Search

The increasing attention to reduce plastic waste drives the design of products containing less plastics. Deli packaging is such a product, ranging from solely plastic packaging, to relatively new paperboard-plastic composites. In this research, the main objective is to quantify the recyclability of different deli packaging types and evaluate the effectiveness of recycling instructions. Therefore, we combine statistical entropy calculations (for the compositional complexity) with energy calculations from generic sorting and separation processes (i.e., the energy required to separate the products into their chemical substances). Deli packaging samples have been collected, categorized, weighed and dismantled. The results indicate that the use of paperboard may be slightly better than using solely plastics when evaluating on a product-level basis. However, since the product types are likely to disturb each other’s waste streams, the analysis should be extended to the whole waste stream in order to fully gauge their impact. Recycling instructions for consumers were found to, in some cases, increase the complexity of monostreams (i.e., plastic and paperboard fractions after dismantling). Although this is evident, for the first time, we develop and apply simple quantitative metrics to describe innate recyclability. The methodology allows to support design-for-recycling decisions for more complicated systems.

Chemical recycling of polymers is taking off as a circular technology, typically targeting pure recyclates. However, this is often not achieved efficiently due to high energy demand of separation and purification steps. In addition, many polymer applications have complex formulations that may be sensitive to impure feedstocks. Substitution of virgin feedstocks by complex recyclates (often containing impurities) requires a good knowledge of the structure/composition–property relations of polymer formulations. As this is often not the case, current practice relies on costly and rather inefficient enumeration experiments, or, at best, classical design-of-experiments approaches. We review the state-of-the art in structure–property modeling, present an example for polyurethane formulations, and propose a hybrid model-based framework. This involves a machine learning workflow for substitution problems in complex polymer formulations, combining existing data, novel reaction kinetics, structure–property models, molecular dynamics, and a minimum of experimental–analytical data where necessary, to build and validate the model.

District heating (DH) systems can improve energy efficiency, reduce greenhouse gas (GHG) emissions, and be a cost‐effective residential space heating alternative over conventional decentralized heating. This study uses radiative forcing (RF), a time‐sensitive life cycle assessment metric, to evaluate space heating alternatives. We compare forest residue and willow biomass resources and natural gas as fuel sources against decentralized heating using heating oil. The comparison is performed for selected locations in the Northeastern United States over a 30‐year production timeline and 100 observation years. The natural gas and willow scenarios are compared with scenarios where available forest residue is unused and adds a penalty of GHG emissions due to microbial decay. When forest residues are available, their use is recommended before considering willow production. Investment in bioenergy‐based DH with carbon capture and storage and natural‐gas‐based DH with carbon capture and storage (CCS) technology is considered to assess their influence on RF. Its implementation further improves the net carbon mitigation potential of DH despite the carbon and energy cost of CCS infrastructure. Soil carbon sequestration from willow production reduces RF overall, specifically when grown on land converted from cropland to pasture, hay, and grassland. The study places initial GHG emissions spikes from infrastructure and land‐use change into a temporal framework and shows a payback within the first 5 years of operation for DH with forest residues and willow.

Plastic packaging typically consists of a mixture of polymers and contains a whole range of components, such as paper, organic residue, halogens, and metals, which pose problems during recycling. Nevertheless, until today, limited detailed data are available on the full polymer composition of plastic packaging waste taking into account the separable packaging parts present in a certain waste stream, nor on their quantitative levels of (elemental) impurities. This paper therefore presents an unprecedented indepth analysis of the polymer and elemental composition, including C, H, N, S, O, metals, and halogens, of commonly generated plastic packaging waste streams in European sorting facilities. Various analytical techniques are applied, including Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), polarized optical microscopy, ion chromatography, and inductively coupled plasma optical emission spectrometry (ICP-OES), on more than 100 different plastic packaging products, which are all separated into their different packaging subcomponents (e.g., a bottle into the bottle itself, the cap, and the label). Our results show that certain waste streams consist of mixtures of up to nine different polymers and contain various elements of the periodic table, in particular metals such as Ca, Al, Na, Zn, and Fe and halogens like Cl and F, occurring in concentrations between 1 and 3000 ppm. As discussed in the paper, both polymer and elemental impurities impede in many cases closed-loop recycling and require advanced pretreatment steps, increasing the overall recycling cost.

Technologies for upgrading fast pyrolysis bio‐oil to drop‐in fuels and coproducts are under development and show promise for decarbonizing energy supply for transportation and chemicals markets. The successful commercialization of these fuels and the technologies deployed to produce them depend on production costs, scalability, and yield. To meet environmental regulations, pyrolysis‐based biofuels need to adhere to life cycle greenhouse gas intensity standards relative to their petroleum‐based counterparts. We review literature on fast pyrolysis bio‐oil upgrading and explore key metrics that influence their commercial viability through life cycle assessment (LCA) and techno‐economic analysis (TEA) methods together with technology readiness level (TRL) evaluation. We investigate the trade‐offs among economic, environmental, and technological metrics derived from these methods for individual technologies as a means of understanding their nearness to commercialization. Although the technologies reviewed have not attained commercial investment, some have been pilot tested. Predicting the projected performance at scale‐up through models can, with industrial experience, guide decision‐making to competitively meet energy policy goals. LCA and TEA methods that ensure consistent and reproducible models at a given TRL are needed to compare alternative technologies. This study highlights the importance of integrated analysis of multiple economic, environmental, and technological metrics for understanding performance prospects and barriers among early stage technologies.

In the last few years, governments all around the world have agreed upon migrating towards carbon-neutral economies as a strategy for restraining the effects of climate change. A major obstacle limiting this achievement is greenhouse gases emissions, for which the aviation sector is a key contributor because of its dependence on fossil fuels. As an alternative, biofuels with similar characteristics to current fossil-fuels and fully compatible with the existing petroleum infrastructure (i.e., drop-in biofuels) are being developed. In this regard, microalgae are a promising feedstock thanks to, among other aspects, their potential for lipid accumulation. This review outlines the development status, opportunities, and challenges of different technologies that are capable of or applicable to transform microalgae into aviation fuels. To this effect, a baseline of the existing jet fuels and the requirements for potential aviation biofuels is initially presented. Then, microalgae production and valorization techniques are discussed with an emphasis on the thermochemical pathways. Finally, an assessment of the present techno-economic feasibility of microalgae-derived aviation fuels is discussed, along with the authors’ point of view on the suitability of these techniques. Further developments are needed to reduce the costs of cultivation and harvesting of microalgae, and a biorefinery approach might improve the economics of the overall process. In addition, while each of the conversion routes described has its advantages and drawbacks, they converge upon the need of optimizing the deoxygenation techniques and the proportion of the suitable type of hydrocarbons that match fuel requirements.

Natural deep eutectic solvents (NADES) represent a green alternative to common organic solvents in the biochemical industry due to their benign behavior and tailorable properties, in particular as media for enzymatic reactions. However, to fully exploit their potential in enzymatic reactions, there is a need for a more fundamental understanding of how these neoteric solvents influence the course of these reac-tions. Thus, the aim of this study is to investigate the influence of NADES with various molar composi-tions on the stability and structure of enzymes, applying molecular dynamics simulations. This can help to better understand the effect of individual compounds of NADES, in addition to eutectic mixtures. More specifically, we simulate the behavior of Candida antarctica lipase B (CALB) enzyme in NADES com-posed of choline chloride with either urea, ethylene glycol or glycerol. Hereto, we monitor the NADES microstructure, the general stability of the enzyme and changes in the structure of its active sites and sur-face residues. Our simulations show that none of the studied NADES systems significantly disrupt the microstructure of the solvent or the stability of the CALB enzyme within the time scales of the simula-tions. The enzyme preserves its initial structure, size and intra-chain hydrogen bonds in all investigated compositions and, for the first time reported, also in NADES with increased hydrogen bond donating com-pound ratios. As the main novelty, our results indicate that, in addition to the composition, the molar ratio can be an additional variable to fine-tune the physicochemical properties of NADES without altering the enzyme characteristics. These findings could facilitate the development and application of task -tailored NADES media for biocatalytic processes. (c) 2022 Elsevier B.V. All rights reserved.

Extended producer responsibility (EPR) schemes have effectively increased the plastic waste that is separately collected. However, due to the structure of the recycling industry, EPR cannot increase recycling rates up to the target levels.Additional policy instruments to increase recycling rates such as recycled content targets, green dot fees bonus for recycled content, recycling targets and taxes on non-recycled plastic packaging have been discussed on a political level in the last years. However, very little research has quantitatively studied the effectiveness of these policy interventions.Using a partial equilibrium model, this paper examines the effectiveness of the implementation of the aforementioned policy instruments to increase recycling rates and the impact on different stakeholders of the value chain: plastic producers, consumers, producer responsibility organization and recyclers.Results show that direct interventions (recycled content standards and recycling targets) have the benefit of decoupling the recycling industry from external markets such as the oil market. They can be a good starting point to increase recycling, but in the long term they may be restricting by not presenting incentives to achieve recycling levels beyond the targeted amounts and by limiting technological innovation. On the contrary, eco-nomic interventions such as a green dot fee bonus or a packaging tax create economic incentives for recycling. However, these incentives are diminished by the lower perceived quality of packaging with higher recycled content levels.

Lead halide perovskites (LHP) are an emerging class of photovoltaic (PV) materials that have drawn intense interest due to their power conversion efficiencies above 23% and their potential for low-cost fabrication. However, the toxicity of lead causes concern about its use in LHP-PV at large scales. Here, we quantified lead intensity and toxicity potential of LHP-PV in potential commercial production. Lead intensity in LHP-PV life cycles can be 4 times lower and potential toxic emissions can be 20 times lower than those in representative U.S. electricity mixes, assuming that PV operational lifetimes reach 20 years. We introduce the metric “toxicity potential payback time”, accounting for toxic emissions in the life cycle of energy cycles, and showed that it is

The use of polyurethanes and, therefore, the quantity of its scrap are increasing. Considering the thermoset characteristic of most polyurethanes, the most circular recycling method is by means of chemical depolymerization, for which glycolysis is finding its way into the industry. The main goal of polyurethane glycolysis is to recover the polyols used, but only limited attempts were made toward recovering the aromatic dicarbamate residues and derivates from the used isocyanates. By the split-phase glycolysis method, the recovered polyols form a top-layer phase and the bottom layer contain transreacted carbamates, excess glycol, amines, urea, and other side products. The hydrolysis of carbamates results in amines and CO2 as the main products. Consequently, the carbamates in the bottom layer of polyurethane split-phase glycolysis can also be hydrolyzed in a separate process, generating amines, which can serve as feedstock for isocyanate production to complete the polyurethane material cycle. In this paper, the full recycling of polyurethanes is reviewed and experimentally studied. As a matter of demonstration, combined glycolysis and hydrolysis led to an amine production yield of about 30% for model systems. With this result, we show the high potential for further research by future optimization of reaction conditions and catalysis.

This work aims to improve the synthesis of renewable hydrochar (HC) co-fired with coal to reduce grenhouse gas (GHG) emission. Acetic acid catalyzed hydrothermal carbonization (cHTC) of Chlorella vulgaris microalgae biomass was investigated based on a 3(3-1) fractional statistical design of the experiment to examine the effects of hydrothermal reaction temperature (T = 180-220 degrees C), biomass-to-suspension-(BSR = 5-25 wt.%), and catalyst-to-suspension (CSR = 0-10 wt.%) ratios on process performance indicators. Analysis of variance was used to assess the experimental data. The results show that the application of homogeneous catalyst improves the fuel ratio and energy recovery efficiency up to 0.38 and 36.3%. Ex-ante cradle-to-gate life cycle assessment was performed to evaluate the impacts of co-firing ratio (CFR) and hydrochar quality on multi-perspective mid-, and endpoint environmental indicators. The highest decarbonization potential (1.54 kg CO2,eq kWh(-1)) is achieved using catalytic hydrochar biofuel produced at 195 degrees C, 25 wt.% BSR, and 8 wt.% CSR levels. The application of catalytic and autocatalytic hydrochar blends improves the overall environmental impacts and greenhouse gas footprint of solid fuel firing facilitating the transition toward low-carbon emission power generation.

Mixed plastic waste streams are to date present in nearly all societies. Depending on the source of the plastic waste stream, the complexity and difficulty to separate and recycle the waste stream differs. In this paper, the concept of statistical entropy is used to quantify the separation complexity of mixed plastic waste streams. To this end, the recently proposed multilevel statistical entropy analysis method is extended by adding a multiproduct system level. Furthermore, an overview is presented of the research questions that can be addressed by different statistical entropy definitions. The proposed extended method is applied to a plastic packaging waste case study in Belgium for which the data are available in the literature. The results indicate that the method based on statistical entropy allows analyzing the separation complexity of real-life mixed plastic waste streams. More specifically, the multilayer films contribute the most to the separation complexity of the studied plastic packaging waste stream. In addition, it is illustrated how the method can be used to identify key contributors to the separation complexity of mixed plastic waste streams and to evaluate measures to reduce the separation complexity of mixed plastic waste streams.

To date, atmospheric concentrations of sulfur hexafluoride (SF6) are the most potent among the greenhouse gases identified by the Intergovernmental Panel on Climate Change (IPCC) and are still rising. In the EU-28, SF6 has been banned from several applications, however, an important exception is gas-insulated electrical switchgear (GIS) for which cost-effective and environmentally sound alternatives were unavailable when the F-Gas regulation was last revised in 2014. To date, after some recent innovations, we argue that the phasing out of SF6 could spur the accelerated development of alternatives with a lower carbon footprint. In the EU-28, the SF6 amount in switchgear is unclear. In this paper, we estimated the SF6 amount to be between 10,800 and 24,700 t (with a mode at 12,700 t) in 2017, resulting in 68 to 140 t of annual emissions from operational leakage only, corresponding to 1.6 to 3.3 Mt of CO2-eq. We additionally calculated the potential greenhouse gas savings over the lifecycle of one exemplary 145 kV gas-insulated switchgear bay upon replacing SF6 by decafluoro-2-methylbutan-3-one (C5-FK) and heptafluoro-2-methylpropanenitrile (C4-FN) mixtures. Projecting these results over the EU-28, a phase-out scenario starting from 2020 onwards could reduce the carbon footprint by a median of 14 Mt of CO2-eq, over a period of 50 years. Extrapolation to medium voltage could be assumed to be of a similar magnitude.

Natural deep eutectic solvents (NADES) are mixtures of naturally derived compounds with a significantly decreased melting point owing to specific interactions among the constituents. NADES have benign properties (low volatility, flammability, toxicity, cost) and tailorable physicochemical properties (by altering the type and molar ratio of constituents); hence, they are often considered to be a green alternative to common organic solvents. Modeling the relation between their composition and properties is crucial though, both for understanding and predicting their behavior. Several efforts have been made to this end. This Review aims at structuring the present knowledge as an outline for future research. First, the key properties of NADES are reviewed and related to their structure on the basis of the available experimental data. Second, available modeling methods applicable to NADES are reviewed. At the molecular level, DFT and molecular dynamics allow density differences and vibrational spectra to be interpreted, and interaction energies to be computed. Additionally, properties at the level of the bulk medium can be explained and predicted by semi-empirical methods based on ab initio methods (COSMO-RS) and equation of state models (PC-SAFT). Finally, methods based on large datasets are discussed: models based on group-contribution methods and machine learning. A combination of bulk-medium and dataset modeling allows qualitative prediction and interpretation of phase equilibria properties on the one hand, and quantitative prediction of melting point, density, viscosity, surface tension, and refractive index on the other. Multiscale modeling, combining molecular and macroscale methods, is expected to strongly enhance the predictability of NADES properties and their interaction with solutes, and thus yield truly tailorable solvents to accommodate (bio)chemical reactions.

Multiple recent reports showed accelerated biodegradation of polyethylene by employing macro-organisms such as mealworms (Tenebrio molitor) and larvae of the greater wax moth (Galleria mellonella), which seemingly chew and digest the plastic. Nevertheless, doubts regarding analytical data were published, and results are not universally transferrable. This paper aims at gaining mechanistic insights and exploring the technological prospects of potential future optimized biodegradation. We used a variety of experimental setups with both species, using both live specimens and homogenated paste, to cover a broad spectrum of potential technological setups, and performed gravimetric, microscopic and spectroscopic analyses. Live larvae showed a preference for specific substrates, yet we argue by comparison to other food sources, evidenced also by energetic uptake, that a diet of LDPE is insufficient for growth. We did not detect mass loss when homogenate paste is brought in contact with LDPE films, nor significant traces of ethylene glycol. We demonstrated that the morphology of the substrate changes after contact with live larvae, indicating some plasticizing action by an excreted liquid. This indicates a mechanism of degradation involving more than the gut microbiome alone. Using streamlined life cycle assessment and techno-economic analysis (LCA/TEA) methods, we showed that the application of these findings as either a remediation or management technology for waste plastics is highly unlikely, given the conversion to microplastics, the absence of valuable products, and the high energy cost. However, the conversion mechanism should be further elucidated for bio-functionalization of liquid alkanes as high-value application, or to mitigate plastic anomalies in composting/digesting food waste.

In recent decades new recycling technologies for mixed plastic waste have emerged. In pyrolysis, the polymer chains are thermally broken (pyrolyzed) to obtain hydrocarbon materials of different molecular weights such as naphtha, oil or waxes, whose yields can be controlled by varying the reaction parameters. Naphtha represents a closed-loop recycling process as it is a feedstock for (poly)olefins; while the co-production of waxes, having several applications in e.g. the construction industry, exemplifies an open-loop recycling process. This paper compares the economic performance of the pyrolysis of mixed polyolefin waste in a closed-loop and open-loop scheme, including a probabilistic approach to the most important variables. From an economic perspective, open-loop pyrolysis as presented outperforms closed-loop recycling, due to the high prices of wax. However, the results present a high dispersion caused by the volatility of the prices of crude oil and its derivates. Considering the current oil price projections, our case study analysis showed that for open-loop recycling there is a future probability of almost a 98% of observing positive results and around 57% of probability in the case of closed-loop recycling, under the assumptions made. Yet, in a future scenario where decarbonized electricity would decrease oil prices, the probability of a positive outcome reduces to 57% for the open-loop case and to less than 8% in the case of closed-loop recycling. To make these pathways attractive to investors, the nameplate capacity should be at least 70 kt/year for open-loop recycling and 115 kt/year for closed-loop recycling. A 120 kt/year plant should operate minimally at 80% of its capacity for open-loop recycling, while closed-loop recycling would demand running close to maximum capacity. Security of feedstock supply therefore is required.

Currently, Belgium is in a transition period after which more household plastic packaging waste will be collected separately in function of increased recycling. The challenge is to identify the most environmentally sound treatment option for the increased selectively collected plastic waste. In this study, mechanical recycling (MR) and thermochemical recycling (TCR) of four newly collected subfractions, being polypropylene (PP), polystyrene (PS), mixed polyolefins (MPO) rigids and polyethylene (PE) films, were investigated through prospective Life Cycle Assessment (LCA), in comparison to incineration with energy recovery. Results showed clear benefits of recycling over incineration with energy recovery. Generally, MR showed a better net environmental impact compared to TCR (for PP, PS, MPO rigids and PE films, respectively, e.g., a global warming impact of 100, -1580, 539 and 101 kg CO2 eq. per ton by TCR, and -1183, -3096, -319 and -1162 kg CO2 eq. per ton by MR, and 2339, 2494, 2108 and 2141 kg CO2 eq. per ton by incineration). This could mainly be explained by the avoided burdens of virgin materials. Whereas TCR avoids the virgin supply of the feedstock for polymer production, MR avoids additionally polymerisation and granulation. MR products, i.e. regranulates or flakes, can be directly used in manufacturing, whereas TCR products require first processes like steam cracking, polymerisation and granulation before being used in manufacturing. As this study assumed a 1:1 substitution ratio between MR regranulates and their virgin alternatives, it presents the most favourable results for MR, which should be kept in mind and further investigated.

Increasing plastic recycling rates is crucial to tackle plastic pollution and reduce consumption of fossil resources. Recycling routes for post-consumer plastic fractions that are technologically and economically feasible remain a challenge. Profitable value chains for recycling mixed film and tray-like plastics have hardly been implemented today, in sharp contrast to recycling of relatively pure fractions such as polyethylene terephthalate and high-density polyethylene bottles. This study examines the economic feasibility of implementing mechanical recycling for plastic waste such as polypropylene, polystyrene, polyethylene films and mixed polyolefins. In most European countries these plastic fractions are usually incinerated or landfilled whilst in fact technologies exist to mechanically recycle them into regranulates or regrinds. Results show that the economic incentives for the recycling of plastic packaging depend predominantly on the product price and product yield. At current price levels, the most profitable plastic fraction to be recycled is PS rigids, with an internal rate of return of 14%, whereas the least profitable feed is a mixed polyolefin fraction with a negative internal rate of return in a scenario with steadily rising oil prices. Moreover, these values would be substantially reduced if oil prices, and therefore plastic product prices decrease. Considering a discount rate of 15% for a 15-year period, mechanical recycling is not profitable if no policy changes would be imposed by governments. Clearly low oil prices may jeopardize the mechanical recycling industry, inducing the need for policies that would increase the demand of recycled products such as imposing minimal recycled content targets.

Horse manure, the improper disposal of which, imposes considerable environmental costs, constitutes an apt feedstock for conversion to renewable fuels and chemicals when tail gas reactive pyrolysis (TGRP) is employed. TGRP is a modification of fast pyrolysis that recycles its noncondensable gases and produces a bio-oil low in oxygen concentration and rich in naphthalene. Herein, we evaluate the coproduction of phenol as a value-added renewable chemical, alongside jet-range fuels within distributed TGRP systems using techno-economic analysis and life cycle assessment. We investigate the metrics global warming potential (GWP), cumulative exergy demand (CExD), and cost for the conversion of 200 dry metric tons per day of horse manure to bio-oil and its subsequent upgrade to hydrocarbon fuel and phenolic chemicals. Assigning credits for the offset of the coproducts, the net GWP and CExD of TGRP jet fuel are 10 g of CO2 eq and 0.4 MJ per passenger kilometer distance traveled, respectively. These values are considerably lower than the GWP and CExD of petroleum-based aviation fuel. The minimum fuel selling price of the TGRP jet fuel ($1.35$1.80 L1) is estimated to be much greater than that of petroleum-based aviation fuel ($0.42 L1), except under optimized fuel conversion and coproduct market conditions ($0.53$0.79 L1) when including a market price for carbon.

When manure is introduced in a hot fluidized bed for gasification or combustion, its inorganic compounds will undergo chemical transformations upon heating. The phosphorus containing salts, which are mostly hydrogen and dihydrogen phosphates or alkali and alkaline earth metals, melt at low temperatures (200–300 °C), before they decompose. In their liquid state, these compounds may drive the formation of ash coatings on bed particles of silica sand, and irreversibly agglomerate multiple particles if they are locally present in high amounts. The recent first time observation of the latter phenomenon led to a new interpretation of an earlier concept, melt induced agglomeration. Decomposition of the aforementioned (di)hydrogen phosphates and reaction of the fresh coatings with silica bed material drives the fluidized bed towards chemical equilibrium upon the ash’s increasing temperature, in which K2Si4O9 is formed aside from Ca3(PO4)2 and CaSiO3. In this situation of (near) chemical equilibrium, a melt is formed if the amount of K2Si4O9 is high and the amount of CaSiO3 is low. Low CaSiO3 may result from a low calcium concentration in the fuel, or by a high phosphorus concentration, since Ca3(PO4)2 is the more stable form. The particle’s silicate melt is concentrated at the interior of the coating, due to the abundance of silica at this location, and any Ca3(PO4)2 makes up the exterior of the coating. If enough silicate melt can find a way through the solid exterior of the coating, entrained particles may deposit onto an inclined refractory wall above the fluidized bed. We support particle deposition as the initiating deposition step, as opposed to gaseous condensation, primarily because of the aluminum and potassium silicate chemistry involved. After deposition, SEM-EDX analysis of a deposit’s cross section revealed a chemical anchoring by chemical reaction between K2Si4O9 and the alumina rich refractory material, creating a strong solid bond of for instance potassium feldspar, which has a high melting point. Deposits can therefore grow larger before they break loose and cause bed disturbances, thus damaging the refractory wall. The comprehensive theory on transient thermal ash transformations, presented in this paper, will allow to adept the design of future thermal energy applications for manure by selecting appropriate additives and refractory bed and/or wall materials.

The leaching of Sb in alkaline environment is known to be mainly governed by the precipitation of Ca- and Fe-antimonates. To reduce Sb leaching from MSWI bottom ash below the regulatory limit for recycling as construction material, Ca- and Fe-containing chemicals and industrial residues were added to this bottom ash. Short term and medium long term leaching tests were performed by lab batch tests and outdoor field tests. This confirmed that the tested chemicals and industrial residues reduce Sb leaching to below the regulatory limit. Carbonation tests with subsequent leaching were performed to provide information on the long term leaching behavior of Sb from MSWI bottom ash. Upon carbonation, Sb leaching from the bottom ash to which Fe2(SO4)3 or Ca- and Fe-containing industrial residues were added, increased over time, but did not exceed the regulatory limit value after full carbonation. When carbonation progressed, Sb leaching from the untreated bottom ash decreased, which could not be explained by the current state of the knowledge on mechanisms for Sb leaching in alkaline environments. As the leaching of Sb after carbonation was altered similarly as that of Cu, we experimentally checked if Sb leaching could also be influenced by the presence of organic acids,. As a result, we showed that Sb leaching from MSWI bottom ash in alkaline environments is indeed influenced by the presence of organic acids like humic and fulvic acids.

Every decision-oriented life cycle assessment (LCAs) entails, at least to some extent, a future-oriented feature. However, apart from the ex-ante LCAs, the majority of LCA studies are retrospective in nature and do not explicitly account for possible future effects. In this review a generic theoretical framework is proposed as a guideline for ex-ante LCA. This framework includes the entire technology life cycle, from the early design phase up to continuous improvements of mature technologies, including their market penetration. The compatibility with commonly applied system models yields an additional aspect of the framework. Practical methods and procedures are categorised, based on how they incorporate future-oriented features in LCA. The results indicate that most of the ex-ante LCAs focus on emerging technologies that have already gone through some research cycles within narrowly defined system boundaries. There is a lack of attention given to technologies that are at a very early development stage, when all options are still open and can be explored at a low cost. It is also acknowledged that technological learning impacts the financial and environmental performance of mature production systems. Once technologies are entering the market, shifts in market composition can lead to substantial changes in environmental performance.

Multilevel statistical entropy analysis (SEA) is a method that has been recently proposed to evaluate circular economy strategies on the material, component and product levels to identify critical stages of resource and functionality losses. However, the comparison of technological alternatives may be difficult, and equal entropies do not necessarily correspond with equal recyclability. A coupling with energy consumption aspects is strongly recommended but largely lacking. The aim of this paper is to improve the multilevel SEA method to reliably assess the recyclability of plastics. Therefore, the multilevel SEA method is first applied to a conceptual case study of a fictitious bag filled with plastics, and the possibilities and limitations of the method are highlighted. Subsequently, it is proposed to extend the method with the computation of the relative decomposition energies of components and products. Finally, two recyclability metrics are proposed. A plastic waste collection bag filled with plastic bottles is used as a case study to illustrate the potential of the developed extended multilevel SEA method. The proposed extension allows us to estimate the recyclability of plastics. In future work, this method will be refined and other potential extensions will be studied together with applications to real-life plastic products and plastic waste streams.

Bottom ash from municipal solid waste incineration is an underutilized secondary resource, which currently gains large attention due to increased landfill costs and the push towards a circular economy. Due to the high concentrations and mobility of pollutants, bottom ash cannot readily replace virgin construction materials. Over the last decade, many research efforts have addressed these issues in view of newly developed engineering applications. However, the required quality of bottom ash varies for each application. In this review we focus on the ternary relationship between engineering applications, chemical barriers/limitations and treatment technologies for municipal solid waste incinerator bottom ash. For each intended engineering application [loose (bulk) construction aggregates; sand, aggregate or cement replacement in concrete; raw material for cement or ceramics] the appropriate treatment technologies are selected to overcome identified chemical barriers. This allows future top-down design decisions, starting from the most promising engineering application of bottom ash. The main chemical barrier for bottom ash recycling as loose construction aggregates is the leaching of heavy metals and/or metalloids. This can be overcome by size separation, carbonation, mild heat treatment or by using mineral additives. In structured concrete, the presence of metallic aluminum or zinc causes early cracking and a high chloride concentration causes corrosion of reinforcement steel. Therefore, recent developments in wet/semi-dry separations facilitated enhanced eddy current separation to remove non-ferrous metals. The washing of bottom ash to remove chloride, is to date the sole technology to prepare bottom ash as raw material for cement kilns. Finally, when bottom ash is used as feedstock for ceramics production, recent knowledge was generated to allow for selecting thermal process parameters in such a way that leaching of both heavy metals and metalloids is minimized.

This study evaluates the potential use of a novel lightweight aggregate (LWA), spherical porous reactive aggregate (SPoRA), produced from waste coal bottom ash, for internal curing of concrete. The engineering properties of SPoRA required for concrete internal curing were assessed including specific gravity, porosity, sphericity, water absorption, and water desorption. SPoRA showed a low oven dry specific gravity, ranging from 0.83 to 1.43, accompanied by high porosity which makes it capable of storing the amount of water needed for concrete internal curing. Through X-ray computed tomography (XCT), the high porosity of SPoRA (39.6%–57.8%, by volume) was measured and confirmed, and its sphericity, which influences the workability of concrete, was evaluated. XCT evaluation also showed that the pore structure of SPoRA is well connected, allowing stored water to move through the pore structure to the outer surface during the self-desiccation of concrete. SPoRA's 72 h water absorption not only passed the requirements of ASTM C1761 for internal curing (water absorption > 5% and minimum of 85% water desorption at 94% relative humidity, RH), but also showed superior performance in comparison to LWAs available in the market, which were also evaluated in this study. Moreover, the SPoRA desorption isotherms showed its capability for releasing a favorable amount of absorbed water as the internal RH decreases during concrete self-desiccation, thereby providing promising desorption behavior for concrete internal curing and can be a promising LWA for internal curing of concrete.

New US Environmental Protection Agency regulations for the disposal of coal combustion residues (CCR) incentivize bottom-up recycling efforts, to convert them into value-added applications. This study examines producing lightweight ceramic aggregates from CCR for concrete/geotechnical applications. More specifically, we argue that industrial residues such as coal bottom ash, despite their heterogeneity and diversity, are apt feedstock materials to constitutively design melt ceramics via high temperature recycling. A lot of knowledge on the feedstock (thermal and melt flow properties) is available, because of the historical interest in (molten) coal ash properties. It is shown how thermodynamics and empirically derived models and experimental observations on the viscosity, surface tension, heat capacity, enthalpy of fusion and thermal conductivity can be used to constitutively design melt ceramics. We created a custom model for the design of spherical porous reactive aggregates (SPoRA) from two different coal bottom ashes, using NaOH as an illustrative fluxing agent. To obtain the desired aggregate design, production should occur above the solidus temperature, yet viscous flow, caused by a low viscosity of the CCR melt, should be limited. The design method developed is able to discern the influence of various design parameters on the experimentally produced ceramic aggregates. A proper match between simulations and experimentally observed object shapes was obtained, allowing to define an operating window (temperature and residence time as function of fluxing agent addition) constitutively. This work shows how the available knowledge on coal ash assists the understanding and design of novel ceramic aggregate recycling processes.

Bio-oil produced from fast pyrolysis of biomass is a promising substitute for crude oil that can meet climate change mitigation goals, but due to its high oxygen content, it requires upgrading to remove oxygen in order to be used as a transportation fuel. Hydrodeoxygenation (HDO) is one means of upgrading fast pyrolysis oil; however, its main limitation is its large hydrogen requirement. We evaluate an alternative electrochemical deoxygenation (EDOx) method that uses catalytic electrode membranes on a ceramic, oxygen-permeable support to generate hydrogen in situ for deoxygenation at the cathode and oxygen removal at the anode. We analyze the life-cycle greenhouse gas (GHG) emissions and scale effects of gas-phase upgrading of pyrolysis oil [300 t/day (MTPD)] using different configurations of EDOx and compare it with the large-scale HDO process (2000 MTPD). We observe that the EDOx configurations have lower total GHG emissions of 58.4 and 7.411 g of CO2 equiv/MJ for vehicles operated with diesel and gasoline, respectively, compared to HDO (39 g of CO2 equiv/MJ). Furthermore, the EDOx processes offers potentially 10 times more small-scale pyrolysis upgrading facilities in the United States compared to HDO, suggesting that small-scale on-site EDOx processes can reach more inaccessible forest biomass resources.

The combustion of poultry litter, which is rich in phosphorus, in a fluidized bed combustor (FBC) is associated with agglomeration problems, which can lead to bed defluidization and consequent shutdown of the installation. Whereas earlier research indicated coating induced agglomeration as the dominant mechanism for bed material agglomeration, it is shown experimentally in this paper that both coating and melt induced agglomeration occur. Coating induced agglomeration mainly takes place at the walls of the FBC, in the freeboard above the fluidized bed, where at the prevailing temperature the bed particles are partially molten and hence agglomerate. In the ash, P2O5 forms together with CaO thermodynamically stable Ca3(PO4)2, thus reducing the amount of calcium silicates in the ash. This results in K/Ca silicate mixtures with lower melting points. On the other hand, in-bed agglomeration is caused by thermodynamically unstable, low melting HPO42- and H2PO4- salts present in the fuel. In the hot FBC these salts may melt, may cause bed particles to stick together and may subsequently react with Ca salts from the bed ash, forming a solid bridge of the stable Ca3(PO4)2 between multiple particles. © 2014 Elsevier Ltd. publisher: Elsevier articletitle: Coating and melt induced agglomeration in a poultry litter fired fluidized bed combustor journaltitle: Biomass and Bioenergy articlelink: http://dx.doi.org/10.1016/j.biombioe.2014.07.013 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved. ispartof: Biomass & Bioenergy vol:69 pages:71-79 status: published

Agglomeration of ash in fluidized bed combustors may result in defluidization and subsequent downtime of the installation. Previous research has shown that Ca-based additives can prevent agglomeration, but the added amount was determined arbitrarily and testing occurred only on lab scale or pilot scale. This paper presents a statistical approach, based on a newly developed agglomeration index, to calculate the amount of CaO that should be added (in the form of a Ca-based mineral, e.g., CaCO3) to the fluidized bed in order to prevent agglomeration. The agglomeration index is based on an understanding of the reactions occurring in the ash, for instance, the formation of potassium silicates with low melting points, and the formation of calcium phosphates and calcium silicates with high melting points. Full-scale testing of partial replacement of silica sand by calcite (CaCO3) as fresh bed material showed that the increased CaO concentration in the ash, with respect to normal operation, appears to reduce both wall and in-bed agglomeration problems. As a measure for agglomeration risk, differential bed pressure variations were statistically analyzed. In the test periods during which CaCO3 was added, the bed pressure variations were smaller and less frequent, and the severity of agglomeration was thus reduced. The proposed strategy can be applied for fuels that are commonly perceived as difficult or unsuited for fluidized bed combustion, and also for other additives than CaCO3, e.g., Al-based minerals. © 2014 American Chemical Society. ispartof: Energy & Fuels vol:28 issue:8 pages:5455-5462 status: published

© 2014, Springer Japan. Solidification/stabilization (S/S) of fly ash and air pollution control residues from MSWI was studied, with and without the use of cement. It appeared that metal and oxyanion leaching from these stabilised residues was comparable after 75 days of curing. Leaching of chloride and sulfate did not decrease by the addition of cement during S/S treatment. In an LCA perspective the environmental impact of the S/S treated mixtures with cement in the toxicity related impact categories was higher than the impact of the S/S treated mixtures without cement. Moreover, the production of cement for application in S/S also causes an impact in the impact categories climate change and terrestrial acidification. For environmental considerations in an LCA perspective S/S without cement should be preferred. ispartof: Journal of Material Cycles and Waste Management vol:17 issue:2 pages:229-236 status: published

Elevated Cr and Mo concentrations are often found in leachates of thermally treated solid waste, but there is no general explanation for this so far. Therefore, we studied the leaching behaviour after thermal treatment as a function of heating temperature and residence time for two types of solid waste: contaminated sludge and bottom ash from municipal solid waste incineration. The leaching behaviour of both waste streams was compared with experiments on synthetic samples, allowing deduction of a general mechanism for Cr and Mo leaching. Cr and Mo showed a similar leaching behaviour: after an initial increase, the leaching decreased again at higher temperatures. Oxidation of these elements from their lower oxidation states to chromate and molybdate at temperatures up to 600 °C was responsible for the increased leaching. At higher temperatures, both Mo and Cr leaching decreased again owing to the formation of an amorphous phase, incorporating the newly formed chromate and molybdate salts, which prevents them from leaching.

As pork is indispensable in the diet of Cuban people, the government was forced to prioritize its production. Pig production causes several environmental impacts related with air, water and soil pollution, which can be quantified with the application of Life Cycle Assessment that allows to optimize products and processes by identifying their environmental impacts. Farming systems considered in different Life Cycle Assessment studies show substantial differences in their characteristics, namely: animal productivity, feed composition, manure management and production period, which influences the environmental performance of each system. Therefore, each study is unique for the system it assesses and should be analyzed individually. In Cuba, the environmental implications of pig production, whose understanding is cornerstone to eventually adopt more environmentally sound practices while ensuring high productivity standards, are yet to be quantified. This study provides some fundamental insights in the life cycle of pig production in the province of Cienfuegos. The assessment if focused in large farms of the province of Cienfuegos which causes large environmental impacts. Large farms accounts for the production of 77% of the pigs delivered to slaughter houses in the province. Pig production in Cienfuegos accounts for 7–12% of Cuban production. The quantification of the environmental impacts of pig production resulted in an impact per finished pig of 120 kg of live weight of 1892 MJ abiotic depletion of fossil fuels, 1019 kg-CO 2 -eq. global warming potential, 36 kg 1.4-dichlorobenzene-eq. human toxicity, 17 kg 1.4-dichlorobenzene-eq. terrestrial toxicity, 1 kg 1.4-ethylene-eq. photo-oxidant formation, 12 kg-SO 2 -eq. acidification potential and 6 kg PO 4 -eq. eutrophication potential. It appeared that the main opportunities to improve the environmental performance of pig production in Cienfuegos are reduction of the impacts of the anaerobic lagoons used for manure management on global warming potential, acidification potential and eutrophication and the impact on acidification potential of pig housing. Direct land spreading of manure appears as the best alternative to lagooning, considering the current situation of pig breeding in Cienfuegos.

The paper starts by reviewing the increasing production of waste and the growing importance of its thermal treatment, which aims at volume reduction of the waste, at the destruction, capture, and concentration of hazardous substances, and at the recovery of energy (WtE). Incineration is a generally applied thermal treatment technique, whereas pyrolysis and gasification are still under development. Within the incineration techniques, bubbling, rotating and circulating fluidized beds have found specific and growing applications. As technical information on fluidized bed waste incinerators is spread throughout literature, the present review paper collates the relevant literature and critically examines the parameters that govern the design and operation of these incinerators. Secondly, the design strategy of a fluidised bed incinerator is outlined, which involves considerations of hydrodynamic (velocities, mixing), thermal (heat balances) and kinetic (reaction rate and burnout) nature. Application of the design equations and recommendations will facilitate the sizing of an appropriate fluidized bed incinerator. Since during waste incineration pollutants are formed, the origin and fate of the pollutants and their abatement are reviewed. Finally, special attention is given to the specific de-fluidization problems often encountered during fluidized bed combustor operation, mainly because of agglomeration and sintering. The mechanisms of agglomeration and sintering are discussed, and possible remedies are given. Additionally, important issues of equipment erosion and uniform feeding of the waste into the fluidized bed reactor are considered. © 2012 Elsevier Ltd. All rights reserved. ispartof: Progress in Energy and Combustion Science vol:38 issue:4 pages:551-582 status: published

The leaching of Sb from waste-to-energy (WtE) bottom ash (BA) often exceeds the Dutch limit value of 0.32mgkg(-1) for recycling of BA in open construction applications. From the immobilization mechanisms described in the literature, it could be concluded that both Ca and Fe play an important role in the immobilization of Sb in WtE BA. Therefore, Ca and Fe containing compounds were added to the samples of the sand fraction of WtE BA, which in contrast to the granulate fraction is not recyclable to date, and the effect on the Sb leaching was studied by means of batch leaching tests. Results showed that addition of 0.5 and 2.5% CaO, 5% CaCl2, 2.5% Fe2(SO4)3 and 1% FeCl3 decreased the Sb leaching from 0.62±0.02mgkgDM(-1) to 0.20±0.02, 0.083±0.044, 0.25±0.01, 0.27±0.002 and 0.29±0.02mgkgDM(-1), respectively. Due to the increase in pH from 11.41 to 12.53 when 2.5% CaO was added, Pb and Zn leaching increased and exceeded the respective leaching limits. Addition of 5% CaCO3 had almost no effect on the Sb leaching, as evidenced by the resulting 0.53mgkgDM(-1) leaching concentration. This paper shows a complementary enhancement of the effect of Ca and Fe, by comparing the aforementioned Sb leaching results with those of WtE BA with combined addition of 2.5% CaO or 5% CaCl2 with 2.5% Fe2(SO4)3 or 1% FeCl3. These lab scale results suggest that formation of romeites with a high Ca content and formation of iron antimonate (tripuhyite) with a very low solubility are the main immobilization mechanisms of Sb in WtE BA. Besides the pure compounds and their mixtures, also addition of 10% of two Ca and Fe containing residues of the steel industry, hereafter referred to as R1 and R2, was effective in decreasing the Sb leaching from WtE BA below the Dutch limit value for reuse in open construction applications. To evaluate the long term effect of the additives, pilot plots of WtE BA with 10% of R1 and 5% and 10% of R2 were built and samples were submitted to leaching tests at regular intervals over time. The Sb leaching from untreated WtE BA was just below or above the Dutch limit value. The Sb leaching from the pilot plots of BA with additives first remained stable around 0.13mgkg(-1) but had a tendency to slightly increase after 6months, indicating the need for further research on the effect of weathering, and more specifically of carbonation, on Sb leaching from WtE BA. publisher: Elsevier articletitle: Immobilization of antimony in waste-to-energy bottom ash by addition of calcium and iron containing additives journaltitle: Waste Management articlelink: http://dx.doi.org/10.1016/j.wasman.2016.05.007 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved. ispartof: Waste Management vol:54 pages:162-168 ispartof: location:United States status: published

The oversupply of organic fertilizers causes an urgent need for alternative treatments of manure. CO2 neutral electricity is produced from poultry manure, a renewable fuel which is relatively dry and has a heating value of 6e8 MJ/kg. The electricity production from manure saves emissions from fossil fuel combustion, resulting in a reduced environmental impact in the impact category climate change. Moreover, as manure contains a large amount of ammoniacal N, and due to nitrification and denitrification processes, land spreading of poultry manure causes larger emissions of NH3, N2O and NOx than combustion. Electricity production from manure therefore outperforms land spreading in the impact categories terrestrial acidification, particulate matter formation, marine eutrophication and photochemical oxidant formation. The fluidized bed combustor of BMC in the Netherlands generates zero waste, as the ash is recovered as a PK fertilizer, which is odorless, dry, sterile and has a lower mass and volume than the manure, making it more suitable for export to regions with a high P demand. The ash does however cause technological problems, such as agglomeration and deposition. publisher: Elsevier articletitle: Electricity from poultry manure: a cleaner alternative to direct land application journaltitle: Journal of Cleaner Production articlelink: http://dx.doi.org/10.1016/j.jclepro.2014.04.016 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved. ispartof: Journal of Cleaner Production vol:96 pages:467-475 ispartof: location:Cincinnati, Ohio status: published

Thermal valorization of biomass or waste in a fluidized bed combustor may result in agglomeration of the bed material, coated with ash, potentially causing defluidization. In this paper, the causes of agglomeration for various fuels are critically reviewed, based on thermodynamic grounds. It is shown that even for phosphorus rich biomass types, in most cases the largest melt phase consists of alkali silicates: Ca phosphates are formed instead of Ca silicates, leading to lower melting points in the CaO-K2O-SiO2 system. Although thermodynamic optimization of the four main ash forming elements (K, Ca, Si and P) only provides an estimate of the amount of melt phase, it is shown that for various fuels the agglomeration behavior can be explained consistent with experimental findings from literature. As a consequence, for most biomass and waste types a similar thermodynamic estimation can be made to predict agglomeration problems and incorporate countermeasures in the design and operation of the fluidized bed combustor. © 2013 Springer Science+Business Media Dordrecht. ispartof: Waste and Biomass Valorization vol:5 issue:5 pages:879-892 status: published

In this paper, the temperature dependence of Cr(III) oxidation in high temperature processes and the subsequent Cr(VI) leaching was studied using synthetic mixtures. It was experimentally shown that in the presence of alkali and alkaline earth salts, oxidation of Cr(III) takes place, consistent with thermodynamic calculations. Heating of synthetic mixtures of Cr2O3 and Na, K, or Ca salts led to elevated leaching of Cr(VI); in the presence of Na, more than 80% of the initial Cr(III) amount was converted to Cr(VI) at 600-800 °C. Kinetic experiments allowed explanation of the increase in Cr(VI) leaching for increasing temperatures up to 600-800 °C. After reaching a maximum in Cr(VI) leaching at temperatures around 600-800 °C, the leaching decreased again, which could be explained by the formation of a glassy phase that prevents leaching of the formed Cr(VI). By way of illustration, Cr(VI) formation and leaching was evaluated for a case study, the fabrication of ceramic material from contaminated sludge. Based on the proposed reaction mechanisms, countermeasures to prevent Cr oxidation (addition of NH4H2PO4, heating under inert atmosphere) were proposed and successfully tested for synthetic mixtures and for the case study.