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Title: Isolation, Identification, and Characterization of Heavy Metal Reducing Bacteria from Tannery Effluent

Author: Md. Ekhlas uddin

Supervisor: Dr. Md. Nural Anwar

Research Field: Environmental Microbiology

Batch: 11th

Session: 2010-2011


The increasing pollution caused by effluents originated from industries is a growing threat worldwide. Tannery effluent is immensely associated with pollution because of the presence of significant amount of environmental contaminants and heavy metals in it. This study investigated the prevalence of such contaminants or indicators in the effluents of a tannery industry, which was found to possess offensive color, low pH, high biological and chemical oxygen demand, and excessive suspended and dissolved solids. The effluent also contained heavy metals, chromium (Cr), lead (Pb), manganese (Mn), copper (Cu) and cadmium (Cd), as measured by atomic absorption spectrophotometer (AAS). Among these, the amount of Cr and Pb was found considerably high. The study also isolated a total of 14 bacterial strains from tannery effluents, which were capable of degrading or reducing the heavy metals, Cr, Pb, Mn, Cu and Cd. Among them, five strains possessing of striking heavy metal reducing property were identified up to species, namely Aeromonas eucrenophila, Bacillus megaterium, B. carboniphilus, B. licheniformis, and B. subtilis based on their cultural, morphological, physiological and biochemical properties. All the bacterial strains were found remarkably resistant against salt of Cr, Pd, Mn, Cu, and Cd at conc. up to 300 ppm, in cases up to 500 ppm. The organisms were further characterized to explore their preferred dose, time, pH, temperature, and carbon sources in causing the maximum reduction of Cr conc. The rate of Cr reduction was significant up to the conc. of 300 ppm. The maximum reduction was, however, observed at 72h, 30°C, and pH 6 or 7. As carbon source, the organisms preferred dextrose compared to sucrose or soluble starch to yield maximum reduction of Cr. Notably, when the optimized conditions were applied, the organisms’ capability in reducing Cr conc. reached even to 90-100%, in several cases. This study explore that heavy metals present in the tannery effluents can thus be treated to a substantial extent by means of biological treatment system through utilization of naturally occurring potential microorganisms in the effluent.