Isolation And Identification Of Denitrifying Bacteria And Its Bioaugmentation On Nitrate Wastewater Treatment

At present, eutrophication has become a global environmental problem. A tention for treatment of nitrogen polution is growing at home and abroad, and biological denitrification technology is popular because of its rapid and safe characteristic. Biological nitrogen removla process was mainly carried out by denitrifying bacteria. To isolate and screen the denitrifying bacteria from natural or artificial ecosystems has become the key step for its application.In our research, denitrifying bacterium strain LZ-14 with faster gas producing and higher nitrogen removal efficiency was screened by dilute soil suspension-spread plate techniques from soil that sampled from the rhizosphere of Arundo donax L. Another 7 denitrifying bacteria strains were screened from rhizosphere of Phragmites communis and Typha latifolia after enrichment. The cells of screened strains were mostly Gram-negative, facultative anaerobic and short rod-shaped. Nitrate reducing and gas producting experiments revealed that all those screened denitrifying bacteria have high nitrogen removal capacity and can be used as a source for nitrogen removal treatment.Our research focused on strain LZ-14 with higher nitrogen removal capacity after comparison between 8 screened strains. Strain LZ-14 can use extensive carbon sources with acetate as the most effective one. Under anoxic condition with temperature at 20℃to 35℃, the strain grew fast and exhibit excellent nitorgen removal ability. The effects of C/N ratio and pH on the growth and denitrification process of strain LZ-14 were also investigated with acetate and nitrate as sole carbon and nitrogen source respectively. The results showed that the optimal C/N ratio was 5 and TN removal rate of 84.5% was achieved in 36 hours with complete removal of 150 mg/L nitrate-N. The favorite initial pH range for strain LZ-14 was 7.0 to 8.0, besides which nearly no cell growth and denitrification could be detected. It was also found that nitrogen removal process was mainly happened in the growth phase of the 12～36 hours with a considerable amount of nitrite accumulation which can be reduced completely in the later 24 hours. By PCR amplification and homology analysis of 16S rDNA sequence, it was found that strain LZ-14(Genbank access number: FJ588910) was close to Pseudomonas stutzeri on the evolutionary tree. The taxonomic status of strain LZ-14 was determined as Pseudomonas which was a typical denitrifying genera.Under laboratory scale, constructed wetlands were conducted to investigate the impact of bioaugmentation by strain LZ-14 to treat natural and artifical nitrate wastewater. The results revealed that in 8 days' experiment, COD_Cr and TN removal efficiency of 53.1% and 75.9% could be achieved when treating with polluted Xinxue river water. Compared with controlled group, the COD_Cr and TN removal efficiencies were incresed by 24.9% and 39.5% respectively. Bioaugmentation was proved to be an effective method to treat nitrate wastewater.