Bioleaching of heavy metals from preservative-treated wood using Aspergillus tubingensis

Although fungal bioleaching with Aspergillus niger has been investigated to remove metal from treated wood wastes, toxicological concerns limit the practical use of the species, necessitating the search for non-toxic species with comparable or greater metal removal efficiency. The removal of metals from wood treated with chromated copper arsenate (CCA) and copper amine-based preservatives was investigated using the non-ochratoxigenic mold Aspergillus tubingensis in comparison to A. niger via bioleaching. Metals were bioleached for 10 days by immersing treated wood sawdust in fungal culture filtrates. Culture filtrates were prepared by growing fungi in malt extract (ME) and sucrose media and then filtering the fungal biomass. Oxalic acid and citric acid were the predominant organic acids in A. tubingensis culture filtrate in ME and sucrose media, respectively. Citric acid present in sucrose media was found to be a more effective leaching agent for metals from preservative-treated wood. Citric acid produced by A. tubingensis and A. niger in sucrose media removed nearly 95% of copper, 80%-85% of chromium, and arsenic from CCA-treated wood, and 80%-90% of copper from wood treated with copper amine-based preservatives. As a result of its non-toxigenic characteristics and high metal removal efficiency, A. tubingensis may be a useful fungus for bioleaching metal components from inorganic preservative-treated wood.