Total recycling of CCA treated wood waste by low-temperature pyrolysis

A system to turn a potentially harmful stream of solid waste into a set of substreams with either commercial value or highly concentrated residual streams is presented. The waste which is considered is metal impregnated (in particular Chromated Copper Arsenate (CCA) treated) wood waste and timber, such as telephone poles, railway sleepers, timber from landscape and cooling towers, wooden silos, hop-poles, cable drums and wooden playground equipment. These waste streams sum up to several 100,000 tons of material per year currently to be dumped in every major country of the European Community (EC). Technologies need to be developed to reduce this CCA treated wood waste, such that all of the metals are contained in a marketable product stream, and the pyrolysis gases and/or pyrolysis liquid are used to their maximum potential with respect to energy recuperation. Pyrolysing the CCA treated wood waste may be a good solution to the growing disposal problem since low temperatures and no oxidising agents are used, which result in lower loss of metals compared to combustion. An experimental labscale pyrolysis system has been developed to study the influence of the pyrolysis temperature and the duration of the pyrolysis process on the release of metals and the mass reduction. The macrodistribution and microdistribution of the metals in the solid pyrolysis residue is studied using Inductively Coupled Plasma Mass Spectrometry (ICP–MS) and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Analysis (SEM–EDXA). Furthermore, a complete mass balance is calculated over the pyrolysis system. Based on these results a semi-industrial pyrolysis system (pilot plant scale) has been developed consisting of three stages: grinding, packed bed pyrolysis and metal separation. Special types of equipment have been developed to carry out the three stages. A new grinding system has been developed, based on a crushing mechanism rather than a cutting mechanism. The crushed wood is introduced by means of a screw feeding system into a reaction column. In this pyrolysis reactor the wood is heated by subjecting it to a flow of hot gases. This causes an adiabatic pyrolysis, which results in volatilisation of the volatile compounds whereas the mineral compounds (containing the metals) remain entrapped in a coal-type residue which is very rich in carbon. The condensable compounds in the pyrolysis gas condense while leaving the reaction zone due to the inverse temperature gradient. The pyrolysis gas leaving the reactor is used as fuel for the hot gas generator. The charcoal which is extracted at the bottom of the reactor, is cooled, compressed, removed and stored, ready to feed the subsequent stage. A specially developed grinder is used to remove the metal particles from the charcoal and the separation between metal and charcoal particles is accomplished in a pneumatic centrifuge as a result of the difference in density. Using this system the ultimate waste is less than 3% of the initial wood mass. Results obtained with a semi-industrial scale prototype confirm the effectiveness of the process.     

Leaching of heavy metals from chromated copper arsenate (CCA) treated wood after disposal

Wood treated by preservatives is commonly found in solid waste. Among the different types of preserved wood, chromated copper arsenate (CCA) treated wood recently has received much attention due to the scale of usage and its significant role in soil and water contamination. As the ash of CCA treated wood would be hazardous if the wood were to be incinerated, this is not a good alternative, and the best available disposal method is thus landfilling in the US, Canada and Australia. Leaching of the metals from preserved wood that is disposed in unlined landfills for construction debris pollutes the soil and water environments. Several factors affecting leaching of the metals from wood, including pH of the leachant, temperature, the duration of leaching and the type of leachant, were investigated. These factors affect each of the metals, chromium, copper and arsenic, differently. A comparison of these effects on each metal was performed. The results of the experiments showed that the pH of the leachants has a significant effect on the leaching process, and sulfuric acid (pH 3) is the most effective leachant compared to nitric and acetic acid (pH 3-4-5). The amounts of leached chromium, copper and arsenic by sulfuric acid (pH 3) during 15 days were, respectively, 0.2, 0.14 and 0.15 mg more than leachates by nitric acid (pH 5) on the basis of 1g of wood (initial contents of 1.03 mg, 0.42 g and 0.8 mg per g of wood). Most of the leaching occurs in the first 5 days, and the rate of leaching decreases significantly after 5 days. Increasing temperature increases the amount of leached metals, and arsenic is the least resistant metal to the leaching when the temperature increases. Increasing the temperature from 15 degrees C to 35 degrees C during 15 days increases the amount of leached chromium, copper and arsenic by acetic acid at pH 5 by about 0.1, 0.4 and 1.2mg per g of wood, respectively.     

Fungicidal value of wood tar from pyrolysis of treated wood

The objective of the paper was to estimate the fungicidal value of wood tar extracted as a product of pyrolysis of wood previously treated with either creosote oil or CCB-type salt preservative. The effectiveness of wood treated with one of these two wood tar residuals was compared to the effectiveness of wood treated with virgin creosote oil (type WEI-B) and an untreated control. Wood was impregnated with alcohol solutions of the two extracted preservatives or virgin creosote oil and then subjected to the Coniophora puteana, Poria placenta and Coriolus versicolor fungi. The fungicidal values of the investigated preservatives were determined with the use of the short agar-block method and the aging test according to the standard EN 84. It was found that wood tar extracted by pyrolysis of old creosote-treated wood and then used to treat wood may have potential as a preservative for wood protection or as a component of preservatives.     

Removal of copper,chromium, and arsenic from CCA-C treated wood by EDTA extraction

Ethylenediaminetetracetic acid (EDTA) is one of the most common chelators used to bind the metal ions in extremely stable complexes in heavy metal contaminated soils and thus to remediate such substrates. EDTA forms water soluble complexes with many metal ions and it is used to release the various metals. In this study, EDTA extraction of copper, chromium, and arsenic from chromated copper arsenate (CCA-C) treated wood was evaluated using batch leaching experiments. CCA-treated wood samples were extracted with eight different concentrations of EDTA for 4, 8, 18, and 24 h at room temperature. Exposing CCA-treated chips and sawdust to EDTA extraction enhanced removal of CCA components compared with extraction by deionized water. Grinding CCA-treated wood chips into 40-mesh sawdust provided greater access to and removal of CCA components. Extraction with 1% EDTA solution for 24 h removed 60% copper, 13% chromium, and 25% arsenic from treated chips. EDTA extraction of treated sawdust samples resulted in 93% copper, 36% chromium, and 38% arsenic removal. CCA leaching from treated wood blocks was also evaluated according to modified AWPA E11-99 standard test method of determining the leachability of wood preservatives. Leaching of CCA components from treated wood blocks with 1% EDTA solution for 14 days caused more copper leaching compared to leaching with deionized water. Leaching with 1% EDTA for 14 days removed 53% copper from the blocks whereas 14% copper was leached from the blocks with deionized water. The results suggest that EDTA extraction removes significant quantities of copper from CCA-treated wood. Thus, EDTA could be important in the remediation of wood waste treated with the newest formulations of organometalic copper compounds and other water-borne wood preservatives containing copper.     

聚合物驱采油污水稳定性的影响因素

研究了聚合物质量浓度、分子量及原油族组分对模拟含油污水油水界面性质的影响。实验结果表明：聚合物驱采油污水的稳定性不但与聚合物含量、分子量有关,还与原油中沥青质、胶质的含量有关;随着含油污水中阴离子型聚丙烯酰胺（APAM）质量浓度的增加,油水界面张力逐渐下降,Zeta电位绝对值和油水界面剪切黏度逐渐上升;APAM分子量越小,油水界面张力降低的程度越大;随剪切速率的增加,油水界面剪切黏度均逐渐降低;当剪切速率小于0.30 s-1时,4种原油族组分对污水稳定性影响的大小顺序为沥青质>胶质>芳香分>饱和分;随沥青质、胶质含量的增加,油水界面张力明显降低,Zeta电位的绝对值显著增大。     

Exergy analysis of the Chartherm process for energy valorization and material recuperation of chromated copper arsenate (CCA) treated wood waste

The Chartherm process (Thermya, Bordeaux, France) is a thermochemical conversion process to treat chromated copper arsenate (CCA) impregnated wood waste. The process aims at maximum energy valorization and material recuperation by combining the principles of low-temperature slow pyrolysis and distillation in a smart way. The main objective of the exergy analysis presented in this paper is to find the critical points in the Chartherm process where it is necessary to apply some measures in order to reduce exergy consumption and to make energy use more economic and efficient. It is found that the process efficiency can be increased with 2.3-4.2% by using the heat lost by the reactor, implementing a combined heat and power (CHP) system, or recuperating the waste heat from the exhaust gases to preheat the product gas. Furthermore, a comparison between the exergetic performances of a ‘chartherisation’ reactor and an idealized gasification reactor shows that both reactors destroy about the same amount of exergy (i.e. 3500 kW kg_wood⁻¹) during thermochemical conversion of CCA-treated wood. However, the Chartherm process possesses additional capabilities with respect to arsenic and tar treatment, as well as the extra benefit of recuperating materials.     

次氯酸钠废液活化法制备柚子皮活性炭

以柚子皮为原料,采用次氯酸钠废液活化法制备了柚子皮活性炭,通过正交实验优化了制备条件,并运用SEM、FTIR和XRD技术对活性炭产品进行了表征。实验结果表明:制备柚子皮活性炭的最佳工艺条件为炭化温度350℃、次氯酸钠废液含量25%(φ)、次氯酸钠废液活化时间25 min、高温活化温度650℃、高温活化时间60 min;最佳条件下,柚子皮活性炭的产率为31.88%、碘吸附值为854 mg/g、亚甲基蓝吸附值为216.9 mg/g。表征结果显示:活化后的柚子皮炭具有更大的孔体积、更有序的孔径排布和更发达的孔隙结构;柚子皮活性炭表面存在大量的含氧基团;柚子皮活性炭的石墨化度为61.32%,具有较高的稳定性。     

Method to recover and reuse chromated copper arsenate wood preservative from spent treated wood

The volume of chromated copper arsenate (CCA) treated wood products coming out of service is expected to increase dramatically during the next decade. There is a need for an alternative waste management approach to landfilling. This paper investigates the variables affecting extraction of CCA components from wood particles and the potential to oxidize and reuse the recovered chemicals. Most of the CCA components could be extracted by 10% H2O2 at 50 degrees C in 6 h with an average extraction efficiency of 95% for Cr, 94% for Cu and 98% for As. The extract containing Cr(III), Cu(II) and As(V) could be oxidized in several stages by aqueous 2.5% w/w H2O2 in less than 2 h to a condition where it was compatible with CCA treating solutions and could be reused for treating new wood. When the recovered extract was mixed with fresh CCA solution in different ratios, the mixed CCA-C solutions had similar solution stability as freshly prepared CCA-C solution and treated wood had similar leaching properties as wood treated with fresh solution.     

Factors affecting TCLP lead leachability from computer CPUs

The factors impacting lead leachability from computer central processing units (CPUs) during the toxicity characteristic leaching procedure (TCLP) were investigated. Several CPUs were disassembled and their component materials were decreased in size to meet the requirements of the TCLP. The impact of CPU composition was examined by leaching different combinations of the CPU components. The ferrous metal content of the mixture greatly impacted lead leaching. TCLP lead concentrations of CPUs predicted by leaching the lead-bearing printed wire boards alone were much greater than those measured when the ferrous metal of the CPU was included in the mixture. The leaching of iron and zinc from the galvanized steel components of the CPU created electrochemical conditions where lead was less soluble. Additional size reduction beyond that required by the TCLP did not result in additional lead leaching. As the volume of head space above the leaching solution increased, the concentration of lead measured increased as well.     

Conversion of CCA-treated wood to ethanol: a method to reduce leaching of metals from disposed treated wood prior to disposal

The objective of this paper is to evaluate the feasibility of producing ethanol from CCA-treated wood that is highly leachable. Following the initial tests, CCA-treated wood was hydrolysed and fermented and the results showed not only that ethanol was produced during the fermentation process but that metals were taken up by the yeast. Toxicity characteristic leaching procedure tests of the hydrolysed wood leached less than 4 mg/L of As while minimal amounts of Cr and Cu remained in the hydrolysed wood which makes landfilling of hydrolysed wood acceptable and less hazardous. A slightly lower amount of ethanol from CCA-treated than untreated wood was produced (6 and 7 g/L, respectively). In general, it suggests that production of ethanol as a source of energy from a hazardous waste (CCA-treated wood) is feasible.     

Evaluation of commercial landscaping mulch for possible contamination from CCA

Wood treated with chromated copper arsenate (CCA) is found in construction and demolition (C&D) debris, and a common use for wood recycled from C&D debris is the production of mulch. Given the high metals concentrations in CCA-treated wood, a small fraction of CCA-treated wood can increase the metal concentrations in the mulch above regulatory thresholds. The objective of this study was to determine the extent of contamination of CCA-treated wood in consumer landscaping mulch and to determine whether visual methods or rapid X-ray fluorescence (XRF) technology can be used to identify suspect mulch. Samples were collected throughout the State of Florida (USA) and evaluated both visually and chemically. Visual analysis focused on documenting wood-chip size distribution, whether the samples were artificially colored, and whether they contained plywood chips which is an indication that the sample was, in part, made from recycled C&D wood. Chemical analysis included measurements of total recoverable metals, leachable metals as per the standardized synthetic precipitation leaching procedure (SPLP), and XRF analysis. Visual identification methods, such as colorant addition or presence of plywood, were found effective to preliminarily screen suspect mulch. XRF analysis was found to be effective for identifying mulch containing higher than 75 mg/kg arsenic. For mulch samples that were not colored and did not contain evidence of C&D wood, none exceeded leachable metal concentrations of 50 microg/L and only 3% exceeded 10 mg/kg for recoverable metals. The majority of the colored mulch made from recycled C&D wood contained from 1% to 5% CCA-treated wood (15% maximum fraction) resulting in leachable metals in excess of 50 microg/L and total recoverable metals in excess of 10 mg/kg. The maximum arsenic concentration measured in the mulch samples evaluated was 230 mg/kg, which was above the Florida residential direct exposure regulatory guideline of 2.1 mg/kg.     

Concentrations of organic wood preservatives in wood chips produced from wood wastes

We investigated the concentrations of wood preservatives in the wood chips produced in wood-waste processing facilities in 1988, 1998–1999, and 2001–2002. Among the wood preservatives used in the past in Japan, halophenols, including PCP, chlordane, and chlorpyrifos, had comparatively high detection rates and high average concentrations in the wood chips produced in 2001–2002. Aldrin and endrin were rarely detected, and DDT was already in low concentrations in those wood chips. Although several types of wood preservative were contained in the wood chips, their concentration levels depended on the sources of the wood wastes. In chips produced from wooden pallets, wooden forms for concrete working, or wood discarded from nondemolition sources, no organochlorine wood preservatives were detected, and chlorpyrifos and chlorophenols were detected at one order of magnitude lower than the average concentrations in chips produced from wood wastes discarded in house demolitions.     

次氯酸钠氧化—磷酸铵镁沉淀法处理草甘膦废水并回收磷

针对草甘膦废水处理与磷回收难题,研究了次氯酸钠氧化草甘膦与磷酸铵镁沉淀法回收磷工艺的可行性。实验结果表明,次氯酸钠氧化草甘膦的最佳工艺条件为:次氯酸钠加入量109 g/L,溶液pH为9.0,氧化时间20 min。次氯酸钠氧化草甘膦的主要降解途径为:C—N键断裂生成羟基乙酸和乙酸;C—P键断裂生成磷酸(主要反应)。正交实验得到的磷酸铵镁沉淀法回收磷的最佳工艺条件为溶液pH 9.0、镁磷摩尔比1.2、氮磷摩尔比1.4、反应时间15 min,在此条件下磷酸盐回收率达99.3%。XRD图谱证实所得固体主要成分为磷酸铵镁。     

微波辐照修复氯丹污染土壤的影响因素

采用微波辐照技术修复氯丹污染土壤,以氯丹的挥发率和分解率为主要评价指标,研究了微波辐照条件对土壤修复效果的影响。实验结果表明:氯丹的挥发率随微波辐照功率的增大而增大,而氯丹的分解率则无明显变化;当活性炭与土壤质量比为9∶120时,氯丹的去除效果最好,去除率达89%;氯丹的挥发性能在前20min内随微波辐照时间的延长而增强,而氯丹的分解性能则刚好相反;当土壤含水率为15%时,氯丹的挥发率最高,为2.5%,而氯丹分解率最小,为16.8%;在酸性偏中性范围内氯丹的去除效果较差,随土壤p H的不断增大,氯丹的挥发率明显升高,且氯丹的分解率也增大。     

内酯型槐糖脂修复石油污染土壤的影响因素

采用内酯型槐糖脂(SL50)修复石油污染土壤。通过单因子实验与正交实验,考察了槐糖脂溶液质量浓度、振荡时间、反应体系初始pH、NaCl加入量以及固液比(土壤质量与表面活性剂溶液体积之比)对污染土壤石油烃洗脱率的影响。单因子模型回归分析结果表明,参数变量均符合二次拟合模型,槐糖脂溶液质量浓度、反应体系初始pH以及NaCl加入量的二次模型拟合效果较好。正交实验结果表明,槐糖脂溶液质量浓度和反应体系初始pH是该实验的敏感性因子,最优洗脱条件为槐糖脂溶液质量浓度40 mg/L、反应体系初始pH 9、NaCl加入量6%(w)。     

锑污染土壤固化-稳定化的影响因素

通过比较不同稳定剂、固化剂、土壤pH条件下土壤中重金属锑的修复效果,研究了锑的固化-稳定化影响因素并探讨了相关稳定化机理.实验结果表明:铁基稳定剂的效果明显优于磷酸二氢钾和腐殖酸钠,而零价铁的稳定化效果更优于硫酸铁和硫酸亚铁,较适宜的稳定剂投加量为5％(w);水泥做固化剂对锑的稳定化效果优于氧化钙,最佳投加量为5％(w...     

Solvent extraction and soil washing treatment of contaminated soils from wood preserving sites: Bench‐scale studies

Bench‐scale solvent extraction and soil washing studies were performed on soil samples obtained from three abandoned wood preserving sites included in the National Priority List. The soil samples from these sites were contaminated with high levels of polyaromatic hydrocarbons (PAHs), pentachlorophenol (PCP), dioxins, and heavy metals. The effectiveness of the solvent extraction process was assessed using liquefied propane or dimethyl ether as solvents over a range of operating conditions. These studies have demonstrated that a two‐stage solvent extraction process using dimethyl ether as a solvent at a ratio of 1.61 per kg of soil could decrease dioxin levels in the soil by 93.0 to 98.9 percent, and PCP levels by 95.1 percent. Reduction percentages for benzo(a)pyrene (BaP) potency estimate and total detected PAHs were 82.4 and 98.6 percent, respectively. Metals concentrations were not reduced by the solvent extraction treatment. These removal levels could be significantly improved using a multistage extraction system. Commercial scale solvent extraction using liquefied gases costs about $220 per ton of contaminated soil. However, field application of this technology at the United Creosote site, Conroe, Texas, failed to perform to the level observed at bench scale due to the excessive foaming and air emission problem. Soil washing using surfactant solution and wet screening treatability studies were also performed on the soil samples in order to assess remediation strategies for sites. Although aqueous phase solubility of contaminants seemed to be the most important factor affecting removal of contaminants from soil, surfactant solutions (3 percent by weight) having nonionic surfactants with hydrophile‐lipophile balance (HLB) of about 14 (Makon‐12 and Igepal CA 720) reduced the PAH levels by an average of 71 percent, compared to no measurable change when pure deionized water was used. Large fractioza of clay and silt (<0.06mm), high le!ezielsof orgaizic contami‐ nants and hzimic acid can makesoil washing less applicable.     

次氯酸钾氧化去除烟气中单质汞的反应机理

采用KClO氧化吸收烟气中的Hg⁰,研究了脱汞性能和反应机理。结果表明：提高反应温度会降低脱汞性能,加快KClO热分解,减小Hg⁰溶解度,抑制氧化还原放热反应;提高Hg⁰浓度会增大Hg⁰在气相主体和气液界面的分压差,进而提高Hg⁰的传质速率,使Hg⁰去除率提高;继续提高Hg⁰浓度,反应限速步骤从气膜移向液膜,使Hg⁰去除率下降;KClO质量分数低于10%时,Hg⁰和KClO溶液的气液两相传质效率由液相控制;Hg⁰去除率随吸收液初始pH的升高而降低,吸收液pH随反应时间的延长而升高。     

Factors affecting degradation of polyethylene terephthalate (PET) during pre-flotation conditioning

In general, plastics are exposed to different degrading agents in every procedure involved in their recovery from waste mixture and from subsequent recycling. In this study, two methods of pre-flotation conditioning were used to determine how these methods affect the general properties of the pre-conditioned PET particles to be recovered from the PET-PVC mixture. The first method comprised the conditioning of PET samples using an alkaline solution of nonionic surfactant (Triton X-100) based on the patent by the Goodyear Tire and Rubber Company. The second method, developed in this study, was a conditioning process which used an alkali-less solution of the same nonionic surfactant (Triton X-100) used in the first method. The following analytical methods were used to characterize properties of the pre-conditioned PET samples that were correlated to relative degradation of the samples: differential scanning calorimetry (DSC), for thermal behavior of the samples; FT-IR spectroscopy, for functional groups present in the samples; and, Pohl’s method, for carboxyl end-group concentration count. Results show that in addition to water the presence of NaOH in the conditioning solution contributes to the further degradation of the polymer.