Optimization of pH, temperature and carbon source for bioleaching of heavy metals by Aspergillus flavus isolated from contaminated soil

Soil contamination with heavy metal content is a growing concern throughout the world as a result of industrial, mining, agricultural and domestic activities. Fungi are the most common and efficient group of heavy metal resistant microbe family which have potential for metal bioleaching. The use of filamentous fungi in bioleaching of heavy metals from contaminated soil has been developed recently. The current study intends to isolate a strain with the ability to degrade the pH value of the liquid medium. Identification results based on morphological and molecular biological analysis gave a 98% match to Aspergillus flavus. Batch experiments were conducted to select the optimal conditions for bioleaching process which indicated that 130 mg/L sucrose, neutral pH and temperature of 30 degrees C were more suitable during 15-day bioleaching experiments using A. flavus. In one-step bioleaching, the bioleaching efficiencies were 18.16% for Pb, 39.77% for Cd and 58.22% for Zn+2 , while two-step bioleaching showed efficiencies of 16.91% for Pb, 49.66% for Cd and 65.73% for Zn+2. Overall, this study indicates that bioleaching of heavy metals in contaminated soil using A. flavus has the potential for contaminated soil remediation.