Study On Co-removal Of Cr(?) And Inorganic Nitrogen By Acinetobacter Sp. WB-1 And Immobilization Of Cr(?) By Coagulation/Flocculation

Inorganic nitrogen ?IN? and hexavalent chrome ?Cr???? are two classes of important pollutants in aquatic environment. The coexistence of IN and Cr??? can cause combined pollution and enhance their tolerance to the treatments, which becomes a tough environmental problem. The traditional physical and chemical techniques have been used for the removal of Cr??? from industrial wastewater, but high cost and secondary contamination make the applicability of these methods restricted. Thus, a bacterial strain named as Acinetobacter sp. WB-1, was isolated from activated sludge under aerobic de-nitrification conditions with the function of co-removal of NO₃^--N and Cr???, to compensate for the lack of traditional methods in the management of IN/Cr??? pollution. The aim of the current study is to ?1? explore the removal capability and removal mechanisms of Cr??? by Acinetobacter sp. WB-1 and further removal of the generated soluble trivalent chrome ?Cr???? by flocculation process; ?2? evaluate the capability of simultaneous removal of NO₃^--N and Cr??? by Acinetobacter sp. WB-1; ?3? analyze the interaction between the removal of inorganic nitrogen and Cr??? by Acinetobacter sp. WB-1.The toxicity of Cr??? for Acinetobacter sp. WB-1 was dependent on the concentration of Cr???, high Cr??? concentration ?higher than 6.00 mg/L? would inhibit the growth of strain and the reduction ability of Cr???, while sodium citrate could also be used as carbon source and electron donor for Cr??? reduction, while sodium citrate could also react with Cr???. The single coexistence of nickel or zinc could inhibit strain WB-1 reducing Cr???, whereas copper could promote the Cr??? reduction. The effective contribution of cellular components involved cytoplasm, supernatant and extracellular polymer substance ?EPS? in the process of Cr??? reduction, And Cr??? was generated in intracellular fraction, extracellular fraction, and EPS. Thus, a mechanism of Cr??? reduction by strain WB-1 including intracellular reduction, extracellular reduction, and surface immobilization of Cr??? was proposed. Furthermore, the immobilization of soluble Cr??? by coagulation/flocculation process was conducted, and the results showed that more than 95.21% of soluble Cr??? could be removed at pH 9.0 in the presence of 50.00 mg/L PAC.The optimum conditions for co-reduction of Cr??? and NO₃^--N were found to be as follows:sodium acetate as carbon source, C/N ratio of 15, rotating speed of 200 r/min, inoculum volume of 10.00%, and 1.00 g/L NaCl. Under these conditions, the initial 200.00 mg/L NO₃^--N removal rate was 91.23% and the initial 3.00 mg/L Cr ?VI? removal rate was 100.00%. Besides, the interaction between Cr?VI? and IN removal showed that 50.00-500.00 mg/L NO3+-N and 50.00-150.00 mg/L of NO₂^--N had no influence on Cr?VI? reduction. The-effect of IN on reduction of Cr?VI? was mainly dependent on the growth of this strain. Different Cr?VI? concentrations had no effect on NH3-N removal, whereas increasing Cr?VI? concentration ?1.00-30.00 mg/L? could affect the reduction rates of NO₃^--N/NO₂^--N. 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.