Research On The Efficacy And Mechanism Of Ozonated Microbubbles To Enhance Air Flotation For Algae Removal

The high concentration of nitrogen and phosphorus in surface water causes algae overgrowth.The traditional dissolved air flotation has the problems of low adhesion efficiency between bubbles and algae cells and can not remove algae derived organic pollutants in water.Ozone has strong oxidizing properties and can effectively remove organic pollutants.The organic combination of ozone and air flotation process can oxidize and degrade organic pollutants while removing algal cells.However,the ozone utilization rate of traditional microporous aeration ozone flotation is not ideal,and the low ozone utilization rate will lead to insufficient organic matter reaction in water and affect the algae removal efficiency of air flotation.In recent years,microbubbles have attracted extensive attention from scholars at home and abroad because of their smaller diameter,longer residence time and better mass transfer efficiency in water phase.Through organic combination of ozone and microbubbles,this study compared and analyzed the differences between ozonated microbubble enhanced air flotation process and traditional microporous aerated ozone air flotation process in bubble characteristics,ozone utilization rate,conventional index removal,algae cell regrowth inhibition and other aspects,and summarized the advantages of ozonated microbubble.The removal rule of ozonated microbubbles on various organic pollutants from algae was investigated,and the adhesion between ozonated microbubbles and floc and the oxidation mechanism of ozonated microbubbles and algae cells were studied.The advantages of ozonized microbubbles were highlighted through the comparative test of ozonized microbubbles enhanced air flotation and traditional microporous aeration ozone air flotation.The results showed that the diameter of ozonated microbubbles ranged from 43?m to55?m,and the diameter of ozonated microbubbles ranged from 550?m to 700?m.The small volume of bubbles increased the specific surface area and reduced the rising speed,and the absorption and utilization rate of ozone were increased by 41.9%and 46.2%,respectively,compared with the traditional process.In addition,the removal rate of conventional indicators by ozonized microbubbles increased with the increase of ozone dosage,and there was no obvious long-term trend of regeneration of algae cells in the treated effluent.The experimental results of ozone microbubbles enhanced air flotation showed that although ozonated microbubbles could lead to the outflow of intracellular substances,they could significantly improve the removal of total organic pollutants.The extracellular MC-LR removal rate was up to 60.1%,the intracellular MC-LR removal rate was above 90%,and the total MC-LR removal rate was up to 93.7%.The process strengthened the removal of aromatic protein like substances and fulvic acid with high molecular weight,humic acid and humus like substances,and effectively degrades macromolecular organics.Increasing ozone concentration increased the removal rate of chlorophyll a,the maximum removal rates of TBM,DBCM,BDCM and TCM were 64.8%,80.5%,72.9%and 89.3%,respectively.Through microscopic observation and analysis,it can be seen that ozone not only reduced the bubble particle size,but also increased the bubble density and particle collision probability.The surface of algae cells in effluent scum formed a large cavity under the action of ozone,and the leaked IOM played an adsorption bridging role in adhesion and the flocs were more compact.Ozone affected the molecular interaction form between flocs,and the free hydroxyl and intermolecular hydrogen bond in aqueous solution strengthened the algae removal ability of the process.Ozonized microbubbles significantly improved the removal rate of DOC,aromatic unsaturated organic matter and nitrogen-containing organic matter in raw water,and effectively degraded biopolymers and humus substances.The decomposition of ozone and the rupture of microbubbles were the main reasons for the generation of hydroxyl radical.After the addition of hydroxyl radical inhibitor TBA,the removal rates of algal cells,UV₂₅₄,turbidity and chlorophyll a decreased by 1.4%,4.9%,0.8%and 8.7%respectively.After the addition of superoxide radical inhibitor SOD,the removal rates of algal cells,UV₂₅₄ and chlorophyll a decreased by 4.8%,14.4%and 24.2%,but the turbidity increased.Therefore,the superoxide radical produced in the process of ozone decomposition was the key to the removal of organic matter.