REMOVAL OF CCA FROM TREATED WOOD BY OXALIC-ACID EXTRACTION, STEAM EXPLOSION, AND BACTERIAL FERMENTATION

Most preservative-treated wood produced and consumed in the United Sta tes is treated with toxic inorganic compounds containing copper, chrom ium, and arsenic. Because chromated copper arsenate (CCA) is fixed to the wood, CCA-treated wood has not been considered toxic or hazardous and it is currently disposed of in approved landfills, Growing public concern about environmental contamination from treated wood combined w ith the removal of greater quantities of CCA-treated wood from service have presented a disposal challenge for this fiber source, In this st udy, CCA-treated wood was processed by acid extraction, steam explosio n, and bacterial fermentation and evaluated for removal of copper, chr omium, and arsenic, Copper was the easiest to remove by these treatmen ts and chromium the most resistant to removal, Exposing CCA-treated wo od to steady-state bacterial growth by continuous culture with Bacillu s licheniformis CC01 did not enhance removal of CCA components compare d to standard mixed culture when acid extraction preceded bacterial fe rmentation. Nor did steam explosion, alone or in conjunction with acid extraction and bacterial fermentation, enhance removal of CCA compone nts; the chromium and arsenic components resisted removal. Grinding CC A-treated wood chips into 20-mesh sawdust provided greater access to a nd removal of CCA components by all processes, However, grinding the c hips was unnecessary if they were treated with acid prior to bacterial fermentation, Extraction with oxalic acid as a precursor to bacterial fermentation with B, licheniformis CC01 removed 90% copper (CuO), 80% chromium (CrO3), and 100% arsenic (As2O5) from treated chips. The com bination of acid extraction and bacterial fermentation removed 80-100% of these metals from CCA-treated wood.