Study On The Influence Mechanism Of Algae On Coagulation Process

The three gorges project is currently the world's largest water conservancy hub project.It has played a major role in ensuring energy security,preventing floods and improving navigation conditions,at the same time,produced effects on the surrounding ecological environment,especially frequent algal bloom in the main stream and tributaries of the three gorges reservoir area from March to October in recent years,which do harm to the water plant where treats the reservoir water as drinking water.The results showed that green algae,diatoms and cyanobacteria were the main species in the three gorges reservoir.Therefore,the study was conducted with the dominant species in the three gorges reservoir area: Microcystis aeruginosa(cyanobacteria),chlorella(green algae),Synedra(diatoms),and Anabaena(cyanobacteria).Effects of different coagulants on the coagulation process of algae,the effects of algal properties on the process of coagulation and flocculation characteristics were studied.The research conclusion obtained are as follows:(1)The influence mechanism of different coagulants on the coagulation process of Microcystis aeruginosa,Chlorella,Anabaena and Synedra was studied.The results showed that the coagulation effect of ferric salt was better than that of aluminum salt.Analysing different coagulants effect mechanism on algae coagulation process with floc particle size distribution,floc strength,Zeta potential,results showed that the floc size and electricity neutralization capacity was the key to affect the coagulation effect of different coagulants.When using ferric salt as coagulant,the larger floc size and the higher electric neutralization capacity,thus the better coagulation effect achieved.(2)The effects of algal features on the coagulation process were studied by coagulation performance.When used iron salt,the best turbidity removal rate: Chlorella(98%)> Synedra(93%)> M.aeruginosa(91%)> Anabaena(79%).The surface area and Zeta potential of algal cells were positively correlated with the coagulant dosage.Therefore,the surface area of algal cells and Zeta potential could be used to predict the coagulant dose.(3)Algae growth,concentration and AOM were also important factors in the algal coagulation process.The coagulation effect was the best during decline phase,followed by the stable phase and the exponential phase.The higher the microcystis concentration,the worse the coagulation effect,and the more coagulant dose needed to achieve the same coagulation effect.The algae blooms can be controlled by increasing the coagulant dose in the higher water level.AOM in all growth periods inhibited the coagulation of Microcystis,Chlorella and Synedra.Algae in decline phase without AOM had the best coagulation performance,followed by the stable phase and the exponential phase,indicated that the main reason for the difference between the different growing period coagulation were the surface of cells change instead of algal organic matter.(4)The effects of algal features on the characteristics of apparent structure,fractal characteristics and Zeta potential were studied.The flocculent morphology of the four types of algae is characterized by different morphological structures,which are mainly related to the morphological structure of the algal cells themselves.The fractal features of the four algae floc were consistent with the variation trend of the amount of coagulation,increased and then decreased,which was related to the change of coagulation mechanism.The fractal dimension values of the four algal flocs: Chlorella(1.78)> Synedra(1.72)> Anabaena(1.51)> Microcystis(1.17),which are consistent with the four types of coagulation effect.The difference of Zeta potential with the coagulant dose reflected the electrochemical neutralization capacity of algae: Microcystis > Anabaena >Synedra > Chlorella.(5)The effects of the species,growth,and AOM of algae on floc characteristics such as floc size,strength and regeneration were studied.The maximum particle size of Synedra and Anabaena floc was 777 and 765 ?m,respectively,which were greater than the 632 ?m of M.aeruginosa.The strength and regeneration capacity of the Synedra floc was the largest,53.75% and 26.54% respectively,Microcystis next,and Anabaena the weakest.Poor strength and regeneration ability of Anabaena floc,maybe caused by the breakage of bond.In the exponential phase,the floc size and strength were greater,but the recovery of the flocs of decline phase was better,because of the difference of algae and AOM.Subsequent experiments also confirmed that AOM had an effect on the size,strength and regeneration capacity of the flocs,and the size of the flocs increased with the AOM,but the strength decreased.By analyzing influence of algae's feature on the coagulation process mechanism,studying the factors affecting the coagulation process and the floc properties after coagulation,to associate physical and chemical characteristics of algae with the process of coagulation.