| Water is the basic substance for human survival,so it is particularly significant to develop green and efficient water treatment technologies when in the face of the increasingly severe water pollution situation.Among the multitude of processes for water purification,flocculation is widely used because of its high efficiency,low cost,simple operation and other advantages.Flocculant is the key to flocculation,which directly affects the flocculation performance in water treatment process.Compared with inorganic flocculants,cationic organic polymer have the superiorities of low dosage,large floc,wide range of pH,etc.Therefore,it is widely used in drinking water and various wastewaters treatment and sludge dewatering.Cationic polyacrylamide(CPAM)is currently the most widely used cationic organic polymer flocculant.The commonly used methods of initiating polymerization include thermal initiation,radiation initiation and UV initiation,Among them,UV-initiated polymerization has been studied due to its advantages such as short-time reaction,low dosage initiator,facile operation,environmental friendliness,etc.However,previous studies have focused on the use of long wavelength ultraviolet light generated by high pressure ultraviolet lamp as the light source,there are rare researches using low pressure as the light source.The low pressure ultraviolet light consumes lower energy,produces less heat,leaves out the condensing device and simplify the synthetic apparatus in comparison with the high pressure ultraviolet light.Facing the serious challenge of global warming,low pressure UV-initiated polymerization is more in line with the trend of low carbon and energy saving.Therefore,in the current work,based on the low pressure UV-initiated polymerization system,CPAM with high intrinsic viscosity and cationic degree was synthesized.The structure and morphology were analyzed by means of different characterizations.At last,the synthesized flocculant was used for the removal of inorganic and organic pollutants.The main research contents and conclusions include:(1)Preparation and optimization of cationic polyacrylamide flocculant.Cationic flocculant PAMC was synthesized using acrylamide(AM)and methacryloyloxyethyl trimethyl ammonium chloride(three DMC)as the monomer,with 2-hydroxy-4-(2-hydroxyethoxy)-2-methyl benzene acetone(Irgacure2959)as photo-initiator underthe 48 W,low pressure ultraviolet light of 254 nm.The effects of monomer concentration,DMC concentration,initiator concentration,pH and illumination time on the intrinsic viscosity of PAMC were studied through single factor experiments.The main factors were determined and the significance of factors were analyzed by orthogonal experiment.(2)Characterization of structure and morphology and analysis of polymerization mechanism.The functional groups,surface morphology,thermal stability and surface charge of PAMC were analyzed by means of Fourier transform infrared spectrometer(FT-IR),nuclear magnetic resonance spectroscopy(1H-NMR),scanning electron microscopy(SEM),thermogravimetric analyzer(TGA-DTA)and Zeta potential analyzer.In addition,based on the free radical polymerization theory and the analysis of the characterization results,the possible polymerization mechanism of PAMC was discussed from the aspects of chain initiation,chain growth,chain termination and chain transfer.(3)Study on the removal of simulated water samples with high turbidity kaolin by synthetic flocculants.The effects of different acidic and alkaline conditions,flocculant dosage and initial turbidity,etc on the removal of kaolin were investigated,The flocculation conditions were optimized by response surface methodology(RSM),and the interaction between the factors was analyzed.Furthermore,the flocculation mechanism of kaolin was investigated through the study of the changes of Zeta and flocculation kinetics.(4)Study on the removal of humic acid from simulated water samples by synthetic flocculants.The effects of initial pH,flocculant dosage and initial concentration,etc on the removal of humic acid were studied through single factor experiments,The effect of flocculant dosage,initial pH of simulated water,stirring time and stirring speed on humic acid removal efficiency was investigated and the significance of factors were analyzed by orthogonal experiments.The structure of flocs was studied by fractal theory,and the changes of humic acid before and after flocculation were investigated by means of three dimensional fluorescence(3D EEM).(5)Study on the removal of kaolin and humic acid mixed simulated watersamples by synthetic flocculants.The effects of flocculant dosage on the removal of kaolin and humic acid and zeta potential changes under different pH conditions were studied.The changes of humic acid in mixed water samples before and after removal were analyzed by three dimensional fluorescence(3D EEM),Synergistic flocculation mechanism between kaolin and humic acid was analyzed. |
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