Online sorting of recovered wood waste by automated XRF-technology: part II. Sorting efficiencies

A Review of the Environmental Benefits of Using Wood Waste and Magnesium Oxychloride Cement as a Composite Building Material

There is an increasing awareness of the negative environmental impact produced by human activity worldwide. The scope of this paper is to analyze the possibilities of the further use of wood waste as a composite building material with magnesium oxychloride cement (MOC), and to identify the environmental benefits offered by this solution. The environmental impact of improper wood waste disposal affects both aquatic and terrestrial ecosystems. Moreover, burning wood waste releases greenhouse gases into the atmosphere, causing various health problems. The interest in studying the possibilities of reusing wood waste increased significantly in recent years. The focus of the researcher shifts from considering wood waste as a burning fuel to generate heat or energy, to considering it as a component of new building materials. Combining MOC cement with wood opens the possibility of creating new composite building materials that can incorporate the environmental benefits offered by the two materials.

pXRF on printed circuit boards: Methodology, applications, and challenges

In order to develop methods to determine the chemical composition of Waste Printed Circuit Boards (WPCB), this study focused on the analysis of 10 metals (Cu, Fe, Sn, Zn, Pb, Ni, Sb, Cr, Mo and Pd) using portable X-ray fluorescence (pXRF) compared to ICP-MS measurements after aqua regia digestion. Different experimental conditions were tested: 3 particle sizes (200 µm, 750 µm and 2 mm) and 3 sample preparations (tube, cup and loose powder). For each condition tested, 8-16 independent replicates were done. ICP measurements with the 200 µm sample, considered as the reference condition in this study, confirmed the homogeneity of the sample at this particle size and the robustness of the sampling protocol (RSD < 5% for all elements). For this particle size, pXRF has low data dispersion too (Cu, Fe, Sn, Zn, Pb, Sb and Cr showed RSD < 10%) and the use of loose powder seems to be a sufficient preparatory step. Moreover, the deviation of pXRF measurements with the 200 µm sample from the reference condition was acceptable (<20%) for Cu, Sn, Zn, Pb, Ni, Sb and Mo. For coarser samples, i.e. 750 µm and 2 mm, the homogeneity was much more doubtful, which needs to be offset by a larger number of repetitions. For these particles sizes, pXRF set to factory-installed mining mode did not produce accurate measurements but could provide a rapid non-intrusive approach for first-level screening to assess the relative difference of metal contents between WPCB samples.

Arsenic, copper, and chromium from treated wood products in the U.S. disposal sector

Construction and demolition (C&D) wood can be recycled as mulch for landscaping or cogeneration. Limitations to such recycling are dependent on metals concentrations in mulch (As, Cu, and Cr) from the inclusion of waterborne-preservative treated wood. The objective of this study was to evaluate the amount of waterborne-preservative treated wood (by wood volume and by mass of metal) that enters the C&D wood waste stream in the U.S. by utilizing a mass balance approach. A model was developed using wood treatment industry production statistics, estimated leaching rates of metal-based preservatives, and typical service lives of wood products. Outputs of the model indicate that the volumes of waterborne preservative treated wood disposed of may exceed 16 million m³ per year by 2030. The peak yearly metal mass disposed of corresponded to 18,400 metric tons for arsenic and 24,500 tons of chromium in 2013. Given the current trends in production, the mass of copper disposed of will increase to 20,900 tons by 2030. In order to meet regulatory guidelines regarding metals in recycled C&D wood, waterborne-preservative treated wood must be separated and removed. This separation mitigates environmental contamination from wood preservatives such as chromated copper arsenate (CCA).

Applicability of a field portable X-ray fluorescence for analyzing elemental concentration of waste samples

Determining the chemical properties of waste is crucial to ensure the most effective utilization of waste. The standard laboratory measurements can produce accurate results, but analysis is labor- and time-consuming. The variety of elements that field portable X-ray fluorescence spectrometry (FPXRF) can detect from selected waste materials was studied, including how the results compared with those of inductively coupled plasma mass spectrometry (ICP-MS) measurements. The selected materials were fine fraction reject from solid recovered fuel production, fly ash, biowaste, and compost. Based on the results, FPXRF is reported to be best suited for waste samples, such as ash and compost, because of their physical properties, as follows: not too moist, quite small particle size, and not too heterogeneous. The results obtained from FPXRF showed the lowest relative standard deviation for ash material. The analysis of the limits of agreement between FPXRF and ICP-MS showed that FPXRF was mainly suitable for qualitative assessment. Furthermore, regression analysis showed a linear correlation between FPXRF and ICP-MS results for calcium and zinc in the selected materials. Keeping the limitations in mind, FPXRF could be used for qualitative analysis in waste treatment processes, such as first quality control of waste materials.

Metals content of recycled construction and demolition wood before and after implementation of best management practices

A limitation to recycling wood from construction and demolition (C&D) waste is contamination of metals from the inadvertent inclusion of preservative treated wood, in particular wood treated with chromated copper arsenate (CCA) and newer copper-based formulations. To minimize contamination many regions have developed best management practices (BMPs) for separating treated from untreated wood. The objective of this study was to evaluate the fraction of preservative treated wood in recycled C&D wood after the implementation of BMPs, using Florida as a case study. Methods involved collecting recycled C&D wood samples from throughout the state, measuring metals concentrations (As, Cu, and Cr) in the samples to compute the fraction of recycled wood treated with waterborne wood preservatives, and comparing measurements with those taken prior to the formalization of BMPs. Metals concentrations were measured using two methods, one based on traditional laboratory digestion methods and another using a more rapid hand-held X-ray Fluorescence (XRF) device in the field. The proportion of waterborne preservative-treated wood in recycled wood products has reduced significantly in the intervening 20 years (from 6% to 2.9%), and the fraction of CCA-treated wood has been reduced even further, to 1.4%. The remaining fraction of waterborne preservative-treated wood is comprised of new formulations of copper-based preservatives. This suggests that restrictions from the wood preservation industry and best management practices implemented at recycling facilities have been effective in reducing heavy metal contamination from pressure treated lumber in recycled wood products.

Quality assessment of recycled wood with and without non-wooden materials from selected recycling companies in Europe

Recycled wood is becoming an important material source for production of new materials and chemicals. Predominantly clean recycled wood should be used for the products with high added value. However, contamination of the recycled wood defines the potential end uses. Thus, it is of the huge commercial and environmental importance to monitor the contamination of the respective material. In the present research, we focused on concentrations of non-wooden materials in recycled wood and the presence of indicative inorganic pollutants, namely: chlorine (Cl), chromium (Cr), copper (Cu), zinc (Zn), lead (Pb), iron (Fe) and bromine (Br). Sampling of various qualities of commercially available recycled wood was performed for one year in recycling companies from Germany, Slovenia, Finland and UK. In addition to the above-mentioned long term monitoring, fraction analysis was also performed on selected batches. For nine different fractions, the water soluble part and lignin content were additionally determined. The results showed that high quality recycled wood had low shares of non-wooden materials and only a few samples exceeded the limit values for inorganic pollutants prescribed by German ordinance Altholzverordnung or EPF standard. On the other hand, mixed recycled wood, of lower quality contained a significantly higher portion of non-wooden material (up to 3%). These mixtures also had higher concentrations of inorganic pollutants. More than 85% of samples exceeded the limit concentration prescribed by the German ordinance Altholzverordnung for recovered wood for at least one of the analysed chemicals. The concentration of chemical elements in samples from nine different size fractions negatively correlated with the particle size in the fractions. The same trend was also observed for the soluble part and the lignin content. In general, it can be concluded that recycled wood deriving from larger annual process capacity volumes with sophisticated sorting systems, contains less non-wooden material and can provide clean wood. On the other hand, the mixed recycled wood contained high concentrations of inorganic elements, regardless of the origin or sorting system.

State-of-the-art of waste wood supply chain in Germany and selected European countries

According to the statistic office of the European Union (Eurostat), Germany is the main producer of waste wood in Europe followed by France, United Kingdom, Italy and Finland. Based on the characteristics of the waste wood, it can be classified in four (4) categories: A I, A II, A III and A IV. This paper focuses in the A I waste wood since is the only category able to be used directly for both material and energy purposes without a previously pre-treatment. Currently, most of this waste wood is used for direct energy production due to the previous government legislation that promoted its use directly in incineration facilities. However, the newest Renewable Energy Act (EEG 2017) may promote the cascade-use of A I waste wood prior to be intended for energy purposes. Nonetheless, the government incentives to the energy sector is not the only bottleneck that the use of A I waste wood as raw material in the wood-based industry has to overcome. The peak availability, collection logistics (collection centers and transportation) and recycling facility location are some of the parameters that must be considered in order to design the "best" supply chain network for A I waste wood. This work presents a detailed description of the effect of the hierarchical strategic decision in the proper design of the waste wood supply chain. Additionally, the global picture of waste wood recycling in different European countries (UK, Italy and Finland) is briefly presented.

Multi-material classification of dry recyclables from municipal solid waste based on thermal imaging

There has been a significant rise in municipal solid waste (MSW) generation in the last few decades due to rapid urbanization and industrialization. Due to the lack of source segregation practice, a need for automated segregation of recyclables from MSW exists in the developing countries. This paper reports a thermal imaging based system for classifying useful recyclables from simulated MSW sample. Experimental results have demonstrated the possibility to use thermal imaging technique for classification and a robotic system for sorting of recyclables in a single process step. The reported classification system yields an accuracy in the range of 85-96% and is comparable with the existing single-material recyclable classification techniques. We believe that the reported thermal imaging based system can emerge as a viable and inexpensive large-scale classification-cum-sorting technology in recycling plants for processing MSW in developing countries.

A review on automated sorting of source-separated municipal solid waste for recycling

A crucial prerequisite for recycling forming an integral part of municipal solid waste (MSW) management is sorting of useful materials from source-separated MSW. Researchers have been exploring automated sorting techniques to improve the overall efficiency of recycling process. This paper reviews recent advances in physical processes, sensors, and actuators used as well as control and autonomy related issues in the area of automated sorting and recycling of source-separated MSW. We believe that this paper will provide a comprehensive overview of the state of the art and will help future system designers in the area. In this paper, we also present research challenges in the field of automated waste sorting and recycling.

Online sorting of recovered wood waste by automated XRF-technology. Part I: detection of preservative-treated wood waste

Waste wood is frequently contaminated with wood treatment preservatives including chromated copper arsenate (CCA) and alkaline copper quat (ACQ), both of which contain metals which contaminate recycled wood products. The objective of this research was to propose a design for online automated identification of As-based and Cu-based treated wood within the recovered wood waste stream utilizing an X-ray fluorescence (XRF) system, and to evaluate the detection parameters of such system. A full-scale detection unit was used for experimentation. Two main parameters (operational threshold (OT) and measurement time) were evaluated to optimize detection efficiencies. OTs of targeted metals, As and Cu, in wood were reduced to 0.02 and 0.05, respectively. The optimum minimum measurement time of 500 ms resulted in 98%, 91%, and 97% diversion of the As, Cu and Cr mass originally contained in wood, respectively. Comparisons with other detection methods show that XRF technology can potentially fulfill the need for cost-effective processing at large facilities (>30 tons per day) which require the removal of As-based preservatives from their wood waste stream.