Bioremediation of hexavalent chromium by an indigenous bacterium Bacillus cereus S10C1: optimization study using two level full factorial experimental design

The present study is focussed on chromium removal by indigenous chromium-resistant microorganisms isolated from soil and sludge samples of an industrial site. The optimal bioremediation conditions, namely temperature, hexavalent chromium (Cr(VI)) initial concentration, pH and time were determined by using a full factorial design at two levels. The results showed that from the 54 bacterial strains, S10C1 identified as Bacillus cereus 4080 LBK (NCBI:txid1396) was the most efficient strain in removing Cr(VI). The analysis of variance (ANOVA) results indicated that pH, Cr(VI) initial concentration, time and the interaction terms (T°–pH), (T°–time) and (Cr(VI) initial concentration–pH), have a significant influence on Cr(VI) removal yield. Moreover, the prescribed first-order regression model fitted well to the experimental data with a high coefficient of determination ( R 2 = 0 . 969 ). According to the response optimizer of Design-Expert software, the optimum conditions for chromium biodegradation were: a pH of 3, a temperature of 55 °C, a Cr(VI) initial concentration of 0.5 mM and a contact time of 20 hours. Under these conditions the experimental Cr(VI) removal percentage was found to be about 92.9% which is close to the predicted value by the statistical design (94.4%).