Role of Iron-Oxidizing Microorganism in Bioleaching of Heavy Metals From Sewage Sludge Contaminated with Textile Dyes

Abstract

This article reports the role of indigenous iron-oxidizing microorganisms in bioleaching of heavy metals from anaerobically digested sewage sludge in presence of toxic dyes namely, methylene blue (MB), Remazol black B (RBB) and mixture of both the dyes (DM). To achieve this goal, different concentrations of dyes (0, 500, 10,000, 15,000 and 25,000 mg/L) were added to the sewage sludge (initial pH ∼ 7) and subsequently, the solubilization of heavy metals (Cu, Ni, Zn and Cr) was measured at time intervals of 48 h for 16 days. The results showed that an increase in dye concentration adversely affected the population of indigenous iron-oxidizing microorganisms, thereby decreased the bioleaching of metals. The metal solubilization from sludge is more adversely affected in presence of RBB and DM than MB. In majority of cases, the maximum metal solubilization was recorded at dye concentration of 5,000 mg/L. Two factor analyses (ANOVA) suggests the impact of both factors: dye concentration and dye type on metal leaching rate in sludge system.

Keywords:

• Acidithiobacillus
• dyes
• heavy metal
• leaching
• sewage sludge