Mechanism Research Of Enhanced Coagulation Performance Of Composite Coagulant

The interaction between two components, Polyaluminium Chloride(PAC) and Poly-dimethyldiallylammonium chloride (PDMDAAC) in composite coagulant and its correlation with the coagulation performance of the composite coagulant were researched in this paper. Meanwhile, the storage stability of the composite coagulant was researched.Acid-alkali titration and Al-Ferron complexation timed spectrophotometry were used to research the influences of intrinsic viscosity and mass percent of PDMDAAC on the basicity and aluminum species distribution in composite coagulants. Jar test model I was employed to research the correlation between these influences and the coagulation performance of composite coagulants. The results showed that the basicity and aluminum species distribution in composite coagulants don't change observably with the intrinsic viscosity of PDMAAC increasing from 0.87dL/g to 3.79dL/g or the PDMDAAC mass percent increasing from 5% to 20%. Jar test results indicated that the increasing of PDMDAAC mass percent enhanced the turbidity removal significantly and the increasing of PDMDAAC intrinsic viscosity enhanced it slightly. Therefore, there is no direct correlation between the influences of PDMDAAC on basicity or aluminum species distribution of PAC in the composite coagulants and the turbidity removal of the composite coagulants.Ubbelohde viscometer was used to research the influence of PAC on the viscosity behavior of PDMDAAC and the five inorganic salts selected as contrast samples added in PDMDAAC respectively were used to compered with PAC in the influence. The jar test modelⅡwas employed to research the correlation between these influences and the coagulation performance of PDMDDAAC. Results showed that the influence of PAC on viscosity behavior of PDMDAAC was ranged among that of AlCl3 and NaCl, and changed with the basicity of PAC, the sequence was from strength to weakness:Na3PO4> Na2SO4> AlCl3> MgCl2≈PAC(B=51%)> PAC(B=68%)> PAC(B=80%)≈PAC(B=88%)≈NaCl. The jar test results indicated that, as coagulants, PAC and AlCl3 could enhance the coagulation performance of PDMDAAC obviously. The salts NaCl, Na2SO4 and MgCl2 had no influence on the coagulation performance while Na3PO4 first weakened then enhanced the performance. Therefore, there is no direct correlation between the influence of PAC on viscosity behavior and the coagulation performance of PDMDAACAl-Ferron complexation timed spectrophotometry was used to test the changes of the Aluminum species in composite coagulants before and after stored at room temperature or at 80℃in water bath, and the jar model testⅢwas employed to evaluate the variation of coagulation performance using composite coagulants. The results showed that no obvious change of aluminum species distribution in composite coagulants, caused by stored in different time at room temperature or at 80℃,could been observed. The jar test results indicated that the obvious changes of removal efficiency in turbidity and CODMn by composite coagulants resulted from storage were still not measured. Therefore, composite coagulants PAC/PDMDAAC had behaved good storage stability.The excellent enthancing coagulation performance of composite coagulant PAC/PDMDAAC, which has good storage stability, might be results from the synergistic effect of PAC and PDMDAAC in coagulation process.