Study On Removal Of Microcystis Aeruginosa From Water By Coagulation Efficiency

Semi-closed water areas such as reservoirs are the main sources of drinking water in urbanized area.Proliferation of algae in water source caused by eutrophication has been aroused much attention,and significantly influence the operation of the normal drinking water plants.Therefore,it has become an important issue to guarantee the safety of drinking water via studying the algae-killing technique.However,the coagulation process in conventional water plants is not ideal for algae removal.Algae and their metabolites have significant effects on the safety of drinking water.coagulation is the most important unit for removal of algal cells by conventional processes.Taking Microcystis aeruginosa as the representative,the removal efficiency of algae cells without EOM?extracellular organic matter?was compared.The removal rate of the algae was 5%,29%and 28%higher than that of the original algae cells,which proved that EOM could impede ferric salt coagulation,under the conditions of pH 7,8 and 9.Floc size(d₅₀)dynamic analysis shows that the largest particles under the three conditions of the M.aeruginosa diameter of d_50,Max were 150?m,200?m and 215?m m,and the corresponding system of d_50,Max were 250?m,600?m and 275?m;Zeta potential is higher and more easily through the compression of electric double layer destabilization with the absence of EOM.Three-dimensional fluorescence?EEM?analysis results confirmed that the EOM and the metal complex reaction,inhibit coagulation.EOM is an important factor affecting the destabilization and coagulation removal of algae cells.The method of moderate pre-oxidation may promote the abscission of EOM and improve the removal efficiency of algae by coagulation.Pre-oxidation is one of the most common method to enhance the algae removal efficiency by coagulation technology.The oxidation of sodium hypochlorite was used to prechlorinate the Microcystis aeruginosa.On the one hand,the prechlorination can cause some of the extracellular material to fall off,thus strengthening the effect of coagulation.on the other hand,it can also oxidize a part of large molecular organic matter into small molecular organics,and then in the process of net trapping and sweeping,the small molecule organic matter are more likely to form flocs,thereby removed easily from the water.When oxidant concentration is 0.8 mg/L,1.6 mg/L,2.0 mg/L,respectively,the algae cells did not split up,and with the increase of the oxidation time,the removal rate of algal cell have been obviously improved.Compared with no pre-oxidation conditions,the removal rate increased by 20%,32%,38%at 0.8 mg/L,1.6 mg/L,2.0 mg/L of oxidant concentration,respectively.It is found that no significant change of zeta potential occurs through detection of zeta potential before and after oxidation reaction.Combining zeta potential and particle growth laws in the process of enhanced pre-oxidation coagulation,it is concluded that the coagulation mechanism is the net trapping and sweeping rather than electricity neutralization.The pre-chlorination will oxidize the part of the extracellular substances and reduce the consumption of the extracellular matter to the coagulant,thus improving the coagulant efficiency.Therefore,it is confirmed that EOM will inhibit the removal of cyanobacteria in the process of coagulation.