| Cationic polyacrylamide is the most widely used flocculant for sludge treatmentand enhancing the performance of sludge dewatering.The degree of chargeneutralization of CPAM has a significantly influence on sludge dewatering efficiencysince the excess sludge produced by municipal sewage plants is a stable colloidsuspension with negatively charged particles evenly distributed. The cationic units inmolecular chain ofthe cationic polyacrylamide prepared by traditional methodsarerandomly distributed, the positive charge is fragmentary, so electrical neutralizationof the cationic polyacrylamide is weak in the coagulation process and coagulation effectis not ideal. In order to redesign the molecular chain sequence of cationicpolyacrylamide and prepare a cationic polyacrylamide which has micro-block structuresand the cationic units are relative aggregation, we need to explore new preparationmethods of cationic polyacrylamide, and this is significant to achieve the targets ofsludge treatment: sludge reduction, stabilization, harmless and resource.Cationic polyacrylamide named P(AM-DAC) initiated by UV was synthesized inthis study with PAAS as template and acrylamide (AM) and acryloyloxyethyl trimethylammonium chloride (DAC) as monomers, respectively. Synthetic conditions werestudied and optimized by single-factor and orthogonal experiment. Results showed thata relative molecular weight of the P(AM-DAC) up to5.33million was attained withn(DAC）/n(PAAS)=1, total monomer mass fraction of30%, DAC concentration of25%,initiator V-50of0.065%, pH of4.5, urea concentration of30%and UV irradiation of60min;The sequence of the factors which impact the relative molecular weight ofP(AM-DAC) is DAC concentration, pH, initiator concentration, urea concentration andUV irradiation time.Effect of PAAS on CPAM structure during polymerization was analyzed bydeterming and comparingthe monomer reactivity ratios in the cases of with and withouttemplate in the polymerization systems. Results showed that the reactivity ratio of DACis larger when add template to the polymerization system, this indicated that reactivityof DAC increased at the presence of template, and which is conducive to the formationof micro-block structures.FTIR,1H-NMR, SEM and DSC-TGA were employed to study the chemicalstructure and thermal stability of the P(AM-DAC), respectively. Results demonstrated that the P(AM-DAC) prepared in this study was a copolymer of AM and DAC withmicro-block structure found at the molecular chain, and with a plenty of nonuniformconcave–convex structures on the surface. Overall, it exhibited a favorable thermalstability between30℃and200℃.Sludge dewatering performance with P(AM-DAC) copolymerized in this paperwas extensively studied. Parameters affecting the dewatering efficiency, such asflocculant dosage, relative molarmass and charge density of the copolymer, pH andtemperature of sludge, P(AM-DAC) with and without removing of PAAS wereexamined. A comparison dewatering efficiency of P(AM-DAC) with and withoutremoving of PAAS was conducted. In addition, dewatering performance of P(AM-DAC)was also compared with CPAM produced by Shandong and Japan industries. Resultsshowed that when the dosageof P(AM-DAC) was30mg/L, the relative molecularweight of P(AM-DAC) was5.33million, the cationic degreeof P(AM-DAC) was25%,the best sludge dewatering efficiency can be achieved. The sludge moisture content wasreduced to74.13%and the filtrate turbidity was down to12.1NTU. The optimum pHrange of thesludge was6~8. The temperature of the sludge had minor effect on sludgedewatering, while the higher temperature, the slightly better sludge dewatering result. Inthe sludge dewatering comparative experiments, the P(AM-DAC) separated templatewas better than the P(AM-DAC) unseparated template. The self-prepared P(AM-DAC)was slightly better than Japanese CPAM products and was obviously better thanShandong CPAM products on sludge dewatering result. The charge neutralization of theP(AM-DAC) played an important role during sludge dewatering. |
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