[Bioaugmented treatment of atrazine by genetically engineered microorganism in different bioreactors]

Removal of atrazine was investigated when genetically engineered microorganism (GEM) was inoculated into membrane bioreactor (MBR) and hybrid bioreactor for bioaugmentation. The performances of atrazine removal in two bioreactors were explored. The variations of GEM density and atzA gene abundance in two bioreactors were also determined. The results indicated that removal activities of COD and ammonia nitrogen were inhibited a little by atrazine and recovered after bioaugmentation by inoculated GEM. The better removal performance of COD and ammonia nitrogen was obtained in MBR. The biological removal efficiency of atrazine was improved significantly when bioaugmented treatment by GEM was applied. The atrazine removal increased gradually and the average removal rates reached up to 38.94% in MBR and 29.36% in hybrid bioreactor in the later running period. After inoculated, GEM densities in two bioreactors decreased rapidly and then tended to be constant. The stable GEM densities in MBR, suspended sludge and adherent biofilm of hybrid bioreactor were 5 x 10(3) CFU/mL, 1.1 x 10(3) CFU/mL and 0.4 x 10(3) CFU/mL, respectively. Fluorescence in situ hybridization (FISH) was used to detect azA gene in two bioreactors and the result indicated that the average relative abundances of atzA gene decreased initially and increased subsequently. The largest average relative abundance of atzA gene was obtained in MBR. The average relative abundance of atzA gene in adherent biofilm is larger than that in suspended sludge in the hybrid bioreactor. The horizontal transfer of atzA gene was the possible important reason responsible for high gene abundance.