CCA removal from treated wood by chemical, mechanical and microbial processing
C A Clausen, R L Smith
Most preservative-treated wood produced and consumed in the U.S. is treated with toxic inorganic compounds containing copper, chromium, and arsenic. Because chromated copper arsenate (CCA) is fixed to the wood, treated wood has not been considered toxic or hazardous and is currently landfilled. Increasing public concern about environmental contamination from treated wood combined with increasing quantities of CCA-treated wood nearing the end of it's service life has presented a recycling challenge for this fiber source. In this study, CCA-treated wood was processed by acid extraction, steam explosion and bacterial fermentation, and evaluated for removal of copper, chromium and arsenic. Copper was the least resistant to removal by these treatments, while chromium was the most resistant to removal. Grinding CCA wood chips into 20-mesh sawdust provided greater access to CCA components and greater removal of CCA metals by acid extraction and bacterial fermentation. Exposing CCA-treated sawdust to Bacillus licheniformis CC01 resulted in 91%, 15% and 45% removal of Cu (as CuO), Cr (as CrO3), and As (as As2O5), respectively. Eighty-one percent CuO, 62% CrO3, and 89% As2O5 was removed from CCA-treated sawdust by oxalic acid extraction alone. Combining acid extraction and bacterial fermentation resulted in similar rates of metal removal from CCA chips and sawdust; 80% reduction in CrO3, 100% removal of As2O5, 90 and 99% removal of CuO from chips and sawdust, respectively. Processing chips by steam explosion did not enhance removal of CCA components alone or in conjunction with acid extraction and bacterial fermentation. Grinding chips following acid extraction and prior to bacterial fermentation did not enhance the ability of the bacterium to remove metals from treated or steam exploded chips. The combination of acid extraction and bacterial fermentation was successful at removing 80-100 percent of the metals from CCA-treated wood sawdust and chips.