Formation, stability and mobility of soluble Cr(III) during Cr(VI) reduction by Pannonibacter phragmitetus BB

Abstract

The reduction of Cr(VI) to Cr(III) by microorganisms is an efficient method for the remediation of Cr(VI) contamination. Cr(VI) can be transformed into Cr(III) in different forms, and one of the important reduction products is soluble Cr(III) in solution. However, information regarding its stability and mobility is limited. In the present study, the formation, thermal stability and mobility of soluble Cr(III), which was formed after Cr(VI) was reduced by Pannonibacter phragmitetus BB, were investigated in detail. The results showed that more than 96.6% of the Cr(VI) (500 mg/L) was transformed into soluble Cr(III) by P. phragmitetus BB. Temperature slightly influenced the formation of soluble Cr(III), which decreased by approximately 7.8% when cultured at 45 °C compared to those at other temperatures. Thermal treatment decreased the concentration of soluble Cr(III) from 485.6 mg/L to 310.6 to 366.4 mg/L, but further increasing the treatment temperature or prolonging the treatment time had a limited influence on the treatment efficiency. In addition, a higher pH is favourable for the mobility of soluble Cr(III), and the adsorption capacity of quartz sand for soluble Cr(III) decreased from 1.84 to 1.21 ug/g as the pH increased from 3.0 to 12.0. These results suggest that environmental risks still exist after the reduction of Cr(VI) by microorganisms. • Most of the Cr(VI) were transformed into soluble Cr(III) by P. phragmitetus BB. • Temperature slightly influenced the formation of soluble Cr(IIII). • Thermal treatment is efficient in treatment of small portion of the soluble Cr(III). • Higher pH is favourable for the mobile of soluble Cr(III).