An Acid-Tolerant Heterotrophic Microorganism Role in Improving Tannery Sludge Bioleaching Conducted in Successive Multibatch Reaction Systems

The bioleaching technique with Acidithiobacillus species has been shown to be an efficient and cost-effective means in removing heavy metals from tannery sludge. However, tannery sludge dissolved organic matter (DOM) is toxic to Acidithiobacillus species and results in decreasing the efficiency of Cr removal from sludge. Here we report the role of an acid-tolerant DOM-degrading heterotrophic microorganism P. spartinae D13 successfully isolated from local tannery sludge in improving activities of A. ferrooxidans LX5 and A. thiooxidans TS6. In tannery sludge DOM-rich liquid culture medium coinoculated with P. spartinae D13 and Acidithiobacillus species, the activities of A. ferrooxidans LX5 and A. thiooxidans TS6 are increased by 33- and 12-fold, respectively. In four successive batches of tannery sludge bioleaching trials by circulating 10% of acidified bioleached sludge, the addition of Pichia spartinae D13 could shorten bioleaching time by 3 days in the first batch and obtained more than 90% of Cr removal efficiency within 6 days. However, the effectiveness of P. spartinae D13 in improving bioleaching maintain only four successive recycle or batches until P. spartinae D13 inoculum is replenished in the fifth batches. Therefore, for enhancing the activity of Acidithiobacillus species in bioleaching system, P. spartinae D13 should be added periodically at a given batch interval.