Behavioral Characteristics Of Oscillatoria Sp. And Its Metabolites In PAFC Coagulation Process

In recent years,the blooming of harmful cyanobacteria is becoming exacerbated in many lakes in our country,both in terms of intensity and frequency,which can directly cause a deterioration in the quality of drinking water through the production of toxic and odorous metabolites,meanwhile,it will be a doom if the occurrence of cyanobacteria blooms in lake which is a source of drinking water.Benthic Oscillatoria sp.may form dense surface blooms especially under eutrophic and calm,stratified conditions,which poses a threat to drinking water safety because it can produce toxic and odorous metabolites.Coagulation is usually the most effective unit operation for removing cyanobacterial cells in typical drinking water treatment plants.Polyaluminum ferric chloride(PAFC)is known to be the most popular conventional coagulant in drinking water treatment plants.However,the research on the removal of cyanobacteria in the coagulation process is mainly directed against Microcystis aeruginosa at present.Due to the different of cells' morphology and physiological characteristics between Oscillatoria sp.and Microcystis aeruginosa,the behavioral characteristics in the coagulation process will also be difference.Therefore,research should be conducted on PAFC's damage-free removal process of Oscillatoria sp.and the behavioral characteristics of it during sediment storage.This study clarified the effect of PAFC,a commonly used coagulant in water purification plants,on the removal of Oscillatoria sp.cells during coagulation,and investigated cells' integrity and activity during the sedimentation process,clarified the toxin/odorous metabolites release during the floc storage process.During the research,the following results were obtained:(1)The optimum coagulation colditions for removing Oscillatoria sp.cells(?104 cells/mL)are PAFC dosage 5.0 mg/L,rapid mixing velocity 200 rpm,rapid mixing time 0.5 min,slow mixing velocity 80 rpm,and slow mixing time 30 min;(2)Oscillatoria sp.cells can gradually adapt to this circumstance and grow rapidly after 4 d storage,PAFC has showed a degree of protection for Osillatoria sp.and delay the growth of cells after 6 days,while ferric and A1 has an obvious promotive effect on microalgal growth.(3)Oscillatoria sp.cells can produce and release CYNs and GSM during flocs storage process,PAFC flocs exhibited adsorption and extracellular CYNs content kept increasing after 6 days,the level of extracellular CYNs followed the sequence:control system>overdose system>optimum system.(4)Compared with Microcystis aeruginosa and Cylindrospermopsis raciborskii,Oscillatoria sp.has higher environmental adaptability,which can grow during flocs storage and continue to release toxins/odorous metabolites with cell integrity highly.The harmful effects of Osillatoria sp.on the environment are much higher than the other two toxin-producing cyanobacteria above.