Ultrasonic-template Copolymerization Of TP(AM-AATPAC) And Its Application In Sludge Dewatering

With the speeding up of urbanization,the increasing sewage emissions produces a large amount of sludge with high moisture content?95%⁹9%?,and hence the sludge dewatering before its final disposal becomes very crucial.Cationic polyacrylamide?CPAM?has been widely used for sludge condition and dewatering.The negatively charged sludge particals are neutralized completely to lose their stability under the effect of electric neutralization and patching,and then aggregate together to form large and compact flocs under the effect of adsorption,bridging and compressed double electric layer.The generated large and compact flocs are more favorable for the sludge precipitation and the reduction of the sludge specific resistance,thus greatly improving the sludge dewatering performance.Therefore,it is of great significance to develop novel CPAM with enhanced sludge dewatering performance.However,the CPAM synthesized by traditional prepareration was limited to further improve and enhance its flocculation and dewatering performance by a significant drawback of the disordered and random cationic monomers distribution in the polymer chain.The randomly scattering cationic units could not maximize the charge neutralization and patching ability completely.As a result,the flocculation efficiency would be discounted greatly.Ultrasonic-template polymerization technology provided a new way for the research of CPAM,which could be employed to synthesize flocculant with microblock structure.The ability of charge neutralization can be greatly enhanced by the novel cationic microblock structure because flocculants with these novel structures were more efficient in neutralizing counterions,thus promoting flocculation and improving the flocculation and sludge dewatering efficiency.In this study,the ultrasonic?US?-initiated template copolymerization was employed to synthesize a novel cationic polyacrylamide TP?AM-AATPAC??TPAA?characterizedbyamicroblockstructureusing?3-Acrylamidopropyl?trimethylammonium chloride?AATPAC?and acrylamide?AM?as monomers,and sodium polyacrylate?NaPAA?as template.The factors affecting the polymer molecular weight and conversion were investigated.Meanwhile,the preparation conditions of TPAA were optimized by response surface test,and the mechanism of template polymerization was also discussed.TPAA was characterized by an evident cationic microblock structure which was observed through the analyses of the reactivity ratio,the polymer composition,the monomer sequence average length and distribution.Besides,the US-initiated template polymerization mechanism was discussed and determined through the investigation of association constant?K_M?and reaction kinetics.The properties of the polymers such as structure,thermal stability and surface morphology were characterized by Fourier transform infrared spectroscopy?FTIR?,¹H(¹³C)nuclear magnetic resonance spectroscopy(¹H(¹³C)NMR),scanning electron microscopy?SEM?and thermogravimetry/differential scanning calorimetry?TG/DSC?.Finally,the role of cationic microblock structure in TPAA and the polymers?TPAA,CPAA and commercial flocculants?flocculantion performance were evaluated by the municipal and dyeing sludge dewatering and condition.The mechanism involved in the process of sludge dewatering and flocculation for TPAA was summarized.The main contents and conclusions of this thesis are as follows:?1?During ultrasonic-template polymerization process,the factors affecting the polymer molecular weight and conversion were investigated,including ultrasonic power,ultrasonic time,initiator concentration,pH,n_AM:n_DMDAAC and n_NaPAA:n_DMDAAC.The significance of the influence factors related to the template polymer molecular weigh and the interaction were discussed through response surface analysis method,and the preparation parameters were also optimized by using this method.The free radical polymerization mechanism for ultrasonic-template initiation was analyzed,and the resulted indicated this mechanism included template adsorption,free radical chain initiation,polymer chain growth,chain transfer and chain termination.?2?The monomers competitive rate calculated by Kelen-Tud?s method showed that template polymerization could increase the cationic monomer?AATPAC?competitive rate in TPAA.Based on the above analytical results,the polymer copolymerization,and the length and distribution of micro blockblock structure were analyzed.It was found that the template polymerization could increase the convertion of the polymer,and also increase the average length and the number?>1?of the AATPAC block structure units in TPAA.?3?In order to deeply comprehend the template polymerization mechanism and the effect of template on the polymerization reaction system,the association constant?K_M?and reaction kinetics were systematically investigated.The value of the K_M manifested that the template polymerization mechanism belong to???ZIP mechanism.For the reaction kinetics,the effect of pH,the total monomer concentration and n_NaPAA:n_AATPACATPAC on conversion rate?C_v?and aggregation rate?R_p?of TPAA were investigated,and the results surported the conclusion of???ZIP mechanism for US-initiated polymerization.?4?The FTIR analysis results revealed that TPAA was successfully synthesized through copolymerization of AM and AATPAC.¹H NMR and ¹³C NMR analytical results showed that the formation of the cationic block structure and the sequence structure distribution of AAA,AAT and TAT in TPAA and CPAA,respectively.The TG/DSC analytical results manifested the favorable thermal stability for TPAA and CPAA.In addition,the double adsorption heat obsearved in the third weightloss phase indicated that the formation of cationic block structure in TPAA.At last,a porous structure with a rough surface area in TPAA was obaerved through SEM.?5?The effect of flocculant dosage,pH,molecular weight and cationic monomer ratio on the urban sludge dewatering and flocculation was investigated.The flocculation performance of TPAA was the most exccent among the flocculants and TPAA also showed a desirable sludge dewatering performance than those of the other three in a wider pH range?pH=4.0⁹.0?.With a rational range,the higher the molecular weight and the proportion of cationic monomer of the flocculant are,the better sludge dewatering performance are.The d₅₀ of the flocs conditioned by TPAA are larger than CPAA,CPDA and commercial CPMA after breakage.The D_f of the sludge flocs was related with the sludge dewatering efficiency,and the sludge flocs with a higher D_f indicated a lower SRF also,and thus a desirable sludge dewatering performance could be obtained.The cationic microblock structure played an important role in strengthening the effect of bridging,charge neutralization and patching.When the flocs were destroyed by the high sheer force,the broken fragments would rapidly aggregate to regrow large and compact flocs under the driving force generated by electrostatic attraction and patching.?6?The effect of flocculant dosage and pH on the dyeing sludge dewatering and flocculation was investigated.The results showed that the sludge dewatering and COD removal efficiency for TPAA were better than those of CPAA,CPDA-1 and CPDA-2 at the same dosage and pH.Due to the cationic block structure in TPAA,it can effectively improve the utilization efficiency of electric charge and enhance the neutralization and patching effect.As a result,the corresponding Zeta potential value of TPAA is the highest amoung the four flocculant at the same dosage.The amide bonds with high acid and alkali stability in TPAA results in a superior sludge dewatering performance in a wide pH range?pH=6.0¹0.0?.In the whole range of dosage(15⁹0 mg·L^-1),The cationic block structure in TPAA contributed much to the highest D_f of the flocs than that CPAA,CPDA-1 and CPDA-2,and which was conducive to the sldge and water separation.These larger and compact flocs acted as a stable skeleton construction and could withstand high pressure test,and hence more and more stable channels and voids formed.Therefore,it was easy for the water moisture to pass though the stable and pressure-resistant channels and voids,and the sludge filtration resistance and moisture content reached the minimum.