Mixed Waste Streams Research Articles

Vision-based sorting in mixed food-inorganic waste stream

Processing food waste is crucial for environmental conservation and resource recovery, but inadequate sorting can lead to inorganic waste mixing with food waste. The mixed waste stream reduces the efficiency of food waste treatment facilities, and the preliminary sorting relies heavily on manual labor. To address the challenge of a non-homogeneous food-inorganic waste stream, this study proposes a vision-based system for effective sorting. A real-life Mixed Food-Inorganic Waste (MFIW) dataset containing over 13,000 samples and four categories of inorganic waste was created. Based on the dataset analysis, a Waste detection model using Deformable Convolution v3 was employed, and the appropriate positioning and classification algorithm was chosen for optimal detection performance. The Waste detection model achieves an mAP50 of 85.21 %, and the average recalls for packages, trash bags, and animal bones exceed 94 %. Additionally, the model runs at a real-time frame rate of 33.61 FPS, highlighting its suitability for industrial applications.

CURRENT PROBLEMS IN THE COMBUSTIBLE MUNICIPAL WASTE MANAGEMENT – A CASE STUDY FOR PRE-RDF, RDF AND SRF MANAGEMENT IN POLAND

Refuse-derived fuel (RDF) is one of the municipal waste processing products generated inmechanical-biological installations. The RDF production allows energy recovery while reducingthe mass of landfilled waste. RDF is produced mainly from mixed waste stream with combustibleproperties. Currently, the main recipient of RDF fuels in Poland is the cement industry, whichaccepts only high-quality fuels. Annually a reduction of combustible waste share in the pre-RDFfraction intensifies difficulties in producing fuels with a sufficiently high calorific value. However,due to the energy transformation, it is planned that RDF would also be used in the heating sector.A positive aspect of this situation is the emergence of alternative recipients of RDF, even with theirlower calorific value. This may improve the market situation of RDF and reduce operation costs formunicipal installations in the long-term perspective.

Aerogel‐To‐Sol‐To‐Aerogel (ASA) Process for Recycling, Repairing, Reprogramming of High‐Performance Organic Aerogels

AbstractWith rising energy demands and costs, the significance of thermally insulating materials is on a constant upward trajectory. While they offer impressive performance, their sustainability is increasingly becoming an essential design feature. The study thus develops an unprecedented strategy that enables recycling, repairing, and reprogramming of superinsulating polyimine aerogels. The principle at play involves the decomposition of polyimine aerogels into a solution of oligomers through transimination reactions with additional amines. This solution can be utilized to create new aerogels with virtually identical properties to the original ones. This aerogel‐to‐sol‐to‐aerogel (ASA) process is also applicable to mixed waste streams and damaged aerogels. Moreover, this method allows to alter the aerogel properties post‐synthetically through careful selection of amines. Since the ASA process is highly reproducible and selective, omits purification steps, and conserves 100% of the initially embedded chemical resources, it presents an innovative tool for the sustainable management of superinsulating aerogels.

Closed-Loop Recyclable and Nonpersistent Polyethylene-like Polyesters.

ConspectusAliphatic polyesters based on long-chain monomers were synthesized for the first time almost a century ago. In fact, Carothers' seminal observations that founded the entire field of synthetic polymer fibers were made on such a polyester sample. However, as materials, they have evolved only over the past decade. This is driven by the corresponding monomers becoming practically available from advanced catalytic conversions of plant oils, and future prospects comprise a possible generation from third-generation feedstocks, such as microalgae or waste. Long-chain polyesters such as polyester-18.18 can be considered to be polyethylene chains with a low density of potential breakpoints in the chain. These do not compromise the crystalline structure or the material properties, which resemble linear high-density polyethylene (HDPE), and the materials can also be melt processed by injection molding, film or fiber extrusion, and filament deposition in additive manufacturing. At the same time, they enable closed-loop chemical recycling via solvolysis, which is also possible in mixed waste streams containing polyolefins and even poly(ethylene terephthalate). Recovered monomers possess a quality that enables the generation of recycled polyesters with properties on par with those of the virgin material. The (bio)degradability varies enormously with the constituent monomers. Polyesters based on short-chain diols and long-chain dicarboxylates fully mineralize under industrial composting conditions, despite their HDPE-like crystallinity and hydrophobicity. Fundamental studies of the morphology and thermal behavior of these polymers revealed the location of the in-chain groups and their peculiar role in structure formation during crystallization as well as during melting. All of the concepts outlined were extended to, and elaborated on further, by analogous long-chain aliphatic polymers with other in-chain groups such as carbonates and acetals. The title materials are a potential solution for much needed circular closed-loop recyclable plastics that also as a backstop if lost to the environment will not be persistent for many decades.

Acid-Cleavable Aromatic Polymers for the Fabrication of Closed-Loop Recyclable Plastics with High Mechanical Strength and Excellent Chemical Resistance.

Although closed-loop recycling of dynamic covalent bond-based plastics does not require catalysts, their mechanical strength and chemical stability remain a major concern. In this study, closed-loop recyclable poly(aryl imine) (PAI) plastics with high mechanical strength and excellent chemical resistance are fabricated by copolymerizing aromatic amines and aromatic aldehydes through dynamic imine bonds. The resulting PAI plastic with a tensile strength of 58.2 MPa exhibits excellent chemical resistance and mechanical stability in acidic and basic aqueous solutions and various organic solvents. The PAI plastics can be depolymerized in a mixed solvent of tetrahydrofuran (THF)/HCl aqueous solution through the dissociation of imine bonds, and the monomers can be facilely recovered with high purity and isolated yields due to the solubility difference between the aromatic amines and aromatic aldehydes in selective solvents. The efficient closed-loop recycling of the PAI plastic can also be realized through monomer conversion because the hydrolysis of the aromatic aldehydes generates aromatic amines. The recovered monomers can be used to re-fabricate original PAI plastics. This PAI plastic can be selectively recovered from complicated mixed polymer waste streams due to the mild depolymerization conditions of the PAI plastic and its high stability in most organic solvents.

Acid‐Cleavable Aromatic Polymers for the Fabrication of Closed‐Loop Recyclable Plastics with High Mechanical Strength and Excellent Chemical Resistance

AbstractAlthough closed‐loop recycling of dynamic covalent bond‐based plastics does not require catalysts, their mechanical strength and chemical stability remain a major concern. In this study, closed‐loop recyclable poly(aryl imine) (PAI) plastics with high mechanical strength and excellent chemical resistance are fabricated by copolymerizing aromatic amines and aromatic aldehydes through dynamic imine bonds. The resulting PAI plastic with a tensile strength of 58.2 MPa exhibits excellent chemical resistance and mechanical stability in acidic and basic aqueous solutions and various organic solvents. The PAI plastics can be depolymerized in a mixed solvent of tetrahydrofuran (THF)/HCl aqueous solution through the dissociation of imine bonds, and the monomers can be facilely recovered with high purity and isolated yields due to the solubility difference between the aromatic amines and aromatic aldehydes in selective solvents. The efficient closed‐loop recycling of the PAI plastic can also be realized through monomer conversion because the hydrolysis of the aromatic aldehydes generates aromatic amines. The recovered monomers can be used to re‐fabricate original PAI plastics. This PAI plastic can be selectively recovered from complicated mixed polymer waste streams due to the mild depolymerization conditions of the PAI plastic and its high stability in most organic solvents.

Semi-supervised segmentation for construction and demolition waste recognition in-the-wild: Adversarial dual-view networks

Precise, and automated segmentation of construction and demolition waste (CDW) is crucial for recognizing the composition of mixed waste streams and facilitating automatic waste sorting. Training a neural network for image segmentation is challenging due to the time and resource-intensive nature of annotating large-scale datasets, particularly for domain-specific waste recognition in cluttered environments. In this paper, we propose a semi-supervised multi-class segmentation approach to recognize CDW in real-world settings, utilizing an adversarial dual-view framework. In doing so, we utilize a critic network to enable mutual learning between views using high-confidence predictions. We collected and annotated images of CDW in-the-wild and experimented with various portions of unlabelled data. By minimizing a multi-task loss function, inclusive of supervised, unsupervised, and adversarial losses, our method achieves a frequency-weighted intersection over union of 0.62 and mean pixel accuracy of 0.76 across eight classes, with equal splits of labelled and unlabelled data. The findings realize the proposed method achieves competitive performance compared to fully supervised methods even with limited labelled data. This is useful in waste recognition practices by reducing the time and resources needed for data annotations. Furthermore, it paves the way for accurate waste sorting, facilitating efficient CDW recycling and resource recovery.

Application of a dual depressant system and microwave irradiation for flotation-based Separation of Polyethylene Terephthalate, Polyvinyl Chloride, and Polystyrene Plastics

The absence of an effective technique for the individual separation of plastics within a plastic mixture remains a paramount concern in the domain of plastic waste management. Recently introduced, the floatation technique has emerged as a method for segregating specific plastics, such as polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), from mixed waste streams. This separation process involves the utilization of traditional dual depressants (chemical agents). The study investigated the impact of pre-microwave irradiation of plastic surfaces at varying microwave output powers (20-100%) on the floatation behavior of each plastic. Additionally, the influence of depressant concentration (200-1600 mg/L) on plastic floatation was examined. The results revealed that pre-microwave irradiation at different output powers and varying depressant concentrations significantly affected the sink-float behavior of the studied plastics, with the exception of PET. It was observed that the microwave irradiation altered the number and type of active sites on the plastics' surfaces. Notably, there was no discernible regular trend in the flotation of plastic with an increase in microwave output power. The outcomes were substantiated by conventional identification techniques, including contact angle (θ) measurement, scanning electron microscopy (SEM) images, and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) spectra analysis. Equations derived through the use of the design of experiment software (Design-Expert®) demonstrated a commendable alignment between the predicted and actual values of plastic flotation. This underscores the efficacy of the applied methodology in forecasting and validating the outcomes of the floatation process.

Divergent methods for polyester and polycarbonate depolymerization with a cobalt catalyst

Catalytic methods for the cyclodepolymerization and solvolysis of polyesters and polycarbonates have been realized with a molecular cobalt catalyst. Nascent strategies to modify these methods for use in mixed plastic waste streams are identified.

Integrating PET chemical recycling with pyrolysis of mixed plastic waste via pressureless alkaline depolymerization in a hydrocarbon solvent

This study presents a proof of concept for a technology train that integrates polyethylene terephthalate (PET) recovery from mixed plastic waste and plastic pyrolysis. PET is depolymerized into terephthalic acid (TPA) by hydrolysis using a low volatility oil as medium, which enables (i) low-pressure operation, and (ii) a selective separation and recovery of TPA from the product mix by a simple process of filtration, washing, and precipitation. Full PET conversion and high TPA recovery (>98 %) were achieved at 260 °C.This technology train is demonstrated to be effective for processing mixed waste streams, leading to higher yield and quality of liquid product from thermal pyrolysis when compared with feedstock that has not been pre-treated. Further, the technology could be readily integrated with a plastics pyrolysis process, whereby a by-product from the pyrolysis could be used as the low-volatility oil.

Environmental sustainability assessment of different end-of-life scenarios for the pulper rejects produced in the paper recycling process

Resource recovery from wastes through recycling processes promotes near-zero-waste residue business models and supports the circular economy's goals by facilitating the closure of loops in industrial systems and reducing energy and resource consumption as well as pollutant emissions. However, the approach is sustainable only when the waste can be valorized, and the environmental impact of the recycling is lower with respect to other end-of-life (EOL) scenarios. Due to the diversity and complexity of wastes streams, these aspects need to be evaluated on a case-by-case basis.This study focuses on a mechanical recycling process for pulper rejects, a mixed waste stream generated during recycled paper production, with two aims: (1) to define a feasible mechanical recycling process and (2) to evaluate its environmental performance through life cycle assessment (LCA) compared to the most common EOL treatments, such as incineration with energy recovery and landfilling. ReCiPe 2016 H method was used to estimate the environmental impacts of all scenarios, adopting both midpoint and endpoint approaches, on a functional unit (FU) defined as 1000 kg of pulper rejects. The LCA results indicate that the pulper rejects recycling is always preferable to landfilling across all impact categories considered. On the contrary, in comparison to incineration, the best environmental option depends on the specific impact category considered. In particular, recycling is the best EOL alternative in terms of impacts on global warming, with an impact 33 % lower, but it is not the most sustainable one in terms of fossil resource consumption, mainly due to the amount of energy required during all steps of the recycling process, while allowing the recovery of materials that would otherwise be lost. Currently, it is not possible to identify an overall ‘winner’ between incineration with energy recovery and recycling for the pulper rejects because the most environmentally sound alternative varies depending on the priority given to different environmental issues. Therefore, further improvements of the pulper rejects recycling pathway performances are required to make the process even more efficient and competitive.

Augmented reality-enabled human-robot collaboration to balance construction waste sorting efficiency and occupational safety and health

Construction waste sorting (CWS) is highly recommended as a key step for construction waste management. However, current CWS involves humans’ manual hand-picking, which poses significant threats to their occupational safety and health (OSH). Robotic sorting promises to change the situation by adopting modern artificial intelligence and automation technologies. However, in practice, it is usually challenging for robots to do an efficient job (e.g., measured by quickness and accuracy) owing to the difficulties in precisely recognizing compositions of the mixed and heterogeneous waste stream. Leveraging augmented reality (AR) as a communication interface, this research aims to develop a human-robot collaboration (HRC) approach to address the dilemmatic balance between CWS efficiency and OSH. Firstly, a model for human-robot collaborative sorting using AR is established. Then, a prototype for the AR-enable collaborative sorting system is developed and evaluated. The experimental results demonstrate that the proposed AR-enabled HRC method can improve the accuracy rate of CWS by 10% and 15% for sorting isolated waste and obscured waste, respectively, when compared to the method without human involvement. Interview results indicate a significant improvement in OSH, especially the reduction of contamination risks and machinery risks. The research lays out a human-robot collaborative paradigm for productive and safe CWS via an immersive and interactive interface like AR.

Coexistence of specialist and generalist species within mixed plastic derivative-utilizing microbial communities

BackgroundPlastic-degrading microbial isolates offer great potential to degrade, transform, and upcycle plastic waste. Tandem chemical and biological processing of plastic wastes has been shown to substantially increase the rates of plastic degradation; however, the focus of this work has been almost entirely on microbial isolates (either bioengineered or naturally occurring). We propose that a microbial community has even greater potential for plastic upcycling. A microbial community has greater metabolic diversity to process mixed plastic waste streams and has built-in functional redundancy for optimal resilience.ResultsHere, we used two plastic-derivative degrading communities as a model system to investigate the roles of specialist and generalist species within the microbial communities. These communities were grown on five plastic-derived substrates: pyrolysis treated high-density polyethylene, chemically deconstructed polyethylene terephthalate, disodium terephthalate, terephthalamide, and ethylene glycol. Short-read metagenomic and metatranscriptomic sequencing were performed to evaluate activity of microorganisms in each treatment. Long-read metagenomic sequencing was performed to obtain high-quality metagenome assembled genomes and evaluate division of labor.ConclusionsData presented here show that the communities are primarily dominated by Rhodococcus generalists and lower abundance specialists for each of the plastic-derived substrates investigated here, supporting previous research that generalist species dominate batch culture. Additionally, division of labor may be present between Hydrogenophaga terephthalate degrading specialists and lower abundance protocatechuate degrading specialists.CMb_gViqtb7nKA_3vS-tKdVideo

Concentrated Ionic Fluids: Is There a Difference Between Chloride‐Based Brines and Deep Eutectic Solvents?

AbstractDeep Eutectic Solvents (DESs) have been lauded as novel solvents, but is there really a difference between them and concentrated aqueous brines? They provide a method of adjusting the activity of water and chloride ions which can affect mass transport, speciation and reactivity. This study proposes a continuum of properties across concentrated ionic fluids and uses metal processing as an example. Charge transport is shown to be governed by fluidity and there is no discontinuity between molar conductivity and fluidity irrespective of cation, charge density or ionic radius. Diffusion coefficients of iron(III) and copper(II) chloride in numerous concentrated ionic fluids show the same linear correlation between diffusion coefficient and fluidity. These oxidising agents were used to etch copper, silver and nickel and while the etching rate increased with fluidity for copper, etching of silver and nickel only occurred at high chloride and low water activity as passivation occurred when water activity increased. Overall, brines provide a high chloride content at a lower viscosity than DESs, but unlike DESs, brines are unable to prevent passivation due to their high water content. The results show how selective etching of mixed metal waste streams can be achieved by tuning chloride and water activity.

Concentrated Ionic Fluids: Is There a Difference Between Chloride-Based Brines and Deep Eutectic Solvents?

Deep Eutectic Solvents (DESs) have been lauded as novel solvents, but is there really a difference between them and concentrated aqueous brines? They provide a method of adjusting the activity of water and chloride ions which can affect mass transport, speciation and reactivity. This study proposes a continuum of properties across concentrated ionic fluids and uses metal processing as an example. Charge transport is shown to be governed by fluidity and there is no discontinuity between molar conductivity and fluidity irrespective of cation, charge density or ionic radius. Diffusion coefficients of iron(III) and copper(II) chloride in numerous concentrated ionic fluids show the same linear correlation between diffusion coefficient and fluidity. These oxidising agents were used to etch copper, silver and nickel and while the etching rate increased with fluidity for copper, etching of silver and nickel only occurred at high chloride and low water activity as passivation occurred when water activity increased. Overall, brines provide a high chloride content at a lower viscosity than DESs, but unlike DESs, brines are unable to prevent passivation due to their high water content. The results show how selective etching of mixed metal waste streams can be achieved by tuning chloride and water activity.

Knowns and unknowns of plastic waste flows in the Netherlands.

Plastic entering the environment is a growing threat for ecosystems. We estimate the annual mass of known Dutch plastic waste generated and littered and where it ends up. We use two methods: (1) a material flow analysis of plastic waste separately collected from 13 economic sectors (including households, industry and imports) and estimate the amount sent to processing plants or exported and (2) a mismanagement model from observations of litter (on Dutch beaches and riverbanks) plus estimates of inadequately managed exported plastic scraps entering the environment abroad. In 2017 (the most recent complete data set available), an estimate of 1990 (±111) kilotonnes [kt] of plastic waste was separately collected. The top three plastic waste generating sectors (74% of the total) were households, clothing and textiles, and importation. Our mismanagement model estimates that 4.3-21.2 kt enters the environment annually; almost all of which occurs in foreign countries after inadequate management of imported Dutch waste. We highlight unknowns, including the source and/or destination of imported (623 kt) and exported (514 kt) plastics, plastics in non-household mixed waste streams and the plastic fraction of some separately collected waste, for example, e-waste. Our results stress the need for improved monitoring and reporting of plastic waste. Beyond the Netherlands, our recommendations could also help other high-income countries' decision-makers reach their circular economy goals.

Perspectives on Thermochemical Recycling of End-of-Life Plastic Wastes to Alternative Fuels.

Due to its resistance to natural degradation and decomposition, plastic debris perseveres in the environment for centuries. As a lucrative material for packing industries and consumer products, plastics have become one of the major components of municipal solid waste today. The recycling of plastics is becoming difficult due to a lack of resource recovery facilities and a lack of efficient technologies to separate plastics from mixed solid waste streams. This has made oceans the hotspot for the dispersion and accumulation of plastic residues beyond landfills. This article reviews the sources, geographical occurrence, characteristics and recyclability of different types of plastic waste. This article presents a comprehensive summary of promising thermochemical technologies, such as pyrolysis, liquefaction and gasification, for the conversion of single-use plastic wastes to clean fuels. The operating principles, drivers and barriers for plastic-to-fuel technologies via pyrolysis (non-catalytic, catalytic, microwave and plasma), as well as liquefaction and gasification, are thoroughly discussed. Thermochemical co-processing of plastics with other organic waste biomass to produce high-quality fuel and energy products is also elaborated upon. Through this state-of-the-art review, it is suggested that, by investing in the research and development of thermochemical recycling technologies, one of the most pragmatic issues today, i.e., plastics waste management, can be sustainably addressed with a greater worldwide impact.

Food waste quantities and composition in Polish households.

Over one-third of the produced food is wasted globally. Most food is wasted at the consumer stage. The use of waste sorting analysis is considered to deliver more precise and less biased results than self-reporting methodologies. Currently, no detailed studies on the amounts and composition of household food waste are available for Poland. In the current paper the results of a food waste generation study in the city of Opole in Poland are presented. Both the residual and biowaste from 1425 citizens living in three different city areas was analysed during five seasonal waste sorting campaigns. The food waste was sorted in 16 avoidable and four non-avoidable fractions. The results of this study showed that in the city of Opole the absolute amount of both the avoidable and non-avoidable food waste is higher in the mixed waste stream than in the biowaste (42.8 kg inh.-1 in the residual waste and 19 kg inh.-1 in the biowaste, yearly). Thus, the total segregation level of food waste constitutes at the moment only 31%. The four main categories of avoidable food waste in the mixed waste are: bread (23.9%), vegetables (23.3%), meat (15.1%) and potatoes (7.8%). For the biowaste, the main four categories include: fruits (35.5%), other vegetables (27.9%), meal leftovers (13.6%) and bread (8.6%). Thus the overall food waste generation is 61.7 kg inh.-1 year-1. When also considering alternative discarding routes (sewerage, fed to animals or home-composted), the total food wastage in Opole amounts to 79.9 kg inh.-1 year-1, out of which 37.1 kg inh.-1 year-1 is avoidable waste and 42.8 kg inh.-1 year-1 non-avoidable waste.

Effect of Few-Layer Graphene on the Properties of Mixed Polyolefin Waste Stream

This work demonstrates how the addition of few-layer graphene (FLG) influences the processability and mechanical properties of the mixed polyolefin waste stream (R-(PE/PP)). Three different types of compounds were investigated: (1) R-(PE/PP) with FLG; (2) blends of R-(PE/PP) with prime polyethylene (PE) or polypropylene (PP) or PP copolymer; and (3) R-(PE/PP) with both the prime polymer and FLG. The processability was assessed by measuring the torque during melt extrusion, the melt flow index (MFI), and viscosity of the compounds. Investigations of the processability and mechanical properties of the composites indicate that the presence of FLG can reinforce the composites without hindering the processability, an unusual but desired feature of rigid fillers. A maximum increase in tensile strength by 9%, flexural strength by 23%, but a reduction in impact strength were observed for the compounds containing R-(PE/PP), 4 wt.% FLG, and 9 wt.% prime PP. The addition of FLG concentrations higher than 4 wt.% in R-(PE/PP), however, resulted in higher tensile and flexural properties while preserving the impact strength. Remarkably, the addition of 10 wt.% FLG increased the impact strength of the composite by 9%. This increase in impact strength is attributed to the dominant resistance of the rigid FLG particles to crack propagation.

Correlations between product distribution and feedstock composition in thermal cracking processes for mixed plastic waste

Thermal conversion can transform the carbon-based waste into valuable chemicals to be further used in the petrochemical industry for a polymeric carbon circular economy. This work’s aim was to identify chemical correlations between the thermal-cracking products and the feedstock polymer composition when using highly blended waste streams. The challenges addressed were to: (i) access a pool of experimental data on the monomer recovery potential of real-life, highly blended waste streams; (ii) estimate the polymer constituents of the mixed waste streams; and (iii) formulate a generic and systematic method to identify correlations between feedstock constituents and cracking products. Different post-consumer waste streams were investigated, including cardboard, automotive shredder residues, cable stripping waste, and textile waste. The cracking experiments were performed in a 2–4MWth industrial-scale Dual Fluidized Bed system at 800 °C using steam as fluidization agent. The polymeric constituents of the feedstocks were estimated using a numerical convex optimization method. To identify correlations between the feedstocks and products, a carbon bond-based classification was introduced. The experimental monomer yield ranged from 0.08 kg/kgf to 0.3 kg/kgf (f = feedstock) for the evaluated materials, corresponding to a carbon feedstock conversion rate between 14 % and 44 %. High yields of valuable monomers were obtained for the materials with the highest polyolefin content. The olefin monomer production correlated positively to the amount of aliphatic carbon in the original material and negatively to the carbon contents of the aromatic rings. From the trends observed, it was concluded that a framework based on carbon bond types is a promising approach to identify such correlations, which could serve as predictive tools for monomer recovery based on material’s composition and overall process conditions.