Current status of food waste generation and management in China

A new paradigm for whole-chain low-carbon utilization of food waste secondary waste based on multivariate evaluations

The rapid growth of China's food and beverage industry has led to a significant increase in food waste, presenting major challenges for its disposal. Anaerobic digestion is the primary treatment method, but its by-products-biogas slurry (BS) and biogas residue (BR)-pose additional treatment challenges. This study proposes and evaluates three management scenarios for these by-products: (1) BS sewage treatment with BR incineration (S1), (2) BS land application with BR composting (S2), and (3) BS sewage treatment with BR composting (S3). The scenarios were comprehensively assessed using material flow analysis, life cycle assessment, and economic benefit analysis. The findings show that S2 achieves the highest carbon utilization efficiency (80.16%) and delivers superior environmental and economic benefits. Scaling up S2 by 2030 could reduce national carbon emissions by 1817.8 kilotons and generate $11.14 billion in economic profit. This study offers a novel model for the sustainable, low-carbon utilization of food waste by-products, providing valuable insights for future organic waste management.

Synergetic anaerobic digestion of food waste for enhanced production of biogas and value-added products: strategies, challenges, and techno-economic analysis

The generation of food waste (FW) is increasing at an alarming rate, contributing to a total of 32% of all the waste produced globally. Anaerobic digestion (AD) is an effective method for dealing with organic wastes of various compositions, like FW. Waste valorization into value-added products has increased due to the conversion of FW into biogas using AD technology. A variety of pathways are adopted by microbes to avoid unfavorable conditions in AD, including competition between sulfate-reducing bacteria and methane (CH4)-forming bacteria. Anaerobic bacteria decompose organic matter to produce biogas, a digester gas. The composition depends on the type of raw material and the method by which the digestion process is conducted. Studies have shown that the biogas produced by AD contains 65-75% CH4 and 35-45% carbon dioxide (CO2). Methanothrix soehngenii and Methanosaeta concilii are examples of species that convert acetate to CH4 and CO2. Methanobacterium bryantii, Methanobacterium thermoautotrophicum, and Methanobrevibacter arboriphilus are examples of species that produce CH4 from hydrogen and CO2. Methanobacterium formicicum, Methanobrevibacter smithii, and Methanococcus voltae are examples of species that consume formate, hydrogen, and CO2 and produce CH4. The popularity of AD has increased for the development of biorefinery because it is seen as a more environmentally acceptable alternative in comparison to physico-chemical techniques for resource and energy recovery. The review examines the possibility of using accessible FW to produce important value-added products such as organic acids (acetate/butyrate), biopolymers, and other essential value-added products.

Decreasing Greenhouse Gas Emissions from the Municipal Solid Waste Sector in Chinese Cites

Municipal solid waste (MSW) management systems play a crucial role in greenhouse gas (GHG) emissions in China. Although the government has implemented many policies to improve the MSW management system, the impact of these improvements on city-level GHG emission reduction remains largely unexplored. This study conducted a comprehensive analysis of both direct and downstream GHG emissions from the MSW sector, encompassing sanitary landfill, dump, incineration, and biological treatment, across 352 Chinese cities from 2001 to 2021 by adopting inventory methods recommended by the Intergovernmental Panel on Climate Change (IPCC). The results reveal that (1) GHG emissions from the MSW sector in China peaked at 70.6 Tg of CO2 equiv in 2018, followed by a significant decline to 47.6 Tg of CO2 equiv in 2021, (2) cities with the highest GHG emission reduction benefits in the MSW sector were historical emission hotspots over the past 2 decades, and (3) with the potential achievement of zero-landfilling policy by 2030, an additional reduction of 203.7 Tg of CO2 equiv is projected, with the emission reduction focus toward cities in South China (21.9%), Northeast China (17.8%), and Southwest China (17.3%). This study highlights that, even without explicit emission reduction targets for the MSW sector, the improvements of this sector have significantly reduced GHG emissions in China.

Impact of Food Waste on Society, Specifically at Retail and Foodservice Levels in Developed and Developing Countries

Food loss and waste pose significant challenges in both industrial and agricultural food production sectors. In recent decades, their environmental and economic impacts have intensified due to increasing food demand, heightened production activities, and varying standards across the global supply chain. Specifically, the complexities surrounding the causes of food waste at the retail and household levels persist as a multifaceted issue, constituting a crucial topic in food policy. This is driven by various interplaying aspects, such as food security, safety, quality, and environmental sustainability, including greenhouse gas emissions from decaying food, water pollution from leaching, and the proliferation of landfills. Additionally, consumer concerns and financial losses exacerbate the urgency of addressing this issue. Therefore, this paper aims to highlight these complexities as a focal point of its discussion by the examination of interconnected causes of food waste and potential solutions and initiatives to reduce food waste occurring at these critical points in the food supply chain. Less attention has been paid to retail and foodservice than production and consumer sectors, and this review specifically focuses on these industries, where food waste is more important than food loss. This review also looks at examples in developing countries which have received less attention until now. We believe that because of the complexity of the process to reduce food waste across the food supply chain, and the many stakeholders involved, the goal of a 50% reduction by 2030 set by the United Nations will be difficult to achieve on time.

What shapes food waste behaviors? New insights from a comprehensive action determination model

The sharp increase in food waste poses a serious threat to food security and environmental sustainability. However, most existing studies have investigated the determinants of food waste behaviors in a separate behavioral process without considering the potential impacts of different factors in an integrated process. To narrow this gap, a comprehensive action determination model (CADM), which integrates network embeddedness and incentive measures, was constructed to explore the impact of various determinants in different processes on food waste behaviors, using data collected from 913 residents in eastern China via an online survey. The empirical results showed that environmental concern was the largest positive factor in predicting personal norms (β = 0.80, p < 0.001), followed by network embeddedness. With the habitual process considered, residents with ingrained waste habits were more likely to waste food (β = 0.38, p < 0.001). Moreover, the normative process alleviates behavioral decisions via intentions to reduce food waste. This study confirmed the differences in the situational process and suggested that menu tips increase food waste behaviors, while incentive measures reinforce the influence of intentions on behavior. We therefore address the insufficient ingredients on the effects of different processes on behavior and provide a new perspective for formulating behavioral intervention policies.

Biohythane production from two-stage anaerobic digestion of food waste: A review

The biotransformation of food waste (FW) to bioenergy has attracted considerable research attention as a means to address the energy crisis and waste disposal problems. To this end, a promising technique is two-stage anaerobic digestion (TSAD), in which the FW is transformed to biohythane, a gaseous mixture of biomethane and biohydrogen. This review summarises the main characteristics of FW and describes the basic principle of TSAD. Moreover, the factors influencing the TSAD performance are identified, and an overview of the research status; economic aspects; and strategies such as pre-treatment, co-digestion, and regulation of microbial consortia to increase the biohythane yield from TSAD is provided. Additionally, the challenges and future considerations associated with the treatment of FW by TSAD are highlighted. This paper can provide valuable reference for the improvement and widespread implementation of TSAD-based FW treatment.

Carbon reduction trade-off between pretreatment and anaerobic digestion: A field study of an industrial-scale biogas plant

With the implementation of municipal solid waste source segregation, the enormous sorted biogenic waste has become an issue that needs to be seriously considered. Anaerobic digestion, which can produce biogas and extract floating oil for biodiesel production, is the most prevalent treatment in China for waste management and greenhouse gas (GHG) emissions reduction, in accordance with Sustainable Development Goal 13 of the United Nations. Herein, a large-scale biogas plant with a capacity of 1000 tonnes of biogenic waste (400 tonnes of restaurant biogenic waste and 600 tonnes of kitchen biogenic waste) per day was investigated onsite using material flow analysis, and the parts of the biogas plant were thoroughly analyzed, especially the pretreatment system for biogenic waste impurity removal and homogenization. The results indicated that the loss of the total biodegradable organic matter was 41.8% (w/w) of daily feedstock and the loss of biogas potential was 18.8% (v/v) of daily feedstock. Life cycle assessment revealed that the 100-year GHG emissions were -61.2 kgCO2-eq per tonne biogenic waste. According to the sensitivity analysis, pretreatment efficiency, including biodegradable organic matter recovery and floating oil extraction, considerably affected carbon reduction potential. However, when the pretreatment efficiency deteriorated, GHG benefits of waste source segregation and the subsequent biogenic waste anaerobic digestion would be reduced.

Comparing and optimizing municipal solid waste (MSW) management focused on air pollution reduction from MSW incineration in China

China is the largest developing country in the world, and its municipal solid waste (MSW) has increased with a compound annual growth rate of 5.1 % since 1980. Incineration, which has the advantages of mass- and volume-reduction as well as energy and heat recovery, has become the mainstream environmentally sound treatment method in China. However, air pollution emissions are the primary reason for limiting MSW incineration (MSWI). Currently, the Chinese government is devoted to comprehensively implementing MSW classification. However, the classification model and the future MSW reduction rate are not yet clear. In this study, we project scenarios of air pollution emissions until 2030 based on the different MSW classification models (MSW reduction rates) and diffusion rates of ultra-low emission technology. A total of 6011 tons (t) of particulate matter, 25,881 t of SO2, 14,915 t of CO, 17,167 t of HCl, and 200,166 t of NOx will be emitted in 2030 under the business-as-usual (BAU) scenario, and air pollutants will not peak under this scenario. Air pollutants will reduce by 11 % of the BAU scenario by only implementing an MSW reduction of 20 % (JPN-model). The optimal scenario (DEU-model, increasing the efficiency of material recovery and upgrading air pollution control devices) means that air pollutants will be reduced by 83.2-96.2 % from the base amount under the BAU scenario. These results provide references for MSW management and air pollution emission reduction from the aspects of MSW classification and technology upgrades in China.

Enhanced volatile fatty acid production from food waste via anaerobic fermentation: effect of irons with different sizes

ABSTRACTFood waste is an excellent organic matter for anaerobic fermentation. This study provided a cost-effective and highly efficient volatile fatty acid (VFA) production strategy by the addition of zero-valent iron (ZVI). Results showed that VFA concentration of 44.6 g/L was obtained with the optimized conditions of 200-mesh iron powder at a dosage of 20.0 g, fermentation time of 11 d, total solids (TS) of 10 wt.%, and fermentation temperature of 37 ℃. Further, the iron of different particle sizes (iron scraps, 200-mesh iron powder, and 800-mesh iron powder) had a differential influence on total organic carbon (TOC), total nitrogen (TN), and VFA concentrations. For the reactor containing 200-mesh iron powder, the conversion rate of organic compound into VFA increased with the increase of dosage, which reached 58.4% at the 40.0 g dosage. The mechanism revealed that the VFA production was enhanced by micro-electrolysis, which can rapidly inactivate bacteria and increase the conversion of macromolecular organics into micromolecular organics.

Using fresh vegetable waste from Chinese traditional wet markets as animal feed: Material feasibility and utilization potential

To develop new animal feed sources and establish a sustainable food upcycling system, the material feasibility and feeding potential of fresh vegetable waste (FVW) were clarified in this study. First, the FVW output of wet markets in Hangzhou, China was tracked and predicted. The results showed that the retail waste ratio of FVW in wet markets reached 9.3 %, predicting that China's FVW will reach 9034 kt in 2030. Second, the study revealed that the nutritive value of FVW was comparable to that of traditional alfalfa feed, suitable for use as animal feed. However, we found a high probability of microbial contamination. Therefore, FVW should have stricter classification and collection methods. Under this premise, the feeding utilization potential of FVW in wet markets is large. In 2030, the crude protein content may replace 2737 kt of alfalfa, saving 7.7 E + 08 m3 of water and 75,018 ha of land.

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.

Revealing the effects of fermented food waste on the growth and intestinal microorganisms of black soldier fly (Hermetia illucens) larvae

The escalating global food waste (FW) issues necessitate sustainable management strategies. Black soldier fly larvae (BSFL) offer a promising solution for FW management by converting organic matter into insect protein. However, the fermentation of FW during production, collection, and transportation induces changes in FW's physicochemical properties and bacterial communities, requiring further exploration of its impact on BSFL growth and gut microbiota. The results showed that feeding FW fermented for different durations (0-10 d) slightly affected the BSFL yield. Feeding FW fermented for 8 d, characterized by a lower pH and higher biodiversity, resulted in a slight increase in larval biomass (222 mg/larvae). Nearly all groups harvested the peak larval biomass after 10 day's bioconversion. The fermentation significantly altered the microbial community of FW, with an increase in the abundance of unclassified_f_Clostridiaceae and a decrease in Lactobacillus abundance. As bioconversion progressed, intricate and mutualistic microbial interactions likely occurred between the BSFL gut and FW substrate, restructuring each other's microbial community. Specifically, the abundance of unclassified_f_Clostridiaceae increased in the BSFL gut, while its abundance in the initial larval gut was extremely low (<1 %). Despite the substrate microbial changes and interactions, a stable core gut microbiota was identified across all BSFL samples, primarily composed of nine genera dominated by Enterococcus and Klebsiella. This core gut microbiome may play a crucial role in facilitating the adaptation of BSFL to various environmental conditions and maintaining efficient FW bioconversion. These findings enhance our understanding of the role of BSFL gut microbiota in FW bioconversion.

Influence of biochar on succession of fungal communities during food waste composting

This study aims to examine the effects of biochar on fungal dynamics during food waste composting. The different dosage of wheat straw biochar from 0 to 15% (0%, 2.5%, 5%, 7.5%, 10%, and 15%) were used as an additive to composting and examined for 42 days. The results showed that Ascomycota (94.64%) and Basidiomycota (5.36%) were the most dominant phyla. The most common fungal genera were Kluyveromyces (3.76%), Candida (5.34%), Trichoderma (2.30%), Fusarium (0.46%), Mycothermus-thermophilus (5.67%), Trametes (0.46%), and Trichosporon (3.38%). The average number of operational taxonomic units were 469, with the greatest abundance seen in the 7.5% and 10% treatments. Redundancy analysis revealed that different concentrations of biochar applied treatments have significantly distinct fungal communities. Additionally, correlation analyses of fungal interactions with environmental elements, performed through a heatmap, also indicate a distinct difference among the treatments. The study clearly demonstrates that 15% of biochar has a positive impact on fungal diversity and improves the food waste composting.

Different stages of microbial community during the anaerobic digestion of food waste

Large-scale food waste (FW) disposal has resulted in severe environmental degradation and financial losses around the world. Although FW has a high biomass energy contents and a growing large number of national projects to recover energy from FW by anaerobic digestion (AD) are being developed. AD is a promising solution for FW management and energy generation when compared to typical disposal options including landfill disposal, incineration, and composting. AD of FW can be combined with an existing AD operation or linked to the manufacture of value-added products to reduce costs and increase income. AD is a metabolic process that requires four different types of microbes: hydrolyzers, acidogens, acetogens, and methanogens. Microbes use a variety of strategies to avoid difficult situations in the AD, such as competition for the same substrate between sulfate-reducing bacteria and methane-forming bacteria. An improved comprehension of the microbiology involved in the anaerobic digestion of FW will provide new insight into the circumstances needed to maximize this procedure, including its possibilities for use in co-digestion mechanisms. This paper reviewed the present scientific knowledge of microbial community during the AD and the connection between microbial diversity during the AD of FW.

Waste and by-products as sources of lycopene, phytoene, and phytofluene - Integrative review with bibliometric analysis

Food loss and waste are severe social, economic, and environmental issues. An example is the incorrect handling of waste or by-products used to obtain bioactive compounds, such as carotenoids. This review aimed to present a comprehensive overview of research on lycopene, phytoene, and phytofluene obtained from waste and by-products. In this study, an integrative literature approach was coupled with bibliometric analysis to provide a broad perspective of the topic. PRISMA guidelines were used to search studies in the Web of Science database systematically. Articles were included if (1) employed waste or by-products to obtain lycopene, phytoene, and phytofluene or (2) performed applications of the carotenoids previously extracted from waste sources. Two hundred and four articles were included in the study, and the prevalent theme was research on the recovery of lycopene from tomato processing. However, the scarcity of studies on colorless carotenoids (phytoene and phytofluene) was evidenced, although these are generally associated with lycopene. Different technologies were used to extract lycopene from plant matrices, with a clear current trend toward choosing environmentally friendly alternatives. Microbial production of carotenoids from various wastes is a highly competitive alternative to conventional processes. The results described here can guide future forays into the subject, especially regarding research on phytoene and phytofluene, potential and untapped sources of carotenoids from waste and by-products, and in choosing more efficient, safe, and environmentally sustainable extraction protocols.

Design and preparation of carbon material catalyst modified with metal framework and sulfonate for biochar generation from low-temperature directional pyrolysis of kitchen waste: Mechanism and performance

In order to reduce the pyrolysis temperature during the process of directional conversion from kitchen waste (KW) into aromatic biochar, a kind of catalyst was prepared with carbon material coated with tri-metallic oxide (Fe₂O₃, MgO and Al₂O₃) combining with sulfonic acid groups (CMO@SA) according to KW compositions. The aromaticity of KW pyrolysis biochar (KWB) increased when the temperature ranged from 170 to 210 °C. The catalytic pyrolysis temperature of KW reduced from 500 to 190 °C for biochar generation with similar aromaticity due to amendment of CMO@SA. The maximum adsorption capacity of catalytic pyrolysis KWB was 160.23 mg/g for dyeing wastewater, which was equivalent to biochar generated at 500 °C. The decrease of pyrolysis temperature was attributed to the reduction of bonds fracture activation-energy among CH, CC and CO under the catalytic function. The catalytic activity and recovery of CMO@SA kept at 92 % and 90 % after five recycle.

Bioconversion of food waste to crayfish feed using solid-state fermentation with yeast

In order to realize the value-added utilization of food waste (FW), the preparation of crayfish (Procambarus clarkii) feed by yeast fermentation was investigated. Firstly, the suitable fermentation condition was obtained through a single factor experiment as follows: the initial moisture of the FW was adjusted to 60% with bran and inoculated with a 2% yeast mixture (Saccharomyces cerevisiae, Candida utilis, and Yarrowia lipolytica, 3:2:1) followed by aerobic solid-state fermentation for 7 days. The crude protein and acid-soluble protein contents in the fermented feed were 25.14% and 5.16%, which were increased by 8% and 140.67%, respectively. The crude fat content was 0.74%, decreased by 68.29%. The content of antioxidant glutathione (571.78 μg/g) increased 63.33%, and the activities of protease and amylase increased nearly 9 and 3 times, respectively. The maximum degradation rates of aflatoxin B1, zearalenone, and deoxynivalenol were 63.83%, 77.52%, and 80.16%, respectively. The fermented feeds were evaluated by substituting (0%, 10%, 30%, 50%, and 100%) commercial diet for crayfish (30-day culture period). When the replacement proportion was 30%, the weight gain of crayfish reached 44.87% (initial body weight 13.98 ± 0.41 g), which was significantly increased by 10.25% compared with the control (p = 0.0005). In addition, the lysozyme and SOD enzyme activities in crayfish hepatopancreas were also increased significantly. Our findings suggest that yeast-fermented feed from FW can replace 30% of crayfish's conventional diet, which may improve crayfish's antioxidant capacity and enhance non-specific immunity by providing molecules such as glutathione.

Mineral residue accelerant-enhanced anaerobic digestion of cow manure: An evaluation system of comprehensive performance

Anaerobic digestion (AD) is an efficient technology for treating biowaste and generating biogas. A reasonable evaluation of AD performance is crucial to its development. Herein, a comprehensive evaluation system covering five dimensions (energy output, process stability, degradation efficiency, digestate fertility, and digestate safety) was established to assess AD performance. Each dimension in the evaluation system was assigned a specific indicator defined by a threshold or range. Additionally, the proposed evaluation system was applied to assess a case study of batch-mode mesophilic AD that employed three industrial waste residues as mineral accelerants (nickel‑iron slag, steel slag, and fly ash). The mineral accelerants enhanced the energy output (methane yield by 66.55 %-87.54 %) and the feedstock degradation (chemical oxygen demand removal ratio by 11.23 %-32.42 %). The digestates also retained promising safety (heavy metal contents of 190-1260 mg/kg) and fertility (total nutrient contents of 3.71 %-4.69 %). The evaluation system reasonably appraised the comprehensive performance of accelerant-enhanced AD systems with cow manure. This work provides a reliable methodology for evaluating and comparing the performance of different novel accelerants and can be applied to evaluate the comprehensive performance of large-scale biogas projects with cow manure.

Health risk assessment of mercury in Nile tilapia (Oreochromis niloticus) fed housefly maggots

The bioaccumulation of total mercury (THg) and methylmercury (MeHg) by housefly maggots (HM) during the conversion of food waste (vegetables and meat (VM) and rice waste) under various waste feed ratios were investigated. Subsequently, Nile tilapia (Oreochromis niloticus) were fed with the commercial feed, commercial dried HM, dried HM, and fresh HM, followed by a human health risk assessment of Hg via fish consumption. The THg concentrations of HM fed with food waste ranged from 39.5 to 100 μg kg^-1 ww. Concentrations of MeHg in the maggots fed with 100 % vegetables and meat (VM) waste (13.7 ± 1.12 μg kg^-1 ww) was significantly higher than that fed with other mixed ratios of rice waste and VM waste (p<0.05). Concentrations of MeHg were positively correlated with the weight and lipid content of houseflies (p<0.05). THg and MeHg concentrations in tilapia fed with the converted HM (dried and fresh HM) were 22.5 ± 6.50 μg kg^-1 ww and 2.43 ± 0.36 μg kg^-1 ww, respectively. There was no significant difference in MeHg between tilapia fed the four experiment diets (p>0.05). Health risk assessment results indicated that mercury in tilapia fed the food waste-grown HM did not pose potential health risks to humans (target hazard quotient < 1). In conclusion, HM could convert food waste into high-quality and safe fish feeds for cultivating tilapia.

Integrated crop-livestock-bioenergy system brings co-benefits and trade-offs in mitigating the environmental impacts of Chinese agriculture

Agricultural bioenergy utilization relies on crop and livestock production, favouring an integrated crop-livestock-bioenergy production model. Yet the integrated system's exact contribution to mitigating various environmental burdens from the crop production system and livestock production system remains unclear. Here we inventory the environmental impacts of each process in three subsystems at both national and regional scales in China, ultimately identifying key processes and impact categories. The co-benefits and trade-offs in nine impact categories are investigated by comparing the life cycle impacts in the background scenario (crop production system + livestock production system) and foreground scenario (integrated system). Freshwater eutrophication is the most serious impact category in both scenarios. Except terrestrial acidification, the mitigation effects on the other eight impact categories vary from 1.8% to 94.8%, attributed to fossil energy and chemical fertilizer offsets. Environmental trade-offs should be deliberated when expanding bioenergy utilization in the identified critical regions.

A novel process for food waste recycling: A hydrophobic liquid mulching film preparation

Appropriate and effective recycling of food waste (FW) has become increasingly significant with the promotion of garbage classification in China. In this study, a novel and green process was developed to recycle FW to prepare a biodegradable composite liquid mulching film (LMF) through crosslinking with sodium alginate (SA). The solid phase of FW was obtained as the raw material after hydrothermal pretreatment to remove pathogens and salts, and to improve the reactivity of active components at a moderate temperature. The prepared LMF had a hydrophobic surface and compact structure due to the lipid in FW and the acetalization reaction and hydrogen bonds among SA, glutaraldehyde and multi-active components of FW, resulting in enhanced water vapor barrier properties. The minimum water vapor permeability of the prepared LMF reached (8.23 ± 0.05) ✕ 10^-12 g cm/(cm²·s·Pa) with 1.82 wt % of plasticizer, 0.74 wt% of crosslinker and a mass ratio of HTP-FW to SA of 3.56:1. The prepared LMF showed good mechanical properties and could maintain its integrity after spraying it on the soil surface for 31 days. In addition, it could effectively prevent the loss of soil moisture and heat, promote the seed germination of Chinese cabbage and achieve 89.14% of weight loss after burying in the soil for 27 days. This study provides a high value-added route to convert the FW to a hydrophobic LMF with superior properties, which addresses not only the problem of food waste but also the pollution of plastic mulching film.

Succession of Microbial Community during the Co-Composting of Food Waste Digestate and Garden Waste

Microorganisms are of critical importance during the composting process. The aim of this study was to reveal the bacterial and fungal compositions of a composting pile of food waste digestate and garden waste, where the succession of the microbial communities was monitored using Illumina MiSeq sequencing. We explored the efficiency of composting of different microorganisms to judge whether the composting system was running successfully. The results showed that the composting process significantly changed the bacterial and fungal structure. Firmicutes, Proteobacteria, and Bacteroidota were the dominant phyla of the bacterial communities, while Ascomycota was the dominant phylum of the fungal communities. Moreover, the highest bacterial and fungal biodiversity occurred in the thermophilic stage. The physical and chemical properties of the final compost products conformed to the national standards of fertilizers. The efficient composting functional microbes, including Cladosporium, Bacillus and Saccharomonospora, emerged to be an important sign of a successfully operating composting system.

Fighting Food Waste by Law: Making Sense of the Chinese Approach

The Standing Committee of the National People's Congress adopted the Anti-food Waste Law of the People's Republic of China in April 2021 to guarantee grain security, conserve resources, and protect the environment. We pursue three research questions: Why has China implemented a law with sanctions to reduce food waste, and why now? Why does the law target the catering industry? To answer these questions, we collected primary data through semi-structured interviews with government officials, as well as secondary data through recorded interviews available online with officials of the Legislative Affairs Commission of the Standing Committee of the National People's Congress (NPCSC) and food waste activists, as well as NPCSC conference reports. We find a legal approach with sanctions was necessary since cultural aspects, specifically conventional Chinese dining habits and pop culture, are difficult to regulate through instruments without sanctions. In addition, we find the Chinese law focuses on the catering industry for a few reasons: (1) More waste is generated by the catering industry than households, (2) waste from the catering industry is easier to monitor than household waste, and (3) this was a response to citizen requests collected during the Anti-food Waste Law public consultation process.

Life cycle assessment and society willingness to pay indexes of food waste-to-energy strategies

Food waste (FW) has received increasing attention because of its immense production quantities and significance to resource and environmental impacts related to disposal approaches. We combined life cycle assessment (LCA) with society's willingness to pay (WTP) index to evaluate energy, water, and environmental impacts on three food waste-to-energy (FWTE) options in China. For anaerobic digestion (AD) mode, the results showed that 1140 MJ of energy consumption could be saved by power generation from methane, power transmission, and biodiesel production from per ton of FW; the cost of climate change for treating FW was 137.8 kg CO₂e t^-1 FW, failing to be climate-sound due to the end life of digestate in practice. The total impact to AD mode in the form of monetized value for WTP was 13.3 CNY t^-1 FW, of which the collection and transportation, pretreatment, AD reaction, wastewater treatment, biodiesel production, and residue landfilling stages contributed by 10.5%, 6.5%, 19.3%, 27.6%, 4.7%, and 75.7%, respectively, while biogas utilization offset it by 43.9%. Notably, a considerable amount of water used in AD prevented it from showing an advantage compared to incineration (-5.1 CNY t^-1 FW), which performed best overall attributing to the generated electricity compensated for primary energy demand, water, and terrestrial acidification to a great extent. Landfilling turned out to be an unappealing FW disposal method due to the low landfill gas capture ratio. Given that AD is touted for its environmental benefits, potential approaches-such as developing a reliable and supportive technology to facilitate digestate recycling into agriculture-were discussed to improve its competitiveness and attractiveness. Our study employed a way to accumulate and compare impact indicators to better interpret FW management impacts and advantages, considering energy recovery, resource recycling, and the environment.

Hierarchical porous structure formation mechanism in food waste component derived N-doped biochar: Application in VOCs removal

Nitrogen-doped (N-doped) hierarchical porous carbon was widely utilized as an efficient volatile organic compounds (VOCs) adsorbent. In this work, a series of N-doped hierarchical porous carbons were successfully prepared from the direct pyrolysis process of three food waste components. The porous biochar that derived from bone showed a high specific surface area (1405.06 m²/g) and sizable total pore volume (0.97 cm³/g). The developed hierarchical porous structure was fabricated by the combined effect of self-activation (Carbon dioxide (CO₂) and water vapor (H₂O)) and self-template. The emission characteristics of activation gas analyzed by Thermogravimetric-Fourier transform infrared spectrometer (TG-FTIR) and the transformation of ash composition in the biochar help to illustrate the pore-forming mechanism. Calcium oxide (CaO) and hydroxylapatite were confirmed as the major templates for mesopores, while the decomposition processes of calcium carbonate (CaCO₃) and hydroxylapatite provided a large amount of activation gas (CO₂ and H₂O) to form micropores. The materials also obtained abundant N-containing surface functional groups (up to 7.84 atomic%) from pyrolysis of protein and chitin. Finally, the porous biochar showed excellent performance for VOCs adsorption with a promising uptake of 288 mg/g for toluene and a high adsorption rate of 0.189 min^-1. Aplenty of mesopores distributed in the materials effectively improved the mass transfer behaviors, the adsorption rate got a noticeable improvement (from 0.118 min^-1 to 0.189 min^-1) benefited from mesopores. Reusable potentials of the hierarchical porous carbons were also satisfying. After four thermal regeneration cycles, the materials still occupied 84.8%-87.4% of the original adsorption capacities.

Resource potential and global warming potential of fruit and vegetable waste in China based on different treatment strategies

Fruit and vegetable waste (FVW) contains rich resources that can be recovered by methods such as incineration, anaerobic digestion to generate heat energy, biogas, and preservation by ensiling. However, a horizontal comparison of the resource potential and environmental impact of different recycling methods employed for FVW has not been conducted. This study quantifies and computes the recycling potential and global warming potential (GWP) of anaerobic digestion, ensiling, and incineration of the FVW generated during primary production in China. First, a gray model was employed to estimate the FVW output in 2030, based on the FVW produced between 2002 and 2017. Next, the resource potential and GWP of anaerobic digestion, incineration, and ensiling were evaluated. Finally, an optimization method was utilized to analyze possible strategies of FVW recycling in 2030. Results indicate that FVW output in China is expected to increase to 170 Mt by 2030, highlighting the need for efficient treatment options. Further, the resource potential and GWP of different waste treatment strategies were notably different. The recycling potential of ensiling was the highest at 1950 MJ/t; while the GWP of anaerobic digestion was the lowest at -31 kg CO2eq. An optimization analysis suggested that the optimal target of 100% would be attained if all FVW is ensiled in 2030. The study provides a basis for informed technical decision-making related to FVW recycling options in the future.

Synergistic hydrothermal treatment of food waste digestate residues and incineration fly ash: dehydration performance and heavy metals safety

The synergistic hydrothermal treatment of food waste digestate residues and fly ash can improve the dehydration performance and safety of products.

Comprehensive insights into the organic fractions on solid-liquid separation performance of anaerobic digestates from food waste

Anaerobic digestion (AD) is an effective approach for food waste treatment and valorization. However, AD is limited by proper disposal of the food waste digestates in megacities. The objective of this study was to elucidate the dominant factors on solid-liquid separation performance of the digestates from food wastes. Results indicated that the composition differences in organic fractions showed significant impacts on solid-liquid separation performance by comparing the digestates from different cities in China. Dissolved organic matter (DOM), especially for proteins and carbohydrates, varied between the digestates in various cities, which may lead to the difference in solid-liquid separation performance. Digestate with lowest proteins (33.86 mg/L) from Shanghai's food waste AD plant had the best dewatering performance. In contrast, digestate from Nanjing's food waste AD plant showed the worst dewatering performance. Pearson's correlation analysis indicated that there is a significant correlation between soluble protein and the dewaterability of digestates (R² > 0.9573, p < 0.03), the lower soluble protein achieved higher dewaterability of digestates.

Advances of waste management practices in India and China along with bibliometric assessment of their research outcomes

This paper presents the progress made by India and China in the field of waste management and its disposal since l996 to 2020. To access it, bibliometric analysis has been carried out using SCOPUS linked SCImago electronic database. Different bibliometric indicators such as documents, citable documents, external and self-citations, and external and self-citations per document along with their annual corresponding growth (ACG) have been calculated in order to explore the progresses made in both the countries. China has contributed 16.3% and India 4.3% to the total documents produced worldwide during 1996-2020 in waste management with the average ACG of 26.42% and 15.37%, respectively, during the same time span. Also, the average ACG for self-citations of published research documents is more than that of external citations for both the countries. In addition to that, the average self-citation magnitude reported for China (28,475) is more than that of India (5223), whereas this trend reverses in the case of average external citation per document with values 16.9 and 28.94, respectively. Moreover, the waste management practices being followed in both countries have also been compared and also presented so that it could be beneficial for the country which is relatively not good in the same.

Urban Metabolism of Food-Sourced Nitrogen among Different Income Households: A Case Study Based on Large Sample Survey in Xiamen City, China

Food consumption is fundamental for urban households if they are to sustain production and daily life. Nitrogen resulting from food consumption has significantly contributed to pollutant emissions in urban ecosystems. Taking Xiamen city, a rapid urbanizing area of southeast China as a case study, we evaluated the food-sourced nitrogen consumption of households based on a large simple onsite questionnaire survey, as well as differences between households in the consumption of plant-based and animal-based foods. A material flow analysis (MFA) was conducted to simulate the urban metabolism of food-sourced nitrogen and environmental emissions among different income groups. The impacts of household attributes, plant-based food consumption, and animal-based food consumption on environmental nitrogen emissions were examined with a structural equation model (SEM). Our results show that the surveyed households' diets were more plant-based and less animal-based. Aquatic products and livestock were the source of 43.7% of food-sourced nitrogen, and 84.5% of the food-sourced nitrogen was discharge into the environment through direct discharge and waste treatment. Soil, water, and air emissions accounted for 62.8%, 30.1%, and 7.1% of the food-sourced nitrogen, respectively. Household income, household size, and household area are all associated with accelerating increases of nitrogen emissions released into the environment, though middle-income group households have the highest food-sourced environmental nitrogen emissions. On this basis, we discuss how to better manage the urban metabolism of food-sourced nitrogen, so as to improve urban household consumption, lower nitrogen emissions, and improve food security.

Anaerobic digestion: An alternative resource treatment option for food waste in China

With the implementation of zero-waste city and waste classification in China, a large amount of food waste (FW) began to appear in concentration, and there was an urgent requirement for appropriate and efficient treatment technology. Traditional FW disposal methods (landfill and incineration) could cause several environmental problems, so resource recycling has become the main development trend of FW in China. In recent years, anaerobic digestion (AD) technology for FW resource treatment has attracted much attention due to its advantages such as the ability to obtain clean energy, low carbon emissions, and suitability for large-scale treatment compared with other recycling technologies (composting, feed, and breeding insects). Chinese policy is conducive to the development of AD for FW, which has the potential to produce methane and achieve economic and environmental benefits. This paper presents an overview of the researches, application situations, and perspectives for the AD of FW resource treatment in China. The bibliometric analysis shows that China has the most interest in the AD of FW compared to other countries, and the amount and characteristics analysis of FW indicates that FW is suitable for treatment by AD. At the same time, this review analyzes the influence factors, methods to promote AD, working mechanism, secondary pollution of AD. Besides, the article introduces and analyzes the current policies, application status, economic and environmental benefits, and problems of AD for FW resource treatment in China. AD is considered as an alternative resource treatment technology for FW, although there are still several problems such as odors, digestate, etc. In the future, China should focus on the reform of management policy, the implementation of the AD circular economy model, and the research of the biorefinery model based on AD technology.

Facile synthesis of tailored mesopore-enriched hierarchical porous carbon from food waste for rapid removal of aromatic VOCs

Due to the large amount, environmental impact, and complex properties of accumulated food waste, its disposal and valorization has become a growing global concern and challenges. In this study, a series of mesopore-enriched hierarchical porous carbons were synthesized from a mixture of two food waste components (peptone and bone). The prepared materials were employed for the rapid adsorption of aromatic volatile organic compounds (VOCs). The pore structures, morphology and surface chemistry of the food waste-based microporous activated carbon (PCs) and mesopore-enriched hierarchical porous carbons (PC/BCs) were characterized and then compared. PC/BCs presented larger pore volume (2.45 cm³/g vs. 1.25 cm³/g) than the PCs because of their activation and the template effect of the bone, allowing them to exhibit satisfactory adsorption capacities (139.5 mg/g for benzene and 440.7 mg/g for toluene) and adsorption rate (0.285 min^-1 for benzene and 0.236 min^-1 for toluene) for aromatic VOCs. In addition, a strong linear relationship (R² = 0.957) was also established between the adsorption rate k and total pore volume, highlighting the role of mesopores in PC/BCs, which contributed 60% to the total pore volume, during the rapid capture of VOCs. Further, PC/BCs also showed excellent thermal regeneration performance for more than four runs. The results of this study provide a feasible approach to fabricating mesopore-enriched hierarchical porous carbon from food waste, which could enable the rapid removal of VOCs.

Effect of high concentration of ammonium on production of n-caproate: Recovery of a high-value biochemical from food waste via lactate-driven chain elongation

Ammonium accumulation is inevitable during the fermentation of food waste (FW), challenging the application of chain elongation process upgrading FW into the high-value biochemical n-caproate, which is a medium chain carboxylate. This study is the first to investigate ammonium inhibition of lactate-driven chain elongation process. The short-term exposure of a Clostridium IV-dominated chain elongating reactor microbiome at an ammonium concentration of 1-4 g L^-1 linearly decreased n-caproate production by 25-80%. High levels of ammonium (≥5 g L^-1) could cause failure of chain elongation, shifting the product from n-caproate to propionate. The involved mechanisms revealed that ammonium reshaped the microbial community from Clostridium IV domination to Clostridium IV and Propionibacterium co-domination (based on 16S rRNA sequencing) and reduced the activities of key enzymes involved in the reversed β-oxidization pathway. We propose an effective strategy from our study, which is the first one to do in our knowledge, to upgrade raw FW without dilution to n-caproate: lowering the ammonium accumulation to 1.0 g L^-1 at the setup phase for adaptation and prolonging the hydraulic retention time (10 days) during the operation phase for the colonization of chain-elongation bacteria. These findings lay a foundation for the implementation of the LCE process on FW, providing an alternative way to alleviate the global FW crisis.

Solid digestate disposal strategies to reduce the environmental impact and energy consumption of food waste-based biogas systems

This study examined the environmental impacts and energy consumption of three solid digestate treatment scenarios to quantify their impacts on the entire food waste (FW)-based biogas system: (1) incineration; (2) composting, and; (3) landfill. The results showed that composting had the largest net energy consumption, but least total environmental impact of 57.3 kWh and 8.75 E-03, respectively, whereas landfill showed the opposite pattern. Moreover, there were significant differences (p < 0.05) and relatively high contributions between the digestate treatment subunits among the three scenarios. The most significant contributions of digestate subunits in methods 1-3 to the 100-year global warming potential (GWP₁₀₀) were 70.5%, 52.5%, and 103.4%, respectively. The results indicated that solid digestate treatment had a significant impact, and reasonable disposal of solid digestate could significantly reduce the environmental impacts and energy consumption of the entire FW-based biogas system.

Hydrothermal carbonization of food waste after oil extraction pre-treatment: Study on hydrochar fuel characteristics, combustion behavior, and removal behavior of sodium and potassium

This study aims to convert oil extracted food waste (OEFW) into hydrochar as potential solid fuel via hydrothermal carbonization (HTC) process. The effect of HTC temperature and residence time on the physicochemical characteristic, combustion behavior, and the removal behavior of sodium and potassium were evaluated. The raw OEFW material was successfully converted into energy densified hydrochar with higher high heating value (HHV) (21.13-24.07 MJ/kg) and higher fuel ratio (0.112-0.146). In addition, carbon content in hydrochar increased to 46.92-51.82% after HTC at various operating conditions. Compared with OEFW, the hydrochar had more stable and longer combustion process with the higher ignition temperature and burnout temperature. Besides, the HTC process showed high removal rates of sodium and potassium. It was found that the HTC temperature resulted in a significant reduction of sodium and potassium in hydrochar as compared to the residence time. The highest removal rate of sodium (70.98%) and potassium (84.05%) was obtained. Overall, the results show that the HTC is a promising alternative for conventional technologies (e.g., incineration and landfill) for treatment and energy conversion of OEFW.

The Potential of Selected Agri-Food Loss and Waste to Contribute to a Circular Economy: Applications in the Food, Cosmetic and Pharmaceutical Industries

The food sector includes several large industries such as canned food, pasta, flour, frozen products, and beverages. Those industries transform agricultural raw materials into added-value products. The fruit and vegetable industry is the largest and fastest-growing segment of the world agricultural production market, which commercialize various products such as juices, jams, and dehydrated products, followed by the cereal industry products such as chocolate, beer, and vegetable oils are produced. Similarly, the root and tuber industry produces flours and starches essential for the daily diet due to their high carbohydrate content. However, the processing of these foods generates a large amount of waste several times improperly disposed of in landfills. Due to the increase in the world’s population, the indiscriminate use of natural resources generates waste and food supply limitations due to the scarcity of resources, increasing hunger worldwide. The circular economy offers various tools for raising awareness for the recovery of waste, one of the best alternatives to mitigate the excessive consumption of raw materials and reduce waste. The loss and waste of food as a raw material offers bioactive compounds, enzymes, and nutrients that add value to the food cosmetic and pharmaceutical industries. This paper systematically reviewed literature with different food loss and waste by-products as animal feed, cosmetic, and pharmaceutical products that strongly contribute to the paradigm shift to a circular economy. Additionally, this review compiles studies related to the integral recovery of by-products from the processing of fruits, vegetables, tubers, cereals, and legumes from the food industry, with the potential in SARS-CoV-2 disease and bacterial diseases treatment.

Comparison of microbial communities during anaerobic digestion of kitchen waste: Effect of substrate sources and temperatures

In this study, batch experiments were conducted to compare the effect of temperature and substrate source on microbial communities in the anaerobic digestion of kitchen waste. The results showed that the microbial communities of anaerobic digestion were not sensitive to varied sources of waste, but shifted with the change in operating temperatures. In the reactors operated at mesophilic conditions, Levilinea, Syntrophomonas, Methanothrix, and Methanosphaerula, etc. were the dominant microbes during the process. While in thermophilic reactors, Levilinea, Ornatilinea, Methanosphaerula and Methanomassiliicoccus, etc. prevailed. Meanwhile, an enrichment in Coprothermobacter, Defluviitoga, Defluviitalea, Tepidimicrobium, Lutispora and Fonticella were observed as the temperature changed from mesophilic to thermophilic, suggesting these genera could be selectively enriched at thermophilic conditions. The results provided fundamental understanding of the microbiology that could support the scale up of food waste anaerobic digestion.

Effect of terminal temperature on the morphology and potentially toxic metals concentrations of biochars derived from paper and kitchen waste

This study investigated the morphology and potentially toxic metal concentrations of paper waste-based biochar (PB) and kitchen waste-based biochar (KB) obtained at 500 and 700 °C. The morphology and potentially toxic metals (Cr, Mn, Cu, Cd, Pb, Zn, Ag, and Ba) concentrations in the biochars were determined by SEM and FT-IR analysis. The Cr, Mn, Cu, and Cd concentrations in PB were low, while the Ba content was relatively high at 0.1 mg∙kg^-1. An increase in the terminal temperature led to an increase in the concentrations of Fe/Mn oxide-bound potentially toxic metals of PB, and a decrease in the concentrations of organic matter-bound potentially toxic metals. The Fe/Mn oxide-bound Cr, Mn, Cu, Pb, and Zn concentrations of KB decreased with an increase in the terminal temperature. Therefore, increasing the terminal temperature could reduce the bioavailability of potentially toxic metals in PB and KB. The environmental risk of the different biochars when used for soil remediation was assessed by the potential ecological risk index (RI), and a case study of a Tibetan soil was also conducted. The potentially toxic metal concentrations leached from both PB and KB were lower than the relevant standards. The findings showed that both PB and KB can be safely used for soil remediation.

Inhibition of N-Vanillylnonanamide in anaerobic digestion of lipids in food waste: Microorganisms damage and blocked electron transfer

To study the inhibited degradation metabolism and anaerobic digestion of typical lipids in food waste, an artificially produced capsaicin, N-Vanillylnonanamide, a typical soluble component in waste lipids, was added to a glycerol trioleate anaerobic digestion system. The microorganisms damage and blocked electron transfer caused by N-Vanillylnonanamide during anaerobic digestion were further clarified. Scanning electron microscopy and transmission electron microscopy images demonstrated that N-Vanillylnonanamide (≥4 wt%) structurally damaged microorganisms via cell membrane breakage, which impair their function. N-Vanillylnonanamide inhibited the activities of the key enzyme CoA, AK, F₄₂₀, and CoM, which are relevant for both degradation metabolism and anaerobic digestion. 16S rRNA analysis showed that dominant bacterial and archaeal communities markedly decreased after anaerobic digestion of glycerol trioleate with N-Vanillylnonanamide (≥4 wt%). For example, the proportion of Methanosarcina decreased from 30 % to 6 %. Current-voltage curves indicated that the electron transfer rate in the community of microorganisms decreased by 99 % from 4.67 × 10^-2 to 5.66 × 10^-4 s^-1 in response to N-Vanillylnonanamide (40 wt%). The methane yield during anaerobic digestion of glycerol trioleate decreased by 84.0 % from 780.21-142.10 mL/g-total volatile solids with N-Vanillylnonanamide (40 wt%).

Estimation and analysis of municipal food waste and resource utilization potential in China

With rapid urbanization, municipal food waste (MFW), which is an important part of municipal solid waste, has attracted considerable attention owing to its environmental impact and polluting nature. There has been little research on the quantity and distribution of food waste (FW) produced in China. This study focused on a systematic estimation and analysis of MFW produced in administrative divisions at the prefecture-level and above in China for the first time. From the national level to the prefectural level, with the shrinking of the research units, more intuitive support was obtained for relevant decisions. On the basis of the estimated results, suggestions are provided for proper FW treatment technologies and operational scale of the facilities, and the resource utilization potential has also been estimated. The distribution results indicated that FW characteristics have great variability in the different economic regions of China. Furthermore, it was found that the available FW has a resource utilization potential that is equivalent to 4669.1 million m³ of biogas, 3.6 million tons of biodiesel, and 1.5 million tons of organic fertilizer (dry weight). It is worth mentioning that this amount of biogas can replace 7.5 million tons of standard coal. However, only a small part of the generated MFW can be treated in the existing treatment plants in China. Finally, current key bottlenecks of FW treatment in China have been discussed, and detailed suggestions are presented for further improvement of MFW management.

Gasification of effluent from food waste treatment process in sub- and supercritical water: H2-rich syngas production and pollutants management

The effluent of food waste (FWE) is generated during food waste treatment process. It contains high organic matter content and is difficult to be efficiently treated. In this study, the sample was collected from a 200 t/d food waste treatment center in Hangzhou, China. Subcritical and supercritical water gasification were employed to decompose and convert FWE into energy. The effects of reaction temperature (300-500 °C), residence time (20-70 min) and activated carbon loading (0.5-3.5 wt%) on syngas production and the remaining pollutants in liquid residue were investigated. It was found that higher reaction temperature and longer residence time favored gasification and pollutant decomposition, resulting in higher H₂ production and gasification efficiencies. It is noteworthy that the NH₃-N was difficult to be converted and removed under current experimental conditions. The addition of activated carbon was found to increase the gasification efficiency. The highest total gas yield, H₂ yield, carbon conversion efficiency, gasification efficiency, total organic carbon removal efficiency and chemical oxygen demand removal efficiency were obtained from gasification at 500 °C for 70 min with 3.5 wt% activated carbon.

High-efficiency methanogenesis via kitchen wastes served as ethanol source to establish direct interspecies electron transfer during anaerobic Co-digestion with waste activated sludge

Kitchen wastes (KW) have been widely investigated for bio-ethanol production, while no study utilizes KW as ethanol source to stimulate the methanogenic communities to perform direct interspecies electron transfer (DIET), since the excess acidity contained after the biological ethanol-type fermentation pretreatment (BEFP) can seriously inhibit the DIET-based syntrophic metabolism. In this study, a strategy that utilized waste activated sludge (WAS) as co-substrate to relieve the excess acidity after BEFP during anaerobic co-digestion (AcoD) was proposed. The results showed that, under the mixed ratio of 1:2 and 1:5 (KW:WAS, volume ratio), both methane production and organic compound removal evidently increased, compared with that treating the sole WAS. Conversely, under the other mixed ratios (sole KW, 5:1, 2:1 and 1:1), no methane but the evident hydrogen production was detected, and syntrophic metabolism of organic acids and alcohols was prevented. Three-dimensional excitation emission matrix (3D-EEM) analysis showed that the protein-like organic compounds contained in both KW and WAS were effectively degraded. Furthermore, the maximum methane production potential from WAS during AcoD (260.5 ± 4.1 and 264.3 ± 2.7 mL/g-COD) was higher than that treating sole WAS (250.8 ± 0.1 mL/g-COD). Microbial community analysis showed that, some genera capable of metabolizing the complex organic compounds with the reduction of the elemental sulfur or equipped with the electrically conductive pili were specially enriched during AcoD under the mixed ratio of 1:2 and 1:5. They might proceed DIET with methanogens, such as Methanosarcina and Methanospirillum species, to maintain the syntrophic metabolism effective and stable, since the abundance of both Methanosarcina and Methanospirillum species evidently increased.

Enhanced hydrogen production from food waste dark fermentation by potassium ferrate pretreatment

Hydrogen generation from food waste anaerobic dark fermentation is identified as a promising strategy for resource recovery. In this work, an innovative strategy of using potassium ferrate (PF), a strong oxidant, to promote anaerobic dark fermentation of food waste to produce hydrogen has been reported. The experimental results revealed that PF enhanced the hydrogen production from food waste, the maximal hydrogen yield was 173.5 mL/g, and the optimal PF dosage was 0.4 g/g total suspended solids. PF shortened the lag phase for hydrogen generation from 120 to 96 h. Mechanisms investigation revealed that PF accelerated the disintegration of organic compounds and increased the soluble organic matter in the liquid phase. The strong oxidation of PF inhibited the processes of hydrolysis, acidification, acetogenesis, homoacetogenesis, and methanogenesis by using synthetic wastewater in the fermentation process. The inhibition of PF on these processes was further verified by the enzyme activity analysis. Economic analysis indicated that 0.1 g/g PF was the optimal dosage. PF treatment is a promising strategy to enhance the production of hydrogen from food waste dark fermentation.

Preparation of biochar from food waste digestate: Pyrolysis behavior and product properties

Solid digestate generated in the anaerobic digestion of food wastes was evaluated as a potential feedstock for biochar preparation by pyrolysis in this study. To understand the pyrolysis mechanism, thermogravimetric experiments were firstly implemented at different heating rates, then apparent activation energy during pyrolysis was calculated by using the Starink isoconversional method, ranging from 144.64 kJ/mol to 293.36 kJ/mol with the conversion increasing in the region from 0.10 to 0.90. The evolutions of released volatiles were accurately and continuously analyzed by TG-FTIR-MS. Results show that dehydration and CO₂ emission were the main reasons for mass loss, and light hydrocarbons were released in step II of the pyrolysis process. Elemental compositions and surface properties of the biochars obtained at different pyrolysis temperatures were characterized by EA, XRF and BET. The obtained results provide an alternative strategy for disposing waste generated in anaerobic digestion of food waste.

LCA analysis of food waste co-digestion

The i-REXFO LIFE project designs an innovative business model with the objective of reducing significantly the amount of landfilled food waste. Given the availability of supermarket food waste in the Umbria region (Italy), the logistics is optimized using a Vehicle Routing Problem Solver, mass and energy balances of the biogas plant are partly calculated and partly measured from a real biogas plant. The data obtained from food waste transport and anaerobic co-digestion process are used as input for LCA analysis. The aim of the methodology is to assess the environmental and economic benefit of the substitution of energy crops (like corn silage) with food waste in anaerobic digestion. Two approaches are adopted: consequential LCA and attributional LCA. Only one impact category is taken into account: climate change. This decision has been taken to focus on two decision making criteria (economic feasibility and GHG emissions reduction). The results show that a reduction of 42% in the carbon footprint of the electricity produced from the biogas plant can be obtained by substituting about 9900 t of corn silage with 6600 t of food waste. Through the combined use of economic analysis and consequential LCA it has been possible to identify an optimized scenario in which: food waste produced from food industries is collected and used to produce energy in Expired Food Energy chains (EFE), while the food obtained from supermarkets is used to promote charity initiatives in actions aiming at the Reduction of Expired Food waste (REF).