Recycling, Volume 6, Issue 3 (September 2021) – 20 articles

Construction waste (CW) is a prime contributor to the stream of total waste worldwide. One of the biggest challenges of the construction industry is to minimise CW and to develop practices of a more sustainable nature for its management and recycling in order to promote its transition towards a more effective circular economy. The implementation of these practices contributes towards mitigating the scarcity of natural resources and the environmental impact of CW. Thus, a preceding and essential step is the estimation of CW during building design, which will allow the adoption of measures for its early reduction and optimisation. For this purpose, Building Information Modelling (BIM) has become a useful methodology to predict waste during the early stages of design. There remains, however, a lack of instrumental development. Therefore, this study proposes a BIM-based method to estimate CW during building design by integrating a consolidated construction waste quantification model in three different BIM platforms. For its validation, the method is applied to the structural system of a Spanish residential building. The results provide evidence that the proposed method is vendor-neutral and enables the automatic identification and quantification of the waste generated by each building element during the design stage in multiple BIM platforms. Full article

Traditionally, construction and demolition waste (CDW) materials have been considered to be unwanted, surplus, or wastage materials or materials with zero value. Such a conceptualisation only embraces a negative aspect, which underpins the disposal of reusable and recyclable CDW materials in landfills, thus damaging the circular economy and the environment. The scope of this research was to conceptualise the circular economy potential of non-hazardous construction and demolition waste, which can be used as a resource for advancing the circular economy and sustainability in the built environment. Thus, the abbreviation ‘CEPCDR’ is used for this purpose. The study employs an integrative literature review to understand in depth whether the rationale in the existing CDW definitions advocates for the circular economy. Instead, the literature showed that the current definitions mainly support quantitative, economic, or classification needs, respectively. That is because they lack consideration of the dynamic nature of CDW materials, which embraces the spatial and temporal dimensions. The former involves the geographic context in which the CDW phenomenon eventuates, while the latter concerns the lifecycle of materials. This study contributes to the body of knowledge by conceptualising the CEPCDR using a holistic approach that includes five dimensions: the social, economic, environmental, spatial, and temporal perspectives. Furthermore, the study seeks to drive future research in measuring the CEPCDR. Full article

The utilization of geopolymer 3D printing for construction products in recent years has been exceptionally substantial, owing to their low carbon dioxide emissions, high-performance properties such as durability, and good thermal and mechanical properties. This automated manufacturing process reduces the need for additional formworks, capital investments, and human resources. Geopolymer 3D printing development is emerging because of its advanced use in construction applications. However, high costs of the initial stages of geopolymer production and 3D printing has inhibited the development of this technology in many countries. This research presents a comprehensive economic evaluation of the investment for each principal stage that facilitates a better deployment of the resources. The study investigated all phases of geopolymer production, from the extraction of raw materials to printing. The cost for the four fundamental stages, namely raw material availability and transportation, pretreatments for raw materials, parameter selection and strength requirements, and printing in factories and on construction sites, were analyzed. The results show that 3D printing of a geopolymer on a construction site is economically more advantageous compared to printing in the factory. The study also verified that raw material transportation cost has the least effect on the finished product cost, whereas pretreatments of raw material and mixing parameters significantly influenced the ultimate cost of the product. Finally, research work suggested the need for future tasks to make geopolymer 3D printing a viable construction approach. Full article

Biosolids’ use in agriculture is an example of industrial symbiosis. The application of biosolids (BS) in agriculture is considered one of the most sustainable sewage sludge (SS) management options, but the quality of biosolids has to meet certain requirements regarding the characteristics of the sludge, those of the land and of the type of crop. Web of Science database has been used to search for the relevant literature. The review of studies undertaken in order to determine the economic effects of the use of biosolids in agriculture shows, in the majority, an increase in crop yield and the reduction in costs, due to the reduction in the requirements for the application of chemical or synthetic fertilizers. If the entire sewage sludge production in Romania for 2019 had been used as fertilizer, the estimated cost reduction for farmers would have been almost 3 million Euros—considering the 230.59 thousand tons of dry matter produced in 2019. The estimated savings for 2019 of the sewage and water utilities, if the sewage sludge had been used in agriculture instead of depositing it at the landfill, would have been about 3.9 million Euros. However, the limits of the symbiosis are due to the size of the farms, the type of plants cultivated, pH, slope inclination, heavy metal content and social acceptance. It is impossible to use all the sewage sludge in agriculture, but these figures are a good estimation of the economic effects. Full article

The recycling of plastic waste is undergoing fast growth due to environmental, health and economic issues, and several blends of post-consumer and post-industrial polymeric materials have been characterized in recent years. However, most of these researches have focused on plastic containers and packaging, neglecting hard plastic waste. This study provides the first experimental characterization of different blends of hard plastic waste and virgin polypropylene in terms of melt index, differential scan calorimetry (DSC), thermogravimetric analysis (TGA), mechanical properties (tensile, impact and Shore hardness) and Vicat softening test. Compared to blends based on packaging plastic waste, significant differences were observed in terms of melt flow index (about 10 points higher for hard plastic waste). Mechanical properties, in particular yield strain, were instead quite similar (between 5 and 9%), despite a higher standard deviation being observed, up to 10%, probably due to incomplete homogenization. Results demonstrate that these worse performances could be mainly attributed to the presence of different additives, as well as to the presence of impurities or traces of other polymers, other than incomplete homogenization. On the other hand, acceptable results were obtained for selected blends; the optimal blending ratio was identified as 78% post-consumer waste and 22% post-industrial waste, meeting the requirement for injection molding and thermoforming. Full article

Toner waste is one of the major electronic waste materials posing serious environmental threat and health hazards. Globally, only about 20–30% of toner waste is recycled, while the remaining percentage is dumped in landfills. Recycling options are limited due to the desirably engineered durability of toners, ascribed to a complicated composition of chemicals, carbon black, and plastic particles, which in turn creates critical challenges in recycling. The World Health Organization has classified toner waste as class 2B carcinogen due to its potential health hazard. In this review, the existing challenges in toner waste recycling are discussed from the perspective of environmental, health, and feasibility aspects. In parallel, the challenges have been opening up alternative strategies to recycle toner wastes. Emerging trends in toner waste recycling include transformation of toner waste into value-added products, utilization as raw material for nanomaterial synthesis, generation of composite electrodes for power generation/storage devices, integration into construction materials, and development of microwave absorbing composites. Considering the enormous volume of toner waste generated globally every year, better recycling and transformation strategies are needed immediately. A circular economy could be established in the future by transforming the enormous toner waste into a resource for other applications. For an effective management of toner waste in the future, an integrated approach involving policies and legislations, infrastructure for collection and treatment, and financial planning among the stakeholders is needed in addition to technological innovations. Full article

Following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident caused by the 2011 Tōhoku earthquake and tsunami, radioactive caesium (r-Cs) was detected in the ash generated by municipal solid waste (MSW) incineration facilities in Fukushima Prefecture. This has led to concerns of r-Cs leaching and subsequent environmental contamination during recycling or landfill disposal. Therefore, it is crucial that the relevant authorities have a thorough understanding of r-Cs leaching behavior to establish suitable prevention methods. In this study, we collected r-Cs-contaminated fly and bottom ash (FA and BA) samples from five MSW incineration facilities in Fukushima Prefecture and conducted tests to clarify their basic physical properties and r-Cs leaching properties. We also examined the possibility of preventing r-Cs leaching by adding 5 wt% acid clay to the FA. FA had greater chloride content and r-Cs leaching rate than BA and was found to absorb moisture and deliquesce when stored under high-humidity conditions. However, the addition of acid clay effectively prevented r-Cs leaching upon contact with moisture. From the results, we propose some specific recommendations to counter the leaching of r-Cs from FA at MSW incineration facilities, which will limit r-Cs leaching during recycling or landfill processes. Full article

The depletion of natural resources and global warming have increased in severity globally. In the industrial field, assembly products, such as electronic products, should be disassembled for recycling and reuse to deal with these problems. Reuse and recycling can contribute to reducing GreenHouse Gas (GHG) emissions and less depletion of natural resources since GHG emissions for virgin material production can be saved using reused components and recycled materials. However, each component of selling revenue and material-based GHG emissions depends on the country because of the different energy mixes of electrical power. Moreover, each collected component embedded in End-of-Life (EOL) products needs to be selected as a life cycle option based on its remaining life. The purpose of this study is to decide life cycle options such as reuse, recycling, and disposal of each component environmentally-friendly and economically in Korea and Japanese cases for computers. Firstly, selecting the life cycle option for each component was formulated by 0–1 integer programming with ε constraints. Next, GHG emissions, profits, and costs in Korea and Japan were estimated and analyzed for each component. Finally, Korean and Japanese cases were analyzed to obtain an economic value in the same material-based GHG saving rate with each component’s life cycle option selection by comparing each EOL product data. In the experiments, GHG recovery efficiency was higher in Japan 43 [g/Yen] than one in Korea 28 [g/Yen]. Therefore, it was better to retrieve and reutilize the components in Korea. However, if the maximum GHG recovery efficiency is desired, Japan is a better option. Full article

In this work, the application of Short-Wave Infrared (SWIR: 1000–2500 nm) spectroscopy was evaluated to identify plastic waste containing brominated flame retardants (BFRs) using two different technologies: a portable spectroradiometer, providing spectra of single spots, and a hyperspectral imaging (HSI) platform, acquiring spectral images. X-ray Fluorescence (XRF) analysis was preliminarily performed on plastic scraps to analyze their bromine content. Chemometric methods were then applied to identify brominated plastics and polymer types. Principal Component Analysis (PCA) was carried out to explore collected data and define the best preprocessing strategies, followed by Partial Least Squares—Discriminant Analysis (PLS-DA), used as a classification method. Plastic fragments were classified into “High Br content” (Br > 2000 mg/kg) and “Low Br content” (Br < 2000 mg/kg). The identified polymers were acrylonitrile butadiene styrene (ABS) and polystyrene (PS). Correct recognition of 89–90%, independently from the applied technique, was achieved for brominated plastics, whereas a correct recognition ranging from 81 to 89% for polymer type was reached. The study demonstrated as a systematic utilization of both the approaches at the industrial level and/or at laboratory scale for quality control can be envisaged especially considering their ease of use and the short detection response. Full article

Electronic waste (e-waste) management and recycling are gaining significant attention due to the presence of precious, critical, or strategic metals combined with the associated environmental burden of recovering metals from natural mines. Metal recovery from e-waste is being prioritized in metallurgical extraction owing to the fast depletion of natural mineral ores and the limited geographical availability of critical and/or strategic metals. Following collection, sorting, and physical pre-treatment of e-waste, electrochemical processes-based metal recovery involves leaching metals in an ionic form in a suitable electrolyte. Electrochemical metal recovery from e-waste uses much less solvent (minimal reagent) and shows convenient and precise control, reduced energy consumption, and low environmental impact. This critical review article covers recent progress in such electrochemical metal recovery from e-waste, emphasizing the comparative significance of electrochemical methods over other methods in the context of an industrial perspective. Full article

Based on mass and energy balance calculations, this work investigates the possibility of recovering heat and nutrients (nitrogen and phosphorus) from municipal sewage sludge using pyrolysis or combustion in combination with a gas scrubbing technology. Considering a wastewater treatment plant (WWTP) with 65,000 t/a of mechanically dewatered digestate (29% total solids), 550 t/a nitrogen and 500 t/a phosphorus were recovered from the 4900 t/a total nitrogen and 600 t/a total phosphorus that entered the WWTP. Overall, 3600 t/a (73%) of total nitrogen was lost to the air (as N₂) and clean water, while 90 t/a (15%) of total phosphorus was lost to clean water released by the WWTP. Both in combustion and in pyrolysis, the nitrogen (3%) released within thermal drying fumes was recovered through condensate stripping and subsequent gas scrubbing, and together with the recovery of nitrogen from WWTP reject water, a total of 3500 t/a of ammonium sulfate fertilizer can be produced. Furthermore, 120 GWh/a of district heat and 9700 t/a of ash with 500 t/a phosphorus were obtained in the combustion scenario and 12,000 t/a of biochar with 500 t/a phosphorus was obtained in the pyrolysis scenario. The addition of a stripper and a scrubber for nitrogen recovery increases the total electricity consumption in both scenarios. According to an approximate cost estimation, combustion and pyrolysis require annual investment costs of 2–4 M EUR/a and 2–3 M EUR/a, respectively, while 3–5 M EUR/a and 3–3.5 M EUR/a will be generated as revenues from the products. Full article

In this work, monopolymer blends of virgin polypropylene and photo-oxidized polypropylene were prepare and characterized. The polypropylene samples were subjected to accelerated ageing to simulate the effects of outdoor exposure of polypropylene. After exposure, samples were pelletized and mixed with the same virgin polymer. The rheological, mechanical and morphological characterization was conducted on both the polymers and the blends. Both viscosity and mechanical properties decrease with increases in the content of recycled, photo-oxidized components and of the level of degradation of this component. In addition, the experimental data were compared with a model that takes into account both the effect of the change of the molecular weight and of the presence of oxygenated groups. Full article

Due to the serious problem of plastic pollution in aquatic environment, many people reject plastic packaging in favour of glass containers which are considered more sustainable. To avoid misjudgements, the sustainability assessment of packaging alternatives should be carried out with a life cycle thinking approach. In this regard, the study presents a comparative Life Cycle Assessment (LCA) of two alternative packaging systems for drinking water: reusable glass bottles and polyethylene (PET) bottles. The case study was performed considering the real data of an Italian mineral water company that bottles and distributes both natural and sparkling water. The environmental impacts of the two packaging systems were estimated with the ReCiPe 2016 (H) evaluation method adopting both midpoint and endpoint approaches. The results showed that the PET bottle is the most sustainable alternative for natural water for many impact categories; while, in the case of sparkling water, the environmental impacts of the two packaging systems are similar and the most environmentally sound solution can vary depending on the impact category. The following are the most significant aspects of the analysis: (1) the number of reuses of a single glass bottle; (2) the distribution distance. Their variation can determine which packaging is the most sustainable. Therefore, a life cycle assessment approach is needed for each specific case. Full article

Commercial polymers have been used in pavement modification for decades; however, a major drawback of these polymers is their high cost. Waste plastic polymers could be used as a sustainable and cost-effective additive for improving asphalt properties, attaining combined environmental–economic benefits. Since 2019, in Australia, trial segments of roads have been built using waste materials, including plastic, requiring that laboratory evaluations first be carried out. This study aims to examine and evaluate the effect of using a domestic waste plastic, polyethylene terephthalate (PET), in modifying C320 bitumen. The assessment of several contents of PET-modified bitumen is carried out in two phases: modified bitumen binders and modified asphalt mixtures. Dynamic shear rheometer (DSR) and rolling thin film oven tests (RTFOT) were utilised to investigate the engineering properties and visco-elastic behaviour of plastic-modified bitumen binders. For evaluating the engineering properties of the plastic-modified asphalt mixtures, the Marshall stability, Marshall flow, Marshall quotient and rutting tests were conducted. The results demonstrated that 6–8% is the ideal percentage of waste plastic proposed to amend and enhance the stiffness and elasticity behaviour of asphalt binders. Furthermore, the 8% waste PET-modified asphalt mixture showed the most improvement in stability and rutting resistance, as indicated by increased Marshal stability, increased Marshall quotient and decreased rut depth. Future fatigue and modulus stiffness tests on waste plastic-modified asphalt mixtures are suggested to further investigate the mechanical properties. Full article

Ship recycling is gaining attention in Indonesia due to the increase in end-of-life ships and uneconomical nationally flagged ships, and is considered a prospective source of economic development and employment opportunity, and yet conceivably poses a threat to the health and safety of workers and the environment. There are international and national regulations that govern ship-recycling activities to ensure that the hazardous impacts of the industry are minimized. We investigated the disparity between current ship-breaking practices in Indonesia and the requirements of related international and national regulations, with the findings intended for use as a stepping stone to proposing a strategy to establish a green and sustainable ship-recycling industry. A benchmark study of the world’s leading ship-recycling countries was conducted, and a gap analysis was performed by comparing existing international and national regulations with current ship-breaking practices in Indonesia. We identified two types of ship-breaking practices in Indonesia: Conventional environmentally unfriendly ship-breaking method, conducted by most Indonesian ship-breaking yards, and a rather modern, more environmentally friendly method, conducted by ship-repair yards. However, neither of the practices met the requirements of the regulations, and improvements are therefore needed to make the ship-recycling industry more green and sustainable, and to gain international recognition. Full article

Multilayer packaging is an important part of the packaging market, but it is not recyclable with conventional methods since it is made of different thermodynamically immiscible materials. In this work, it was shown that it is possible to produce a PET//LDPE laminate in a pilot plant for lamination by using an adhesive consisting of maleimide- and furan-functionalized polyurethane prepolymers that cure through the Diels–Alder reaction. The material could then be delaminated in a small-scale recycling plant using a solvent-based recycling process by partially opening the Diels–Alder adducts through the influence of temperature. The PET and LDPE could be recovered without any adhesive residues before each material was regranulated, and in the case of the PE, a film was produced via cast film extrusion. The obtained PET granulate exhibited a slight, approximately 10%, decrease in molecular weight. However, since small amounts of LDPE could not be separated, compatibilization would still be required here for further use of the material. The obtained LDPE film was characterized by means of infrared spectrometry, differential scanning calorimetry, tensile testing, determination of the melt index, and molecular weight. The film showed lower crosslinking than usual for LDPE recycling and exhibited good mechanical properties. In this work, it was thus shown that upscaling of the laminate production with the modified adhesive and also its recycling at the pilot plant scale is possible and thus could be an actual option for recycling multilayer packaging. Full article

The cement industry is a major contributor to greenhouse gas emissions on a global scale. Consequently, there has been an increasing interest, in both academia and business, in low-carbon concretes in which Ordinary Portland Cement (OPC) is partially or fully replaced with industrial side streams. However, the realization of the environmental benefits of such materials depends on how competitive they are in the construction market, where low costs are a major competitive factor. This is not straightforward, as many types of concretes exist. Raw material prices vary, and costs can be influenced by governmental regulations via carbon pricing. This study presents a case study estimating the cost prices of four different geopolymer concretes with different material compositions and carbon footprints, considering the raw material price variability and the potential impact of carbon emissions regulation (carbon price). The case study demonstrates how material mix cost comparisons can be made openly and systematically. The results imply that carbon pricing, at the rates currently applied, does not significantly change the cost price difference between traditional and geopolymer concretes. Instead, cost-competitiveness of low carbon concretes depends heavily on the material mix type and the availability of critical side streams. Full article

The potential of using cold water brown macroalgae Fucus vesiculosus for biocrude production via non-catalytic supercritical hydrothermal liquefaction (HTL) was studied. Demineralization, residue neutralization, and high value-added product (alginate and fucoidan) extraction processes were carried out before using the biomass for HTL biocrude production. Acid leaching was carried out using three demineralization agents: distilled water, dilute citric acid solution, and the diluted acidic aqueous by-product from a continuous HTL pilot facility. Alginate was extracted via H₂SO₄ and NaCO₃ bathing, and fucoidan was extracted using CaCl₂. Experimental data show that none of the leaching agents was greatly efficient in removing inorganics, with citric acid leaching with extensive neutralization reaching the highest ash removal efficiency of 47%. The produced 6 sets of biocrudes were characterized by elemental and thermogravimetric analyses. Short (10-min retention) HTL and the extent of leaching residue neutralization were also investigated. Highest biocrude yields were recorded when liquefying non-neutralized citric acid leaching, alginate, and fucoidan extraction residues. On the other hand, thermochemical conversions of short retention time HTL, full neutralization extent, and baseline (dried raw macroalgae) biomass performed worse. Specifically, the highest biocrude yield of 28.2 ± 2.5 wt.% on dry ash-free feedstock basis was recorded when liquefying alginate extraction residues. Moreover, the highest energy recovery of 52.8% was recorded when converting fucoidan extraction residues. Full article

This work investigates the effect of ground rubber tire (GRT) particle size and their concentration on the morphological, mechanical, physical, and thermal properties of thermoplastic elastomer (TPE) blends based on recycled high-density polyethylene (rHDPE). In our methodology, samples are prepared via melt blending (twin-screw extrusion followed by compression molding) to prepare different series of blends using GTR with three different particle sizes (0–250 μm, 250–500 μm, and 500–850 μm) for different GTR concentrations (0, 20, 35, 50, and 65 wt.%). The thermal properties are characterized by differential scanning calorimeter (DSC), and the morphology of the blends is studied by scanning electron microscopy (SEM). The mechanical and physical properties of the blends are investigated by quasi-static tensile and flexural tests, combined with impact strength and dynamic mechanical analysis (DMA). The SEM observations indicate some incompatibility and inhomogeneity in the blends, due to low interfacial adhesion between rHDPE and GTR (especially for GTR > 50 wt.%). Increasing the GTR content up to 65 wt.% leads to poor interphase (high interfacial tension) and agglomeration, resulting in the formation of voids around GTR particles and increasing defects/cracks in the matrix. However, introducing fine GTR particles (0–250 μm) with higher specific surface area leads to a more homogenous structure and uniform particle dispersion, due to improved physical/interfacial interactions. The results also show that for a fixed composition, smaller GTR particles (0–250 μm) gives lower melt flow index (MFI), but higher tensile strength/modulus/elongation at break and toughness compared to larger GTR particles (250–500 μm and 500–850 μm). Full article

This paper investigates the mechanical properties of two different types of recycled concrete, which use wood and rubber, relative to those characteristics of pure concrete, in terms of maximum load and natural frequencies. This paper contributes to the state of the art in this area in a number of ways. Firstly, the paper provides furtherance to the progressively growing literature in the field of recycled concrete and mechanical properties of materials. Secondly, the paper investigates the mechanical properties of two different types of recycled concrete by means of investigating the natural frequency of the samples, which is a new contribution. Lastly, the results from predicting the natural frequencies of concrete using fuzzy logic have been effectively assessed and compared with the analytical results. Results from the study show that the pure concrete samples produced maximum natural frequency, then concrete samples with wood, and lastly, concrete samples with rubber. The tolerance between the lab test results and fuzzy logic is approximately 5%. These results could have significant implications for furthering recycled concrete research and for designing machine foundations. Evidence of the applicability of fuzzy logic as a predictive and analysis tool for the mechanical properties of recycled concrete are discussed. Full article