The civil engineering sector accounts for a significant percentage of global material and energy consumption and is a major contributor of waste material. The ability to recycle and reuse concrete ...and demolition waste is critical to reducing environmental impacts in meeting national, regional and global environmental targets. Handbook of recycled concrete and demolition waste summarises key recent research in achieving these goals.Part one considers techniques for managing construction and demolition waste, including waste management plans, ways of estimating levels of waste, the types and optimal location of waste recycling plants and the economics of managing construction and demolition waste. Part two reviews key steps in handling construction and demolition waste. It begins with a comparison between conventional demolition and construction techniques before going on to discuss the preparation, refinement and quality control of concrete aggregates produced from waste. It concludes by assessing the mechanical properties, strength and durability of concrete made using recycled aggregates. Part three includes examples of the use of recycled aggregates in applications such as roads, pavements, high- performance concrete and alkali-activated or geopolymer cements. Finally, the book discusses environmental and safety issues such as the removal of gypsum, asbestos and alkali-silica reaction (ASR) concrete, as well as life-cycle analysis of concrete with recycled aggregates.Handbook of recycled concrete and demolition waste is a standard reference for all those involved in the civil engineering sector, as well as academic researchers in the field. * Summarises key recent research in recycling and reusing concrete and demolition waste to reduce environmental impacts and meet national, regional and global environmental targets * Considers techniques for managing construction and demolition waste, including waste management plans, ways of estimating levels of waste, the types and optimal location of waste recycling plants * Reviews key steps in handling construction and demolition waste
This review focuses on the characteristics of the most widely used biopolymers that contain starch, polylactic acid, cellulose and/or polybutylene succinate. Because worldwide production of bio-based ...materials has grown dynamically, their waste is increasingly found in the existing waste treatment plants. The development of recycling methods for bio-based materials remains a challenge in the implementation of a circular economy. This article summarizes the recycling methods for bio-based materials, which, in the hierarchy of waste management, is much more desirable than landfilling. Several methods of recycling are available for the end-of-life management of bio-based products, which include mechanical (reuse of waste as a valuable raw material for further processing), chemical (feedstock recycling) and organic (anaerobic digestion or composting) ones. The use of chemical or mechanical recycling is less favourable, more costly and requires the improvement of systems for separation of bio-based materials from the rest of the waste stream. Organic recycling can be a sustainable alternative to those two methods. In organic recycling, bio-based materials can be biologically treated under aerobic or anaerobic conditions, depending on the characteristics of the materials. The choice of the recycling method to be implemented depends on the economic situation and on the properties of the bio-based products and their susceptibility to degradation. Thus, it is necessary to label the products to indicate which method of recycling is most appropriate.
•Investigation of optimal timing of pricing in a dual-channel reverse supply chain.•Consideration of a supply chain consisting of a recycling company and a collector.•We have the following two major ...findings.•There is a first-mover advantage to acquisition price announcement.•The company should announce the online price before announcing the transfer price.
The rapid development of information technologies enables recycling companies to purchase and collect used products from consumers through both traditional and Internet-based online channels. Because an online channel transmits price information instantly to consumers, choosing the best time to announce the recycling price (i.e., acquisition price) of used products to consumers has become a critical problem for recycling companies. This paper seeks to solve this problem by developing a game-theoretic model describing a dual-channel reverse supply chain consisting of a recycling company and a third-party collector in which the recycling company purchases products not only through a third-party collector, but also directly from consumers online. We derive two major results by solving the model. The first is that first-mover advantage arises, which indicates that each firm constituting a dual-channel reverse supply chain should announce its own recycling price before the other. This first result is notable because it is exactly opposite to conventional wisdom that the second-mover advantage of pricing usually emerges when price competition occurs among firms in a horizontal relationship, which is well known in noncooperative game theory. The second result is that the recycling company can maximize its own profit and consumers' surplus by announcing its recycling price in the online channel before or upon, but not after, determining the transfer price paid to the collector for products collected in the offline channel. Both results can be used as practical decision-making guidelines in dual-recycling channel reverse supply chain management.
This study assesses the environmental impact of polyethylene terephthalate (PET) bottle-to-fibre recycling using the methodology of life-cycle assessment (LCA). Four recycling cases, including ...mechanical recycling, semi-mechanical recycling, back-to-oligomer recycling and back-to-monomer recycling were analysed. Three allocation methods are applied for open-loop recycling, i.e. the “cut-off” approach, the “waste valuation” approach and the “system expansion” approach. Nine environmental impact indicators were analysed, i.e. non-renewable energy use (NREU), global warming potential (GWP), abiotic depletion, acidification, eutrophication, human toxicity, fresh water aquatic ecotoxicity, terrestrial ecotoxicity and photochemical oxidant formation. The LCA results are compared with virgin PET fibre and other commodity fibre products, i.e. cotton, viscose, PP (polypropylene) and PLA (polylactic acid). The LCA results show that recycled PET fibres offer important environmental benefits over virgin PET fibre. Depending on the allocation methods applied for open-loop-recycling, NREU savings of 40–85% and GWP savings of 25–75% can be achieved. Recycled PET fibres produced by mechanical recycling cause lower environmental impacts than virgin PET in at least eight out of a total of nine categories. Recycled fibres produced from chemical recycling allow to reduce impacts in six to seven out of a total of nine categories compared to virgin PET fibres. Note that while mechanical recycling has a better environmental profile than chemical recycling, chemically recycled fibres can be applied in a wider range of applications than mechanically recycled fibres.
Increased demand of fibre reinforced plastic (FRP) composites has led to high volumes of manufacturing scrap and end-of-life waste. Restrictions on landfill disposal and the high energy for virgin ...material production call for cost effective composite recycling technology. Unfortunately there is limited high integrity environmental related data in literature, to help assess the life cycle benefits of composite recycling, particularly glass fibre reinforced plastic (GFRP). In this work new approaches based on bottom-up unit process modelling were used to model and experimentally validate the energy demand in mechanical recycling of GFRP. Total energy requirement was classified into sources by machine functions (basic energy) and for actual cutting process (tip energy) as modelled from material specific cutting energy for GFRP. The mechanics of cutting was utilised to model the specific energy from orthogonal tests. The model was then extended and validated to cater for mechanical recycling with a milling based granulator recycling machine. Energy demand was modelled and validated for a number of industrial granulators. This paper provides valuable information on the impact of processing rate and granulator capacity in relation to reducing the energy demand in recycling of thermoset based glass fibre (GFRPT). The bottom-up approach is an important framework that can be used to model the energy and environmental footprint of other recycling unit processes. This information provides vital data for life cycle analysis, enabling the assessment of resource hot spots and quantifying the environmental benefits of end-of-life options.
•Bottom up resource modelling approach was aspired by theoretical science.•Tip energy in mechanical recycling was modelled from orthogonal machining tests.•Total energy demand was derived from mathematical model of cutting energy.•The energy model was validated using an industrial scale granulator.•Vital life cycle data for mechanical recycling of glass fibre composite is proposed.
Globally, there is rising awareness of the severity of the plastic waste problem, and the implications of plastics accumulation in the environment. Current methods of waste management are anticipated ...to be insufficient in mitigating the long-term negative impact on society and the environment. Plastics recycling is one of many solutions that have been proposed, one of the most ecologically-friendly, as well as holding great economic potential by its realization into a circular economy. The technological know-how already exists for a number of different methods for plastic recycling; however, they are broadly uneven in their implementation due to feasibility and cost issues. Here, we review and compare methods of tertiary recycling—that is, complete breakdown of plastics into its chemical component materials—and offer an analysis of the potential obstacles that have to be addressed to increase waste plastic recycling rates. While chemical recycling methods are simpler and are already pilot tested at an industrial level, biological recycling either via microorganisms or biological-derived enzymes are as yet unproven but highly promising technologies. Looking forward, trend shifts towards more ecologically-friendly processes will drive initiatives to close the loop on commercial plastic production.
•There is a major environmental issue about the printed circuit boards throughout the world.•Different physical and chemical recycling techniques have been reviewed.•Nonmetallic fraction of PCBs is ...the unwanted face of this waste stream.•Several applications of the nonmetallic fraction of waste PCBs have been introduced.
E-waste, in particular waste PCBs, represents a rapidly growing disposal problem worldwide. The vast diversity of highly toxic materials for landfill disposal and the potential of heavy metal vapors and brominated dioxin emissions in the case of incineration render these two waste management technologies inappropriate. Also, the shipment of these toxic wastes to certain areas of the world for eco-unfriendly “recycling” has recently generated a major public outcry. Consequently, waste PCB recycling should be adopted by the environmental communities as an ultimate goal.
This article reviews the recent trends and developments in PCB waste recycling techniques, including both physical and chemical recycling. It is concluded that the physical recycling techniques, which efficiently separate the metallic and nonmetallic fractions of waste PCBs, offer the most promising gateways for the environmentally-benign recycling of this waste. Moreover, although the reclaimed metallic fraction has gained more attention due to its high value, the application of the nonmetallic fraction has been neglected in most cases. Hence, several proposed applications of this fraction have been comprehensively examined.
In a sustainable circular economy, polymers capable of chemical recycling to monomers are highly desirable. We report an efficient monomer‐polymer recycling of polydithioacetal (PDTA). Pristine PDTAs ...were readily synthesized from 3,4,5‐trimethoxybenzaldehyde and alkyl dithiols. They then exhibited depolymerizability via ring‐closing depolymerization into macrocycles, followed by entropy‐driven ring‐opening polymerization (ED‐ROP) to reform the virgin polymers. High conversions were obtained for both the forward and reverse reactions. Once crosslinked, the network exhibited thermal reprocessability enabled by acid‐catalyzed dithioacetal exchange. The network retained the recyclability into macrocyclic monomers in solvent which can repolymerize to regenerate the crosslinked network. These results demonstrated PDTA as a new molecular platform for the design of recyclable polymers and the advantages of ED‐ROP for which polymerization is favored at higher temperatures.
Polydithioacetals depolymerize to a mixture of macrocycles that regenerates the parent polymers via entropy‐driven ring‐opening polymerization. When crosslinked, they demonstrate covalent adaptable network (CAN) behavior at elevated temperatures. The swollen CANs are also depolymerizable to macrocycles, which are polymerized back to the CANs. Polydithioacetals are thus desirable candidates as chemically recyclable thermoplastics and thermosets.
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