Waste biorefinery towards a sustainable circular bioeconomy: a solution to global issues

Recovery of green phenolic compounds from lignin-based source: Role of ferulic acid esterase towards waste valorization and bioeconomic perspectives

The production of chemicals/products so far relies on fossil-based resources with the creation of several environmental problems at the global level. In this situation, a sustainable and circular economy model is necessitated to mitigate global environmental issues. Production of biowaste from various processing industries also creates environmental issues which would be valorized for the production of industrially important reactive and bioactive compounds. Lignin acts as a vital part in biowaste composition which can be converted into a wide range of phenolic compounds. The phenolic compounds have attracted much attention, owing to their influence on diverse not only organoleptic parameters, such as taste or color, but also active agents for active packaging systems. Crop residues of varied groups, which are an affluent source of lignocellulosic biomass could serve as a renewable resource for the biosynthesis of ferulic acid (FA). FA is obtained by the FA esterase enzyme action, and it can be further converted into various tail end phenolic flavor green compounds like vanillin, vanillic acid and hydroxycinnamic acid. Lignin being renewable in nature, processing and management of biowastes towards sustainability is the need as far as the global industrial point is concerned. This review explores all the approaches for conversion of lignin into value-added phenolic compounds that could be included to packaging applications. These valorized products can exhibit the antioxidant, antimicrobial, cardioprotective, anti-inflammatory and anticancer properties, and due to these features can emerge to incorporate them into production of functional foods and be utilization of them at active food packaging application. These approaches would be an important step for utilization of the recovered bioactive compounds at the nutraceutical and food industrial sectors.

Resilience towards organic load and activated sludge variations in co-fermentation for carboxylic acid production

Two perturbations were investigated in acidogenic co-fermentation of waste activated sludge (WAS) and food waste in continuous mesophilic fermenters: increasing the organic loading rate (OLR) and changing the WAS. A control reactor maintained an OLR of 11 gVS/(L·d), while a test reactor had a prolonged OLR change to 18 gVS/(L·d). For each OLR, two WAS were studied. The change in OLR led to differentiated fermentation product profile without compromising the fermentation yields (∼300 mgCOD/gVS). At 11 gVS/(L·d), the product profile was dominated by acetic, butyric, and propionic acids while at 18 gVS/(L·d) it shifted to acetic acid, ethanol, and caproic acid. Reverting the OLR also reverted the fermentation profile. The biomass immigration with the WAS changed the fermentation microbial structure and introduced acetic acid-consuming methanogens, which growth was only delayed by the OLR increase. Microbial monitoring and post-fermentation tests can be used for early detection of acetic acid-consuming events.

Applications of the Methylotrophic Yeast Komagataella phaffii in the Context of Modern Biotechnology

Komagataella phaffii (formerly Pichia pastoris) is a methylotrophic yeast widely used in laboratories around the world to produce recombinant proteins. Given its advantageous features, it has also gained much interest in the context of modern biotechnology. In this review, we present the utilization of K. phaffii as a platform to produce several products of economic interest such as biopharmaceuticals, renewable chemicals, fuels, biomaterials, and food/feed products. Finally, we present synthetic biology approaches currently used for strain engineering, aiming at the production of new bioproducts.

Eco-friendly and safe alternatives for the valorization of shrimp farming waste

The seafood industry generates waste, including shells, bones, intestines, and wastewater. The discards are nutrient-rich, containing varying concentrations of carotenoids, proteins, chitin, and other minerals. Thus, it is imperative to subject seafood waste, including shrimp waste (SW), to secondary processing and valorization for demineralization and deproteination to retrieve industrially essential compounds. Although several chemical processes are available for SW processing, most of them are inherently ecotoxic. Bioconversion of SW is cost-effective, ecofriendly, and safe. Microbial fermentation and the action of exogenous enzymes are among the significant SW bioconversion processes that transform seafood waste into valuable products. SW is a potential raw material for agrochemicals, microbial culture media, adsorbents, therapeutics, nutraceuticals, and bio-nanomaterials. This review comprehensively elucidates the valorization approaches of SW, addressing the drawbacks of chemically mediated methods for SW treatments. It is a broad overview of the applications associated with nutrient-rich SW, besides highlighting the role of major shrimp-producing countries in exploring SW to achieve safe, ecofriendly, and efficient bio-products.

Lignocellulosic materials valorization in second generation biorefineries: an opportunity to produce fungal biopigments

Second generation biorefineries play an important role in the production of renewable energy and fuels, utilizing forest and agro-industrial residues and by-products as raw materials. The integration of novel bioproducts, such as: xylitol, β-carotene, xylooligosaccharides, and biopigments into the biorefinery's portfolio can offer economic benefits in the valorization of lignocellulosic materials, particularly cellulosic and hemicellulosic fractions. Fungal biopigments, known for their additional antioxidant and antimicrobial properties, are appealing to consumers and can have applications in various industrial sectors, including food and pharmaceuticals. The use of lignocellulosic materials as carbon and nutrient sources for the growth medium helps to reduce production costs, increasing the competitiveness of fungal biopigments in the market. In addition, the implementation of biopigment production in biorefineries allows the utilization of underutilized fractions, such as hemicellulose, for value-added bioproducts. This study deals with the potential of fungal biopigments production in second generation biorefineries in order to diversify the produced biomolecules together with energy generation. A comprehensive and critical review of the recent literature on this topic has been conducted, covering the major possible raw materials, general aspects of second generation biorefineries, the fungal biopigments and their potential for incorporation into biorefineries.

Highly efficient and reusable CuAu nanoparticles supported on crosslinked chitosan hydrogels as a plasmonic catalyst for nitroarene reduction

The synthesis of CuAu-based monometallic (MNPs) and bimetallic nanoparticles (BNPs) supported on chitosan-based hydrogels for their application as catalysts is presented. The hydrogels consisted of chitosan chains cross-linked with tripolyphosphate (TPP) in the form of beads with an approximate average diameter of 1.81 mm. The MNPs and BNPs were obtained by the adsorption of metallic ions and their subsequent reduction with hydrazine, achieving a metallic loading of 0.297 mmol per gram of dry sample, with average nanoparticle sizes that were found between 2.6 and 4.4 nm. Both processes, metal adsorption and the stabilization of the nanoparticles, are mainly attributed to the participation of chitosan hydroxyl, amine and amide functional groups. The materials revealed important absorption bands in the visible region of the light spectra, specifically between 520 and 590 nm, mainly attributed to LSPR given the nature of the MNPs and BNPs inside the hydrogels. Subsequently, the hydrogels were evaluated as catalysts against the reduction of 4-nitrophenol (4NP) into 4-aminophenol (4AP), followed by UV-visible spectroscopy. The kinetic advance of the reaction revealed important improvements in the catalytic activity of the materials by synergistic effect of BNPs and plasmonic enhancement under visible light irradiation, given the combination of metals and the light harvesting properties of the nanocomposites. Finally, the catalytic performance of hydrogels containing BNPs CuAu 3:1 showed an important selectivity, recyclability and reusability performance, due to the relevant interaction of the BNPs with the chitosan matrix, highlighting the potential of this nanocomposite as an effective catalyst, with a potential environmental application.

High cell density sequential batch fermentation for enhanced propionic acid production from glucose and glycerol/glucose mixture using Acidipropionibacterium acidipropionici

BACKGROUND

Propionic acid fermentation from renewable feedstock suffers from low volumetric productivity and final product concentration, which limits the industrial feasibility of the microbial route. High cell density fermentation techniques overcome these limitations. Here, propionic acid (PA) production from glucose and a crude glycerol/glucose mixture was evaluated using Acidipropionibacterium acidipropionici, in high cell density (HCD) batch fermentations with cell recycle. The agro-industrial by-product, heat-treated potato juice, was used as N-source.

RESULTS

Using 40 g/L glucose for nine consecutive batches yielded an average of 18.76 ± 1.34 g/L of PA per batch (0.59 gPA/gGlu) at a maximum rate of 1.15 gPA/L.h, and a maximum biomass of 39.89 gCDW/L. Succinic acid (SA) and acetic acid (AA) were obtained as major by-products and the mass ratio of PA:SA:AA was 100:23:25. When a crude glycerol/glucose mixture (60 g/L:30 g/L) was used for 6 consecutive batches with cell recycle, an average of 35.36 ± 2.17 g/L of PA was obtained per batch (0.51 gPA/gC-source) at a maximum rate of 0.35 g/L.h, and reaching a maximum biomass concentration of 12.66 gCDW/L. The PA:SA:AA mass ratio was 100:29:3. Further addition of 0.75 mg/L biotin as a supplement to the culture medium enhanced the cell growth reaching 21.89 gCDW/L, and PA productivity to 0.48 g/L.h, but also doubled AA concentration.

CONCLUSION

This is the highest reported productivity from glycerol/glucose co-fermentation where majority of the culture medium components comprised industrial by-products (crude glycerol and HTPJ). HCD batch fermentations with cell recycling are promising approaches towards industrialization of the bioprocess.

Environmental impacts of valorisation of crude glycerol from biodiesel production - A life cycle perspective

Biodiesel production produces significant quantities of impure crude glycerol as a by-product. Recent increases in the global biodiesel production have led to a surplus of crude glycerol, rendering it a waste. As a result, different methods for its valorisation are currently being investigated. This paper assesses the life cycle environmental impacts of an emerging technology for purification of crude glycerol - a multi-step physico-chemical treatment - in comparison to incineration with energy recovery commonly used for its disposal. For the former, three different acids (H3PO4, H2SO4 and HCl) are considered for the acidification step in the purification process. The results suggest that the H2SO4-based treatment is the best option with 17 net-negative impacts out of the 18 categories considered; this is due to system credits for the production of purified glycerol, heat and potassium salts. In comparison to incineration with energy recovery, the H2SO4-based process has lower savings for the climate change impact (-311 versus -504 kg CO2 eq./t crude glycerol) but it performs better in ten other categories. Sensitivity analyses suggest that that the impacts of the physico-chemical treatment are highly dependent on crude glycerol composition, allocation of burdens to crude glycerol and credits for glycerol production. For example, treating crude glycerol with lower glycerol content would increase all impacts except climate change and fossil depletion due to the higher consumption of chemicals and lower production of purified glycerol. Considering crude glycerol as a useful product rather than waste and allocating to it burdens from biodiesel production would increase most impacts significantly, including climate change (22-40 %), while fossil depletion, freshwater and marine eutrophication would become net-positive. The findings of this research will be of interest to the biodiesel industry and other industrial sectors that generate crude glycerol as a by-product.

Environmental impact scenarios of organic fraction municipal solid waste treatment with Black Soldier Fly larvae based on a life cycle assessment

Biowaste treatment with Black Soldier Fly (BSF) larvae is an alternative option for organic waste valorization. Its environmental impacts should be assessed and compared with conventional treatment options. The research aims to evaluate the treatment of organic fraction of municipal solid waste (OFMSW) with BSF larvae through a life cycle assessment (LCA). This study employed data inventories from literature and aimed to provide a wide range of production parameter values to identify the potentialities of BSF treatment in the best-case and worst-case scenarios. The SimaPro9, the database Ecoinvent3.5, and the impact assessment method IMPACT 2002+ have been employed for the analysis. A sensitivity analysis of relevant parameters was conducted, considering the avoided impacts that can be obtained thanks to the exploitation of larvae proteins for bioplastics or fishmeal production. Research findings highlight six main environmental impact indicators: respiratory inorganics (kg PM2.5-eq), ozone layer depletion (kg CFC-11-eq), terrestrial ecotoxicity (kg TEG soil), land occupation (m2 organic arable), global warming (kg CO2-eq), and non-renewable energy (MJ primary). The most relevant process generating impacts is BSF breeding, followed by boiling, storage, and OFMSW treatment. The environmental performance is better when the conventional fishmeal substituted, thanks to BSF larvae production, is made from areas 10,000 km far, implementing a 100% renewable energy scenario, reducing the energy consumption by 50%, increasing the lifespan of the equipment to 15 years, and products are employed locally. The current study represents the first attempt to evaluate the global higher or lower environmental impact scenario related to OFMSW treatment through BSF larvae.

Algae-Based Biopolymers for Batteries and Biofuel Applications in Comparison with Bacterial Biopolymers-A Review

Algae-based biopolymers can be used in diverse energy-related applications, such as separators and polymer electrolytes in batteries and fuel cells and also as microalgal biofuel, which is regarded as a highly renewable energy source. For these purposes, different physical, thermochemical, and biochemical properties are necessary, which are discussed within this review, such as porosity, high temperature resistance, or good mechanical properties for batteries and high energy density and abundance of the base materials in case of biofuel, along with the environmental aspects of using algae-based biopolymers in these applications. On the other hand, bacterial biopolymers are also often used in batteries as bacterial cellulose separators or as biopolymer network binders, besides their potential use as polymer electrolytes. In addition, they are also regarded as potential sustainable biofuel producers and converters. This review aims at comparing biopolymers from both aforementioned sources for energy conversion and storage. Challenges regarding the production of algal biopolymers include low scalability and low cost-effectiveness, and for bacterial polymers, slow growth rates and non-optimal fermentation processes often cause challenges. On the other hand, environmental benefits in comparison with conventional polymers and the better biodegradability are large advantages of these biopolymers, which suggest further research to make their production more economical.

A Drug Discovery Approach to a Reveal Novel Antioxidant Natural Source: The Case of Chestnut Burr Biomass

Currently, many environmental and energy-related problems are threatening the future of our planet. In October 2022, the Worldmeter recorded the world population as 7.9 billion people, estimating that there will be an increase of 2 billion by 2057. The rapid growth of the population and the continuous increase in needs are causing worrying conditions, such as pollution, climate change, global warming, waste disposal, and natural resource reduction. Looking for novel and innovative methods to overcome these global troubles is a must for our common welfare. The circular bioeconomy represents a promising strategy to alleviate the current conditions using biomass-like natural wastes to replace commercial products that have a negative effect on our ecological footprint. Applying the circular bioeconomy concept, we propose an integrated in silico and in vitro approach to identify antioxidant bioactive compounds extracted from chestnut burrs (an agroforest waste) and their potential biological targets. Our study provides a novel and robust strategy developed within the circular bioeconomy concept aimed at target and drug discovery for a wide range of diseases. Our study could open new frontiers in the circular bioeconomy related to target and drug discovery, offering new ideas for sustainable scientific research aimed at identifying novel therapeutical strategies.

Enhanced ethanol production from paper sludge waste under high-solids conditions with industrial and cellulase-producing strains of Saccharomyces cerevisiae

Reported ethanol titres from hydrolysis-fermentation of the degraded fibres in paper sludge (PS) waste, generally obtained under fed-batch submerged conditions, can be improved through fermentation processes at high solids loadings, as demonstrated in the present study with two industrial PS wastes at enzyme dosages appropriate for solids loadings up to 40% (w/w). The industrial yeast,Saccharomyces cerevisiaestrain Ethanol Red®, was compared to two genetically engineeredS. cerevisiaestrains, namely Cellusec® 1.0 and Cellusec® 2.0, capable of xylose utilisation, and xylose utilisation and cellulase production, respectively. High-solids batch fermentations were conducted in 3 L horizontal rotating reactors and ethanol titres of 100.8 and 73.3 g/L were obtained for virgin pulp and corrugated recycle PS, respectively, at 40% (w/w) solids loading using Ethanol Red®. Xylose utilisation by Cellusec® 1.0 improved ethanol titres by up to 10.3%, while exogenous cellulolytic enzyme requirements were reduced by up to 50% using cellulase-producing Cellusec® 2.0.

Effect of K+ and Ca2+ Cations on Structural Manganese(IV) Oxide for the Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

The promising influences of K+ and Ca2+ ions in the development of effective MnO2 for the selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid (FDCA) were studied for the catalytic performance under a high-pressure reaction of aqueous O2 (0.5 MPa) in a basic system. Various oxidation states of manganese in MnO2 were able to accelerate the oxidation of 5-formyl-2-furancarboxylic acid to FDCA in the rate-determining step. The results were in good agreement that Ca2+ played a key role in the highest FDCA yield up to 85% due to the associated cations on the local coordination to enhance the high surface area and the electronic effect on the manganese ion. Both K-MnO2 and Ca-MnO2 catalysts showed excellent catalytic activities without a significant change in the efficiency in the reusability experiments.

Innovative production of value-added products using agro-industrial wastes via solid-state fermentation

The prevalence of organic solid waste worldwide has turned into a problem that requires comprehensive treatment on all fronts. The amount of agricultural waste generated by agro-based industries has more than triplet. It not only pollutes the environment but also wastes a lot of beneficial biomass resources. These wastes may be utilized as a different option/source for the manufacturing of many goods, including biogas, biofertilizers, biofuel, mushrooms and tempeh as the primary ingredients in numerous industries. Utilizing agro-industrial wastes as good raw materials may provide cost reduction and lower environmental pollution levels. Agro-industrial wastes are converted into biofuels, enzymes, vitamin supplements, antioxidants, livestock feed, antibiotics, biofertilizers and other compounds via solid-state fermentation (SSF). By definition, SSF is a method used when there is little to no free water available. As a result, it permits the use of solid materials as biotransformation substrates. Through SSF methods, a variety of microorganisms are employed to produce these worthwhile things. SSFs are therefore reviewed and discussed along with their impact on the production of value-added items. This review will provide thorough essential details information on recycling and the use of agricultural waste.

Upcycling of food waste streams to valuable biopigments pyocyanin and 1-hydroxyphenazine

Phenazines, including pyocyanin (PYO) and 1-hydroxyphenazine (1-HP) are extracellular secondary metabolites and multifunctional pigments of Pseudomonas aeruginosa responsible for its blue-green color. These versatile molecules are electrochemically active, involved in significant biological activities giving fitness to the host, but also recognized as antimicrobial and anticancer agents. Their wider application is still limited partly due to the cost of carbon substrate for production, which can be solved by the utilization of carbon from food waste within the biorefinery concept. In this study, a variety of food waste streams (banana peel, potato peel, potato washing, stale bread, yoghurt, processed meat, boiled eggs and mixed canteen waste) was used as sole nutrient source in submerged cultures of P. aeruginosa BK25H. Stale bread was identified as the most suitable substrate to support phenazine biopigments production and bacterial growth. This was further increased in 5-liter fermenter when on average 5.2 mg L-1 of PYO and 4.4 mg L-1 of 1-HP were purified after 24 h batch cultivations from the fermentation medium consisting of homogenized stale bread in tap water. Purified biopigments showed moderate antimicrobial activity, and showed different toxicity profiles, with PYO not being toxic against Caenorhabditis elegans, a free-living soil nematode up to 300 µg mL-1 and 1-HP showing lethal effects at 75 µg mL-1. Therefore, stale bread waste stream with minimal pretreatment should be considered as suitable biorefinery feedstock, as it can support the production of valuable biopigments such as phenazines.

Supercharging carbohydrate-binding module alone enhances endocellulase thermostability, binding, and activity on cellulosic biomass

Lignocellulosic biomass recalcitrance to enzymatic degradation necessitates high enzyme loadings incurring large processing costs for industrial-scale biofuels or biochemicals production. Manipulating surface charge interactions to minimize non-productive interactions between cellulolytic enzymes and plant cell wall components (e.g., lignin or cellulose) via protein supercharging has been hypothesized to improve biomass biodegradability, but with limited demonstrated success to date. Here we characterize the effect of introducing non-natural enzyme surface mutations and net charge on cellulosic biomass hydrolysis activity by designing a library of supercharged family-5 endoglucanase Cel5A and its native family-2a carbohydrate binding module (CBM) originally belonging to an industrially relevant thermophilic microbe Thermobifida fusca . A combinatorial library of 33 mutant constructs containing different CBM and Cel5A designs spanning a net charge range of -52 to 37 was computationally designed using Rosetta macromolecular modelling software. Activity for all mutants was rapidly characterized as soluble cell lysates and promising mutants (containing mutations either on the CBM, Cel5A catalytic domain, or both CBM and Cel5A domains) were then purified and systematically characterized. Surprisingly, often endocellulases with mutations on the CBM domain alone resulted in improved activity on cellulosic biomass, with three top-performing supercharged CBM mutants exhibiting between 2-5-fold increase in activity, compared to native enzyme, on both pretreated biomass enriched in lignin (i.e., corn stover) and isolated crystalline/amorphous cellulose. Furthermore, we were able to clearly demonstrate that endocellulase net charge can be selectively fine-tuned using protein supercharging protocol for targeting distinct substrates and maximizing biocatalytic activity. Additionally, several supercharged CBM containing endocellulases exhibited a 5-10 °C increase in optimal hydrolysis temperature, compared to native enzyme, which enabled further increase in hydrolytic yield at higher operational reaction temperatures. This study demonstrates the first successful implementation of enzyme supercharging of cellulolytic enzymes to increase hydrolytic activity towards complex lignocellulosic biomass derived substrates.

Nutrient recovery from municipal solid waste leachate in the scope of circular economy: Recent developments and future perspectives

Holistically considering the current situation of the commercial synthetic fertilizer (CSF) market, recent global developments, and future projection studies, dependency on CSFs in agricultural production born significant risks, especially to the food security of foreign-dependent countries. The foreign dependency of countries in terms of CSFs can be reduced by the concepts such as the circular economy and resource recovery. Recently, waste streams are considered as a source in order to produce recovery-based fertilizers (RBF). RBFs produced from different waste streams can be substituted with CSFs as input for agricultural applications. Municipal solid waste leachate (MSWL) is one of the waste streams that have a high potential for RBF production. Distribution of the published papers over the years shows that this potential was noticed by more researchers in the millennium. MSWL contains a remarkable amount of nitrogen and phosphorus which are the main nutrients required for agricultural production. These nutrients can be recovered with many different methods such as microalgae cultivation, chemical precipitation, ammonia stripping, membrane separation, etc. MSWL can be generated within the different phases of municipal solid waste (MSW) management. Although it is mainly composed of landfill leachate (LL), composting plant leachate (CPL), incineration plant leachate (IPL), and transfer station leachate (TSL) should be considered as potential sources to produce RBF. This study compiles studies conducted on MSWL from the perspective of nitrogen and phosphorus recovery. Moreover, recent developments and limitations of the subject were extensively discussed and future perspectives were introduced by considering the entire MSW management. Investigated studies in this review showed that the potential of MSWL to produce RBF is significant. The outcomes of this paper will serve the countries for ensuring their food security by implementing the resource recovery concept to produce RBF. Thus, the risks born with the recent global developments could be overcome in this way besides the positive environmental outcomes of resource recovery.

Production of single-component cellulose-based hydrogel and its utilization as adsorbent for aqueous contaminants

The growing concern for the environment has resulted in renewed interest in bio-based resources. This study aims to produce a hydrogel adsorbent from cellulose and examine its adsorption performance. In pursuit of this goal, we report a simple one-pot synthesis of cellulose acetate sulfate (CAS), followed by the formation of CAS hydrogels and their subsequent adsorption performances. The CAS includes both hydrophilic and hydrophobic functional groups, enable the formation of a single-component hydrogel through intermolecular interactions in deionized water. The thermal reversibility of CAS hydrogels makes them easily processable into various shapes. The durability of the CAS hydrogel adsorbents can be improved by introducing divalent cations (e.g., Ca²⁺), which create ionically crosslinked hydrogels. The ionically a crosslinked CAS hydrogel adsorbent exhibits a maximum adsorption capacity of 245 mg/g for methylene blue (MB) at 23 °C and a pH of 7. The adsorption behavior of MB on the CAS hydrogel follows both the pseudo-second-order model and the Langmuir adsorption isotherm model. Furthermore, the CAS hydrogel adsorbent maintains a 70 % removal ratio after five cycles. The simplicity of synthesis and hydrogel formation opens up new possibilities for producing and utilizing cellulose-based hydrogels as adsorbents for aqueous contaminants.

Perceiving biobased plastics as an alternative and innovative solution to combat plastic pollution for a circular economy

Plastic waste from fossil-based sources, including single-use packaging materials, is continuously accumulating in landfills, and leaching into the environment. A 2021 UN Environment Programme (UNEP) report suggests that the plastic pollution is likely to be doubled by 2030, posing a major challenge to the environment and the overall global plastic waste management efforts. The use of biobased plastics such as polyhydroxyalkanoates (PHAs) as a biodegradable substitute for petroleum-based plastics could be a feasible option to combat this issue which may further result in much lower carbon emissions and energy usage in comparison to conventional plastics as additional advantages. Though recent years have seen the use of microbes as biosynthetic machinery for biobased plastics, using various renewable feedstocks, the scaled-up production of such materials is still challenging. The current study outlays applications of biobased plastics, potential microorganisms producing biobased plastics such as Cupriavidus necator, Bacillus sp., Rhodopseudomonas palustris, microalgae, and mixed microbial cultures, and inexpensive and renewable resources as carbon substrates including industrial wastes. This review also provides deep insights into the operational parameters, challenges and mitigation, and future opportunities for maximizing the production of biobased plastic products. Finally, this review emphasizes the concept of biorefinery as a sustainable and innovative solution for biobased plastic production for achieving a circular bioeconomy.

Xylose isomerase from Piromyces sp. E2 is a promiscuous enzyme with epimerase activity

Xylose isomerase catalyzes the isomerization of D-xylose to D-xylulose with promiscuous activity for other saccharides including D-glucose, D-allose, and L-arabinose. The xylose isomerase from the fungus Piromyces sp. E2 (PirE2_XI) is used to engineer xylose usage by the fermenting yeast Saccharomyces cerevisiae, but its biochemical characterization is poorly understood with divergent catalytic parameters reported. We have measured the kinetic parameters of the PirE2_XI and analyzed its thermostability and pH-dependence towards different substrates. The PirE2_XI shows promiscuous activity towards D-xylose, D-glucose, D-ribose and L-arabinose with variable effects depending on different divalent ions and epimerizes D-xylose at C3 to produce D-ribulose in a substrate/product dependent ratio. The enzyme follows Michaelis-Menten kinetics for the substrates used and although K_M values for D-xylose are comparable at 30 and 60 °C, the k_cat/K_M is three-fold greater at 60 °C. The purified PirE2_XI shows maximal activity at 65 °C in the pH range of 6.5-7.5 and is a thermostable enzyme, maintaining full activity over 48 h at 30 °C or 12 h at 60 °C. This is the first report demonstrating epimerase activity of the PirE2_XI and its ability to isomerize D-ribose and L-arabinose, and provides a comprehensive in vitro study of substrate specificity, effect of metal ions and temperature on enzyme activity and these findings advance the knowledge of the mechanism of action of this enzyme.

From trash to treasure: Sourcing high-value, sustainable cellulosic materials from living bioreactor waste streams

The appreciation of how conventional and fossil-based materials could be harmful to our planet is growing, especially when considering single-use and non-biodegradable plastics manufactured from fossil fuels. Accordingly, tackling climate change and plastic waste pollution entails a more responsible approach to sourcing raw materials and the adoption of less destructive end-of-life pathways. Livestock animals, in particular ruminants, process plant matter using a suite of mechanical, chemical and biological mechanisms through the act of digestion. The manure from these "living bioreactors" is ubiquitous and offers a largely untapped source of lignocellulosic biomass for the development of bio-based and biodegradable materials. In this review, we assess recent studies made into manure-based cellulose materials in terms of their material characteristics and implications for sustainability. Despite the surprisingly diverse body of research, it is apparent that progress towards the commercialisation of manure-derived cellulose materials is hindered by a lack of truly sustainable options and robust data to assess the performance against conventional materials alternatives. Nanocellulose, a natural biopolymer, has been successfully produced by living bioreactors and is presented as a candidate for future developments. Life cycle assessments from non-wood sources are however minimal, but there are some initial indications that manure-derived nanocellulose would offer environmental benefits over traditional wood-derived sources.

Valorization of Food Waste Slurry as Potential Candidate for Lipid Accumulation: A Concept of Oleaginous Bio-Refinery

In the current state of huge waste production and energy crisis, there is a need to find additional alternate energy resources and options for waste management. The present study was designed to measure the potential of different fruit wastes to serve as substrate for lipid accumulation in oleaginous bacteria. For this purpose, three novel bacterial strains (AF3, KM1 and KM10) isolated from the crude oil samples were systematically compared for their lipid accumulation potential using three types of waste including orange waste (OW), mango waste (MW) and apple waste (AW). Using waste as sole substrate, it was observed that maximum lipid accumulation by each strain was above 20%, which confirms that the bacteria belong to the oleaginous group. However, each bacterial isolate represented differential accumulative capacity with varying organic matter removal efficiency. Maximum lipid accumulation was achieved by KM10 (>25%) with AW as substrate, and KM1 (>24%) with MW as substrate; however, AF3 represented only 21% lipid accumulation using AW as substrate. Similarly, the maximum removal efficiency was recorded for KM10 in AW, followed by OW, where >60% and >50% of volatile solids (VS) removal, respectively, were achieved over the period of 7 days of incubation. This showed that the oleaginous strains also exhibit excellent waste treatment efficiency. The 16s RNA gene sequencing results showed that these KM1 and KM10 strains were Serratia surfactantfaciens and Serratia liquefaciens. In the end, a circular economy model was presented to highlight the significance of the mechanisms, which offers dual benefits over the linear economy model. Overall, the findings of the present study revealed that the novel oleaginous strains not only provide considerable lipid accumulation, but are simultaneously capable of low-cost waste treatment.

Carbon capture by macroalgae Sarcodia suae using aquaculture wastewater and solar energy for cooling in subtropical regions

Rapid growth in the aquaculture industry and corresponding increases in nutrient and organic carbon levels in coastal regions can lead to eutrophication and increased greenhouse gas emissions. Macroalgae are the organisms primarily responsible for the capture of CO₂ and removal of nutrients from coastal waters. In the current study, we developed a novel wastewater treatment system in which the red macroalga, Sarcordia suae, is used to capture CO₂ under thermostatic conditions in subtropical regions. In 2020 (without temperature control), the carbon capture rate (CCR) of Sarcordia suae varied considerably with the season: winter/spring (2.1-3.9 g-C m^-2 d^-1) and summer (0.09 g-C m^-2 d^-1). In 2021, solar powered cooling reduced summer seawater temperatures from 31 to 33 °C to 23-25 °C with a corresponding increase in the mean CCR: winter/spring (2-7 g-C m^-2 d^-1) and summer (1.33 g-C m^-2 d^-1). The proposed aquaculture wastewater system proved highly efficient in removing nitrogen (20.7 mg-N g^-1 DW d^-1, DW = dry weight) and phosphorus (4.4 mg-P g^-1 DW d^-1). Furthermore, the high density of Sarcodia (1.10 ± 0.03 g cm^-3) would permit the harvesting and subsequent dumping of Sarcodia in deep off-shore waters. This study demonstrated a low-cost land-based seaweed cultivation system for capturing CO₂ and excess nutrients from aquaculture wastewater year-round under temperature controlled environments in subtropical regions.

Utilization of agricultural waste biomass and recycling toward circular bioeconomy

The major global concern on energy is focused on conventional fossil resources. The burning of fossil fuels is an origin of greenhouse gas emissions resulting in the utmost threat to the environment and subsequently which leads to global climate changes. As far as sustainability is concerned, fuels and materials derived from organic or plant wastes overcome this downside establishing the solution to the fossil resource crisis. In this context, exploration of agricultural residue appears to be a suitable alternative of non-renewable resources to support the environmental feasibility and meet the high energy crisis. The use of agricultural waste as a feedstock for the biorefinery approach emerges to be an eco-friendly process for the production of biofuel and value-added chemicals, intensifying energy security. Therefore, a prospective choice of this renewable biomass for the synthesis of green fuel and other green biochemicals comes up with a favorable outcome in terms of cost-effectiveness and sustainability. Exploiting different agricultural biomass and exploring various biomass conversion techniques, biorefinery generates bioenergy in a strategic way which eventually fits in a circular bioeconomy. Sources and production of agricultural waste are critically explained in this paper, which provides a path for further value addition by various technologies. Biorefinery solutions, along with a life cycle assessment of agricultural waste biomass toward a wide array of value-added products aiding the bioeconomy, are summarized in this paper.

Strategies for enhancing the efficacy of anaerobic digestion of food industry wastewater: An insight into bioreactor types, challenges, and future scope

Food waste have become a growing concern worldwide with raising population and economic growth. Wastewater discharged from food industries contains many valuable and toxic components that have a negative impact on the ecological system. Large amounts of wastewater are discharged from the food industry, which necessitates the creation of effective technologies. Wastewater from the food industry can be seen as a rich source of energy and a primary source for generating valuable products. Waste disposal and resource recovery are sustainably valued by anaerobic digestion of wastewater from the food sector. The characteristics, composition, and nature of wastewater produced from various food sectors are elaborated upon in this review. An overview of the anaerobic digestion process for wastewater treatment in the food industry is included. Enhancement strategies for the anaerobic digestion process have been discussed in detail. In addition, various types of reactors utilized for performing anaerobic digestion is illustrated. Though anaerobic digestion process possesses advantages, the challenges and future scope are examined for improving the outcome.

Biorefinery and sustainability for the production of biofuels and value-added products: A trends analysis based on network and patent analysis

Biorefineries are modern mechanisms used for producing value-added products and biofuels from different biomass sources. However, a crucial challenge is to achieve a sustainable model for their adequate implementation. Challenges related to technical efficiency and economic feasibility are two of the most relevant problems. Therefore, the present study sought to determine the current trends in basic research and technological development around biorefining and sustainability. We carried out a co-occurrence analysis and a patent analysis using data obtained from the Scopus and Lens databases to provide a general overview of the current state of this area of knowledge. The co-occurrence analysis intends to provide an overview of biorefining and sustainability based on terms associated with these two concepts as a starting point to determine the progress and existing challenges of the field. The results of the patent analysis consisted in identifying the main technological sectors, applicants, and territories where inventions associated with biorefining are registered. The analysis of the information showed that bioeconomy, techno-economic aspects, circular economy, technical issues associated with biomass production, and biofuels represent the focal point of basic research in a wide range of disciplines. Technology development is focused on fermentation, enzymes, and microorganisms, among other areas, which shows the validity of these traditional techniques in addressing the problems faced by the bioeconomy. This scenario shows that developed economies are the driving force behind this area of knowledge and that the PCT system is fundamental for the protection and commercialization of these inventions in places different from where they originated. Furthermore, the challenge lies in learning to work in alternative and complementary technological sectors, beyond microbiology and enzyme applications, in pursuit of the sector's technical and economic feasibility.

Subcritical water pretreatment enhanced methane-rich biogas production from the anaerobic digestion of brewer's spent grains

ABSTRACTThis study evaluated the effectiveness of a semi-continuous flow-through subcritical water hydrolysis (SWH) pretreatment of brewer's spent grains (BSG) for subsequent application in the anaerobic digestion (AD) process. BSG pretreatment was conducted at 160 °C and 15 MPa with a flow rate of 10 mL water min-1 and 15 g water g-1 BSG. The results revealed that SWH attacked the hemicellulose structure, releasing arabinose (46.54 mg g-1) and xylose (39.90 mg g-1) sugars, and proteins (34.89 mg g-1). The start-up of anaerobic reactors using pretreated BSG (747.71 L CH4 kg-1 TVS) increased the methane yield compared with the reactor without pretreatment (53.21 L CH4 kg-1 TVS). For the process with pretreatment, the generation of electricity (134 kWh t-1 BSG) and heat (604 MJ t-1) are responsible for the mitigation of 43.90 kg CO2 eq t-1 BSG. The adoption of SWH as an eco-friendly pretreatment of biomass for AD could be a technological route to increase methane-rich biogas and bioenergy production, supporting the circular economy transition by reducing the carbon footprint of the beer industry.

Recent Update on anaerobic digestion of paddy straw for biogas production: Advancement, limitation and recommendations

At present, development and production of advanced green energy sources are highly demanded, and this may offer a clean and sustainable environment to our modern society. In this reference, biogas is emerging as a promising green energy source and seems to have high potential to replace fossil-fuel based energy sources in the coming future. Further, lignocellulosic biomass (LCB) based biogas production technology has been found to be highly promising owing to several advantages associated therewith. Rich inorganic content, renewable nature, huge availability and low-cost are the key beneficial factors of LCB-based feedstock l to produce biogas. Among the varieties of LCB, paddy straw is one of the most demanding feedstocks and is highly rich in organic compounds that are imperative to producing biogas. Nevertheless, it is noticed that paddy straw as a waste material is usually disposed-off by direct burning, whereas it exhibits low natural digestibility due to the presence of high lignin and silica content which causes severe environmental pollution. On the other hand, paddy straw can be a potential feedstock to produce biogas through anaerobic digestion. Therefore, based on the current ongoing research studies worldwide, this review evaluates the advancements made in the AD process. Meanwhile, existing limitations and future recommendations to improve the yield and productivity of the biogas using paddy straw have been discussed. The emphasis has also been given to various operational parameters developments, related shortcomings, and strategies to improve biogas production at pilot scale.

Parametric optimization of the production of cellulose nanocrystals (CNCs) from South African corncobs via an empirical modelling approach

In this study, cellulose nanocrystals (CNCs) were obtained from South African corncobs using an acid hydrolysis process. The delignification of corncobs was carried out by using alkali and bleaching pretreatment. Furthermore, the Box-Behnken Design (BBD) was used as a design of experiment (DOE) for statistical experimentations that will result in logical data to develop a model that explains the effect of variables on the response (CNCs yield). The effects (main and interactive) of the treatment variables (time, temperature, and acid concentration) were investigated via the response methodology approach and the obtained model was used in optimizing the CNCs yield. Surface morphology, surface chemistry, and the crystallinity of the synthesized CNC were checked using scanning electron microscopy (SEM), a Fourier Transform Infra-red spectroscopy (FTIR), and an X-ray diffraction (XRD) analysis, respectively. The SEM image of the raw corncobs revealed a smooth and compact surface morphology. Results also revealed that CNCs have higher crystallinity (79.11%) than South African waste corncobs (57.67%). An optimum yield of 80.53% CNCs was obtained at a temperature of 30.18 °C, 30.13 min reaction time, and 46 wt% sulfuric acid concentration. These optimized conditions have been validated to confirm the precision. Hence, the synthesized CNCs may be suitable as filler in membranes for different applications.

Valorization of leftover green tea residues through conversion to bioactive peptides using probiotics-aided anaerobic digestion

Bioactive peptides (BPs) are protein fragments that benefit human health. To assess whether leftover green tea residues (GTRs) can serve as a resource for new BPs, we performed in silico proteolysis of GTRs using the BIOPEP database, revealing a wide range of BPs embedded in GTRs. Comparative genomics and the percentage of conserved protein analyses enabled us to select a few probiotic strains for GTR hydrolysis. The selected probiotics digested GTRs anaerobically to yield GTR-derived peptide fractions. To examine whether green tea (GT) peptide fractions could be potential mediators of host-microbe interactions, we comprehensively screened agonistic and antagonistic activities of 168 human G protein-coupled receptors (GPCRs). NanoLC-MS/MS analysis and thin-layer chromatography allowed the identification of peptide sequences and the composition of glycan moieties in the GTRs. Remarkably, GT peptide fractions produced by Lactiplantibacillus plantarum APsulloc 331261, a strain isolated from GT, showed a potent-binding activity for P2RY6, a GPCR involved in intestinal homeostasis. Therefore, this study suggests the potential use of probiotics-aided GTR hydrolysates as postbiotic BPs, providing a biological process for recycling GTRs from agro-waste into renewable resources as health-promoting BPs.

Advances in Komagataella phaffii Engineering for the Production of Renewable Chemicals and Proteins

The need for a more sustainable society has prompted the development of bio-based processes to produce fuels, chemicals, and materials in substitution for fossil-based ones. In this context, microorganisms have been employed to convert renewable carbon sources into various products. The methylotrophic yeast Komagataella phaffii has been extensively used in the production of heterologous proteins. More recently, it has been explored as a host organism to produce various chemicals through new metabolic engineering and synthetic biology tools. This review first summarizes Komagataella taxonomy and diversity and then highlights the recent approaches in cell engineering to produce renewable chemicals and proteins. Finally, strategies to optimize and develop new fermentative processes using K. phaffii as a cell factory are presented and discussed. The yeast K. phaffii shows an outstanding performance for renewable chemicals and protein production due to its ability to metabolize different carbon sources and the availability of engineering tools. Indeed, it has been employed in producing alcohols, carboxylic acids, proteins, and other compounds using different carbon sources, including glycerol, glucose, xylose, methanol, and even CO2.

Rhodotorula sp.-based biorefinery: a source of valuable biomolecules

The development of an effective, realistic, and sustainable microbial biorefinery depends on several factors, including as one of the key aspects an adequate selection of microbial strain. The oleaginous red yeast Rhodotorula sp. has been studied as one powerful source for a plethora of high added-value biomolecules, such as carotenoids, lipids, and enzymes. Although known for over a century, the use of Rhodotorula sp. as resource for valuable products has not yet commercialized. Current interests for Rhodotorula sp. yeast have sparked from its high nutritional versatility and ability to convert agro-food residues into added-value biomolecules, two attractive characteristics for designing new biorefineries. In addition, as for other yeast-based bioprocesses, the overall process sustainability can be maximized by a proper integration with subsequent downstream processing stages, for example, by using eco-friendly solvents for the recovery of intracellular products from yeast biomass. This review intends to reflect on the current state of the art of microbial bioprocesses using Rhodotorula species. Therefore, we will provide an analysis of bioproduction performance with some insights regarding downstream separation steps for the extraction of high added-value biomolecules (specifically using efficient and sustainable platforms), providing information regarding the potential applications of biomolecules produced by Rhodotorula sp, as well as detailing the strengths and limitations of yeast-based biorefinery approaches. Novel genetic engineering technologies are further discussed, indicating some directions on their possible use for maximizing the potential of Rhodotorula sp. as cell factories. KEY POINTS: • Rhodotorula sp. are valuable source of high value-added compounds. • Potential of employing Rhodotorula sp. in a multiple product biorefinery. • Future perspectives in the biorefining of Rhodotorula sp. were discussed.

Metal-Free N-Doped Carbons for Solvent-Less CO2 Fixation Reactions: A Shrimp Shell Valorization Opportunity

High anthropogenic CO₂ emissions are among the main causes of climate change. Herein, we investigate the use of CO₂ for the synthesis of organic cyclic carbonates on metal-free nitrogen-doped carbon catalysts obtained from chitosan, chitin, and shrimp shell wastes, both in batch and in continuous flow (CF). The catalysts were characterized by N₂ physisorption, CO₂-temperature-programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and CNHS elemental analysis, and all reactivity tests were run in the absence of solvents. Under batch conditions, the catalyst obtained by calcination of chitin exhibited excellent performance in the conversion of epichlorohydrin (selected as a model epoxide), resulting in the corresponding cyclic carbonate with 96% selectivity at complete conversion, at 150 °C and 30 bar CO₂, for 4 h. On the other hand, in a CF regime, a quantitative conversion and a carbonate selectivity >99% were achieved at 150 °C, by using the catalyst obtained from shrimp waste. Remarkably, the material displayed an outstanding stability over a reaction run time of 180 min. The robustness of the synthetized catalysts was confirmed by their good operational stability and reusability: ca. (75 ± 3)% of the initial conversion was achieved/retained by all systems, after six recycles. Also, additional batch experiments proved that the catalysts were successful on different terminal and internal epoxides.

Biochemical Methane Potential of a Biorefinery’s Process-Wastewater and its Components at Different Concentrations and Temperatures

A sustainable circular bioeconomy requires the side streams and byproducts of biorefineries to be assimilated into bioprocesses to produce value-added products. The present study endeavored to utilize such a byproduct generated during the synthesis of 5-hydroxymethylfurfural as a potential feedstock for biogas production. For this purpose, biochemical methane potential tests for the full process-wastewater, its components (5-hydroxymethylfurfural, furfural, levulinic acid, and glycolic acid), together with furfural’s metabolites (furfuryl alcohol and furoic acid), and phenols (syringaldehyde, vanillin, and phenol), were conducted at mesophilic and thermophilic temperatures to assess their biodegradability and gas production kinetics. 0.1, 0.2, 0.3, and 0.4 g COD of the test components were added separately into assays containing 35 mL of inoculum. At their lowest concentrations, the test components, other than the process-wastewater, exhibited a stimulatory effect on methane production at 37 °C, whereas their increased concentrations returned a lower mean specific methane yield at either temperature. For similar component loads, the mesophilic assays outperformed the thermophilic assays for the mean measured specific methane yields. Components that impaired the anaerobic process with their elevated concentrations were phenol, vanillin, and 5-hydroxymethylfurfural. Poor degradation of the process-wastewater was deduced to be linked to the considerable share of 5-hydroxymethylfurfural in the process-wastewater governing its overall characteristics. With excessive recalcitrant components, it is recommended to use such waste streams and byproducts as a substrate for biogas plants operating at moderate temperatures, but at low rates.

Efficient production of the β-ionone aroma compound from organic waste hydrolysates using an engineered Yarrowia lipolytica strain

This study demonstrates the feasibility of establishing a natural compound supply chain in a biorefinery. The process starts with the biological or chemical hydrolysis of food and agricultural waste into simple and fermentative sugars, followed by their fermentation into more complex molecules. The yeast strain, Yarrowia lipolytica, was modified by introducing high membrane affinity variants of the carotenoid cleavage dioxygenase enzyme, PhCCD1, to increase the production of the aroma compound, β-ionone. The initial hydrolysis process converted food waste or sugarcane bagasse into nutrient-rich hydrolysates containing 78.4 g/L glucose and 8.3 g/L fructose, or 34.7 g/L glucose and 20.1 g/L xylose, respectively. During the next step, engineered Y. lipolytica strains were used to produce β-ionone from these feedstocks. The yeast strain YLBI3120, carrying a modified PhCCD1 gene was able to produce 4 g/L of β-ionone with a productivity of 13.9 mg/L/h from food waste hydrolysate. This is the highest yield reported for the fermentation of this compound to date. The integrated process described in this study could be scaled up to achieve economical large-scale conversion of inedible food and agricultural waste into valuable aroma compounds for a wide range of potential applications.

Walnut Shell Biowaste Valorization via HTC Process for the Removal of Some Emerging Pharmaceutical Pollutants from Aqueous Solutions

This research emphasizes the performance of some eco-friendly carbon materials as hydrochars (HC) obtained by the hydrothermal carbonization (HTC) process applied to walnut shell (WS) biowaste. These materials display promising properties that can be used for environmental applications such as emerging pharmaceutical pollutant retention from water sources. Thus, three hydrochars coded HCWS1, HCWS2, and HCWS3 were obtained using a dynamic autoclave in specific conditions—temperature of 220 °C, autogenous pressure, 1:10 biomass–water weight ratio—and for three different reaction times, 1 h, 6 h, and 12 h. The HCWSs were characterized by means of ATR-FTIR and SEM-EDS analyses and tested as possible adsorbents to assess the removal efficiencies of some emerging pharmaceutical pollutants (paracetamol and methylene blue) by UV–VIS spectrophotometry. Kinetic and adsorption studies were carried out. The best results were obtained for the HCWS3 hydrochar. Further perspectives include an activation step of the hydrochars and their testing on other emerging pharmaceutical pollutants.

Bibliometric Analysis of Current Status of Circular Economy during 2012–2021: Case of Foods

Food is usually recognized as a limited resource in sustainability, recognized by the United Nations (UN) Sustainable Development Goal (SDG) 2, which aims to achieve zero hunger. It is expected that the circular economy (CE) can improve processes related to food production. The objective of the present study was to apply a bibliometric approach using VOSviewer visualization software as a research tool to analyze the relevant literature from the Scopus database in the field of circular economy and its relation to improvements in food issues throughout 2012–2021. A total of 1316 articles were analyzed. Italy was the most productive country with 313 articles, with Wageningen University & Research the organization with the most publications with 39 articles. The top 10 institutions originated from Italy, The Netherlands, France, and Denmark. Sustainability was the most productive journal with 107 articles. Bioresource Technology had the highest average citation frequency (44.68). The study helps initiate investigations to adapt the results obtained and create new strategies for increasing food circular economy efforts.

Biotechnological interventions in food waste treatment for obtaining value-added compounds to combat pollution

Over the last few decades, the globe is facing tremendous effects due to the unnecessary piling of municipal solid waste among which food waste holds a greater portion. This practice not only affects the environment in terms of generating greenhouse gas emissions but when left dumped in landfills will also trigger poverty and malnutrition. This review focuses on the global trend in food waste management strategies involved in the effective utilization of food waste to produce various value-added products in a microbiology aspect, thereby diminishing the negative impacts caused by the unnecessary side effects of non-renewable energy sources. The review also detailed the efficiency of microorganisms in the production of various bio-energies as well. Further, recent attempts to the exploitation of genetically modified microorganisms in producing value-added products were enlisted. This also attempted to address food waste valorization techniques, the combined applications of various processes for an enhanced yield of different compounds, and addressed various challenges. Further, the current challenges involved in various processes and the effective measures to tackle them in the future have been addressed. Thus, the present review has successfully addressed the circular bio-economy in food waste valorization.

Production of bioethanol from food waste: Status and perspectives

There is an immediate global requirement for an ingenious strategy for food waste conversion to biofuels in order to replace fossil fuels with renewable resources. Food waste conversion to bioethanol could lead to a sustainable process having the dual advantage of resolving the issue of food waste disposal as well as meeting the energy requirements of the increasing population. Food waste is increasing at the rate of 1.3 billion tonnes per year, considered to be one-third of global food production. According to LCA studies discarding these wastes is detritus to the environment, therefore; it is beneficial to convert the food waste into bioethanol. The CO₂ emission in this process offers zero impact on the environment as it is biogenic. Among several pretreatment strategies, hydrothermal pretreatment could be a better approach for pretreating food waste because it solubilizes organic solids, resulting in an increased recovery of fermentable sugars to produce bioenergy.

Organic waste recycling for carbon smart circular bioeconomy and sustainable development: A review

The development of sustainable and low carbon impact processes for a suitable management of waste and by-products coming from different factors of the industrial value chain like agricultural, forestry and food processing industries. Implementing this will helps to avoid the negative environmental impact and global warming. The application of the circular bioeconomy (CB) and the circular economic models have been shown to be a great opportunity for facing the waste and by-products issues by bringing sustainable processing systems which allow to the value chains be more responsible and resilient. In addition, biorefinery approach coupled to CB context could offer different solution and insights to conquer the current challenges related to decrease the fossil fuel dependency as well as increase efficiency of resource recovery and processing cost of the industrial residues. It is worth to remark the important role that the biotechnological processes such as fermentative, digestive and enzymatic conversions play for an effective waste management and carbon neutrality.

Microalgae-Based Biorefineries: Challenges and Future Trends to Produce Carbohydrate Enriched Biomass, High-Added Value Products and Bioactive Compounds

Simple Summary

Microalgae-based biorefineries allow the simultaneous production of microalgae biomass enriched in a particular macromolecule and high-added and low-value products if a proper selection of the microalgae species and the cultivation conditions are adequate for the purpose. This review discusses the challenges and future trends related to microalgae-based biorefineries stressing the multi-product approach and the use of raw wastewater or pretreated wastewater to improve the cost-benefit ratio of biomass and products. Emphasis is given to the production of biomass enriched in carbohydrates. Microalgae-bioactive compounds as potential therapeutical and health promoters are also discussed. Future and novel trends following the circular economy strategy are also discussed.

Abstract

Microalgae have demonstrated a large potential in biotechnology as a source of various macromolecules (proteins, carbohydrates, and lipids) and high-added value products (pigments, poly-unsaturated fatty acids, peptides, exo-polysaccharides, etc.). The production of biomass at a large scale becomes more economically feasible when it is part of a biorefinery designed within the circular economy concept. Thus, the aim of this critical review is to highlight and discuss challenges and future trends related to the multi-product microalgae-based biorefineries, including both phototrophic and mixotrophic cultures treating wastewater and the recovery of biomass as a source of valuable macromolecules and high-added and low-value products (biofertilizers and biostimulants). The therapeutic properties of some microalgae-bioactive compounds are also discussed. Novel trends such as the screening of species for antimicrobial compounds, the production of bioplastics using wastewater, the circular economy strategy, and the need for more Life Cycle Assessment studies (LCA) are suggested as some of the future research lines.

Examining Knowledge Diffusion in the Circular Economy Domain: a Main Path Analysis

The circular economy (CE) field has recently attracted significant interest from academics and practitioners. CE represents a departure from the linear economy, which is characterised by unsustainable resource production and consumption. The growing number of publications necessitates a comprehensive analysis of this field. This is the first systematic examination of the knowledge base and knowledge diffusion pathways in the CE domain. We analyse a Web of Science dataset containing 5431 articles published between 1970 and 2020. To create a comprehensive review of the CE domain, we conducted a keyword co-occurrence network analysis. We examined four distinct types of main paths using the main path analysis (MPA) technique: forward, backward, global, and key-route. According to the analyses, CE research focuses on six primary research themes: CE and sustainability, bioeconomy, CE practices, lifecycle assessment and industrial symbiosis, construction activities, and waste management. In addition, the MPA demonstrates that the CE literature has recently focused on Industry 4.0 technologies and their contribution to CE. This is the first attempt to depict the genealogy of CE research so that scholars can comprehend the domain's evolutionary structure, identify hot topics, and capture the history, development status, and potential future directions of CE research.

Nepenthes mirabilis Fractionated Pitcher Fluid Use for Mixed Agro-Waste Pretreatment: Advocacy for Non-Chemical Use in Biorefineries

This study determined whether it is feasible to pretreat mixed agro-waste of different particle sizes using the pitcher fluid of Nepenthes mirabilis (N. mirabilis), which is known to digest leaf litter due to the enzyme cocktail contained in the fluid. This is due to the need for the holocellulolysis (a source of fermentable sugars) of mixed agro-waste to produce fermentable hydrolysates. The pitcher fluid was fractionated (<3 kDa, ˃3 kDa, <10 kDa, ˃10 kDa) and slurrified with the mixed agro-waste, i.e., 25% (w/w) for each waste—orange peels, apple peels, maize cobs, grape pomace, and oak plant leaf litter of various particle sizes, i.e., >75 µm x < 106 µm and >106 µm. The process of producing a high concentration of total reducible sugars (TRSs) with the lowest production of total phenolic compounds (TPCs) was determined to be a particle size of >106 µm, pretreatment for 72 h, and an enzyme fraction of <10 kDa, whereby 97 g/L of TRSs were produced with a significantly lower TPCs load (1 g/L). Furthermore, the <10 kDa showed preferable physico-chemical properties, with the highest reduction-oxidation potential including acidity. Several enzymes, i.e., β-1,3-Glucanase, Putative peroxidase 27, Thaumatin-like protein, among others, were identified in the <10 kDa fraction, i.e., enzymes known to perform various functions in plant-based waste. Therefore, there is a need for the renewable energy industry to consider solely using pitcher fluids to pretreat mixed agro-waste for fermentable hydrolysates’ production, which can be used as liquid feedstock for the bioenergy and/or biorefinery industries for environmental pollution reduction.

Exploring Yeast Diversity to Produce Lipid-Based Biofuels from Agro-Forestry and Industrial Organic Residues

Exploration of yeast diversity for the sustainable production of biofuels, in particular biodiesel, is gaining momentum in recent years. However, sustainable, and economically viable bioprocesses require yeast strains exhibiting: (i) high tolerance to multiple bioprocess-related stresses, including the various chemical inhibitors present in hydrolysates from lignocellulosic biomass and residues; (ii) the ability to efficiently consume all the major carbon sources present; (iii) the capacity to produce lipids with adequate composition in high yields. More than 160 non-conventional (non-Saccharomyces) yeast species are described as oleaginous, but only a smaller group are relatively well characterised, including Lipomyces starkeyi, Yarrowia lipolytica, Rhodotorula toruloides, Rhodotorula glutinis, Cutaneotrichosporonoleaginosus and Cutaneotrichosporon cutaneum. This article provides an overview of lipid production by oleaginous yeasts focusing on yeast diversity, metabolism, and other microbiological issues related to the toxicity and tolerance to multiple challenging stresses limiting bioprocess performance. This is essential knowledge to better understand and guide the rational improvement of yeast performance either by genetic manipulation or by exploring yeast physiology and optimal process conditions. Examples gathered from the literature showing the potential of different oleaginous yeasts/process conditions to produce oils for biodiesel from agro-forestry and industrial organic residues are provided.

Achieving superior carbon transfer efficiency and pH control using membrane carbonation with a wide range of CO2 contents for the coccolithophore Emiliania huxleyi

The economic viability of microalgal-derived products relies on rapid CO₂ transfer in a cost-effective manner. Many industrial gas streams contain concentrated CO₂ that, if converted to useful products, would lower greenhouse gas emissions and valorize the wasted CO₂. Membrane carbonation (MC) uses non-porous hollow-fiber gas-transfer membranes to deliver CO₂ without bubble formation, which makes it possible to achieve a high carbon-transfer efficiency (CTE). However, inert gasses in the industrial streams (e.g., N₂, O₂, and H₂O) can significantly lower the CO₂-delivery rate. The means to overcome the buildup of inert gases in the membrane lumen is to manage the distal end of the membranes to sweep out inert gases while not wasting significant CO₂. A MC-venting strategy was evaluated for CO₂ inputs from 5% to 100%. Abiotic tests using a restricted exit flow could achieve >95% CTE_abiotic for industrial CO₂ streams. When integrated with semi-continuous cultivation of a marine coccolithophore, Emiliania huxleyi, CO₂ delivery and venting were on-demand based on a pH set points and pH-actuated feed and venting valves. MC using the venting strategy achieved 100% CTE_biotic when delivering 100% and 50% CO₂, which was better than 50% CTE_biotic obtained from pH-controlled sparging of 100% CO₂-sparging. E. huxleyi consistently fixed ~80% of the delivered CO₂ into biomass, and the remaining ~20% to calcite coccoliths. The compact size of MC modules, stable pH control, and no shear forces from bubble agitation during the CO₂ delivery made MC an ideal match for cultivation of coccolithophores, which are sensitive to shear forces and pH fluctuations.

Emerging potential of spent coffee ground valorization for fuel pellet production in a biorefinery

Abstract

The global market for fuel pellets (FPs) has been steadily growing because of a shift to coal substitutes. However, sustainability and the availability of biomass are the main issues. Various kinds of bio-wastes can be valorized through cutting-edge technologies. In the coffee industry, a valuable organic waste called spent coffee grounds (SCGs) is generated in bulk. SCG can be divided into two components, namely spent coffee ground oil and defatted spent coffee grounds (DSCG). SCG and DSCG can be used to produce FPs with excellent higher heating values. This review highlights that burning FPs composed of 100% SCG is not feasible due to the high emission of NOx. Moreover, the combustion is accompanied by a rapid temperature drop due to incomplete combustion which leads to lower boiler combustion efficiencies and increased carbon monoxide emissions. This was because of the low pellet strength and bulk density of the FP. Mixing SCG with other biomass offers improved boiler efficiency and emissions. Some of the reported optimized FPs include 75% SCG + 20% coffee silverskin, 30% SCG + 70% pine sawdust, 90% SCG + 10% crude glycerol, 32% SCG + 23% coal fines + 11% sawdust + 18% mielie husks + 10% waste paper + 6% paper pulp, and 50% SCG + 50% pine sawdust. This review noted the absence of combustion and emissions analyses of DSCG and the need for their future assessment. Valorization of DSCG offers a good pathway to improve the economics of an SCG-based biorefinery where the extracted SCGO can be valorized in other applications. The combustion and emissions of DSCG were not previously reported in detail. Therefore, future investigation of DSCG in boilers is essential to assess the potential of this industry and improve its economics.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s10668-022-02361-z.

Polyhydroxyalkanoate (PHA) Biopolyesters - Emerging and Major Products of Industrial Biotechnology

Background: Industrial Biotechnology (“White Biotechnology”) is the large-scale production of materials and chemicals using renewable raw materials along with biocatalysts like enzymes derived from microorganisms or by using microorganisms themselves (“whole cell biocatalysis”). While the production of ethanol has existed for several millennia and can be considered a product of Industrial Biotechnology, the application of complex and engineered biocatalysts to produce industrial scale products with acceptable economics is only a few decades old. Bioethanol as fuel, lactic acid as food and PolyHydroxyAlkanoates (PHA) as a processible material are some examples of products derived from Industrial Biotechnology.

Purpose and Scope: Industrial Biotechnology is the sector of biotechnology that holds the most promise in reducing our dependence on fossil fuels and mitigating environmental degradation caused by pollution, since all products that are made today from fossil carbon feedstocks could be manufactured using Industrial Biotechnology – renewable carbon feedstocks and biocatalysts. To match the economics of fossil-based bulk products, Industrial Biotechnology-based processes must be sufficiently robust. This aspect continues to evolve with increased technological capabilities to engineer biocatalysts (including microorganisms) and the decreasing relative price difference between renewable and fossil carbon feedstocks. While there have been major successes in manufacturing products from Industrial Biotechnology, challenges exist, although its promise is real. Here, PHA biopolymers are a class of product that is fulfilling this promise.

Summary and Conclusion: The authors illustrate the benefits and challenges of Industrial Biotechnology, the circularity and sustainability of such processes, its role in reducing supply chain issues, and alleviating societal problems like poverty and hunger. With increasing awareness among the general public and policy makers of the dangers posed by climate change, pollution and persistent societal issues, Industrial Biotechnology holds the promise of solving these major problems and is poised for a transformative upswing in the manufacture of bulk chemicals and materials from renewable feedstocks and biocatalysts.