Study On Bioaugmented Treatment Of Atrazine And Directed Evolution Of Indigenous Atrazine-Degrading Bacteria

Atrazine and conventional pollutants removal bioaugmented by genetically engineered microorganism (GEM) were investigated in this study in both membrane bioreactor (MBR) and conventional activated sludge reactor (CAS). Fluorescence in situ hybridization (FISH) was used to analyze the transfer of atzA gene between GEM and indigenous strains. The polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) were used to analyze the microbial community variation of both reactors in different running stages.The results indicated that high removal efficiency of atrazine was obtained in both bioreactors bioaugmented by GEM. The average removal efficiencies of atrazine in MBR and CAS bioreactors reached up to 88.6% and 85.3%, respectively. Atrazine removal bioaugmented by GEM would be helpful to maintain high sludge bioactivity in both bioreactors. The removal activities of COD and ammonia nitrogen were inhibited a little by atrazine and recovered after bioaugmentation by inoculated GEM. In MBR and CAS bioreactors, the removal efficiencies of COD reached up to 96.0% and 91.5% respectively and the removal efficiencies of ammonia nitrogen reached up to 98.6% and 95.7%, respectively. The performance of MBR was better than CAS.The GEM density decreased quickly in both bioreactors after GEM inoculation and then became stable. The stable GEM densities in MBR and CAS were 2.1×10~3 CFU/mL and 1.7×103 CFU/mL, respectively. The average relative abundances of atzA gene decreased initially and increased subsequently, indicating that the atzA gene transferred into the indigenous strains after a long-term adaptation. Microbial community varied in different running stages of two bioreactors. The biodiversity and stability of microbial community decreased in the presence of atrazine and recovered after efficient atrazine removal was realized. MBR was better than CAS to maintain biodiversity and stability of microbial community.