Treated Wood Waste Research Articles

Effects of liquefaction time and temperature on heavy metal removal and distribution in liquefied CCA-treated wood sludge

Wood liquefaction was studied as a recycling method for chromated copper arsenate (CCA)-treated wood waste. The effects of liquefaction temperature and time on the removal of the heavy metals and their distribution in liquefied CCA-treated wood sludge were investigated. The residue content decreased as the temperature increased from 120 to 180 °C regardless of the reaction time. It decreased gradually with the increase of reaction time under liquefaction temperatures 120 and 150 °C. But it decreased as the reaction time increased from 30 to 60 min then increased when the reaction time increased to 90 min under liquefaction temperature 180 °C due to the re-condensation of decomposed wood components. The total concentrations of arsenic, chromium, and copper in the sludge samples increased, while the percentage of the removed metals decreased, with increasing liquefaction temperature, which could be related to the changes of wood residue content and the fate of the heavy metals under different liquefaction conditions. The exchangeable/acid extractable fraction of all three heavy metals decreased as the liquefaction temperature increased. At the same time, Cr and As increased in both oxidizable and reducible fractions. The amount of Cr in the oxidizable fraction increased 40% as the liquefaction temperature increased from 120 to 180 °C. The major change of Cu distribution was the increase in reducible fraction with the increase of liquefaction time. The results of this study suggested that high liquefaction temperature tends to inhibit the heavy metal recovery when liquefaction is used as a recycling method for CCA-treated wood waste.

Electrokinetic removal of creosote from treated timber waste: a comprehensive gas chromatographic view

The applicability of electro-remediation to remove creosote contaminants from treated wood wastes and to assess the behaviour of its components when submitted to an electric field was studied on woodchips from treated railway sleepers of Pinus pinaster Ait. 15 days experiments were performed using a laboratory cell, with constant current density set at 0.2 mA cm−2 and an open electrolyte flow rate of 0.5 mL min−1. The anolyte and catholyte solutions were collected and extracted by solid phase extraction. The resulting extracts were analysed by one dimensional gas chromatography hyphenated with mass spectrometry (1D-GC/MS) and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC/TOFMS). The chemical groups of creosote components were identified and its behaviour on process described. Polycyclic aromatic hydrocarbons, phenols and the majority of the S- and O- heterocycles were found to move in the electrokinetic cell towards the anode compartment, due to electroosmosis, whereas the majority of the positively charged N-heterocycles (aza-heterocycles) moved towards the cathode compartment, due to electromigration.

Determination of total arsenic in coal and wood using oxygen flask combustion method followed by hydride generation atomic absorption spectrometry

A simple and sensitive procedure for the determination of total arsenic in coal and wood was conducted by use of oxygen flask combustion (OFC) followed by hydride generation atomic absorption spectrometry (HGAAS). The effect of various items (composition of absorbent, standing time between the combustion and filtration, particle size and mass of sample) was investigated. Under the optimized conditions of the OFC method, nine certified reference materials were analyzed, and the values of arsenic concentration obtained by this method were in good accordance with the certified values. The limit of detection (LOD) and relative standard deviation (RSD) of the method were 0.29 μg g −1 and less than 8%, respectively. In addition, eight kinds of coals and four chromated copper arsenate (CCA)-treated wood wastes were analyzed by the present method, and the data were compared to those from the microwave-acid digestion (MW-AD) method. The determination of arsenic in solid samples was discussed in terms of applicable scope and concentration range of arsenic.

Mathematical modelling of slow pyrolysis of a particle of treated wood waste

Low-temperature pyrolysis is a possible method for the disposal of wood waste treated with chromated copper arsenic (CCA). A mathematical model (heat and mass transfer) including chemical reactions of the thermal degradation of a particle of wood is presented. A spherical particle is heated by a convective nitrogen flow. The progress of the pyrolysis process is characterized by three main steps: (1) drying of the wet sample; (2) heating of the sample until ignition of pyrolysis reactions; (3) pyrolysis and subsequent production of char and volatiles. The mathematical model is based on the volume averaging concept and it uses Shafizadeh and Chin [F. Shafizadeh, P.S. Chin, Thermal deterioration of wood, wood technology: chemical aspects, ACS Symposium Series 43 (1977) 57–81] pyrolysis model to describe the reaction pathway. It is solved by the line method, taking time as the preferred variable. Our model predicts intra-particle profiles for several variables (temperature, moisture content, concentration of wood). Simulations are presented with a spherical particle of 1 cm radius.

Assessing the Current and Future Impacts of the Disposal of Chromated Copper Arsenate-Treated Wood in Unlined Landfills

Several states have recently considered altering disposal requirements for chromated copper arsenate (CCA)-treated wood waste, particularly Florida, where CCA-treated wood waste is disposed in unlined construction and demolition (C&D) debris and Class III municipal solid waste (MSW) landfills. The primary concern is the potential for CCA-treated wood waste to elevate arsenic levels in groundwater downgradient of the disposal sites. To address this concern, we evaluated the impact of past disposal practices of these wastes in unlined Florida C&D and Class III landfills by conducting a statistical analysis of two sets of groundwater data compiled by the Florida Department of Environmental Protection (FDEP). The databases contain water quality data from C&D and Class III landfills in Florida covering 15 yr of record from February 1992 through February 2007 and together provide the most complete datasets to evaluate this issue. Comparative statistics of the different population groups in the databases showed that the arithmetic mean concentrations of total arsenic were in most cases higher in background wells than in wells downgradient of the landfills. The statistical analysis indicates that past disposal of CCA-treated wood in C&D and Class III landfills in Florida has not increased arsenic levels downgradient of the landfills. Policy decisions regarding the continued disposal of CCA-treated wood waste as a nonhazardous waste in unlined landfills must therefore be based on a scientifically sound assessment of potential future impacts. Quantitative predictions of future impacts are difficult and pose several scientific challenges. Therefore, future management decisions should be based on a more accurate and comprehensive risk analysis that assesses the risks and benefits of different alternatives and takes into account the natural attenuation capacity of soils and aquifer solids for arsenic and the practical limitations of managing this waste stream as a hazardous waste.

EXTANT CONTENTS OF CHROMIUM, COPPER AND ARSENIC IN WASTE CCA-TREATED TIMBER

The segregation and disposal of chromated copper arsenate ( CCA )-treated wood waste when recycling building waste materials is a serious issue. We examined the contents of CCA preserved cedar timber by PIXE analysis. CCA preserved timber contained large amounts of these metals both on the surface and core of the wood. The ratio of chromium, copper and arsenic contained on the surface was 1:2:1, and in contrast, the ratio in the core was 1:1:2. In other words, the arsenic content was highest in the core. Moreover, the chemical form of arsenic in both parts of the wood was only inorganic arsenic; the same form of arsenic in preservative components known as carcinogenic substances. These findings mean that the complete separation of waste CCA preserved timber from construction and demolition wood is needed.

Agglomeration of Metals During Pyrolysis of Chromated Copper Arsenate (CCA) Treated Wood Waste

Agglomeration of Metals During Pyrolysis of Chromated Copper Arsenate (CCA) Treated Wood Waste

Adsorption of Copper, Chromium, and Arsenic from Chromated Copper Arsenate (CCA) Treated Wood onto Various Adsorbents

Substantial progress has been made in remediation of preservative treated waste wood by chemical extraction with several mineral and organic acids and biodegradation using bacteria and fungi in recent years. Non-conventional low-cost adsorbents are used to bind the metal ions in extremely stable complexes in heavy metal contaminated soils or polluted waters and thus to remediate such substrates. In this study, various adsorbents from industrial and agricultural processes were evaluated in removal of copper, chromium, and arsenic from chromated copper arsenate (CCA)- treated wood by using batch extracting experiments. Most adsorbents used in the study had the potential to remove copper ele- ment from CCA-treated wood, while chromium was the most resistant element against removal in most cases. In general, as amount of adsorbents in the extraction process and extraction duration increased, the percentage of elements removed increased. The adsorbents used in the study could be important in the remediation of wood treated with organic or water- borne wood preservatives containing copper since the use of the adsorbents is one key to unfix copper from treated wood treated.

3-57.廃CCA処理木材由来炭化物のガス化反応特性((13)発電・複合技術1,Session 3 バイオマス等)

3-57.廃CCA処理木材由来炭化物のガス化反応特性((13)発電・複合技術1,Session 3 バイオマス等)

Formation of metal agglomerates during carbonisation of chromated copper arsenate (CCA) treated wood waste: Comparison between a lab scale and an industrial plant

This paper compares the results obtained by scanning electron microscopy coupled to X-ray analysis (SEM-EDXA) of the solid product after carbonisation of treated wood waste in a lab scale and in an industrial installation. These setups (lab scale and industrial) are characterized by different operating conditions of the carbonisation process. Moreover, the wood waste input to the processes differs significantly. From this study, it is clear that some similarities but also some differences exist between the lab scale study and the study with the industrial Chartherm plant. In both reactors, a metal (and mineral) agglomeration process takes place, even in the case of untreated wood. The agglomerates initially present in the wood input may serve as a seed for the metal agglomeration process during “chartherisation”. The industrial setup leads to a broader range of agglomerates’ size (0.1–50 μm) and composition (all possible combinations of Cu, Cr, As and wood minerals). Some agglomerates contain the three metals but the major part is a combination of wood minerals and one or two of the three preservative metals, while all agglomerates analysed in the lab scale product contain the three metals. The separate influence of wood input characteristics and process conditions cannot be derived from these experiments, but the observations suggest that the higher the CCA retention in the wood input is, the easier is the metal agglomeration process during chartherisation of CCA treated wood waste. From the analyses performed in this study it seems that copper behaves differently in the sense that it agglomerates easily, but the resulting particles are small (<1 μm).

Elemental analysis of ash residue from combustion of CCA treated wood waste before and after electrodialytic extraction

Element distribution in a combined fly ash and bottom ash from combustion of copper chromate arsenate (CCA) treated wood waste was investigated by scanning electron microscopy (SEM/EDX) before and after electrodialytic extraction. The untreated ash contained various particles, including pieces of incompletely combusted wood rich in Cr and Ca, and irregular particles rich in Si, Al and K. Cr was also found incorporated in silica-based matrix particles. As was associated with Ca in porous (char) particles, indicating that Ca-arsenates had been formed during combustion. Cu was associated with Cr in the incompletely combusted wood pieces and was also found in almost pure form in a surface layer of some matrix particles – indicating surface condensation of volatile Cu species. In treated ash, Ca and As were no longer found together, indicating that Ca-arsenates had been dissolved due to the electrodialytic treatment. Instead particles rich in Ca and S were now found, indicating precipitation of Ca-sulphates due to addition of sulphuric acid in connection with the electrodialytic treatment. Cu and Cr were still found associated with incompletely combusted wood particles and incorporated in matrix particles. Chemical analyses of untreated and treated ash confirmed that most As, but only smaller amounts of Cu and Cr was removed due to the electrodialytic extraction. Overall metal contents in the original ash residue were: 1.4 g As, 2.76 g Cu and 2.48 g Cr, after electrodialytic extraction these amounts were reduced by 86% for As, 15% for Cu and 33% for Cr.

Influence of corn steep liquor and glucose on colonization of control and CCB (Cu/Cr/B)-treated wood by brown rot fungi

There are increasing problems with regard to the disposal of treated wood waste. Due to heavy metals or arsenic in impregnated wood waste, burning and landfill disposal options are not considered to be environmentally friendly solutions for dealing with this problem. Extraction of the heavy metals and recycling of the preservatives from the wood waste is a much more promising and environmentally friendly solution. In order to study the scale up of this process, copper/chromium/boron-treated wood specimens were exposed to copper tolerant ( Antrodia vaillantii and Leucogyrophana pinastri) and copper sensitive wood decay fungi ( Gloeophyllum trabeum and Poria monticola). Afterwards, the ability of fungal hyphae to penetrate and overgrow the wood specimens was investigated. The fungal growths were stimulated by immersing the specimens into aqueous solution of glucose or corn steep liquor prior to exposure to the fungi. The fastest colonization of the impregnated wood was by the copper tolerant A. vaillantii. Addition of glucose onto the surface of the wood specimens increased the fungi colonization of the specimens; however, immersion of the specimens into the solution of corn steep liquor did not have the same positive influence. These results are important in elucidating copper toxicity in wood decay fungi and for using these fungi for bioremediation of treated wood wastes.

Characterization of residues from thermal treatment of treated wood and extraction of Cu, Cr, As and Zn

Thermal treatment of chromated copper arsenate (CCA) impregnated waste wood is a way to utilize the energy resource of the wood and at the same time to reduce the volume of the waste. An issue of concern in relation to the thermal treatment is As emission to the air. Meanwhile, there is still a matter to cope with when methods to avoid As emission are implemented: the residues with increased concentrations of Cu, Cr and As. In the present paper two different residues after thermal treatment are characterized: a mixed bottom and fly ash from combustion of CCA impregnated wood, and a charcoal from pyrolysis of treated waste wood. By SEM/EDX it was seen that the charcoal still showed wood structure with both tracheids and rays and that Cu, Cr and As were found inside this wood structure. Cu was found alone while Cr and As were often found together. By chemical analysis it was found, too, that the charcoal contained a high concentration of Zn, probably from paint. Chemical extraction experiments in HNO3 were conducted with the charcoal and it was found that the order of extraction (in percentage) was Zn > Cu > As > Cr. A SEM/EDX investigation of the mixed ash from combustion showed the presence of small particles with wood structure with elevated Cu and Cr concentrations, but most particles were irregular shaped matrix particles rich in Si, Al and K. Cr was abundant in many different particles including the lignin skeleton of the small, unburned wood pieces, but also inside silica-based matrix particles. Ca was often found associated with char-like (porous) particles, indicating that Ca-arsenates had been formed during combustion. Cu was often associated with Cr in the unburned wood pieces, whereas it was less abundant inside the silica-based matrix particles. Cu was also found in an almost pure form in a small layer on the surface of some matrix particles indicating condensation of volatile Cu species. Chemical extraction with inorganic acids showed the order of percentages mobilized as: As > Cu > Cr.

Review of disposal technologies for chromated copper arsenate (CCA) treated wood waste, with detailed analyses of thermochemical conversion processes

Several alternative methods for the disposal of chromated copper arsenate (CCA) treated wood waste have been studied in the literature, and these methods are reviewed and compared in this paper. Alternative disposal methods include: recycling and recovery, chemical extraction, bioremediation, electrodialytic remediation and thermal destruction. Thermochemical conversion processes are evaluated in detail based on experiments with model compounds as well as experimental and modelling work with CCA treated wood. The latter category includes: determination of the percentage of arsenic volatilised during thermal conversion of CCA treated wood, identification of the mechanisms responsible for arsenic release, modelling of high temperature equilibrium chemistry involved when CCA treated wood is burned, overview of options available for arsenic capture, characterisation of ash resulting from (co-)combustion of CCA treated wood, concerns about polychlorinated dibenzo- p-dioxins/furans (PCDD/F) formation. Finally, the most appropriate thermochemical disposal technology is identified on short term (co-incineration) and on long term (low-temperature pyrolysis or high-temperature gasification).

Capturing the arsenic fraction of CCA treated waste wood in the solid instead of in the gas phase during pyrolysis

Recycling of preservative‐treated waste wood can be an environmental problem due to toxic elements being emitted into the environment. Pyrolyzing CCA‐treated wood at low temperature without any oxidizing agent is applied to capture the arsenic fraction in the solid residue. The influence of well‐defined process parameters such as pyrolysis temperature, time and heating rate are studied. Arsenic contents in the gas phase were measured by a wet chemical method while structural analysis of the arsenic reaction products was determined with Transmission Electron Microscopy.

Effect of different extracting solutions on the electrodialytic remediation of CCA-treated wood waste Part I.: Behaviour of Cu and Cr

Removal of Cu and Cr from chromated copper arsenate (CCA)-treated wood waste under batch electrodialytic conditions was studied. The effect of different types of extracting solutions, such as deionised water or aqueous solutions of NaCl, formic acid, oxalic acid, and EDTA, on the magnitude and direction of the fluxes of Cu- and Cr-containing species in the electrodialytic cell was investigated. Oxalic acid was found to have the best performance if simultaneous removal of the two elements is required (removal efficiencies of 80.5% for Cu and 87.4% for Cr, respectively). A mixture of oxalic acid and formic acid also led to similar removal efficiencies. In these experiments, the target elements were accumulated in both the anode and cathode compartments of the electrodialytic cell due to the formation of negatively charged complexes with the organic acids used besides the free cationic forms. The latter were not present if EDTA was the extracting solution resulting in directing the Cu and Cr fluxes to the anode compartment. Contrary, these fluxes were exclusively to the cathode compartment if deionised water or an aqueous solution of NaCl were used. These extracting solutions proved suitable for solubilising (re-mobilisation) of Cu but were less efficient for Cr removal (less than 20% removal). Overall, the results obtained show the important role of the proper selection of the type and composition of the extracting solution for the success of subsequent electrodialytic removal of Cu and Cr from CCA-treated wood waste.

Metal Retention in the Solid Residue after Low-Temperature Pyrolysis of Chromated Copper Arsenate (CCA)-Treated Wood

Based on previous research work, it is expected that dry recuperation of the metals in chromated copper arsenate (CCA)-treated wood waste can be achieved by low-temperature pyrolysis if a combination of pyrolysis temperature and residence time can be found, for which the two requirements: (1) zero-emission of metals, and (2) metal agglomeration are satisfied. To determine the working conditions for zero metal release, pyrolysis experiments with precisely controlled temperature and residence time and accurately known input metal concentrations of the CCA-treated wood samples, were conducted. Temperatures lower than 327°C are considered, since the release of arsenic is thought to be controlled by the reduction reaction of As2O5 to As2O3, which occurs sharply at 327°C. Metal retentions are calculated based on the measured metal concentrations in the pyrolysis residue and in the dried CCA-treated wood. The results suggest that pyrolysis at 300°C for 20 min gives rise to zero release for the three metals (Cr, Cu, and As), while pyrolysis at 320°C leads to nonnegligible metal releases. Thus, the experimental results suggest that the decomposition temperature of As2O5 is lower than 320°C. However, due to the high experimental uncertainty the observations are inconclusive. For future industrial applications, this study already shows that very careful control of process parameters will be required to ensure a zero arsenic emission. Moreover, this study indicates that an arsenic sampling and analysis method has to be developed and validated to be able to measure the arsenic emissions directly with high accuracy, instead of measuring metal retentions in the solid residue.

Arsenic release during pyrolysis of CCA treated wood waste: current state of knowledge

Low-temperature pyrolysis is evaluated as a possible technique for the disposal of chromated copper arsenate (CCA) treated wood waste. Theoretical and experimental studies are performed in order to gain more insight in the mechanism of arsenic release. In this paper, the most important observations and results of modelling are brought together in order to present the current state of knowledge. Lab-scale pyrolysis experiments show that pyrolysis at 300 °C for 20 min gives rise to inconclusive release for the three metals. However, arsenic releases are substantial for all experiments using a temperature of 320 °C. A speciation study shows the presence of trivalent arsenic in the pyrolysis residue, indicating that arsenic, present in pentavalent state in the CCA solution and in the CCA treated wood, is partly reduced to the trivalent state during pyrolysis. Arsenic release can be modelled by a simple first order single-reaction kinetic scheme for the temperature range from 350 to 450 °C. Based on the order of magnitude of the kinetic constants, the reaction is identified as a reduction reaction. Thermogravimetric (TG) analysis of hydrated chromium arsenate (the major arsenic compound in CCA treated wood) reveals that thermal decomposition probably results in the formation of solid Cr 2O 3 and gaseous H 2O, O 2 and As 4O 6, indicating again that As(V) is reduced to As(III) and arsenic is released in trivalent form. TG studies of the pure arsenic oxides (As 2O 5 and As 2O 3) show that at temperatures lower than 500 °C the reduction reaction As 2O 5→As 2O 3+O 2 does not take place. At higher temperatures decomposition is observed. As 2O 3, however, is already released at temperatures as low as 200 °C. This release is driven by temperature dependent vapour pressures. It can be concluded that the wood, char and pyrolysis vapours form a reducing environment, thereby influencing the thermal behaviour of the arsenic oxides. An other explanation for the difference in thermal behaviour could be that part of the arsenic in the CCA treated wood is already present in the trivalent form.

Pilot scale evaluation of sorting technologies for CCA treated wood waste.

Two sorting technologies including a chemical stain method and an x-ray fluorescence technique were investigated for separating chromated copper arsenate (CCA) treated wood from other wood types in the wood waste stream. Stains were investigated in both laboratory and field settings. Studies included specially mixed solutions with chrome azurol, 1-(2-pyridylazo)-2-naphthol (PAN) and rubeanic acid chemicals. X-ray fluorescence was tested in the laboratory using a commercially available x-ray fluorescence spectrometer. Laboratory scale experiments showed that both technologies were able to detect CCA treated wood in mixtures of treated wood and untreated wood, with detection limits on the order of 3 to 5% CCA. Results from field experiments at construction and demolition facilities indicate that although the chemical stains can be effectively used to identify CCA treated wood waste in field settings, their use will be limited to sorting relatively small wood waste piles due to increased labor and time needed for processing the wood waste. Operational parameters for sorting using x-ray fluorescence technology were established. These parameters concluded that arsenic was the most sensitive metal for analysis, analysis time was less than 2 seconds per wood sample, and the maximum separation distance between the sample and the x-ray probe was 2.5 cm. X-ray technology shows considerable promise for separating large quantities of CCA-treated wood from other wood types in the field using an on-line sorting system.

The chemistry of chromated copper arsenate III. Recovery of arsenic content from treatment plant sludges

Chemical sludges from timber preservation with chromated copper arsenate are environmental hazards currently without any commercial value. A simple, inexpensive and efficient process to separate out the arsenate component of the sludges has been identified. The resulting solution can readily be used as a raw material for manufacturing new preservative. While some organic material does accompany the arsenate, this does not appear to have any detrimental effect on the product. The approach appears applicable to other chromated copper arsenate-contaminated wastes including treated wood wastes.