Food waste biorefinery: Sustainable strategy for circular bioeconomy

Sustainability of food waste biorefinery: A review on valorisation pathways, techno-economic constraints, and environmental assessment

The need to increase circularity of industrial systems to address limited resources availability and climate change has triggered the development of the food waste biorefinery concept. However, for the development of future sustainable industrial processes focused on the valorisation of food waste, critical aspects such as (i) the technical feasibility of the processes at industrial scale, (ii) the analysis of their techno-economic potential, including available quantities of waste, and (iii) a life cycle-based environmental assessment of benefits and burdens need to be considered. The goal of this review is to provide an overview of food waste valorisation pathways and to analyse to which extent these aspects have been considered in the literature. Although a plethora of food waste valorisation pathways exist, they are mainly developed at lab-scale. Further research is necessary to assess upscaled performance, feedstock security, and economic and environmental assessment of food waste valorisation processes.

Biodegradable and non-biodegradable fraction of municipal solid waste for multifaceted applications through a closed loop integrated refinery platform: Paving a path towards circular economy

An increase in population, rapid urbanization and industrialization has accelerated the rate of municipal solid waste generation. The current disposal of solid waste is a burgeoning issue and it's in immediate need to shift the existing disposal processes to a sustainable manner. Circular economy (CE) is a conceptual model which is been used for better use of resources and minimization of waste in a closed loop approach which could be appropriate for waste management. In this context, the present review illustrates the effective use of biodegradable and non-biodegradable fraction of solid waste in a closed loop integrated refinery platforms for the recovery of bioenergy resources and for the production of value added products. The biodegradable fraction of solid waste could be treated by advanced biological processes with the simultaneous production of bioenergy such as biohydrogen, biomethane, bioelectricity, etc., and other value added products like butanol, ethanol, methanol etc. The scheme illustrates the closed loop approach, the bioenergy generated from the biodegradable fraction of solid waste could be used for the operation of internal combustion engines and the energy could be further used for processing the waste. The non-biodegradable fraction of solid waste could be used for construction and pavement processes. Overall the study emphasizes the paradigm shift of solid waste management concepts from linear economy to a circular economy following the "Zero Waste" concept. The study also explains the circular economy policies practiced for solid waste management that stimulates the economy of the country and identify the pathways to maximize the local resources. In addition the review addresses the advanced information and communication technologies to unfold the issues and challenges faced in the solid waste management. The smart governance of managing waste using the "Internet of Things" (IoT) is one of the great precursors of technological development that could lead innovations in waste management.

Use of Ionic Liquids and Deep Eutectic Solvents in Polysaccharides Dissolution and Extraction Processes towards Sustainable Biomass Valorization

A shift to a bioeconomy development model has been evolving, conducting the scientific community to investigate new ways of producing chemicals, materials and fuels from renewable resources, i.e., biomass. Specifically, technologies that provide high performance and maximal use of biomass feedstocks into commodities with reduced environmental impact have been highly pursued. A key example comprises the extraction and/or dissolution of polysaccharides, one of the most abundant fractions of biomass, which still need to be improved regarding these processes' efficiency and selectivity parameters. In this context, the use of alternative solvents and the application of less energy-intensive processes in the extraction of polysaccharides might play an important role to reach higher efficiency and sustainability in biomass valorization. This review debates the latest achievements in sustainable processes for the extraction of polysaccharides from a myriad of biomass resources, including lignocellulosic materials and food residues. Particularly, the ability of ionic liquids (ILs) and deep eutectic solvents (DESs) to dissolve and extract the most abundant polysaccharides from natural sources, namely cellulose, chitin, starch, hemicelluloses and pectins, is scrutinized and the efficiencies between solvents are compared. The interaction mechanisms between solvent and polysaccharide are described, paving the way for the design of selective extraction processes. A detailed discussion of the work developed for each polysaccharide as well as the innovation degree and the development stage of dissolution and extraction technologies is presented. Their advantages and disadvantages are also identified, and possible synergies by integrating microwave- and ultrasound-assisted extraction (MAE and UAE) or a combination of both (UMAE) are briefly described. Overall, this review provides key information towards the design of more efficient, selective and sustainable extraction and dissolution processes of polysaccharides from biomass.

Hydrothermal liquefaction of biogenic municipal solid waste under reduced H2 atmosphere in biorefinery format

Municipal solid waste (MSW), an inexorable by-product of anthropogenic activities composes of nearly 50% of the organic (biogenic) fraction. Hydrothermal liquefaction (HTL) was studied to facilitate thermal depolymerization of organic fraction of MSW to biocrude at sub-critical region of water (200 °C; 100 bar pressure) employing H₂ induced reducing conditions. Food, vegetable, and composite wastes were evaluated as feedstocks to produce HTL derivatives in the form of liquor (biocrude and aqueous phase), biochar and bio-gas. The biocrude (HTL_OF) showed middle oil as major fraction along with C₆-C₂₂ compounds. Composite waste resulted in relatively higher yield of biocrude fraction. The aqueous phase (HTL_AF) documented the presence of reducing sugars, sotolon and furfurals as major fraction. Biochar (HTL_BC) composition showed maximum carbon fraction followed by hydrogen and oxygen. H₂ induced reduced condition facilitated conversion of the biogenic MSW at relatively lower input conditions to various biobased fractions cohesively addressing the basic biorefinery requirement.

Biocatalysis and biomass conversion: enabling a circular economy

This paper is based on a lecture presented to the Royal Society in London on 24 June 2019. Two of the grand societal and technological challenges of the twenty-first century are the 'greening' of chemicals manufacture and the ongoing transition to a sustainable, carbon neutral economy based on renewable biomass as the raw material, a so-called bio-based economy. These challenges are motivated by the need to eliminate environmental degradation and mitigate climate change. In a bio-based economy, ideally waste biomass, particularly agricultural and forestry residues and food supply chain waste, are converted to liquid fuels, commodity chemicals and biopolymers using clean, catalytic processes. Biocatalysis has the right credentials to achieve this goal. Enzymes are biocompatible, biodegradable and essentially non-hazardous. Additionally, they are derived from inexpensive renewable resources which are readily available and not subject to the large price fluctuations which undermine the long-term commercial viability of scarce precious metal catalysts. Thanks to spectacular advances in molecular biology the landscape of biocatalysis has dramatically changed in the last two decades. Developments in (meta)genomics in combination with 'big data' analysis have revolutionized new enzyme discovery and developments in protein engineering by directed evolution have enabled dramatic improvements in their performance. These developments have their confluence in the bio-based circular economy. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

Fruit and vegetable waste management: Conventional and emerging approaches

Valorization of Fruit and Vegetable Wastes (FVW) is challenging owing to logistic-related problems, as well as to their perishable nature and heterogeneity, among other factors. In this work, the main existing routes for food waste valorization are critically reviewed. The study focuses on FVW because they constitute an important potential source for valuable natural products and chemicals. It can be concluded that FVW management can be carried out following different processing routes, though nowadays the best solution is to find an adequate balance between conventional waste management methods and some emerging valorization technologies. Presently, both conventional and emerging technologies must be considered in a coordinated manner to enable an integral management of FVW. By doing so, impacts on food safety and on the environment can be minimized whilst wasting of natural resources is avoided. Depending on the characteristics of FVW and on the existing market demand, the most relevant valorization options are extraction of bioactive compounds, production of enzymes and exopolysaccharides, synthesis of bioplastics and biopolymers and production of biofuels. The most efficient emergent processing technologies must be promoted in the long term, in detriment of the conventional ones used nowadays. In consequence, future integral valorization of FVW will probably comprise two stages: direct processing of FVW into value-added products, followed by processing of the residual streams, byproducts and leftover matter by means of conventional waste management technologies.

Valorization of waste eggshell-derived bioflocculant for harvesting T. obliquus: Process optimization, kinetic studies and recyclability of the spent medium for circular bioeconomy

Waste eggshell-derived bioflocculant was used for harvesting T. obliquus in a circular bioeconomy approach. It was found that 120 mg L^-1 bioflocculant can flocculate 98.62 ± 0.43% of T. obliquus cells within 25 min at optimal pH 4.0 and temperature 35 °C. The influence of bioflocculant concentration, pH and temperature on zeta potential was evaluated to understand the flocculation mechanism. Microscopic and FESEM-EDX images were analyzed to evaluate the microalgal structural changes. Adsorption mechanism of bioflocculant over the microalgal cells was determined by performing adsorption kinetic studies. Pseudo-second order kinetic model was a suitable fit for the data obtained from the experiments, which indicated chemisorption as the probable mechanism. The spent medium recovered after harvesting process was successfully recycled for subsequent cultivation of T. obliquus, thus reducing the dependency on fresh medium. The FAME composition of the biomass treated with bioflocculant was not altered.

Sustainable Use of Fruit and Vegetable By-Products to Enhance Food Packaging Performance

Fruit and vegetable by-products are the most abundant food waste. Industrial processes such as oil, juice, wine or sugar production greatly contribute to this amount. These kinds of residues are generally thrown away in form of leftover and used as feed or composted, but they are a great source of bioactive compounds like polyphenols, vitamins or minerals. The amount of residue with potential utilization after processing has been estimated in millions of tons every year. For this reason, many researchers all around the world are making great efforts to valorize and reuse these valuable resources. Of greatest importance is the by-product potential to enhance the properties of packaging intended for food applications. Therefore, this overview collects the most recent researches dealing with fruit and vegetable by-products used to enhance physical, mechanical, antioxidant and antimicrobial properties of packaging systems. Recent advances on synthetic or bio-based films enriched with by-product components are extensively reviewed, with an emphasis on the role that by-product extracts can play in food packaging materials.

Purification and immobilization of engineered glucose dehydrogenase: a new approach to producing gluconic acid from breadwaste

BACKGROUND

Platform chemicals are essential to industrial processes. Used as starting materials for the manufacture of diverse products, their cheap availability and efficient sourcing are an industrial requirement. Increasing concerns about the depletion of natural resources and growing environmental consciousness have led to a focus on the economics and ecological viability of bio-based platform chemical production. Contemporary approaches include the use of immobilized enzymes that can be harnessed to produce high-value chemicals from waste.

RESULTS

In this study, an engineered glucose dehydrogenase (GDH) was optimized for gluconic acid (GA) production. Sulfolobus solfataricus GDH was expressed in Escherichia coli. The K m and V max values for recombinant GDH were calculated as 0.87 mM and 5.91 U/mg, respectively. Recombinant GDH was immobilized on a hierarchically porous silica support (MM-SBA-15) and its activity was compared with GDH immobilized on three commercially available supports. MM-SBA-15 showed significantly higher immobilization efficiency (> 98%) than the commercial supports. After 5 cycles, GDH activity was at least 14% greater than the remaining activity on commercial supports. Glucose in bread waste hydrolysate was converted to GA by free-state and immobilized GDH. After the 10th reuse cycle on MM-SBA-15, a 22% conversion yield was observed, generating 25 gGA/gGDH. The highest GA production efficiency was 47 gGA/gGDH using free-state GDH.

CONCLUSIONS

This study demonstrates the feasibility of enzymatically converting BWH to GA: immobilizing GDH on MM-SBA-15 renders the enzyme more stable and permits its multiple reuse.

Urban biocycles - Closing metabolic loops for resilient and regenerative ecosystem: A perspective

Cities are at crossroads, confronting challenges posed by increasing population growth, climate change and faltering livability. These problems are prompting urban areas to chart novel path towards adopting sustainable production/consumption strategies. The alluring concept of circular economy (CE) that focuses on reuse and recycling of materials in technical and biological cycles to reduce waste generation is a critical intervention. Present article aims on precisely highlighting the importance of biogenic materials which have an immense potential to be transformed into a source of value in an urban ecosystem. It also sets out to explore the scope of implementing 'urban biocycles' that strategically directs the flow of resources, their use, extracting value in the form of nutrients, energy and materials post consumption within an urban metabolic regime. The concepts discussed contribute to biocycle economy by outlining emerging requirements, identification of common strategies, policies and emerging areas of research in line with sustainable development goals.

Non-sterile fermentation of food waste with indigenous consortium and yeast - Effects on microbial community and product spectrum

This work presents examples of non-sterile mixed culture fermentation of food waste with a cultivated indigenous consortium (IC) gained from food waste, which produces lactic and acetic acids, combined with Saccharomyces cerevisiae, which produces ethanol. All results are flanked by microbial analysis to monitor changes in microbial community. At pH 6 and inoculated with yeast or IC, or both mixed sugars conversion was equal to 71%, 51%, or 67%, respectively. Under pH unregulated conditions metabolic yields were 71%, 67%, or up to 81%. While final titer of acetic acid was not affected by pH (100-200 mM), ethanol and lactic acid titers were. Using mixed culture and pH 6, sugars were almost equally used for formation of ethanol and lactic acid (400-500 mM). However, under pH unregulated conditions 80% of the substrate was converted into ethanol (900-1000 mM).

Valorisation of pectin-rich agro-industrial residues by yeasts: potential and challenges

Pectin-rich agro-industrial residues are feedstocks with potential for sustainable biorefineries. They are generated in high amounts worldwide from the industrial processing of fruits and vegetables. The challenges posed to the industrial implementation of efficient bioprocesses are however manyfold and thoroughly discussed in this review paper, mainly at the biological level. The most important yeast cell factory platform for advanced biorefineries is currently Saccharomyces cerevisiae, but this yeast species cannot naturally catabolise the main sugars present in pectin-rich agro-industrial residues hydrolysates, in particular d-galacturonic acid and l-arabinose. However, there are non-Saccharomyces species (non-conventional yeasts) considered advantageous alternatives whenever they can express highly interesting metabolic pathways, natively assimilate a wider range of carbon sources or exhibit higher tolerance to relevant bioprocess-related stresses. For this reason, the interest in non-conventional yeasts for biomass-based biorefineries is gaining momentum. This review paper focuses on the valorisation of pectin-rich residues by exploring the potential of yeasts that exhibit vast metabolic versatility for the efficient use of the carbon substrates present in their hydrolysates and high robustness to cope with the multiple stresses encountered. The major challenges and the progresses made related with the isolation, selection, sugar catabolism, metabolic engineering and use of non-conventional yeasts and S. cerevisiae-derived strains for the bioconversion of pectin-rich residue hydrolysates are discussed. The reported examples of value-added products synthesised by different yeasts using pectin-rich residues are reviewed.

Key Points • Review of the challenges and progresses made on the bioconversion of pectin-rich residues by yeasts. • Catabolic pathways for the main carbon sources present in pectin-rich residues hydrolysates. • Multiple stresses with potential to affect bioconversion productivity. • Yeast metabolic engineering to improve pectin-rich residues bioconversion.

Compositional variability of food wastes and its effects on acetone-butanol-ethanol fermentation

Converting food waste into butanol via acetone, butanol, and ethanol (ABE) fermentation provides the potential to recover energy and value-added chemicals from food waste. However, the high variability of food waste compositions has hindered the consistency and predictability of butanol production, impeding the development of a robust industrial fermentation process. This study characterized the compositional variation of collected food wastes and determined correlations between food waste compositional attributes and butanol yields for a better prediction of food waste fermentation with Clostridium. The total sugar, starch, fiber, crude protein, fat and ash contents (on dry basis) in the food waste samples were in a range of 0.5-53.5%, 0-25.2%, 0.6-26.9%, 5.5-21.5%, 0.1-37.9%, and 1.4-13.7%, respectively. The high variability of food waste composition resulted in a wide range (3.5-11.5 g/L) of butanol concentrations with an average of 8.2 g/L. Pearson's correlation analysis revealed that the butanol concentrations were strongly and positively correlated with equivalent glucose and starch contents in food waste, strongly and negatively correlated with fiber content, and weakly correlated with total sugar, protein, fat, and ash contents. The regression models constructed based on equivalent glucose and fiber contents reasonably predicted the butanol concentration, with the R² of 0.80. Our study investigated the variability of food waste composition and, for the first time, unveiled relationships between food waste compositional attributes and fermentation yields, contributing to a greater understanding of food waste fermentation, which, in turn, assists in developing new strategies for increased consistency and predictability of food waste fermentation.

Food waste from restaurant sector - Characterization for biorefinery approach

The aim of this study is the analysis of food waste (FW) composition from local catering services to assess potential biorefinery development. Moisture content of different FW samples showed that 27-47% (w/w) was organic material. Main components were lipids (25.7-33.2, w/w), starch (16.2-29.4%, w/w) and proteins (23.5-18.3%, w/w) on a dry basis. A metal profile with Na and Mg as main components, followed by trace elements, i.e. Zn or Fe, was also found in food waste samples. Statistical tests in combination with principal component analysis provides an efficient methodology to establish specific composition variations between FW from different catering services, while relating them to FW typology. The combination of chemical characterization with statistical study constitutes a promising decision-making tool for FW processing and valorization. The innovative methodology presented in this study provides systematic evaluation of FW composition and variability to allow selection of the most appropriate valorization paths.

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

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

Innovation and strategic orientations for the development of advanced biorefineries

Advanced biorefineries, which aim at valorizing biomass (from agriculture, forestry, aquaculture, among others) into a wide spectrum of products and bioenergy, are seen today as key to implement a sustainable biobased economy. Although different concepts of biorefinery are currently under development, further research and improvement are still required to obtain environmentally friendly and economically feasible commercial scale biorefineries. Valorization of all biomass components and integration of different disciplines are some of the strategies that have been considered to improve the economic and environmental performance. This paper summarizes and discusses the most recent innovations and strategic orientations for the development of advanced biorefineries. Focus is given on the valorization of non-carbohydrate components of biomass (protein, acetic acid and lignin), on-site and tailor-made production of enzymes, big data analytics, and interdisciplinary efforts. The idea is to provide new insights and directions to support the development and large-scale implementation of biorefineries.

Preparation and Characterization of Environmentally Friendly Controlled Release Fertilizers Coated by Leftovers-Based Polymer

In this work, a novel bio-based polyurethane (PU) was synthesized by using a leftovers (SF)-based polyol and isocyanate for controlled release fertilizers (CRFs). Its chemical structure, surface elemental compositions and distribution were examined by Fourier transform infrared (FTIR), energy dispersive spectroscopy (EDX) and a multifunctional imaging electron spectrometer (XPS). The microstructure morphology of CRFs were examined by SEM. The nutrient release behaviors of CRFs were observed in water. The results demonstrated that SF-based PU-coated urea (FPU) had a denser structure and better nutrient releasing ability. Findings from this work indicated that the use of SF as a coating material of environment-friendly CRFs had great potential, and would hopefully be used for horticultural and agricultural applications.

Bioengineering of anaerobic digestion for volatile fatty acids, hydrogen or methane production: A critical review

Anaerobic digestion (AD) is a well-established technology used for producing biogas or biomethane alongside the slurry used as biofertilizer. However, using a variety of wastes and residuals as substrate and mixed cultures in the bioreactor makes AD as one of the most complicated biochemical processes employing hydrolytic, acidogenic, hydrogen-producing, acetate-forming bacteria as well as acetoclastic and hydrogenoclastic methanogens. Hydrogen and volatile fatty acids (VFAs) including acetic, propionic, isobutyric, butyric, isovaleric, valeric and caproic acid and other carboxylic acids such as succinic and lactic acids are formed as intermediate products. As these acids are important precursors for various industries as mixed or purified chemicals, the AD process can be bioengineered to produce VFAs alongside hydrogen and therefore biogas plants can become biorefineries. The current review paper provides the theory and means to produce and accumulate VFAs and hydrogen, inhibit their conversion to methane and to extract them as the final products. The effects of pretreatment, pH, temperature, hydraulic retention time (HRT), organic loading rate (OLR), chemical methane inhibitions, and heat shocking of the inoculum on VFAs accumulation, hydrogen production, VFAs composition, and the microbial community were discussed. Furthermore, this paper highlights the possible techniques for recovery of VFAs from the fermentation media in order to minimize product inhibition as well as to supply the carboxylates for downstream procedures.

Production of Oligosaccharides from Agrofood Wastes

The development of biorefinery processes to platform chemicals for most lignocellulosic substrates, results in side processes to intermediates such as oligosaccharides. Agrofood wastes are most amenable to produce such intermediates, in particular, cellooligo-saccharides (COS), pectooligosaccharides (POS), xylooligosaccharides (XOS) and other less abundant oligomers containing mannose, arabinose, galactose and several sugar acids. These compounds show a remarkable bioactivity as prebiotics, elicitors in plants, food complements, healthy coadyuvants in certain therapies and more. They are medium to high added-value compounds with an increasing impact in the pharmaceutical, nutraceutical, cosmetic and food industries. This review is focused on the main production processes: autohydrolysis, acid and basic catalysis and enzymatic saccharification. Autohydrolysis of food residues at 160–190 °C leads to oligomer yields in the 0.06–0.3 g/g dry solid range, while acid hydrolysis of pectin (80–120 °C) or cellulose (45–180 °C) yields up to 0.7 g/g dry polymer. Enzymatic hydrolysis at 40–50 °C of pure polysaccharides results in 0.06–0.35 g/g dry solid (DS), with values in the range 0.08–0.2 g/g DS for original food residues.

Anaerobic granulation: A review of granulation hypotheses, bioreactor designs and emerging green applications

Successful installations and operation of many granulation-base treatment plants all over the world in the recent years are reported. A better knowledge towards reactor operation and system performance has led to a growing interest in the technology. While the technology is well accepted and abundant research work has been carried out, insight unfolding the granulation fundamentals and its engineering applications remains unclear. This paper presents a review of some major hypotheses describing the evolvement of anaerobic granules. A number of physico-chemical hypotheses based on thermodynamics and structural hypotheses incorporating microbial considerations for anaerobic granulation have been developed. Features of anaerobic granulation and bioreactor designs are also reviewed. Advances in granulation research with respect to hydrogen production, degradation of recalcitrant or toxic compounds and emissions mitigation are delineated. Prospects and challenges of anaerobic granulation in wastewater treatment are also outlined.

Towards transparent valorization of food surplus, waste and loss: Clarifying definitions, food waste hierarchy, and role in the circular economy

In this study, the key gaps of food waste prevention have been addressed in the context of the emerging circular economy. First, current terminology related to food waste was reviewed and clarified, in particular, the terms food surplus, waste and losses. This work highlights why the clarity of these definitions is crucial for the sustainability of future food waste management systems, especially in the context of circular economy. Through a simple matrix, definitions are linked to the concepts of edibility and possibility of avoidance, leading to six distinct categories of food waste: i) edible, ii) naturally inedible (pits), iii) industrial residue, iv) inedible due to natural causes (pests), v) inedible due to ineffective management and vi) not accounted for. Category I encompasses surplus food only; category II-V food waste and category VI food losses. Based on this, an updated pyramid for food waste hierarchy is proposed, distinguishing surplus food and a new category for material recycling, in order to reflect the future food waste biorefineries in the circular bioeconomy. Nutrient and energy recovery are two separate categories and the terms recovery and recycling are clarified. Finally, a circular economy framework is presented for food surplus and waste, considering closing the loop throughout the whole food supply chain, in connection with the concept of strong and weak sustainability. This is presented along with a review of key EU policies related to food waste and examples of initiatives from the Member States.

Changes in global trends in food waste composting: Research challenges and opportunities

Increasing food waste (FW) generation has put significant pressure on the environment and has increased the global financial costs of its appropriate management. Among the traditional organic waste recycling technologies (i.e., incineration, landfilling and anaerobic digestion), composting is an economically feasible and reliable technology for FW recycling regardless of its technical flaws and social issues. The global scenario of FW generation, technical advancement in FW composting and essential nutrient recovery from organic waste with waste recycling are discussed in this article. Recent research on various strategies to improve FW composting, including co-composting, the addition of organic/inorganic additives, the mitigation of gaseous emission, and microbiological variations are comprehensively explained. Subsequently, it is shown that the performing FW composting in an existing mechanical facility can improve organic waste degradation and produce value-added mature compost to save on costs and increase the technological feasibility and viability of FW composting to some extent.

Stabilizing lactate production through repeated batch fermentation of food waste and waste activated sludge

Bio-valorization of organic waste streams, such as food waste and waste activated sludge, to lactic acid (LA) has recently drawn much attention. It offers an opportunity for resource recovery, alleviates environmental issues and potentially turns a profit. In this study, both stable and high LA yield (0.72 ± 0.15 g/g total chemical oxygen demand) and productivity rate (0.53 g/L•h) were obtained through repeated batch fermentation. Moreover, stable solubilization and increase in the critical hydrolase activities were achieved. Depletions of ammonia and phosphorus were correlated with the LA production. The relative abundance of the key LA bacteria genera (i.e., Alkaliphilus, Dysgonomonas, Enterococcus and Bifidobacterium) stabilized in the repeated batch reactor at a higher level (44.5 ± 2.53%) in comparison with the batch reactor (26.2 ± 4.74%). This work show a practical way for the sustainable valorization of organic wastes to LA by applying the repeated batch mode during biological treatment.

Biorefineries in circular bioeconomy: A comprehensive review

Biorefinery is a sustainable means of generating multiple bioenergy products from various biomass feedstocks through the incorporation of relevant conversion technologies. With the increased attention of circular economy in the past half-decade with the emphasis of holistically addressing economic, environmental, and social aspects of the industrial-sector, biorefinery acts as a strategic mechanism for the realization of a circular bioeconomy. This study presents a comprehensive review of different biorefinery models used for various biomass feedstocks such as lignocelluloses, algae, and numerous waste-types. The review focuses on how biorefinery is instrumental in the transition of various biomass-based industries in a circular bioeconomy. The results reveal that the social-economic aspect of the industrial sector has a major influence on the full adoption of biorefineries in circular bioeconomy. Biomass wastes have played a major role in the implementation of biorefinery in circular bioeconomy. The current challenges are also presented along with future perspectives.

Catalytic Oxidations in a Bio-Based Economy

The role of bio- and chemo-catalytic aerobic oxidations in the production of commodity chemicals in a bio-refinery is reviewed. The situation is fundamentally different to that in a petrochemicals refinery where the feedstocks are gaseous or liquid hydrocarbons that are oxidized at elevated temperatures in the vapor or liquid phase under solvent-free conditions. In contrast, the feedstocks in a biorefinery are carbohydrates that are water soluble solids and their conversion will largely involve aerobic oxidations of hydroxyl functional groups in water as the solvent under relatively mild conditions of temperature and pressure. This will require the development and use of cost-effective and environmentally attractive processes using both chemo- and biocatalytic methods for alcohols and polyols.

Agroindustrial waste as a resource for volatile fatty acids production via anaerobic fermentation

This study evaluated the feasibility of the anaerobic digestion as a sustainable valorisation strategy for volatile fatty acids production from agroindustrial waste (cucumber, tomato and lettuce). High bioconversion efficiencies were reached by operating the reactors at 25 °C, 3 g VS·d^-1·L^-1 with pH adjustment. Cucumber fermentation achieved the highest bioconversion (52.6%), whereas tomato degradation was the least efficient bioprocess (40.1%) due to the low pH (5.6) that partially inhibited the hydrolytic and acidogenic activities. In all cases, carboxylic acid profiles were mainly composed of volatile fatty acids with even carbon number. The developed microbial community exhibited high hydrolytic and acidogenic activities associated to carbohydrates degradation. This microbial population was dominated by Firmicutes phylum and showed a lack of acetogenic bacteria related with CH₄ production, resulting in a remarkably high VFAs accumulation.

Biohythane production from food processing wastes - Challenges and perspectives

The food industry generates enormous quantity of food waste (FW) either directly or indirectly including the processing sector, which turned into biofuels for waste remediation. Six types of food processing wastes (FPW) such as oil, fruit and vegetable, dairy, brewery, livestock and finally agriculture based materials that get treated via dark fermentation/anaerobic digestion has been discussed. Production of both hydrogen and methane is daunting for oil, fruit and vegetable processing wastes because of the presence of polyphenols and essential oils. Moreover, acidic pH and high protein are the reasons for increased concentration of ammonia and accumulation of volatile fatty acids in FPW, especially in dairy, brewery, and livestock waste streams. Moreover, the review brought to forefront the enhancing methods, (pretreatment and co-digestion) operational, and environmental parameters that can influence the production of biohythane. Finally, the nature of feedstock's role in achieving successful circular bio economy is also highlighted.

Biomolecules from municipal and food industry wastes: An overview

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

Sustainable food waste management towards circular bioeconomy: Policy review, limitations and opportunities

Research attention is increasingly drawn on constructing a circular bioeconomy and enhancing the value of material flows. Circular bioeconomy aims to achieve sustainable consumption and production with reduction of greenhouse gas emission. This study identifies research gaps on how circular bioeconomy can be achieved through sustainable food waste management by comparing the similarities and differences in concepts of bioeconomy and circular economy, reviewing the benefits and limitations of the existing policies, and evaluating the global situations of food waste and its management on household and commercial basis to promote circular bioeconomy. Future development on food waste management is expected to capitalise on the multi-functionality of products, boundary and allocation in a circular system, and trade-off between food waste and resources. With future technological advances, food waste management in circular bioeconomy policy can facilitate the accomplishment of sustainable development goals.

Techno-Economic Study of CO2 Capture of a Thermoelectric Plant Using Microalgae (Chlorella vulgaris) for Production of Feedstock for Bioenergy

A current concern is the increase in greenhouse gas emissions, mainly CO2, with anthropogenic sources being the main contributors. Microalgae have greater capacity than terrestrial plants to capture CO2, with this being an attraction for using them as capture systems. This study aims at the techno-economic evaluation of microalgae biomass production, while only considering technologies with industrial scaling potential. Energy consumption and operating costs are considered as parameters for the evaluation. In addition, the capture of CO2 from a thermoelectric plant is analyzed, as a carbon source for the cultivation of microalgae. 24 scenarios were evaluated while using process simulation tools (SuperPro Designer), being generated by the combination of cultivations in raceway pond, primary harvest with three types of flocculants, secondary harvest with centrifugation and three filtering technologies, and finally the drying evaluated with Spray and Drum Dryer. Low biomass productivity, 12.7 g/m2/day, was considered, achieving a capture of 102.13 tons of CO2/year in 1 ha for the cultivation area. The scenarios that included centrifugation and vacuum filtration are the ones with the highest energy consumption. The operating costs range from US $ 4.75–6.55/kg of dry biomass. The choice of the best scenario depends on the final use of biomass.

Cow manure as additive to a DMBR for stable and high-rate digestion of food waste: Performance and microbial community

Cow manure (CM) was added to a dynamic membrane bioreactor (DMBR) operated under anaerobic condition for enhancing food waste (FW) digestion for over 300 days with stepwise increase of organic loading rates (OLRs) from 1.07 to 11.9 g COD/L/day. At a FW/CM ratio of 3.5:1 (based on volatile solids), the mixed liquor pH was always above 8.0 and no apparent volatile fatty acids (VFAs) accumulation occurred even at the highest OLR of 11.9 g COD/L/day (hydraulic retention time as 10 days and solid retention time as 15.5 days, correspondingly), indicating a very stable operation condition which resulted in an average CH₄ yield as high as 250 mL/g COD and CH₄ production as high as 2.71 L CH₄/L/day. The hardly biodegradable organic components, such as cellulose, hemicellulose, and lignin, were effectively degraded by 78.3%, 58.8%, and 47.5%, respectively. Significantly high anaerobic digestion reaction ratios, especially the hydrolysis ratio which is usually the limiting factor, were calculated based on experimental results. Furthermore, the high lignocellulase contents and coenzyme F₄₂₀ levels, along with the decrease of cellulose crystallinity from 72.6% to 16.4% in the feedstock, provided strong evidence of an enhanced biological activity by CM addition. By high-throughput sequencing analysis, more abundant and diverse bacterial, archaeal, and fungal genera were identified from the DMBR sludge. With CM addition, the biodegradation of lignocellulose might have produced sufficient H₂ and CO₂ for the hydrogenotrophic methanogens such as Methanoculleus, Methanomassiliicoccus, and Methanobacterium, which were highly tolerant to ammonium inhibition, and then the elevated ammonium level would have provided high buffering capacity in the DMBR thus ensuring a stable condition for high rate FW digestion and CH₄ production.

Kinetic Study of Corn and Sugarcane Waste Oxidative Pyrolysis

The behavior of the kinetics and pyrolysis of the corn and sugarcane waste (cob corn, husk corn, and bagasse) produced in Colombia have been evaluated in a thermobalance as a step toward their valorization, in order to recover this type of waste. For this, a kinetic model has been developed consisting of a multicomponent mechanism that seeks to describe the formation of volatile materials. This model evaluates the decomposition of hemicellulose, cellulose, and lignin from three parallel and independent reactions network. It also involves the production of other products such as fixed coal and ashes. The evaluation of the model from the kinetic parameters and the thermogravimetric curves were compared with other types of waste, in the same way the chemical characteristics of the studied waste were determined. Although the wastes of this study are completely different, it was found that the degradation behavior of the residues of this study are very similar to other lignocellulosic materials, which demonstrates again that the pyrolysis valorization is possible.

Green Extraction Approaches for Carotenoids and Esters: Characterization of Native Composition from Orange Peel

Orange peel is a by-product produced in large amounts that acts as a source of natural pigments such as carotenoids. Xanthophylls, the main carotenoid class found in citrus fruit, can be present in its free form or esterified with fatty acids, forming esters. This esterification modifies the compound’s chemical properties, affecting their bioavailability in the human body, and making it important to characterize the native carotenoid composition of food matrices. We aimed to evaluate the non-saponified carotenoid extracts of orange peel (cv. Pera) obtained using alternative green approaches: extraction with ionic liquid (IL), analyzed by high performance liquid chromatography coupled to a diode array detector with atmospheric pressure chemical ionization and mass spectrometry HPLC-DAD-APCI-MS, and supercritical fluid extraction (SFE), followed by supercritical fluid chromatography with atmospheric pressure chemical ionization and triple quadrupole mass spectrometry detection (SFC-APCI/QqQ/MS) in an online system. Both alternative green methods were successfully applied, allowing the total identification of five free carotenoids, one apocarotenoid, seven monoesters, and 11 diesters in the extract obtained with IL and analyzed by HPLC-DAD-APCI-MS, and nine free carotenoids, six carotenoids esters, 19 apocarotenoids, and eight apo-esters with the SFE-SFC-APCI/QqQ/MS approach, including several free apocarotenoids and apocarotenoid esters identified for the first time in oranges, and particularly in the Pera variety, which could be used as a fruit authenticity parameter.

Multi-Criteria and Life Cycle Assessment of Wood-Based Bioenergy Alternatives for Residential Heating: A Sustainability Analysis

Moving towards a global bioeconomy can mitigate climate change and the depletion of fossil fuels. Within this context, this work applies a set of multi-criteria decision analysis (MCDA) tools to prioritise the selection of five alternative bioenergy systems for residential heating based on the combination of three commercial technologies (pellet, wood stove and traditional fireplace) and two different feedstocks (eucalypt and maritime pine species). Several combinations of MCDA methods and weighting approaches were compared to assess how much results can differ. Eight indicators were used for a sustainability assessment of the alternatives while four MCDA methods were applied for the prioritisation: Weighted Sum Method (WSM), Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), Elimination and Choice Expressing Reality (ELECTRE), and Preference Ranking Organization Method for Enrichment Evaluation (PROMETHEE). Regarding the sustainability performance indicators, the highest environmental impacts were calculated for the fireplace alternatives, and there was not a best environmental option. Also, no clear trend was found for the economic and social dimensions. The application of MCDA tools shows that wood stove alternatives have the best sustainability performance, in particular wood stove with combustion of maritime pine logs (highest scores in the ranking). Regarding the worst alternative, fireplaces with combustion of eucalypt logs ranked last in all MCDA rankings. Finally, a sensitivity analysis for the weighting of the performance indicators confirmed wood stoves with combustion of maritime pine logs as the leading alternative and the key role of the analysts within this type of MCDA studies.

Grid columnar flat panel photobioreactor with immobilized photosynthetic bacteria for continuous photofermentative hydrogen production

A biophotoreactor with a transparent glass flat panel with polymethyl methacrylate (PMMA) grid columnar for enhanced biofilm growth with Rhodopseudomonas palustris GCA009 was developed and tested at 590 nm incident light. Continuous photofermentative hydrogen production from glucose was tested using this novel reactor. At light intensity of 210 W/m², feed substrate concentration of 56.0 mmol/L, and crossflow velocity of 1.68 × 10^-6 m/s, a maximum hydrogen production rate of 32.6 mmol/L-d (3.56 mmol/m²-h), hydrogen yield of 1.15 mol H₂/mol glucose and light conversion efficiency of 5.34% can be achieved. Since the revised grid columnar effectively enlarged the surface area of reactor and enhanced cell attachment, the present reactor design led to higher hydrogen production rates than literature works.

Microalgal bioenergy production under zero-waste biorefinery approach: Recent advances and future perspectives

In view of the globalization and energy consumption, an economic and sustainable biorefinery model is essential to address the energy security and climate change. From this perspective, renewable biofuel production from microalgae along with a wide range of value-added co-products define its potential as a biorefinery feedstock. However, economic viability of microalgal biorefinery at its current state is not considered sustainable. Reduce, recycle, and reuse of waste derived from algal bioenergy conversion process will lead to an energy efficient and sustainable zero-waste microalgal biorefinery. This review focuses on three major aspects of zero-waste microalgal biorefinery approach; (1) recent advances on microalgal bioenergy conversion processes (chemical, biochemical and thermochemical); (2) mitigation and transformation of liquid and solid waste and (3) techno-economic analysis (TEA) and lifecycle assessment (LCA). In addition, the study also focuses on the challenges and future perspectives for an advanced microalgal biorefinery model.

Aligning Microbial Biodiversity for Valorization of Biowastes: Conception to Perception

Generation of biowastes is increasing rapidly and its uncontrolled, slow and persistent fermentation leads to the release of Green-house gases (GHGs) into the environment. Exploration and exploitation of microbial diversity for degrading biowastes can result in producing diverse range of bioactive molecules, which can act as a source of bioenergy, biopolymers, nutraceuticals and antimicrobials. The whole process is envisaged to manage biowastes, and reduce their pollution causing capacity, and lead to a sustainable society. A strategy has been proposed for: (1) producing bioactive molecules, and (2) achieving a zero-pollution emission by recycling of the GHGs through biological routes.

Microalgae and Phototrophic Purple Bacteria for Nutrient Recovery From Agri-Industrial Effluents: Influences on Plant Growth, Rhizosphere Bacteria, and Putative Carbon- and Nitrogen-Cycling Genes

Microalgae (MA) and purple phototrophic bacteria (PPB) have the ability to remove and recover nutrients from digestate (anaerobic digestion effluent) and pre-settled pig manure that can be Utilized as bio-fertilizer and organic fertilizer. The objective of this study was to compare the effectiveness of MA and PPB as organic fertilizers and soil conditioners in relation to plant growth and the soil biological processes involved in nitrogen (N) and carbon (C) cycling. To this end, a glasshouse experiment was conducted using MA and PPB as bio-fertilizers to grow a common pasture ryegrass (Lolium rigidum Gaudin) with two destructive harvests (45 and 60 days after emergence). To evaluate the rhizosphere bacterial community, we used barcoded PCR-amplified bacterial 16S rRNA genes for paired-end sequencing on the Illumina Mi-Seq. Additionally, we used phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analysis for the detection of putative functional genes associated with N and soil-C cycling. There was a significant increase in plant growth when the soil was amended with PPB, which almost performed as well as the chemical fertilizers. Analysis of the rhizosphere bacteria after the second harvest revealed a greater abundance of Firmicutes than in the first harvest. Members of this phylum have been identified as a biostimulant for plant growth. In contrast, the MA released nutrients more slowly and had a profound effect on N cycling by modulating N mineralization and N retention pathways. Thus, MA could be developed as a slow-release fertilizer with better N retention, which could improve crop performance and soil function, despite nutrient losses from leaching, runoff, and atmospheric emissions. These data indicate that biologically recovered nutrients from waste resources can be effective as a fertilizer, resulting in enhanced C- and N-cycling capacities in the rhizosphere.

Elemental Composition of Biochar Obtained from Agricultural Waste for Soil Amendment and Carbon Sequestration

For an agricultural country such as Thailand, converting agricultural waste into biochar offers a potential solution to manage massive quantities of crop residues following harvest. This research studied the structure and chemical composition of biochar obtained from cassava rhizomes, cassava stems and corncobs, produced using a patented locally-manufactured biochar kiln using low-cost appropriate technology designed to be fabricated locally by farmers. The research found that cassava stems yielded the highest number of Brunauer-Emmett-Teller (BET) surface area in the biochar product, while chemical analysis indicated that corncobs yielded the highest amount of C (81.35%). The amount of H in the corncob biochar was also the highest (2.42%). The study also showed biochar produced by slow pyrolysis was of a high quality, with stable C and low H/C ratio. Biochar’s high BET surface area and total pore volume makes it suitable for soil amendment, contributing to reduced soil density, higher soil moisture and aeration and reduced leaching of plant nutrients from the rhizosphere. Biochar also provides a conducive habitat for beneficial soil microorganisms. The findings indicate that soil incorporation of biochar produced from agricultural crop residues can enhance food security and mitigate the contribution of the agricultural sector to climate change impacts.

Organic contaminants of emerging concern in Norwegian digestates from biogas production

The aim of this study was to analyze a variety of environmental organic contaminants of emerging concern (CEC) and their metabolites in representative digestate samples from Norwegian biogas production plants. Biogas digestates can be a valuable source for soil amendments and/or fertilizers in commercial agriculture. It is important to assess whether the digestates contain harmful contaminants in order to avoid unintended exposure of human consumers. In total 19 biogas digestates from 12 biogas production plants in Norway were collected and analyzed. Furthermore, process related parameters such as pretreatment of substrates, additives, flocculation and temperature conditions were considered for interpretation of the results. The CEC levels found in the digestates were shown to be dependent on the original composition of the substrate, dry-matter content, and conditioning of the substrate. The sunscreen octocrylene (147 μg L-1) and acetaminophen (paracetamol; 58.6 μg L-1) were found at the highest concentrations in liquid digestates, whereas octocrylene (>600 ng g-1, on a wet weight basis = ww) and the flame retardant TCPP (tris(1-chloro-2-propyl) phosphate, >500 ng g-1 ww) were found at the highest levels in solid digestates, exceeding even the upper limit of quantification (uLOQ) threshold. The highest levels of total CECs were measured in solid digestates (1411 ng g-1 ww) compared to liquid digestates (354 μg L-1 equals 354 ng g-1). The occurrence of CECs in digestate samples, even after extensive and optimized anaerobic digestion, indicates that the operational conditions of the treatment process should be adjusted in order to minimize CEC contamination.

A review on the conversion of volatile fatty acids to polyhydroxyalkanoates using dark fermentative effluents from hydrogen production

The production of bio/microbial-based polymers, polyhydroxyalkanoates (PHAs) from volatile fatty acids (VFAs) of dark fermentative effluents in the bio-H₂ reactor is being paid attention, owing to their commercial demand, applications and as carbon as well as energy storage source. Since, they are the cheap precursors for such valuable renewable biopolymers which all possess the properties; those are analogous to the petro-derived plastics. Several studies were stated, related to the consumption of both individual and mixed VFAs for the potential PHAs production. Their biodegradability nature makes them extremely desirable alternative to fossil-derived synthetic polymers. In this regard, this review summarizes the use of bio-based PHAs production via both microbial and biochemical pathways using dark fermentative bio-H₂ production from waste streams as feedstock. Furthermore, this review deals the characteristics, synthesis and production of the bio-based PHAs along with their co-polymers and applications to give an outlook on future research.

Biowaste Management in Italy: Challenges and Perspectives

The aim of this work is the development of a methodology for the technical and environmental assessment of biowaste valorization in 2G biorefineries. Italy was chosen as case study, considering years 2016–2017. Approach: the Italian context was evaluated through the following key parameters: Gross domestic power, climate, demography, and population density distribution described the Italian framework. The four most abundant biowaste categories were defined through their amounts and geo-localization: wastewater and sewage sludge (WSS, 4.06 Mt/y), organic fraction of municipal solid waste (OFMSW, 1.7 Mt/y), agricultural livestock waste (ALW, 5.7 Mt/y), and waste deriving from the food industry (FIW, 2.6 Mt/y). The geo-localization and quantitative evaluations of the available biowaste amounts were aimed at defining the dimension and localization of the biorefinery plant and at optimizing supply and transport chains, while the qualitative characteristic were aimed to evaluate the most promising process among thermo-valorization (TH) and anaerobic digestion (AD). Results: All considered biowastes were appropriate for biorefinery processes, since carbon content exceeds 40% and the carbon–nitrogen ratio was between 10 and 30. All biowaste categories were evaluated as feedstocks for two biorefinery processes: anaerobic digestion (AD) and thermo-valorization (TH) with energy recovery. Compared to TH, AD achieved in all cases the best performances in terms of produced energy and avoided CO2 emissions. The primary energy production of AD and TH for WSS, OFMSW, ALW, and FIW were respectively: 7.89 vs. 2.4 kWh/kg; 8.7 vs. 2.6 kWh/kg; 10.85 vs. 5.5 kWh/kg; and 12.5 vs. 7.8 kWh/kg. The main findings of this work were: the adoption of AD was technically more suitable than TH; AD increased the avoided CO2 emissions of 10%–89.9% depending on biowaste category.