Utilization of distillery wastewater for hydrogen production in one-stage and two-stage processes involving photofermentation

Sustainable Production of Biofuels and Biochemicals via Electro-Fermentation Technology

The energy crisis and climate change are two of the most concerning issues for human beings nowadays. For that reason, the scientific community is focused on the search for alternative biofuels to conventional fossil fuels as well as the development of sustainable processes to develop a circular economy. Bioelectrochemical processes have been demonstrated to be useful for producing bioenergy and value-added products from several types of waste. Electro-fermentation has gained great attention in the last few years due to its potential contribution to biofuel and biochemical production, e.g., hydrogen, methane, biopolymers, etc. Conventional fermentation processes pose several limitations in terms of their practical and economic feasibility. The introduction of two electrodes in a bioreactor allows the regulation of redox instabilities that occur in conventional fermentation, boosting the overall process towards a high biomass yield and enhanced product formation. In this regard, key parameters such as the type of culture, the nature of the electrodes as well as the operating conditions are crucial in order to maximize the production of biofuels and biochemicals via electro-fermentation technology. This article comprises a critical overview of the benefits and limitations of this emerging bio-electrochemical technology and its contribution to the circular economy.

A mini review on microwave and contemporary based biohydrogen production technologies: a comparison

Hydrogen gas, along with conventional fossil fuels, has been used as a green fuel with enormous potential. Due to the rapid depletion of fossil fuels, a new dimension of hydrogen production technology has arrived to reduce reliance on nonrenewable energy sources. Microwave-based hydrogen production is a more promising and cost-effective technology than other existing green hydrogen production methods such as fermentation and gasification. Microwave heating may be superior to traditional heating due to several advantages such as less power consumption compared to other methods, higher yield, and a higher rate of conversion. Compared to another process for hydrogen production, the microwave-driven process worked efficiently at lower temperatures by providing more than 70% yield. The process of production can be optimized by using properly sized biomass, types of biomass, water flow, temperature, pressure, and reactor size. This method is the most suitable, attractive, and efficient technique for hydrogen production in the presence of a suitable catalyst. Hot spots formed by microwave irradiation would have a substantial impact on the yield and properties of microwave-processed goods. The current techno-economic situation of various technologies for hydrogen production is discussed here, with cost, efficiency, and durability being the most important factors to consider. The present review shows that a cost-competitive hydrogen economy will necessitate continual efforts to increase performance, scale-up, technical prospects, and political backing.

Coriolus versicolor laccase-based inorganic protein hybrid synthesis for application in biomass saccharification to enhance biological production of hydrogen and ethanol

In this study, a bio-friendly inorganic protein hybrid-based enzyme immobilization system using partially purified Coriolus versicolor laccase (CvLac) was successfully applied to biomass hydrolysis for the enhancement of sugar production aimed at generating biofuels. After four days of incubation, the maximum CvLac production was achieved at 140 U/mg of total protein in the presence of inducers such as copper and wheat bran after four days of incubation. Crude CvLac immobilized through inorganic protein hybrids such as nanoflowers (NFs) using zinc as Zn3(PO4)2/CvLac hybrid NFs (Zn/CvLac-NFs) showed a maximum encapsulation yield of 93.4% and a relative activity of 265% compared to free laccase. The synthesized Zn/CvLac-NFs exhibited significantly improved activity profiles and stability compared to free enzymes. Furthermore, Zn/CvLac-NFs retained a significantly high residual activity of 96.2% after ten reuse cycles. The saccharification of poplar biomass improved ∼2-fold in the presence of Zn/CvLac-NFs, with an 8-fold reduction in total phenolics compared to the control. The Zn/CvLac-NFs treated biomass hydrolysate showed high biological hydrogen (H2) production and ethanol conversion efficiency of up to 2.68 mol/mol of hexose and 79.0% compared to the control values of 1.27 mol of H2/mol of hexose and 58.4%, respectively. The CvLac hybrid NFs are the first time reported for biomass hydrolysis, and a significant enhancement in the production of hydrogen and ethanol was reported. The synthesis of such NFs based on crude forms of diverse enzymes can potentially be extended to a broad range of biotechnological applications.

Light-dependent biohydrogen production: Progress and perspectives

The fourth industrial revolution anticipates energy to be sustainable, renewable and green. Hydrogen (H₂) is one of the green forms of energy and is deemed a possible solution to climate change. Light-dependent H₂ production is a promising method derived from nature's most copious resources: solar energy, water and biomass. Reduced environmental impacts, absorption of carbon dioxide, relative efficiency, and cost economics made it an eye-catching approach. However, low light conversion efficiency, limited ability to utilize complex carbohydrates, and the O₂ sensitivity of enzymes result in low yield. Isolation of efficient H₂ producers, development of microbial consortia having a synergistic impact, genetically improved strains, regulating bidirectional hydrogenase activity, physiological parameters, immobilization, novel photobioreactors, and additive strategies are summarized for their possibilities to augment the processes of bio-photolysis and photo-fermentation. The challenges and future perspectives have been addressed to explore a sustainable way forward in a bio-refinery approach.

Enhanced photo-fermentative biohydrogen production from biowastes: An overview

Clean energy like hydrogen can be a promising strategy to solve problems of global warming. Photo-fermentation (PF) is an attractive technology for producing biohydrogen from various biowastes cost-effectively and environmentally friendly. However, challenges of low light conversion efficiency and small yields of biohydrogen production still limit its application. Thus, advanced strategies have been investigated to enhance photo-fermentative biohydrogen production. This review discusses advanced technologies that show positive outcomes in improving biohydrogen production by PF, including the following. Firstly, genetic engineering enhances light transfer efficiency, change the activity of enzymes, and improves the content of ATP, ammonium and antibiotic tolerance of photosynthetic bacteria. Secondly, immobilization technology is refined. Thirdly, nanotechnology makes great strides as a scientific technique and fourthly, integration of dark and photo-fermentation technology is possible. Some suggestions for further studies to achieve high levels of efficiency of photo-fermentative biohydrogen production are mentioned in this paper.

Investigating and modelling the effect of light intensity on Rhodopseudomonas palustris growth

Photosynthetic bacteria can be useful biotechnological tools - they produce a variety of valuable products, including high purity hydrogen, and can simultaneously treat recalcitrant wastewaters. However, while photobioreactors have been designed and modelled for photosynthetic algae and cyanobacteria, there has been less work on understanding the effect of light in photosynthetic bacterial fermentations. In order to design photobioreactors, and processes using these organisms, robust models of light penetration, utilisation and conversion are needed. This article uses experimental data from a tubular photobioreactor designed to focus in on light intensity effects, to model the effect of light intensity on the growth of Rhodopseudomonas palustris, a model photosynthetic bacterium. The work demonstrates that growth is controlled by light intensity, and that this organism does experience photolimitation below 200 W/m2 and photoinhibition above 600 W/m2. This has implications for outdoor applications, as there will be low growth during the periods of limited light, and growth may be inhibited during the light intensive hours of mid-day. Further, the work presents a model for light penetration in cylindrical photobioreactors, which tends to be the most common geometry. The model developed showed good fit to the experimental data for each light intensity investigated, with high R2 values and NRMSE values all below 20%. The work extends the modelling tools for these organisms, and will allow for better photobioreactor design, and the integration of modelling tools in designing processes which use photosynthetic bacteria. This article is protected by copyright. All rights reserved.

Valorization of Distillery Stillage for Bioenergy Production: A Review

In alcohol distilleries, the amount of distillery stillage generated can be up to 15 times larger than the amount of alcohol produced. The stillage has high concentrations of organics and nitrogen, a low pH, and a dark brown color. Currently, stillage is mainly used for soil fertilization. For this purpose, it requires thickening and is used seasonally, which creates storage problems and transport costs. To reduce environmental pollution, physicochemical and biological processes have been employed for the treatment of distillery stillage. However, according to bioeconomy principles, the stillage should be transformed into value-added products. Therefore, this review paper focuses on methods of stillage processing that enable energy recovery. Due to its high content of organic compounds, stillage is often used as a raw material for biogas production. Accordingly, anaerobic digestion of stillage is discussed, including an overview of the bioreactors used and the effects of operational parameters on organics removal and biogas production. The necessity of integrating anaerobic stillage treatment with other treatment processes is presented. As complex compounds that are present in the stillage (mainly polyphenols and melanoidin) are difficult to biodegrade and have antibacterial activities, the effect of their recovery on biogas production is described. Next, the possibility of converting distillery stillage to bioethanol and biohydrogen is presented. In addition, bioelectrochemical treatment of distillery stillage using microbial fuel cells is discussed. For all these treatment methods, current challenges and opportunities are given.

Current trends for distillery wastewater management and its emerging applications for sustainable environment

Ethanol distillation generates a huge volume of unwanted chemical liquid known as distillery wastewater. Distillery wastewater is acidic, dark brown having high biological oxygen demand, chemical oxygen demand, contains various salt contents, and heavy metals. Inadequate and indiscriminate disposal of distillery wastewater deteriorates the quality of the soil, water, and ultimately groundwater. Its direct exposure via food web shows toxic, carcinogenic, and mutagenic effects on aquatic-terrestrial organisms including humans. So, there is an urgent need for its proper management. For this purpose, a group of researchers applied distillery wastewater for fertigation while others focused on its physico-chemical, biological treatment approaches. But until now no cutting-edge technology has been proposed for its effective management. So, it becomes imperative to comprehend its toxicity, treatment methods, and implication for environmental sustainability. This paper reviews the last decade's research data on advanced physico-chemical, biological, and combined (physico-chemical and biological) methods to treat distillery wastewater and its reuse aspects. Finally, it revealed that the combined methods along with the production of value-added products are one of the best options for distillery wastewater management.

Food Waste Biorefinery: Pathway towards Circular Bioeconomy

Food waste biorefineries for the production of biofuels, platform chemicals and other bio-based materials can significantly reduce a huge environmental burden and provide sustainable resources for the production of chemicals and materials. This will significantly contribute to the transition of the linear based economy to a more circular economy. A variety of chemicals, biofuels and materials can be produced from food waste by the integrated biorefinery approach. This enhances the bioeconomy and helps toward the design of more green, ecofriendly, and sustainable methods of material productions that contribute to sustainable development goals. The waste biorefinery is a tool to achieve a value-added product that can provide a better utilization of materials and resources while minimizing and/or eliminating environmental impacts. Recently, food waste biorefineries have gained momentum for the production of biofuels, chemicals, and bio-based materials due to the shifting of regulations and policies towards sustainable development. This review attempts to explore the state of the art of food waste biorefinery and the products associated with it.

A comparative review on clean hydrogen production from wastewaters

This paper provides a unique review of hydrogen production methods with wastewater treatment to depict a clean and sustainable approach. Various methods for hydrogen production from wastewaters are identified and discussed with recent details by discussing the critical challenges, opportunities, and future directions. Five main performance sectors are considered in detail for each hydrogen production method of the recent case studies, including economic, environmental, social, technical, and reliability. Eight hydrogen production methods are reviewed, including anaerobic method, photo fermentation, dark fermentation, electrolysis, electrodialysis, photocatalysis, photoelectrochemical methods, and super water gasification. A comparative assessment of six reviewed methods for hydrogen production, including environmental, economic, energetic, and exergetic impacts, is evaluated. The comparative assessment results indicate that dark fermentation technology is the most economical method, and it is followed by microbial electrolysis and photofermentation. The most environmentally friendly method for the lowest global warming potential (GWP) is the microbial electrolysis method, and it is followed by photocatalysis and photoelectrochemical methods. Furthermore, the highest energy and exergy efficiencies have been recorded for the microbial electrolysis to be 68% and 64.7%, respectively.

Purple phototrophic bacteria for resource recovery: Challenges and opportunities

Sustainable development is driving a rapid focus shift in the wastewater and organic waste treatment sectors, from a "removal and disposal" approach towards the recovery and reuse of water, energy and materials (e.g. carbon or nutrients). Purple phototrophic bacteria (PPB) are receiving increasing attention due to their capability of growing photoheterotrophically under anaerobic conditions. Using light as energy source, PPB can simultaneously assimilate carbon and nutrients at high efficiencies (with biomass yields close to unity (1 g COD_biomass·g COD_removed^-1)), facilitating the maximum recovery of these resources as different value-added products. The effective use of infrared light enables selective PPB enrichment in non-sterile conditions, without competition with other phototrophs such as microalgae if ultraviolet-visible wavelengths are filtered. This review reunites results systematically gathered from over 177 scientific articles, aiming at producing generalized conclusions. The most critical aspects of PPB-based production and valorisation processes are addressed, including: (i) the identification of the main challenges and potentials of different growth strategies, (ii) a critical analysis of the production of value-added compounds, (iii) a comparison of the different value-added products, (iv) insights into the general challenges and opportunities and (v) recommendations for future research and development towards practical implementation. To date, most of the work has not been executed under real-life conditions, relevant for full-scale application. With the savings in wastewater discharge due to removal of organics, nitrogen and phosphorus as an important economic driver, priorities must go to using PPB-enriched cultures and real waste matrices. The costs associated with artificial illumination, followed by centrifugal harvesting/dewatering and drying, are estimated to be 1.9_, 0.3-2.2 and 0.1-0.3 $·kg_{dry biomass}^-1. At present, these costs are likely to exceed revenues. Future research efforts must be carried out outdoors, using sunlight as energy source. The growth of bulk biomass on relatively clean wastewater streams (e.g. from food processing) and its utilization as a protein-rich feed (e.g. to replace fishmeal, 1.5-2.0 $·kg^-1) appears as a promising valorisation route.

Photosynthetic bacteria-based technology is a potential alternative to meet sustainable wastewater treatment requirement?

A paradigm shift is underway in wastewater treatment from pollution removal to resource or energy recovery. However, conventional activated sludge (CAS) as the core technology of wastewater treatment is confronted with severe challenges on high energy consumption, sludge disposal and inevitable greenhouse gas emission, which are posing a serious impact on the current wastewater industry. It is urgent to find new alternative methods to remedy these defects. Photosynthetic bacteria (PSB) have flexible metabolic modes and high tolerance, which enhance the removal of nutrients, heavy metals and organic contaminants efficiency in different wastewater. The unique phototrophic growth of PSB breaks the restriction of nutrient metabolism in the CAS system. Recent studies have shown that PSB-based technologies can not only achieve the recovery of nutrient and energy, but also improve the degradation efficiency of refractory substances. If the application parameters can be determined, there will be great prospects and economic effects. This review summarizes the research breakthroughs and application promotion of PSB-based wastewater treatment technology in recent years. Comparing discussed the superiority and inferiority from the perspective of application range, performance differences and recovery possibility. Pathways involved in the nutrient substance and the corresponding influencing parameters are also described in detail. The mode of PSB biodegradation processes presented a promising alternative for new wastewater treatment scheme. In the future, more mechanical and model studies, deterministic operating parameters, revolutionary process design is need for large-scale industrial promotion of PSB-based wastewater treatment.

Waste based hydrogen production for circular bioeconomy: Current status and future directions

The present fossil fuel-based energy sector has led to significant industrial growth. On the other hand, the dependence on fossil fuels leads to adverse impact on the environment through releases of greenhouse gases. In this scenario, one possible substitute is biohydrogen, an eco-friendly energy carrier as high-energy produces. The substrates rich in organic compounds like organic waste/wastewater are very useful for improved hydrogen generation through the dark fermentation. Thus, this review article, initially, the status of biohydrogen production from organic waste and various strategies to enhance the process efficiency are concisely discussed. Then, the practical confines of biohydrogen processes are thoroughly discussed. Also, alternate routes such as multiple process integration approach by adopting biorefinery concept to increase overall process efficacy are considered to address industrial-level applications. To conclude, future perspectives besides with possible ways of transforming dark fermentation effluent to biofuels and biochemicals, which leads to circular bioeconomy, are discussed.

Biomolecules from municipal and food industry wastes: An overview

Biological wastes generated from food and fruit processing industries, municipal markets, and water treatment facilities are a major cause of concern for Health Departments and Environmentalists around the world. Conventional means of managing these wastes such as transportation, treatment, and disposal, are proving uneconomical. The need is to develop green and sustainable technologies to circumvent this ever-growing and persistent problem. In this article, the potential of diverse microbes to metabolize complex organic rich biowastes into a variety of bioactive compounds with diverse biotechnological applications have been presented. An integrated strategy has been proposed that can be commercially exploited for the recovery of value-adding products ranging from bioactive compounds, chemical building blocks, energy rich chemicals, biopolymers and materials, which results in a self-sustaining circular bioeconomy with nearly zero waste generation and complete degradation.

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.