Raw Food Waste Research Articles

Effect of inoculum sources on caproic acid production from food waste through lactate-based chain elongation: Properties and microbial succession

Caproic acid (CA) production is a promising way to valorize food waste (FW), but the low CA yield seriously restricts its application. Inoculum source as a key factor can affect the microbial communities and CA fermentation processes, but was not fully explored. In the present study, three common inoculum sources namely anaerobic digestion sludge (AD), pit mud (PM) and raw FW (RFW) were selected as inocula to initiate CA production from FW. The organics conversion properties, microbial community succession processes and bacterial metabolism pathways were investigated. Results showed that carbohydrates were effectively degraded into lactic acid and then to CA based on lactate-based chain elongation. The CA yield (0.37 g-COD/g-VS) using AD was higher than that inoculated with PM (0.26 g-COD/g-VS) and RFW (0.32 g-COD/g-VS). Although microbial communities in inocula were totally different, they exhibited similar succession with Firmicutes and Bacteroidetes as the dominant functional phyla. Logically, lactic acid-producing bacteria (e.g. Lactobacillus, Limosilactobacillus and Sporolactobacillus) were enriched at the early stage to prepare electron donor (lactate), and then were replaced by chain elongation bacteria for CA production. However, unclassified_Ruminococcaceae was dominant in reactor with AD, unclassified_Ruminococcaceae, Bifidobacterium, Clostridium_sensu_stricto and unclassified_Prevotellaceae were largely detected in reactors inoculated with PM and RFW, which resulted in different CA yield. This study provides useful information for caproate production from FW, and widens the knowledge of cleaner production from wastes.

Hydrothermal carbonization of combined food waste: A critical evaluation of emergent products

Hydrothermal carbonization (HTC) increasingly appears as an eco-friendly method for managing food waste (FW). In this work, a combination of FW was subjected to HTC, and products were critically evaluated. This involved a lab-scale pressure reactor and optimization of HTC conditions: temperature (220–340 °C) and residence time (90–260 min) via central composite design type of response surface methodology (CCD-RSM). Results showed varying temperatures and residence time to impact the hydrochar (HC) and hydrothermal carbonization aqueous phase (HTC-AP) properties. Although HC produced through HTC exhibited lower ash content (<2%) despite higher fixed carbon (>55 %) with respect to the raw FW, the heating value of HC ranged from 19.2 to 32.5 MJ/kg. Temperature primarily influenced FW conversion, affecting carbonaceous properties. Saturated fatty acids (SFA) were found to be predominant in the HTC-AP under all tested operating conditions (77.3, 48.4, and 37.1 wt% for HTC at 340, 280, and 220 °C in 180 min, respectively). Total phosphorus recovery in HC and HTC-AP respectively peaked at 340 °C and 220 °C in 180 min. The study concludes that HTC holds promise for energy-dense biofuel production, nutrient recovery, and fostering a circular economy.

Urban food waste and socioeconomic drivers in China

Food waste negatively impacts societal well-being, environmental, and economic sustainability. Previous studies have typically conducted single-site surveys or overlook changes in food waste due to new consumption models. Here, we conducted a national survey on food waste across diverse dining contexts in urban China from 2021 to 2024. Our findings reveal that urban areas generate a staggering 137 million tonnes (Mt) of food waste annually, accounting for 26% of total food consumption, and 55 Mt is edible waste, representing a significant loss of resources. Per capita, annual food waste amounts to 55 kg raw, 59 kg edible, and 34 kg inedible. Eating out, education and disposable income are the main drivers of food waste. Higher economic and educational levels increase waste, while gender, age, and family size indirectly influence waste through complex socioeconomic relationships. Restaurants emerge as the largest contributors to edible food waste, while households lead in overall waste production. Significant variations in waste patterns were observed across different operational models, with decentralized kitchens facing more severe raw food waste issues compared to central kitchens. Notably, the prevalence of vegetable and staple food waste across all consumption settings, with meat waste being more common when dining out. With China in the initial stages of developing a top-level food waste reduction strategy, our findings provide crucial insights for policy making and industrial practices.

Upcycling mixed-material waste with elemental sulfur: applications to plant oil, unseparated biomass, and raw post-consumer food waste

Herein we report the preparation of high sulfur-content materials (HSMs) using food waste and elemental sulfur.

COMPARING PHOSPHORUS RECOVERY AND OPTIMUM TIME DIGESTION FROM SINGLE AND MIXING SUBSTRATES BY USING ANAEROBIC MESOPHILIC DIGESTION TECHNIQUE

Phosphorus (P) is considered a limited and non-renewable mineral source that is essential in our daily lives, especially for the agricultural industry to produce fertilizer. Food Waste (FW), Palm Oil Mill Effluent Sludge (POMES), and Water Treatment Sludge (WTS) are wastes that are claimed to contain nutrients such as P. One of the methods that can be used to recover P is through the Anaerobic Mesophilic Digestion (AMD) technique. Therefore, this study was carried out to investigate the highest P recovery and time digestion from single and mixing substrates. The physicochemical and biological properties of raw FW, POMES, and WTS were determined, and it was reported that wastes were suitable to undergo the AMD process. Mesophilic conditions 350C (±1) were used as the appropriate conditions for the anaerobic bacteria (AB) to reproduce and grow. Results for single substrates found that POMES recovered the highest P with 57.88% (±1.24), and optimum digestion was at day 12. While FW and WTS recovered P with 31.94% (±0.76) and 26.47% (±1.51), respectively, the optimum digestion times for both wastes were at days 18 (FW) and 21 (WTS), respectively, which were longer than POMES. In mixing substrates, FW-POMES contributed to the highest P recovery value with 68.34% (±1.49), and the optimum time digestion was on day 9. Followed by WTS-POME, FW-WTS, and FW-POMES-WTS with values of 60.42% (±2.12) (day 15), 48.05% (±2.51) (day 8), and 20.85% (±1.33) (day 3), respectively. The better synergetic effect within anaerobic bacteria (AB) in mixing substrates with FW-POMES could eventually influence the highest P removal from the substrate in a short period of time. Moreover, this study also provides information on new strategies used in recovering P. Keyword(s) : Phosphorus recovery, Food Waste; Palm Oil Mill Effluent Sludge; Water Treatment Sludge; Anaerobic Mesophilic Digestion

Nitrogen fertilizer replacement values of organic amendments: determination and prediction

AbstractThe nitrogen fertilizer replacement value (NFRV) quantifies the value of organic amendments as a nitrogen (N) fertilizer, and is commonly defined as the extent to which organic fertilizer N can replace mineral fertilizer N. NFRVs can be calculated by comparing the crop N uptake from equal N application rates of mineral and organic fertilizer, or by comparing the N rates of both fertilizers needed to obtain equal crop N uptake. Currently, NFRVs are mainly known for animal manure, whereas other organic waste products may become available as fertilizer products in the future. In this study, a pot experiment with spring wheat was performed to (1) assess NFRVs of a range of organic amendments; (2) compare NFRVs based on equal N application with NFRVs based on equal N uptake; and (3) assess which product characteristics explain observed variation. Observed NFRVs varied between 6.2 and 78.8%, with the lowest value for raw food waste and the highest for fishmeal. NFRVs were overestimated when calculated based on equal N application rate (with on average 6.9% point), and more so at high N application rate (9.0% point). NFRVs should therefore be calculated based on equal N uptake from organic and mineral fertilizers. Nitrogen concentration of the organic fertilizer provided the best explanation of variation observed in NFRVs (R2 = 0.86). These findings give valuable insights into the large variation in value of organic waste streams as organic fertilizer and can support decisions on sustainable N application rates, to increase crop N uptake and reduce N losses to the environment.

Antioxidant, anti-inflammatory, anti-adipogenesis activities and proximate composition of Hermetia illucens larvae reared on food waste enriched with different wastes.

The use of insects as a food source is not a new idea, but it has gained momentum in recent years due to the need for sustainable protein source in livestock feedstuffs and for more environmentally friendly organic waste treatment. In the case of black soldier fly larvae, Hermetia illucens, research has focused on their ability to convert organic waste into usable nutrients and their potential as a protein source for animal and human consumption. In this study, black soldier fly larvae were reared on raw food waste (FW) mixed with garlic peel waste (G) and hydronic growth media waste (H) and the proximate composition and bioactive potential of black soldier fly larvae extract (SFL) were compared. Analysis showed that protein content of SFL fed with G was 4.21% higher and lipid content was 9.93% lower than FW. Similar results were obtained for SFL fed with H. Antioxidant activity of SFL-G was higher than that of SFL-FW and SFL-H. SFL-G treatment exhibited enhanced anti-inflammatory and anti-adipogenesis activities as well compared to SFL-FW. Current results suggested that feeding black soldier fly larvae with food waste added with garlic peel and hydroponic growth media waste resulted in increased nutritional value, polyphenol content and bioactivity for SFLs. In this context, garlic peel waste-added food waste was suggested a promising substrate for black soldier fly larvae to obtain high-quality protein source with enhanced antioxidant, anti-inflammatory and anti-adipogenic potential.

Thermal behaviour of hydrochar derived from hydrothermal carbonization of food waste using leachate as moisture source: Kinetic and thermodynamic analysis

The effect of leachate (L) as a reaction medium in hydrothermal carbonization (HTC) of food waste (FW) on the thermal behaviour of the resulting hydrochar (H) was investigated. The physicochemical and structural characterization of FW hydrochar produced using leachate (FWH-L) at different process temperatures (180/210/240 °C) confirmed the improved properties over raw FW. Kinetic analysis using Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman methods revealed that FWH-L have a lower activation energy (Ea) than raw FW. The average Ea values for raw FW by FWO, KAS and Friedman methods were 196.18, 196.85, 206.34 kJ/mol, respectively, while for FWH-L they were 127.89, 124.22 and 134.5 kJ/mol, respectively. The computed thermodynamic parameters showed that FWH-L has improved combustion behaviour. The results of FWH-L are well comparable to FW hydrochar produced using distilled water (FWH-DW). These findings demonstrated that residual ions in leachate would act as a catalyst, benefiting the HTC degradation reaction path.

Hydrothermal carbonization of food waste: Effect of leachate on physicochemical and energetic properties of hydrochar

It has never been more important than now to address the growing problem of unmanaged municipal solid waste (MSW) in developing countries. This study deals with hydrothermal carbonization (HTC) of food waste (FW) at temperatures of 180 °C, 210 °C and 240 °C for a fixed period of 6 h to produce hydrochar (H) using leachate (L) as an alternative moisture source. As the process temperature increases from180°C to 240 °C, the mass yield (MY) for FW hydrochar produced from leachate (FWH-L) decreases from 54.06 % to 43.25 % while the higher heating value (HHV) rises from around 21 MJ/kg to 29 MJ/kg. The MY and HHV of FWH-L were comparable with FWH produced conventionally using distilled water (FWH-DW). The results obtained from Van Krevelen diagram indicates that FWH falls under the lignite coal category. Moreover, FWH can be used as a sustainable alternative solid fuel because of HHV values compared to raw food waste (16.13 MJ/kg).

Feasibility of hydrogen recovery and optimization of gas production from protein-rich food waste by bio-electrochemical system

Microbial electrolysis cell (MEC) can realize effective disposal of organic waste and hydrogen recovery. However, it is not clear whether protein-rich food waste (FW) with complex structural characteristics can be degraded effectively in MEC. And the metabolism process of protein in MEC is still unclear. In this study, feasibility of hydrogen recovery from protein-rich FW by bio-electrochemical system and the anode enrichment strategies were investigated. The results showed that the anaerobic digestated liquid of protein-rich FW is more suitable for hydrogen recovery than raw FW. And the unfavorable protein metabolites to anode electroactive microbe utilization hinder the hydrogen recovery rate from protein by MEC. However, hydrogen production increased by 72.67% when anodic microbes were enriched with protein instead of sodium acetate. The analysis of anode electroactive bacteria and protein metabolites process revealed that protein-enrich strategies could strengthen the co-occurrence of bacteria genus Aeromonas and Blvii28 and thereby shift the protein metabolism towards acidogenic process, which increasing the substrate bio-availability to anode electroactive microbe.

Continuous co-generation of biohydrogen and biomethane through two-stage anaerobic digestion of hydrothermally pretreated food waste

Increasing accumulation of food waste (FW) exerts pressure on resource conservation and environmental protection, while conventional anaerobic digestion (AD) of raw FW for bioenergy recovery and waste minimization often encounters limitations such as fast acidification and process failure. Herein, mild hydrothermal pretreatment (HTP: 140 °C, 20 min) of raw FW was employed to advance subsequent AD performances in a long-term continuous mode. With a decreased overall hydraulic retention time (HRT) from 30 to 18 days, the two-stage system digesting HTP-treated FW maintained very stable and robust biohydrogen (38.1 mL/gVS) and biomethane (439.6 mL/gVS) co-production, whereas both the two-stage system digesting raw FW and the one-stage system digesting HTP-treated FW exhibited deteriorating trends with significantly lower energy yields by 61.1% and 28.1%, respectively. Microbial community analyses revealed the less involvement of carbohydrate-fermenting and proteolytic microbes in the second-stage biomethane reactors as a result of the enhanced hydrolysis and acidogenesis of FW through HTP and first-stage biohydrogen fermentation. A proximate energy balance assessment indicated that the energy gain of increased biogas generation offset the extra heat requirement for the HTP of FW, while a significant treatment capacity enhancement of 66.7% was achieved given the HRT reduction from 30 to 18 days through this integrated system.

Producing insect protein from food waste digestate via black soldier fly larvae cultivation: A promising choice for digestate disposal

The treatment of food waste digestate with high salinity is a big challenge. This paper evaluated the possibility of using black soldier fly larvae for food waste digestate disposal and insect protein production. Results showed that both digestates from hydrogen and methane fermentations were rich in protein and lipid contents, which benefited the BSFL cultivation. The BSFL reared on digestates from hydrogen and methane fermentations of food waste performed better in pre-pupal weight (19.12% and 41.13% higher, respectively), body length (3.62% and 18.21% higher, respectively) and crude protein contents (7.85% and 39.05% higher, respectively) than that reared on raw food waste. In addition, the maximum body weight growth rate (Rm) of BSFL cultivated on both digestates were 28.28% and 47.10% higher than that of BSFL cultivated on raw food waste, respectively. During BSFL cultivation, organic matter reduction between 40.97% and 46.07% were achieved. Digestates from hydrogen and methane fermentations represent favorable feeding substrates for BSFL cultivation. Using BSFL to treat AD digestate not only provides a digestate disposal approach, but also produces insect biomass and organic fertilizer as value-added byproducts, which shows tremendous potential in digestate disposal.

The Potential of Fermented Food from Southeast Asia as Biofertiliser

The intensive amount of chemical usage in agricultural practices could contribute to a significant impact on food safety issues and environmental health. Over-usage of chemical fertilisers may alter soil characteristics and contaminate water sources, leading to several human and animal health issues. Recently, there have been efforts to use microbial biofertilisers as a more sustainable and environmentally friendly agricultural practice in the common household of Southeast Asia. Traditionally, this method tends to utilise leftover food materials and readily available bacterial cultures, such as yoghurt drinks, and ferment them under a specific period in either solid or liquid form. So far, most of the testimonial-based feedbacks from local communities have been positive, but only limited information is available in the literature regarding the usage of biofertiliser fermented food (BFF). Previously, raw food waste has been used in the agriculture system to promote plant growth, however, the functional role of fermented food in enhancing plant growth have yet to be discovered. An understanding of the symbiotic relationship between fermented food and plants could be exploited to improve agricultural plant production more sustainably. Fermented food is known to be rich in good microbial flora (especially lactic acid bacteria (LAB)). LAB exist in different sources of fermented food and can act as a plant growth-promoting agent, improving the nutrient availability of food waste and other organic materials. Therefore, in this review, the potential use of seafood-based, plant-based, and animal-based fermented food as biofertiliser, especially from Southeast Asia, will be discussed based on their types and microbial and nutritional contents. The different types of fermented food provide a wide range of microbial flora for the enrichment of proteins, amino acids, vitamins, and minerals content in enhancing plant growth and overall development of the plant. The current advances of biofertiliser and practices of BFF will also be discussed in this review.

Self-sustaining smoldering as a novel disposal approach for food waste with high moisture content

This work aims to explore the self-sustaining smoldering treatment (SSST) for the destruction of food waste. The food waste used in this work mainly consists of cereal, vegetable, and meat. To examine the processing procedures and parameters, three experimental groups (raw food waste, food-waste paste and food-waste paste blended with anthracite) and five variables (moisture content, sand size, sand-to-food waste ratio, air flow and food waste-to-coal ratio) were extensively investigated. Results show that raw food waste with 40% moisture content can be disposed by SSST with the mass destruction ratio over 90%. However, the robustness of SSST for raw food waste is constrained by the heterogeneous issue due to a variety of components and sizes of food waste. This issue is addressed through stir pre-processing of raw food waste as food-waste paste. The robustness of SSST for food waste is significantly further enhanced only if a slight mass fraction of anthracite (<20% of raw food waste) is supplemented. This provides an alternative solution for employing SSST for raw food waste with very high moisture content.

Effects of Lipase Addition, Hydrothermal Processing, Their Combination, and Co-Digestion with Crude Glycerol on Food Waste Anaerobic Digestion

To enhance anaerobic fermentation during food waste (FW) digestion, pretreatments can be applied or the FW can be co-digested with other waste. In this study, lipase addition (LA), hydrothermal pretreatment (HTP), and a combination of both methods (HL) were applied to hydrolyze organic matter in FW. Furthermore, the effects of crude glycerol (CG), which provided 5%, 10%, and 15% of the volatile solids (VS) as co-substrate (denoted as CG5, CG10, and CG15, respectively), on the anaerobic digestion of FW were assessed. With an increasing proportion of CG in the co-digestion experiment, CG10 showed higher methane production, while CG15 negatively affected the anaerobic digestion (AD) performance owing to propionic acid accumulation acidifying the reactors and inhibiting methanogen growth. As the pretreatments partially decomposed hard-to-degrade substances in advance, pretreated FW showed a stronger methane production ability compared with raw FW, especially using the HL method, which was significantly better than co-digestion. HL pretreatment was shown to be a promising option for enhancing the methane potential value (1.773 NL CH4/g VS) according to the modified Gompertz model.

The Effects of Additives on the Pelletization of Raw and Torrefied Food Waste

This study evaluates the effect of various binders on the pelletization of raw and torrefied food waste (FW) towards its physical properties, including density, moisture reabsorption, and tensile strength of the formed pellets. Three binders; starch, lignin, and vegetable oil, were used to make the raw and torrefied FW pellets. It was found that the addition of lignin helps to improve the density of both, raw and torrefied FW pellets by 40% for raw FW pellets and up to 27% improvement for the torrefied FW pellets. In addition, increasing the concentration of lignin may also reduce moisture reabsorption from 48% to 40% of raw FW pellets, and the sorption was further reduced for the torrefied FW pellets. The addition of lignin improves the tensile strength, mainly the torrefied FW pellets. Results show that lignin inclusion demonstrates significant enhancement to the physical properties of FW pellets.

Sustainable Green Charcoal Briquette from Food Waste via Microwave Pyrolysis Technique: Influence of Type and Concentration of Binders on Chemical and Physical Characteristics

Turning the food waste into a fuel source such as charcoal briquette was one of the alternatives in managing the food wastes disposal. In this present work, food waste was converted into charcoal by microwave irradiation technique. Application of binders such as potato starch and carboxymethyl cellulose (CMC) at ratios of 5%,10% and 15% for briquetting purpose were investigated in terms of its chemical and physical characteristics. Result showed that the briquette formed using the starch as the binder performed better in combustion quality than that of carboxymethylcellulose (CMC). A good quality of charcoal briquette has capability to withstand impact during packaging, handling, and transportation. Standard physical characteristic that was tested for briquette includes moisture content, compressive strength, and impact resistance. Calorific value of briquette was studied to analyse energy content in the briquette. The study showed that food waste charcoal has calorific value comparable to that of the commercial charcoal. However, the addition of binders showed some reduction in the energy content, with more reduction when CMC is added. In terms of combustion characteristic, the addition of binders does not alter the combustion profile in comparison to the raw food waste charcoal’s profile. The ignition and burnout temperatures of the food waste charcoal briquette showed a better performance with and without binders as compared to the commercial charcoal. In terms of physical characteristics, CMC has showed as an excellent binder with highest shatter index value. Overall, in terms of chemical properties, addition of 10% starch showed a better performance, while addition of 10% CMC showed a better performance in terms of physical characteristics. This finding is beneficial for briquette industry in the development of green product using biomass, but further research is essential before production of briquette take place.

Anaerobic digestion affecting nitrous oxide and methane emissions from the composting process

Composting and anaerobic digestion are the most common ways to treat organic residues. Sometimes the organic rest after anaerobic digestion is also composted. In this study we investigated greenhouse gas emissions from composting raw food waste compared to composting solid digestate of food waste. Cumulative methane emissions over 3 weeks were found to be almost 12 times higher from composting digested food waste than from raw food waste suggesting that the microbial community transferred from the anaerobic digestion to the compost process enhanced these emissions. Cumulative nitrous oxide emissions were also higher when composting solid digestate was compared to composting raw food waste, but the global warming potential was mostly driven by the impact of methane emissions. In conclusion, methane production during digestate composting can be high, therefore eliminating methane producing microbes in digestate before composting could be a promising way to reduce greenhouse gas emissions.

Biochemical and Thermochemical Routes of H2 Production from Food Waste: A Comparative Review

AbstractHydrogen production from food waste by biochemical and thermochemical methods is reviewed herein. Generally, fermentation, a biochemical method, is considered to be more suitable for hydrogen production from food waste, and the performance of fermentation units depends on many factors, e.g., substrate composition, type of pretreatment, reactor configuration, and operating parameters, e.g., organic loading rate, hydraulic retention time, pH, and temperature. Controlling so many factors is tedious, expensive, and results in a slow process. On the other hand, thermochemical methods involve fewer factors and steps, can be much faster and less costly, and can also be used for efficient hydrogen production from food waste. Steam gasification has produced good hydrogen yields from raw food waste.

Energy from food waste

Energy from food waste