Screening And Identification Of Two Strains Of Heterotrophic Nitrifying Bacteria And Characterization Of Their Capacity For Nitrogen Removal

Nitrogen is one of the major pollutants of water pollution, when too much nitrogen was dissolved in water, it will cause the deterioration of water quality and a wide range of hazards. Currently, in wastewater treatment process, the method of biological denitrogenation was most widely used. However, traditional bio-treatment method generally includes two processes-aerobic nitrification and anoxic denitrification, which have the problems of complexity, high cost and low efficiency. In recent years, the discovery of heterotrophic nitrification bacteria provides a new way for biological nitrogen removal, and their applications in wastewater treatment become more and more popular. Compared with traditional denitrifying bacteria, heterotrophic nitrification bacteria grew faster, had a much higher nitrogen removal efficiency, and required lower environmental conditions. Therefore, isolation of highly efficient heterotrophic nitrification microorganisms, which could achieve low-cost restoration for ammonia contaminated water, has become a hot spot for scientific research.In this paper, six strains of heterotrophic nitrification bacteria were screened from piggery wastewater, while ammonia was used as the sole nitrogen source of heterotrophic nitrification culture medium. Among them, strains P2 and P9 could remove nitrogen most rapidly. Based on analysis of physiological characteristics and phylogenetic analysis of 16S rDNA sequences, strains P2 and P9 were identified as Paracoccus sp. and Shinella sp., respectively. Results showed that heterotrophic nitrification could occur by the strains when they utilized organics. After cultivation of 24 h, the ammonia removal rates by the strains were up to 80% approximately; meanwhile, there was almost no nitrite and nitrate accumulation. However, aerobic denitrification could not occur by the strains when NO3-or NO2- was provided as the sole nitrogen source, respectively. Apart from that, the ammonia removal characteristics of strains P2 and P9 were also investigated. The results indicated that, for heterotrophic nitrification, with the strain P2 and P9, the optimal carbon source was sodium succinate, and the optimal C/N ratio was 9. Besides, the pH values rose from 6.8 to 8.9 in the whole ammonia removal process.Nitrogen removal ability of strains P2 and P9 individually or mixed were evaluated in the treatment of actual piggery wastewater. It’s found that the growth and nitrogen removal ability of the two strains depended much on the quantity of small molecule carbon source, and the nitrogen removal capability of strain P2 or P9 in wastewater with small molecule carbon source was improved evidently. The effect was strengthened especially when the two strains were mixed together. In addition, studies showed that little nitrite or nitrate was produced during the nitrogen removal process by strains P2 and P9, and ammonia could be removed both through assimilation and alienation. On the whole, nitrogen removal ability of strains P2 and P9 were relatively strong, and they may exhibit broad application prospects in wastewater treatment industry.