Potential of newly isolated bacterial strains for simultaneous removal of hexavalent chromium and reactive black-5 azo dye from tannery effluent

BACKGROUND Effluents discharged from tannery industry contain significant amount of chromium and synthetic dyes. Both chromium and dyes can be transformed individually into less toxic forms, but very little is known about their simultaneous treatment. The present study was aimed at isolating bacteria capable of removing toxic hexavalent chromium (CrVI) and reactive black‐5 azo dye simultaneously in liquid mineral salt medium (MSM). RESULTS About 150 bacterial isolates were collected from tannery wastewater and sludge through enrichment of the MSM with CrVI (2 mg L−1) and reactive black‐5 dye (100 mg L−1) under static (batch) condition. Bacterial strains KI (Pseudomonas putida ) and SL14 (Serratia proteamaculans) were able to reduce simultaneously 93% CrVI and 100% color of reactive black‐5 azo dye in 24 h at pH 7.2 and 35 °C in a batch culture. Individually, 100% reduction of CrVI and reactive black‐5 dye was achieved in 12 h by strain KI and SL14. CONCLUSION These bacterial strains are one of the most efficient bacteria capable of reducing toxic CrVI and synthetic reactive dye simultaneously and could be used for developing bioreactors to treat tannery effluent prior to its discharge into the environment. © 2012 Society of Chemical Industry