Sustainable Development of Food Waste Biorefineries

The sustainable development of food waste biorefineries is crucial for a number of reasons, and these reasons have environmental, economic, and social dimensions. These biorefineries help mitigate the significant problem of food waste, which is a major environmental challenge, by turning this waste into valuable products, thereby reducing the volume of the waste discarded into landfills and decreasing emissions of carbon dioxide and methane, potent greenhouse gases. In addition, recycling food waste through biorefineries conserves natural resources and minimizes the environmental impact associated with the production and processing of raw materials, thus contributing to a more sustainable and circular economy (CE) [1].

Processing food waste in biorefineries can significantly reduce its environmental impact compared to traditional waste management methods such as landfilling and incineration, while the production of biochemicals, biofuels, biogas, etc., from food waste provides renewable energy sources that can replace fossil fuels, further reducing carbon emissions [2].

The biorefinery concept refers to the sustainable processing of biomass (in this Special Issue, food wastes) into a wide spectrum of bio-based products (such as chemicals and materials) and bioenergy (biofuels, power, heat) [3]. Similar to conventional fossil refineries converting crude oil into multiple products like fuels, lubricants, and chemicals, biorefineries aim to maximize the value derived from biowastes by using integrated and sustainable process configurations to produce multiple outputs [4]. In this context, there are two key components to the biorefinery concept: biomass and sustainable conversion technologies [3].

Resource consumption could be optimized by integrating both of these biorefinery concepts, reducing waste generation rates and improving economic viability. Because of that, this integration involves not only the efficient use of all components of biomass, but also minimizes its environmental impact and contributes to a circular economy.

Regarding biomass feedstocks, the raw material for biorefineries can include agricultural residues, forest residues, dedicated energy crops, micro and macro-algae, and organic waste from various sources such as food wastes. These feedstocks are processes using sustainable conversion technologies able to transform the biomass into the desired products. There are two main types of technologies used here: biochemical and thermochemical processes. Biochemical processes use microorganisms or enzymes to convert biomass into products. This includes fermentation (to produce ethanol or other chemicals), anaerobic digestion (to produce biogas), and enzymatic hydrolysis. Thermochemical processes use heat and chemical reactions to convert raw materials into desired products. This includes processes like pyrolysis (producing bio-oil), gasification (producing syngas), hydrothermal liquefaction, etc.

A wide spectrum of different products can be obtained by means of biorefinery transformation processes, such as biochemicals derived from biomass, which can be used as building blocks for producing polymers, solvents, and other industrial chemicals and bio-based materials including bioplastics, biofibers, and other renewable materials. Also, a wide spectrum of high-energy-density chemicals can be obtained, including ethanol, biodiesel, biogas, and advanced biofuels (e.g., biobutanol, biohydrogen) [5].

From an economic perspective, food waste biorefineries transform a stream of low-value waste into valuable products such as biofuels, bioplastics, chemicals, fertilizers, etc., creating new revenue streams and economic opportunities and stimulating local economies by creating jobs in the collection, processing, and conversion of food waste, as well as fostering the innovation and growth of new industries focused on sustainable technologies. In addition, biorefineries can reduce the waste management costs for municipalities and businesses, allowing those savings to be redirected towards other sustainability initiatives. In this sense, the biorefinery concept also allows for a more efficient use of resources, simultaneously creating a sustainable economy. This is because, in using all of the biomass and producing multiple products, biorefineries enhance the overall efficiency of their raw material and the value derived from it. Moreover, this higher efficiency in the use of raw material also leads to environmental benefits due to the reduction of the exploitation of natural resources and their associated energy consumption, greenhouse gas emissions, effluent generation, etc., promoting the sustainability of raw materials and energy consumption [5]. These changes could create new economies by creating new jobs and promoting the development of local industries around biomass supply chains, reducing transport and logistics costs. Finally, this concept could lead to interesting energy scenarios due to the more diversified and secure energy supply created. In terms of the actual structure of global energy, it is attractive to make countries less dependent on energy imports and diversify their energy supply sources.

From a social point of view, these biorefineries improve waste management practices, fostering awareness and education on the importance of reducing, reusing, and recycling food waste, which can lead to broader societal shifts towards more sustainable behaviors. These biorefineries not only increase energy security by diversifying energy sources and reducing our dependence on imported fossil fuels, but they also reduce our dependence on the by-products from biorefineries, such as compost and biofertilizers, which are used to enrich soils and improve agricultural productivity, closing the nutrient cycle and supporting sustainable agricultural practices. This approach also aligns with several United Nations Sustainable Development Goals (SDGs), such as Goal 2 (Zero Hunger), Goal 7 (Affordable and Clean Energy), Goal 12 (Responsible Consumption and Production) and Goal 13 (Climate Action), contributing to more efficient resource management and fostering a circular economy, making it a vital component of global sustainability efforts.

Additionally, this new biorefinery scenario presents significant challenges and calls for considerations related to the technological development required to ensure a proper processing of the substrates in order to reach adequate efficiencies at achievable economical costs. In this sense, biorefineries need to be economically competitive with traditional petrochemical refineries and other industrial processes. Another important aspect is the availability of a reliable, sustainable, and cost-effective supply of biomass feedstock, which is critical to achieve the desired results. Finally, in a mainly competitive economic environment, supportive policies should also be implemented to promote the development and adoption of biorefinery technologies that, in some cases, could be burdened by higher economical costs [6].

In summary, the biorefinery concept represents a holistic approach to biomass utilization, aiming to produce a wide array of products and energy in an efficient and sustainable way. The potential integration various bio-technologies and bio-processes may play a significant role in advancing the bioeconomy and contributing to environmental sustainability.

This Editorial is part of the Special Issue “Sustainable Development of Food Waste Biorefineries”, which highlights new opportunities and challenges in advancing assessments of the performance of food waste biorefineries, focusing on technological advancements and management initiatives, including the recovery of material and energy from these wastes.

Fifteen manuscripts were submitted to this Special Issue, and all of them were subject to Fermentation’s rigorous review process. Ten research papers were then accepted for publication and inclusion in this Special Issue.

As shown in

Table 1. Analysis of the contributions published in this Special Issue.

N# Contribution	Contribution Type	Research Area	Focus	Type of Biomass	Approach
1	Research Article	Acidogenic fermentation	Fatty acids generation	Food waste	Laboratory research
2	Research Article	Sustainability assessment	Rural areas	Food waste	Full-scale study
3	Research Article	Autolysis enzymes	Nutritional compounds	Spent yeast residue	Case study
4	Research Article	Modelling amino acids fermentation and flash distillation	Ammonium bicarbonate extraction	Anaerobic digestion digestate	Laboratory research and modeling
5	Research Article	Anaerobic digestion	Energy and CO2	Craft brewery wastes	Bench-scale research
6	Brief Report	Modeling	Biomethane	Whey and sugar cane	Laboratory research
7	Research Article	Holistic valorization	Antioxidants, phenolic compounds, PHA, and ethanol	Cocoa by-products	Laboratory research
8	Research Article	Acidogenic fermentation and modeling	H2 and VFA	Corn bioethanol effluent	Laboratory research and modeling
9	Research Article	Anaerobic digestion	VFA, caproic acid	Winery effluent	Laboratory research
10	Research Article	Anaerobic digestion	Carboxylic acid	Synthetic amino acid medium	Laboratory research

, the contributions contained herein cover both material and energy valorization technologies. The majority of these contributions relate to experimental work in the laboratory and industry, but modelling and sustainability studies were also included in this Special Issue. Nine contributions were research articles and only one was a brief report (Table 1).

The article by Pooja Radadiya et al. (contribution 1) discusses the effects of one of the most relevant variables, pH, on the production of short- and medium-chain fatty acids when fermenting food wastes under acidogenic conditions in a leachate bed reactor. To do so, they evaluated the hydrolysis and acidogenesis of a simulated food waste at pH values ranging from 5.5 to 8.5, as well as under uncontrolled conditions. In this research, the authors observed that the optimum pH was 6.5. Butyrate was the predominant fermentative product when operating at 5.5–6.5, whereas acetate was dominant when operating at pH 7.5–8.5. Under uncontrolled pH conditions, lactate was the predominant fermentation product.

The article by Carlos Ariel Cardona et al. (contribution 2) focuses on a sustainability assessment of food waste biorefineries in rural areas of Colombia. In this work, the authors analyze the sustainability of food wastes biorefineries in boosting the rural economy in Colombia, paying special attention to six food wastes (acai, annatto, sugarcane bagasse, rejected plantain and avocado, and organic kitchen food waste) from three different rural areas (Chocó, Caldas, and Sucre). In this study, it was observed that biogas production was the most convenient for the complete use of these residues, while levulinic acid was the most feasible and sustainable by-product to generate.

Joana F. Fundo et al.’s article (contribution 3) explores the optimizing of autolysis conditions for genetically engineered yeast residues to enhance their downstream processing and valorization. This research identifies that increasing the pH to 8 and conducting autolysis at 50 °C for 2 h significantly improves the release of valuable compounds like amino acids and minerals. This method efficiently reduces processing times and costs, yielding higher concentrations of leucine, aspartic acid, and potassium. The autolysis process also generated higher dry weight yields and a higher protein content in the supernatants compared to the untreated samples. Additionally, the autolyzed yeast residues were increased in essential amino acids, making them a rich source of nutrients. This innovative approach presents a sustainable and cost-effective method for converting yeast residues into valuable products which are particularly useful in animal feed supplementation and have other potential commercial applications.

The fourth article, by Alejandro Moure Abelenda et al., focuses on the modelling of amino acid fermentations (arginine, glycine, and histidine) and on the study of the subsequent flash distillation of the digestate to recover ammonium bicarbonate. The most adequate flash distillation conditions included a high moisture content, and the process was enhanced by adding hydrochloric acid or sodium hydroxide to maximize the stabilization of the digestates.

The article by Dhanashree Rawalgaonkar et al. (contribution 5) investigates the feasibility of anaerobic digestion (AD) and CO₂ recovery systems in small craft breweries. Utilizing biochemical methane potential tests and anaerobic sequencing batch reactor studies, their research assesses the production of biomethane from high-strength brewery waste, including hops. Their results indicate that the co-digestion of yeast waste with 20% hops slightly reduces the methane yield but remains economically feasible. The developed spreadsheet tool evaluates economic feasibility based on production volume, waste management, and energy costs, revealing that AD and CO₂ recovery are viable for breweries producing over 50,000 barrels annually. Additionally, their study highlights the environmental and economic benefits of implementing these systems, such as reduced waste surcharges and lower energy costs, thus promoting sustainability in the craft brewing industry. Future recommendations include pilot-scale AD studies with varying hop dosages and the further exploration of resource recovery pathways, including compressed natural gas and liquefied CO₂.

The article by Huaita Pacari Arotingo Guandinango et al. (contribution 6) deals with the modeling of biomethane generation from the anaerobic digestion of whey and sugar cane mixtures made in Ecuador. The experimental results were fitted to six different kinetic models, five of which were previously studied by other authors while the sixth one was developed in this work by modifying an existing first-order model. From the experimental results, the authors observed that the model developed in their work and the modified two-stage Gompertz model were those with the best fitting. Additionally, their model depended on five parameters, one less than the modified two-stage Gompertz model, making it more robust and straightforward.

In the seventh article of this Special Issue, Licelander Hennessey Ramos et al. focus on the valorization of cocoa pod husks (CPHs) and cocoa bean shells (CBSs), major by-products of the cocoa industry. Their research characterizes the chemical composition of these residues, highlighting the richness of their protein, lipid, and bioactive compound contents. CBSs exhibited higher protein and lipid contents compared to CPHs. The study demonstrated that both CPHs and CBSs contain significant amounts of phenolic compounds, particularly pyrogallol, which grants them antioxidant properties. The alkaline pretreatment and then enzymatic hydrolysis of CPH efficiently released glucose, which supported the growth of Cupriavidus necator DSM 545 and Saccharomyces cerevisiae Fm17 to produce polyhydroxyalkanoates (PHAs) and bioethanol, respectively. Their findings suggest that cocoa residues can be sustainably converted into high-value bioproducts, promoting a circular economy in the cocoa industry. Future research could explore the further optimization of pretreatment conditions and the scalability of their bioconversion processes.

The eighth article, by María Eugenia Ibañez López et al., studied the generation of volatile fatty acids and hydrogen during the acidogenic fermentation of corn bioethanol effluent under uncontrolled pH conditions. The researchers evaluated acidogenic fermentation with starting pHs ranging from 4 to 6. When starting at pH 4, the system develops extreme acidic conditions that stop fermentation, causing uncoupling growth during the fermentative process. However, when starting the fermentation at pH 5 and 6, the initial substrate was completely fermented, and significant amounts of fermentation products were obtained. The optimum initial pH for uncontrolled pH fermentation was found to be pH 5, which yielded the highest biomass growth rate and highest hydrogen and butyric yields.

The ninth text published in this Special Issue, by M. Eugenia Ibáñez-López et al., explores the optimization of the anaerobic digestion of winery wastewater (WW) using an upflow anaerobic sludge blanket (UASB) reactor. Their research focuses on producing volatile fatty acids (VFAs), with an emphasis on caproic acid (HCa), by varying the hydraulic retention time (HRT) to 8, 5, and 2.5 h. Their results indicate that a 5 h HRT optimizes VFA production, yielding a maximum HCa concentration of 0.9 gCOD/L and enhancing the overall production of VFAs by approximately 20%. Microbial analysis revealed the dominance of Firmicutes, particularly Clostridium species, which are known to produce HCa. This study demonstrates the potential of UASB reactors in biorefineries to efficiently convert WW into valuable bioproducts, promoting sustainability in the wine industry. Further research is recommended to explore other operational conditions and to scale up the process for industrial application.

The tenth article, which is by Leandro Conrado et al., focuses on the biotransformation of proteinogenic amino acids into volatile fatty acids (VFAs) under anaerobic conditions with methanogenesis inhibition. Through batch experiments on a microbiome from an anaerobic digester, this study found that lysine, glutamate, and serine primarily produced butyrate, while other amino acids generated lesser amounts of propionate, iso-butyrate, and iso-valerate. 16S rRNA gene amplicon sequencing identified Anaerostignum, Intestimonas, Aminipila, and Oscillibacter as the key microbes in butyrate production. The findings suggest that these amino acids could be significant feedstocks for VFA production in non-methanogenic conditions, highlighting the potential of optimizing biorefining processes to produce higher-value carboxylic acids.

The contributions published within this Special Issue were the following papers:

• Radadiya, P.; Latika, A.; Fei, X.; Lee, J.; Mishra, S.; Hussain, A. The Effect of pH on the Production and Composition of Short- and Medium-Chain Fatty Acids from Food Waste in a Leachate Bed Reactor at Room Temperature. Fermentation 2023, 9(6), 518; https://doi.org/10.3390/fermentation9060518.
• Cardona, C.A.; Ortiz-Sanchez, M.; Salgado, N.; Solarte-Toro, J.C.; Orrego, C.E.; Perez, A.; Acosta, C.D.; Ledezma, E.; Salas, H.; Gonzaga, J.; Delgado, S. Sustainability Assessment of Food Waste Biorefineries as the Base of the Entrepreneurship in Rural Zones of Colombia. Fermentation 2023, 9(7), 609; https://doi.org/10.3390/fermentation9070609.
• Fundo, J.F.; Deuchande, T.; Rodrigues, D.A.; Pimentel, L.L.; Vidigal, S.S.M.P.; Rodríguez-Alcalá, L.M.; Pintado, M.E.; Amaro, A.L. Induced Autolysis of Engineered Yeast Residue as a Means to Simplify Downstream Processing for Valorization—A Case Study. Fermentation 2023, 9(7), 673; https://doi.org/10.3390/fermentation9070673.
• Moure Abelenda, A.; Aggidis, G.; Aiouache, F. Modelling of Amino Acid Fermentations and Stabilization of Anaerobic Digestates by Extracting Ammonium Bicarbonate. Fermentation 2023, 9(8), 750; https://doi.org/10.3390/fermentation9080750.
• Rawalgaonkar, D.; Zhang, Y.; Walker, S.; Kirchman, P.; Zhang, Q.; Ergas, S.J. Recovery of Energy and Carbon Dioxide from Craft Brewery Wastes for Onsite Use. Fermentation 2023, 9(9), 831; https://doi.org/10.3390/fermentation9090831.
• Arotingo Guandinango, H.P.; Espín Valladares, R.C.; Núñez Pérez, J.; Lara Fiallos, M.V.; Pereda Reyes, I.; Pais-Chanfrau, J.M. Modelisation of the Biomethane Accumulation in Anaerobic Co-Digestion of Whey and Sugarcane Molasse Mixtures. Fermentation 2023, 9(9), 834; https://doi.org/10.3390/fermentation9090834.
• Ramos, L.H.; Cisneros-Yupanqui, M.; Santisteban Soto, D.V.; Lante, A.; Favaro, L.; Casella, S.; Basaglia, M. Exploitation of Cocoa Pod Residues for the Production of Antioxidants, Polyhydroxyalkanoates, and Ethanol. Fermentation 2023, 9(9), 843; https://doi.org/10.3390/fermentation9090843.
• Ibañez-López, M.E.; Díaz-Domínguez, E.; Suffo, M.; Makinia, J.; García-Morales, J.L.; Fernández-Morales, F.J. Biorefinery Approach for H₂ and Acids Production Based on Uncontrolled pH Fermentation of an Industrial Effluent. Fermentation 2023, 9(11), 937; https://doi.org/10.3390/fermentation9110937.
• Ibáñez-López, M.E.; Frison, N.; Bolzonella, D.; García-Morales, J.L. Enhancing Anaerobic Digestion with an UASB Reactor of the Winery Wastewater for Producing Volatile Fatty Acid Effluent Enriched in Caproic Acid. Fermentation 2023, 9(11), 958; https://doi.org/10.3390/fermentation9110958.
• Conrado, L.; McCoy, J.; Rabinovich, L.; Davoudimehr, M.; Stamatopoulou, P.; Scarborough, M. Anaerobic Conversion of Proteinogenic Amino Acids When Methanogenesis Is Inhibited: Carboxylic Acid Production from Single Amino Acids. Fermentation 2024, 10(5), 237; https://doi.org/10.3390/fermentation10050237.

Analyzing the papers published in this Special Issue reveals several research gaps in this field. It is worth noting that no research or technical studies were carried out using thermochemical processing technologies. Additionally, only one study was carried out at full scale. In this sense, more full-scale studies are required to determine the technical feasibility of the processes developed. Finally, more studies focused on the economic aspects of biorefineries should be developed in order to accurately determine whether the projects and investments proposed are financially viable and able to generate a positive return.