High-quality Recycling Research Articles

Sustainable High Quality Recycling of Aggregates from Waste-to-Energy, Treated in a Wet Bottom Ash Processing Installation, for Use in Concrete Products.

Nowadays, more efforts towards sustainability are required from the concrete industry. Replacing traditional aggregates by recycled bottom ash (BA) from municipal solid waste incineration can contribute to this goal. Until now, only partial replacement has been considered to keep the concrete workability, strength and durability under control. In this research, the feasibility of a full aggregate replacement was investigated for producing prefabricated Lego bricks. It was found that the required compressive strength class for this purpose (C20/25) could be achieved. Nevertheless, a thorough understanding of the BA properties is needed to overcome other issues. As BA is highly absorptive, the concrete’s water demand is high. This workability issue can be dealt with by subjecting the fine BA fraction to a crushing operation to eliminate the porous elements and by pre-wetting the fine and coarse BA fractions in a controlled manner. In addition, a reactive NaOH washing is needed to avoid formation of longitudinal voids and the resulting expansion due to the metallic aluminum present in the BA. Regarding the long-term behavior, heavy metal leaching and freeze-thaw exposure are not problematic, though there is susceptibility to acetic and lactic acid attack and maybe increased sensitivity to alkali-silica reaction.

Application of near-infrared spectroscopy for the fast detection and sorting of wood–plastic composites and waste wood treated with wood preservatives

The aim of this work was to increase the amount of recycled waste wood in the wood-processing industry. Contaminations such as plastics and wood preservatives therefore have to be identified and removed. A promising technique to detect this foreign matter is near-infrared (NIR) spectroscopy. For several organic and inorganic active compounds for wood preservation, the NIR reflectance spectra acquired with sensors with the capability of on-line measurements were characterized. Some of them were significantly different from those of previously published spectra. Moreover, untreated wood was distinguishable from wood treated with preservatives. Confounding factors, such as the water content, wood species and solvent of the preservative, were examined which had so far massively interfered the NIR detection and classification. Chemometric-based solutions are presented in this work to cope with analytical challenges arisen from the complexity of waste wood samples. This formed the basis for a sorting trial in which treated wood chips were detected in real time with an NIR spectrometer and automatically separated by pneumatic nozzles, showing that the laboratory experiments can be transferred into small industrial scale. Additionally, the experiments showed that wood–plastic composites (WPC) of different plastic types were distinguishable with NIR spectroscopy and can be sorted by ejection based on this information. Unmixed material is a major prerequisite for a high-quality recycling of WPC and has never been demonstrated on a technical scale. Furthermore, three different NIR devices (hyperspectral imaging camera, miniaturized spectrometer and sorting plant) were evaluated regarding their applicability in the waste wood recycling process.

The manufacture of lightweight aggregates from recycled masonry rubble

At present, heterogeneous and fine-grained masonry rubble can only be recycled at very low level. To overcome this limitation, the material was employed as feedstock for the production of lightweight aggregates in a thermal process similar to that used in the manufacture of expanded clay and expanded slate. To that end, the fundamental suitability of masonry rubble as a raw material was evaluated. Experiments were carried out which indicated that lightweight granules with defined, adjustable properties similar to those of natural-material-based aggregates could be manufactured from masonry rubble. Structural lightweight concretes produced with these secondary aggregates achieved comparable performance to lightweight concretes produced with conventional expanded clay. Lightweight recycled building material aggregates represent a product that hardly requires any primary resources in its manufacture. In principle, the technique also seems to be well suited for high-quality recycling of other mineral waste materials.

Influence of Ground Tyre Rubber Devulcanisates on Morphology and Properties of Tread Tyre Formulation

The use of reclaimed and devulcanised material in virgin rubber compounds has attracted the attention of many rubber industries due to increasing raw material costs, diminishing resources and growing awareness of environmental issues. Several methods have been developed to reclaim rubber waste, for example, thermo-and chemo-mechanical processes, microwave regeneration, microbial action and ultrasonic regeneration. However, extensive research on processes for high-quality recycling materials based on waste tyres is still lacking. In this study, optimised processing conditions for the devulcanisation of whole passenger car tyres using diphenyldisulphide (DPDS) as a devulcanisation aid will be applied. The devulcanised ground tyre rubber (D-GTR) obtained from the process was blended on top of the original tyre tread formulation at different concentrations. The results so far indicate that the addition of D-GTR influences the properties of the blend, but to a lesser extent than the commercially used powder or reclaim types do, for which loadings less than 5% can be applied. The main reason for the influence of D-GTR on the rubber properties is inhomogeneities in the D-GTR/virgin rubber blend and quality aspects of raw GTR.

The setting of ecodesign standards to promote improved waste recycling

The underpinning idea of extended producer responsibility rules has been to provide incentives for manufacturers to design products that are easy to recycle. However, current incentives for design for recycling are limited, due to the problems in assigning costs for collection and recycling of individual products to the relevant producers. An alternative way to promote design for recycling, or to increase recycling, is to use mandatory standards for ecodesign, or stipulate that recycled materials must be used in new products. The European Union’s Ecodesign Directive has mainly been used to regulate the energy efficiency of products, but there is now interest in using the Directive to trigger resource efficiency and design for recycling. In this contribution we look at potential ecodesign standards, and discuss how requirements on recycled content could be applied to trigger high quality recycling of plastic waste from electrical and electronic equipment. We further discuss the need to engage several actors throughout product chains, and whether market dynamics should be a decisive factor when deciding on whether mandatory regulation is necessary or not. (Less)

The potential contribution of sustainable waste management to energy use and greenhouse gas emission reduction in the Netherlands

Future limitations on the availability of selected resources stress the need for increased material efficiency. In addition, in a climate-constrained world the impact of resource use on greenhouse gas emissions should be minimized. Waste management is key to achieve sustainable resource management. Ways to use resources more efficiently include prevention of waste, reuse of products and materials, and recycling of materials, while incineration and anaerobic digestion may recover part of the embodied energy of materials. This study used iWaste, a simulation model, to investigate the extent to which savings in energy consumption and CO2 emissions can be achieved in the Netherlands through recycling of waste streams versus waste incineration, and to assess the extent to which this potential is reflected in the LAP2 (currently initiated policy). Three waste streams (i.e. household waste, bulky household waste, and construction and demolition waste) and three scenarios compare current policy to scenarios that focus on high-quality recycling (Recycling+) or incineration with increased efficiency (Incineration+). The results show that aiming for more and high-quality recycling can result in emission reductions of 2.3MtCO2 annually in the Netherlands compared to the reference situation in 2008. The main contributors to this reduction potential are found in optimizing the recycling of plastics (PET, PE and PP), textiles, paper, and organic waste. A scenario assuming a higher energy conversion efficiency of the incinerator treating the residual waste stream, achieves an emission reduction equivalent to only one third (0.7MtCO2/year) of the reduction achieved in the Recycling+ scenario. Furthermore, the results of the study show that currently initiated policy only partially realizes the full potential identified. A focus on highest quality use of recovered materials is essential to realize the full potential energy and CO2 emission reduction identified for the Netherlands. Detailed economic and technical analyses of high quality recycling are recommended to further evaluate viable integrated waste management policies.

Challenges of metal recycling and an international covenant as possible instrument of a globally extended producer responsibility

As illustrated by the case studies of end-of-life vehicles and waste electric and electronic equipment, the approach of an extended producer responsibility is undermined by the exports of used and waste products. This fact causes severe deficits regarding circular flows, especially of critical raw materials such as platinum group metals. With regard to global recycling there seems to be a responsibility gap which leads somehow to open ends of waste flows and a loss or down-cycling of potential secondary resources. Existing product-orientated extended producer responsibility (EPR) approaches with mass-based recycling quotas do not create adequate incentives to supply waste materials containing precious metals to a high-quality recycling and should be amended by aspects of a material stewardship. The paper analyses incentive effects on EPR for the mentioned product groups and metals, resulting from existing regulations in Germany. It develops a proposal for an international covenant on metal recycling as a policy instrument for a governance-oriented framework to initiate systemic innovations along the complete value chain taking into account product group- and resource group-specific aspects on different spatial levels. It aims at the effective implementation of a central idea of EPR, the transition of a waste regime still focusing on safe disposal towards a sustainable management of resources for the complete lifecycle of products.

Matching construction and demolition waste supply to recycling demand: a regional management chain model

Construction and demolition (C&D) waste can be either directly disposed in landfills or processed in recycling plants as aggregates. Depending upon its physical properties, this recycled waste can be used in a variety of construction applications and also reduce dependence on natural aggregates. Since the recycling of C&D waste reduces landfill and conserves natural aggregate resources, most environmental policies aim at increasing C&D recycling. An optimization model is presented to understand the dynamics and planning of a C&D waste recycling network as an integrated set of supply-and-demand chains at the regional level. The model optimizes for minimum costs, includes assessment of technical and environmental performance, and shows the effects of potential policy interventions. A case study using the model revealed that disposal taxes are a cost-effective lever to increase total recycling, but not necessarily high-quality recycling. Increased transport costs reduce the recycling rate considerably, as recycling requires longer transport distances than disposal. The expected strong increase in the supply of C&D waste associated with the population decline (and associated shrinkage) projected for 2050 in Germany requires new sinks, e.g. intensified use of recycled aggregates in concrete, to preserve current high recycling rates. Les déchets de construction et de démolition (C&D) peuvent être directement éliminés dans des décharges ou bien traités dans des usines de recyclage sous forme de granulats. En fonction de leurs propriétés physiques, ces déchets recyclés peuvent être utilisés dans une variété d'applications de construction et réduisent également la dépendance à l'égard des granulats naturels. Etant donné que le recyclage des déchets C&D réduit l'enfouissement en décharge et préserve les ressources en granulats naturels, la plupart des politiques environnementales visent à accroître le recyclage des déchets C&D. Un modèle d'optimisation est présenté pour comprendre la dynamique et la planification d'un réseau de recyclage de déchets C&D comme étant un ensemble intégré des chaînes de l'offre et de la demande au niveau régional. Ce modèle est optimisé pour l'obtention de coûts minima, comprend une évaluation des performances techniques et environnementales, et montre les effets des possibles interventions politiques. Une étude de cas utilisant ce modèle a révélé que les taxes d'élimination sont un levier de rentabilité permettant d'accroître le recyclage total, mais pas nécessairement un recyclage de haute qualité. L'accroissement des frais de transport réduit considérablement le taux de recyclage, dans la mesure où le recyclage exige des distances de transport plus longues que l'élimination en décharge. Le fort accroissement prévu de l'offre en déchets de construction et de démolition, associé au déclin de la population (et à la décroissance liée) projeté pour 2050 en Allemagne, nécessite de nouveaux modes de séquestration des déchets, par exemple une utilisation renforcée de granulats recyclés dans le béton, afin de préserver les taux élevés actuels de recyclage. Mots clés: déchets de construction et de démolition, gestion de la demande, flux de masse, déclin de la population, réseau de recyclage, gestion des déchets

Emulation-based control of a disassembly system for LCD monitors

Growing environmental concern and increasing responsibility towards product stewardship lead companies to institute new concepts to improve the environmental performance of their products and processes. Particularly, end-of-life treatment of waste electrical and electronic (WEEE) is a challenge due to rapidly changing technologies and strongly growing volumes. Disassembly has great importance as a preliminary stage for a high-quality recycling. A partly automated disassembly system could adapt to a large variety of products and different degrees of devaluation. But developing control systems still require customization for each different product and process. Testing of them is a difficult and time-consuming process, and often impossible until all the equipment has been installed. Modern simulation technology allows one to connect simulation models with real controller systems. This paper will introduce advantages of an emulation approach for the control logic development and validation. The approach will be applied on a hybrid disassembly system for LCD monitors.

Recycling of Rare Earth Magnet Scraps Part III Carbon Removal from Nd Magnet Grinding Sludge under Vacuum Heating

The removal of the carbon from Nd magnet scraps is indispensable for high-quality recycling by the induction melting method as a preliminary process. The Nd magnet scraps can be decarburized to a level of less than 0.03 mass% by using an oxygen source at high temperatures, as reported in Part 1. The decarburized Nd magnet scraps can then be deoxidized by using the Ca reduction to a level that allows commercial melting in an induction furnace, as reported in Part II. However, the undesirable iron oxide (Fe2O3) which causes a disadvantage for Ca reduction is inevitably generated by using an oxygen source at high temperatures. The aim of this work is to investigate an economical decarburization method in which only the carbon sources in Nd magnet scraps are decarburized, without generating iron oxide. The grinding sludge as Nd magnet scraps is effectively decarburized to a level of less than 0.03 mass% without generating any iron oxide by heating at above 1073 K under a pressure of less than 5.32×10−2 Pa. The amount of oxygen in the decarburized powder is about 8 mass%, which is lower in comparison with its value in Part 1. In this report, the decarburization mechanism under reduced pressure using the grinding sludge, and its economic significance prior to the decarburizing method described in Part 1, are discussed.