Application of nanotechnology in dark fermentation for enhanced biohydrogen production using inorganic nanoparticles

Fermentation is an important innovation by mankind and this process is used for converting organic substrate into useful products. Using natural conditions, specifically, light and dark conditions, photo-fermentation and dark fermentation techniques can be developed and operated under controlled conditions. Generally, products such as biofuels, bioactive compounds and enzymes have been produced using the dark fermentation method. However, the major requirement for today's industralized world is biofuels in its clean and pure forms. Biohydrogen is the most efficient and cleanest form of energy produced using dark fermentation of organic substrates. Nevertheless, the quantity of biohydrogen produced via dark fermentation is low. In order to increase the product quantity and quality, several internal and external stress or alterations are made to conventional fermentation conditions. In recent times, nanotechnology has been introduced to enhance the rate of dark fermentation. Nanoparticles (NPs), specifically, inorganic NPs such as silver, iron, titanium oxide and nickel have increased the production rate of biohydrogen. Therefore, the present review focuses on exploring the potential of nanotechnology in the dark fermentation of biohydrogen production, the mechanisms involved, substrates used and changes to be made to increase the production efficiency of dark fermentation.     

Fermentative hydrogen production - An alternative clean energy source

Hydrogen generation from wastewater is one of the promising approaches through biological route. So, exploitation of wastewater as substrate for hydrogen production with concurrent wastewater treatment is an attractive and effective way of tapping clean energy from renewable resources in a sustainable approach. In this direction, considerable interest is observed on various biological routes of hydrogen production using bio-photolysis, photo fermentation and heterotrophic dark fermentation process or by a combination of these processes. Therefore, in this communication, utilizing industrial wastewater as primary substrate for dark fermentation process is reviewed and different parametric aspects associated with this sustainable approach for better energy production is discussed. The industrial wastewaters that could be the source for bio hydrogen generation, such as rice slurry wastewater, food and domestic wastewaters, citric acid wastewater and paper mill wastewater, are also discussed in this article.     

Scaling-up bio-hydrogen production from food waste: Feasibilities and challenges

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.     

Hydrogen production via dark fermentation by bacteria colonies on porous PDMS-scaffolds

The development of biofuels and the question of finding renewable energy sources are important issues nowadays, due to the increasing shortage of other supplies. Hydrogen has gained very much attention as biofuel, as it is highly energetic and a clean energy source. A very interesting method to produce hydrogen is dark fermentation. It generates a clean energy from organic wastes with low value and at low energy requirements. The production of hydrogen and bio-hydrogen from waste and wastewaters can have a positive environmental impact in terms of creation of highly effective energy fuel and reduction of waste. Due to their nutrients, organic waste and wastewaters are suitable substrates to obtain bio-hydrogen. In this paper we investigate the behaviour and the stability of porous scaffolds containing iron oxide particles in a dark fermentation environment and explore the possibility of hosting mixed cultures of clostridia on them, aiming to an increase in hydrogen production. We address the effect of embedding hematite particles (in different concentrations) in the scaffolds, to see whether there is an increase in bio-hydrogen-production. This latter can be enhanced, if particles of various metal oxides are present, as they can increase bacterial growth and encourage the bioactivity of species that produce hydrogen. The scaffolds analysed consist of polydimethylsiloxane (PDMS) containing Fe₂O₃ particles and were produced via the sugar template method. X-ray diffraction patterns, SEM images as well as dark fermentation tests in batch procedure are presented and discussed. Bacteria colonies could be detected after long treatment in municipal wastewater and production of biohydrogen was ascertained for all samples investigated.     

Trends in dark biohydrogen production strategy and linkages with transition towards low carbon economy: An outlook,cost-effectiveness,bottlenecks and future scope

The conventional fossil fuel showed a persistent and intense decline steadily over the past two decades have led to global deterioration of limited sustainable energy supplies. Furthermore, price fluctuations and its serious ecological consequences had piqued the interest of researchers mostly in domain of alternative renewable energy. Among all existing fuels, biohydrogen is documented because of its carbon-neutral, simple and sustainable output, low carbon emissions, and large energy density. Hydrogen (H₂) generation from dark fermentation of biowaste is an enticing sustainable method which promotes in the creation of low carbon economy. This review details the overview of hydrogen yield form renewable feedstock through dark fermentation. It also detailed the recent trends such as pretreatment, addition of various additives, integrated options, etc., employed towards the enhancement of fermentation process to enrich the hydrogen production. Discussion about the inhibitory substances that affects the performance of fermentation process was incorporated. In addition, it elaborates the economic feasibility, challenges and limitation of the process along with future scope for the development of sustainable hydrogen economy.     

A bibliometric analysis of the hydrogen production from dark fermentation

Hydrogen energy plays an important role in solving the environmental problems caused by the fuel crisis and greenhouse gas emissions. However, hydrogen application on an industrial scale still requires technological advances, especially in choosing the best technological route for the recovery of renewable and cost-effective hydrogen. Therefore, this bibliometric review evaluated the research progress, trends, updates, and hotspots on hydrogen production from dark fermentation. The Web of Science© database was used to select the documents from 2000 to 2021, and the VOSviewer© and Bibliometrix softwares were used to carry out the bibliometric investigation. The results demonstrated that 3071 documents (2755 articles and 316 reviews) studied the hydrogen production from dark fermentation over the last 21 years. The number of publications exponentially increased in the last five years, which can be associated with the demand for new technologies to produce clean energy sources and decrease the environmental impacts caused by petroleum-based fuel. Keyword analysis revealed that the studies focused on the operational parameters, process optimization, pretreatment, and microbial community, aiming to increase the hydrogen yield during dark fermentation. Finally, this comprehensive review provides future directions for applying dark fermentation to produce hydrogen as a sustainable and renewable fuel in a biorefiney concept.     

Hydrogen production from agricultural waste by dark fermentation: A review

The degradation of the natural environment and the energy crisis are two vital issues for sustainable development worldwide. Hydrogen is considered as one of the most promising candidates as a substitute for fossil fuels. In this context, biological processes are considered as the most environmentally friendly alternatives for satisfying future hydrogen demands. In particular, biohydrogen production from agricultural waste is very advantageous since agri-wastes are abundant, cheap, renewable and highly biodegradable. Considering that such wastes are complex substrates and can be degraded biologically by complex microbial ecosystems, the present paper focuses on dark fermentation as a key technology for producing hydrogen from crop residues, livestock waste and food waste. In this review, recent findings on biohydrogen production from agricultural wastes by dark fermentation are reported. Key operational parameters such as pH, partial pressure, temperature and microbial actors are discussed to facilitate further research in this domain.     

Fermentative hydrogen production from wastewaters: A review and prognosis

Biohydrogen is a promising candidate which can replace a part of our fossil fuels need in day-to-day life due its perceived environmental benefits and availability through dark fermentation of organic substrates. Moreover, advances in biohydrogen production technologies based on organic wastewater conversion could solve the issues related to food security, climate change, energy security and clean development in the future. An evaluation of studies reported on biohydrogen production from different wastewaters will be of immense importance in economizing production technologies. Here we have reviewed biohydrogen production yields and rates from different wastewaters using sludges and microbial consortiums and evaluated the feasibility of biohydrogen production from unexplored wastewaters and development of integrated bioenergy process. Biohydrogen production has been observed in the range of substrate concentration 0.25–160 g COD/L, pH 4–8, temperature 23–60 °C, HRT 0.5–72 h with various types of reactor configuration. The most efficient hydrogen production has been obtained at an organic loading rate (OLR) 320 g COD/L/d, substrate concentration 40 g COD/L, HRT 3 h, pH 5.5–6.0, temperature 35 °C in a continuously-stirred tank reactor system using mixed cultures and fed with condensed molasses fermentation soluble wastewater. The net energy efficiency analysis showed vinasse wastewater has the highest positive net energy gain followed by glycerin wastewater and domestic sewage as 140.39, 68.65, 51.84 kJ/g COD feedstock with the hydrogen yield (HY) of 10 mmol/g COD respectively.     

Current challenges and future technology in photofermentation-driven biohydrogen production by utilizing algae and bacteria

Biohydrogen is perceived as the versatile fuel of the future, having the ability to replace fossil fuels in many industrial and commercial sectors and offering the promise of fulfilling future renewable energy demands. Among various options available for the generation of biohydrogen, photofermentation with the help of microbes and algae is one of the most eye-catching approaches due to its relative efficiency, cost economics, and reduced environmental impacts. Generation of biohydrogen by dark fermentation, microbial electrolysis cell as well as photofermentation, along with their bioprocesses, already have been discussed in earlier literature. Photofermentation offers advantages of both biophotolysis (utilization of light energy) and dark fermentation (utilization of organic waste materials as substrate). Many researchers have been reported successful biohydrogen production from photofermentation-based techniques, however not much information is available regarding the considerable gap in industrial and economic challenges in the production of biohydrogen at the commercial level through photofermentation. Efforts have been made in this review to provide updated information on various new technologies being used in this sector, such as the integration of photofermentation with dark fermentation, the use of recombinant DNA technology, and the use of bionanotechnology to improve biohydrogen production through the utilization of various waste. Various challenges in this sector, as well as future perspectives, have been meticulously addressed in order to explore the future of green biohydrogen production for a sustainable future.     

Study of future power interconnection scheme in ASEAN

The current energy supply trajectory in the Association of Southeast Asian Nations (ASEAN) region is not sustainable. Factors such as rising standards of living and demographic patterns, including population growth, lead to continuous increase in power demand, which is difficult to meet using limited fossil fuel resources. Thus, a transition toward clean energy sources is needed in the region. While ASEAN member countries are rich in clean energy resources, such resources are located far from demand centers; thus, allocation of clean energy is necessary to increase its utilization. In this study, power demand is forecasted using a combination of prediction methods. A model to evaluate the installed capacity and power exchange potential is proposed to deal with mismatch between the location of the clean energy base and the load center. Furthermore, the concept of cross-regional allocation of clean energy between the ASEAN region, China, and South Asia is presented. A power interconnection scheme among the ASEAN member countries as well as neighboring countries is proposed based on the power exchange potential. The proposed grid interconnection scheme contributes to the utilization of clean energy in the ASEAN region, increasing the proportion of clean energy in the generation mix, which ensures that the region becomes a sustainable and resilient society with a clean and low carbon development route. Furthermore, the proposed power interconnection scheme will generate valuable economic, social, environmental, and resource allocation benefits.     

Generation of green hydrogen using self-sustained regenerative fuel cells: Opportunities and challenges

The ever-increasing energy demand, depleting fossil fuel reserves, and rising temperatures due to greenhouse gas emissions have necessitated the transition towards the generation of green and clean energy through renewable energy sources. Solar energy is one such renewable energy source that has received significant attention owing to its abundance and inexhaustibility. However, solar energy alone cannot replace fossil fuels in the energy portfolio. There exists a need to develop another clean energy source that can potentially act as an alternative to conventional fuels. Hydrogen proves to be an ideal candidate in this domain and can be sustainably generated by water electrolysis by powering the electrolyzer using solar energy. The hydrogen thus synthesized has net zero carbon emissions and is a suitable asset for decarbonizing the environment. This review encompasses the generation of hydrogen using PV-Electrolyzer systems and addresses the challenges associated with the same. Overcoming these drawbacks can ensure a strong position for hydrogen as an alternative fuel in the energy infrastructure. By employing electrolyzers that are fueled by renewable energy and then using that hydrogen to feed a fuel cell, this study aims to clarify the potential and constraints of producing green hydrogen. Since this area of research has not yet been fully investigated, a review article that enables and encourages academics to develop original solutions is urgently needed.     

A review on bioconversion processes for hydrogen production from agro-industrial residues

Hydrogen is a renewable gas, efficient to produce energy that makes it a suitable alternative and effective solution for a carbon-free environment. Unlike other fossil fuels, combustion of hydrogen does not produce toxic compounds, such as greenhouse gases, carbon monoxide, hydrocarbons, etc., resulting in less environmental pollution. Agro-industrial residues contain several lignocelluloses that favor the growth of microorganisms to produce valuable products such as hydrogen. Of the diverse techniques in hydrogen production, bioconversion proves to be an efficient method in permuting agro-industrial residues into hydrogen. This review provides detailed information on the bioconversion processes and factors involved in hydrogen production from agro-industrial residues including different fermentation processes such as dark fermentation and photo-fermentation, and fuel cell systems such as microbial electrolysis cell and microbial fuel cell. Different pretreatment techniques to enhance the availability of lignocellulose for hydrogen production have been elaborated in this review. Various factors including pH, temperature and nutrient composition of feed, affecting the production efficiency and purity of the products during fermentation have been discussed.     

Impact of hydrogen on the environment

The present work considers the impact of hydrogen fuel on the environment within the cycles of its generation and combustion. Hydrogen has been portrayed by the media as a fuel that is environmentally clean because its combustion results in the formation of harmless water. However, hydrogen first must be generated. The effect of hydrogen generation on the environment depends on the production process and the related by-products. Hydrogen available on the market at present is mainly generated by using steam reforming of natural gas, which is a fossil fuel. Its by-product is CO₂, which is a greenhouse gas and its emission results in global warming and climate change. Therefore, hydrogen generated from fossil fuels is contributing to global warming to the similar extent as direct combustion of the fossil fuels. On the other hand hydrogen obtained from renewable energy, such solar energy, is environmentally clean during the cycles of its generation and combustion. Consequently, the introduction of hydrogen economy must be accompanied by the development of hydrogen that is environmentally friendly. The present work considers several aspects related to the generation and utilisation of hydrogen obtained by steam reforming and solar energy conversion (solar-hydrogen).     

A novel method for determining effects of fire damage on the safety of the Type I pressure hydrogen storage tanks

Consumption of the fossil fuels causes greenhouse gas effect and environmental pollution, which are two basic problems of our age. As a result of this problem, clean and renewable alternative energy sources are beginning to replace fossil fuels. Nowadays, the use of hydrogen energy, which is one of the clean energy, is increasing in transportation and industrial areas. Increasing of hydrogen energy usage, scientists are attempting to solve the many safety problems (such as fire, burst, impact and hydrogen embrittlement) that can occur during the storage and consumption of hydrogen energy. In this study, during the event of fire, the safety of metallic Type I pressure hydrogen storage tanks is investigated by using a novel approach. In this new approach, the mechanical strength drops of the tank materials that is related with temperature rising are added to the safety calculations. In the study, 6061 T6 aluminum and SS 316L stainless steel alloys were used as hydrogen tank material. The safety of hydrogen tanks modelled using these alloys was investigated under different temperature conditions (22, 100, 200 and 300 °C) and internal pressure (15, 20 and 25 MPa).     

Insights into evolutionary trends in molecular biology tools in microbial screening for biohydrogen production through dark fermentation

Access to clean energy is vital to combat global warming and climate change, and nothing but hydrogen could better deliver it with ease to secure future energy needs. Biohydrogen could be produced in different routes including photolysis, water-gas shift reaction, dark, photo-fermentation and combination of both. Dark fermentative hydrogen production (DFHP) is efficient in comparison with photo-fermentation and utilizing organic waste ensures land usage and water for agriculture. Several microbes are involved in the process of biohydrogen production via dark fermentation and characterizing them at molecular level unveils holistic approach and understanding. Limited resources were available in terms of molecular tools for microbial characterization and this paper attempts to review the evolution of advanced molecular techniques including their merits and demerits. Understanding the composition of micro-flora is important in DFHP and could be classified as pure, co-cultures, enriched mixed cultures and mixed microbiota. These cultures act as seed sources for batch and continuous fermentations that help in understanding the efficiency of these methods. The schematics and systematic assessment of the various molecular tools (cloning, PCR-DGGE, FISH, NGS, CE-SSCP) for quantification, identification, detection and characterization of the microbial cell activity have been elaborated. Lastly, a comparative tabulation recapitulates the merits and drawbacks of each technique discussed. This provides valued information for choosing the right kind of microbial and molecular assessment tool for future characterization. Such analysis aids in suitable identification and characterization of microflora as potential biocatalysts for biohydrogen production through dark fermentation.     

Biohythane production from organic waste: Recent advancements,technical bottlenecks and prospects

The availability of fossil fuels is a major factor that determines the economy of a country. However, possible exhaustion of fossil fuel deposits as well as increased pollution, and other adverse effects on the environment has prompted us to search for alternative fuels. This resulted in the development of hythane, a blend of hydrogen with methane, at concentrations of 10%–30%. The breakdown of organic substrates using sequential dark fermentation (DF) and anaerobic digestion (AD) leads to biohythane production. The quality and quantity of biohythane can be improved by altering the following aspects: selection, development, and/or genetic engineering of suitable microbial consortium; the use of cheap, appropriate substrates; improved design of bioreactors; and the implementation of two-stage fermentation system. This review focusses on the mechanism of biohythane production and the different aspects involved in increasing both its production rate and quality. A comparative study has also been done to demonstrate the superiority of biohythane over other biofuels.     

合成气乙醇发酵的微生物研究

生物质合成气发酵是一种独特的、经济可行的乙醇生产新方法,它包括气化和发酵两个方面,对环境改善和能源供给有积极的意义.在合成气发酵产乙醇的微生物中,Clostridium ljungdahlii和Clostfidium carboxidivorans P7最有应用价值.它们利用合成气的途径是wood-ljungdahl途径.文章概述了合成气发酵产乙醇的菌种和培养条件,建立了生长动力学模型,提出了合成气发酵产乙醇工业化过程中存在的问题和应用前景.     

An application of the degree-hours method to estimate the residential heating energy requirement and fuel consumption in Istanbul

Cold season heating energy requirements in buildings can be estimated with the degree-hours method based on human comfort levels and available meteorological temperature records for a given area. Such estimations are especially significant for cities where fossil fuel consumption must be eliminated in favor of clean energy alternatives to reduce air pollution. This paper considers the city of Istanbul in Turkey and presents a detailed account for practical energy requirements and fuel consumption calculations.     

Potential of renewable hydrogen production for energy supply in Hong Kong

Hong Kong is highly vulnerable to energy and economic security due to the heavy dependence on imported fossil fuels. The combustion of fossil fuels also causes serious environmental pollution. Therefore, it is important to explore the opportunities for clean renewable energy for long-term energy supply. Hong Kong has the potential to develop clean renewable hydrogen energy to improve the environmental performance. This paper reviews the recent development of hydrogen production technologies, followed by an overview of the renewable energy sources and a discussion about potential applications for renewable hydrogen production in Hong Kong. The results show that although renewable energy resources cannot entirely satisfy the energy demand in Hong Kong, solar energy, wind power, and biomass are available renewable sources for significant hydrogen production. A system consisting of wind turbines and photovoltaic (PV) panels coupled with electrolyzers is a promising design to produce hydrogen. Biomass, especially organic waste, offers an economical, environmental-friendly way for renewable hydrogen production. The achievable hydrogen energy output would be as much as 40% of the total energy consumption in transportation.     

On the wind energy in Turkey

Increase in negative effects of fossil fuels on the environment has forced many countries, including Turkey, to use renewable energy sources. Today, clean, domestic and renewable energy is commonly accepted as the key for future life, not only for Turkey but also for the world. As wind energy is an alternative clean energy source compared to the fossil fuels that pollute the atmosphere, systems that convert wind energy to electricity have developed rapidly. Turkey is an energy importing country, more than half of the energy requirement has been supplied by imports. Turkey's domestic fossil fuel resources are extremely limited. In addition, Turkey's geographical location has several advantages for extensive use of wind power. In this context, renewable energy resources appear to be one of the most efficient and effective solutions for sustainable energy development and environmental pollution prevention in Turkey. Since wind energy will be used more and more in the future, its current potential, usage, and assessment in Turkey is the focus of the present study. The paper not only presents a review of the potential and utilization of the wind power in Turkey but also provides some guidelines for policy makers.