Removal Of Oscillatoria Sp.in Drinking Water Treatment By N-TiO₂ Ballasted Coagulation And Degradation Of The Sludge By Visible-light Catalysis

Oscillatoria sp.,which is a kind of filamentous cyanobacteria and release a variety of toxins and odor metabolites during the growth in the drinking water source,posing a serious threat to the safety of drinking water.Coagulation-sedimentation process is the main method to remove algae in the drinking water treatment process.However,due to the negative charge and floatability of the cyanobacteria cells,coagulation flocs are loose and the sedimentation effect is not satisfactory.In addition,Oscillatoria sp.in the sludge will growth and release algal toxins and other harmful substances,which will cause a secondary pollution.In view of the poor settling property of the flocs and the release of algal toxins during the growth of algal cells in the sediment,this paper uses N-TiO2 as the ballasted particles to enhance the coagulation removal efficiency of PAFC,which is commonly used in drinking water plants.At the same time,with the help of the visible light catalytic property of N-TiO2 particles in the sediment,the algae cells and their metabolic products will be effectively degraded.The response mechanisms of Oscillatoria sp.on N-TiO2 were also explored.Finally,the coagulation and degradation effects of N-TiO2 on cyanobacteria with different shapes was explored by comparing M.aeruginosa and Oscillatoria sp..The main results are as follows:(1)The ballasted coagulation of N-TiO2 particle increased the size and density of the flocs,and improved the sedimentation efficiency.When 5 mg/L PAFC and 75 mg/L N-TiO2 particles were added,about 98.9%Oscillatoria sp.cells could be removed by ballasted coagulation,and the residual N-TiO2 particles in supernatant was less than 1 mg/L.(2)Light intensity and dosage of N-TiO2 are the main factors that affect the degradation effect of the sludge containing algae cells.The degradation effect of the algal sludge is positively related to light intensity and N-TiO2 dosage.75 mg/L N-TiO2 could degrade about 96.4%of chlorophyll-a and 94.6%of cylindrospermopsins in the sludge after 12 hours under 10000 lux light and realize the harmless treatment of the sludge.(3)Compared with the spherical M.aeruginosa,the enhanced coagulation effect of ballasted coagulation is more significant for filamentous Oscillatoria sp.,however,the Oscillatoria sp.is more tolerant to the photocatalytic oxidation stress of N-TiO2.Under the same photocatalytic degradation conditions,Oscillatoria sp.and its toxins(CYN)are more difficult to be degraded,so Oscillatoria sp.sludge has a greater threat to the environment.In this study,visible light catalyst particles(N-TiO2)were used as ballasted particles,then ballasted coagulation was combined with visible light catalytic oxidation to realize an efficient purification of the raw water and the algae sludge containing Oscillatoria sp.,which provided a new idea for the drinking water plant to treat the algae containing raw water during the bloom period.