Bioreduction of Cr(VI) by Acinetobacter sp. WB‐1 during simultaneous nitrification/denitrification process

BACKGROUND The co‐existence of NH3‐N and Cr(VI) in natural water is a common and growing problem. The electron competition ability of Cr(VI) with NO3‐N/NO2‐N enabled the reduction of Cr(VI) complex during the process of simultaneous nitrification/denitrification (SND). The current study focused on exploring the interaction between Cr(VI) reduction and SND by Acinetobacter sp. WB‐1. RESULTS Different Cr(VI) concentrations had no effect on NH3‐N removal, while increased Cr(VI) concentration (1–30 mg L−1) could affect the rates of reduction of NO3‐N/NO2‐N. However, NH3‐N at concentrations ranging from 100 to 400 mg L−1 had no influence on Cr(VI) reduction. The location/contribution of cellular components demonstrated cytoplasm and filtered spent medium had the ability to reduce Cr(VI) to Cr(III). Cell debris could not reduce Cr(VI) but could accumulate Cr(III). CONCLUSION The denitrification process was more sensitive to the presence of Cr(VI) than the nitrification process. The inhibition of NO3‐N reduction was due to the toxicity and electron competition ability of Cr(VI). The inhibitory effect on NO2‐N reduction was mainly dependent on the toxicity of Cr(VI) to NO2‐N reductase. Cr(VI) removal by strain WB‐1 was suggested to be realized through surface immobilization along with intracellular and extracellular reduction.