Tomo Kakitani

Bioremediation of CCA-treated wood by brown-rot fungi Fomitopsis palustris, Coniophora puteana, and Laetiporus sulphureus

This study evaluated oxalic acid accumulation and bioremediation of chromated copper arsenate (CCA)-treated wood by three brown-rot fungi Fomitopsis palustris, Coniophora puteana, and Laetiporus sulphureus. The fungi were first cultivated in a fermentation broth to accumulate oxalic acid. Bioremediation of CCA-treated wood was then carried out by leaching of heavy metals with oxalic acid over a 10-day fermentation period. Higher amounts of oxalic acid were produced by F. palustris and L. sulphureus compared with C. puteana. After 10-day fermentation, oxalic acid accumulation reached 4.2 g/l and 3.2 g/l for these fungi, respectively. Fomitopsis palustris and L. sulphureus exposed to CCA-treated sawdust for 10 days showed a decrease in arsenic of 100% and 85%, respectively; however, C. puteana remediation removed only 18% arsenic from CCA-treated sawdust. Likewise, chromium removal in F. palustris and L. sulphureus remediation processes was higher than those for C. puteana. This was attributed to low oxalic acid accumulation. These results suggest that F. palustris and L. sulphureus remediation processes can remove inorganic metal compounds via oxalic acid production by increasing the acidity of the substrate and increasing the solubility of the metals.

Electron microscopic study on pyrolysis of CCA (chromium, copper and arsenic oxide)-treated wood

The effectiveness of pyrolysis as a possible technique for disposing of CCA (chromium, copper and arsenic oxide)-treated wood was studied. A CCA-treated sample given an extra heat treatment at 450 degreesC for 10 min was thoroughly investigated in order to establish the details of the reaction in which arsenic is captured in the pyrolysis residue prior to volatilization. Composition and structure of the metal compounds in the pyrolysis residue were examined by transmission electron microscopy (TEM). A large number of particles were found of variable diameter between 10 and 100 nm. The smaller ones were mostly spherical, sometimes faceted. The larger ones were lumpy. CCA compounds and their reaction products like Cr2As4O12 and As2O3 were identified in conventional TEM by selected area electron diffraction. In high resolution, the nanoparticles exhibited lattice fringes as indication of their monocrystalline character, fitting, e.g., the d(210) = 0.204 nm of Cr. The volatility of arsenic during pyrolysis of CCA-treated wood was measured by XRF (X-ray fluorescence) analysis at temperatures up to 500 degreesC and at times up to I h. Weight change and arsenic content of the pyrolysis residue were measured after dissolution in HNO3. More than 20% of arsenic was already lost at 300 degreesC, which may have been caused mainly by the volatilization of the unreacted arsenic compound after reduction of As(V) in As2O5 to As(III) in As2O3. Arsenic is probably released as As4O6, which is very difficult to capture and toxic. By an additional heat treatment, this reduction can be prevented and the dry separation of the metals may be allowed

Characteristics of a bioxalate chelating extraction process for removal of chromium, copper and arsenic from treated wood

The disposal of wood waste treated with chromated copper arsenate (CCA) is a problem in many countries. We have proposed a novel chelating extraction technique for CCA-treated wood using bioxalate, a solution of oxalic acid containing sufficient sodium hydroxide to adjust the pH to 3.2, which is an effective way to obtain an extraction efficiency of 90% for chromium, copper, and arsenic. The purpose of the present study was to investigate the characteristics of bioxalate extraction of CCA-treated wood. Extractions of CCA-treated western hemlock chips with solutions of bioxalate, oxalic acid, and sodium hydroxide were carried out. The use of bioxalate was confirmed as the most effective extraction technique for chromium, copper and arsenic, with an efficiency of 90%. Extraction with simple oxalic acid was ineffective for copper (less than 40% extraction efficiency), but effective for chromium and arsenic, with 90% efficiency. Sodium hydroxide showed a similar tendency, being ineffective for chromium and copper (less than 20% extraction efficiency), but relatively effective for arsenic (around 70-80% efficiency). We also discovered an interesting phenomenon whereby the addition of sodium hydroxide to a simple oxalic acid solution during the oxalic acid extraction progress resulted in dramatically increased extraction efficiency for copper, chromium and arsenic, up to 90%. Although oxalic acid was ineffective for copper extraction, the addition of sodium hydroxide during the oxalic acid extraction process rendered it effective.

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.