Tolerance levels of sulfur-oxidizing micro-organisms to Methylene blue and Remazol black B dyes during sewage sludge bioleaching

Abstract

The present study was undertaken to investigate the tolerance levels of indigenous sulfur-oxidizing micro-organisms to Methylene blue (MB), Remazol black B (RBB), and mixture of both the dyes (DM) during bioleaching of heavy metals from sewage sludge. The experiments were performed with anaerobically digested sewage sludge at initial neutral pH of the sludge containing 0–35,000 mg/l of the MB, RBB, and DM. The results show that the bioleaching process was affected by the increase in concentration of MB, which decreased the growth of indigenous sulfur-oxidizing micro-organisms leading to the slow rate of decrease in pH and hence decreased solubilization of metals. Similar effects were observed on the activity of indigenous sulfur-oxidizing micro-organisms using RBB and a mixture (DM) of MB and RBB. The presence of RBB and DM were found to be more toxic as compared to MB at the same initial concentration of the dyes. At initial concentration of 30,000 mg/l, a drastic reduction in pH drop was observed with decreased solubilization of metals, irrespective of any dye. The results of the present study shall be useful to develop a suitable bioleaching process for the sludges contaminated with a variety of dyes.

Keywords:

• Sewage sludge
• Heavy metal
• Leaching
• Acidithiobacillus
• Dyes