A review on biological recycling in agricultural waste-based biohydrogen production: Recent developments

Hydrogen-producing conditions and mutation mechanisms of a highly efficient mutant strain Ethanoligenens harbinense YR-3

In this study, the optimal hydrogen (H2) production conditions of the high-efficiency H2-producing mutant strain Ethanoligenens harbinense YR-3 (carbon-nitrogen ratio 5.5, phosphate buffer 80 mM, initial pH 6.0, biotin 1.4 mg/L) are obtained by intermittent experiments. The maximum specific H2 production rate of YR-3 (2.85 mol H2/mol glucose) was 1.4 times that of the wild strain ZGX4 (2.04 mol H2/mol glucose). The liquid-phase products are mainly ethanol and acetic acid, indicating that the metabolic pathway has not changed. Two-dimensional electrophoresis and mass spectrometry were used to compare and analyze the protein map differences between YR-3 and ZGX4. The results show that 1,6-fructose diphosphate aldolase and the flavoprotein in hydrogenase are highly expressed. This study will provide a theoretical basis for the genetic modification of high-efficiency H2-producing strains and the improvement of H2 production capacity.

Environmental Impact of Waste Treatment and Synchronous Hydrogen Production: Based on Life Cycle Assessment Method

Based on the life cycle assessment methodology, this study systematically analyzes the energy utilization of environmental waste through photocatalytic treatment and simultaneous hydrogen production. Using 10,000 tons of organic wastewater as the functional unit, the study evaluates the material consumption, energy utilization, and environmental impact potential of the photocatalytic waste synchronous hydrogen production system (specifically, the synchronous hydrogen production process of 4-NP wastewater with CDs/CdS/CNU). The findings indicate that potential environmental impacts from the photochemical treatment of environmental waste and synchronous hydrogen production primarily manifest in freshwater ecological toxicity, marine ecological toxicity, terrestrial ecological toxicity, and non-carcinogenic toxicity to humans. These ecological impacts stem from the catalyst's adsorption and metal leaching during the photo-degradation and hydrogen production processes of environmental waste. By implementing reasonable modifications and morphological refinements to the catalyst, these effects can be mitigated while achieving enhanced efficiency in environmental waste processing and simultaneous hydrogen production. The research outcomes provide valuable insights for advancing sustainable development in green technology for environmental waste treatment and energy utilization.

Metabolic flux analysis of hydrogen production network by Ethanoligenens harbinense B49: effect of product inhibition

In order to further understand the effect of product inhibition on the metabolism of hydrogen production bacteria, and to seek an effective way to increase the hydrogen yield in fermentation, a simplified metabolic model of Ethanoligenens harbinense B49 was constructed to analyse the metabolic flux under acetate and ethanol inhibition separately and to analyse the flux changes of the nodes. Based on the changes in metabolic flux distribution, Glucose 6-phosphate (G6P), Pyruvate (PYR), and Acetyl-CoA (AcCoA) were identified as key nodes of hydrogen production in the metabolic network. Robustness analysis showed that G6P was flexible, while AcCoA and PYR were weakly rigid, indicating that acetate flux could be increased by adding inhibitors or using genetic manipulation. Furthermore, releasing inhibition of acetate could effectively increase hydrogen production. These findings suggested that the addition of acetate separation in ethanol-type fermentation process is expected to improve hydrogen production, which might be a promising way to full-scale produce biohydrogen in industrial applications. Further, for the first time, we report the effect of product inhibition on key nodes in the E. harbinense B49 hydrogen production metabolism network.

Innovative Strategies for Upcycling Agricultural Residues and Their Various Pharmaceutical Applications

This review investigates innovative strategies for upcycling agricultural residues into valuable pharmaceutical compounds. The improper disposal of agricultural residues contributes to significant environmental issues, including increased greenhouse gas emissions and ecosystem degradation. Upcycling offers a sustainable solution, transforming these residues into high-value bioproducts (antioxidants, antitumor agents, antidiabetic compounds, anti-inflammatory agents, and antiviral drugs). Nanotechnology and microbial biotechnology have a crucial role in enhancing bioavailability and targeted delivery of bioactive compounds. Advanced techniques like enzymatic hydrolysis, green solvents, microwave processing, pyrolysis, ultrasonic processing, acid and alkaline hydrolysis, ozonolysis, and organosolv processes are explored for their effectiveness in breaking down agricultural waste and extracting valuable compounds. Despite the promising potential, challenges such as variability in residue composition, scalability, and high costs persist. The review emphasizes the need for future research on cost-effective extraction techniques and robust regulatory frameworks to ensure the safety, efficacy, and quality of bioproducts. The upcycling of agricultural residues represents a viable path towards sustainable waste management and production of pharmaceutical compounds, contributing to environmental conservation and public health improvements. This review provides an analysis of the current literature and identifies knowledge gaps, offering recommendations for future studies to optimize the use of agricultural residues in the drug industry.

Valorization of Agriculture Residues into Value-Added Products: A Comprehensive Review of Recent Studies

Global agricultural by-products usually go to waste, especially in developing countries where agricultural products are usually exported as raw products. Such waste streams, once converted to "value-added" products could be an additional source of revenue while simultaneously having positive impacts on the socio-economic well-being of local people. We highlight the utilization of thermochemical techniques to activate and convert agricultural waste streams such as rice and straw husk, coconut fiber, coffee wastes, and okara power wastes commonly found in the world into porous activated carbons and biofuels. Such activated carbons are suitable for various applications in environmental remediation, climate mitigation, energy storage, and conversions such as batteries and supercapacitors, in improving crop productivity and producing useful biofuels.

Biohydrogen from waste feedstocks: An energy opportunity for decarbonization in developing countries

In developing economies, the decarbonization of energy sector has become a global priority for sustainable and cleaner energy system. Biohydrogen production from renewable sources of waste biomass is a good source of energy incentive that reduces the pollution. Biohydrogen has a high calorific value and emits no emissions, producing both energy security and environmental sustainability. Biohydrogen production technologies have become one of the main renewable sources of energy. The present paper entails the role of biohydrogen recovered from waste biomasses like agricultural waste (AW), organic fraction of municipal solid waste (OFMSW), food processing industrial waste (FPIW), and sewage sludge (SS) as a promising solution. The main sources of increasing yield percentage of biohydrogen generation from waste feedstock using different technologies, and process parameters are also emphasized in this review. The production paths for biohydrogen are presented in this review article, and because of advancements in R and D, biohydrogen has gained viability as a biofuel for the future and discusses potential applications in power generation, transportation, and industrial processes, emphasizing the versatility and potential for integration into existing energy infrastructure. The investigation of different biochemical technologies and methods for producing biohydrogen, including anaerobic digestion (AD), dark fermentation (DF), photo fermentation (PF), and integrated dark-photo fermentation (IDPF), has been overviewed. This analysis also discusses future research, investment, and sustainable energy options transitioning towards a low-carbon future, as well as potential problems, economic impediments, and policy-related issues with the deployment of biohydrogen in emerging nations.

Nonsterile Process for Biohydrogen Production: Recent Updates, Challenges, and Opportunities

Hydrogen (H2), a clean and versatile energy carrier, has recently gained significant attention as a potential solution for reducing carbon emissions and promoting sustainable energy systems. The yield and efficiency of the biological H2 production process primarily depend on sterilization conditions. Various strategies, such as heat inactivation and membrane-based sterilization, have been used to achieve desirable yields via microbial fermentation. Almost every failed biotransformation process is linked to nonsterile conditions at any reaction stage. Therefore, the production of renewable biofuels as alternatives to fossil fuels is more attractive. Pure sugars have been widely documented as a costly feedstock for H2 production under sterile conditions. Biotransformation under nonsterile conditions is more desirable for stable and sustainable operation. Low-cost feeds, such as biowaste, are considered suitable alternatives, but they require appropriate sterilization to overcome the limitations of inherited or contaminating microbes during H2 production. This article describes the status of microbial fermentative processes for H2 production under nonsterile conditions and discusses strategies to improve such processes for sustainable, cleaner production.

Life-cycle analysis of biohydrogen production via dark-photo fermentation from wheat straw

This study presents a life-cycle analysis using energy conversion characteristics as an evaluation index to assess the feasibility of this production method. The results indicate that for a system processing 1000 kg/h of wheat straw, the addition of 12000 kg/h of 2 wt% H2SO4 and 120 kg/h of CH3COONa yields 340,000 L/h of H2 and 348.6 kW of electricity. The energy conversion efficiency from the feedstock to the product is 21.4 %, while the efficiency from the hydrolysate to the product is 62.2 %. The total CO2 emission is 27.1 kg/h. Variations in the hydrolysate have the most significant impact on energy conversion efficiency. This study explores the feasibility of industrial-scale biohydrogen production via dark-photo fermentation from wheat straw and analyzes the energy characteristic indices and the sensitivity of these indices to key parameters.

Agri-residues and agro-industrial waste substrates bioconversion by fungal cultures to biocatalyst lipase for green chemistry: A review

Huge amounts of agri-residues generated from food crops and processing are discarded in landfills, causing environmental problems. There is an urgent need to manage them with a green technological approach. Agri-residues are rich in nutrients such as proteins, lipids, sugars, minerals etc., and provide an opportunity for bioconversion into value-added products. Considering the importance of lipase as a biocatalyst for various industrial applications and its growing need for economic production, a detailed review of bioconversion of agri-residues and agro-industrial substrate for the production of lipase from fungal species from a technological perspective has been reported for the first time. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram was used for the identification and selection of articles from ScienceDirect, Google Scholar, and Scopus databases from 2010 to 2023 (July), and 108 peer-reviewed journal articles were included based on the scope of the study. The composition of agri-residues/agro-industrial wastes, fungal species, lipase production, industrial/green chemistry applications, and the economic impact of using agri-residues on lipase costs have been discussed. Bioconversion procedure, process developments, and technology gaps required to be addressed before commercialization have also been discussed. This process expects to decrease the environmental pollution from wastes, and low-cost lipase can help in the growth of the bioeconomy.

Improved sequential production of hydrogen and caproate by addition of biochar prepared from cornstalk residues

This study proposes a new model in which ethanol and acetate produced by dark fermentation are processed by Clostridium kluyveri for chain elongation to produce caproate with an addition of biochar prepared from cornstalk residues after acid pretreatment and enzymatic hydrolysis (AERBC) in the dark fermentation and chain elongation processes. The results show a 6-25% increase in hydrogen production in dark fermentation with adding AERBC, and the maximum concentration of caproate in the new model reached 1740 mg/L, 61% higher than that in the control group. In addition, caproate was obtained by dark fermentation, using liquid metabolites as substrates with an initial pH range of 6.5-7.5. Finally, the electron balance and electron transfer efficiency in the new model were analyzed, and the role of AERBC in dark fermentation and chain elongation was investigated. This study provides a new reference for the use of dark-fermented liquid metabolites and cornstalk residue.

Enhancement on photobiological hydrogen production from corn stalk via reducing hydrogen pressure in bioreactors by way of phased decompression schemes

In this project, it was verified that properly reducing the bioreactor hydrogen partial pressure (HPP) could significantly enhance the photo-fermentative hydrogen production (PFHP) by corn stalk. The maximal cumulative hydrogen yield (CHY) of 82.37 mL/g was obtained under full decompression to 0.4 bar, which was 35% higher than that without decompression. To increase CHY and save the pressure control cost, 12-hour, 24-hour and 36-hour decompression schemes were provided, and the optimal decompression phase in fermentation under each scheme was investigated. The 12-hour decompression scheme was suitable for 24-36 h of fermentation; the 24-hour decompression scheme implemented within 12-36 h of fermentation had a more desirable CHY; when adopting the 36-hour decompression scheme, operation during 12-48 h yielded a CHY of 81.70 mL/g that approximated whole process decompression. The strategies of decompression at the appropriate phase of fermentation were innovative, which offered a new option for optimizing PFHP economically.

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

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

Transformation of Agro-Waste into Value-Added Bioproducts and Bioactive Compounds: Micro/Nano Formulations and Application in the Agri-Food-Pharma Sector

The agricultural sector generates a significant amount of waste, the majority of which is not productively used and is becoming a danger to both world health and the environment. Because of the promising relevance of agro-residues in the agri-food-pharma sectors, various bioproducts and novel biologically active molecules are produced through valorization techniques. Valorization of agro-wastes involves physical, chemical, and biological, including green, pretreatment methods. Bioactives and bioproducts development from agro-wastes has been widely researched in recent years. Nanocapsules are now used to increase the efficacy of bioactive molecules in food applications. This review addresses various agri-waste valorization methods, value-added bioproducts, the recovery of bioactive compounds, and their uses. Moreover, it also covers the present status of bioactive micro- and nanoencapsulation strategies and their applications.

Pyrolysis of Aesculus chinensis Bunge Leaves as for Extracted Bio-Oil Material

Biomass rapid pyrolysis technology is easy to implement in continuous production and industrial application, and has become one of the leading technologies in the field of world renewable energy development. Agricultural and forestry waste is an important resource of renewable energy in China. In general, abandoned leaves in forest areas cause serious waste of resources. Its utilization may help to settle the problems of energy deficiency and environment pollution. In this study, Aesculus chinensis Bunge leaves (A. Bunge) are used as the research object to study the pyrolysis and extract. The results showed that there are a lot of bioactive components in A. Bunge leaves extract, including acetamide, 5-hydroxymethylfurfural, R-limonene, d-mannose, and dihydroxyacetone. The active components of A. Bunge leaves supply scientific evidence for the exploration and exploitation of this plant. The pyrolysis products of A. Bunge leaves are rich in organic acids, aldehydes, and ketones, which means that A. Bunge leaves can be used as a crude material for the manufacturing of bio-oil or bio-fuel. The pyrolysis products include batilol, pregnenolone, benzoic acid, butyrolactone, and propanoic acid, which can be used in biological medicine, chemical crude materials, and industrial raw material reagents. Therefore, A. Bunge leaves can be used as a good crude material for bio-oil or biofuel production. Combining A. Bunge leaves and fast pyrolysis methods can effectively solve the problem of forestry and agricultural residues in the future.

Machine learning technology in biohydrogen production from agriculture waste: Recent advances and future perspectives

Agricultural waste biomass has shown great potential to deliver green energy produced by biochemical and thermochemical conversion processes to mitigate future energy crises. Biohydrogen has become more interested in carbon-free and high-energy dense fuels among different biofuels. However, it is challenging to develop models based on experience or theory for precise predictions due to the complexity of biohydrogen production systems and the limitations of human perception. Recent advancements in machine learning (ML) may open up new possibilities. For this reason, this critical study offers a thorough understanding of ML's use in biohydrogen production. The most recent developments in ML-assisted biohydrogen technologies, including biochemical and thermochemical processes, are examined in depth. This review paper also discusses the prediction of biohydrogen production from agricultural waste. Finally, the techno-economic and scientific obstacles to ML application in agriculture waste biomass-based biohydrogen production are summarized.

Elucidating the Role of Biofilm-Forming Microbial Communities in Fermentative Biohydrogen Process: An Overview

Amongst the biofuels described in the literature, biohydrogen has gained heightened attention over the past decade due to its remarkable properties. Biohydrogen is a renewable form of H2 that can be produced under ambient conditions and at a low cost from biomass residues. Innovative approaches are continuously being applied to overcome the low process yields and pave the way for its scalability. Since the process primarily depends on the biohydrogen-producing bacteria, there is a need to acquire in-depth knowledge about the ecology of the various assemblages participating in the process, establishing effective bioaugmentation methods. This work provides an overview of the biofilm-forming communities during H2 production by mixed cultures and the synergistic associations established by certain species during H2 production. The strategies that enhance the growth of biofilms within the H2 reactors are also discussed. A short section is also included, explaining techniques used for examining and studying these biofilm structures. The work concludes with some suggestions that could lead to breakthroughs in this area of research.

Intensification of Acidogenic Fermentation for the Production of Biohydrogen and Volatile Fatty Acids—A Perspective

Utilising ‘wastes’ as ‘resources’ is key to a circular economy. While there are multiple routes to waste valorisation, anaerobic digestion (AD)—a biochemical means to breakdown organic wastes in the absence of oxygen—is favoured due to its capacity to handle a variety of feedstocks. Traditional AD focuses on the production of biogas and fertiliser as products; however, such low-value products combined with longer residence times and slow kinetics have paved the way to explore alternative product platforms. The intermediate steps in conventional AD—acidogenesis and acetogenesis—have the capability to produce biohydrogen and volatile fatty acids (VFA) which are gaining increased attention due to the higher energy density (than biogas) and higher market value, respectively. This review hence focusses specifically on the production of biohydrogen and VFAs from organic wastes. With the revived interest in these products, a critical analysis of recent literature is needed to establish the current status. Therefore, intensification strategies in this area involving three main streams: substrate pre-treatment, digestion parameters and product recovery are discussed in detail based on literature reported in the last decade. The techno-economic aspects and future pointers are clearly highlighted to drive research forward in relevant areas.

Closing of Carbon Cycle by Waste Gasification for Circular Economy Implementation in Poland

Domestic coal and waste resources, which are valuable sources of carbon, can support efforts to transform a linear economy into a circular carbon economy. Their use, as an alternative to conventional, imported fossil resources (crude oil, natural gas) for chemical production, provides an opportunity for Poland to solve problems related to competitiveness, security of supply, and sustainable development in various industries. This is important for Poland because it can provide it with a long-term perspective of economic growth and development, taking into account global trends (e.g., the Paris Agreement) and EU legislation. The article presents a concept to support the transformation from linear toward a circular carbon economy under Polish conditions. The carried-out analyses showed that coal, RDF, and plastic waste fuels can be a valuable source of raw material for the development of the chemical industry in Poland. Due to the assumed availability of plastic waste and the loss of carbon in the production process, coal consumption is estimated at 10 million t/yr, both in the medium- and long-term. In case where coal consumption is reduced and an additional source of ‘green hydrogen’ is used, CO2 emissions could be reduced even by 98% by 2050. The presented results show the technical and economic feasibility of the proposed solution and could be the basis for development of the roadmap for transition of the linear to circular economy under Polish condition.

Sequential Dark-Photo Batch Fermentation and Kinetic Modelling for Biohydrogen Production Using Cheese Whey as a Feedstock

The present work describes the utilisation of cheese whey to produce biohydrogen by sequential dark-photo fermentation. In first stage, cheese whey was fermented by Enterobacter aerogenes 2822 cells in a 2 L double-walled cylindrical bioreactor to produce hydrogen/organic acids giving maximum biohydrogen yield and cumulative hydrogen of 2.43 ± 0.12 mol mol^-1 lactose and 3270 ± 143.5 mL at cheese whey concentration of 105 mM lactose L^-1. The soluble metabolites of dark fermentation when utilised as carbon source for photo fermentation by Rhodobacter sphaeroides O.U.001, the yield, and cumulative hydrogen was increased to 4.22 ± 0.20 mol mol^-1 VFA and 3800 ± 170 mL, respectively. Meanwhile, an overall COD removal of about 38.08% was also achieved. The overall biohydrogen yield was increased from 2.43 (dark fermentation) to 6.65 ± 0.25 mol mol^-1 lactose. Similarly, the modelling for biohydrogen production in bioreactor was done using modified Gompertz equation and Leudeking-Piret model, which gave adequate simulated fitting with the experimental values. The carbon material balance showed that acetic acid, lactic acid, and CO₂ along with microbial biomass were the main by-products of dark fermentation and comprised more than 75% of carbon consumed.