Study On Ultrasonic Synthesis Of P(AM-DAC) And Sludge Dewatering

Water demand increases with the development of society.And sludge collected from water treatment plant has been sharply increasing as well.The treatment and disposal of sludge have become the urgent problems that need to be solved.Sludge dewatering is an important way to solve these problems.But before that,sludge conditioning using coagulation is indispensable.Sludge conditioning improves the efficiency of sludge dewatering via reducing water content in sludge and promoting sludge properties.Flocculant plays a key role in coagulation.Cationic polyacrylamide has been used in the sludge conditioning due to its high molecular weight,stable structure,high treatment efficiency and high dissolubility.It is interesting to study the novel efficient flocculant for sludge conditioning.Ultrasonic initiation as a high efficient initiation method has been applied in the synthesis of cationic flocculant in recent years.Ultrasonic would generate cavitation bubble in the reaction solution.The momentary condition of high temperature and pressure caused by the expansion and burst of cavitation bubble triggers a series of free radical reactions.At the same time,ultrasonic enhances chemical reaction efficiency and reduces activation energy.However,ultrasonic has been rarely used in the preparation of cationic polyacrylamide.It is meaningful to investigate the synthesis of cationic polyacrylamide using ultrasonic initiation and the application of synthesized flocculant.In this study,ultrasonic initiation was applied in the preparation of cationic polyacrylamide.The key factors in the preparation were investigated and optimized.The composition,structure and characteristics of cationic polyacrylamide were studied via infrared spectrum analysis,nuclear magnetic resonance analysis,thermogravimetric analysis and scanning electron microscopy analysis.In the application of cationic polyacrylamide for the sludge conditioning of dyeing sludge and domestic sludge,the different efficiency of sludge conditioning was obtained at the different coagulation condition.The main contents and conclusions were as follows:(1)Synthesis of cationic polyacrylamide(P(AM-DAC))P(AM-DAC)was successfully synthesized via ultrasonic initiation using two monomer of allyl ethyl three methyl ammonium chloride(DAC)and acrylamide(AM)and initiator of VA044.The effect of factors on the intrinsic viscosity of P(AM-DAC)in the synthesis were studied through single factor analysis.And the optimal synthesis condition was AM:DAC of 6:4,total monomer content of 40%,initiator concentration of 0.02%,pH of 4,urea content of 0.4‰,EDTA content of 0.4‰,reaction temperature of 35? and ultrasonic time of 20 min.In this optimal synthesis condition,the highest intrinsic viscosity of P(AM-DAC)of 1266 ml?g-1 was obtained.(2)Characterization of P(AM-DAC)The characteristic absorption peaks and proton peaks of P(AM-DAC)were found in the infrared spectrum and 1H-NMR spectrum,respectively.It confirmed P(AM-DAC)was synthesized via the copolymerization of AM and DAC.The results of thermogravimetric analysis confirmed that P(AM-DAC)possessed the acceptable thermostability at the temperature range of 30-200?.The plicated porous structure at the surface of P(AM-DAC)improved the sludge conditioning and sludge dewatering.(3)Application of P(AM-DAC)in sludge dewateringThe synthesized flocculants via ultrasonic initiation were applied in the sludge dew atering of dyeing sludge and excess activated sludge.In the dyeing sludge treatment,the optimal dosage of P(AM–DAC)was 50 mg?L-1 and the optimal pH was 8.In the treat ment of excess activated sludge,the optimal dosage of P(AM–DAC)and pH changed to40 mg?L-1 and 7,respectively.Charge neutralization of P(AM–DAC)was improved wi th the increase of cationic degree at the range of 0 to 30% in the sludge dewatering.Ho wever,the increase of cationic degree would not obviously enhance coagulation when c ationic degree was more than 30%.At the optimal cationic degree,the higher intrinsic v iscosity contributed to the better dewatering performance of P(AM–DAC)in terms of th e bigger flocs size,the lower specific resistance of sludge,the better settling performanc e,the lower residual turbidity and the higher solid content of filter cake.