Isolation And Characteristic Of An Aerobic Denitrifier With High Nitrogen Removal Efficiency

Aerobic denitrifying bacteria DL-23, isolated from aerobic domesticated activated sludge, was demonstrated to have high ability of denitrification and heterotrophic nitrification under aerobic condition. Sequence analysis of 16S rDNA plus bacterial morphology observation and physiological biochemistry classified it as Paracoccus denitrificans.The influence of different environmental factors which affect its performance of aerobic denitrification was discussed by single factor-shaking culture experiments. The results showed that the optimum culture of denitrification was succinate as carbon source, COD/N ratio of 10, 37℃,160 rpm. Under this conditions,420 mg/L NO3-N was significantly removed in 30 h, the nitrate removal efficiency was 97.7%, with an maximum removal rate high to 23.1 mg/L·h. TN and COD removal rate reached 53.2% and 90%, respectively, which means that high efficient and synchronous removal of nitrate and organic matter under aerobic conditions was achieved. Between a certain initial NO3-N concentrations range from 200 to 600 mg/L, strain DL-23 could proceed nitrogen removal effectively, the TN removal rate increased as the nitrate load added. Meanwhile, strain DL-23 exhibited an amazing nitrite tolerance and rapid degradation ability, under 658 mg/L NO2-N load, completely removal was attained in 48 h. Strain DL-23 showed wide rage of pH tolerance, it could proceed aerobic denitrification effectively in the initial pH widely between 6 and 8. The increase of inoculation amount could accelerated rate of denitrification, shorten the denitrogen period.P. denitrificans DL-23 has heterotrophic nitrification-aerobic denitrification ability, ammonia could be converted into gas products under aerobic conditions. The ability of simultaneous nitrification and denitrification by single strain was achieved. After optimization (succinate, C/N ratio of 10,37℃,160 rpm), DL-23 removed 385 mg/L NH4+-N within 24 h with ammonia as nitrogen source, the removal rate reached 100%, among which 18.8%was eliminated through aerobic denitrification,79% was used for bacteria assimilation synthesis, the maximum ammonia removal rate was 30.3 mg/L·h. At high ammonia load of 750 mg/L, NH4+-N and TN removal efficiency was 78.6% and 21%, respectively. Exhibiting high removal ability of ammonia.P. denitrificans DL-23 was immobilized by polyvinyl alcohol(PVA) and sodium alginate(SA). The immobilized bacteria showed an improved resistance of pH, under strong acid(pH 5.0) and alkali (pH 9.0)culture conditions, the efficiency of denitrification was increased; Immobilized bacteria also reduced the inhibition effect of low and high temperatures compared to free bacteria. Furthermore, the immobilized bacteria has good recycled use stability. These results suggest that P. denitrificans DL-23 may be a good candidate for aerobic wastewater treatment.