Removal of copper, chromium, and arsenic from CCA-treated wood by organic acids released by mold and staining fungi

This study evaluated the potential of mold and staining fungi, Aspergillus niger, Aureobasidium pullulans, Gliocladium virens, Penicillium funiculosum, Rhizopus javanicus, Ceratocystis pilifera, C. peceae, Alternaria alternata, Trichoderma viride, and Cladosporium herbarum, to remove copper, chromium, and arsenic elements from chromated copper arsenate (CCA) treated wood. As a first step, the fungi were cultivated in a mixture of glucose, sucrose, and malt extract to produce oxalic acid. This study only evaluated the amount of oxalic acid produced by the fungi; however, the fungi may have the ability to secrete other organic acids during their cultivation. Bioremediation of CCA-treated sawdust samples passed through a U.S. standard 40-mesh screen (420 μm) was then carried out through leaching of heavy metals with oxalic acid, which occurred during the first step. Oxalic acid production by A. niger and R. javanicus was higher than for the other fungi and reached 4.6 and 3.5 g/L after a 10-day fermentation process. All mold and staining fungi caused more than 70 percent copper removal; however, chromium removal rates varied from 20 to 50 percent. Arsenic removal showed variations among the mold and staining fungi from 30 to 90 percent. These results suggest that fungal remediation processes can remove inorganic metal compounds via organic acid production, increasing the acidity of the substrate and increasing the solubility of the metals.