CCA-treated wood disposed in landfills and life-cycle trade-offs with waste-to-energy and MSW landfill disposal

Identification and quantification of Cr, Cu, and As incidental nanomaterials derived from CCA-treated wood in wildland-urban interface fire ashes

In addition to the combustion of vegetation, fires at the wildland-urban interface (WUI) burn structural materials, including chromated copper arsenate (CCA)-treated wood. This study identifies, quantifies, and characterizes Cr-, Cu-, and As-bearing incidental nanomaterials (INMs) in WUI fire ashes collected from three residential structures suspected to have originated from the combustion of CCA-treated wood. The total elemental concentrations were determined by inductively coupled plasma-time of flight-mass spectrometry (ICP-TOF-MS) following acid digestion. The crystalline phases were determined using transmission electron microscopy (TEM), specifically using electron diffraction and high-resolution imaging. The multi-element single particle composition and size distribution were determined by single particle (SP)-ICP-TOF-MS coupled with agglomerative hierarchical clustering analysis. Chromium, Cu, and As are the dominant elements in the ashes and together account for 93%, 83%, and 24% of the total mass of measured elements in the ash samples. Chromium, Cu, and As phases, analyzed by TEM, most closely match CrO₃, CrO₂, eskolaite (Cr₂O₃), CuCrO₂, CuCr₂O₄, CrAs₂O₆, As₂O₅, AsO₂, claudetite (As₂O₃, monoclinic), or arsenolite (As₂O₃, cubic), although a bona fide phase identification for each particle was not always possible. These phases occur predominantly as heteroaggregates. Multi-element single particle analyses demonstrate that Cr occurs as a pure phase (i.e., Cr oxides) as well as in association with other elements (e.g., Cu and As); Cu occurs predominantly in association with Cr and As; and As occurs as As oxides and in association with Cu and Cr. Several Cr, Cu, and As clusters were identified and the molar ratios of Cr/Cu and Cr/As within these clusters are consistent with the crystalline phases identified by TEM as well as their heteroaggregates. These results indicate that WUI fires can lead to significant release of CCA constituents and their combustion-transformed by-products into the surrounding environment. This study also provides a method to identify and track CCA constituents in environmental systems based on multi-element analysis using SP-ICP-TOF-MS.

A life cycle and product type based estimator for quantifying the carbon stored in wood products

BACKGROUND

Timber harvesting and industrial wood processing laterally transfer the carbon stored in forest sectors to wood products creating a wood products carbon pool. The carbon stored in wood products is allocated to end-use wood products (e.g., paper, furniture), landfill, and charcoal. Wood products can store substantial amounts of carbon and contribute to the mitigation of greenhouse effects. Therefore, accurate accounts for the size of wood products carbon pools for different regions are essential to estimating the land-atmosphere carbon exchange by using the bottom-up approach of carbon stock change.

RESULTS

To quantify the carbon stored in wood products, we developed a state-of-the-art estimator (Wood Products Carbon Storage Estimator, WPsCS Estimator) that includes the wood products disposal, recycling, and waste wood decomposition processes. The wood products carbon pool in this estimator has three subpools: (1) end-use wood products, (2) landfill, and (3) charcoal carbon. In addition, it has a user-friendly interface, which can be used to easily parameterize and calibrate an estimation. To evaluate its performance, we applied this estimator to account for the carbon stored in wood products made from the timber harvested in Maine, USA, and the carbon storage of wood products consumed in the United States.

CONCLUSION

The WPsCS Estimator can efficiently and easily quantify the carbon stored in harvested wood products for a given region over a specific period, which was demonstrated with two illustrative examples. In addition, WPsCS Estimator has a user-friendly interface, and all parameters can be easily modified.

Ecotoxic, genotoxic, and cytotoxic potential of leachate obtained from chromated copper arsenate-treated wood ashes

Preservative treatments increase the durability of wood, and one of the alternative treatments involves the use of chromated copper arsenate (CCA). Due to the toxicity of CCA, the disposal of CCA-treated wood residues is problematic, and burning is considered to provide a solution. The ecotoxicological potential of ash can be high when these components are toxic and mutagenic. The aim of this study was to evaluate the toxicity and genotoxicity of bottom ash leachates originating from CCA-treated wood burning. Physical-chemical analysis of the leachates revealed that in treated wood ashes leachate (CCA-TWBAL), the contents of arsenic and chromium were 59.45 mg.L^-1 and 54.28 mg.L^-1, respectively. In untreated wood ashes leachate (UWBAL), these contents were 0.70 mg.L^-1 and 0.30 mg.L^-1, respectively. CCA-TWBAL caused significant toxicity in Lactuca sativa, Allium cepa, and microcrustacean Artemia spp. (LC50 = 12.12 mg.mL^-1). Comet assay analyses using NIH3T3 cells revealed that concentrations ranging from 1.0 and 2.5 mg.mL^-1 increase the damage frequency (DF) and damage index (DI). According to MTT assay results, CCA-TWBAL at concentrations as low as 1 mg.mL^-1 caused a significant decrease in cellular viability. Hemolysis assay analyses suggest that the arsenic and chromium leachate contents are important for the ecotoxic, cytotoxic, and genotoxic effects of CCA-TWBAL.

An LCA-based model for assessing prevention versus non-prevention of construction waste in buildings

Waste generated by the Construction Sector represents an environmental problem in many countries. To achieve increasingly eco-efficient waste management, Life Cycle Assessment (LCA) provides an objective method for the quantification of the potential impact that waste management exerts on the environment. Traditionally, LCA has focused on the evaluation of non-prevention scenarios once the waste is generated, mainly by showing the benefits of recycling vs. disposal. Consequently, the literature has hardly addressed the positive environmental impacts caused by waste prevention, that is, the reduction at source, which constitutes the preferred option of any waste management hierarchy. Therefore, this study proposes a model to simulate the environmental performance of the prevention vs. the non-prevention of construction waste production. The model is applied to an urban system of residential buildings in Spain. The results provide evidence of the environmental benefits achieved with the prevention scenario. The prevention scenario reduces the construction waste generated in the non-prevention scenarios by up to 57%. Furthermore, it allows a potential reduction of up to 4.6 and 171.1 times the impact caused by the disposal scenario; and up to 1.7 and 8.3 times those of the recycling scenario. The model can be implemented in other contexts with other reference buildings, and enables the environmental benefits of reduction strategies to be studied, thereby providing a tool to guide and support decision-making during the building design stage. Moreover, the results obtained can help professionals and policymakers to incorporate effective construction waste prevention measures in waste prevention plans and programs.

Heavy metals in leachate, impacted soils and natural soils of different landfills in Malaysia: An alarming threat

Landfills are a potential threat to human health and the environment, especially from the detrimental and toxic heavy metals. This study focuses on the assessment of heavy metals contamination in leachate and surface soils from different landfills in Malaysia. Maximum quality rating scale (QRS) values of As (787) and Cr (552) denotes progressive deterioration of leachate contamination in landfill. The impacted soils showed high heavy metal concentrations especially at non-sanitary unlined landfills, as compared to background values, and natural soil nearby the landfills. In addition, to examine the environmental impacts of the landfill area (soil) in more detail, specific indexes; geo-accumulation index (Igeo), pollution index (PI) and integrated pollution index (IPI) were determined. Maximum As (3.122) and Cd (2.633) for Igeo and As (34.037) and Cd (20.881) for PI revealed that the soil samples in non-sanitary landfills were moderate to strongly polluted. The difference in range of IPI values for sanitary (0.294-0.322) and non-sanitary landfill soils (1.263-1.956) confirmed advanced decline of the soil quality in non-sanitary landfills. Arsenic concentrations were found to be statistically significant (ANOVA) for leachate and impacted soil in landfills investigated. It is also important to realize that rise in metal contents in landfill environments were not only caused by anthropogenic sources such as from the waste disposed, but also some other factors such as redox conditions, anoxic environments, pH, oxidation state of metals and microbial activities. Those conditions will actively promotes leaching of metals from waste and also natural soils in the landfill.

South African log resource availability and potential environmental impact of timber construction

We investigated the South African log resource availability and the potential global warming impact of an increasing wood-based residential building market. We have shown that, with the use of wood resources currently exported as chips, as well as planting trees in areas that have been earmarked for afforestation, a sustainable residential building market, where all constructions are wood-based, is possible. However, in the short term, imports of wooden building components might be necessary if rapid growth in woodbased building occurs. Basic modelling analyses show that if the market share of wood-based buildings increases to 20% of new constructions, the embodied energy and global warming potential of the residential building sector could decrease by 4.9%. If all new constructions were wood based, the total embodied energy and global warming potential of the residential building sector could decrease by up to 30%.

Experimental modeling of the acute toxicity and cytogenotoxic fate of composite mixtures of chromate, copper and arsenate oxides associated with CCA preservative using Clarias gariepinus (Burchell 1822)

Concurrent occurrence of chromium (Cr), copper (Cu) and arsenic (As) from chromated copper arsenate (CCA) wood preservative in aquatic ecosystems demands that their joint-actions in eliciting toxic effects be assessed for adequate understanding of the health risk they may pose to biota. Clarias gariepinus was exposed to As₂O₃ , CrO₃ and CuO and their composite mixtures (1:1 and 1:1:1) at various concentrations (0 – 600 mg/L) for 96-h to determine the acute toxicity using OECD (1992) protocol. C. gariepinus was then exposed to sub-lethal concentrations corresponding to 6.25, 12.5, 25.0, 50.0 and 100% of the 96-h LC₅₀ for 7 days to assess the cytogenotoxic effects using piscine micronucleus (MN) test. The 96-h LC₅₀ showed that the metals/metalloid demonstrated differential interactions in a concentration dependent pattern. The 96-h LC₅₀ showed that Cr was the most toxic while Cu and As:Cu were indeterminate (Cr > Cr:Cu > As:Cr > As > As:Cr:Cu > Cu = As:Cu indeterminate). Isobologram and synergistic ratio (SR) models predicted antagonistic interaction between Cu:Cr and As:Cr and synergism between As:Cu in the causation of morbidity and mortality of C. gariepinus. Interaction factor model predicted antagonism as common interactive mechanism among the metal/metalloid mixtures in the induction of MN and abnormal nuclear erythrocytes in C. gariepinus. Predicted interactions among the three metals/ metalloid were largely antagonism and synergism towards the induction of acute toxicity and cytogenotoxicity. The models employed herein may be useful in establishing environmental safe limits for mixtures of metals/metalloids against the induction of acute toxicity and DNA damage in lower aquatic vertebrates.

Critical review on life cycle assessment of conventional and innovative waste-to-energy technologies

In this study 315 peer-reviewed studies on environmental life cycle assessment (LCA) of waste-to-energy (WtE) technologies were critically analysed. The technologies considered were anaerobic digestion, hydrothermal carbonization, pyrolysis, gasification and incineration. It was found that overall increasingly more studies are concerned with LCA on waste-treatment systems. Although incineration and anaerobic digestion were primarily assessed, especially in recent years, a growing number of LCA-studies investigated advanced thermal treatment options. The geographical scope within the studies under review focused mainly on European (195 studies) and Asian (68 studies) regions. In regards to their quality, a majority of the analysed studies were marked by several shortcomings and showed poor compliance with the ISO 14040 and ISO 14044. 55 studies did not present a functional unit and >45% of all reviewed studies did not present a life cycle inventory. More than 50% of the reviewed studies omitted a sensitivity analysis and a comprehensive assessment of all impact categories was not present in most studies. By selecting studies that analysed two or more different WtE treatment options, the global warming potential and the acidification potential of the considered five different technologies were compared. By contrasting advanced treatment options against incineration, substantial environmental benefits of advanced treatment options could not be observed. However, only 34 studies fulfilled the criteria to be taken into account for this comparison. The main finding within this scope, was that anaerobic digestion and gasification seemed to outcompete incineration in the conversion process of waste. Cascaded waste treatment, i.e. combining several treatment technologies, was only present in few studies. Environmental benefits could be assigned to these treatment paths in most cases. Lastly, techno-economic aspects are highlighted and appropriate policies are deducted from the obtained results.

Waste wood as bioenergy feedstock. Climate change impacts and related emission uncertainties from waste wood based energy systems in the UK

Considering the urgent need to shift to low carbon energy carriers, waste wood resources could provide an alternative energy feedstock and at the same time reduce emissions from landfill. This research examines the climate change impacts and related emission uncertainties of waste wood based energy. For this, different grades of waste wood and energy application have been investigated using lifecycle assessment. Sensitivity analysis has then been applied for supply chain processes and feedstock properties for the main emission contributing categories: transport, processing, pelletizing, urea resin fraction and related N₂O formation. The results show, depending on the waste wood grade, the conversion option, scale and the related reference case, that emission reductions of up to 91% are possible for non-treated wood waste. Compared to this, energy from treated wood waste with low contamination can achieve up to 83% emission savings, similar to untreated waste wood pellets, but in some cases emissions from waste wood based energy can exceed the ones of the fossil fuel reference - in the worst case by 126%. Emission reductions from highly contaminated feedstocks are largest when replacing electricity from large-scale coal and landfill. The highest emission uncertainties are related to the wood's resin fraction and N₂O formation during combustion and, pelletizing. Comparing wood processing with diesel and electricity powered equipment also generated high variations in the results, while emission variations related to transport are relatively small. Using treated waste wood as a bioenergy feedstock can be a valid option to reduce emissions from energy production but this is only realisable if coal and landfill gas are replaced. To achieve meaningful emission reduction in line with national and international climate change targets, pre-treatment of waste wood would be required to reduce components that form N₂O during the energy conversion.

Arsenic leaching and speciation in C&D debris landfills and the relationship with gypsum drywall content

The effects of sulfide levels on arsenic leaching and speciation were investigated using leachate generated from laboratory-scale construction and demolition (C&D) debris landfills, which were simulated lysimeters containing various percentages of gypsum drywall. The drywall percentages in lysimeters were 0, 1, 6, and 12.4wt% (weight percent) respectively. With the exception of a control lysimeter that contained 12.4wt% of drywall, each lysimeter contained chromated copper arsenate (CCA) treated wood, which accounts for 10wt% of the C&D waste. During the period of study, lysimeters were mostly under anaerobic conditions. Leachate analysis results showed that sulfide levels increased as the percentage of drywall increased in landfills, but arsenic concentrations in leachate were not linearly correlated with sulfide levels. Instead, the arsenic concentrations decreased as sulfide increased up to approximately 1000μg/L, but had an increase with further increase in sulfide levels, forming a V-shape on the arsenic vs. sulfide plot. The analysis of arsenic speciation in leachate showed different species distribution as sulfide levels changed; the fraction of arsenite (As(III)) increased as the sulfide level increased, and thioarsenate anions (As(V)) were detected when the sulfide level further increased (>10⁴μg/L). The formation of insoluble arsenic sulfide minerals at a lower range of sulfide and soluble thioarsenic anionic species at a higher range of sulfide likely contributed to the decreasing and increasing trend of arsenic leaching.

Developments in life cycle assessment applied to evaluate the environmental performance of construction and demolition wastes

This paper provides a review of the literature that applies the life cycle assessment (LCA) methodology to the assessment of the environmental performance of the life cycle of construction and demolition waste (CDW) management systems. This article is focused on generating a general mapping of the literature and on identifying the best practices in compliance with LCA framework and proposing directions for future LCA studies in this field. The temporal evolution of the research in this field and the aim of the studies have grown in parallel with the legal framework related to waste and energy efficiency of buildings. Most studies have been published in Europe, followed by USA. Asia and Australia, being at an incipient application stage to the rest of the world. Topics related to "LCA of buildings, including their EoL" and "LCA of general CDW management strategies" are the most frequently analysed, followed by "LCA of EoL of construction elements" and "LCA of natural material vs recycled material". Regarding the strategies, recycling off-site and incineration, both combined with landfill for the rejected fractions, are the most commonly applied. Re-use or recycling on-site is the strategy least applied. The key aspect when LCA is applied to evaluate CDW management systems is the need to normalise which processes to include in the system boundary and the functional unit, the use of inventory data adapted to the context of the case study and the definition of a common set of appropriate impact assessment categories. Also, it is important to obtain results disaggregated by unit processes. This will allow the comparison between case studies.

Effect of moisture control and air venting on H2S production and leachate quality in mature C&D debris landfills

The effect of air venting and moisture variation on H2S production and the leaching of metals/metalloids (arsenic, copper, chromium, and boron) from treated wood in aged mature construction and demolition (C&D) debris landfills were examined. Three simulated C&D debris landfill lysimeters were constructed and monitored, each containing as a major debris component either wooden pallets, chromated copper arsenate (CCA) treated wood, or alkaline copper quaternary (ACQ) treated wood. The lysimeters were operated with alternating periods of water addition (a total of 160 L in four equal amounts) and air venting (68.4 m(3)per day for 121 days in two phases). Moisture addition did not increase H2S levels in the long term, and a significant drop in H2S concentration was observed (up to 99%) when aerobic conditions were promoted through air venting. H2S concentrations increased after venting stopped up to values approximately two orders of magnitude lower than observed prior to venting. Venting had the immediate consequence of suppressing biological H2S production, and the longer-term effect of decreasing organic matter that could otherwise be utilized in this process. Under aerobic conditions, the levels of arsenic, chromium, and boron in leachate decreased up to 96%, 49%, and 68%, respectively, while copper was found to increase up to 200% in CCA and 445% in ACQ column leachates.

Methodology for assessing thioarsenic formation potential in sulfidic landfill environments

Arsenic leaching and speciation in landfills, especially those with arsenic bearing waste and drywall disposal (such as construction and demolition (C&D) debris landfills), may be affected by high levels of sulfide through the formation of thioarsenic anions. A methodology using ion chromatography (IC) with a conductivity detector was developed for the assessment of thioarsenic formation potential in sulfidic landfill environments. Monothioarsenate (H2AsSO3(-)) and dithioarsenate (H2AsS2O2(-)) were confirmed in the IC fractions of thioarsenate synthesis mixture, consistent with previous literature results. However, the observation of AsSx(-) (x=5-8) in the supposed trithioarsenate (H2AsS3O(-)) and tetrathioarsenate (H2AsS4(-)) IC fractions suggested the presence of new arsenic polysulfide complexes. All thioarsenate anions, particularly trithioarsenate and tetrathioarsenate, were unstable upon air exposure. The method developed for thioarsenate analysis was validated and successfully used to analyze several landfill leachate samples. Thioarsenate anions were detected in the leachate of all of the C&D debris landfills tested, which accounted for approximately 8.5% of the total aqueous As in the leachate. Compared to arsenite or arsenate, thioarsenates have been reported in literature to have lower adsorption on iron oxide minerals. The presence of thioarsenates in C&D debris landfill leachate poses new concerns when evaluating the impact of arsenic mobilization in such environments.

Demonstration of the efficiency and robustness of an acid leaching process to remove metals from various CCA-treated wood samples

In recent years, an efficient and economically attractive leaching process has been developed to remove metals from copper-based treated wood wastes. This study explored the applicability of this leaching process using chromated copper arsenate (CCA) treated wood samples with different initial metal loading and elapsed time between wood preservation treatment and remediation. The sulfuric acid leaching process resulted in the solubilization of more than 87% of the As, 70% of the Cr, and 76% of the Cu from CCA-chips and in the solubilization of more than 96% of the As, 78% of the Cr and 91% of the Cu from CCA-sawdust. The results showed that the performance of this leaching process might be influenced by the initial metal loading of the treated wood wastes and the elapsed time between preservation treatment and remediation. The effluents generated during the leaching steps were treated by precipitation-coagulation to satisfy the regulations for effluent discharge in municipal sewers. Precipitation using ferric chloride and sodium hydroxide was highly efficient, removing more than 99% of the As, Cr, and Cu. It appears that this leaching process can be successfully applied to remove metals from different CCA-treated wood samples and then from the effluents.

The fate of heavy metals during combustion and gasification of contaminated biomass-a brief review

The literature on the presence of heavy metals in contaminated wastes is reviewed. Various categories of materials produced from domestic and industrial activities are included, but municipal solid waste, which is a more complex material, is excluded. This review considers among the most abundant the following materials - wood waste including demolition wood, phytoremediation scavengers and chromated copper arsenate (CCA) timber, sludges including de-inking sludge and sewage sludge, chicken litter and spent pot liner. The partitioning of the metals in the ashes after combustion or gasification follows conventional behaviour, with most metals retained, and higher concentrations in the finer sizes due to vaporisation and recondensation. The alkali metals have been shown to catalyse the biomass conversion, particularly lithium and potassium, although other metals are active to a lesser extent. The most prevalent in biomass is potassium, which is not only inherently active, but volatilises to become finely distributed throughout the char mass. Because the metals are predominantly found in the ash, the effectiveness of their removal depends on the efficiency of the collection of particulates. The potential for disposal into soil depends on the initial concentration in the feed material.

Recycling and reuse of waste from electricity distribution networks as reinforcement agents in polymeric composites

Of the waste generated from electricity distribution networks, wooden posts treated with chromated copper arsenate (CCA) and ceramic insulators make up the majority of the materials for which no effective recycling scheme has been developed. This study aims to recycle and reuse this waste as reinforcement elements in polymer composites and hybrid composites, promoting an ecologically and economically viable alternative for the disposal of this waste. The CCA wooden posts were cut, crushed and recycled via acid leaching using 0.2 and 0.4N H2SO4 in triplicate at 70°C and then washed and dried. The ceramic insulators were fragmented in a hydraulic press and separated by particle size using a vibrating sieve. The composites were mixed in a twin-screw extruder and injected into the test specimens, which were subjected to physical, mechanical, thermal and morphological characterization. The results indicate that the acid treatment most effective for removing heavy metals in the wood utilizes 0.4NH2SO4. However, the composites made from wood treated with 0.2NH2SO4 exhibited the highest mechanical properties of the composites, whereas the use of a ceramic insulator produces composites with better thermal stability and impact strength. This study is part of the research and development project of ANEEL (Agência Nacional de Energia Elétrica) and funded by CPFL (Companhia Paulista de Força e Luz).

From hazardous waste to valuable raw material: hydrolysis of CCA-treated wood for the production of chemicals

Solid wood, metal finnish: Instead of burning waste wood treated with chromated copper arsenite (CCA) or disposing of it in landfills, the CCA-treated wood can be used as a raw material for the production of chemicals. Catalytic or alkaline oxidation together with very mild sulfuric acid extraction produces an easily enzymatically hydrolyzable material. Usage as a raw material for the chemical industry in this manner demonstrates a sustainable and value-added waste management process.

Mobilization of iron and arsenic from soil by construction and demolition debris landfill leachate

Column experiments were performed to examine (a) the potential for leachate from construction and demolition (C&D) debris landfills to mobilize naturally-occurring iron and arsenic from soils underlying such facilities and (b) the ability of crushed limestone to remove these aqueous phase pollutants. In duplicate columns, water was added to a 30-cm layer of synthetic C&D debris, with the resulting leachate serially passed through a 30-cm soil layer containing iron and arsenic and a 30-cm crushed limestone layer. This experiment was conducted for two different soil types (one high in iron (10,400mg/kg) and the second high in iron (5400mg/kg) and arsenic (70mg/kg)); also monitored were control columns for both soil types with water infiltration alone. Despite low iron concentrations in the simulated C&D debris leachate, elevated iron concentrations were observed when leachate passed through the soils; reductive dissolution was concluded to be the cause of iron mobilization. In the soil containing elevated arsenic, increased iron mobilization from the soil was accompanied by a similar but delayed arsenic mobilization. Since arsenic sorbs to oxidized iron soil minerals, reductive dissolution of these minerals results in arsenic mobilization. Crushed limestone significantly reduced iron (to values below the detection limit of 0.01mg/L in most cases); however, arsenic was not removed to any significant extent.

The behavior and long-term fate of metals in simulated landfill bioreactors under aerobic and anaerobic conditions

The long-term behavior and fate of metals in leachate from four simulated bioreactor landfills were explored using lysimeters under both aerobic and anaerobic conditions for a maximum of 1650 days. Metal concentrations varied with time and stage of landfill activity. The behavior of selected metals (Al, As, Cr, Cu, Fe, Pb, and Zn) significantly differed between aerobic and anaerobic conditions. Leachate from the aerobic lysimeters contained greater concentrations of Al, Cu, and Pb compared to leachate derived from the anaerobic lysimeters (average concentrations of Al, Cu and Pb in the aerobic/anaerobic lysimeters were 8.47/0.78 mg/L, 1.61/0.04 mg/L and 0.10/0.03 mg/L, respectively). In the anaerobic lysimeters, As, Fe and Zn leached at greater concentrations (average concentrations of As, Fe and Zn in the aerobic/anaerobic lysimeters were 0.40/1.14 mg/L, 13.5/136 mg/L and 15.3/168 mg/L, respectively). Though no significant difference in overall Cr concentrations was observed in leachate samples from aerobic and anaerobic lysimeters, during the alkali and methane phases approximately 45% of Cr was presented as Cr(VI) under aerobic conditions, whereas no Cr(VI) was detected under anaerobic conditions.

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

Sorting of waste wood is an important process practiced at recycling facilities in order to detect and divert contaminants from recycled wood products. Contaminants of concern include arsenic, chromium and copper found in chemically preserved wood. The objective of this research was to evaluate the sorting efficiencies of both treated and untreated parts of the wood waste stream, and metal (As, Cr and Cu) mass recoveries by the use of automated X-ray fluorescence (XRF) systems. A full-scale system was used for experimentation. This unit consisted of an XRF-detection chamber mounted on the top of a conveyor and a pneumatic slide-way diverter which sorted wood into presumed treated and presumed untreated piles. A randomized block design was used to evaluate the operational conveyance parameters of the system, including wood feed rate and conveyor belt speed. Results indicated that online sorting efficiencies of waste wood by XRF technology were high based on number and weight of pieces (70-87% and 75-92% for treated wood and 66-97% and 68-96% for untreated wood, respectively). These sorting efficiencies achieved mass recovery for metals of 81-99% for As, 75-95% for Cu and 82-99% of Cr. The incorrect sorting of wood was attributed almost equally to deficiencies in the detection and conveyance/diversion systems. Even with its deficiencies, the system was capable of producing a recyclable portion that met residential soil quality levels established for Florida, for an infeed that contained 5% of treated wood.

Application of a CCA-treated wood waste decontamination process to other copper-based preservative-treated wood after disposal

Chromated copper arsenate (CCA)-treated wood was widely used until 2004 for residential and industrial applications. Since 2004, CCA was replaced by alternative copper preservatives such as alkaline copper quaternary (ACQ), copper azole (CA) and micronized copper quaternary (MCQ), for residential applications due to health concerns. Treated wood waste disposal is becoming an issue. Previous studies identified a chemical process for decontaminating CCA-treated wood waste based on sulfuric acid leaching. The potential application of this process to wood treated with the copper-based preservatives (alkaline copper quaternary (ACQ), copper azole (CA) and micronized copper quaternary (MCQ)) is investigated here. Three consecutive leaching steps with 0.1 M sulfuric acid at 75°C for 2 h were successful for all the types of treated wood and achieved more than 98% copper solubilisation. The different acidic leachates produced were successively treated by coagulation using ferric chloride and precipitation (pH=7) using sodium hydroxide. Between 94 and 99% of copper in leachates could be recovered by electrodeposition after 90 min using 2 A electrical current. Thus, the process previously developed for CCA-treated wood waste decontamination could be efficiently applied for CA-, ACQ- or MCQ-treated wood.

Soil arsenic surveys of New Orleans: localized hazards in children's play areas

Arsenic (As) ranks first on the 2005 and 2007 hazardous substances priority lists compiled for the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). This study describes two New Orleans soil As surveys: (1) a survey of composite soil samples from 286 census tracts and (2) a field survey of soil As at 38 play areas associated with the presence of chromated-copper-arsenate (CCA)-treated wood on residential and public properties. The survey of metropolitan New Orleans soils revealed a median As content of 1.5 mg/kg (range <0.2-16.4) and no distinctive differences between the soils of the city core and outlying areas. Play area accessible soils associated with CCA-treated wood (N = 32) had a median As of 57 mg/kg and 78% of the samples were ≥12 mg/kg, the Louisiana soil As standard. The field survey of play areas for CCA-treated wood (N = 132 samples at 38 sites) was conducted with a portable energy-dispersive X-ray fluorescence (XRF) analyzer. Seventy-five of 132 wood samples (56.8%) were deemed CCA-treated wood. Of the 38 play areas surveyed, 14 (36.8%) had CCA-treated wood. A significant association (Fisher's exact p-value = 0.348 × 10(-6)) was found between CCA-treated wood and soil As (N = 75). At one elementary school CCA-treated woodchips (As range 813-1,654 mg As/kg) covered the playgrounds. The situation in New Orleans probably exists in play areas across the nation. These findings support a precautionary program for testing soils and wood for hazardous substances at all play areas intended for children.

Optimization of a chemical leaching process for decontamination of CCA-treated wood

Increasing volumes of discarded Chromated Copper Arsenate (CCA)-treated wood require the development of new treatment and recycling options to avoid the accumulation of wood wastes in landfill sites, resulting in dispersion of contaminants in the environment. The aim of this study is to design an economic chemical leaching process for the extraction of arsenic, chromium and copper from CCA-treated wood. Choice of chemical reagent, reagent concentration, solid-to-liquid ratio, temperature, reaction time and wood particle size are parameters which have been optimized. Sulphuric acid was found to be the cheapest and most effective reagent. Optimum operation conditions are 75 degrees C with 0.2N H(2)SO(4) and 150 g wood L(-1). Under these conditions, three leaching steps lasting 2h each allowed for 99% extraction of arsenic and copper, and 91% extraction of chromium. Furthermore, arsenic concentration in TCLP leachate is reduced by 86% so the environmental hazard is reduced. Decontamination process cost is estimated to 115US$ per ton of treated wood. These results demonstrate the feasibility of chemical remediation and that sulphuric acid leaching is a promising option for CCA-treated wood waste management.

Landfill disposal of CCA-treated wood with construction and demolition (C&D) debris: arsenic, chromium, and copper concentrations in leachate

Although phased out of many residential uses in the United States, the disposal of CCA-treated wood remains a concern because significant quantities have yet to be taken out of service, and it is commonly disposed in landfills. Catastrophic events have also led to the concentrated disposal of CCA-treated wood, often in unlined landfills. The goal of this research was to simulate the complex chemical and biological activity of a construction and demolition (C&D) debris landfill containing a realistic quantity of CCA-treated wood (10% by mass), produce leachate, and then evaluate the arsenic, copper, and chromium concentrations in the leachate as an indication of what may occur in a landfill setting. Copper concentrations were not significantly elevated in the control or experimental simulated landfill setting (alpha = 0.05). However, the concentrations of arsenic and chromium were significantly higher in the experimental simulated landfill leachate compared to the control simulated landfill leachate (alpha = 0.05, p < 0.001). This indicates that disposal of CCA-treated wood with C&D debris can impact leachate quality which, in turn could affect leachate management practices or aquifers below unlined landfills.

Application of the US decision support tool for materials and waste management

The US Environmental Protection Agency (US EPA) launched the Resource Conservation Challenge (RCC) in 2002 to help reduce waste and move towards more sustainable resource consumption. The objective of the RCC is to help communities, industries, and the public think in terms of materials management rather than waste disposal. Reducing cost, finding more efficient and effective strategies to manage municipal waste, and thinking in terms of materials management requires a holistic approach that considers life-cycle environmental tradeoffs. The US EPA's National Risk Management Research Laboratory has led the development of a municipal solid waste decision support tool (MSW-DST). The computer software can be used to calculate life-cycle environmental tradeoffs and full costs of different waste management or materials recovery programs. The environmental methodology is based on the use of life-cycle assessment and the cost methodology is based on the use of full-cost accounting. Life-cycle inventory (LCI) environmental impacts and costs are calculated from the point of collection, handling, transport, treatment, and disposal. For any materials that are recovered for recycling, offsets are calculated to reflect potential emissions savings from use of virgin materials. The use of the MSW-DST provides a standardized format and consistent basis to compare alternatives. This paper provides an illustration of how the MSW-DST can be used by evaluating ten management strategies for a hypothetical medium-sized community to compare the life-cycle environmental and cost tradeoffs. The LCI results from the MSW-DST are then used as inputs into another US EPA tool, the Tool for the reduction and assessment of chemical and other environmental impacts, to convert the LCI results into impact indicators. The goal of this paper is to demonstrate how the MSW-DST can be used to identify and balance multiple criteria (costs and environmental impacts) when evaluating options for materials and waste management. This type of approach is needed in identifying strategies that lead to reduced waste and more sustainable resource consumption. This helps to meet the goals established in the US EPA's Resource Conservation Challenge.