible enhancement of biohydrogen production.
Recently, nanoparticles have drawn a lot of interest as catalysts to enhance the effectiveness and output of biohydrogen generation processes. This review article provides a comprehensive bibliometric analysis of the significance of nanotechnology in dark fermentative biohydrogen production. The study examines the scientific literature from the database of The Web of Science© while the bibliometric investigation utilized VOSviewer© and Bibliometrix software tools to conduct the analysis. The findings revealed that a total of 232 articles focused on studying dark fermentation for hydrogen production throughout the entire duration. The extracted data was used to analyze publication trends, authorship patterns, and geographic distribution along with types and effects of nanoparticles on the microbial community responsible for dark fermentative biohydrogen production. The findings of this bibliometric analysis provide valuable insights into the advancements and achievements in the utilization of nanoparticles in the dark fermentation process used to produce biohydrogen.
Biohydrogen, through biological or fermentation processes, is one of the best options for clean energy production, as the process consumes low energy and is more environmentally friendly. The process involves various types of substrates and microorganisms, where, in particular, the microorganisms could be a single or coculture, introduced as free cells or in immobilized form. Among the advantages of immobilized culture in fermentation is its ability to maximize the physical retention of microbial biomass while minimizing mass transfer. Various types of bioreactor setups can be considered to facilitate the fermentation process using immobilized culture, such as continuous stirred tank reactor (CSTR), upflow anaerobic sludge bioreactor (UASB), fluidized bed reactor (FBR), and packed/fixed bed reactor (PBR), or either in modified or integrated mode. This chapter focuses on the various bioreactor design that facilitates the fermentation process using immobilized culture for varying substrate and inoculum, both in batch and continuous systems. This chapter also compares the advantages and disadvantages of different bioreactor types, including the biohydrogen production performance of each bioreactor.
The recent interest in the production of biohydrogen (bio-H2) from biomass in laboratory scale has enhanced, while there is a need for subsequent technical advancements in the associated biological processes to make it economically viable. H2 is considered as one of the most competitive substitutes for fossil fuels where biological processes are reflected as the most eco-friendly alternatives for meeting future H2 demands. The bio-H2 from agricultural waste is especially advantageous since these biomass is readily available, biodegradable, inexpensive, and renewable. Such wastes are composed of complex lignocellulosic substrates that can be biologically degraded by the complex microbial consortia where dark fermentation coupled with other biological processes like photofermentation and microbial electrolysis cell under various operating conditions has been proved to be a key technology for H2 production from various agricultural wastes. This study emphasizes on different technological advancements in terms of pre-treatment of biomasses for lignin removal, reactor design optimization, and hybridization of different techniques for H2 production from agri-wastes with a special focus on the role of nanoparticles and biotechnological advancements for process stabilization and enhancement of H2 production. The study has revealed that despite the proven efficiency of the various approaches, a detailed and in-depth research is needed for understanding the cellulosic H2 generation process at a molecular level.
The rising food waste generation induces major issues of food security, pollution, and depletion of resources and arable land, thus calling for novel recycling practices such as converting food waste into fuels. Here we review the production of dihydrogen, thereafter named ‘hydrogen,’ and biodiesel from food waste, with focus on food waste composition and hydrolysis, hydrogen production and biodiesel production. Hydrogen production is done by dark fermentation and photofermentation. Biodiesel is produced by production of lipid-rich biomass using food waste and transesterification. We discuss lipids accumulation in oleaginous microorganisms and in black soldier fly larvae. Upscaling of hydrogen and biodiesel production is also presented. Optimal hydrogen yield ranges from 1 to 7 mol H2/mol hexose. After fermentation, the residual glucose should be less than 10% and volatile fatty acids should be less than 40%. Biomass lipids containing less than 1% polyunsaturated fatty acids is ideal for biodiesel production.
Increased production of renewable energy sources is becoming increasingly needed. Amidst other strategies, one promising technology that could help achieve this goal is biological hydrogen production. This technology uses micro-organisms to convert organic matter into hydrogen gas, a clean and versatile fuel that can be used in a wide range of applications. While biohydrogen production is in its early stages, several challenges must be addressed for biological hydrogen production to become a viable commercial solution. From an experimental perspective, the need to improve the efficiency of hydrogen production, the optimization strategy of the microbial consortia, and the reduction in costs associated with the process is still required. From a scale-up perspective, novel strategies (such as modelling and experimental validation) need to be discussed to facilitate this hydrogen production process. Hence, this review considers hydrogen production, not within the framework of a particular production method or technique, but rather outlines the work (bioreactor modes and configurations, modelling, and techno-economic and life cycle assessment) that has been done in the field as a whole. This type of analysis allows for the abstraction of the biohydrogen production technology industrially, giving insights into novel applications, cross-pollination of separate lines of inquiry, and giving a reference point for researchers and industrial developers in the field of biohydrogen production.
In the global race to produce green hydrogen, wastewater-to-H2 is a sustainable alternative that remains unexploited. Efficient technologies for wastewater-to-H2 are still in their developmental stages, and urgent process intensification is required. In our study, a mechanistic model was developed to characterize hydrogen production in an AnMBR treating high-strength wastewater (COD > 1000 mg/L). Two aspects differentiate our model from existing literature: First, the model input is a multi-substrate wastewater that includes fractions of proteins, carbohydrates, and lipids. Second, the model integrates the ADM1 model with physical/biochemical processes that affect membrane performance (e.g., membrane fouling). The model includes mass balances of 27 variables in a transient state, where metabolites, extracellular polymeric substances, soluble microbial products, and surface membrane density were included. Model results showed the hydrogen production rate was higher when treating amino acids and sugar-rich influents, which is strongly related to higher EPS generation during the digestion of these metabolites. The highest H2 production rate for amino acid-rich influents was 6.1 LH2/L-d; for sugar-rich influents was 5.9 LH2/L-d; and for lipid-rich influents was 0.7 LH2/L-d. Modeled membrane fouling and backwashing cycles showed extreme behaviors for amino- and fatty-acid-rich substrates. Our model helps to identify operational constraints for H2 production in AnMBRs, providing a valuable tool for the design of fermentative/anaerobic MBR systems toward energy recovery.
The global transition towards clean and sustainable energy sources has led to an increasing interest in green hydrogen production. This study presents a sustainable way to the development and assessment of a solar-assisted green hydrogen production. The basic objective of this study is to investigate the practicability and influence of utilizing solar radiation to drive the electrolysis process for green hydrogen generation. The system design combines photovoltaic solar panels to capture solar radiation and convert it into electrical energy. This energy is utilized to operate an electrolyzer with similar electrodes as zinc that facilitates the water-splitting reaction resulting in the production of hydrogen gas. The solar panel temperature along with global radiation has been monitored. The hydrogen production is analyzed at three different voltage values i.e. 11V, 12V, and 13V. After sixty minutes of operations, the maximum amount of hydrogen (2952 ml) is produced at 13V. Therefore, the fabricated electrolyzer was found stable and economic feasible throughout the tests for hydrogen production.
Hydrogen is measured as one of the capable substitute fuel for fossil fuels. Creation of clean energy sources and consumption of dissipated materials make natural hydrogen production a unique and promising candidate to meet the escalating energy requirements as an alternative of fossil fuel. Bio-hydrogen production from agricultural waste is very advantageous since agricultural wastes are abundant, economical, renewable, and eco-friendly. Water splitting, steam reforming of hydrocarbons, and autothermal techniques are the best-applicable methods for hydrogen gas production, but not economical owing to high energy needs. In comparison to chemical methods of hydrogen gas, bio-production has considerable merits like bio-photolysis of water by algae and dark fermentation and photo-fermentation of untreated materials through bacteria. Diverse agriculture desecrated materials are presented to produce bio-hydrogen to fulfill its demand. New technique for bio-hydrogen production is the dark fermentation and photo-fermentation scheme. This chapter will summarize the manufacturing of bio-hydrogen using agriculture waste materials with current developments and qualified advantages.KeywordsBio-hydrogenAgriculture wasteDark and photo-fermentationsWaste bioprocessing
Modernisation of industrial and transportation sector would have not imaginable without the help of fossil fuels, but constant usage has led to many environmental concerns. As a step forward, for safer next generation living we are forced to look into green fuels like bio‑hydrogen and higher alcohols. This review mainly focuses on bio‑hydrogen production via biological pathways, genetic improvements, knowledge gap, economics, and future directions. Dark and photo fermentation process with the factor influence the process (pH regulation, temperature, hydraulic retention time, organic loading rate, Maintenance, Nutrient) is studied. Integration of dark fermentation and microbial electrolysis cell is the most trending progression for sustainable bio‑hydrogen production. Genetic improvement of microbe for biohydrogen production via inactivation of hydrogenase (H2ase) and improve oxygen tolerant H2ase. In future, bioaugmentation, multidisciplinary integrated process and microbial electrolysis needs to be experimented in industrial level scale for successful commercialization. About 41.47 mmol H2/g DCW h at 40 g/L of optimum biohydrogen production was obtained through glycerol fermentation. From the studies, the cost of biohydrogen production was found to high with respect to the direct bio photolysis it cost around 7.54 kg-1 and for fermentation it cost around $7.61 kg-1.
Significant efforts are being made to produce biofuels to replace fossil fuels and address the issues caused by global climate change. Due to its potential better conversion efficiency to
useable power, decreased emission of pollutants, and high energy density, H2 is one of the prospective options that are seen as a desirable future clean energy carrier. Although there are numerous technologies available for producing H2, this review concentrates on fermentative H2 production techniques, their drawbacks, and current developments. While being a promising method, fermentative strategies still have several drawbacks, including low H2 production yields. Many approaches have been used to address these issues; among them, the field of metabolic pathway engineering has made enormous strides. To improve
H2 generation, this paper reviewed and discussed several metabolic pathways and modified strains. As well as the challenges involved in H2 scale-up from a laboratory setting to a
commercial scale.
Although many studies related to biohydrogen have been reported, the productivity of biohydrogen production remains low. To achieve its implementation at an industrial scale, higher productivity is critical. Research on various bioreactor configurations and factors influencing hydrogen production has also been extensively investigated for mass production. Therefore, a review of the prevailing issues associated with bioreactor operation and the recent advancement in alleviating the challenges of biohydrogen production will be discussed in this chapter. Four challenges have been identified, namely, physical, biological, chemical, and economical, which enhancement strategies for improving biohydrogen productivity accompany each challenge.
Interest in biohydrogen (bioH 2 ) production from dark fermentation (DF) has increased due to green routes involving reusing by‐products, wastewater, and residues from agroindustry. Moreover, bioH 2 as an energy carrier of the future leads to clean combustion with the formation of a single product (water) and also releases 242 kJ mol −1 or 121 kJ g −1 energy per mass unit. As a result, it could be transformed into electrical energy using a fuel cell or an internal combustion engine. However, several studies state that the yield of bioH 2 production in anaerobic reactors by dark fermentation (DF) is still low when compared to the yields of conventional hydrogen processes and technologies such as water electrolysis CH 4 reform, and gasification coal, among others. Therefore, in the literature, different anaerobic technologies have been investigated, for example, changing the conventional systems to high‐rate reactors and studies on the pre‐treatment of inoculum, types of substrates, and genetic modifications of hydrogen‐producing microorganisms. Therefore, this chapter shows the principal biochemical routes and main types of reactors used in wastewater‐fed bioH 2 ‐producing systems. Finally, essential recommendations are highlighted.
Hydrogen (H2) is one of the most promising renewable energy sources, anaerobic bacterial H2 fermentation is considered as one of the most environmentally sustainable alternatives to meet the potential fossil fuel demand. Bio-H2 is the cleanest and most effective source of energy provided by the dark fermentation utilizing organic substrates and different wastewaters. In this study, the bio-H2 production was achieved by using the bacteria Acinetobacter junii-AH4. Further, optimization was carried out at different pH (5.0–8.0) in the presence of wastewaters as substrates (Rice mill wastewater (RMWW), Food wastewater (FWW) and Sugar wastewater (SWW). In this way, the optimized experiments excelled with the maximum cumulative H2 production of 566.44 ± 3.5 mL/L (100% FWW at pH 7.5) in the presence of Acinetobacter junii-AH4. To achieve this, a bioreactor (3 L) was employed for the effective production of H2 and Acinetobacter junii-AH4 has shown the highest cumulative H2 of 613.2 ± 3.0 mL/L, HPR of 8.5 ± 0.4 mL/L/h, HY of 1.8 ± 0.09 mol H2/mol glucose. Altogether, the present study showed a COD removal efficiency of 79.9 ± 3.5% by utilizing 100% food wastewater at pH 7.5. The modeled data established a batch fermentation system for sustainable H2 production. This study has aided to achieve an ecofriendly approach using specific wastewaters for the production of bio-H2.
Biohydrogen is a clean and viable energy carrier generated through various green and renewable energy sources such as biomass. This review focused on the application of membrane bioreactors (MBRs), emphasizing the combination of these devices with biological processes, for bio-derived hydrogen production. Direct biophotolysis, indirect biophotolysis, photo-fermentation, dark fermentation, and conventional techniques are discussed as the common methods of biohydrogen production. The anaerobic process membrane bioreactors (AnMBRs) technology is presented and discussed as a preferable choice for producing biohydrogen due to its low cost and the ability of overcoming problems posed by carbon emissions. General features of AnMBRs and operational parameters are comprehensively overviewed. Although MBRs are being used as a well-established and mature technology with many full-scale plants around the world, membrane fouling still remains a serious obstacle and a future challenge. Therefore, this review highlights the main benefits and drawbacks of MBRs application, also discussing the comparison between organic and inorganic membranes utilization to determine which may constitute the best solution for providing pure hydrogen. Nevertheless, research is still needed to overcome remaining barriers to practical applications such as low yields and production rates, and to identify biohydrogen as one of the most appealing renewable energies in the future.
In recent years, graphene oxide membranes showed interesting performances in terms of high permeating flux and perm-selectivity in several applications of gas separation because of their inherent properties combined to a low energy consumption. In this paper, a graphene oxide layer is coated on modified TiO 2 -alumina tubular substrate in order to prepare graphene oxide nanocomposite membranes useful for hydrogen separation. Nanocomposite graphene oxide membrane samples were obtained by using vacuum deep coating method, depositing the graphene oxide solution as single layers on TiO 2 -alumina substrate. Temperature and pressure variations were evaluated to achieve high H 2 permeance, high H 2 /CO 2 selectivity and membrane performance stability during the experimental tests. Furthermore, it was found that the temperature increase causes a perm-selectivity (H 2 /N 2 and H 2 /CO 2 ) decrease, while the transmembrane pressure increase involves a general improvement of the perm-selectivity.
The partial pressure of hydrogen is a significant factor for dark fermentation. The effect of reduced hydrogen partial pressure as well as different operation condition was investigated in this study. The results showed that hydrogen production enhanced when partial pressure reduced. The reduction of hydrogen partial pressure (reduced by 20%, interval=2h) increased the efficiency of hydrogen production by 54%(202.15mL) compared with the control group. The kinetic parameters of hydrogen production show that the maximum hydrogen production (Pmax) and the maximum hydrogen production rate (Rmax) were increased by the reduction of hydrogen partial pressure. And the hydrogen production delay time (λ) decreased. Moreover, with the decrease of hydrogen partial pressure, ethanol content gradually increased, acetic acid/ethanol ratio decreased, total VFAs increased. The compositions of soluble microbial products as well as ecological factors were affected by hydrogen partial pressure.
The availability of fermentable sugars in POME is one of the critical factors that determine the fermentative biohydrogen production yield. This study was carried out to determine the pretreatment conditions viz., temperature, hydrolysis time and acid concentration that can yield the highest monomeric sugars, to be utilized for production of biohydrogen from POME by mixed culture dark fermentation. Two different acids were used, nitric acid and phosphoric acid in the pretreatment of POME. Batch fermentation was performed to determine the potential of pretreated POME as a substrate for the production of biohydrogen under the tested pretreatment conditions. Higher hydrogen yield was successfully achieved using pretreated POME as compared to raw POME by mixed culture. Maximum hydrogen production was 0.181 (mmol/L/h), which corresponded to the yield of 1.24 mol H2/mol glucose achieved at 0.8% (w/v) phosphoric acid with initial total reducing
sugar concentration of 18.47 g/L. Hence, the results implied that POME pretreated with 0.8% (w/v) phosphoric acid is a potential substrate for efficient biohydrogen fermentation yield that is 97% higher than untreated POME. While POME pretreated with 1% (w/v) of nitric acid showed 65% improvement in biohydrogen yield as compared to untreated POME. Therefore, the results implied that both pretreatment methods of POME showed significant increase in the biohydrogen production.
Marine macroalgae are promising substrates for biofuel production. Pretreating macroalgae with chemicals could remove microbial inhibitors and enhance the accessibility of the microorganisms involved in the process to the substrates leading to increased product yield. In the present study, Padina tetrastromatica a seaweed species was subjected to different chemical pretreatment in order to remove phenolic content and to enhance biohydrogen production. Different mineral acids (i.e., HCl, H2SO4, and HNO3) and bases (NaOH and KOH) were applied for effective pretreatment of the seaweed. Dilute sulphuric acid treatment of seaweed resulted in the highest cumulative biohydrogen production of 78 ± 2.9 mL/0.05 g VS and reduced phenolic content to 1.6 ±0.072 mg gallic acid equivalent (GAE)/g. Optimization of three variables for pretreatment (i.e., substrate concentration, acid concentration, and reaction time) was examined by Response Surface Methodology. After the optimization of the pretreatment conditions, phenolic content was decreased to 0.06 mg GAE/g. and enhanced biohydrogen production was observed. Structural changes due to pretreatment was studied by FTIR and XRD analyses. The results clearly indicated that the dilute sulphuric acid pretreatment was effective in removing phenolic content and enhancing biohydrogen production.
Attempting to associate waste treatment to the production of clean and renewable energy, this research sought to evaluate the biological production of hydrogen using wastewater from the cassava starch treatment industry, generated during the processes of extraction and purification of starch. This experiment was carried out in a continuous anaerobic reactor with a working volume of 3L, with bamboo stems as the support medium. The system was operated at a temperature of 36°C, an initial pH of 6.0 and under variations of organic load. The highest rate of hydrogen production, of 1.1 L.d-1.L-1, was obtained with application of an organic loading rate of 35 g.L-1.d-1, in terms of total sugar content and hydraulic retention time of 3h, with a prevalence of butyric and acetic acids as final products of the fermentation process. Low C/N ratios contributed to the excessive growth of the biomass, causing a reduction of up to 35% in hydrogen production, low percentages of H2 and high concentrations of CO2in the biogas.
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.
This study reviewed the recent updates on the pretreatment methods employed towards the enhancement of hydrogen production. Low hydrogen yield was considered to be a current obstacle for hydrogen utility on the industrial scale. On pretreating, the wastewater, the structure of the macromolecule gets dissipated and destroyed which reduces the polymerization potency. It favors the availability of monomers for the fermentation process. Various pretreatment methods with operating conditions and parameters were documented along with their pros and cons. Mainly, the pretreatment methods adopted for reducing the toxicity levels of wastewater to enhance biohydrogen production are dealt with in detail. Pretreatment methods have shown a positive impact on most of the cases studied. It acts on various components of wastewater and makes it amenable for the hydrogen-producing microbiome. Energy balance methodologies have also been provided towards the selection of a cost-effective and sustainable approach. Perspectives and recommendations on pretreatment systems were directed towards the development of a successful hydrogen economy. Overall documentation details the significance of pretreatment in the fermentation process for higher hydrogen yield.
Membrane bioreactors (MBRs) have been widely used as advanced wastewater treatment process in recent years. However, MBR system has a membrane fouling problem, which makes the system less competitive. Thus there have been great efforts for fouling mitigation. In this study, two types of TiO 2 immobilized ultrafiltration membranes (TiO 2 entrapped and deposited membranes) were prepared and applied to activated sludge filtration in order to evaluate their fouling mitigation effect. Membrane performances were changed by addition of TiO 2 nanoparticles to the casting solution. TiO 2 entrapped membrane showed lower flux decline compared to that of neat polymeric membrane. Fouling mitigation effect increased with nanoparticle content, but it reached limit content above which fouling mitigation did not increase. Regardless of polymeric materials, membrane fouling was mitigated by TiO 2 immobilization. TiO 2 deposited membrane showed greater fouling mitigation effect compared to that of TiO 2 entrapped membrane, since larger amount of nanoparticle was located on membrane surface. It can be concluded that TiO 2 immobilized membranes are simple and powerful alternative for fouling mitigation in MBR application.
Alternanthera philoxeroides, a notorious invasive aquatic weed, is a typical lignocellulosic feedstock for fermentative biohydrogen production. To improve the dark fermentation performance, steam-heated acid pretreatment and enzymolysis were employed to release reducing sugars from A. philoxeroides, and Enterobacter aerogenes ZJU1 mutagenized by 60Co-γ irradiation was used as the inoculum. Dilute acid accompanied by steam heating significantly disrupted the fiber structures of A. philoxeroides. Scanning electron microscopic images revealed that many pores and fissures were generated in the surface of A. philoxeroides after pretreatment. X-ray diffraction and Fourier transform infrared spectroscopy analyses showed that the pretreatment facilitated the transformation of cellulose I to cellulose II in A. philoxeroides biomass, resulting in the increase of amorphous regions and the decrease of crystallinity. Under the optimum pretreatment condition (1.0 v/v% H2SO4, 135 °C for 15 min), the reducing sugar yield reached 0.354 g/g A. philoxeroides, which was further increased to 0.575 g/g A. philoxeroides after enzymolysis. The biohydrogen yield increased by 59.9% from 38.9 mL/g volatile solids (VS) of raw A. philoxeroides to 62.2 mL/gVS of the pretreated one. As compared to the wild strain, E. aerogenes ZJU1 contributed to an increase of 31.8% in the biohydrogen yield from pretreated A. philoxeroides. Further optimization of bacteria suspensions significantly increased the maximum biohydrogen production rate from 1.42 to 4.64 mL/gVS/h, advanced the biohydrogen production peak, and resulted in an increase of 42.8% in biohydrogen yield to 89.8 mL/gVS.
H2 production by dark fermentation using mixed cultures has been studied intensively during the last two decades, and its feasibility has been demonstrated. Different substrates, operational conditions, and reactor technologies have been widely studied and there is a general agreement that the use of non-sterile fermentable substrates is required to make the process feasible for scaling up. Nonetheless, stability problems during long term operation may hinder its application at large scale. This work, written by members of the Latin American Biohydrogen Network, analyse and discuss instability causes and possible solutions in the H2 production by dark fermentation. It is concluded that instability is mostly linked to the biotic aspects of the process (i.e., changes in the microbial community composition, presence of organisms that consume hydrogen and compete for the substrate, and accumulation of fermentation products); regardless of the reactor configuration. However, some problems like excessive growth of microorganisms and methanogens presence were mostly reported in fixed bed reactors and granular sludge reactors. The novelty of this work relies on the comprehensive revision of the main causes behind the unstable and low hydrogen production and how these causes are linked to the technology used. The strategies to overcome the problems as well as the potential implications are also analysed.
Biohydrogen was produced using a granular biomass reactor coupled to a submerged internal membrane. The reactor performance was evaluated under different organic loading rates (OLR) ranging from 5 to 60 g L⁻¹ d⁻¹ and hydraulic retention times (HRT) from 5.5 to 1.25 h. The UASB reactor was operated at 35 °C and pH 4.5. It was observed that the membrane introduction to the reactor does not affect the granule size or integrity. The maximum hydrogen production rate was obtained at 30 g L⁻¹ d⁻¹ and 4 h of HRT (475 ± 15 mLH2 L⁻¹ h⁻¹). A further increase of the OLR resulted in a lower hydrogen production due to a shift of the metabolism to solvent production. The use of membranes allowed the application of relatively low HRT; however, HRT lower than 2 h promoted the homoacetogenic metabolism, decreasing the hydrogen production. The results indicate that the membrane fouling is not only affected by the total EPS formed but also by the operational flux applied.
In order to address existing environmental concerns as a result of non-renewable energy sources and to meet future energy demands, biohydrogen offers a suitable alternative energy reserve. Discrete as well as integrative methods of biohydrogen production have been analyzed over time, optimized for achieving high yields. In addition, key process parameters such as temperature, pH, hydraulic retention time, substrate concentration etc., which influence the rate of production have been clarified. Several studies have exploited industrial waste as feed sources for the production of biohydrogen; however, lower yields from these add an additional requirement for suitable pretreatment methods. The present communication examines various pretreatment methods used to increase the accessibility of industrial wastewater/waste for biohydrogen production. Furthermore, a brief overview addresses challenges and constraints in creating a biohydrogen economy. The impacts of pretreating wastes on biohydrogen generation and the latest trends are also supplied. This study helps in the critical understanding of agro-industrial wastes for biohydrogen production, thereby encouraging future outcomes for a sustainable biohydrogen economy.
Biohydrogen production from agro waste biomass through combinative pretreatments is an emerging cost effective, alternative energy technology. The present study aimed to ascertain the extent to which the combinative dispersion thermochemical disintegration (DTCD) enhances the cost effective and energy efficient biohydrogen production from rice straw. The efficiency of the combinative pretreatment was evaluated in terms of degree of disintegration and biohydrogen generation. The optimal conditions for combinative pretreatments are pH 10, temperature 80 °C, rpm 12000 and disintegration time 30 mins. A higher degree of disintegration of about 20.9% was achieved through DTCD pretreatment when compared to dispersion thermal disintegration (DTD) (13.2%) and disperser disintegration (DD) (9.5%). The specific energy spent to achieve maximal degree of disintegration for the three pretreatments were in the following order: DD (1469 kJ/kg Rice Straw) > DTD (1044 kJ/kg Rice Straw) > DTCD (742 kJ/kg Rice Straw). Hence, a considerable amount of energy could be saved through this combinative pretreatment. First order kinetic model (exponential rise to maximum) of biohydrogen production is helpful in deriving the two parameters of uncertainty: substrate biodegradability and hydrolysis rate constant. These two parameters evaluate the maximal biohydrogen yield potential of rice straw through combinative pretreatments. As expected, a higher biohydrogen yield of about (129 mL/g COD) was observed in DTCD when compared to DTD (81 mL/g COD) DD (58 mL/g COD) and Control (8 mL/g COD). To gain insights into the feasibility of implementing the pretreatment at large scale, scalable studies are essential in terms of energy balance and cost. A higher positive net energy of about 0.39621 kWh/kg rice straw was achieved for DTCD when compared to others.
Biohydrogen as one of the most appealing energy vector for the future represents attractive avenue in alternative energy research. Recently, variety of biohydrogen production pathways has been suggested to improve the key features of the process. Nevertheless, researches are still needed to overcome remaining barriers to practical application such as low yields and production rates. Considering practicality aspects, this review emphasized on anaerobic membrane bioreactors (AnMBRs) for biological hydrogen production. Recent advances and emerging issues associated with biohydrogen generation in AnMBR technology are critically discussed. Several techniques are highlighted that are aimed at overcoming these barriers. Moreover, environmental and economical potentials along with future research perspectives are also addressed to drive biohydrogen technology towards practicality and economical-feasibility.
This review surveys the implementation of anaerobic membrane bioreactors in municipal wastewater treatment at ambient temperature. High chemical oxygen demand (COD) removal efficiencies and methane conversion rates were achieved under various conditions, while also achieving a low sludge yield of 0.04–0.09 g volatile suspended solids (VSS)/g COD. A survey of energy demands for pilot-scale anaerobic membrane bioreactors showed that they could be energy neutral or even positive, even though high energy (0.08–0.35 kWh/ m3) is required to clear membrane fouling. Thus, the use of anaerobic membrane bioreactors in municipal wastewater treatment at ambient temperature is very promising. However, some challenges such as membrane fouling control, methane in effluent, low COD/ SO42–-S ratio, and deficiencies in alkalinity should be addressed, especially the latter. Future research perspectives relating to the challenges and further research are proposed.
Hydrogen producing granules (HPGs) are most promising biological methods used to treat organic rich wastes and generate clean hydrogen energy. This review provides information regarding types of immobilization, supporting materials and microbiome involved on HPG formation and its performances. In this review, importance has been given to three kinds of immobilization techniques such as adsorption, encapsulation, and entrapment. The HPG, characteristics and types of organic and inorganic supporting materials followed for enhancing hydrogen yield were also discussed. This review also considers the applications of HPG for sustainable and high rate hydrogen production. A detailed discussion on insight of key mechanism for HPGs formation and its performances for stable operation of high rate hydrogen production system are also provided.
The growing of food waste generation is gradually becoming a global problem due to the improper management of it. According to the Food and Agriculture Organization (FAO), United Nation, more than 1.3 million tonnes of food is being wasted. Food waste and food processing waste are abundant - which are rich in organic acids and nutrients. These acids and nutrients can be utilized for attractive and efficient generation of renewable and sustainable fuels such as biohydrogen through fermentation process. Many investigations have revealed a significant biohydrogen generation using food wastes from restaurant, dining hall and food processing industries. During the hydrogen generation through fermentation, several parameters influence the yield of hydrogen. Some of them are method of pre-treatment, feed composition, fermentation temperature, culture and substrate, solution pH, etc. Also, the presence of inert intermediates produced during the reaction in fermentation process reduces the process efficiency. Few studies have shown that the use of nanoparticles in fermentation process along with the application of short & cyclic ultrasound is beneficial to increase the process efficiency. The augmentation in ultrasound-assisted process is due to the physical and chemical effects of ultrasound in the medium through the phenomenon of cavitation. During the transient collapse of cavitation bubbles, several reactive species are produced which further participate in the thermochemical and biochemical reactions. Thus, enhances the rate of reaction by annihilation the complex sugars in food wastes. Additionally, the cavitational effect helps to reduce the growth of hydrogen inhibiting microorganism in the feed. This review demonstrates the potentiality of food waste for production of biohydrogen through fermentation process including a brief overview of process parameters that affect the fermentation process. Additionally, an overview of integrated fermentative process coupled with nanoparticles and ultrasound is also discussed for enhanced biohydrogen generation from food waste.
Submerged ceramic membrane reactor treating industrial wastewater was combined with granular activated carbon (GAC) particles to control membrane fouling and organic removal efficiency. The GAC particles were suspended along the membrane surface under bulk recirculation only through the reactor without any gas sparging. Membrane support coated with Al2O3 layer (CPM) and uncoated one (UPM) was compared at constant flux mode of filtration. The membrane support consisted of 80% of pyrophyllite and 20% of alumina. Under up-flow velocity of 0.031 m s-1 through bulk recirculation only without GAC particles, the fouling rates were observed as 0.011 and 0.013 bar h-1 for the CPM and UPM, respectively. With suspension of GAC particles, fouling mitigation was enhanced considerably and this effect was more pronounced with CPM than UPM under the same upflow velocity (90 vs. 57%). In addition, the GAC suspension increased critical flux by 46% higher with CPM than that observed without the carbon particles. The organic removal efficiency of the UPM was lower than that of CPM while the fouling rate was much greater probably due to pore blocking caused by organic dye compounds. For the both membranes, suspension of GAC particles along the membrane surface increased organic removal efficiency higher than 90%. The organic removal efficiency was enhanced by increasing permeate flux, but it became lower as upflow velocity was higher.
Biohydrogen from microalgal biomass has shown particular advantage due to its high growth rate and high bioenergy production. As a representative of microalgae, Chlorella vulgaris was chosen as substrate along with digested sludge (DS) as inoculum in this research. In order to improve the hydrolysis of algal biomass and enhance biohydrogen production, pretreatment methods like acid and thermal pretreatment were employed. Thermal pretreatment showed better results than acid pretreatment of microalgal biomass. 100 °C for 60 min was identified as the optimum condition for the thermal pretreatment of C. vulgaris by response surface methodology (RSM) analysis. Experiments were also carried out to identify the optimum substrate to inoculum ratio (SIR) for the process. SIR of 8 generated the highest hydrogen yield of 190.90 mL H2/g-VS. Moreover, the overall energy balance of the process was evaluated and the results showed a positive energy balance of 1790.13 kJ/kg. The results indicated that optimization of pretreatment methods and substrate to inoculum ratio was effective in enhancing biohydrogen production from microalgal biomass and digested sludge.
Biofouling in membrane bioreactors (MBRs), which is defined as the unwanted accumulation of microorganisms on the membrane surface, has been intensively studied for more than two decades. However, it remains a critical limiting factor to the more widespread use of MBR for wastewater treatment. The concept of quorum sensing (QS) / quorum quenching (QQ) was proposed as an anti-fouling strategy for MBRs in 2002 and the first paper on that issue was published in 2009. Since then, many studies have demonstrated and proved the potential of QQ for biofouling control in MBR through various means. The evolution of QQ-MBR has had a run of eight years in terms of QQ-microorganisms, QQ-media, and the size of the QQ-MBRs tested. This review provides an overview on the QS/QQ studies related to the elucidation and control of biofouling in MBRs, including the identification of QS signals, the isolation of QS signal producing or degrading microorganisms, and various engineering approaches to apply enzymatic or bacterial QQ in the form of QQ-media to mitigate membrane biofouling. The challenges confronting these applications and future directions of QQ-based biofouling control strategies for MBR are discussed.
Hydrogen has potential as a renewable energy source due to its outstanding clean energy content. The production of hydrogen from food waste by dark fermentation gains attention from researchers across the world as it requires lower energy and chemicals compared to other chemical routes, not to mention that the use of food waste as raw material could help lessen the global waste dumping crisis. Currently, the knowledge of hydrogen production from food waste by dark fermentation is still limited in a laboratory scale. This article intends to provide up-to-date status quo on this technology. Factors affecting production potential, appropriate condition of production, feasibility of scaled-up production and economic value analysis of such technology is summarized and analyzed.
Fouling is one of the acute concerns during the application of reverse osmosis (RO) technology for wastewater reclamation. This study emphasizes the effectiveness of CO 2 injection for scale inhibition on the surface of membranes during wastewater reclamation. The main objective of CO 2 injection is to reduce pH of feed stream for avoiding inorganic scale precipitation. Two different experimental setups (lab-and pilot-scale) were installed and each was operated with four different RO modules including control (without any scale inhibitor), dosage of antiscalant, CO 2 injection and simultaneous dosage of antiscalant and CO 2 in an influent line. The pH of influent stream was reduced by CO 2 purging at the level of 6 and 5. Data from operational setups, water analysis and morphological study of membrane from each module was used to establish comparative result. In comparison with other modules, the RO modules operated with CO 2 were found successful to mitigate the inorganic scale formation on the surface of membrane. Furthermore, the RO modules operated with CO 2 presented the successful restoration of system performance with clean-in-place.
This book will provide assistance to the broad range of readers involved in the crude oil import and production; renewable energy production; biomass analysis and bioconversion; greenhouse gas emissions; techno-economic analysis and government policies for implementing biofuels in India. This book presents important aspects on the large scale production of biofuels following a bio-refinery concept and its commercialization and sustainability issues. Hence, it is a useful resource to policy makers, policy analysts, techno-economic analysts and business managers who deal with commercialization and implementation of bio-based energy and other value-added products. The following features of this book attribute its distinctiveness: 1.As a first uniquely focused scientific and technical literature on bioenergy production in the context of India. 2.To its coverage of technological updates on biomass collection, storage and use, biomass processing, microbial fermentation, catalysis, regeneration, solar energy and monitoring of renewable energy and recovery process. 3.To the technical, policy analysis, climate change, geo-political analysis of bioenergy and green transportation fuels at industrial scale.
An Anaerobic Membrane BioReactors (AnMBR) model is presented in this paper based on the combination of a simple fouling model and the Anaerobic Model 2b (AM2b) to describe biological and membrane dynamic responses in an AnMBR. In order to enhance the model calibration and validation, Trans-Membrane Pressure (TMP), Total Suspended Solid (TSS), COD, Volatile Fatty Acid (VFA) and methane production were measured. The model shows a satisfactory description of the experimental data with R(2)≈0.9 for TMP data and R(2)≈0.99 for biological parameters. This new model is also proposed as a numerical tool to predict the deposit mass composition of suspended solid and Soluble Microbial Products (SMP) on the membrane surface. The effect of SMP deposit on the TMP jump phenomenon is highlighted. This new approach offers interesting perspectives for fouling prediction and the on-line control of an AnMBR process.
In this study, the phase separated effect of dispersion induced ozone pretreatment (DOP) was investigated. Solid reduction, biomass lysis and biomethane production were used as essential parameters to assess the potential of DOP over ozone pretreatment (OP). A higher suspended solid reduction of about 25.2 % was achieved in DOP than OP 18%. The ozone dosage of 0.014 gO3/g SS supported a maximal biomass lysis of about 32.8% when the biosolids were subjected to prior dispersion at 30 sec and 3000 rpm. However, the same ozone dosage without phase separation achieved 9.6 % biomass lysis. The second exponential model results of the biomethane assay showed that DOP enhanced the accessibility of disintegrated biosolids for methane production and induced about 1150 mL/g VS of methane production. The energy analysis reveals that DOP provides significant amount of positive net energy (152.65 kWh/ton) when compared to OP (-12.42 kWh/ton).
Effect of wastewater characteristics on bioenergy recovery in sewage treatment by anaerobic membrane bioreactor (AnMBR) was investigated. Based on COD removal, sludge concentration change and COD mass balance, nonionic surfactant or operation at 20-25 ˚C had no effect on the energy recovery with COD conversion of 72-79%. The anaerobic microbes can cope with the characteristic by releasing more SMP/EPS or changing its community structure. Compared with Control (6.99×10⁷ kJ/d, HRT 12 h), with suspended solid or operation at 15 °C and 10 °C, the captured energy was only 5.90×10⁷ kJ/d, 6.0×10⁷ kJ/d and 3.10×10⁷ kJ/d, respectively while the energy in dissolved methane was 1.08×10⁷ kJ/d, 0.98×10⁷ kJ/d and 1.26×10⁷ kJ/d. Hence, the recovery efficiency was decreased by 15.6%, 14.2% and 55.7%. The recovery also decreased by 26% (5.17×10⁷ kJ/d) in the presence of anionic surfactant. The toxicity of anionic surfactant to the anaerobic microbes and lower growth rate of microorganism at psychrophilic temperatures were responsible to the decrease of bioenergy recovery efficiency. SS accumulation will finally increase the loading rate of sludge and decrease the bioenergy recovery from the long-term view.
Escherichia coli growth and H2 production were followed in the presence of heavy metal ions and their mixtures during glycerol or glucose fermentation at pH 5.5–7.5. Ni²⁺ (50 μM) with Fe²⁺ (50 μM) but not sole metals stimulated bacterial biomass during glycerol fermentation at pH 6.5. Ni²⁺+Fe³⁺ (50 μM), Ni² +Fe³⁺+Mo⁶⁺ (20 μM) and Fe³⁺+Mo⁶⁺ (20 μM) but not sole metals enhanced up to 3-fold H2 yield but Cu⁺ or Cu²⁺ (100 μM) inhibited it. At pH 7.5 stimulating effect on biomass was observed by Ni²⁺+Fe²⁺+Mo⁶⁺. H2 production was enhanced 2.7 fold particularly by Ni²⁺+Fe³⁺+Mo⁶⁺ at the late stationary growth phase. Whereas at pH 5.5 increased biomass was when Fe²⁺+Mo⁶⁺ or Mo⁶⁺ were added. H2 yield was decreased compared with that at pH 6.5, but metal ions again enhanced it. During glucose fermentation at pH 6.5 biomass was increased by the mixtures of metal ions, and 1.2 fold increased H2 yield was observed. At pH 7.5 Ni²⁺+Fe²⁺ increased biomass but Cu⁺ or Cu²⁺ had suppressing effect; Fe³⁺+Mo⁶⁺ stimulated H2 production. At pH 5.5 biomass also was raised by Ni²⁺+Fe²⁺+Mo⁶⁺; H2 yield was increased upon Mo⁶⁺ and Mo⁶⁺+Fe²⁺ or Mo⁶⁺+Fe³⁺ additions. The results point out the importance of Ni²⁺, Fe²⁺, Fe³⁺ and Mo⁶⁺ and some of their combinations for E. coli bacterial growth and H2 production mostly during glycerol but not glucose fermentation and at acidic conditions (pH 5.5 and 6.5). They can be used for optimizing fermentation processes on glycerol, controlling bacterial biomass and developing H2 production biotechnology.
The goal of the current article is to update new findings in membrane fouling and emerging fouling mitigation strategies reported in recent years (post 2010) as a follow-up to our previous review published in Water Research (2009). According to a systematic review of the literature, membrane bioreactors (MBRs) are still actively investigated in the field of wastewater treatment. Notably, membrane fouling remains the most challenging issue in MBR operation and attracts considerable attention in MBR studies. In this review, we summarized the updated information on foulants composition and characteristics in MBRs in the immediate past five years, which greatly improves our understanding of fouling mechanisms. Furthermore, the emerging fouling control strategies (e.g., mechanically assisted aeration scouring, in-situ chemical cleaning, enzymatic and bacterial degradation of foulants, electrically assisted fouling mitigation, and nanomaterial-based membranes) are comprehensively reviewed. As a result, it is found that the fundamental understanding of dynamic changes in membrane foulants during a long-term operation is essential for the development and implementation of fouling control methods. Recently developed strategies for membrane fouling control denoted that the improvement of membrane performance is not our ultimate and only goal, less energy consumption and more green/sustainable fouling control ways are more promising to be developed and thus applied in the future. Overall, such a literature review not only demonstrates current challenges and research needs for scientists working in the area of MBR technology, but also can provide more useful recommendations for industrial communities based on the related application cases.
Submerged and external anaerobic dynamic membrane bioreactors (AnDMBRs) have been compared in terms of removal efficiency, filtration characteristics and microbial community structure. High COD removal efficiencies were obtained with both submerged and external AnDMBRs. To obtain an effective dynamic membrane (DM) layer enabling high quality permeate, longer time was required in the external AnDMBR configuration compared to the submerged one. A difference in microbial community structure was identified using pyrosequencing analyses between the submerged and external AnDMBRs. The number of archaeal types decreased in the bulk sludge of the external AnDMBR. External sludge recirculation might have had a negative effect on the archaeal community in the bulk sludge of the external AnDMBR. However, the sludge recirculation in the external AnDMBR configuration led to a filtration at lower total filtration resistance and TMP in comparison to the submerged one at the same gas sparging rate. Results showed that the submerged AnDMBR system can provide a shorter start-up period, slightly better permeate quality in terms of COD concentration, and higher biogas production in comparison to the external one in gas-lift mode.
Membrane bioreactor (MBR) technology is considered a well-established, mature technology with many full-scale plants around the world treating municipal and industrial wastewater. However, membrane fouling and energy consumption still remain serious obstacles and challenges in the wider spread of the MBR technology. Therefore, considerable research and development efforts are still underway. Recent developments are primarily focused on aspects related to energy reduction, fouling control and novel configurations for enhanced process performance. This review addresses the recent work on the above mentioned aspects and it discusses the overall life cycle of MBRs and the market prospects for MBR technology. Novel MBR configurations and integrations with other technologies are also reviewed. Finally, the challenges that need to be addressed in order to facilitate market penetration of MBR technology are highlighted.
Lignocellulosic materials like food and yard wastes are difficult to hydrolyse and this results in decreased bio-hydrogen yields. As such, this study investigated the potential of microwave (MW) and ultrasound (UtS) irradiations for pre-treating food and yard wastes prior to dark fermentation. The specific energy was varied from 0 to 6946 kJ/kg total solids for each pre-treatment and the results obtained showed that both pre-treatments generally enhanced solids and organic matter solubilisation, with the effects more significant at high pre-treatment conditions. However, none of the pre-treatment conditions improved bio-hydrogen production. The main reasons identified for the low H2 yields were the possible formation of inhibitors due to pre-treatments while the higher concentrations of propionic acid and ethanol among the end-product metabolites could also have suppressed bio-hydrogen production. Consequently, neither MW nor UtS irradiation is feasible as pre-treatment of food and yard wastes for enhanced bio-hydrogen production under the range of specific energies studied.
Aerobic pre-treatment was applied prior to two-stage anaerobic digestion process. Three different food wastes samples, namely carbohydrate rich, protein rich and lipid rich, were prepared as substrates. Effect of aerobic pre-treatment on hydrogen and methane production was studied. Pre-aeration of substrates showed no positive impact on hydrogen production in the first stage. All three categories of pre-aerated food wastes produced less hydrogen compared to samples without pre-aeration. In the second stage, methane production increased for aerated protein rich and carbohydrate rich samples. In addition, the lag phase for carbohydrate rich substrate was shorter for aerated samples. Aerated protein rich substrate yielded the best results among substrates for methane production, with a cumulative production of approximately 351 ml/gVS. With regard to non-aerated substrates, lipid rich was the best substrate for CH4 production (263 ml/gVS). Pre-aerated P substrate was the best in terms of total energy generation which amounted to 9.64 kJ/gVS. This study revealed aerobic pre-treatment to be a promising option for use in achieving enhanced substrate conversion efficiencies and CH4 production in a two-stage AD process, particularly when the substrate contains high amounts of proteins.
Heterogeneous photocatalysis is a promising technology especially for environmental
remediation. Despite more than a decade of worldwide research in developing photocatalytic
efficiency improving techniques, many questions regarding the large scale application of
photocatalytic reactors still remain unanswered. Recently, improving the photocatalytic
efficiency has gained scientific attention because it might lead to more economical and robust
photocatalytic operation for environmental remediation. In this review, fundamental and
comprehensive assessments of the photocatalytic concepts and their applications for
environmental remediation are reviewed. The existing challenges and strategies to improve the
photocatalytic efficiency are discussed. Further, recent developments and future research
prospects on photocatalytic systems for environmental applications are also addressed.
The objective of this study was to determine the impact of solubilization during thermo-chemo-sonic pretreatment of waste activated sludge (WAS) on anaerobic biodegradability and cost for biogas production. The results revealed that it was possible to achieve 40-50% of solubilization of WAS when ultrasonic energy input was doubled (11520 to 27000kJ/kg TS). The cost to achieve 30-35% of solubilization of WAS was calculated to be 0.22-0.24 USD/L, which was relatively lower than the cost of 0.53-0.8 USD/L when 40-50% of solubilisation of WAS was achieved. There was no significant difference in biodegradability (0.60-0.64 gCOD/gCOD) for samples with solubilization efficiency of 35-50%. Comparing energetic balance and economic assessment of samples with different solubilization percentages, the results showed that samples with 30 to 35% of solubilization had lower net cost (7.98 to 2.33 USD/Ton of sludge) and negative energy balance compared to samples with other percentages of solubilization.
Discussions on the positive effect of nano-sized metal addition to dark fermentation biohydrogen production have been raised but the real stimulation mechanism remains unclear. In this study, biohydrogen production enhancement by nanoparticle metal addition was tested using a strain of a known hydrogen producer, Clostridium pasteurianum. Gene expression and growth activity were evaluated. Biochemical hydrogen potential tests on the added TiO2 and Fe nanoparticles were performed at 35 °C with various metal concentrations (control and 50, 100, 200, 400, and 800 ppm). Comparison with the control showed that adding 50 ppm Fe nanoparticles could significantly increase the hydrogen production, which was expressed H2 gas volume, by 24.9%. The corresponding hydrogen production rate increased to 8.7 H2-L/L-d. This positive stimulation effect gradually decreased with increasing metal concentrations added. The effect eventually caused inhibition when the metal concentration reached 400 and 800 ppm. The highest maximum hydrogen production rate (Rmax) and the potential hydrogen production (P) in the simulation kinetic model were 45.2 mL/h and 255.7 mL, respectively. Despite increase in the gas production, metal addition did not increase the overall hydrogen yield (mol H2/mol xylose). Hence, this stimulation may not occur on the microorganism metabolism level. Analysis of gene expression indicated that addition of Fe nanoparticles did not remarkably improve the hydrogen enzyme activity of C. pasteurianum. Overall, hydrogen production stimulated by adding nano-metals was not directly related to enzyme activity improvement.
The low-pressure wet oxidation was used to solubilize the waste activated sludge for recovering carbon source, and the treated sludge was applied for the fermentative hydrogen production. The experimental results showed that after low pressure oxidation treatment, the concentration of soluble chemical oxygen demand (SCOD), polysaccharides and protein present in the liquid phase was increased by 2.0, 2.2 and 102.5 times, respectively. Bio-hydrogen production was successfully operated using solubilized sludge as substrate. Through comparing the hydrogen production from glucose, the treated sludge and mixture of the sludge and glucose, it was found that the hydrogen yield of tests using different substrates showed a positive relation with the ratio of acetic acid to butyric acid in soluble metabolites and the ratio of polysaccharides to SCOD in substrates. It can be concluded that the waste activated sludge treated by low pressure wet oxidation can be used as low-cost substrate for bio-hydrogen production.
Biohydrogen Production: Fundamentals and Technology Advances covers the fundamentals of biohydrogen production technology, including microbiology, biochemistry, feedstock requirements, and molecular biology of the biological hydrogen production processes. It also gives insight into scale-up problems and limitations. In addition, the book discusses mathematical modeling of the various processes involved in biohydrogen production and the software required to model the processes. The book summarizes research advances that have been made in this field and discusses bottlenecks of the various processes, which presently limit the commercialization of this technology. The authors also focus on the process economy, policy, and environmental impact of this technology, since the future of biohydrogen production depends not only on research advances, but also on economic considerations (the cost of fossil fuels), social espousal, and the development of H2 energy systems. The book describes the fundamentals of this technology interwoven with more advanced research findings. Further reading is suggested at the end of each chapter. Since the beauty of any innovation is its applicability, socioeconomic impact, and cost energy analysis, the book examines each of these points to give you a holistic picture of this technology. Illustrative diagrams, flow charts, and comprehensive tables detailing the scientific advancements provide an opportunity to understand the process comprehensively and meticulously. Written in a lucid style, the book supplies a complete knowledge bank about biohydrogen production processes.
The improvement of batch photofermentative biohydrogen production was investigated using ultrasonication pre-treatment on a combined effluent of palm oil and pulp and paper mills. The effects of the amplitude (30-90%) and ultrasonication duration (5-60 min) were investigated in terms of their influences on the biohydrogen yield and chemical oxygen demand (COD) removal. The recommended ultrasonication parameters were found at the higher ranges of amplitude and duration (A70T45). Using A70T45 ultrasonication, the production of biohydrogen at 30 °C could be enhanced up to 8.72 mL H2/mLmedium, with a total COD removal of 36.9%. During pre-treatment at A70T45, an energy input of 775 J/mL was supplied to disintegrate complex compounds into simpler structures. As a result, an increase in the soluble organic matter concentration was achieved, which led to enhanced biohydrogen production. On the other hand, the lowest biohydrogen yield (4.67 mL H2/mLmedium) and total COD removal (28.8%) were obtained in the control without pre-treatment. The enthalpy of the photofermentation process was estimated to be 141.1 kJ/mol with a threshold temperature of 30.9 °C based on a modified Arrhenius approach.
Dark fermentative bio-hydrogen production is not commercially exploited due to several factors hindering its production, making the process unfeasible on large scale. This study provided an in depth and critical review of different factors of the dark fermentation process namely H2-consumers and lactic acid bacteria in mixed microflora, light and heavy metal ions, furan derivatives and phenolic compounds, ammonia and H2 concentrations and soluble metabolites viz. acetic acid, ethanol, propionic acid and butyric acid that may negatively affect H2 production. For each of the inhibitors, the mechanism behind process inhibition was explained while strategies for reducing inhibition were outlined. Among the different inhibitors studied, furan derivatives and phenolic compounds suppressed biohydrogen production to a larger extent while the most common strategies reviewed for reducing inhibition included inoculum pre-treatment for suppressing H2-consumers and dilution of reactor contents for decreasing inhibitor concentrations. Although these options are encouraging on small scale, the economic and technical feasibilities of implementing these strategies on larger scale require further investigation.
Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
The pH and hydraulic retention time (HRT) of a chemostat reactor were varied according to a central composite design methodology with the aim of modeling and optimizing the conversion of starch into hydrogen by microorganisms in an anaerobic digested sludge. Experimental results from 23 runs indicate that a maximum hydrogen production rate of 1600 L/m(3)/d under the organic loading rate of 6 kg starch m(3)/d obtained at pH = 5.2 and HRT = 17 h. Throughout this study, the hydrogen percentage in the biogas was approximately 60% and no methanogenesis was observed. while the reactor was operated with HRT of 17 h, hydrogen was produced within a pH range between 4.7 and 5.7. Alcohol production rate was greater than hydrogen production rate if the pH was lower than 4.3 or higher than 6.1. Supplementary experiments confirm that the optimum conditions evaluated in this study were highly reliable; while a hydrogen production yield of 1.29 l H-2/g starch-GOD was obtained. An examination of the response surfaces, including hydrogen, volatile fatty acids (VFA) and alcohols production, led us to the belief that clostridium sp. predominated in the anaerobic hydrogen-producing microorganisms in this study. Experiment results obtained emphasize that the response of metabolites was a more useful indicator than hydrogenic activity for obtaining efficient hydrogen production. Furthermore, expressions of contour plots indicate that Response-Surface Methodology may provide easily interpretable advice on the operation of a hydrogen-producing bioprocess. (C) 2000 John Wiley & Sons, Inc.
Microbial consortia are ubiquitous in nature and are implicated in processes of great importance to humans, from environmental remediation and wastewater treatment to assistance in food digestion. Synthetic biologists are honing their ability to program the behavior of individual microbial populations, forcing the microbes to focus on specific applications, such as the production of drugs and fuels. Given that microbial consortia can perform even more complicated tasks and endure more changeable environments than monocultures can, they represent an important new frontier for synthetic biology. Here, we review recent efforts to engineer synthetic microbial consortia, and we suggest future applications.