Pyrolysis process for the treatment of food waste

Recycling of domestic sludge cake as the inoculum of anaerobic digestion for kitchen waste and its benefits to carbon negativity

Organic waste recovery has been a concerning issue in line with resource conservation. In the present study, the kitchen waste of vegetables, fish, and beef was digested anaerobically using domestic sludge as the inoculum, the methane and carbon dioxide were monitored, and the environmental benefits of the anaerobic digestion (AD) process were evaluated. AD using sludge cake as the inoculum was shown to treat kitchen waste effectively. Raw beef was found to produce more gas than raw fish or vegetables. Investigations also indicated that celluloses within vegetables were not as readily biodegradable as the proteins in beef and fish. Moreover, cooking altered the protein structures in beef and fish, thus increasing methane production. Meanwhile, oil inhibited methane generation as carbon dioxide generation remained, implying that the hydrolysis and acedogenesis still proceeded in the digestion process containing oil. Anaerolineaceae and Synergistaceae are the two most abundant microbial species observed in an anaerobic digestion system. However, the carbon conversions to liquid (i.e., leachate), solid (i.e., digestate), and gaseous (i.e., methane and carbon dioxide) occurred in the AD process, showing a diverse transforming process from waste to reusable valuables. Moreover, the kitchen waste treatment by domestic sludge cake was shown to have positive effects on reducing carbon dioxide emissions compared to the conventional treatment of kitchen waste and domestic sludge. More environmental benefits could be expected if the resulting products (i.e., methane gas, leachate, digestate) were applied as an energy source, liquid fertilizers, and soil conditioners.

Preparation of Supercapacitor Carbon Electrode Materials by Low-Temperature Carbonization of High-Nitrogen-Doped Raw Materials from Food Waste

To address the problem of the low nitrogen (N) content of carbon materials prepared through the direct carbonization of food waste, soybean meal and egg whites with high N contents were selected to carry out carbonization experiments on food waste. At 220 °C, the effects of hydrothermal carbonization and microwave carbonization on the properties of supercapacitor electrode materials were investigated. The results show that food waste doped with soybean meal and egg whites could achieve good N doping. At a current density of 1 A·g-1, the specific capacitance of the doped carbon prepared by hydrothermal doping is as high as 220.00 F·g-1, which is much greater than that of the raw material prepared through the hydrothermal carbonization of food waste alone, indicating that the hydrothermal carbonization reactions of soybean meal, egg white, and food waste promote the electrochemical properties of the prepared carbon materials well. However, when a variety of raw materials are mixed for pyrolysis carbonization, different raw materials cannot be fully mixed in the pyrolysis process, and under the etching action of potassium hydroxide, severe local etching and local nonetching occur, resulting in a severe increase in the pore size distribution and deterioration of the electrochemical performance of the prepared carbon materials. At a current density of 1 A·g-1, the specific capacitance of these prepared carbon materials is 157.70 F·g-1, whereas it is only 62.00 F·g-1 at a high current density of 20 A·g-1. Therefore, this study suggests that the hydrothermal carbonization process is superior to the microwave pyrolysis carbonization process for preparing supercapacitor electrode materials with multiple samples doped with each other.

Valorization of food waste: A comprehensive review of individual technologies for producing bio-based products

BACKGROUND

The escalating global concerns about food waste and the imperative need for sustainable practices have fuelled a burgeoning interest in the valorization of food waste. This comprehensive review delves into various technologies employed for converting food waste into valuable bio-based products. The article surveys individual technologies, ranging from traditional to cutting-edge methods, highlighting their respective mechanisms, advantages, and challenges.

SCOPE AND APPROACH

The exploration encompasses enzymatic processes, microbial fermentation, anaerobic digestion, and emerging technologies such as pyrolysis and hydrothermal processing. Each technology's efficacy in transforming food waste into bio-based products such as biofuels, enzymes, organic acids, prebiotics, and biopolymers is critically assessed. The review also considers the environmental and economic implications of these technologies, shedding light on their sustainability and scalability. The article discusses the role of technological integration and synergies in creating holistic approaches for maximizing the valorization potential of food waste. Key finding and conclusion: This review consolidates current knowledge on the valorization of food waste, offering a comprehensive understanding of individual technologies and their contributions to the sustainable production of bio-based products. The synthesis of information presented here aims to guide researchers, policymakers, and industry stakeholders in making informed decisions to address the global challenge of food waste while fostering a circular and eco-friendly economy.

Techno-economic and environmental analyses of the pyrolysis of food waste to produce bio-products

Food waste has become a source of concern as it is generated abundantly worldwide and needs to be valorised into new products. In this study, cucumber, tomato, and carrot wastes were investigated as pyrolysis feedstocks as a single component (cucumber), a binary component mixture (cucumber and tomato), and a ternary component blend (cucumber, tomato, and carrot). Fourteen scenarios were simulated and evaluated based on varying the feedstock blend (single, binary, and tertiary), temperature (300 and 500 °C), and feedstock moisture content (5, 20, and 40%). Using an established empirical model, the effect of these parameters on product yields, techno-economic implications, energy requirements, and life cycle analysis (LCA) outcomes were investigated. The best performers of each scenario were determined, and their strengths and weaknesses were identified and compared with other scenarios. In terms of product yields, all three systems (single, binary, and tertiary) followed a similar pattern: bio-oil yields increased as temperature and feedstock moisture content increased, while biochar yields decreased as temperature and feedstock moisture content increased. The production of syngas, on the other hand, was only observed at elevated temperatures. The total energy requirement exhibited an increase with increasing temperature and feedstock moisture content. The economic evaluation revealed that the return on investment (ROI) value for the single component at 5% moisture content at 300 °C is 29%, with a payback period (PB) of only 3.4 years, which is potentially very appealing. The water footprint increased with increasing pyrolysis temperature but decreased with increasing moisture content in all scenarios. The land footprint is observed to remain constant despite changes in process conditions. The study's findings contribute to the pyrolysis process's scalability, technological advancement, and commercialisation.

Environmental sustainability assessment of a new food waste anaerobic digestion and pyrolysis hybridization system

This research conducted an environmental life cycle assessment (LCA) to evaluate an anaerobic digestion-co-pyrolysis (ADCo-Py) system in which pyrolysis was added to traditional food waste (FW) anaerobic digestion (AD) systems to treat the solid fraction and impurities separated from FW. The solid fraction, including impurities such as wooden chopsticks, plastics, eggshells, and bones, is usually incinerated, while pyrolysis can be a viable alternative to optimize FW treatment. The environmental impact of ADCo-Py was compared with stand-alone AD, pyrolysis, and ADCo-INC (AD with incineration of separated solids). The results indicated that both ADCo-Py (-1.726 kg CO2-Eq/kgFW) and ADCo-INC (-1.535 kg CO2-Eq/kgFW) outperform stand-alone AD (-0.855 kg CO2-Eq/kgFW) and pyrolysis (-0.181 kg CO2-Eq/kgFW) in mitigating global warming potential (GWP). Additionally, pretreatments were found to have the most significant influence on GWP, ecotoxicity potential (ETP), and acidification potential (AP). The two-step pretreatment in ADCo-Py, including the separation of solids and drying, significantly improved the environmental sustainability of the system when compared with standalone pyrolysis.

Antibiotic resistance genes fate during food waste management - Comparison between thermal treatment, hyperthermophilic composting, and anaerobic membrane bioreactor

The fate of eight different antibiotic resistance genes (ARGs) in food waste (sul1, sul2, tetO, tetW, ermF, ermB, ampC, oxa-1), intI1, and rpoB were monitored during thermal treatment (pyrolysis and incineration), hyperthermophilic composting, and anaerobic membrane bioreactor (AnMBR) treatment. ARGs in food waste ranged from 2.9 × 106 to 3.5 × 109 copies/kg with ampC being the least abundant and sul1 being the most abundant. Thermal treatment achieved removal below detection limits of all ARGs. Only two ARGs (sul1 and ampC) persisted in hyperthermophilic composting. While all genes except for ermB decreased in the AnMBR effluent relative to the food waste feed, sul1 remained at relatively high abundance. Biosolids on the contrary, accumulated tetO, ampC and sul2 in all tested operating conditions. Thermal treatment, despite limited resource recovery, provides the most effective mitigation of ARG risk in food waste.

A strategic review on sustainable approaches in municipal solid waste management andenergy recovery: Role of artificial intelligence,economic stability andlife cycle assessment

The consumption of energy levels has increased in association with economic growth and concurrently increased the energy demand from renewable sources. The need under Sustainable Development Goals (SDG) intends to explore various technological advancements for the utilization of waste to energy. Municipal Solid Waste (MSW) has been reported as constructive feedstock to produce biofuels, biofuel carriers and biochemicals using energy-efficient technologies in risk freeways. The present review contemplates risk assessment and challenges in sorting and transportation of MSW and different aspects of conversion of MSW into energy are critically analysed. The circular bioeconomy of energy production strategies and management of waste are also analysed. The current scenario on MSW and its impacts on the environment are elucidated in conjunction with various policies and amendments equipped for the competent management of MSW in order to fabricate a sustained environment.

Syngas production from fast pyrolysis and steam gasification of mixed food waste

Food waste generation is a worldwide phenomenon and disposing off it in an environmentally benign way has been a challenge. Thermochemical processes have the potential for not only processing mixed food waste effectively from an environmental point of view but also producing bioenergy in all three forms: solid (biochar), liquid (bio-oil) and gas (syngas). In this study, two thermochemical processes - fast pyrolysis and steam gasification - aimed for producing syngas as main product were carried out at three different temperatures: 600°C, 700°C and 800°C, and resulting syngas was characterised and compared for syngas yield, syngas composition, hydrogen yield and high heating value (HHV). The steam flow rate (SFR) was maintained at 0.625 mL min^-1 for all gasification experiments. The syngas yield obtained from steam gasification was higher (1.2 m³ kg^-1) than the syngas yield from fast pyrolysis (0.81 m³ kg^-1). In addition, the hydrogen fraction was much higher in syngas from steam gasification (63.58%) than that from fast pyrolysis (45.03%). Furthermore, carbon conversion efficiency (CCE) and apparent thermal efficiency (ATE) were determined to compare the performance of these two processes. CCE was higher (63.6%) for steam gasification than that for pyrolysis (52.3%) which suggested that steam gasification was much more effective than fast pyrolysis to produce syngas of higher quality.

A potential phosphorus fertilizer to alleviate the coming "phosphorus crisis"-biochar derived from enhanced biological phosphorus removal sludge

The coming crisis of phosphate rock depletion initiates the development of various solid waste derived P fertilizer. Enhanced biological phosphorus removal (EBPR) sludge is ideal waste biomass to produce biochar-P-fertilizer. Here, the form and transformation pattern of released phosphorus (P) of EBPR sludge biochar pyrolyzed at different temperatures were comprehensively investigated. As pyrolysis temperature increased, the proportion of released polyphosphates (Poly-P) increased. The main Poly-P released from low-temperature biochar was tripolyphosphates (Tri-P), while those released from high-temperature were Tri-P and cyclic Poly-P. The presence of Ca²⁺ could strongly inhibit P-release of low-temperature biochar (e.g., pyrolyzed at 400 °C, E400) but had little effect on that of high-temperature biochar (e.g., 700 °C, E700). All the P species released from E400 and E700 could be efficiently utilized by Pseudomonas putida. Except for the cyclic Poly-P released from E700, the other P species could also be efficiently utilized by Escherichia coli. In short, Poly-P in biochar could hardly precipitate with Ca²⁺ and can be utilized by certain soil microorganisms. Therefore, high-temperature EBPR sludge biochar (>600 °C) containing a high proportion of Poly-P could be ideal P fertilizer. This study provides a new insight on pyrolysis way to recover P from the sludge.

Understanding the management of household food waste and its engineering for sustainable valorization- A state-of-the-art review

Increased urbanization and industrialization accelerated demand for energy, large-scale waste output, and negative environmental consequences. Therefore, the implementation of an effective solid-waste-management (SWM) policy for the handling of food waste is of great importance. The global food waste generation is estimated at about 1.6 gigatons/yr which attributes to an economic revenue of 750 billion USD. It can be converted into high-value enzymes, surfactants, Poly-hydroxybutyrate, biofuels, etc. However, the heterogeneous composition of food with high organic load and varying moisture content makes their transformation into value-added products difficult. This review aims to bring forth the possibilities and repercussions of food waste management. The socio-economic challenges related to SWM are comprehensively discussed particularly in terms of environmental concern. The engineering aspect in the collection, storage, and biotransformation of food waste into useful value-added products such as biofuels, advanced biomaterials, bioactive compounds, and platform chemicals are critically reviewed for efficient food waste management.

Improving photocatalytic activity under visible light over a novel food wastes biochar-based BiOBr nanocomposite

Biochar (C) applied in synthesizing photocatalysts to eliminate water pollution has been intensively investigated. Herein we report the first use of biochar pyrolyzed from food wastes at 400 ^°C (400C) and 700 ^°C to construct C/BiOBr composites via a facile hydrolysis approach. Photocatalytic performances could be significantly improved by choosing the appropriate carbonization temperature and adjusting the content of C in C/BiOBr composites. The prepared 1%400C/BiOBr exhibited the best photodegradation capacity towards methylene orange (20 mg/L) and tetracycline (50 mg/L). A series of characterization results illustrated that smooth structure and surface properties (oxygen functional groups and persistent free radicals) of 400C played an important role in enhancing the photocatalytic activities. Mechanism exploration suggested that h⁺ and ˙O₂^- were the main active species thus contributing to photodegradation. This study provided a new insight into utilization of biochar derived from food wastes in photocatalysis and environmental remediation.

Pyrolysis of food waste and food waste solid digestate: A comparative investigation

The effects of anaerobic digestion (AD) on pyrolysis were elaborated by comparing the pyrolysis performance of food waste (FW) and food waste solid digestate (FWSD). The pyrolysis mechanisms of FW and FWSD were revealed by experimental and kinetic analysis. The properties and potential applications of pyrolytic products from FW and FWSD were discussed. The results showed that part of organic matters of FW were consumed during AD, which altered the pyrolysis performance of FWSD. The pyrolytic gas from FW had better quality due to its higher lower heating value (LHV) (20.52 kJ/Nm³). The pyrolytic oil and biochar derived from FWSD showed better qualities as oil fuel and carbon-based absorbent. Pyrolysis of FWSD produced less nitrogen-containing pollutants (NCPs) indicated that AD coupled with pyrolysis is more environmental-friendly to treat FW. This study provides potential approach and theoretical guidance for the treatment and resource utilization of FW and FWSD.

State-of-the-art of the pyrolysis and co-pyrolysis of food waste: Progress and challenges

The continuous growth of population and the steady improvement of people's living standards have accelerated the generation of massive food waste. Untreated food waste has great potential to harm the environment and human health due to bad odor release, bacterial leaching, and virus transmission. However, the application of traditional disposal techniques like composting, landfilling, animal feeding, and anaerobic digestion are difficult to ease the environmental burdens because of problems such as large land occupation, virus transmission, hazardous gas emissions, and poor efficiency. Pyrolysis is a practical and promising route to reduce the environmental burden by converting food waste into bioenergy. This paper aims to analyze the characteristics of food waste, introduce the production of biofuels from conventional and advanced pyrolysis of food waste, and provide a basis for scientific disposal and sustainable management of food waste. The review shows that co-pyrolysis and catalytic pyrolysis significantly impact the pyrolysis process and product characteristics. The addition of tire waste promotes the synthesis of hydrocarbons and inhibits the formation of oxygenated compounds efficiently. The application of calcium oxide (CaO) exhibits good performance in the increment of bio-oil yield and hydrocarbon content. Based on this literature review, pyrolysis can be considered as the optimal technique for dealing with food waste and producing valuable products.

Thermochemical conversion of municipal solid waste into energy and hydrogen: a review

The rising global population is inducing a fast increase in the amount of municipal waste and, in turn, issues of rising cost and environmental pollution. Therefore, alternative treatments such as waste-to-energy should be developed in the context of the circular economy. Here, we review the conversion of municipal solid waste into energy using thermochemical methods such as gasification, combustion, pyrolysis and torrefaction. Energy yield depends on operating conditions and feedstock composition. For instance, torrefaction of municipal waste at 200 °C generates a heating value of 33.01 MJ/kg, while the co-pyrolysis of cereals and peanut waste yields a heating value of 31.44 MJ/kg at 540 °C. Gasification at 800 °C shows higher carbon conversion for plastics, of 94.48%, than for waste wood and grass pellets, of 70-75%. Integrating two or more thermochemical treatments is actually gaining high momentum due to higher energy yield. We also review reforming catalysts to enhance dihydrogen production, such as nickel on support materials such as CaTiO₃, SrTiO₃, BaTiO₃, Al₂O₃, TiO₃, MgO, ZrO₂. Techno-economic analysis, sensitivity analysis and life cycle assessment are discussed.

Effects of demineralization on food waste biochar for co-firing: Behaviors of alkali and alkaline earth metals and chlorine

A significant amount of chlorine, and alkali and alkaline earth metal (AAEM) in food waste has been a major limitation to the utilization of food waste as fuel. The present study aims to investigate the behavior of chlorine and AAEM in food waste biochar during pyrolysis, demineralization, and combustion. Food waste compost (FWC) and food waste feedstock (FWF) were selected as raw materials. Three different pyrolysis temperatures from 300 to 500 °C and two demineralization processes, water and CO_2-saturated water, were employed. As the pyrolysis temperature increased, crystallized salt was removed through demineralization, which further increased the heating value. Effective removal of chlorine was demonstrated in both demineralization methods. During demineralization, re-adsorption of Ca on food waste biochar occurred, which was alleviated by CO₂-water demineralization. The total amounts of volatilized Cl and AAEM after CO₂-water demineralization were reduced by 74.79-99.38% for FWF and 98.34-99.9% for FWC compared to raw biochar. Furthermore, slagging and fouling potentials for all food waste biochar samples were estimated using various indices. The proposed behavior of Cl and AAEM in food waste biochar during various fabrication conditions provides insight into how food waste biochar can be applied in thermos-electric power plant for co-firing with coal.

Engineered biochars for recovering phosphate and ammonium from wastewater: A review

Biochar has gained great scientific attention as a promising agent for agricultural and environmental applications. A variety of biochars with excellent properties such as high porosity, surface area and functional groups have been developed for nutrients recovery from wastewater. Compared to pristine biochar, engineered biochar with enlarged surface area and abundant functional groups has been prepared which shows a new type of carbon-based material with enhanced adsorption potential for nutrients in wastewater. To date, a few reviews have been specifically focused on several important aspects of engineered biochar, such as its application to recover phosphate and ammonium from wastewater and subsequent use as a slow-release fertilizer. In this work, novel modification/treatment methods including activation with acid/alkali, functionalization with amides, thiols and oxidizing agents, metal salt impregnation, loading with various minerals and carbon-based materials are reviewed for preparing engineered biochar with improved adsorption capacity. Various sources of biomass for producing biochars were estimated, and the intrinsic characteristics and potential of biochar products for simultaneous recovery/removal of phosphate and ammonium from wastewater were evaluated. Relevant interaction mechanisms of phosphate and ammonium adsorption on engineered biochars have been discussed in details. Finally, important future prospects as well as industrial/commercial-scale application of engineered biochars for phosphate and ammonium recovery from wastewater have been emphasized. We believe that this review will provide broad scientific opportunities for thorough understanding of applying engineered biochar as a low-cost and environmentally sustainable material for nutrients recovery from wastewater.

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.

Stabilization of PFAS-contaminated soil with activated biochar

Biochars are considered potential sustainable sorbents to reduce the leaching of per- and polyfluoroalkyl substances (PFAS) from contaminated soils. However, biochar characteristics must probably be optimized to achieve useful sorption capacity. In the present work, eight waste timber biochars were produced, including biochars activated to different degrees, at different temperatures, and using both steam and CO₂. In laboratory batch experiments, the eight biochars were amended to soil samples from two different horizons, with low and high total organic carbon (TOC, 1.6% and 34.2%, respectively), of a heavily PFAS-contaminated soil (1200-3800 μg kg^-1 PFAS_tot), at varying doses (0, 0.1, 0.5, 1.0 and 5.0%). With a 5% amendment to the low-TOC soil, all eight biochars resulted in strongly reduced leachate PFAS concentrations (by 98-100%). At the same amendment dose in the high-TOC soil, leachate concentration reductions were more modest (23-100%). This was likely due to a strong PFAS-sorption to the high-TOC soil itself, as well as biochar pore clogging in the presence of abundant organic matter, resulting in fewer sorption sites available to PFAS. Reduction in PFAS leaching was proportional to the degree of activation and activation temperature. Thus, lower amendment doses of activated biochars were needed to reduce PFAS leaching to the same level as with the non-activated biochar. Activation however, came at a tradeoff with biochar yield. Furthermore, the adsorption ability of these biochars increased proportionally with PFAS-fluorocarbon chain length, demonstrating the role of hydrophobic interactions in reduction of PFAS leaching. Development of internal surface area and porosity was proposed as the main factor causing the improved performance of activated biochars. This study shows that woody residues such as waste timber can be used to produce effective sorbents for the remediation of PFAS-contaminated soil. It also highlights the desirability of sorbate and matrix-specific optimization of biochar production.

Different reaction behaviours of light or heavy density polyethylene during the pyrolysis with biochar as the catalyst

Polyethylene is a major contributor of plastic waste, which can be converted into liquid fuel via catalytic pyrolysis. In this study, the pyrolysis of light or heavy density polyethylene (LDPE and HDPE) and their mixture with the biochar produced from gasification of poplar wood as catalyst was investigated. The results showed that, during the co-pyrolysis of LDPE and HDPE in absence or presence of biochar catalyst, cross-interaction of reaction intermediates originated from the degradation of LDPE and HDPE substantially promoted the formation of gaseous products and the evolution of heavy organics with π-conjugated structures in the tar. During the pyrolysis of HDPE, more heavy tar while less wax was produced, while it was contrary during the pyrolysis of LDPE. In the catalytic pyrolysis of LDPE, the volatiles could be effectively cracked over the biochar catalyst, forming more gases, while in the catalytic pyrolysis of HDPE, instead of catalyzing the cracking of the heavy components, the biochar catalyzed the polymerisation reactions. The properties of the biochar catalyst in terms of crystallinity, surface functionality, and internal structures also changed remarkably due to the transfer of oxygen-containing species from the polyethylene to biochar and the interaction of biochar with volatiles in the pyrolysis.

Opportunities for holistic waste stream valorization from food waste treatment facilities: a review

Difficult-to-biodegrade fractions (DBFs) generated from the biological treatment of food waste (FW) account for approximately 30% of the actual waste. These wastes are difficult to degrade or are considered indigestible residues of the aerobic and anaerobic fermentation treatment of FW treatment facilities. The currently applied disposal routes for DBFs exert environmental pressure and underutilize waste as resources. Therefore, these challenges must be overcome. An innovative strategy for the enhancement of the energy value and beneficial products from FW and the associated DBFs is proposed in this review. We propose conceptual future optimization routes for FW and DBFs via three types of technology integration. Pyrolysis techniques thoroughly treat DBFs to produce various value-added bio-energy products, such as pyrogenic bio-char, syngas, and bio-oil. Anaerobic digestion treats FW while utilizing pyrolysis products for robust performance enhancement and bio-methane upgrade. This holistic route offers conceptual information and proper direction as crucial knowledge for real application to harness the inherent resources of waste streams generated from FW treatment facilities.

Valorisation of food waste via hydrothermal carbonisation and techno-economic feasibility assessment

Food waste constitutes a remarkable portion of municipal solid waste. About one-third of the global food waste produced is lost with the food supply chain. Food waste in many countries is still dumped of in landfill or incinerated simultaneously with other municipal wastes. Food waste requires proper management and recycling techniques in order to minimise its environmental burden and risk to human life. Despite considerable research on food waste conversion still, there is a shortage of comprehensive reviews of the published literature. In this review, we provide a mini global perspective of food waste with special emphasis on New Zealand and their conversion into the useful material through hydrothermal carbonisation (HTC). Other thermal technologies such as incineration and pyrolysis are also briefly discussed. The review discusses why HTC is more suitable thermal technology than others, which are currently available. Recognising the importance of techno-economic feasibility of HTC, we present a cost analysis on the production of value-added products via HTC with examples taken from the literature to gather information in the feasibility assessment process. Finally, key challenges and future directions for a better productive way of handling food waste are being suggested.

Activated carbons from common nettle as potential adsorbents for CO2 capture

Activated carbons (ACs) prepared from common nettle (Urtica Dioica L.) were studied in terms of carbon dioxide adsorption. ACs were prepared by KOH chemical activation in a nitrogen atmosphere at temperatures (ranging from 500 to 850°C). The pore structure and the surface characterization of the ACs were specified based on adsorption-desorption isotherms of nitrogen measured at –196°C and carbon dioxide at 0°C. The specific surface area was calculated according to the BET equation. The pore volume was estimated using the DFT method. The highest values of the specific surface area (SSA) showed activated carbons produced at higher carbonization temperatures. All samples revealed presence of micropores and mesopores with a diameter range of 0.3–10 nm. The highest value of the CO2 adsorption, 4.22 mmol/g, was found for the material activated at 700°C.

Three-Dimensional Excitation and Emission Fluorescence-Based Method for Evaluation of Maillard Reaction Products in Food Waste Treatment

Hydrothermal treatment (HT) of food waste (FW) can form Maillard reaction products (MRPs), the biorefractory organic matter due to the occurrence of Maillard reaction. However, the integrating qualitative and quantitative approach to assess MRPs is scarce. The goal of this study was to develop a method to characterize and quantify MRPs created by HT of FW. MRPs were identified by molecular weight fractionation, indirect spectrometric indicators, and three-dimensional excitation-emission fluorescence (3DEEM) analysis. The 3DEEM method combined with fluorescence regional integration (FRI) and parallel factor (PARAFAC) analyses was able to differentiate clearly between MRPs and other dissolved organic compounds compared to other approaches. The volume of fluorescence Φ from FRI and maximum fluorescence intensity Fmax from PARAFAC were found to be suitable quantitative parameters for determination of MRPs in the hydrothermal FW system. These two parameters were validated with samples from hydrothermal FW under various operating temperatures and pH.

Co-pyrolysis characteristics and kinetic analysis of organic food waste and plastic

In this work, typical organic food waste (soybean protein (SP)) and typical chlorine enriched plastic waste (polyvinyl chloride (PVC)) were chosen as principal MSW components and their interaction during co-pyrolysis was investigated. Results indicate that the interaction accelerated the reaction during co-pyrolysis. The activation energies needed were 2-13% lower for the decomposition of mixture compared with linear calculation while the maximum reaction rates were 12-16% higher than calculation. In the fixed-bed experiments, interaction was observed to reduce the yield of tar by 2-69% and promote the yield of char by 13-39% compared with linear calculation. In addition, 2-6 times more heavy components and 61-93% less nitrogen-containing components were formed for tar derived from mixtures.

The volatilization of heavy metals during co-combustion of food waste and polyvinyl chloride in air and carbon dioxide/oxygen atmosphere

The volatilization of three heavy metals (Cd, Cr and Zn) during food waste and PVC and their blending combustion in N₂/O₂ or CO₂/O₂ atmosphere in a lab-scale tubular furnace was investigated. The concentration of heavy metals in combustion ash was decreased with the increment of furnace temperature in most cases. The replacement of 80N₂/20O₂ by 80CO₂/20O₂ decreased the volatilization rate of Cd and Cr, but increased Zn. The increased amount of PVC added into food waste led to less content of Zn in combustion ash, 5% PVC added into food waste decreased the volatilization rate of Cr but 15% PVC added led to the higher volatilization. The volatilization rate of Zn in 70CO₂/30O₂ was significantly lower than in 85CO₂/15O₂ or 80CO₂/20O₂. The result contributes to the understanding of heavy metal volatilization during incineration and emission control of MSW oxy-fuel combustion.

Utilization of spent dregs for the production of activated carbon for CO2 adsorption

The objective of this work was preparation of activated carbon from spent dregs for carbon dioxide adsorption. A saturated solution of KOH was used as an activating agent. Samples were carbonized in the furnace at the temperature of 550°C. Textural properties of activated carbons were obtained based on the adsorption-desorption isotherms of nitrogen at −196°C and carbon dioxide at 0°C. The specific surface areas of activated carbons were calculated by the Brunauer – Emmett – Teller equation. The volumes of micropores were obtained by density functional theory method. The highest CO2 adsorption was 9.54 mmol/cm3 at 0°C – and 8.50 mmol/cm3 at 25°C.