In Vitro Evaluation of Bio Reduction of Hexavalent Chrome by Marine Microorganisms Isolated in the Cartagena Bay for Wastewater Treatment

Abstract

Contamination problems by heavy metals and specifically by hexavalent chromium generated by different production processes impact aquifers worldwide and require effective remediation methods for their control. The exploration of microorganisms in saline environments with the capacity to bio reduce hexavalent chromium (????6+) to trivalent chromium (????3+), allows an alternative to the use of biotechnological processes, reducing its toxicity. In the present study, marine microorganisms were isolated from water and sediments, adapted to high concentrations of hexavalent chromium, from 300ppm to 1000ppm with bio reductive potential in wastewater. Bio reduction bioassays were carried out in selective liquid and solid culture media, to which potassium dichromate (K2Cr2O7) was added. Morphological and biochemical identification was carried out with API, preserving colonies. Spectrophotometric validation was developed to evaluate (???? 6+), verifying the bio reduction efficiency in laboratory bioassays with King broth and 300 ppm of potassium dichromate. The different broths were evaluated for enrichment, being the nutritive broth and King the best, showing high turbidity and growth in a short time. Among bacteria isolated from water and sediment, the latter showed rapid growth from 18 to 24 h. Gram positive and negative bacilli (Bacillus subtilis, Bacillus brevis, Bacillus megaterium, Escherichia coli and Citrobacter kosseri) were found at 500/1000 ppm and biochemically characterized. Bio reduction percentages greater than 91% were obtained at 96 h, in concentrations of 300ppm of hexavalent chromium. Thanks to the selective isolation, tolerance and resistance to hexavalent chromium, these microorganisms proved to be bio reductive of this metal. Therefore, the use of these microorganisms on a full scale can be considered as a result for wastewater treatment where hexavalent chromium is used. Likewise, the use of microorganisms used in the bio reduction process is an alternative to Environmental Microbial Biotechnology that will bring benefits by reducing contamination.