Hydrogen production from sugar beet juice using an integrated biohydrogen process of dark fermentation and microbial electrolysis cell

Microbial shifts and VFA production in the optimization of anaerobic digestion by thermal hydrolysis coupled with vacuum fermentation

This study investigated a novel thermal-hydrolysis combined with a vacuum fermentation system for high-grade volatile fatty acids (VFA) recovery, and the corresponding changes in the microbial community. Four systems with and without hydrothermal pre-treatment (HTP) and vacuum were mobilized; results revealed that integration of HTP with vacuum has the highest potential in terms of VFA recovery, sludge disintegration, and solid reduction. HTP and vacuum fermentation systems were associated with the highest COD solubilization (45 %), and VFA yield (0.32 g COD/g VSS added). Vacuum fermenters with and without pre-treatment have the highest specific denitrification rates of 7.6 and 7.2 mg NO3-N/g VSS.h, respectively, compared to all other samples and control (acetate). Changes brought about by vacuum fermentation included a shift in the microbial community toward enriching fermenters, mainly Caprothermobacteria and Thermotagea, responsible for VFA production.

Dark fermentation of pretreated hydrolysates of pineapple fruit waste for the production of biohydrogen using bacteria isolated from wastewater sources

In the present study, both acidic and alkaline hydrolysate of pineapple waste was utilised for the production of biohydrogen using locally isolated bacterial strains. The bacteria were isolated from different wastewater sources and were identified as Proteus mirabilis, Pseudomonas aeruginosa, Bacillus altitudinus, Bacillus subtilis, Paenibacillus alvei, and Lysinibacillus sphaericus. Experimental results showed that the highest biohydrogen yield of 836.33 ± 48.02 mL H2 was produced from alkaline hydrolysate with Bacillus altitudinis during the 96thhr of fermentation. Among the different bacterial strains, B. altitudinis showed higher H2 production. Comparatively alkaline hydrolysates exhibited a higher yield of hydrogen than acidic hydrolysates. The final pH of the experiment was found to be in acidic range. The total VFA concentration ranged between 930 ± 207.85 mg/L to 3050 ± 476.97 mg/L. Both sugar degradation and COD reduction were more than 80% in the acidic and alkaline hydrolysates while the lowest sugar degradation and COD reduction were observed for the untreated biomass. The rationale behind this study was to convert the waste biomass into energy by utilising the potential of native bacterial communities.

Electrochemical promotion of organic waste fermentation: Research advances and prospects

The current methods of treating organic waste suffer from limited resource usage and low product value. Research and development of value-added products emerges as an unavoidable trend for future growth. Electro-fermentation (EF) is a technique employed to stimulate cell proliferation, expedite microbial metabolism, and enhance the production of value-added products by administering minute voltages or currents in the fermentation system. This method represents a novel research direction lying at the crossroads of electrochemistry and biology. This article documents the current progress of EF for a range of value-added products, including gaseous fuels, organic acids, and other organics. It also presents novel value-added products, such as 1,3-propanediol, 3-hydroxypropionic acid, succinic acid, acrylic acid, and lysine. The latest research trends suggest a focus on EF for cogeneration of value-added products, studying microbial community structure and electroactive bacteria, exploring electron transfer mechanisms in EF systems, developing effective methods for nutrient recovery of nitrogen and phosphorus, optimizing EF conditions, and utilizing biosensors and artificial neural networks in this area. In this paper, an analysis is conducted on the challenges that currently exist regarding the selection of conductive materials, optimization of electrode materials, and development of bioelectrochemical system (BES) coupling processes in EF systems. The aim is to provide a reference for the development of more efficient, advanced, and value-added EF technologies. Overall, this paper aims to provide references and ideas for the development of more efficient and advanced EF technology.

A study of electron source preference and its impact on hydrogen production in microbial electrolysis cells fed with synthetic fermentation effluent

Fermentation effluents from organic wastes contain simple organic acids and ethanol, which are good electron sources for exoelectrogenic bacteria, and hence are considered a promising substrate for hydrogen production in microbial electrolysis cells (MECs). These fermentation products have different mechanisms and thermodynamics for their anaerobic oxidation, and therefore the composition of fermentation effluent significantly influences MEC performance. This study examined the microbial electrolysis of a synthetic fermentation effluent (containing acetate, propionate, butyrate, lactate, and ethanol) in two-chamber MECs fitted with either a proton exchange membrane (PEM) or an anion exchange membrane (AEM), with a focus on the utilization preference between the electron sources present in the effluent. Throughout the eight cycles of repeated batch operation with an applied voltage of 0.8 V, the AEM-MECs consistently outperformed the PEM-MECs in terms of organic removal, current generation, and hydrogen production. The highest hydrogen yield achieved for AEM-MECs was 1.26 L/g chemical oxygen demand (COD) fed (approximately 90% of the theoretical maximum), which was nearly double the yield for PEM-MECs (0.68 L/g COD fed). The superior performance of AEM-MECs was attributed to the greater pH imbalance and more acidic anodic pH in PEM-MECs (5.5-6.0), disrupting anodic respiration. Although butyrate is more thermodynamically favorable than propionate for anaerobic oxidation, butyrate was the least favored electron source, followed by propionate, in both AEM- and PEM-MECs, while ethanol and lactate were completely consumed. Further research is needed to better comprehend the preferences for different electron sources in fermentation effluents and enhance their microbial electrolysis.

A Review on Opportunities and Limitations of Membrane Bioreactor Configuration in Biofuel Production

Biofuels are a clean and renewable source of energy that has gained more attention in recent years; however, high energy input and processing cost during the production and recovery process restricted its progress. Membrane technology offers a range of energy-saving separation for product recovery and purification in biorefining along with biofuel production processes. Membrane separation techniques in combination with different biological processes increase cell concentration in the bioreactor, reduce product inhibition, decrease chemical consumption, reduce energy requirements, and further increase product concentration and productivity. Certain membrane bioreactors have evolved with the ability to deal with different biological production and separation processes to make them cost-effective, but there are certain limitations. The present review describes the advantages and limitations of membrane bioreactors to produce different biofuels with the ability to simplify upstream and downstream processes in terms of sustainability and economics.

Production of short-chain fatty acids (SCFAs) as chemicals or substrates for microbes to obtain biochemicals

Carboxylic acids have become interesting platform molecules in the last years due to their versatility to act as carbon sources for different microorganisms or as precursors for the chemical industry. Among carboxylic acids, short-chain fatty acids (SCFAs) such as acetic, propionic, butyric, valeric, and caproic acids can be biotechnologically produced in an anaerobic fermentation process from lignocellulose or other organic wastes of agricultural, industrial, or municipal origin. The biosynthesis of SCFAs is advantageous compared to chemical synthesis, since the latter relies on fossil-derived raw materials, expensive and toxic catalysts and harsh process conditions. This review article gives an overview on biosynthesis of SCFAs from complex waste products. Different applications of SCFAs are explored and how these acids can be considered as a source of bioproducts, aiming at the development of a circular economy. The use of SCFAs as platform molecules requires adequate concentration and separation processes that are also addressed in this review. Various microorganisms such as bacteria or oleaginous yeasts can efficiently use SCFA mixtures derived from anaerobic fermentation, an attribute that can be exploited in microbial electrolytic cells or to produce biopolymers such as microbial oils or polyhydroxyalkanoates. Promising technologies for the microbial conversion of SCFAs into bioproducts are outlined with recent examples, highlighting SCFAs as interesting platform molecules for the development of future bioeconomy.

Agro-waste to sustainable energy: A green strategy of converting agricultural waste to nano-enabled energy applications

The rising demands of the growing population have raised two significant global challenges viz. energy crisis and solid-waste management, ultimately leading to environmental deterioration. Agricultural waste (agro-waste) contributes to a large amount of globally produced solid waste, contaminating the environment, and raising human-health issues on improper management. It is essential for a circular economy to meet sustainable development goals and to design strategies to convert agro-waste into energy using nanotechnology-based processing strategies, by addressing the two significant challenges. This review illustrates the nano-strategic aspects of state-of-the-art agro-waste applications for energy harvesting and storage. It details the fundamentals related to converting agro-waste into energy resources in the form of green nanomaterials, biofuels, biogas, thermal energy, solar energy, triboelectricity, green hydrogen, and energy storage modules in supercapacitors and batteries. Besides, it highlights the challenges associated with agro-waste-to-green energy modules with their possible alternate solutions and advanced prospects. This comprehensive review will serve as a fundamental structure to guide future research on smart agro-waste management and nanotechnological innovations dedicated to its utilization for green energy applications without harming the environment. The nanomaterials assisted generation and storage of energy from agro-waste is touted to be the near-future of smart solid-waste management strategy for green and circular economy.

Bioelectrochemical systems (BESs) for agro-food waste and wastewater treatment, and sustainable bioenergy-A review

Producing food by farming and subsequent food manufacturing are central to the world's food supply, accounting for more than half of all production. Production is, however, closely related to the creation of large amounts of organic wastes or byproducts (agro-food waste or wastewater) that negatively impact the environment and the climate. Global climate change mitigation is an urgent need that necessitates sustainable development. For that purpose, proper agro-food waste and wastewater management are essential, not only for waste reduction but also for resource optimization. To achieve sustainability in food production, biotechnology is considered as key factor since its continuous development and broad implementation will potentially benefit ecosystems by turning polluting waste into biodegradable materials; this will become more feasible and common as environmentally friendly industrial processes improve. Bioelectrochemical systems are a revitalized, promising biotechnology integrating microorganisms (or enzymes) with multifaceted applications. The technology can efficiently reduce waste and wastewater while recovering energy and chemicals, taking advantage of their biological elements' specific redox processes. In this review, a consolidated description of agro-food waste and wastewater and its remediation possibilities, using different bioelectrochemical-based systems is presented and discussed together with a critical view of the current and future potential applications.

A Review of Biohydrogen Production from Saccharina japonica

Saccharina japonica (known as Laminaria japonica or Phaeophyta japonica), one of the largest macroalgae, has been recognized as food and medicine for a long time in some Asian countries, such as China, South Korea, Japan, etc. In recent years, S. japonica has also been considered the most promising third-generation biofuel feedstock to replace fossil fuels, contributing to solving the challenges people face regarding energy and the environment. In particular, S. japonica-derived biohydrogen (H2) is expected to be a major fuel source in the future because of its clean, high-yield, and sustainable properties. Therefore, this review focuses on recent advances in bio-H2 production from S. japonica. The cutting-edge biological technologies with suitable operating parameters to enhance S. japonica’s bio-H2 production efficiency are reviewed based on the Scopus database. In addition, guidelines for future developments in this field are discussed.

Comparing VFA Composition, Biomethane Potential, and Methane Production Kinetics of Different Substrates for Anaerobic Fermentation and Digestion

Solid waste is one of the largest sources of greenhouse gases (GHGs) today. The carbon footprint of landfills also has a large impact on global warming. Therefore, it is becoming more urgent to study the possibility of better environmentally friendly approaches for solid waste management and its safe disposal. The digestion of solid waste is a biological process that breaks down the organic content of the solid waste and thus stabilizes it. It also allows the recovery of valuable resources (such as biogas) and the utilization of stabilized waste in various industries. In this study, six substrates were studied to determine their biomethane potential (BMP) in anaerobic digestion. The substrates were fermented and digested anaerobically, and the biogas production was measured. The methane yield of food waste substrates had a higher methane yield between 354 and 347 mL/g-TCOD, and a biodegradability of 89–87%. Wastewater sludge substrates yielded between 324 and 288 mL/g-TCOD with a biodegradability of 81–73%. A kinetics analysis using first-order and Gompertz models was performed for biodegradation and methane production.

Biohydrogen production from Euglena acus microalgae available in Bangladesh

Hydrogen is generally considered as an ideal non-polluting future energy carrier because it releases energy and water as a byproduct on combustion. Besides, hydrogen possesses the highest energy density on mass basis compared to any other fuel. However, hydrogen production in a sustainable and environmentally friendly way still remains a challenge. Recently, biohydrogen production from green microalgae has gained significant attention due to availability of the feedstock, which are environmentally friendly and renewable. Biohydrogen production from photosynthetic microalgae is attractive, however in the current context, it has a low yield, and an optimization of the affecting parameters including algae concentration, light intensity, culture medium, etc. is critical. In this study, biohydrogen was produced in laboratory from Euglena acus microalgae as it was locally available in Bangladesh.•The effect of two different culture mediums (i.e. sulfur-rich and sulfur-deprived TAP mediums) for microalgae cultivation and biohydrogen yield were studied.•Depending on the concentration of microalgae (50% and 75% by weight) in the medium solution ∼3 ml to 5 ml biohydrogen was obtained.

Differential impact of acidic and alkaline conditions on hydrothermal pretreatment, fermentation and anaerobic digestion of sludge

Anaerobic digestion and fermentation processes in wastewater sludge treatment are limited by several factors, including the slow breakdown of complex organic matter and solubilization of solids. In this study, thermochemical pretreatment of thickened waste activated sludge using high temperature (>170 °C) was investigated to understand the impact of the pretreatment on the volatile fatty acids (VFA) production and its fractions during the fermentation process. Furthermore, the influence the thermochemical pretreatment on sludge disintegration and methane recovery was investigated. A range of acidic and alkaline conditions over the pH range of 4.5-10 was examined. Sludge (pH adjusted) was exposed to hydrothermal pretreatment (HTP) at a temperature of 170 °C for 30 min. Pretreated samples were then subjected to batch fermentation and methane potential tests which revealed that acidic and alkaline conditions resulted in increased sludge solubilization during HTP. Acidic conditions were associated with a higher VFA production yield of up to 185 mg chemical oxygen demand/g total chemical oxygen demand. Alkaline conditions led to a higher methane production yield where the maximum yield (276 mL CH₄/g total chemical oxygen demand_added) was found to occur at pH 10. Therefore, alkaline sludge used for fermentation has shown technical and economic feasibility for sludge carbon recovery.

Overview of pretreatment technologies on vegetable, fruit and flower market wastes disintegration and bioenergy potential: Indian scenario

Disposal of segregated organic fractions of centralized wholesale market wastes (i.e. vegetable, fruit and flower markets waste) in dumpsites/landfills are not only a serious issue but also underutilizes the huge potency of these organic wastes. Anaerobic digestion (AD) is a promising technology for converting organic wastes into methane, as a carbon-neutral alternative to conventional fuels. The major challenges related to the AD process are poor biodegradation of wastes and buffering capacity within the anaerobic digester that lowers the biogas yield. To accelerate biodegradation and to enhance the process efficacy of anaerobic digestion, several pretreatment technologies (mechanical, thermal, biological, chemical and combined pre-treatments) for organic wastes prior to the AD process were developed. This review article presents a comprehensive analysis of research updates in pretreatment techniques for vegetable, fruit and flower markets wastes for enhancing biogas yields during the AD process. The technological aspects of the pretreatment process are described and their efficiency comparison with the resultant process yields and environmental benefits are also discussed. The challenges and technical issues associated with each pretreatment and future research directions for overcoming the field implementation issues are also proposed.

High current density via direct electron transfer by hyperthermophilic archaeon, Geoglobus acetivorans, in microbial electrolysis cells operated at 80 °C

Utilization of hyperthermophilic electro-active microorganisms in microbial electrolysis cells (MECs) that are used for hydrogen production from organic wastes offers significant advantages, such as increased reaction rate and enhanced degradation of insoluble materials. However, only a limited number of hyperthermophilic bioelectrochemical systems have been investigated so far. This study is the first to illustrate hydrogen production in hyperthermophilic MECs with a maximum rate of 0.57 ± 0.06 m³ H₂/m³d, where an iron reducing archaeon, Geoglobus acetivorans, was used as inoculum. In fact, this is the first study to report that G. acetivorans, as the fourth hyperthermophilic electro-active archaeon. In single chamber MECs operated at 80 °C with a set potential of 0.7 V, a peak current density of 1.53 ± 0.24 A/m² has been attained and this is the highest record of current produced by pure culture hyperthermophilic microorganisms. Turnover cyclic voltammetry curve illustrated a sigmoidal shape (midpoint of -0.40 V vs. Ag/AgCl), and together with linear relation of scan rate and peak anodic current, proves the biofilm attachment to the anode and its capability of direct electron transfer. Along with simple substrate (acetate), G. acetivorans effectively utilized dark fermentation effluent for hydrogen production in MECs.

Butyrate production and purification by combining dry fermentation of food waste with a microbial fuel cell

This study developed and evaluated a high-purity butyrate producing bioprocess from food waste by combining dry fermentation (DF) with a microbial fuel cell (MFC). Acclimatization of a DF reactor with an enrichment culture resulted in high food waste degradation (VS removed, %) and butyrate production. A high VS degradation of 81%, butyrate concentration of up to 24 gCOD_butyrate/L and butyrate yields of 497 gCOD_butyrate/kg VS_added was obtained in the DF reactor. As a result, butyrate comprised 83% of all short chain fatty acids (SCFA) in the DF broth. Acetate (10%) and propionate (7%) comprised the rest of the SCFA. The butyrate composition was further purified by feeding the DF broth to a multi-electrode MFC enriched with anode respiring bacteria (ARB) such as Geobacter sp. (>55%). The ARB in the MFC removed acetate and propionate while purified butyrate was recovered in the MFC effluent. Butyrate purity in the MFC effluent reached as high as 99% at hydraulic retention time of 72 h. Along with butyrate purification, the MFC produced electric power in a range of 0.1-0.6 Wh/gCODbutyrate_recovered (or 0.01-7.85 kWh/ton of food waste), demonstrating that MFCs can be an energy-positive butyrate purification bioprocess.

Improving the method of determining the mass fraction of magnesium carbonate and the study of the chemical composition of carbonate rocks for the effective conduct of the technological process of sugar production

The article considers an improved method for determining the content of magnesium carbonate in the carbonate rock. An adjusted method for determining the content of magnesium carbonate was included in the complete establishment of chemical analysis of limestone, which includes the determination of moisture, impurities insoluble in hydrochloric acid, the amount of one and a half oxides of aluminum and iron, calcium carbonate and magnesium carbonate (advanced method), calcium sulfate, alkali metal oxides of potassium and sodium. The obtained experimental data were entered into a single table and summed up the material balance of all components of the carbonate rock. As a result, it was found that this technique includes the following criteria: it is the most accurate, most accessible, and cheap. The use of adjusted methods for determining the content of calcium and magnesium carbonate in limestone will make it possible to establish the objective chemical composition of the carbonate rock and avoid several technological problems. Namely, the excess of uncontrolled magnesium carbonate contributes to the formation of the liquid phase, which in turn reduces the concentration of chemically active lime and promotes the formation of melts in the lime kiln, deteriorating filtration rates, clogging the evaporating station, and so on. Therefore, having information about the real component composition of limestone, the technologist will be able to adjust the technological process in advance, which will lead to the preservation of natural resources while the quality of finished products will not decrease.

An improved method for determining the mass fraction of calcium carbonate in the carbonate bedrock

In the article it is offered to enter in the technological audit of the lime department of sugar factory the adjusted technique of the definition of the maintenance of calcium carbonate in carbonate breed. For this purpose, a complete chemical analysis of limestone was performed, which includes determination of moisture content, impurities insoluble in hydrochloric acid, the amount of one and a half oxides of aluminum and iron, calcium carbonate (advanced method), and magnesium carbonate, calcium sulfate, alkali metal oxides, potassium, and sodium. The obtained experimental data are summarized in one table and the material balance of all components of carbonate bedrock is summarized. The proposed method made it possible to obtain objective data on the component composition of the carbonate material. This, in turn, avoids many technological problems, namely to reduce the formation of melts in the lime kiln, improve the filtration of juices, increase the ability of lime to chemically interact with water, reduce the volume of water on the juicer etc. Thus, the use of the recommended method for determining calcium carbonate (CaCO3), as part of the technological audit, will allow early adjustment of the process, which will give maximum energy and resource savings, as well as increase the level of environmental friendliness of the enterprise.

Membrane-Based Electrolysis for Hydrogen Production: A Review

Hydrogen is a zero-carbon footprint energy source with high energy density that could be the basis of future energy systems. Membrane-based water electrolysis is one means by which to produce high-purity and sustainable hydrogen. It is important that the scientific community focus on developing electrolytic hydrogen systems which match available energy sources. In this review, various types of water splitting technologies, and membrane selection for electrolyzers, are discussed. We highlight the basic principles, recent studies, and achievements in membrane-based electrolysis for hydrogen production. Previously, the Nafion™ membrane was the gold standard for PEM electrolyzers, but today, cheaper and more effective membranes are favored. In this paper, CuCl–HCl electrolysis and its operating parameters are summarized. Additionally, a summary is presented of hydrogen production by water splitting, including a discussion of the advantages, disadvantages, and efficiencies of the relevant technologies. Nonetheless, the development of cost-effective and efficient hydrogen production technologies requires a significant amount of study, especially in terms of optimizing the operation parameters affecting the hydrogen output. Therefore, herein we address the challenges, prospects, and future trends in this field of research, and make critical suggestions regarding the implementation of comprehensive membrane-based electrolytic systems.

Recent Developments in Microbial Electrolysis Cell-Based Biohydrogen Production Utilizing Wastewater as a Feedstock

Carbon constraints, as well as the growing hazard of greenhouse gas emissions, have accelerated research into all possible renewable energy and fuel sources. Microbial electrolysis cells (MECs), a novel technology able to convert soluble organic matter into energy such as hydrogen gas, represent the most recent breakthrough. While research into energy recovery from wastewater using microbial electrolysis cells is fascinating and a carbon-neutral technology that is still mostly limited to lab-scale applications, much more work on improving the function of microbial electrolysis cells would be required to expand their use in many of these applications. The present limiting issues for effective scaling up of the manufacturing process include the high manufacturing costs of microbial electrolysis cells, their high internal resistance and methanogenesis, and membrane/cathode biofouling. This paper examines the evolution of microbial electrolysis cell technology in terms of hydrogen yield, operational aspects that impact total hydrogen output in optimization studies, and important information on the efficiency of the processes. Moreover, life-cycle assessment of MEC technology in comparison to other technologies has been discussed. According to the results, MEC is at technology readiness level (TRL) 5, which means that it is ready for industrial development, and, according to the techno-economics, it may be commercialized soon due to its carbon-neutral qualities.

Variation of the Prokaryotic and Eukaryotic Communities After Distinct Methods of Thermal Pretreatment of the Inoculum in Hydrogen-Production Reactors from Sugarcane Vinasse

The aim of this study is to evaluate the effect of different thermal pretreatments of the inoculum on the diversity of the microbial community producing hydrogen from sugarcane vinasse. High-throughput sequencing of the 16S and 18S rRNA genes was performed. The reactor samples were also selected for the isolation of strict anaerobes. Decreased microbial diversity was observed with increasing pretreatment temperatures, with Firmicutes predominating: 90% to 97%. The highest abundance of Staphylococcus (7.9%) was found in pretreatment at 120 °C / 20 min at pH 6. The fungal analysis revealed a high prevalence of Candida (47%), Agaricomycetes, Pezizomycotina and Aspergillus in assays with higher H₂ production (90° C / 10 min at pH 6). Three species of Clostridium were isolated: C. bifermentans, C. saccharoperbutylacetonicum and C. saccharobutylicum. The isolates were tested separately and in co-cultures for the production of hydrogen. Hydrogen-producing capacity by co-culture of Clostridium species was increased by 18%. Knowing microorganisms and understanding the interaction between eukaryotes and prokaryotes is essential to obtain strategies for biotransformation of vinasse for the production of bioenergy.

The influence of cavitation effects on the purification processes of beet sugar production juices

In the juices of sugar beet, the viscosity of the produced viscosity is determined. They contain sugars and non-sugary compounds. If they are in the form of associated or complex compounds, then when their state changes. Well under the action of external factors or at their removal from a solution it is obligatory. Its rheological properties will also change. Therefore, with the help of determining the viscosity, it is possible to conclude the complex processes that take place in juices under the action of the effects of vapor condensation cavitation, namely: the force between Leculiary bonds, the size of molecules, and the length of chemical bonds, etc. The paper presents studies of the influence of vapor-condensation cavitation effects on the change of such rheological properties of cell and diffusion juice as viscosity and surface tension. The viscosity of the steam-treated juice is affected by complex transformational changes that occur with the associated compounds under the effects of vapor-condensation cavitation, which leads to their destruction and this leads to a decrease in their molecular weight and changes in concentration. Studies have shown that with increasing steam consumption for juice processing in the range of 0 – 1.5% by weight of juice the upper tension increases. Such legitimacy is also an indirect confirmation of the processes of destruction of the association. important compounds of diffusion juice under the influence of the effects of steam condensation cavitation.

Biohythane production via single-stage fermentation using gel-entrapped anaerobic microorganisms: Effect of hydraulic retention time

Research of single-stage anaerobic biohythane production is still in an infant stage. A single-stage dark fermentation system using separately-entrapped H₂- and CH₄-producing microbes was operated to produce biohythane at hydraulic retention times (HRTs) of 48, 36, 24, 12 and 6 h. Peak biohythane production was obtained at HRT 12 h with H₂ and CH₄ production rates of 3.16 and 4.25 L/L-d, respectively. At steady-state conditions, H₂ content in biohythane and COD removal efficiency were in ranges of 7.3-84.6 % and 70.4-77.9%, respectively. During the fermentation, the microbial community structure of the entrapped H₂-producing microbes was HRT-independent whereas entrapped CH₄-producing microbes changed at HRTs 12 and 6 h. Caproiciproducens and Methanobacterium were the dominant genera for producing H₂ and CH₄, respectively. The novelty of this work is to develop a single-stage biohythane production system using entrapped anaerobic microbes which requires fewer controls than two-stage systems.

Volatile Fatty Acids and Biomethane Recovery from Thickened Waste Activated Sludge: Hydrothermal Pretreatment’s Retention Time Impact

The main objective of this study was to evaluate the hydrothermal pretreatment’s retention time influence on the volatile fatty acids and biomethane production from thickened waste activated sludge under mesophilic conditions. Six different retention times of 10, 20, 30, 40, 50, and 60 min were investigated while the hydrothermal pretreatment temperature was kept at 170 °C. The results showed that the chemical oxygen demand (COD) solubilization increased by increasing the hydrothermal pretreatment retention time up to 30 min and stabilized afterwards. The highest COD solubilization of 48% was observed for the sample pretreated at 170 °C for 30 min. Similarly, the sample pretreated at 170 °C for 30 min demonstrated the highest volatile fatty acids yield of 14.5 g COD/Lsubstrate added and a methane yield of 225 mL CH4/g TCODadded compared to 4.3 g COD/Lsubstrate added and 163 mL CH4/g TCODadded for the raw sample, respectively. The outcome of this study revealed that the optimum conditions for solubilization are not necessarily associated with the best fermentation and/or digestion performance.

Hydrogen production from macroalgae by simultaneous dark fermentation and microbial electrolysis cell

Hydrogen production from Saccharina Japonica by simultaneous dark fermentation (DF) and microbial electrolysis cell (MEC), called sDFMEC, was studied. In the novel sDFMEC process, substrates were converted to H₂ and volatile fatty acids (VFAs) by DF in the bulk phase, and VFAs are simultaneously oxidized by the exoelectrogens in the microbial film on anode electrode with further production of H₂ at the cathode. The sDFMEC process was compared with DF and a combined process of DF and MEC in series (DF-MEC) in terms of H₂ production. The overall H₂ production from S. Japonica in sDFMEC process was higher (438.7 ± 13.3 mL/g-TS), than DF (54.6 ± 0.8 mL/g-TS) and DF-MEC (403.5 ± 7.9 mL/g-TS) process, respectively, which is approximately 3-times higher than those reported in the literature.

The influence of cavitation effects on the purification processes of beet sugar production juices

The existing technology for the purification of diffusion juice and its hardware design has not fundamentally changed over the past four decades. The lack of the necessary theoretical developments and experimental data hinders the development of existing and the development of new technological processes. Therefore, the main direction of improving the purification efficiency of juices of sugar beet production is the disclosure of its unused reserves and their implementation in practice. The scientific problem of choosing the rational direction for improving the technology of juice purification, which ensures the production of consumer granulated sugar in the face of changes in a wide range of quality of raw materials, is relevant and has important economic importance, especially in the context of the transition of beet sugar factories to a market economy. One way to solve it is to make fuller use of the adsorption capacity of calcium carbonate particles while increasing the filtration properties of saturation sediments. Therefore, the study investigates the effect of cavitation effects – vapor condensation and hydrodynamic processing of diffusion juice on the processes of purification of diffusion juice, juices of preliminary defecation, first and second saturations. The analysis of the influence of various effects of cavitation processing of juices from the point of view of improving the purification efficiency, the optimal place of the purification process in the technological scheme of production is established.

Hyperthermophilic Treatment of Grass and Leaves to Produce Hydrogen, Methane and VFA-Rich Digestate: Preliminary Results

In this study, the feasibility of hydrogen and methane production from grass and leaves via hyperthermophilic anaerobic digestion was investigated. The hyperthermophilic treatment of grass at 70 °C resulted in the highest concentrations of volatile fatty acids (TVFA) and reducing sugars in the supernatant of over 21 and 6.5 g/L reported on day 3 and 4 of the experiment. In contrast, hydrolysis and acidification of leaves performed slower and with lower efficiency, as the peak concentrations of TVFA and reducing sugars were observed at the end of the process. However, the highest cumulative hydrogen and methane yields of 69.64 mLH2/gVS and 38.63 mLCH4/gVS were reported for leaves digested at 70 °C, whereas the corresponding maximum productions observed for grass were 50 mLH2/gVS and 1.98 mLCH4/gVS, respectively. A temperature increase to 80 °C hampered hydrogen and methane production and also resulted in lower yields of volatile fatty acids, reducing sugars and ammonia as compared to the corresponding values reported for 70 °C.

Industrial wastewater to biohydrogen: Possibilities towards successful biorefinery route

The aim of this review is to summarize the modern developments and enhancement strategies reported for improving the biorefinery route of industrial wastewater to biohydrogen. Recent developments towards biohydrogen production chiefly involves culture enrichment, pretreatment of biocatalysts, co culture fermentation, metabolic and genetic engineering, ecobiotechnological approaches and the coupling process of biohydrogen. In addition, an overview of dark fermentation, pathways involved, microbes involved in biohydrogen production, industrial wastewater as substrate have been focused. The utilization of organic residuals of dark fermentation for subsequent value added products are highlighted. More apparently, the two stage coupling process and its possibilities towards biorefinery has been reviewed comprehensively. Moreover, comparative energy and economic aspects of biohydrogen production from industrial wastewater and its prospects towards pilot scale applications are also spotlighted. Though all the enhancement strategies have both benefits and disadvantages, coupling process is considered as the most successful biorefinery route for biohydrogen production.

Enhancement of hydrogen production and energy recovery through electro-fermentation from the dark fermentation effluent of food waste

To enhance hydrogen production efficiency and energy recovery, a sequential dark fermentation and microbial electrochemical cell (MEC) process was evaluated for hydrogen production from food waste. The hydrogen production, electrochemical performance and microbial community dynamics were investigated during startup of the MEC that was inoculated with different sludges. Results suggest that biogas production rates and hydrogen proportions were 0.83 ​L/L d and 92.58%, respectively, using anaerobic digested sludge, which is higher than that of the anaerobic granular sludge (0.55 ​L/L d and 86.21%). The microbial community were predominated by bacterial genus Acetobacterium, Geobacter, Desulfovibrio, and archaeal genus Methanobrevibacter in electrode biofilms and the community structure was relatively stable both in anode and cathode. The sequential system obtained a 53.8% energy recovery rate and enhanced soluble chemical oxygen demand (sCOD) removal rate of 44.3%. This research demonstrated an important approach to utilize dark fermentation effluent to maximize the conversion of fermentation byproducts into hydrogen.

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Sequential dark fermentation and microbial electrolysis cell was evaluated.

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The best bio-electrochemical performance with anaerobic digested sludge in the microbial electrolysis cells startup.

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Acetobacterium, Geobacte and Methanobrevibacter were the dominant genera in electrode biofilms.

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53.8% energy recovery was achieved in the sequential electro-fermentation process.

The Studying the processing of food dye from beet juice

The manuscript describes a new method of red beet processing and the technology of manufacturing food colorant from the juice concentrate, which is natural, safe and useful analogue to existing expensive offers on the market of similar goods that have chemical origin not useful for regular consumption. Nowadays in order to give to food products a colour, close to natural coloring of fruits and vegetables, expensive synthetic dyes are used, which might have cancer-inducing effect when being accumulated by human organism. Therefore improving the technology for producing food grade dye from red beet juice is remarkably important task. Currently, there is a problem for vegetable processors – pectin substances complicate the process, like the illumination of juice and negatively affect its storage capacity. The article below reveals and substantiates the necessity of using a natural carbon-containing adsorbent shungite for the purification of beet juice from pectin substances. On the basis of the study, the authors suggest a more cost-effective way of producing a food dye from juice concentrate, which allows avoiding usage of expensive enzyme processing additives.

The Use of Acidic Hydrolysates after Furfural Production from Sugar Waste Biomass as a Fermentation Medium in the Biotechnological Production of Hydrogen

This study investigates a simultaneous processing of sugar beet pulp (SBP) for furfural, hydrogen and methane production using various pretreatment methods. In the experiments, sugar beet pulp was first subjected to thermal and thermochemical pretreatment at 140 °C. Then hydrolysates from these operations were investigated for their potential for methane and hydrogen production in batch tests. The experiments showed that thermal pretreatment of SBP resulted in the highest biogas and methane yields of 945 dm3/kg volatile solids (VS) and 374 dm3 CH4/kg VS, respectively, and a moderate hydrogen production of 113 dm3 H2/kg VS, which corresponded to a calculated energy production of 142 kWh/t; however, only low amount of furfural was obtained (1.63 g/L). Conversely, the highest furfural yield of 12 g/L was achieved via thermochemical pretreatment of SBP; however, biogas production from hydrolysate was much lower (215 dm3/kg VS) and contained only 67 dm3/kg VS of hydrogen. Meanwhile, in the experiment with lower amounts of sulfuric acid (2%) used for pretreatment, a moderate furfural production of 4 g/L was achieved with as high as 220 dm3/kg VS of hydrogen and the corresponding energy yield of 75 kWh/t.

Electron donation characteristics and interplays of major volatile fatty acids from anaerobically fermented organic matters in bioelectrochemical systems

Anaerobic fermentation liquid of waste organic matters (WOMs) is rich in volatile fatty acids (VFAs), which can be treated with bioelectrochemical systems for both electrical energy recovery and organics removal. In this work, four major VFAs in the fermented WOMs supernatant were selected to examine their electron donation characteristics for power output and their complicated interplays in microbial fuel cells (MFCs). Results indicated a priority sequence of acetate, propionate, n-butyrate and i-valerate when served as the sole electron donor for electricity generation. The MFC solely fed with acetate showed the highest coulombic efficiency and power density, and the longest period for electricity production. When two of the VFAs were added with equal proportion, both acids contributed positively to electricity generation, while the selective or competitive use of substrates by diverse microorganisms behaved as an antagonism effect to prolong the degradation time of each VFA. When acetate and propionate, the preferable substrates for electricity generation, were mixed in various proportions, their large concentration difference led to improved electrical performance but decreased organic removal rate.

Comparison of Two Process Schemes Combining Hydrothermal Treatment and Acidogenic Fermentation of Source-Separated Organics

This study compares the effects of pre- and post-hydrothermal treatment of source- separated organics (SSO) on solubilization of particulate organics and acidogenic fermentation for volatile fatty acids (VFAs) production. The overall COD solubilization and solids removal efficiencies from both schemes were comparable. However, the pre-hydrolysis of SSO followed by acidogenic fermentation resulted in a relatively higher VFA yield of 433 mg/g VSS, which was 18% higher than that of a process scheme with a post-hydrolysis of dewatered solids from the fermentation process. Regarding the composition of VFA, the dominance of acetate and butyrate was comparable in both process schemes, while propionate concentration considerably increased in the process with pre-hydrolysis of SSO. The microbial community results showed that the relative abundance of Firmicutes increased substantially in the fermentation of pretreated SSO, indicating that there might be different metabolic pathways for production of VFAs in fermentation process operated with pre-treated SSO. The possible reason might be that the abundance of soluble organic matters due to pre-hydrolysis might stimulate the growth of more kinetically efficient fermentative bacteria as indicated by the increase in Firmicutes percentage.

Applications of Emerging Bioelectrochemical Technologies in Agricultural Systems: A Current Review

Background: Bioelectrochemical systems (BESs) are emerging energy-effective and environment-friendly technologies. Different applications of BESs are able to effectively minimize wastes and treat wastewater while simultaneously recovering electricity, biohydrogen and other value-added chemicals via specific redox reactions. Although there are many studies that have greatly advanced the performance of BESs over the last decade, research and reviews on agriculture-relevant applications of BESs are very limited. Considering the increasing demand for food, energy and water due to human population expansion, novel technologies are urgently needed to promote productivity and sustainability in agriculture. Methodology: This review study is based on an extensive literature search regarding agriculture-related BES studies mainly in the last decades (i.e., 2009–2018). The databases used in this review study include Scopus, Google Scholar and Web of Science. The current and future applications of bioelectrochemical technologies in agriculture have been discussed. Findings/Conclusions: BESs have the potential to recover considerable amounts of electric power and energy chemicals from agricultural wastes and wastewater. The recovered energy can be used to reduce the energy input into agricultural systems. Other resources and value-added chemicals such as biofuels, plant nutrients and irrigation water can also be produced in BESs. In addition, BESs may replace unsustainable batteries to power remote sensors or be designed as biosensors for agricultural monitoring. The possible applications to produce food without sunlight and remediate contaminated soils using BESs have also been discussed. At the same time, agricultural wastes can also be processed into construction materials or biochar electrodes/electrocatalysts for reducing the high costs of current BESs. Future studies should evaluate the long-term performance and stability of on-farm BES applications.

A review of research trends in the enhancement of biomass-to-hydrogen conversion

Different types of biomass are being examined for their optimum hydrogen production potentials and actual hydrogen yields in different experimental set-ups and through different chemical synthetic routes. In this review, the observations emanating from research findings on the assessment of hydrogen synthesis kinetics during fermentation and gasification of different types of biomass substrates have been concisely surveyed from selected publications. This review revisits the recent progress reported in biomass-based hydrogen synthesis in the associated disciplines of microbial cell immobilization, bioreactor design and analysis, ultrasound-assisted, microwave-assisted and ionic liquid-assisted biomass pretreatments, development of new microbial strains, integrated production schemes, applications of nanocatalysis, subcritical and supercritical water processing, use of algae-based substrates and lastly inhibitor detoxification. The main observations from this review are that cell immobilization assists in optimizing the biomass fermentation performance by enhancing bead size, providing for adequate cell loading and improving mass transfer; there are novel and more potent bacterial and fungal strains which improve the fermentation process and impact on hydrogen yields positively; application of microwave irradiation and sonication and the use of ionic liquids in biomass pretreatment bring about enhanced delignification, and that supercritical water biomass processing and dosing with metal-based nanoparticles also assist in enhancing the kinetics of hydrogen synthesis. The research areas discussed in this work and their respective impacts on hydrogen synthesis from biomass are arguably standalone. Thence, further work is still required to explore the possibilities and techno-economic implications of combining these areas for developing robust and integrated biomass-to-hydrogen synthetic schemes.

Hydrogen peroxide production in a pilot-scale microbial electrolysis cell

A pilot-scale dual-chamber microbial electrolysis cell (MEC) equipped with a carbon gas-diffusion cathode was evaluated for H2O2 production using acetate medium as the electron donor. To assess the effect of cathodic pH on H2O2 yield, the MEC was tested with an anion exchange membrane (AEM) and a cation exchange membrane (CEM), respectively. The maximum current density reached 0.94-0.96 A/m2 in the MEC at applied voltage of 0.35-1.9 V, regardless of membranes. The highest H2O2 conversion efficiency was only 7.2 ± 0.09% for the CEM-MEC. This low conversion would be due to further H2O2 reduction to H2O on the cathode or H2O2 decomposition in bulk liquid. This low H2O2 conversion indicates that large-scale MECs are not ideal for production of concentrated H2O2 but could be useful for a sustainable in-situ oxidation process in wastewater treatment.

Development of a production chain from vegetable biowaste to platform chemicals

BACKGROUND

A future bioeconomy relies on the development of technologies to convert waste into valuable compounds. We present here an attempt to design a biotechnological cascade for the conversion of vegetable waste into acetoin and electrical energy.

RESULTS

A vegetable waste dark fermentation effluent containing mainly acetate, butyrate and propionate was oxidized in a bioelectrochemical system. The achieved average current at a constant anode potential of 0 mV against standard hydrogen electrode was 177.5 ± 52.5 µA/cm². During this step, acetate and butyrate were removed from the effluent while propionate was the major remaining component of the total organic carbon content comprising on average 75.6%. The key players with regard to carbon oxidation and electrode reduction were revealed using amplicon sequencing and metatranscriptomic analysis. Using nanofiltration, it was possible to concentrate the propionate in the effluent. The effluent was revealed to be a suitable medium for biotechnological production strains. As a proof of principle, the propionate in the effluent of the bioelectrochemical system was converted into the platform chemical acetoin with a carbon recovery of 86%.

CONCLUSIONS

To the best of our knowledge this is the first report on a full biotechnological production chain leading from vegetable waste to the production of a single valuable platform chemical that integrates carbon elimination steps leading to the production of the valuable side product electrical energy.

Electrokinetic analyses in biofilm anodes: Ohmic conduction of extracellular electron transfer

This review explores electron transfer kinetics from an electron donor to the anode in electrically conductive biofilm anodes. Intracellular electron transfer (IET) from the donor to the anode is well described with the Monod equation. In comparison, mechanisms of extracellular electron transfer (EET) conduction are unclear yet, complicating EET kinetics. However, in biofilm anodes where potential gradient to saturated current density is less than ∼300 mV, Ohmic conduction successfully describe conductive EET mainly with biofilm conductivity (K_bio) and biofilm thickness (L_f). High K_bio essential for production of high current density is found in Geobacter pure or enriched biofilm anodes, but other exoelectrogens could make biofilms electrically conductive. IET is rate-limiting for current density in conductive biofilms, and biofilm density of active exoelectrogens and L_f are operating parameters that can be optimized further to improve current density.

A review on the applications of microbial electrolysis cells in anaerobic digestion

Anaerobic digestion (AD) has been widely used for biogas or biofuel generation from waste treatment. Because a low production rate and instability of AD occur frequently, various technologies have been applied to improvement of AD. Microbial electrolysis cells (MECs), an emerging technology, can convert organic matter into hydrogen, methane, and other value-added products. Recent studies showed that application of MEC to AD (MEC-AD) can accelerate degradation of a substrate (including recalcitrant compounds) and alter AD microbial community by enriching exoelectrogens and methanogens thus increasing biogas production. With stable microbial communities established, improvement of MEC-AD for methane production was achieved. MEC-AD process can be monitored in real-time by detecting electric signals, which linearly correlate with substrate concentrations. This review attempts to evaluate interactions among the decomposition of substrates, MEC-AD system, and the microbial community. This analysis should provide useful insights into the improvement of methane production and the performance of MEC-AD.

Microbial electrohydrogenesis linked to dark fermentation as integrated application for enhanced biohydrogen production: A review on process characteristics, experiences and lessons

Microbial electrohydrogenesis cells (MECs) are devices that have attracted significant attention from the scientific community to generate hydrogen gas electrochemically with the aid of exoelectrogen microorganisms. It has been demonstrated that MECs are capable to deal with the residual organic materials present in effluents generated along with dark fermentative hydrogen bioproduction (DF). Consequently, MECs stand as attractive post-treatment units to enhance the global H₂ yield as a part of a two-stage, integrated application (DF-MEC). In this review article, it is aimed (i) to assess results communicated in the relevant literature on cascade DF-MEC systems, (ii) describe the characteristics of each steps involved and (iii) discuss the experiences as well as the lessons in order to facilitate knowledge transfer and help the interested readers with the construction of more efficient coupled set-ups, leading eventually to the improvement of overall biohydrogen evolution performances.

Aquatic weeds as the next generation feedstock for sustainable bioenergy production

Increasing oil prices and depletion of existing fossil fuel reserves, combined with the continuous rise in greenhouse gas emissions, have fostered the need to explore and develop new renewable bioenergy feedstocks that do not require arable land and freshwater resources. In this regard, prolific biomass growth of invasive aquatic weeds in wastewater has gained much attention in recent years in utilizing them as a potential feedstock for bioenergy production. Aquatic weeds have an exceptionally higher reproduction rates and are rich in cellulose and hemicellulose with a very low lignin content that makes them an efficient next generation biofuel crop. Considering their potential as an effective phytoremediators, this review presents a model of integrated aquatic biomass production, phytoremediation and bioenergy generation to reduce the land, fresh water and fertilizer usage for sustainable and economical bioenergy.

Hydrogen production by dark fermentation from pre-fermented depackaging food wastes

In this study, a specific fraction of food waste, i.e. depackaging waste, was studied as substrate for hydrogen production by dark fermentation. During storage and transport of this liquid mixture, inhibitory compounds like acids or alcohol might be produced by endogenous flora. A factorial fractional design based on the composition of the substrate was used to determine the best condition to convert this substrate into hydrogen. First results indicated that the consortium used might convert high quantity of lactate into hydrogen. A batch culture confirmed that lactate was used as the main carbon source and a global yield of 0.4mol_H2·mol_lactate^-1 was obtained. This study demonstrated the ability of the consortium tested to convert different carbon sources (carbohydrates or lactate) with good efficiency. These data represented an important parameter in the prospect of using an industrial substrate whose composition is liable to vary according to the conditions of storage and transport.

Biohydrogen production from food waste: Current status, limitations, and future perspectives

Among the various biological routes for H₂ production, dark fermentation is considered the most practically applicable owing to its capability to degrade organic wastes and high H₂ production rate. Food waste (FW) has high carbohydrate content and easily hydrolysable in nature, exhibiting higher H₂ production potential than that of other organic wastes. In this review article, first, the current status of H₂ production from FW by dark fermentation and the strategies applied for enhanced performance are briefly summarized. Then, the technical and economic limitations of dark fermentation of FW are thoroughly discussed. Economic assessment revealed that the economic feasibility of H₂ production from FW by dark fermentation is questionable. Current efforts to further increase H₂ yield and waste removal efficiency are also introduced. Finally, future perspectives along with possible routes converting dark fermentation effluent to valuable fuels and chemicals are discussed.