Enhancement Of Nitrogen Removal By Heterotrophic Nitrification-aerobic Denitrification Mixed Strains And Study Of Urea Removal

The highly efficient heterotrophic nitrification-aerobic denitrification strain DM01 was isolated from the domesticated aerobic SBR reactor.Based on the analysis of biochemical characteristics and 16S rDNA gene sequences homology,indicating that strain DM01 was most closely related to members of genus Pseudomonas.The characteristics of nitrification and denitrification and nitrogen removal mechanism were also researched.And then,the highly efficient mixed strains was obtained by combination of the Pseudomonas mendocina sp.DM01 and other strains,and using it for enhancing aerobic SBR.Lastly,studying the effects of different metal ions and salinity on the urea removal by mixed strains.The conclusion are as follow:?1?The optimum nitrification conditions for Pseudomonas mendocina sp.DM01was:pH 7.0,temperature 30?,speed 130 r/min,C/N 10,carbon source was sodium citrate;the optimum aerobic denitrification was:pH 8.0,temperature 30?,speed 150r/min,C/N 10,carbon source was sodium citrate.The strain can adapt to a wide range of NH₄⁺-N and NO₃^--N concentration,the nitrogen removal efficiency was above90.0%when NH₄⁺-N and NO₃^--N concentration within 50²00 mg/L,the nitrogen removal efficiency still above 70.0%under 300⁴00 mg/L.?2?Pseudomonas mendocina sp.DM01 has mmonia monooxygenase,nitrite reductase,hydroxylamine oxidase and periplasmic nitrate reductase.The nitrogen removal mechanism as follow:NH₄⁺-N?NH₂OH?NO₂^--N?NO₃^--N?gaseous nitrogen,and part of nitrogen was converted into endogeenous nitrogen of cells.?3?The nitrogen efficiency of mixed strains?DM01+YH01+YH02?was higher than each of single strains.NH₄⁺-N and NO₃^--N removal efficiency of mixed strains reached more than 95.0%within 48 h.The aerobic SBR nitrification reactor was enhanced by mixed strains,after 50 d running,significantly improve the nitrogen removal efficiency and got a stable performances.The intermediate products NO₃^--N and NO₂^--N were hardly found in the reactor,and NH₄⁺-N and TN average removal efficiency higher 11.8%and 12.1%than control group.The aerobic SBR denitrification reactor also enhanced by mixed strains,the NO₃^--N and TN average removal efficiency higher 14.2%and 13.6%than the control group.?4?The optimum urea removal conditions for mixed strains were:temperature35?,rotating speed 150 r/min,pH 6.0-9.0,C/N 12,carbon source was sodium citrate.The urea removal rate effectively increased while stepping up initial inoculum concentration.Mixed strains could remove urea under interference of different metal ions and salinity,and showed strong tolerable ability to severe conditions.But mixed strains reproduction were inhibited with increased Cu²⁺,Zn²⁺,Cd²⁺,Ni²⁺,salinity concentration,besides that,the urea and TN removal efficiency were also decreased.However,Fe²⁺within rage of 5.0²0.0 mg/L has positive effects on mixed strains growth and urea removal.