Study On Elimination Efficacy And Mechanism Of Microcystis Aeruginosa In Water By Dielectric Barrier Discharge Plasma

Microcystis aeruginosa（M.aeruginosa）,as a representative dangerous algae in cyanobacteria blooms,has long been a serve threat to human drinking water resources.While,the quick,efficient and pollution free removal of M.aeruginosa by traditional techniques is too hard to realize.A self-cooling dielectric barrier discharge plasma（DBDP）reactor was applied in this study to eliminate M.aeruginosa from water.Effect factors,such as its voltage,type of discharge gas,ventilation flow,initial p H and cell density of algae solution,were investigated and studied to figure out their relationships between them and the removal efficiency of self-cooling DBDP reactor.Based on the above studies,mechanisms of eliminating M.aeruginosa by DBDP were discussed through various different aspects,including changes in cell morphology,variations of dissolved organic matter in solution,damage of cytomembrane,variations of enzyme activity,species of reactive oxygen species（ROS）and their roles in the system,etc.Main results are as follows:（1）Increase of the active species production within the reactor was aroused by the enhancement of the applied voltage,thus improving the removal efficiency of M.aeruginosa;ROS generated by oxygen played a better role in elimination of M.aeruginosa compared with air and N₂;transformation of O₃ to·OH in solution was promoted by the increase of the initial p H,therefore strengthen the elimination effect of M.aeruginosa;better removal efficiency and elimination effect were reached with lower initial algae density.When the applied voltage is 19.0 k V,p H is 11 and 1.0 L·min^-1 O₂ is injected into the solution with algae density lower than 10⁷ cells·m L^-1,over 99%of M.aeruginosa are eliminated within 60 min and the toxins released during the DBDP treatment is also reduced below the safety range.（2）Cells of M.aeruginosa treated by DBDP become discrete,and their surface folds and depressions occur.Prolong treatment time leads to the rupture of algal cells and the leakage of intracellular substances,which results in transparency and removal of cells.Meanwhile,the cell membrane integrity of M.aeruginosa rapidly lost,and the value of Malondialdehyde increased significantly.Activity of Superoxide dismutase and Catalase decreased,the content of chlorophyll-a,phycocyanin,aromatic amino acids and other biological active substances decreased,and the level of intracellular reactive oxygen increased significantly.（3）Besides the formation of O₃ and H₂O₂,radicals like·OH,¹O₂and·O₂^-were also generated in the DBDP reactor.Results show that neutral electrical species like ¹O₂,O₃and H₂O₂ can easily penetrate the cell membrane of M.aeruginosa and resulted in the broken of cytomembrane.Other electronegative free radicals can then enter the cell and decompose intracellular organic matter,eventually decompose the organic material released in the inactivation process into CO₂ and H₂O.This study proves a fast,efficient and pollution-free technique to remove M.aeruginosa from water.Meanwhile,it either provides the theoretical basis for the application of no-thermal plasma technology in solving algae contamination issues.