Abstract: In order to efficiently remove Cr（VI）from industry wastewater,two strains of bacteria that remarkably reduced Cr（VI）were isolated from the wastewater in a dyeing factory of Tianjin. The effect of removing Cr（VI）by the mixture of bacteria-microalgae system and the optimized conditions were studied,as well as the activity of Cr（VI）reductase was determined. 16S rRNA gene sequence alignment was used to identify the bacterial isolates,and Placket-Burman,the Steepest Ascent,Box-Behnken experimental design and response surface methodology were conducted to analyze the interactions among each factor. In addition,the Cr（VI）reductase activities of two bacteria were determined. The result showed that two strains of Cr（VI）reducing bacteria belonged to the genus Serratia and the genus Delftia. The optimal conditions for removing Cr（VI）by the mixture of bacteria-microalgae were as follows：the temperature was 29.74℃,the Cu²⁺ concentration was 27.65 mg/L,the glucose content was 2.41%（W/V）,the sodium pyruvate content was 2%（W/V）,the inoculum was 7%,and the pH was 7.0,and no NaCl,respectively. Under the optimized conditions,the removal rate of Cr（VI）by the mixture of bacteria-microalgae reached 97.89% in 24 h. The optimal temperature of the Cr（VI）reductase for two strains S-3 and D-7 was 30℃. The optimal pH of the Cr（VI）reductase for the strain S-3 was 6.0,and the kinetic constant of the enzymatic reaction was K_m=86.94 μmol/L,V_max=2.71 µmol/（L·min）. The optimal pH of the Cr（VI）reductase for the strain D-7 was 7.0,and the kinetic constant of the enzymatic reaction was K_m=103.18 μmol/L,V_max=3.38 µmol/（L·min）. In conclusion,the optimized mixture of bacteria-microalgae may not only increase the removal rate of Cr（VI）,but also shorten the treatment time,and it has a promising application prospect in the treatment of chromium-containing wastewater.

Key words: mixture of bacteria-microalgae, microbial removal, Cr（Ⅵ）, response surface methodology