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Biotechnol Lett (2009) 31:7176 DOI 10.1007/s10529-008-9829-8
ORIGINAL RESEARCH PAPER
Chromate reduction by PVA-alginate immobilized Streptomyces griseus in a bioreactor
Ashwini C. Poopal R. Seeta Laxman
Received: 6 May 2008 / Revised: 7 August 2008 / Accepted: 15 August 2008 / Published online: 6 September 2008 Springer Science+Business Media B.V. 2008
Abstract Microbial reduction of toxic Cr6? to the
less toxic Cr3? is potentially a useful bioremediation process. Among the matrices tested for whole cell immobilization of an efcient chromate-reducing Streptomyces griseus strain, PVA-alginate was the most effective and was used for reduction of Cr(VI) in a bioreactor. Cr6? reduction efciency decreased as Cr6? was increased from 2 to 12 mg l-1 but increased with an increase in biomass concentration. However, increasing the ow rate from 2 to 8 ml h-1
did not signicantly affect Cr6? reduction. The reduction was faster in simulated efuent than in synthetic medium and complete removal of 8 mg Cr6? l-1 from efuent and synthetic medium occurred in 2 and 12 h, respectively. Our results indicate that immobilized S. griseus cells could be applied for the large-scale bioremediation of chro-mate-containing efuents and wastewaters.
Keywords Bioremediation Chromate reduction
Immobilized cells Polyvinyl alcohol-alginate
Streptomyces griseus
Introduction
Hexavalent chromium generated from several industrial processes is discharged in to rivers/streams and is toxic and mutagenic to most organisms. Chemical remediation processes are either inefcient or suffer from high capital and operating costs. The use of biological methods to remediate metal contaminated wastewaters is an emerging eld and biotransformation of hexavalent chromium (Cr6?) to the non-toxic trivalent form (Cr3?) therefore offers a viable alternative. The potential of several bacterial strains to detoxify chromate has been described with a view of developing processes for microbiological detoxication of polluted waters. Most of the previous studies on biological reduction of Cr6? were conducted in batch reactors. The development of bioreactors consisting of a bed of chromate reducing bacteria immobilized to an inert support is considered as an economical, effective, safe and sustainable procedure for chromate detoxication (Ganguli and Tripathi 2002). Bioreactors with immobilized microorganisms are being increasingly used for wastewater treatment achieving high performance and stability due to high cell densities, absence of cell washout, and extended biochemical or bio-transformation reaction time. Various bioreactors, such as continuous stirred tank...