The Research Of Flocculation To Remove Cyanobacteria By Chitosan Modified Vermiculite

Cyanobacteria blossomwould destroy the ecological balance of water,resulting in the deterioration of water quality andthreatening the health of human by affecting the safety drinking water.Using clay flocculation to remove algae is considered as one of most promising methods for the algaeremoval.In this paper,the modified vermiculite with chitosan is used to remove cyanobacteria.The effects of the modified approach,vermiculite particle size,dosage,dosage ratio of chitosan vermiculite,algae density,initial pH,algae growth,the impact of extracellular organic matter(EOM)as well as other factors on the algaeremoval are well studied.By analyzing the Zeta potential and algae floc,the mechanism of chitosan modified vermiculite flocculation of algae is studied,and compared of algae removal effect with the PAC,the following conclusions and the following conclusions are drawn:(1)Individual vermiculite flocculation algae removal rates only between 10% and 15%,modified vermiculite with five modifier,vermiculite modified by chitosan was the best.Chitosan flocculation algae the best flocculation condition is: dosage of 1.8mg / L,removal rates of turbidity,algal density and chlorophyll a(chl-a)were 93.21%,96.17% and 95.63%.(2)When the particle size and dosage of vermiculite are respectively 120 and18 mg / L,and the ratio of chitosan and vermiculite is 1:15,using the method of flocculationton remove cyanobacteria could achieve better results;In this way,the turbidity,algal density and removal rates of chl-a could reach 95.16%,96.67%,100%,which is far better than using chitosan flocculation alone.The maximum difference of removing algal cells with different densities could be 10%,indicating that chitosan flocculation method has great removal capacity which can be used for preventing algae outbreak.In addition,the pH value of the water will affect the removal efficiency a lot.When pH is greater than 8,the efficiency of the algal removal would decline a lot.(3)The late decline algal cell's value DOC higher than others,and difficult to handle compared with other growing,the removal of algal cells rates is only about 30%.Excessive EOM will suppress algae flocculation.The EOM contents in water after removal is about logarithmic phase of 4.6 times,but the removal of algal cells is only 1/3 of normal value.EOM will increase the dosage of chitosan modified vermiculite by 3 times to reach the same removal effects.EOM has high inhibitory effect to remove algae when the solution is low(DOC<10 mL),but has inverse effect when the solution is high(DOC>30 mL).(4)Modified Chitosan could change Zeta potential intopositive,and neutralize negative potentials of the algal cells.According to the SEM analysis and fractal dimension calculation,thealgal cells vermiculite is mainly used as condensation nuclei to form spherical floc wrapped into net structures,fractal dimension is 1.832,higher than chitosan,both synergies and enhance the adhesion bridging and netting roll sweep.The main mechanisms of chitosan modified vermiculite are electrical neutralization,adhesion bridges,netting roll sweep effect.(5)The results of removal of algal cells between PAC and chitosan modified vermiculite was less than 5%,but the settling time of PACis six times than that of.Floc form of Chitosan Modified Vermiculite is globular,larger,more dense,stronger anti-disturbance and settling velocity faster.PAC could lead to the problems of aluminum residues.Chitosan modified vermiculite is natural andhas ecological benefits,for the algae floc would be collectedas plantfertilizer.Therebyusing chitosan modified vermiculite for algae removal is feasible.