Biorremoção de cromo por biossurfactantes produzidos a partir de melaço de soja em sistema de flotação por ar dissolvido

Abstract

The industrial branch has as characteristic the use of great volumes of water and, often, of heavy metals, generating liquid effluents with preoccupying concentrations of these metals, among which stands the chrome. Such element in its hexavalent state presents high toxicity and carcinogenic properties, thus requiring treatment for its removal. There are several techniques used for this purpose, and dissolved air flotation (DAF) has been widely used because it presents several advantages. Therefore, the present work studied the use of dissolved air flotation in chromium bioremediation, using as binder the biosurfactant produced by Pseudomonas aeruginosa from soybean molasses. The biosurfactant, rhamnolipid, was evaluated for surface tension, emulsification index and biosurfactant concentration, whose values were 34.16 mN/m, 100% and 9.02 g/L, respectively. In addition, several preliminary tests were carried out to evaluate the influence of saturated water volume, pH, biosurfactant concentration, presence of coagulant (ferrous sulphate) and stirring speed in the chromium removal process. The results of these tests showed that pH and iron concentration were determining factors in reducing the content of hexavalent chromium. Thereby, a central composite design (CCD) with two variables and three replicates at the central point was proposed to optimize the removal of chromium from aqueous solutions. The independent variables analyzed were pH (3,17 – 8,83) and iron concentration (0 – 225 mg/L) in the medium, while the studied responses were the percentages of removal of chromium (VI) and total. To execute the CCD, all experiments were performed in duplicate with initial Cr (VI) concentration of 100 mg/L, 500 mL of solution volume, 200 mL of saturated water, 6 minute fast mixing step at 120 rpm and concentration of biosurfactant equal to 9 g/L. The results showed that in acidic pH and high concentrations of iron the percentage of Cr (VI) removal increased, whereas for total chromium the best result was for higher iron concentration and pH near neutral. Thus, in order to validate the experiments, the values of 3.5 for pH and 180 mg/L for the iron concentration were used. The percentages of Cr (VI) and total Cr removal obtained in the validation were 100 and 57.55%, respectively, and those predicted by the model were 100 and 57.79%, respectively. From the analysis of the results achieved, it became evident that the DAF and the biosurfactant produced were efficient in the removal of chromium from aqueous solutions.