Effect Of Cationic Polyacrylamide Microstructure On Sludge Conditioning Performance

Cationic acrylamide (CPAM) is the most commonly used sludge condtioning agent.The amount of sludge that needs to be treated increased fast with the incrase emission ofmunicipal and industrial wastewater and the wasterwater treatment depth. Consequently,CPAM demand was increased vastly. However, the preparation technology of CPAM inour country needs to be improved. The sludge conditioning performance was improvedthrough increasing the relative molecular weight of CPAM for traditional methods. Fewstudies have focused on effect of CPAM sequence distribution (i.e. microstructure) onsludge conditioning and improving the sludge condtioning performance throughoptimizing the micrstructure of CPAM.In this present study, effect of charge density on CPAM unit sequence distributionwas extensively studied. Sludge conditioning performance by different microstructureCPAM was compared and analyzed through previous CPAM microstructure conclusion.The needed sequence distribution of CPAM with acceptable sludge conditioningperformance was given. Accordingly, the UV initiated template polymerization studywas conducted. Main contents and conclusions were as following:①The reactivity ratio of AM and DAC through UV initiated solutionpolymerization was measured and calculated. The microstructure of CPAM withdifferent charge density was analysed based on the reactivity ratios. Results indicatedthat blockness percent and mean sequence length of acrylamide (AM) unit decreased,whereas those of cationic unit increased with CD. Fourier transform infrared (FT IR)spectroscopy, thermo gravimetric analysis (TGA),1H and13C nuclear magneticresonance (1H NMR and13C NMR) spectroscopy to study were used to characterize thecomponents and structure features. The components of the copolymer were confirmedand1H NMR can be used to examine whether two monomers have been copolymerized.Furthermore,1H NMR, a valuable method in estimating cationic blockness percent ofP(AM-DAC), was proposed for the first time.②Effect of charge density on sludge conditioning performance was compared andanalyzed through measuring turbidity, filter cake moisture content (FCMC), specificresistance of filtration (SRF), and zeta potential. The negative relationship betweenoptimum dosage and charge density suggested that microstructure played an importantrole in flocculating suspended particles. It was pointed out that CPAM with low charge density and blocked cationic units should perform well in sludge conditioning.③Cationic polyacrylamide initiated by UV was synthesized in this study withPAAS as template and acrylamide (AM) and acryloyloxyethyl trimethyl ammoniumchloride (DAC) as monomers based on the previous conclusion, respectively. Effect ofratio between template polymer unit and cationic monomer (T:D) on reactivity ratio wasmeasured and calcuated. The addition of template could increase the reactive behaviorof DAC and decrease the reactive behavior of AM and the template function was themost obvious when T:D was1.0. The template polymer was further characterized by FTIR, TGA,1H NMR and13C NMR. According to1H NMR spectra, AM and DAC werecompolymerized and the blocked cationic structure of the template polymer.④Synthetic conditions were studied and optimized to improve the flocculantbridging effect by single-factor and orthogonal experiment with intrinsic viscosity as theoptimize goal. Results showed that an intrinsic viscosity of the P(AM-DAC) up to11.42dL/g was attained, total monomer mass fraction of30%, DAC concentration of25%, initiator V-50of0.065%, pH of4.5, urea concentration of30%and UV irradiationof60min when T:D was1.0; The sequence of the factors which impact the intrinsicviscosity of template polymer was DAC concentration, pH, initiator concentration, ureaconcentration and UV irradiation time.⑤The dewatering performance and mechanism of template copolymer wascompared with CPAM prepared through solution polymerization. Results showed thattemplate polymer with the highest intrinsic viscosity performed best in sludgeconditioning as both charge neutralization and bridging effect was excellent. Copolymerwith template removal performed than those without template removal. The reason wasthat the template polymer affected the copolymer charge neutralization performance. Inaddition, it was suggeted that the market application foreground of UV initiatedtemplate compolymer was acceptable as the flocculants performed better than thosebought from the market.