Recycling, Volume 4, Issue 2 (June 2019) – 12 articles

One of the most efficient ways to recycle elastomeric residues from industrial processes is to incorporate them into compositions. The study of these new compositions is interesting in terms of reducing cost, the consumption of raw materials, and the generation of new waste, working towards sustainable development. Thus, this research aimed to produce and characterize elastomeric blends containing one phase comprised of ethylene–propylene–diene monomer rubber (EPDM) industrial waste aged by the action of ultraviolet radiation (UV) in a UV chamber, and the other comprised of raw EPDM, containing different concentrations of residue. Therefore, the mechanical properties and the vulcanization characteristics of the blends containing different concentrations of EPDM residue—aged and un-aged—were analyzed and compared to the properties of a standard formulation (Control). The results showed that the aging of the waste for a period of 156 h did not trigger a severe degradation process. Additionally, its reuse into new compositions promoted improvements of the studied mechanical properties without compromising the vulcanization characteristics due to the higher molecular stiffness of the samples. Full article

Economic and regulatory pressures on the global composites industry have encouraged the research and development of technology for the recycling of fiber reinforced polymer composites. Although significant advancements have been made in the recycling of carbon fiber composites, more progress is needed in the recovery of glass fibers, which make up the overwhelming volume of the composites market. In this study, wind turbine blades and automotive sheet moulding compound (SMC) were subjected to a two temperature step pyrolysis. This multistep process yielded improvements in the recovered E-glass fiber’s tensile strength, by as much as 19%, and strain to failure, by as much as 43%, over a single high temperature step pyrolysis. Despite these gains, pre-pyrolysis fiber measurements indicate that pre-existing damage may inherently limit the quality of glass fiber recoverable from pyrolysis without any post processing. Full article

Circular economy is currently characterized by various definitions, measurement approaches, and critical analyses thereof coexisting alongside each other. Whether the concept eventually prevails or collapses will depend to some extent on our success in harmonizing assessment methods among public, scientific, and private institutions, as well as across different materials and scales. Therefore, in this article, we present a generic material flow analysis framework that might serve as a common basis for circularity assessment, and test it by means of three case studies. It proved impossible to eliminate all subjective assumptions when transforming a real complex system into the generic framework, especially regarding the definition of by-products. However, by introducing subsystems it is at least possible to make such assumptions transparent. Therefore, adequate comparability across regions, materials, and scales is provided. Moreover, the generic system allows for coupled analysis of multiple materials simultaneously so that interactions between them can be studied, as well and a deeper insight into overall sustainability of the system can be gained. Full article

In the present study, we recycled waste carpet using a vacuum-assisted resin transfer molding (VARTM) process. Three different variations of carpet composites were fabricated, namely, neat epoxy, clay-coated, and clay-infused carpet composites. The carpet composite samples were degraded hygrothermally as well as under a cyclic UV condensation condition. Presence of clay was shown to impede the moisture absorption and UV degradation in the carpet composites. Flexural properties also showed that the presence of clay slows the degradation process of the composites. The flame retardancy result indicated that the presence of clay in the polymer network decreases the ignition time of the carpet composites. Full article

Essential energy needs are not always met in poor and rural areas of developing counties; therefore, natural energy sources are necessary to mitigate this problem. Rural areas inhabitants utilize methane as a replacement for cooking gas to reduce their gas bill. Methane gas can be produced from a biogas digester; however, operating a large digester in a densely populated village in Jordan can be challenging due to inefficient village waste management systems. On the other hand, using a small-scale portable biogas digester to generate biogas could overcome these problems. In this work, three biogas digester feedstocks for a small portable biogas digester from natural sources available in Jordanian villages such as human and animal waste were designed and evaluated. The three feedstocks are food waste, human waste, and a mixture of human and food waste. The parameters tested were the digester size and the biogas production. The results showed that the best digester for portable application was that which digested a mixture of human and food waste; for a five-member family, this type of digester provided 115% of the family’s cooking gas requirements with a digester volume of 0.54 m³. This design, while applicable for a typical rural Jordanian family, can also be utilized globally. Full article

Today, considerable amounts of resources are landfilled or incinerated, and recyclable materials such as metal, glass, plastic, and paper are disposed of as residual waste instead of being sorted into recyclable fractions. Recycling is one way of transitioning towards a circular economy and a more resource-efficient society. However, in many older cities there is insufficient space for waste bins, which makes waste sorting difficult. The aim of the study was to test how the introduction of a new kerbside collection system, using different-coloured plastic bags, would influence the amounts of residual waste and separately collected food waste. Coloured plastic bags were introduced in an old city centre in Kalmar, in the southeast of Sweden. This type of kerbside collection was applied to 38 apartments with a total of 87 residents for four weeks. Results show that residual waste decreased directly by 15 percent and the collected amount of food waste increased directly by 35 percent. The residents perceived that the sorting system facilitated sorting and that the sorting of recyclable materials increased. Kerbside collection, close to properties, seemed to be an important factor in reducing the amount of residual waste, leading to increased sorting, and hence improved recycling. Full article

This paper reviews the partnership between the public and the private sectors in providing efficient solid waste management (SWM) services. While the responsibility of providing SWM services lies with the public sector, the sector has not been able to meet the demand for efficient service delivery, especially in developing countries. In a bid to increase efficiency and lower costs incurred in rendering these services, the involvement of the private sector has been sought. With a focus on major Nigerian cities, partnerships between the local government and private operators in SWM have been analysed based on the level to which the partnership has improved the SWM services. This paper provides an understanding that the success of any public-private partnership relies on the extent to which all stakeholders perform their duties. If the public sector is slack in monitoring and supervising the activities of the private operators, the latter may focus on profit generation while neglecting efficient service delivery. Also, legislation is an important part of SWM. Without the right legislation and enforcement, waste generators will not be mandated to dispose their waste properly. The public sector as a facilitator is responsible for creating an environment for private operators to function, particularly through legislation, enforcement and public sensitization. Full article

In the aerospace industry, many composite parts are manufactured by processes using plastic vacuum bags made of polyamide 6 (PA6) as a consumable material. This implies that after demolding the part, this plastic material should be discarded, generating a considerable amount of waste. Tons of vacuum bags are discarded and incinerated per month by several companies in this sector, which highlights the need to recycle and/or reuse this material. PA6/linear low-density polyethylene (LLDPE) blends are of great technological interest because they can combine the excellent thermo-mechanical and oxygen barrier properties of the PA6 with high impact strength, good processability, and low cost of LLDPE. The replacement of neat PA6 by the post-processing vacuum bags residue PA6 may be a new strategy for the recycling of this material. In this work, PA6/LLDPE/maleic anhydride-grafted LLDPE (LLDPE-g-MA) (90/5/5) blends were prepared using a co-rotational twin-screw extruder and the neat PA6 was replaced by different contents of post-processing PA6 (5, 10, 15 and 20 wt.%). The mechanical, thermal, and morphological characterization was evaluated. The increase in the content of post-processing PA6 caused an increase in the crystallinity degree of the LLDPE phase, acting as a nucleating agent to the LLDPE phase, reducing the toughening effect of this phase in the blends and, therefore, providing this phase to act as a reinforcing agent. Full article

Environmental policies of the European Union aim to increase recycling and re-use of waste-streams. One of the economically most profitable ways of re-using waste is to use it as a fertilizer. In this study, recycled nitrogen fertilizers were manufactured from industrial side-streams (sawdust, fly-ash, ammonium sulfate and lignosulfonate). A sequential extraction procedure was applied to all the products tested in this paper to make sure that the environmental requirements of a recycled fertilizer would be fulfilled. A mass fraction of up to 7.0% of nitrogen was achieved with sawdust granule and 7.2% with fly-ash-sawdust granule, indicating that the granules would be well suited to be used as nitrogen-containing fertilizers. Nitrogen release from sawdust granule was more controlled than from commercial salpetre. Sawdust combined with fly-ash can hence give a balanced nutrient mix when used together. Bioavailabilities and pseudo-total contents of harmful elements (As, Cd, Cr, Cu, Ni, Pb, and Zn) were small in all granules and cause no harm in field or forest fertilizer use. Full article

The inappropriate disposal of millions of tons of domestically produced used cooking oil (UCO), either down domestic household drains or in landfill, causes significant detrimental effects on the environment but also constitutes the loss of a valuable resource, since used cooking oil is a sought-after feedstock for biodiesel production. This paper presents findings from a social reverse logistics system, called InnovOleum, for collecting and recycling domestic used cooking oil through schools. The disruptive, social aspect of InnovOleum derives from the provision of funds from the sale of the collected used cooking oil to be invested within the participating schools in ongoing environmental education and green infrastructure and technology. To date, over 200,000 Euros have been distributed to schools for this purpose. No other schemes with similar potential to fully harness the environmental and social benefits from the collection and conversion of domestically produced used cooking oil have been found in literature. This publication can therefore significantly contribute to the knowledge base and facilitate the transfer of this scheme elsewhere. Full article

In order to transform the economy into one that is circular, that recovers most materials through reuse, remanufacturing and recycling, these activities need to grow significantly. Waste management has substantially incorporated recycling as an end-of-life treatment but has still largely failed to incorporate remanufacturing and reuse as possible material recovery routes. This article aims to provide useful information to establish centers for urban remanufacture (CUREs), by analyzing fifteen existing initiatives that facilitate reuse and remanufacture by providing access to secondary materials or manufacturing tools. The study consists of a review of selected initiatives complemented with targeted interviews to fill in missing information. Most initiatives provided access to secondary materials (13 of 15 initiatives), and almost all used different manufacturing tools (14 of 15 initiatives). Besides their regular opening hours, initiatives were mainly engaged in capacity building activities, which were done through predefined or improvised workshops. Most initiatives relied on external support to finance their operations (9 of 15 initiatives). However, one of the self-financed initiatives is the oldest initiative in the study, operating since 1998. Based on the results and tacit knowledge collected in this study, a framework is suggested to serve as a guide for establishing future CUREs. Full article

The European Union’s circular economy strategy aims to increase the recycling and re-use of products and waste materials. According to the strategy, the use of industry waste material should be more effective. A chemical precipitation method to simultaneously remove phosphorus and nitrogen from synthetic (NH₄)₂HPO₄ solution and the liquid phase of anaerobic digestate using fly ash as a precipitant was tested. Fly ash is a waste material formed in the power plant process. It mainly contains calcium oxide (CaO) and magnesium oxide (MgO). Saturated precipitant solution was prepared from fly ash, which was added in small proportions to (NH₄)₂HPO₄ solution during the experiment. Fly ash’s effectiveness as a precipitant was compared with that of commercial CaO and MgO salts, and it can be observed that fly ash removed as much ammonium and phosphate as commercial salts. Fly ash sufficiently removed ammonium nitrogen and phosphate from the liquid phase of anaerobic digestate, which led to the formation of ammonium magnesium hydrogen phosphate hydrate, struvite (NH₄MgPO₄·6H₂O), and calcium hydroxide phosphate, monetite, CaPO₃(OH). In this study, we have shown for the first time that fly ash can be used to manufacture recycled, slow-release fertilizers from anaerobic digestate. Full article