Isolation, Identification And Characterization Of An Immobilized Bacterium Producing N₂ From NH₄(+) Under An Aerobic Condition

To treat wastewater efficiently by a one-step process of nitrogen removal, a new bacterial strain producing N2 gas from NH4+ under an aerobic condition was isolated and identified. The cell was motile and a Gram-negative rod, and usually occurred in pairs. By 16S-rDNA analysis, the isolated strain was identified as Enterobacter asburiae with 96% similarity. The isolate showed that the capacity of N2 production under an oxic condition was approximately three times higher than that under an anoxic condition. Thus, the consumption of NH4+ by the isolate was significantly different in the metabolism of N2 production under the two different environmental conditions. The optimal conditions of the immobilized isolate for N2 production were found to be pH 7.0, 30˚C and C/N ratio 5, respectively. Under all the optimum reaction conditions, N2 production by the immobilized isolate resulted in reduction of ORP with both the consumption of DO and the drop of pH. The removal efficiencies of CODCr and TN were 56.1 and 60.9%, respectively. The removal rates of CODCr and TN were the highest for the first 2.5 hrs with the removal CODCr/TN ratios of 32.1, and afterwards the rates decreased as reaction proceeded. For application of the immobilized isolate to a practical process of ammonium removal, a continuous operation was executed with a synthetic medium of a low C/N ratio. The continuous bioreactor system exhibited a satisfactory performance at 12.1 hrs of HRT, in which the effluent concentrations of NH4+-N was measured to be 15.4 mg/L with its removal efficiency of 56.0%. The maximum removal rate of NH4+-N eached 1.6 mg NH4+-N/L/hr at 12.1 hrs of HRT (with N loading rate of 0.08 Kg-N/m3-carrier/d). As a result, the application of the immobilized isolate appears a viable alternative to the nitrification denitrification processes. KCI Citation Count: 0