Research On The Isolation And Degradation Characteristics Of The Cold-Adapted And Halotolerant Nitrobenzene-Degrading Bacterium

Nitrobenzene (NB), which is an important chemical material, is widely used in the manufacture of organic products, such as aniline, drugs, explosive and soap. Nitrobenzene has proven to be a carcinogen and been a huge threat to human health. Thus, nitrobenzene is listed as a priority pollutant by the US Environmental Protection Agency.Compared to physical-chemical methods, biological methods can mineralize nitrobenzene at a lower cost. The activity of activated sludge in urban sewage treatment system is low in the north of China. Therefore, microbial metabolic rate was inhibited, so that limited the ability of microbial nitrobenzene degradation.In addition to toxic pollutants, there are enormous inorganic salts in the nitrobenzene wastewater, such as Cl-, Na+, Ca2+, SO42-. It has a very important significance to screen high efficiency low temperature and salt tolerant nitrobenzene-degradation strains to deal with the nitrobenzene wastewater.In this study, sixteen strains that use nitrobenzene as carbon source at low temperature and high salinity were domesticated and isolated from activated sludge in the aeration tank of Shenyang Northern Sewage Treatment Plant. Then investigate their ability to degrade nitrobenzene. The results showed five strains, X1, X3, X7, X11 and X14 respectively, had strong ability of nitrobenzene degradetion and the rates were all over 40%. Through rescreening, the ability of strain X7 for the growth and nitrobenzene degradation were better than the other 4 strains. Therefore, strain X7 was identifed as a cold-adapted and halotolerant nitrobenzene-degrading bacterium. According to strain X7’s morphological, physiological and biochemical characteristics and 16S rDNA gene sequence, strain X7 was identified as Myroides odoratus.The optimal degradation conditions of strain X7 were as follows:optimal temperature 15℃, pH 7.0, rotary speed 150 rpm, inoculum concentration 10% and salinity 1.0%-3.0%. At the initial concentration of nitrobenzene of 150 mg/L, the degradation rate was 51.50%. However, the addition of glucose and peptone could increase the degradation rate to 58.92% and 60.24% respectively. The maximum tolerated concentration of strain X7 to nitrobenzene was 350 mg/L.Study the stain X7 degradation kinetics of nitrobenzene under the optimal degradation condition. The results showed that when the initial concentration of nitrobenzene was less than 120 mg/L, the degradation kinetics of nitrobenzene was fit with zero order kinetic, the correlation coefficient is 0.9874-0.9925. When the initial nitrobenzene concentration was over 120 mg/L, the degradation kinetics of nitrobenzene can be expressed by Andrews equation. The kinetic parameters were as follows:μmax=1.32684, Ks,=37.75747, Kt,=110.63896.