Performance And Mechanism Of Polyferric-Organic Polymer Composite Flocculants In Surface Water Treatment

In order to ensure the safety of drinking water and improve the coagulation efficiency in the treatment of surface water,and especially enhance the organic matter removal in micro-polluted source waters,a series of composite coagulants polyferric chloride(PFC)-polydimethyldiallyammonium chloride(PDADMAC)with different basicity(B)of PFC,different mass fraction(w(P))and intrinsic viscosity(η)of PDADMAC were prepared and applied to surface water treatment in this study.The advantage of PFC-PDADMAC over PFC,PDADMAC and successive addition of PFC and PDADMAC in coagulation efficiency and the difference of them in coagulation mechanism were revealed by comparative study of them.Further.the reaction between PFC-PDADMAC and pollutants and the interacting of PFC and PDADMAC in coagulation process were also explained.The effect of B value,w(P) andηvalue on coagulation efficiency,chemical species distribution of Fe(Ⅲ)in coagulation process,floc growth process,breakage resistance capability of floc.the regrowth ability of broken floc,shape of floc and coagulation mechanism were studied by a variety of methods and technology,such as jar test,zeta potential measurement,Fe-Ferron method and static light scatter technology.The main conclusions are as follows:(1)PFC-PDADMAC was more efficient than PFC and PDADMAC in turbidity and organic matter removal in surface water treatment,and it achieved high removal rate at lower coagulant dosage.Compared with successive addition of PFC and PDADMAC,PFC-PDADMAC gave higher turbidity and organic matter removal and achieved better coagulation efficiency within a broader dosage range which contributed to avoid deterioration of treated water resulted from the fluctuation of raw water quality to some extent;Further,the flocs formed by PFC-PDADMAC had better settling property,and PFC-PDADMAC yielded more active component of ferric salts coagulants in coagulation process.PFC-PDADMAC showed weaker charge neutralization ability but much stronger adsorption and bridging ability than succecive addition of PFC and PDADMAC.Consequently.PFC-PDADMAC achieved good performance in surface water treatmenr by synergic effect of PFC and PDADMAC.(2)PFC-PDADMAC achieved better turbidity and organic matter removal at lower B value,higher w(P)andηvalue.Moreover,The effect of w(P)on the coagulation performance was remarkable,while the effect of B value was relatively slight.(3)B value had significant effect on the chemical species distribution of Fe(Ⅲ)in coagulation process,and PFC-PDADMAC with lower B value yielded more active coagulating component of ferric salts coagulants.In contrast,w(P)andηonly had slight effect on it.(4)Charge neutralization is the dominant flocculation mechanism for PFC-PDADMAC with different B value,w(P)andηwhich were investigated in this study,and the charge neutralization ability of PFC-PDADMAC was enhanced to some extent by reducing B value,increasing w(P)orηvalue properly.(5)The flocs formed by PFC-PDADMAC with lower B value,higher w(P)orηvalue showed higher growth rate and achieved larger floc size in steady phase of coagulation process.Further,w(P)had significant effect on floc growth rate and floc size,while the effect of B value was relatively slight.(6)The flocs formed by PFC-PDADMAC with lower B value,higher w(P)orηvalue showed better breakage resistance capability,regrowth ability and had more compact structure.Moreover,The effect of w(P)on the aboving floc characteristic was remarkable,while the effect of B value was slight.The aboving results indicate that PFC-PDADMAC is a new-type and highly efficient inorganic-organic composite coagulant which applies to surface water treatment.Further.this thesis lays fundamental basis for the developing of PFC-PDADMAC and provides guidences for the practical application of it.