challenges to a circular economy – the presence of

CHALLENGES TO A CIRCULAR ECONOMY – THE PRESENCE OF IMPURITIES IN WOOD WASTE FOR RECYCLING G. FARACA*, A. BOLDRIN*, A. DAMGAARD AND T.F. ASTRUP * Department of Environmental Engineering, Technical University of Denmark, Miljøvej, 2800 Kgs. Lyngby, Denmark

SUMMARY: In this study we evaluated the presence of material and chemical impurities in wood waste collected for recycling. The preliminary results suggest that presence of impurities shall not be overlooked, as it may contaminate secondary products in case of recycling. Quantitative recycling targets alone do not tackle the quality issue, which is fundamental in order to maximize the use of resources and move toward a circular economy.

1. INTRODUCTION In the past decades, efforts to reduce and avoid the negative impacts of waste on the environment and human health have been central to the European Union (EU) environmental policy. Recently, the concept of circular economy gained importance in order to keep resources in the society as long as possible [EC, 2015]. Since a circular economy aims at minimizing the inflow of new resources [EEA 2016], reuse and recycling of waste have been promoted as its main driving forces. However, one of the challenges to the circular economy is the presence of impurities within the recyclables that may act as a critical hindrance in many ways. Among recyclable fractions, wood waste (WW) occurs in very large amounts, especially within bulky waste delivered at recycling stations. WW typically arises from construction and demolition activities, refurbishment of houses, end of life furniture and packages. Estimated lifetime of wood items is, apart for wooden packaging, long (>10 years) or very long (>50 years). WW is a valuable material as it has potential for both recycling and energy recovery [Sathre & Gustavsson, 2006]. Since the Waste Framework Directive (EU Directive 2008/98/EC) strictly hindered the landfilling of waste unless being the only disposal option, incineration with energy recovery from wood waste has substantially increased, especially in Scandinavian countries, where district heating systems are substantially based on energy from biomass [Krook et al., 2006]. In addition, taxes and other incentives were imposed individually by EU member countries to encourage the use of renewable energies as a step toward a society less dependent from fossil fuels [Krook et al., 2004]. However, applying a circular economy approach to WW would likely result in a cascade of the resource’s use, as its quality degrades over time [Winder and Bobar, 2016]. In this context, cascading means that WW is first recycled for a material application; next, it may be reused/recycled for further material applications; and finally, the biomass is combusted with energy utilization [Dornburg, 2005]. The largest material use of WW is its production to particleboard (a type of engineered woodbased panel), that involves drying and shredding of the material to obtain wood chips that are subsequently pressed together with the addition of glues or binders [Vis et al., 2016]. For an Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

efficient use of the wood resource high quality recycling shall be preferred, and factors leading to downcycling or loss of functionality shall be minimized. Impurities in WW constitute a key factor that hinders high quality recycling and make the energy recovery solution more attractive [Värmeforsk, 2012]. Impurities may be defined as material or chemical contaminants. In the case of WW, material impurities generally include metals, plastics, textiles, glass, inert, adhesives, paints, waxes, preservatives, and fire retardants [Edo et al, 2015]. On the other hand, chemical contaminants in WW originate from treatment of wood products with finishes, paints, oils, binders, adhesives, gluing agents, preservatives and flame retardants [see e.g. TRADA, 2005]. From these sources substances such as metals and persistent organic pollutants (POPs) may originate and accumulate in the wood. For resources to be used in a circular way, the presence of chemicals in waste products is critical as they may re-enter the life cycle of the new recycled product along with the targeted material (risk-cycling) [Augustsson et al., 2016]. Therefore, achieving a clean and safe circular economy relies on methods to monitor levels of impurities in the waste, identify contaminated waste flows and separate them before recycling. The objective of this study was to characterize and quantify presence of impurity materials and chemical pollutants in post-consumer WW collected at recycling centers and meant for recyling. This paper describes preliminary results that were achieved throughout the project.

2. MATERIALS AND METHODS 2.1 Composition of wood waste For the purpose of this study, two sampling campaigns were conducted. The first sampling campaign covered post-consumer wood waste collected for recycling. Thirty-four samples were collected from three recycling centers located in three municipalities in Denmark. The second sampling campaign covered pre-consumer wood, to be used as a reference. Seven samples of solid wood and engineered wood were collected as shop left-overs in Copenhagen. Each sample weighted about 15 kg and was mass and size reduced in order to obtain circa 300 g of wood powder suitable for chemical analysis (see Figure 1). All samples were classified according to their application and their expected management option (see Table 1).

Figure 1. Processing steps performed on thirty-four wood waste and seven pre-consumer wood

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

samples from their collection to the laboratory. 2.2 Material impurities Material impurities occurring in the wood samples were characterized into three classes: • Misplacements: non wooden items as well as items too contaminated with foreign materials (e.g. mirrors with wooden frames, speakers, pillows, etc.) • Unavoidable external items: non wooden items that were essential during the use phase of the wood waste (e.g. nails, staples,joints, plastics, textiles, etc.) • Material detrimental to recycling: wooden items whose properties would lower the quality of a recycled product (e.g. medium-density fiberboard, hardboard, etc.) Table 1. Characterization of samples of wood waste by application (A, B, C, D, E, F), sampling location (recycling centers – municipalities: Middelfart - a, Gelsted - b, Glamsbjerg - c; retailer: Johannes Fögg – d), expected management option (recycling, incineration, special treatment). MDF = medium density fibreboard. C&D = construction and demolition. Category A: cut-offs or left-overs

B: packaging

Subcategory: description

Sampling location

Expected management

Cut-off, left-over or large wood-chips from untreated wood

b

Recycling

Cut-offs from MDF

a, b, c

Incineration

Pallets, clean wood /w composite construction,

a, b, c

Recycling

Pallets, made from MDF or similar

a

Incineration

Other wood packaging, clean wood (boxes, crates etc)

a, b, c

Recycling

Wood from construction and rebuilding indoors

a, b, c

Recycling

a

Incineration

C: Old wood from demolition and rebuilding, Construction MDF or with isolation and demolition Old wood from demolition and rebuilding, outdoors Furniture, untreated wood D: Furniture

a, b, c

Incineration in special plants Recycling

Furniture with MDF, covered in textile, etc

a, c

Incineration

Furniture, upholstered

a, c

Incineration

Wood pressure-treated with preservatives

a, b, c c a, c

Incineration in special plants Landfill Incineration

a, b, c

Incineration

d

Recycling

Particleboard

d

Recycling

Plywood

d

Recycling

MDF, hardboard

d

Incineration

Impregnated wood

d

Incineration in special plants

Composite building materials from C&D E: Misplacements Wood, rotten or covered by plants Miscellaneous (items made out of plastic, glass, metal, cardboard) Solid wood F: preconsumer wood

a, c

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2.3 Chemical impurities Sixty-five elements were chemically analyzed as well as three classes of organic compounds (27 polycyclic aromatic hydrocarbons – PAHs, 15 phenols, and 7 polychlorinated byphenils – PCBs). Samples were analyzed in triplicates. For analysis of trace elements, all samples underwent microwave digestion (Anton Paar, Multiwave 3000), followed by Inductively Coupled Plasma Mass Spectrometry – ICP-MS (Agilent Technologies, 7700x series) or Inductively Coupled Plasma Optical Emission Spectrometry – ICP-OES (Varian, Vista-MPX) depending on the elements. Quantification of PAHs, phenols, and PCBs was achieved by microwave assisted extraction (MAE), followed by a solid phase extraction (SPE) based clean-up protocol and quantification by gas chromatography – mass spectrometry (GC-MS).

3. RESULTS AND DISCUSSION 3.1 Material impurities Material impurities were found to account for 12-59 % of the RWW collected for recycling. This fact has two consequences: in case impurities are not sorted out, they will enter the feedstock stream for recycling and either undermine the recycled product’s quality (it’s the case of low quality wood) or create processing problems (e.g. plastics and textiles stuck in the machinery). On the other hand, if impurities are sorted out, the amount of RWW actually recycled will be lower than the recycling rate recorded in statistics. Indeed, statistics are expressed in terms of mass of material sent to recycling, implicitly favouring large and heavy waste stream and not distinguishing between resource efficiency and environmentally safe [Arm et al., 2016]. In both cases the efficiency of a circular economy is not maximized, either because the waste material is not used at its highest potential or because the recycling loop is not closed (losses occur). 3.2 Chemical impurities Inorganic elements were found in concentration ranges greatly varying according to the application categories of the samples. Concentration levels in samples of waste wood were always higher than those in samples of pre-consumer wood. The (preliminary) results were in accordance with other studies [e.g. Edo et al., 2015; Krook et al., 2004]. Presence of organic compounds was really low, although due to their persistence in the environment background concentration may not be negligible. When comparing the concentration levels found in samples of waste wood with the limits set by the European Panel Federation for presence of contaminants in recycled particleboard [EPF, 2002], such limits are overall met. However, it is worth noticing that companies decide to comply with such limits on a voluntary agreement, and no other pan-European legislation regulating the chemical composition of wood waste for recycling exists. If a circular economy is the overall aim to be achieved, it must be ensured that manufactured products are free from toxic compounds. Therefore, quantitative recycling targets alone do not take into consideration the quality issue, which is the key to ensure that a product’s cascade use is as efficient and as long as possible.

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

4. CONCLUSIONS In this study, the presence of impurity materials and chemical pollutants in wood waste meant for recycling was characterized and quantified. Also, the importance that recycling of wood waste (including impurities) has on the achievement of a circular economy was addressed and discussed. Our (preliminary) results suggest that impurities may be a relevant portion of wood waste collected for recycling, and that such impurities may hinder high quality recycling or lead to the recycling of chemicals embedded in the recyclables (risk-cycling). This study thereby shows that recycling alone may not lead to a clean circular economy and additional efforts are needed for an improved recyclable feedstock. Social and technological solutions must be searched in order to enhance the quality of wood waste for its second life in a new product (e.g. social awareness, proper sorting of the waste at collection points, labeling and legislation). This research contributes to the general discussion that a shift from quantity to quality is needed in recycling practices.

ACKNOWLEDGEMENTS The authors greatly acknowledge the Danish Environmental Protection Agency for funding the projects. We also greatly thank the sorting company Econet A/S for giving the opportunity to sample wood waste.

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