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Microbial alchemy: upcycling of brewery spent grains into high-value products through fermentation
Critical Reviews in Biotechnology
Abstract
Spent grains are one of the lignocellulosic biomasses available in abundance, discarded by breweries as waste. The brewing process generates around 25-30% of waste in different forms and spent grains alone account for 80-85% of that waste, resulting in a significant global waste volume. Despite containing essential nutrients, i.e., carbohydrates, fibers, proteins, fatty acids, lipids, minerals, and vitamins, efficient and economically viable valorization of these grains is lacking. Microbial fermentation enables the valorization of spent grain biomass into numerous commercially valuable products used in energy, food, healthcare, and biomaterials. However, the process still needs more investigation to overcome challenges, such as transportation, cost-effective pretreatment, and fermentation strategy. to lower the product cost and to achieve market feasibility and customer affordability. This review summarizes the potential of spent grains valorization via microbial fermentation and associated challenges.
Spent grain is the solid fraction remaining after wort removal. It is nutritionally rich, composed of fibers—mainly hemicellulose, cellulose, and lignin—proteins, lipids, vitamins, and minerals, and must be managed properly. Spent grain is a by-product with high moisture, high protein and high fiber content and is susceptible to microbial contamination; thus, a suitable, cost-effective, and environmentally friendly valorization method of processing it is required. This by-product is used as a raw material in the production of many other food products—bakery products, pasta, cookies, muffins, wafers, snacks, yogurt or plant-based yogurt alternatives, Frankfurter sausages or fruit beverages—due to its nutritional values. The circular economy is built on waste reduction and the reuse of by-products, which find opportunities in the regeneration and recycling of waste materials and energy that become inputs in other processes and food products. Waste disposal in the food industry has become a major issue in recent years when attempting to maintain hygiene standards and avoid soil, air and water contamination. Fortifying food products with spent grain follows the precepts of the circular bio-economy and industrial symbiosis of strengthening sustainable development. The purpose of this review is to update information on the addition of spent grain to various foods and the influence of spent grain on these foods.
An experiment was conducted to evaluate the inclusion effects of Dried Brewery Spent Grain (DBSG) to know its effect on growth performance and meat quality on poultry. Completely randomized design was used to compare the treatments in five replications. The treatments used were 15% DBSG (T1), 20% DBSG (T2), 25% DBSG (T3), Commercial feed (T4) and (0% DBSG) scavenging bird was used as a control. Each treatment contained 10 birds including 200 chickens in the whole investigation. The major factors body weight, carcasses and organs weight, cholesterol, total protein, albumin, and calcium were evaluated. Results showed that mean body weight of the experimental bird after 60 days was not significantly different (p>0.05) among the dietary treatments, i.e., T1 (781.46 g), T2 (738.36 g), T3 (728.91 g) and T4 (753.38 g). Carcass, breast muscle, thigh, wing, shank, liver and spleen were not significantly different (p>0.05) in weight between DBSG included diet and commercial feed. However, dressing percentage (59.3%) of T4 and gizzard (43.20 gm.) in T3 was significantly higher than other treatments. The significantly higher (p<0.05) amount of cholesterol found in T4 (312.01 mg/dl) followed by control diet (239.46 mg/dl), both of which were above than reference range (129-297 mg/dl). However, in other treatments i.e., T1, T2 and T3, the cholesterol content was in between the reference range. Similarly, same level (p>0.05) of total protein, albumin and calcium content in blood serum observed in BSG included diet and commercial diet. Hence, 15% to 20% inclusion of BSG could be the optimum level in diets of New Hampshire chickens.
This paper explores the transformation of biowastes from food industry and agriculture into high-value products through four examples. The objective is to provide insight into the principles of green transition and a circular economy. The first two case studies focus on the waste generated from the production of widely consumed food items, such as beer and coffee, while the other two examine the potential of underutilized plants, such as burdock and willow, as sources of valuable compounds. Phenolic compounds are the main target in the case of brewer’s spent grain, with p-coumaric acid and ferulic acid being the most common. Lipids are a possible target in the case of spent coffee grounds with palmitic (C16:0) and linoleic (C18:2) acid being the major fatty acids among those recovered. In the case of burdock, different targets are reported based on which part of the plant is used. Extracts rich in linoleic and oleic acids are expected from the seeds, while the roots extracts are rich in sugars, phenolic acids such as chlorogenic, caffeic, o-coumaric, syringic, cinnamic, gentisitic, etc. acids, and, interestingly, the high-value compound epicatechin gallate. Willow is well known for being rich in salicin, but picein, (+)-catechin, triandrin, glucose, and fructose are also obtained from the extracts. The study thoroughly analyzes different extraction methods, with a particular emphasis on cutting-edge green technologies. The goal is to promote the sustainable utilization of biowaste and support the green transition to a more environmentally conscious economy.
Plant protein sources, as a part of developing sustainable food systems, are currently of interest globally. Brewer’s spent grain (BSG) is the most plentiful by-product of the brewing industry, representing ~85% of the total side streams produced. Although nutritionally dense, there are very few methods of upcycling these materials. High in protein, BSG can serve as an ideal raw material for protein isolate production. This study details the nutritional and functional characteristics of BSG protein isolate, EverPro, and compares these with the technological performance of the current gold standard plant protein isolates, pea and soy. The compositional characteristics are determined, including amino acid analysis, protein solubility, and protein profile among others. Related physical properties are determined, including foaming characteristics, emulsifying properties, zeta potential, surface hydrophobicity, and rheological properties. Regarding nutrition, EverPro meets or exceeds the requirement of each essential amino acid per g protein, with the exception of lysine, while pea and soy are deficient in methionine and cysteine. EverPro has a similar protein content to the pea and soy isolates, but far exceeds them in terms of protein solubility, with a protein solubility of ~100% compared to 22% and 52% for pea and soy isolates, respectively. This increased solubility, in turn, affects other functional properties; EverPro displays the highest foaming capacity and exhibits low sedimentation activity, while also possessing minimal gelation properties and low emulsion stabilising activity when compared to pea and soy isolates. This study outlines the functional and nutritional properties of EverPro, a brewer’s spent grain protein, in comparison to commercial plant protein isolates, indicating the potential for the inclusion of new, sustainable plant-based protein sources in human nutrition, in particular dairy alternative applications.
Lignocellulosic materials are valuable resources in today's bioprocess technologies; however, their recalcitrance is a major barrier in industry regarding their conversion to microbial products. For this purpose, in this study, the synthesis of ionic liquids (ILs), its function in the hydrolysis of lignocellulosic materials, its biochemistry and possible toxic effects were investigated. In addition, the bioconversion of lignocellulosic materials pretreated with ionic liquids to biofuels (bioethanol, biobutanol, biogas and hydrogen) and various biochemicals is discussed in detail. For this, the focus is on the potential of ILs for industrial integration and use in large-scale reactors. ILs offer significant advantages due to their potential for ease of use and their features such as recovery and reuse after pretreatment. However, there are economic and technical problems that need to be solved to expand ILs in industrial systems and increase their use potential. To overcome these problems and the usability of ILs technologies in industry, techno-economic analyses has been examined and compared with traditional processes.
Background
Pretreatment is an indispensable stage of the preparation of lignocellulosic biomass with key significance for the effectiveness of hydrolysis and the efficiency of the production of cellulosic ethanol. A significant increase in the susceptibility of the raw material to further degradation can be attained as a result of effective delignification in high-pressure conditions. With this in mind, a method of high-pressure pretreatment using microwave radiation and various solvents (water, 40% w/v NaCS, 1% v/v H2SO4, 1% w/v NaOH or 60% v/v EtOH with an addition of 1% v/v H2SO4) was developed, enabling the acquisition of biomass with an increased susceptibility to the process of enzymatic hydrolysis. The medium obtained in this way can be used for the production of cellulosic ethanol via high-gravity technology (lignocellulosic media containing from 15 to 20% dry weight of biomass). For every type of biomass (pine chips, beech chips and wheat straw), a solvent was selected to be used during the pretreatment, guaranteeing the acquisition of a medium highly susceptible to the process of enzymatic hydrolysis.
Results
The highest efficiency of the hydrolysis of biomass, amounting to 71.14 ± 0.97% (glucose concentration 109.26 ± 3.49 g/L) was achieved for wheat straw subjected to microwave-assisted pretreatment using 40% w/v NaCS. Fermentation of this medium produced ethanol concentration at the level of 53.84 ± 1.25 g/L. A slightly lower effectiveness of enzymatic hydrolysis (62.21 ± 0.62%) was achieved after high-pressure microwave-assisted pretreatment of beech chips using 1% w/v NaOH. The hydrolysate contained glucose in the concentration of 91.78 ± 1.91 g/L, and the acquired concentration of ethanol after fermentation amounted to 49.07 ± 2.06 g/L. In the case of pine chips, the most effective delignification was achieved using 60% v/v EtOH with the addition of 1% v/v H2SO4, but after enzymatic hydrolysis, the concentration of glucose in hydrolysate was lower than in the other raw materials and amounted to 39.15 ± 1.62 g/L (the concentration of ethanol after fermentation was ca. 19.67 ± 0.98 g/L). The presence of xylose and galactose was also determined in the obtained fermentation media. The highest initial concentration of these carbohydrates (21.39 ± 1.44 g/L) was observed in beech chips media after microwave-assisted pretreatment using NaOH. The use of wheat straw after pretreatment using EtOH with an addition of 1% v/v H2SO4 for the preparation of fermentation medium, results in the generation of the initial concentration of galactose and xylose at the level of 19.03 ± 0.38 g/L.
Conclusion
The achieved results indicate a high effectiveness of the enzymatic hydrolysis of the biomass subjected to high-pressure microwave-assisted pretreatment. The final effect depends on the combined use of correctly selected solvents for the different sources of lignocellulosic biomass. On the basis of the achieved results, we can say that the presented method indicates a very high potential in the area of its use for the production of cellulosic ethanol involving high-gravity technology.
The production of biosurfactants (BSs) using acid-hydrolysated brewer’s spent grain (BSG) as carbon source by Rhodotorula mucilaginosa LBP5 yeast was evaluated in this research. BSG was subjected to acid hydrolysis (120 °C for 30 min) to release sugars, which were quantified by high-performance liquid chromatography (HPLC) confirming the presence of arabinose (10 g/L), xylose (25 g/L), glucose (10 g/L), and cellobiose (1.4 g/L). BS production was carried out according to a 2⁴ factorial design under different conditions of temperature, inoculum, BSG concentration, and pH. The concentration of by-products (acetic acid, furfural, and hydroxymethylfurfural) was less than 1.5 g/L. The best condition for BS production was under 31 °C, pH 5.5, inoculum 1.45 g/L (w/v), and 16.1% (m/v) of BSG, considering surface tension (ST) emulsification index as response. Once the best production condition was established, the BS produced by R. mucilaginosa LBP5 showed emulsifying properties (65%), reduced TS to 35 mN/m and stability under extreme conditions of temperature (40–80 °C), pH (4–10), and NaCl (2–8%). The BS was anionic in nature and its functional groups were identified via infrared spectroscopy with Fourier transform (FT-IR), indicating that the BS is possibly of the glycolipid type with a critical micelle concentration of 1.5 g/L. We conclude that BSG was considered a promising carbon source for the production of low-cost BS by R. mucilaginosa LBP5.
Graphical abstract
Ćupter is Herzegovinian candy made of must and flour/semolina. Much research about the incorporation of brewers’ spent grains into the human diet has been published. The purpose of this study was to partially replace semolina (Samples 1 and 2) and flour (Samples 3 and 4) with brewers’ spent grains originating from industrial (Samples 1 and 4) and craft breweries (Samples 2 and 3) and study nutritive, chemical, and preference properties of the product. In this research, the authors aimed to find application of this already proven functional ingredient in ćupter production. Values for pH were higher for all samples compared to the traditional recipe. Samples produced with flour had higher values of water activity (0.86 ± 0.01) and moisture (41.82 ± 1.68 and 41.11 ± 1.41). Ash content increased with BSG addition, but between samples, there were no significant differences. Collected data showed significant differences in fat levels. Higher protein content was measured for Samples 4 (6.60 ± 0.17) and 1 (6.13 ± 0.07). The highest total sugar content was measured for Sample 1. The general appearance for all samples was “moderately like”. Nutritive value was improved with the addition of BSG, but recipes and drying should be modified to improve consumer acceptance.
Quinoa straw is rich in hemicellulose, and it could be hydrolyzed into xylose. It is a promising energy resource alternative that acts as a potential low-cost material for producing xylitol. In this study, quinoa straw was used as a substrate subjected to the hydrolysis of dilute sulfuric acid solution. Based on the production of xylose and inhibitors during hydrolysis, the optimal conditions for the hydrolysis of hemicellulose in quinoa straw were determined. Detoxification was performed via activated carbon adsorption. The optimal detoxification conditions were determined on the basis of major inhibitor concentrations in the hydrolysate. When the addition of activated carbon was 3% at 30 °C for 40 min, the removal of formic acid, acetic acid, furfural, and 5-HMF could reach 66.52%, 64.54%, 88.31%, and 89.44%, respectively. In addition to activated carbon adsorption, vacuum evaporation was further conducted to perform two-step detoxification. Subsequently, the detoxified hydrolysate was used for xylitol fermentation. The yield of xylitol reached 0.50 g/g after 96 h of fermentation by Candida tropicalis (CICC 1779). It is 1.2-fold higher than that obtained through the sole vacuum evaporation method. This study validated the feasibility of xylitol production from quinoa straw via a biorefinery process.
Advanced biofuels can reduce fossil fuel use and the number of harmful compounds released during combustion, by reducing the use of fossil fuels. Lignocellulosic materials, especially waste biomass, are suitable substrates for the production of advanced biofuels. Among the most expensive steps in the production of ethanol is enzyme-based hydrolysis. Using microorganisms can reduce these costs. This study investigated the effectiveness of hydrolyzing three waste lignocellulosic biomass materials (barley straw, oak shavings, spent grains) into ethanol, after biological pretreatment with Trichoderma viride fungi. The number of fermentable sugars obtained from each substrate was subjected to preliminary study, and the correlation between the temperature and fungal activity in the decomposition of lignocellulosic materials was determined. Ethanol was produced by the separate hydrolysis and fermentation (SHF) method. It was found that not all lignocellulosic biomass is suitable to decomposition and hydrolysis in the presence of T. viride. Regardless of the process temperature, the average enzymatic activity of fungi (activity index) ranged from 1.25 to 1.31. 94 mL of distillate, with a 65% (v/v) ethanol concentration produced by the hydrolysis and fermentation of the sugars released from the barley straw.
This work is focused on the development of sustainable process for the valorisation of the main by-product generated in the brewing industry brewer’s spent grain (BSG). A two-step process combining subcritical water treatment and pervaporation (PV) was proposed to hydrolyse the hemicelluloses fraction of this lignocellulosic biomass and further removal/recovery of some of the degradation products of sugars by using two different organophilic membranes polydimethylsiloxane (PDMS) and polyoctilmethylsiloxane (POMS) membranes. Specifically furfural is the dehydration product of pentoses and it is one of the top biomass-based chemicals being an important platform chemical. For synthetic binary mixtures lower total permeation flux but higher enrichment factors for furfural were determined for POMS. When dealing with subW hydrolysates POMS membranes yielded the highest furfural recovery 94.1 % with permeate concentrations as high as 40 g/L. Furthermore it was assessed that PV is a suitable detoxification method that yielded a retentate nearly free of furfural allowing its use as growth media in the opposite to the subW hydrolysate with inhibitory furfural concentrations for microbial bioprocesses.
Industrial beer production generates brewer's spent grains (BSG) as a primary solid waste. The disposal of industrial waste can cause negative environmental side effects, including greenhouse gas emissions. This study evaluated the dry anaerobic digestion (AD) of BSG for bioenergy recovery as a solution toward a more sustainable brewery. The laboratory-scale agitated tank batch reactor (6.8 L) was started up with BSG (25%), mesophilic inoculum (45%), and water (30%). The experimental results showed 82.12% solids biodegradation, 57.38% soluble chemical oxygen demand removal, and an accumulated methane yield of 10.53 L CH4 kg-1 TVS. The methane production efficiency was evaluated by the modified Gompertz, Cone, and first-order kinetic models. The Cone model fitted methane evolution better than the modified Gompertz and first-order kinetic models. The biogas produced from the dry AD of BSG could generate electricity (0.133 MWh ton-1) and heat (598.45 MJ ton-1), mitigating 0.0099 and 0.0335 tCO2eq ton −1 BSG, respectively, for electricity and heat. The implementation of dry AD could supply 7.38% of the electricity and 6.86% of the heat required for beer production. Finally, in a biorefinery concept, dry AD can be an alternative route for solid waste management and bioenergy recovery, contributing to reduce the environmental impact of breweries.
Novel environmentally friendly pretreatments have been developed in recent years to improve biomass fractionation. Solid-state fermentation (SSF) and treatment with ionic liquids show low environmental impact and can be used in biorefinery of biomass. In this work, these processes were assessed with brewery spent grain (BSG). First, BSG was used as a substrate to produce cellulases and xylanases by SSF with the fungi Aspergillus brasiliensis CECT 2700 and Trichoderma reesei CECT 2414. Then, BSG was pretreated with the ionic liquid [N1112OH][Gly] and hydrolyzed with the crude enzymatic extracts. Results showed that SSF of BSG with A. brasiliensis achieved the highest enzyme production; meanwhile, the pretreatment with ionic liquids allowed glucan and xylan fractions to increase and reduce the lignin content. In addition, a mixture of the extracts from both fungi in a ratio of 2.5:0.5 Aspergillus/Trichoderma (v/v) efficiently hydrolyzed the BSG previously treated with the ionic liquid [N1112OH][Gly], reaching saccharification percentages of 80.68%, 54.29%, and 19.58% for glucan, xylan, and arabinan, respectively. In conclusion, the results demonstrated that the BSG biorefinery process developed in this work is an effective way to obtain fermentable sugar-containing solutions, which can be used to produce value-added products.
Decomposition of lignocellulosic plant biomass by four filamentous fungi was carried out to facilitate subsequent anaerobic degradation and biogas formation. Agricultural side products, wheat straw and corn stover and forestry energy plant willow chips were selected as plant biomass sources. The substrates were confronted by pure cultures of Penicillium aurantiogriseum (new isolate from rumen), Trichoderma reesei (DSM768), Gilbertella persicaria (SZMC11086) and Rhizomucor miehei (SZMC11005). In addition to total cellulolytic filter paper degradation activity, the production of endoglucanase, cellobiohydrolase, β-glucosidase enzymes were followed during the pretreatment period, which lasted for 10 days at 37°C. The products of pretreatments were subsequently tested for mesophilic biogas production in batch reactors. All 4 strains effectively pretreated the lignocellulosic substrates albeit in varying degrees, which was related to the level of the tested hydrolytic enzyme activities. Penicillium aurantiogriseum showed outstanding hydrolytic enzyme production and highest biogas yield from the partially degraded substrates. Corn stover was the best substrate for biomass decomposition and biogas production. Scanning electron microscopy confirmed the deep penetration of fungal hyphae into the lignocellulosic substrate in all cases.
On account of its minimal expense and a high potential for change into energy-producing products, lignocellulosic biomass is the future of bioenergy and energy. Notwithstanding, their true capacity is restricted by the utilization of inefficient and unstable enzymes. Therefore, the present work aim to investigate the cellulose degradation potential of two isolated fungal species Aspergillus terreus and Trichoderma harzanium followed by bioethanol production from acid-thermal pre-treated rice straw (RS). The experiments were conducted in two phases. In phase-I of experiments, the isolated cellulose-degrading fungal species (Aspergillus terreus and Trichoderma harzanium) were employed for enzymatic hydrolysis of pretreated RS which was separated into two fractions namely: (Hydrolysate liquid) HL and (Residual pulp) RP. In phase-II of experiments, the enzymatically hydrolyzed substrate was subjected to yeast fermentation for bioethanol production. Using 18S rRNA sequencing, the microbial diversity study of the isolated species is covered in detail. The results revealed that the isolated fungal species A. terreus and T. harzanium resulted in 80 % of cellulose degradation. The highest bioethanol yield of 0.38 and 0.42 g/g of glucose was obtained from HL using Aspergillus terreus and Trichoderma harzanium treatment followed by yeast fermentation. The bioethanol yield of 0.17 g/g of cellulose was obtained from HL using both the fungal species.
Spent brewery grains (BSG) are the main by-product of beer production and are incorporated in rations of food-delivering animals, mainly dairy cows. Like other agricultural commodities, BSG can be contaminated by a broad spectrum of natural and synthetic undesirable substances , which can be hazardous to animal and human health as well as to the environment. The co-occurrence of mycotoxins, phytoestrogens, other fungal and plant secondary metabolites, along with pesticides, was investigated in 21 BSG samples collected in dairy farms in Austria. For this purpose, a validated multi-metabolite liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) was employed. Metabolites derived from Fusarium, Aspergillus, Alternaria and pesticide residues, were ubiquitous in the samples. Zearalenone (ZEN), T-2 and HT-2 toxins were the only regulated mycotoxin detected, albeit at concentrations below the European guidance values for animal feeds. Ergot alkaloids, Penicillium-derived metabolites, and phytoestrogens had occurrence rates of 90, 48 and 29%, respectively. Penicillium metabolites presented the highest levels among the fungal compounds, indicating contamination during storage. Aflatoxins (AFs), ochratoxins and deoxynivalenol (DON) were not detected. Out of the 16 detected pesticides, two fungicides, ametoctradin (9.5%) and mandi-propamid (14.3%) revealed concentrations exceeding their respective maximum residue level (MRL) (0.01 mg kg À1) for barley in two samples. Although based on European guidance and MRL values the levels of the detected compounds probably do not pose acute risks for cattle, the impact of the long-time exposure to such mixtures of natural and synthetic toxicants on animal health and food safety are unknown and must be elucidated. ARTICLE HISTORY
Raw brewers’ spent grain (BSG), a by-product of beer production and produced at a large scale, presents a composition that has been shown to have potential as feedstock for several biological processes, such as polyhydroxyalkanoates (PHAs) production. Although the high interest in the PHA production from waste, the bioconversion of BSG into PHA using microbial mixed cultures (MMC) has not yet been explored. This study explored the feasibility to produce PHA from BSG through the enrichment of a mixed microbial culture in PHA-storing organisms. The increase in organic loading rate (OLR) was shown to have only a slight influence on the process performance, although a high selectivity in PHA-storing microorganisms accumulation was reached. The culture was enriched on various PHA-storing microorganisms, such as bacteria belonging to the Meganema, Carnobacterium, Leucobacter, and Paracocccus genera. The enrichment process led to specialization of the microbiome, but the high diversity in PHA-storing microorganisms could have contributed to the process stability and efficiency, allowing for achieving a maximum PHA content of 35.2 ± 5.5 wt.% (VSS basis) and a yield of 0.61 ± 0.09 CmmolPHA/CmmolVFA in the accumulation assays. Overall, the production of PHA from fermented BSG is a feasible process confirming the valorization potential of the feedstock through the production of added-value products.
The present study reports the mixed culture acidogenic production of biohydrogen and carboxylic acids (CA) from brewery spent grains (BSG) in the presence of high concentrations of cobalt, iron, nickel, and zinc. The metals enhanced biohydrogen output by 2.39 times along with CA biosynthesis by 1.73 times. Cobalt and iron promoted the acetate and butyrate pathways, leading to the accumulation of 5.14 gCOD/L of acetic and 11.36 gCOD/L of butyric acid. The production of solvents (ethanol + butanol) was higher with zinc (4.68 gCOD/L) and cobalt (4.45 gCOD/L). A combination of all four metals further enhanced CA accumulation to 42.98 gCOD/L, thus surpassing the benefits accrued from supplementation with individual metals. Additionally, 0.36 and 0.31 mol green ammonium were obtained from protein‐rich brewery spent grain upon supplementation with iron and cobalt, respectively. Metagenomic analysis revealed the high relative abundance of Firmicutes (>90%), of which 85.02% were Clostridium, in mixed metal‐containing reactors. Finally, a significant correlation of dehydrogenase activity with CA and biohydrogen evolution was observed upon metal addition.
For decades, lignocellulosic biomass has been introduced to the public as the most important raw material for the environmentally and economically sustainable production of high-valued bioproducts by microorganisms. However, due to the strong recalcitrant structure, the lignocellulosic materials have major limitations to obtain fermentable sugars for transformation into value-added products, e.g., bioethanol, biobutanol, biohydrogen, etc. In this review, we analyzed the recent trends in bioenergy production from pretreated lignocellulose, with special attention to the new strategies for overcoming pretreatment barriers. In addition, persistent challenges in developing for low-cost advanced processing technologies are also pointed out, illustrating new approaches to addressing the global energy crisis and climate change caused by the use of fossil fuels. The insights given in this study will enable a better understanding of current processes and facilitate further development on lignocellulosic bioenergy production.
Lignocellulosic biomass (LCB) has the potential to replace fossil fuels, thanks to the concept of biorefinery. This material is formed mainly by cellulose, lignin, and hemicellulose. To maximize the valorization potential of this material, LCB needs to be pretreated. Milling is always performed before any other treatments. It does not produce chemical change and improves the efficiency of the upcoming processes.
Additionally, it makes LCB easier to handle and increases bulk density and transfer phenomena of the next pretreatment step. However, this treatment is energy consuming, so it needs to be optimized. Several mills can be used, and the equipment selection depends on the characteristics of the material, the final size required, and the operational regime: continuous or batch. Among them, ball, knife, and hammer mills are the most used at the laboratory scale, especially before enzymatic or fermentative treatments. The continuous operational regime (knife and hammer mill) allows us to work with high volumes of raw material and can continuously reduce particle size, unlike the batch operating regime (ball mill).
This review recollects the information about the application of these machines, the effect on particle size, and subsequent treatments. On the one hand, ball milling reduced particle size the most; on the other hand, hammer and knife milling consumed less energy. Furthermore, the latter reached a small final particle size (units of millimeters) suitable for valorization.
Brewer’s spent grain (BSG) accounts for approximately 85% of the total mass of solid by-products in the brewing industry and represents an important secondary raw material of future biorefineries. Currently, the main application of BSG is limited to the feed and food industry. There is a strong need to develop sustainable pretreatment and fractionation processes to obtain BSG hydrolysates that enable efficient biotransformation into biofuels, biomaterials, or biochemicals. This paper aims to provide a comprehensive insight into the availability of BSG, chemical properties, and current and potential applications juxtaposed with the existing and emerging markets of the pyramid of bio-based products in the context of sustainable and circular bioeconomy. An economic evaluation of BSG for the production of highly valuable products is presented in the context of sustainable and circular bioeconomy targeting the market of Central and Eastern European countries (BIOEAST region).
The double effect of supercritical carbon dioxide, sc-CO2, in a biorefinery concept applied to brewer’s spent grain (BSG) was assessed in this work. Extraction conditions to remove and valorize the lipophilic fraction were studied (20 – 40 MPa and 40 - 80 °C) obtaining a maximum yield of 5.70 ± 0.07 g /100 gBSG at 80 °C and 40 MPa. High pressures and temperatures resulted in higher content of total phenolic and flavonoid compounds, as well as higher antioxidant capacity. It was observed an improvement of the enzymatic hydrolysis yield by cellulase in the sc-CO2 treated BSG compared to the non-treated. This improvement could be partially attributed to the removal of the lipid fraction and to morphological changes of BSG after sc-CO2. Based on this double benefit, sc-CO2 can play an important role on biomass valorization.
Tamarindus indica is one of the tropical medicinal plants that has been attributed curative potential of numerous diseases by many rural dwellers. This study was designed to evaluate the antioxidant, antibacterial activities and also to determine the various chemical constituents responsible for its pharmacological activities. The methanol extract of Tamarindus indica fruit pulp was analyzed by Gas Chromatography/Mass Spectrometer to determine the volatile compounds present. The antioxidant activities were performed using DPPH and FRAP method and the antibacterial activity was tested against some common pathogens by macro broth dilution method. The GCMS analysis shows the presence of 37 compounds, out of which 14 had their peak area percentages ≥ 1% and only two compounds had no reported pharmacological activities. Most of the bioactive compounds including 5-Hydroxymethylfurfural (31.06%)-3-O-Methyl-d-glucose (16.31%), 1,6-anhydro-β-D-Glucopyranose (9.95%), 5-methyl-Furancarboxaldehyde (3.2%), Triethylenediamine (1.17%), 1-(2-furanyl)-1-Propcanone (2.18%), Methyl 2-furoate (3.14%), Levoglucosenone (3.21%), methyl ester-Hepta-2,4-dienoic acid, (8.85%), 2,3-dihydro-3,5-dihydrox-4H-Pyran-4-one (3.4%), O-α-D-glucopyranosyl-(1.fwdarw.3)-β-D-fructofuranosyl-α-D-Glucopyranoside (2.18%), n-Hexadecanoic acid (1.38%), 2-Heptanol, acetate (1.29%), 5-[(5-methyl-2-fur-2-Furancarboxaldehyde (1.08%), 3-Methyl-2-furoic acid (1.05%) and cis-Vaccenic acid (2.85%)have been reported with different activities such as antibacterial, antifungal, antitubercular, anticancer, antioxidant and other prophylactic activities. The extract demonstrated inhibitory potential against all tested pathogen. However, Plesiomonas shigellosis ATCC 15903 and Bacillus pumillus ATCC 14884 are more sensitive with the MIC of 0.22 and 0.44 mg/ml respectively. The antioxidant activity was relatively low due to the low phenolic content of the extract. This shows that there is a strong correlation between antioxidant activities and phenolic content. GC–MS analysis revealed the presence of bioactive phytoconstituents with various biological activities and this justifies the rationale behind its usage as a curative therapy by many local dwellers.
This study aims to evaluate the financial and economic feasibility of implementing a biorefinery to process the solid waste, called brewers’ spent grain, generated in the production of craft beer into special flour. In addition, to present a path for open innovation in the possibility of replication of the process and technology used in the plant. The inappropriate disposal generates an environmental problem, but individually, depending on the production volume of the brewery, the cost of processing the waste can be unfeasible. On the other hand, such waste embeds a high nutritional value for human food. This study followed the precepts of the circular bio-economy and industrial symbiosis strengthening of sustainable development. The research method is the Monte Carlo simulation, including four different scenarios and projections. The results indicate the financial and economic viability of industrial plants—biorefineries—for the transformation of the residue into special flour in three of the four scenarios studied in the five-year cycle. In the Monte Carlo simulation, no losses are evident in any of the 10,000 interactions. The sensitivity analysis demonstrates that the sensitivity of the supply is slightly higher than the price of the final product. Results may be useful to support the development of new, innovative products relying on collaboration among internal and external partners and open innovation concerns.
The production cost of biodegradable and biobased polymer like polyhydroxybutyrate (PHB) is still higher than that of petroleum-based plastics. A potential solution for reducing its production cost is using a cheap carbon source and medium for PHB production and avoiding a process of sterilization. In this study, we screened a novel PHB-producing microbial strain using sugarcane molasses as the carbon source without sterilization and found Priestia sp. YH4 from the marine environment. Culture conditions, such as carbon, NaCl, temperature, pH, inoculum size, and cultivation time, were optimized for obtaining the highest PHB production by YH4 resulting in 5.94 g/L of dry cell weight (DCW) and 61.7 % of PHB content in the 5 mL culture. In addition, it showed similar PHB production between the cultures with or without sterilization in Marine broth media. When cultured using only tap water, sugarcane molasses, and NaCl in a 5 L fermenter, 24.8 g/L DCW was produced at 41 h yielding 13.9 g/L PHB. Finally, DSC (Differential Scanning Calorimetry) and GPC (Gel Permeation Chromatography) were used to analyze thermal properties and molecular weights resulting in Tm = 167.2 °C, Tc = 67.3 °C, Mw = 2.85 × 105, Mn = 1.05 × 105, and PDI = 2.7, respectively. Therefore, we showed the feasibility of more economical process for PHB production by finding novel strain, utilizing molasses with minimal media components and avoiding sterilization.
Despite its potential as a sustainable feedstock for producing renewable fuels and chemicals, lignocellulosic biomass (LCB) remains largely untapped due to problems associated with its deconstruction and the toxicity of its sugar-rich hydrolysates in microbial conversion processes. Using genetic modification to facilitate inhibitor tolerance, the present study aimed to construct a robust yeast cell factory for cellulosic ethanol bioproduction from non-detoxified LCB. To this effect, two putative nitroreductase genes (KmHBN1 and KmFRM2) hypothesized to be possible mediators of oxidative stress response were separately overexpressed and disrupted in Kluyveromyces marxianus. In contrast to KmFRM2 modified strains (disrupted or overexpressed) with no significant change, the inhibitor tolerance to phenols, furfural, and acetic acid cocktail was improved in YKmHBN1-URA3 strain overexpressing KmHBN1. Although the recombinant KmHBN1 and KmFRM2 had nitroreductase activity, they did not degrade or convert inhibitors. The change of intracellular reactive oxygen species level (ROS) of KmHBN1 disrupted or overexpressed strains indicated that KmHBN1 affected intracellular ROS elimination. Cells with disrupted KmHBN1 failed to respond to ROS created during inhibitor metabolism, and this disruption also led to reduced expression of respiratory chain genes which translates to a decreased inhibitor tolerance. The overexpression of KmHBN1 not only enhanced the ethanol production from glucose in the presence of inhibitors but also improved ethanol productivity (18.75%) from simultaneously-saccharified and co-fermented inhibitor-ladened corn cob. These findings unlock a new pathway for the creation of robust yeast strains to aid in the biorefinery conversion of lignocellulosic feedstock.
For recycling agricultural wastes into the production of biofuel, fermentation technology is currently gaining more attention. Bioethanol is a widely used biofuel, however in industries, the fermentation of hemicellulosic feedstock is challenging since fermenting yeasts consume fewer xylose. To enhance the availability of renewable biofuels, Pioneers are keen to develop industrial strains that assimilate xylose along with glucose. In attempt to eliminate the obstacle, xylanolytic yeast with enhanced xylanase production were investigated. A thermotolerant yeast species, Pichia kudriavzevii strain SVMS2019, isolated from the cow's rumen was studied for xylanase production under solid-state fermentation with simultaneous degradation and saccharification of alkali-treated wheat straw biomass for the liberation of xylose sugars and then conversion into bioethanol. After statistical optimization through response surface methodology, the xylanase enzyme yield was enhanced up to 2.23 fold; the optimum conditions were 30 °C, pH 3.5, 72 h of incubation, and 1.5% of pretreated wheat straw to produce 273.02 IU/ml xylanase activity. The maximum of crude xylanase activity was shown at 50 °C and pH 6. The fermentation of xylose to ethanol by Pichia kudriavzevii SVMS2019, bioethanol was obtained at a maximum of about 3.18% at 42 °C in 72 h intervals. Through the novel source, we have obtained the strain that has a significant of hemicellulosic enzymatic saccharification with 2.23 fold increase in xylanase production yield through statistical optimization and produce bioethanol. While xylanolytic activity of yeast has been optimized, potential benefit of cellulosic hydrolytic activity also need to be studied to achieve the co-utilization of glucose and xylose.
Macroalgae (seaweed) is considered a favorable feedstock for polyhydroxyalkanoates (PHAs) production owing to its high productivity, low land and freshwater requirement, and renewable nature. Among different microbes Halomonas sp. YLGW01 can utilize algal biomass-derived sugars (galactose and glucose) for growth and PHAs production. Biomass-derived byproducts furfural, hydroxymethylfurfural (HMF), and acetate affects Halomonas sp. YLGW01 growth and poly(3-hydroxybutyrate) (PHB) production i.e., furfural > HMF > acetate. Eucheuma spinosum biomass-derived biochar was able to remove 87.9 % of phenolic compounds from its hydrolysate without affecting sugar concentration. Halomonas sp. YLGW01 grows and accumulates a high amount of PHB at 4 % NaCl. The use of detoxified unsterilized media resulted in high biomass (6.32 ± 0.16 g cdm/L) and PHB production (3.88 ± 0.04 g/L) compared to undetoxified media (3.97 ± 0.24 g cdm/L, 2.58 ± 0.1 g/L). The finding suggests that Halomonas sp. YLGW01 has the potential to valorize macroalgal biomass into PHAs and open a new avenue for renewable bioplastic production.
This study evaluated the techno-economic assessment of xylo-oligosaccharides (XOs) production from brewer's spent grains (BSG) in a single and two sequential flow-through subcritical water hydrolysis (SWH) reactors at different temperatures (80–180 °C). The process with a single reactor produced the highest yield (72.83 mg XOs g⁻¹ BSG) at 180 °C. The SWH in two sequential reactors produced up to 52.47 mg XOs g⁻¹ BSG for the process operated at 80 °C followed by 130 °C. The lowest cost of manufacturing (18.36 USD kg⁻¹ XOs) was obtained for the process with two sequential reactors. Although the fixed capital investment was 0.82-fold lower for the process with a single reactor, the gross profit of the process with two sequential reactors was 30% higher, which resulted in a return on investment of 54.26% and a payback of 1.84 years. In conclusion, SWH is a potential eco-friendly process to produce XOs from BSG.
This study reports high gravity fed-batch simultaneous saccharification and fermentation (FB-SSF) of sequentially pretreated sugarcane bagasse (SCB) for enhanced bioethanol by employing multiple inhibitor tolerant Kluyveromyces marxianusJKH5 C60. FB-SSF with intermittent feeding of SCB (total 20% solid loading) and enzyme (total dose of 20 FPU/g) at 6 and 12 h resulted in superior bioethanol production at42 °C. Under optimizedlab-scaleFB-SSF, the maximum ethanoltiter, efficiency and productivities were73.4±1.2 g/L,78% and 3.0 g/L/h, respectively, after 72 h in presence of inhibitors (acetic acid, furfural, and vanillin at 3, 1, and 1 g/L, respectively). Furthermore, pentose rich dilute acid hydrolysate of SCB was subjected to fermentation by Pichia stipitis NCIM 3499, resulting in ethanol titer of 6.8 g/L. Overall ethanol yield during the developed process was 260.1 g/kg native SCB, which proves industrial potential of the developed bioethanol conversion process.
In this study, fourteen types of biochar produced using seven biomasses at temperatures 300 °C and 600 °C were screened for phenolics (furfural and hydroxymethylfurfural (HMF)) removal. Eucheuma spinosum biochar (EB-BC 600) showed higher adsorption capacity to furfural (258.94±3.2 mg/g) and HMF (222.81±2.3 mg/g). Adsorption kinetics and isotherm experiments interpreted that EB-BC 600 biochar followed the pseudo-first-order kinetic and Langmuir isotherm model for both furfural and HMF adsorption. Different hydrolysates were detoxified using EB-BC 600 biochar and used as feedstock for engineered Escherichia coli. An increased polyhydroxyalkanoates (PHA) production with detoxified barley biomass hydrolysate (DBBH: 1.71±0.07 g PHA/L), detoxified miscanthus biomass hydrolysate (DMBH: 0.87±0.03 g PHA/L) and detoxified pine biomass hydrolysate (DPBH: 1.28±0.03 g PHA/L) was recorded, which was 2.8, 6.4 and 3.4 folds high as compared to undetoxified hydrolysates. This study reports the mechanism involved in furfural and HMF removal using biochar and valorization of hydrolysate into PHA.
The gradually increasing need for fossil fuels demands renewable biofuel substitutes. This has fascinated an increasing investigation to design innovative energy fuels that have comparable Physico-chemical and combustion characteristics with fossil-derived fuels. The efficient microbes for bioenergy synthesis desire the proficiency to consume a large quantity of carbon substrate, transfer various carbohydrates through efficient metabolic pathways, capability to withstand inhibitory components and other degradation compounds, and improve metabolic fluxes to synthesize target compounds. Metabolically engineered microbes could be an efficient methodology for synthesizing biofuel from cellulosic biomass by cautiously manipulating enzymes and metabolic pathways. This review offers a comprehensive perspective on the trends and advances in metabolic and genetic engineering technologies for advanced biofuel synthesis by applying various heterologous hosts. Probable technologies include enzyme engineering, heterologous expression of multiple genes, CRISPR-Cas technologies for genome editing, and cell surface display.
Brewer’s Spent Grain (BSG) is the major by-product of the brewing industry. BSG is principally composed of carbohydrates and proteins, with substantial amount of lipids. Presently, BSG usage is restricted to low-grade applications such as ruminant feed or landfills. The high volume, nutrient-rich composition, low cost (€35/ton), abundance, and around the year availability, makes it a promising and renewable feedstock for biorefinery development. The current review begins with beer production process, where BSG is produced. Further, it appraises emerging biotechnological advancements and green processes targeting BSG valorisation ensuring maximal resource recovery. Particularly, it illustrates diverse marketable products obtained by repurposing carbohydrate and protein fraction of BSG using either isolated or cascading approach. We believe that this review will encourage more research groups to work on developing innovative technologies for integrated and holistic valorisation of BSG. Inclusive efforts towards reduced water consumption and waste minimisation is further advocated, which are presently primary challenges associated with beer industry. It will leave a significant imprint on environmental sustainability and pave a way for developing circular bio-based economy.
The recent scenario has witnessed the augmenting demand for energy precursors primarily from renewable ways in respect of the natural environment. The high energy along with the cost-intensive nature of the conventional approaches directed the researchers to find out an effective and promising method that principally uses the microwave for the pretreatment. The formation of heat energy from electromagnetic energy through polar particle rotation would be noted to be the core principle of the aforesaid effective approach. The microwave treatments speed up the destruction of complex structure of the biomass by applying a specific range of heat over the polar parts in a selective manner in the aqueous medium. In this review, the implementation of microwave-assisted green approaches for modeling an integrated circular bioeconomic strategy to potentially use lignocellulosic biomass for bioproducts is discussed.
Hydrogen has gained attention as an alternative source of energy because of its non-polluting nature as on combustion it produces only water. Biological methods are eco-friendly and have benefits in waste management and hydrogen production simultaneously. The use of algal biomass as feedstock in dark fermentation is advantageous because of its low lignin content, high growth rate, and carbon-fixation ability. The major bottlenecks in biohydrogen production are its low productivity and high production costs. To overcome these issues, many advances in the area of biomass pretreatment to increase sugar release, understanding of algal biomass composition, and development of fermentation strategies for the complete recovery of nutrients are ongoing. Recently, mixed substrate fermentation, multistep fermentation, and the use of nanocatalysts to improve hydrogen production have increased. This review article evaluates the current progress in algal biomass pretreatment, key factors, and possible solutions for increasing hydrogen production.
To convert biomass into biofuel, pretreatment is the first stage required to de-structure lignocellulose – twin-screw extrusion is one of the viable pretreatment technologies. The enzymatic hydrolysis of corncobs pretreated with twin-screw extrusion to obtain sugar was evaluated. Corncob extrusion (115–130 °C; 14 rpm) was enhanced through the employment of additives (water and glycerol, 25:25, % w/w). By reproducing the response surface methodology (RSM) technique, the maximized glucose productivity (0.69 g L⁻¹ h⁻¹) and conversion of cellulose to glucose (90.4 % w/w), as well as hemicellulose to xylose and arabinose (44.0 % w/w) were established with the dosage of the commercial enzymatic complex Cellic Ctec2 (32 FPU/gdry lignocellulosic material) and solids loading (17.8 % w/w). Total sugar yield was of 471 kg (glucose 323 kg; xylose and arabinose 148 kg) for a dried corncob ton. Kinetic constants of the Michaelis-Menten model, Vmax and Km, for converting cellulose to glucose were of 6.00 % (w/w)/h and 22.59 gcellulose/Lsolution, respectively. A residue-free and effective corncob extrusion pretreatment enhanced high solids loading enzymatic hydrolysis to achieve a glucose-rich solution.
Lignocellulosic biorefinery based on its sugar-platform has been considered as an efficient strategy to replace fossil fuel-based refinery. In the bioconversion process, pretreatment is an essential step to firstly open up lignocellulose cell wall structure and enhance the accessibility of carbohydrates to hydrolytic enzymes. However, various lignin and/or carbohydrates degradation products (e.g. phenolics, 5-hydroxymethylfurfural, furfural) also generated during pretreatment, which severely inhibit the following enzymatic hydrolysis and the downstream fermentation process. Among them, the lignin derived phenolics have been considered as the most inhibitory compounds and their inhibitory effects are highly dependent on the source of biomass and the type of pretreatment strategy. Although liquid-solid separation and subsequent washing can remove the lignin derived phenolics and other inhibitors, this is undesirable in the realistic industrial application where the whole slurry of pretreated biomass need to be directly used in the hydrolysis process. This review summarizes the phenolics formation mechanism for various commonly applied pretreatment methods and discusses the key factors that affect the inhibitory effect of phenolics on cellulose hydrolysis. In addition, the recent achievements on the rational design of inhibition mitigation strategies to boost cellulose hydrolysis for sugar-platform biorefinery are also introduced. This review also provides guidance for rational design detoxification strategies to facilitate whole slurry hydrolysis which helps to realize the industrialization of lignocellulose biorefinery.
Accelerated solvent extractor (ASE) was used in extraction of proteins from brewers’ spent grain (BSG) using water as solvent in near subcritical conditions (<100 °C, ∼100 bar). Variables in the study were extraction time (20, 60 and 120 min) and NaOH concentration (0.01, 0.05 and 0.1 N) in the extraction solvent. Extractions were performed so that sample in aforementioned conditions was extracted in four different temperatures (21 (RT), 40, 60 and 80 °C). In between each extraction temperature extraction solvent was changed to fresh solvent. Ultrasonic and mild H2SO4 pretreatments of BSG prior alkaline extraction (0.1 N NaOH, 60 min) were also experimented. Dissolved proteins were precipitated from the extracts by adjusting pH to 3, centrifuged and dried. Protein contents in dried precipitates, and in dried residual BSG after the extractions was determined using Kjeldahl method. The combined amount of precipitated proteins from four extractions varied from 21.3 to 65.3% (db) from the total amount of proteins in fresh BSG. Alkaline extraction of H2SO4 pretreated BSG provided the highest, and 0.01 N NaOH as the extraction solvent the lowest proteins yields. Protein contents in the precipitated and dried extracts was more than three times the protein contents in BSG (18.6%) in 16 of the 41 analyzed extracts. Highest protein contents (69.7%) in dried extract was obtained when dried BSG was extracted with 0.05 N NaOH for 60 min at 40 °C. Water-extraction near subcritical conditions was shown to be a promising method to concentrate proteins from BSG with high protein contents and with low chemicals load.
Biomass valorization in converting biomass into value-added products and energy has gained researchers’ attention. In this study, valorization of oil palm empty fruit bunch (OPEFB) towards biofuels production was focused. Combination of deep eutectic solvent (DES) and ultrasonication was employed to pretreat the OPEFB. The pretreatment was conducted in a sonicator at 210 W, 50°C for 30 min. Choline chloride-lactic acid (ChCl-LA) outperformed choline chloride-urea (ChCl-U) and choline chloride-glycerol (ChCl-G) because of its acidity and low viscosity properties. Besides having the highest cellulose digestibility (36.7% of reducing sugars yield), ChCl-LA pretreated biomass had the lowest lignin content of 18.8% and biomass crystallinity of 0.895. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) results further confirmed its biomass disruption ability. Ultrasonic-assisted DES pretreatment exhibited a synergetic effect, whereby the reducing sugars yield was double compared to without ultrasound. Also, its pretreatment performance was better than other pretreatment methods, such as acid, alkaline and steam explosion pretreatments. The DESs were effectively recovered with a slight decrease in delignification and cellulose digestibility efficiencies. These collectively proven the feasibility and effectiveness of ultrasound-assisted DES pretreatment in converting the biomass to sugars, which could be essential for biofuels production.
Xylitol, a five-carbon sugar alcohol, has a steady global market and finds application as a natural sugar substitute in various food and confectionery products. Biocatalytic xylitol production, although touted as a greener alternative to conventional chemical catalysis, suffers from certain challenges, the primary being high cost of production. This study demonstrates a process for food-grade xylitol production from corncob biomass with energy reduction through two major process modifications. A non-conventional fermentation strategy was adopted whereby adjusting aeration without agitation, xylitol with high yield (0.86 ± 0.015 g/g), and productivity (0.74 gL⁻¹h⁻¹) could be produced by a GRAS Pichia caribbica MTCC 5703 strain. Xylitol was recovered from the broth in the form of crystals using a combination of membrane-based filtration and crystallization. The crystals demonstrated ~98 % purity when quantified with ¹H NMR. Oral toxicity analysis of the crystals demonstrated no adverse effect in female Winstar rats (at a loading of 2000 mg/kg body weight of animals). Overall process statistics showed that 0.584 kg of food-grade xylitol crystals could be produced from 3.5 kg of corncob biomass. The two-process modifications during fermentation and xylitol recovery enabled an energy saving of ~20.842 kW/kg of crystals, providing tremendous advantages for biorefinery-based large-scale xylitol production from corncob biomass.
Sphingobium yanoikuyae BBL01 can produce exopolysaccharides (EPS) and polyhydroxyalkanoates (PHAs). The effect of side products (furfural, hydroxymethylfurfural (HMF), vanillin, and acetate) produced during pretreatment of biomass was evaluated on S. yanoikuyae BBL01. It was observed that a certain concentration range (0.01-0.03%) of these compounds can improve growth, EPS production, and polyhydroxybutyrate (PHB) accumulation. The addition of HMF increases glucose and xylose utilization while other side products have a negative effect. The C/N of 5 favors EPS production (3.24±0.05 g/L), while a higher C/N ratio of 30 promotes PHB accumulation (38.7±0.08% w/w) when commercial sugar is used as a carbon source. Pine biomass-derived biochar was able to remove 40±2.1% of total phenolic. Various biomass hydrolysates were evaluated and the use of detoxified pine biomass hydrolysate (DPH) as a carbon source resulted in the higher coproduction of EPS (2.83±0.03 g/L) and PHB (40.8±2.4% w/w).
Biobased products are complete or partial derivatives from naturally occurring/growing materials such as agricultural, plants, and forest materials and serve as an alternative to traditional product derivatives of petroleum. Technically, biobased product counterparts can replace almost every fossil resource-based industrial material. Adopting life cycle analysis and circular economy concepts has also accelerated the move towards biobased products. It meets the criteria for easy recycling and can facilitate the shift from linear fossil-based productions to a greener circular economy. In line with the Renewable and Sustainable Energy Reviews (RSER) policy, this Virtual Special Issue (VSI) published two types of articles, high-quality review papers and original research papers with a strong review component. After a rigorous peer-review process, 32 articles were accepted and published in this VSI. This editorial overview these articles and examines their contribution to the field. This RSER VSI has contributed with new insights on value-added biobased products from various bioresources to their applications, technical challenges and advancement in a sustainable manner.
Urbanization and pollution are the major issues of the current time own to the exhaustive consumption of fossil fuels which have a detrimental effect on the nation's economies and air quality due to greenhouse gas (GHG) emissions and shortage of energy reserves. Algae, an autotrophic organism provides a green substitute for energy as well as commercial products. Algal extracts become an efficient source for bioactive compounds having anti-microbial, anti-oxidative, anti-inflammatory, and anti-cancerous potential. Besides the conventional approach, residual biomass from any algal-based process might act as a renewable substrate for fermentation. Likewise, lignocellulosic biomass, algal biomass can also be processed for sugar recovery by different pre-treatment strategies like acid and alkali hydrolysis, microwave, ionic liquid, and ammonia fiber explosion, etc. Residual algal biomass hydrolysate can be used as a feedstock to produce bioenergy (biohydrogen, biogas, methane) and biochemicals (organic acids, polyhydroxyalkanoates) via microbial fermentation.
Brewers’ spent grains (BSG) account for 85% of the dry raw material used in the brewing process. Pretreatment of BSG may make its organic content more amenable for anaerobic digestion (AD) but at the expense of added energy. This work evaluated ultrasonication (US) of BSG as a pretreatment prior to AD. US + AD produced biogas containing 56% methane, which is 27% greater than the control reactor that did not receive US pretreatment. The US pretreatment increased the methane yield (107.28 L CH4 kg⁻¹ TVS) in 4-fold higher when compared with the AD reactor without pretreatment (26.72 L CH4 kg⁻¹ TVS). AD and US + AD energy recovery routes were assessed for: (i) electric, and thermal energy recovery, and (ii) production of biomethane for vehicular use. The US + AD system could generate 0.23 MWh t⁻¹ BSG of electrical energy and 1.2 × 10³ MJ t⁻¹ BSG of thermal energy. AD without pretreatment generates 0.15 MWh t⁻¹ BSG of electrical energy and 0.79 × 10³ MJ t⁻¹ BSG of thermal energy. The energy required for US pretreatment was estimated as 0.29 MWh t⁻¹, while the theoretical electric energy generation was 0.23 MWh t⁻¹. Accordingly, US pretreatment generates sufficient electrical energy to offset most of the energy it consumes, with net co-production of thermal energy for on-site use with additional heat surplus. From an environmental perspective, the AD process potentially avoids greenhouse gases emissions of 0.056 tCO2eq t⁻¹ BSG, and the US + AD process could avoid 0.083 tCO2eq t⁻¹ BSG if the thermal energy from biogas is used to offset the use of natural gas for heating. Finally, AD produces green energy that contributes to brewery decarbonization, and US pretreatment combined with AD has promise for meeting all the thermal energy needs of a low-carbon brewery.