Optimization of growth conditions for maximum hexavalent chromium reduction by the microbial consortium isolated from chromite mines

Abstract

Hexavalent chromium (Cr(VI)) contamination is one of the important threat to the environment. Detoxification of Cr(VI) can be achieved with the use of chromium resistant bacteria. Three chromium resistant organisms were isolated from the soil of chromite mines and identified as Serratia nematodiphila, Bacillus cereus and Bacillus sp. SDIP3 using 16S rRNA sequencing. A consortium was developed with the isolated bacterial strains after the acclimatisation. The effect of environmental factors, such as temperature, pH and nutrient sources were studied for the maximum chromium reduction by the consortium at the Cr(VI) concentration of 25 μg/mL. The reduction of Cr(VI) was optimum at the temperature 35ºC and pH 7. The Cr(VI) reduction was more effective with the glucose as carbon source, inoculum age of 24 h and 4% of inoculum volume. The statistical optimisation of parameters such as pH, temperature and carbon source concentration for the maximum reduction of Cr(VI) was done by Response surface methodology using Box-Behnken design (BBD). The consortium has shown 92% reduction of Cr(VI) under the optimised conditions. This consortium was further used in continuous reactor system to reduce the Cr(VI) to less toxic trivalent chromium.