A novel cascade biorefinery approach to transform food waste into valuable chemicals and biogas through thermal pretreatment integration

Optimization of methane production from solid tuna waste: Thermal pretreatment and co-digestion

Fish canning industries generate large amounts of solid waste during their processing operations, creating a significant environmental challenge. Nonetheless, this waste can be efficiently and sustainably treated through anaerobic digestion. In this study, the potential of biogas production from anaerobic digestion of thermally pretreated and co-digested solid tuna waste was investigated. The thermal pretreatment of raw fish viscera resulted in a 50 % increase in methane yield, with a production of 0.27 g COD-CH4/g COD added. However, this pretreatment did not lead to a significant increase in biogas production for cooked tuna viscera. When non-thermally pretreated raw viscera was tested, a large accumulation of volatile fatty acids and long chain fatty acids was observed, with levels reaching 21 and 6 g COD/L, respectively. On the other hand, anaerobic co-digestion of cooked tuna viscera with fat waste significantly enhanced methane production, achieving 0.87 g COD-CH4/g COD added. In contrast, co-digestion of cooked tuna viscera with dairy waste and sewage sludge resulted in notably lower yields of 0.36 and 0.46 g COD-CH4/g COD added, respectively. These results may be related to the C/N ratio, which was found to be within the optimal range for anaerobic digestion only in the tuna and fat waste co-digestion assay.

Thermally enhanced solid-liquid separation process in food waste biorefinery: modelling the anaerobic digestion of solid residues

The biochemical valorization potential of food waste (FW) could be exploited by extracting decreasing added-value bio-based products and converting the final residues into energy. In this context, multi-purpose and versatile schemes integrating thermal and biochemical conversion processes will play a key role. An upstream thermal pretreatment + solid-liquid separation unit was here proposed to optimize the conversion of the liquid fraction of FW into valuable chemicals through semi-continuous fermentation process, and the conversion of the residual solid fraction into biomethane through anaerobic digestion. The solid residues obtained after thermal pretreatment presented a higher soluble COD fraction, which resulted in higher methane production with respect to the raw residues (0.33 vs. 0.29 Nm3CH4 kg-1VSfed) and higher risk of acidification and failure of methanogenesis when operating at lower HRT (20d). On the contrary, at HRT = 40 d, the pretreatment did not affect the methane conversion rates and both tests evidenced similar methane productions of 0.33 Nm3CH4 kg-1VSfed. In the reactor fed with pretreated residue, the association of hydrogenotrophic methanogens with syntrophic bacteria prevented the acidification of the system. Modelling proved the eligibility of the FW solid residues as substrates for anaerobic digestion, given their small inert fractions that ranged between 0% and 30% of the total COD content.

Recycling of gas-to-liquid sludge as a potential organic amendment: Effect on soil and cotton properties under hyperarid conditions

Gas-to-liquid (GTL) sludge is a specific wastewater treatment by-product, which is generated during the industrial process of natural gas conversion to transportation fuels. This least studied sludge is pathogen-free and rich in organic carbon and plant nutrients. Therefore, it can be reused for soil enhancement as a sustainable management strategy to mitigate landfill gas emissions. In this field study, we compared the performance of soil treatments with GTL sludge to the more conventional chemical fertilizers and cow manure compost for the cultivation of cotton under hyperarid conditions. After a complete growing season, GTL sludge application resulted in the enhancement of soil properties and plant growth compared to conventional inputs. As such, there was a significant dose-dependent increase of soil organic matter (4.01% and 4.54%), phosphorus (534 and 1090 mg kg-1), and cumulative lint yield (4.68 and 5.67 t ha-1) for GTL sludge application rates of 1.5% and 3%, respectively. The produced fiber quality was adequate for an upland cotton variety (Gossypium hirsutum var. MAY 344) and appeared more dependent on the prevailing climate conditions than soil treatments. On the other hand, the adverse effects generally related to industrial sludge reuse were not significant and did not affect the designed agro-environmental system. Accordingly, plants grown on GTL sludge-amended soils showed lower antioxidant activity despite significant salinity increase. In addition, the concentrations of detected heavy metals in soil were within the standards' limits, which did not pose environmental issues under the described experimental conditions. Leachate analysis revealed no risks for groundwater contamination with phytotoxic metals, which were mostly retained by the soil matrix. Therefore, recycling GTL sludge as an organic amendment can be a sustainable solution to improve soil quality and lower carbon footprint. To reduce any environmental concerns, an application rate of 1.5% could be provisionally recommended since a two-fold increase in sludge dose did not result in a significant yield improvement.

Sustainable valorization of pitaya (Hylocereus spp.) peel in a semi-continuous high-pressure hydrothermal process to recover value-added products

This study evaluated the use of a semi-continuous high-pressure hydrothermal process for the recovery of value-added products from pitaya peel. The process was carried out at 15 MPa, a water flow rate of 2 mL/min, a solvent-to-feed ratio of 60 g water/g pitaya peel, and temperatures ranging from 40 to 210 °C. The results show that extraction temperatures (between 40 and 80 °C) promoted the recovery of betacyanin (1.52 mg/g), malic acid (25.6 mg/g), and citric acid (25.98 mg/g). The major phenolic compounds obtained were p-coumaric acid (144.63 ± 0.42 µg/g), protocatechuic acid (91.43 ± 0.32 µg/g), and piperonylic acid (74.2 ± 0.31 µg/g). The hydrolysis temperatures (between 150 and 210 °C) could produce sugars (18.09 mg/g). However, the hydrolysis process at temperatures above 180 °C generated Maillard reaction products, which increased the total phenolic compounds and antioxidant activity of the hydrolysates. Finally, the use of semi-continuous high-pressure hydrothermal process can be a sustainable and promising approach for the recovery of value-added compounds from pitaya peel, advocating a circular economy approach in the agri-food industry.

Food waste biorefinery towards circular economy in Australia

Staggering amounts of food waste are produced in Australia, and this review provides food waste based biorefinery opportunities in moving towards a circular economy in Australia. The current food waste scenario in Australia including an overview of primary food waste sources, government regulation, and current management practices is presented. The major food waste streams include fruit and vegetable (waste from wine grapes, citrus, apple, potato, and tomato), nuts (almond processing waste), seafood (Fish waste), dairy whey, sugarcane bagasse, and household and businesses. The composition of these waste streams indicated their potential for use in biorefineries to produce value-added products via various pathways combining direct extraction and biological and thermochemical conversion. Finally, the efforts made in Australia to utilize food waste as a resource, as well as the challenges and future directions to promote the development of concrete and commercially viable technologies for food waste biorefinery, are described.

Deep insight into oriented propionate production from food waste: Microbiological interpretation and design practice

Using mixed microbial cultures (MMCs) for oriented volatile fatty acids (VFAs) refining in an open environment is a typical challenge due to the microbial diversiform and the process complexity. Especially for carbohydrate-rich waste (such as food waste), butyrate-type fermentation is usually dominant in a single-stage MMCs anaerobic process, while the production of odd-carbon VFAs (such as propionate) is difficult although it plays a significant role in chemicals industries. In this study, firstly, we gave a new perspective on the rationality of the oriented propionate production using MMCs with lactate as feedstock by conducting in-depth microbial informatics and reaction analysis. Secondly, we verified the feasibility of the "food waste-lactate-propionate" route to reverse the original butyrate-type fermentation situation and explore mechanisms for maintaining stability. In the first stage, a defined lactate fermentation microbiome was used to produce lactate-containing broth (80% of total chemical oxygen demand) at pH=4. In the second stage, an undomesticated undefined anaerobic microbiome was used to drive propionate production (45.26% ± 2.23% of total VFAs) under optimized conditions (C/N = 100:1-200:1 and pH=5.0). The low pH environment in the first stage enhanced the lactic acid bacteria to resist the invasion of non-functional flanking bacteria, making the community stable. In the second stage, the system maintained the propionate-type fermentation due to the absence of the ecological niche of the invasive lactic acid bacteria; The selection of propionate-producing specialists was a necessary but not sufficient condition for propionate-type fermentation. At last, this study proposed an enhanced engineering strategy framework for understanding elaborate MMCs fermentation.

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.

An inclusive trend study of techno-economic analysis of biofuel supply chains

Biofuels have gained much attention as a potentially sustainable alternative to fossil fuels to tackle climate change and energy scarcity. Hence, the increasing global interest in contributing to the biofuel supply chain (BSC), from biomass feedstock to biofuel production, has led to a huge amount of scientific production in recent years. In this vein, techno-economic analysis (TEA) of biofuel production to estimate total costs and revenues is highly important for transitioning towards a bioeconomy. This research aims to provide a comprehensive image of the body of knowledge in TEA evolution within the BSC domain. To this end, a systematic science mapping analysis, supported by a bibliometric analysis, is carried out on 1104 articles from 1986 to 2021. As a result, performance indicators of the scientific production within the target literature are presented to explain how this literature has evolved. Besides, thematic trends and conceptual structures of TEA of biofuel production are discovered. The results show that (i) biofuel production and consumption need promotion through tax measures and price subsidies, (ii) the development of cost-competitive algal biofuels has faced many challenges over recent years, and (iii) TEA of algal biofuels to identify commercial improvements and increase the economic feasibility is still lacking, which calls for more in-depth investigations. Consequently, current challenges and future perspectives of TEA in the BSC domain are rendered. The provided insights enable researchers and decision-makers involved in BSCs to (i) capture the most influential contributors to the field and (ii) identify major research hotspots and potential directions for further development.

Polyelectrolyte Precipitation: A New Green Chemistry Approach to Recover Value-Added Proteins from Different Sources in a Circular Economy Context

Proteins have always been vital biological molecules used for industrial purposes, human nutrition and health. Nowadays, seeking new alternatives and sources of these biomolecules is becoming an increasing research trend derived from the present consumer awareness between food consumption and health promotion, but also on environmental sustainability. Although there are different consolidated/traditional downstream processes to obtain proteins, such as chromatography tools, alkali hydrolysis, precipitation by inorganic salts and organic solvents, their industrial-scale application still demands urgent innovation due to the poor recovery yields, high costs and time-consuming steps, environmental impact as well as some toxic concerns. Polyelectrolyte precipitation represents a green, innovative alternative for protein recovery; however, there are reduced data regarding its pilot or industrial-scale application. In this literature work, the action mechanism and principles with regards to its functionality and insights for its application on a big scale are reviewed. Overall, this review discusses the novelty and sustainability of protein precipitation by polyelectrolytes from different sources against traditional techniques as well as highlights the relationship between protein source, production relevance and bioactive properties that are key factors to maximize the application of this extractive method on a circular economy context.

The fourth industrial revolution in the food industry-part II: Emerging food trends

The food industry has recently been under unprecedented pressure due to major global challenges, such as climate change, exponential increase in world population and urbanization, and the worldwide spread of new diseases and pandemics, such as the COVID-19. The fourth industrial revolution (Industry 4.0) has been gaining momentum since 2015 and has revolutionized the way in which food is produced, transported, stored, perceived, and consumed worldwide, leading to the emergence of new food trends. After reviewing Industry 4.0 technologies (e.g. artificial intelligence, smart sensors, robotics, blockchain, and the Internet of Things) in Part I of this work (Hassoun, Aït-Kaddour, et al. 2022. The fourth industrial revolution in the food industry-Part I: Industry 4.0 technologies. Critical Reviews in Food Science and Nutrition, 1-17.), this complimentary review will focus on emerging food trends (such as fortified and functional foods, additive manufacturing technologies, cultured meat, precision fermentation, and personalized food) and their connection with Industry 4.0 innovations. Implementation of new food trends has been associated with recent advances in Industry 4.0 technologies, enabling a range of new possibilities. The results show several positive food trends that reflect increased awareness of food chain actors of the food-related health and environmental impacts of food systems. Emergence of other food trends and higher consumer interest and engagement in the transition toward sustainable food development and innovative green strategies are expected in the future.

Biorefining food waste through the anaerobic conversion of endogenous lactate into caproate: A fragile balance between microbial substrate utilization and product inhibition

New technologies development and renewable source exploitation are key tools to realize the European Green Deal and to boost the bio-based economy. In this context, fermentation of organic residues as food waste is an efficient method to obtain marketable products such as carboxylic acids widely applied in industrial production. Under favourable thermodynamic conditions, short chain fatty acids deriving from primary fermentation could be biologically converted into medium-chain fatty acids as caproate via chain elongation (CE) process, by using ethanol or lactate as electron donors. This study evaluates the effectivity of producing caproate from Food Waste extract rich in organics with in situ electron donor production. The test carried out at OLR 15 gCOD L^-1d^-1 showed high Volatile Fatty Acids (from acetic to caproic acid) yields (0.37 g g^-1COD_fed), with a maximum caproate concentration of 8 g L^-1. The associated microbiome was composed by lactate-producing bacteria (Corynebacterium, Lactobacillus, and Olsenella) and by chain elongators (Clostridiaceae and Caproiciproducens). By stressing the system with OLR increase up to 20 gCOD L^-1d^-1, the CE process was inhibited by the high concentration of caproate (low occurrence of Clostridiaceae and Caproiciproducens). Nevertheless, after few days of stop-feeding regime imposed to the system, the microbiome restored its capability to proceed with lactate-based CE pathways. Different batch tests carried out with the inhibited biomass at increasing initial caproate concentration confirmed its impact on lactate utilization kinetics.

Bioconversion of food and lignocellulosic wastes employing sugar platform: A review of enzymatic hydrolysis and kinetics

Bioenergy and biochemicals can be sustainably produced through fermentation and anaerobic digestion (AD). However, this bioconversion processes could be more economical if the hydrolysis rates of substrates in bioreactors can be accelerated. In this review, the feasibilities of including enzymatic hydrolysis (EH) in various bioconversion systems were studied to facilitate the biological synergy. The reaction kinetics of EH in bioconversion systems comparing pretreated lignocellulosic biomass (LCB) and food waste (FW) substrates were reviewed. Possible strategies to improve the hydrolysis efficiency were explored, including co-cultivation during enzyme production and replacement of pure enzyme with on-site produced fungal mash during EH. Key insights into improvement of current AD and fermentation technologies were summarized and further formed into suggestions of future directions in techno-economic feasibility of biorefinery using mixture of the first-generation food crop feedstock with FW; and/or co-digestion of FW with LCB.