Manganese (II) Removal from Aqueous Solutions by Bacillus cereus: an Optimization Study Using Experimental Design and Response Surface Methodology

The present study was carried out in order to investigate the removal of soluble Mn2+ from an aqueous solution using Bacillus cereus. A manganese aqueous solution at 50 mg L-1 was treated, and the product was less than 1 mg L-1 of residual concentration, which complied with environmental regulations. Before the optimization, B. cereus was able to remove Mn2+ ions from an aqueous solution; however, the residual content was around 2.5 mg L-1. Screening experiments aiming at defining the effects of the growth medium composition indicated that both casamino acid-peptone and yeast extract contributed to manganese removal. These experiments also showed the interaction between these two components of the culture media, nevertheless the use of glucose did not prove significant. Considering these observations, the Doehlert design was used to generate a response surface. The model was significant with the p value lower than 0.05 and the lack-of-fit not significant (p > 0.05). The optimized composition of the growth medium was defined as 0.5 g L-1 of casamino acid-peptone and 0.25 g L-1 of yeast extract, whereas glucose could be removed from the original growth medium. When the optimized condition of the growth medium was used, the time required for manganese removal was reduced from 21 to 8 days. After optimization, B. cereus was capable of producing high manganese removal, reducing the residual concentration to levels below 1.0 mg L-1.