The Preparation Of Chitosan Modified By Quaternary Ammonium Salt And It's Effect On Membrane Fouling

With the rapid development of economy and continuous improvement of industrial level,source water pollution is becoming more and more serious,and the current conventional water supply treatment technology is increasingly difficult to meet the sanitary standard of drinking water(GB5749-2006).Membrane technology is gradually applied to water treatment,but serious membrane pollution hinders the development of membrane technology.In this study,chitosan quaternary ammonium salt coagulant was prepared by using 3-chloro-2-hydroxypropyltrimethylammonium chloride(CTA)modified chitosan(CS),and CS-CTA was applied to the coagulation-microfiltration process to study its influence on effluent water quality and membrane pollution.The effects of reaction temperature,mass ratio of CTA/CS,NaOH/CTA mass ratio and reaction time on the degree of substitution of CS-CTA were studied,and the preparation of chitosan quaternary ammonium salt was optimized by response surface method.The results showed that the degree of substitution of CS-CTA was affected by the following four factors:reaction temperature>mass ratio of NaOH/CTA>mass ratio of CTA/CS>reaction time.After optimization,the best preparation conditions of chitosan quaternary ammonium salt of CTA/CS quality ratio 4.929 8 h,reaction time,reaction temperature of 68.4?,NaOH/CTA quality ratio 1.17,under the condition of the predictive value of 96.34%,the experimental values is 96.29%,the response surface predicted results are in agreement with the experimental value results.The coagulation experiment of CS-CTA on simulated water samples of humic acid-kaolin was conducted to study the coagulation effect of CS-CTA.Furthermore,the characteristics of CS-CTA flocs were analyzed.The experimental results showed that the optimal coagulation conditions of CS-CTA were 4.0mg/L,pH=5,optimal stirring conditions were 300r/min for 30s,150r/min for 5min,and 50r/min for 15min.The particle size of the flocs increased first and then decreased with the increase of the dosage of CS-CTA and the pH value of the water sample.When the adding amount was 3mg/L and the pH value of the water sample was 7,the particle size of the flocs was the largest.With the increase of shear force,the strength of flocs decreases gradually,and the recovery factors of flocs increase first and then decrease.Under different pH,floc strength coefficient(?~')increased first and then decreased with the increase of pH.The fractal dimension of flocs increased with the increase of adding amount.With the increase of pH value,the fractal dimension of flocs first decreased and then increased.At pH=5,the fractal dimension of flocs was the least.The fractal dimension of flocs under acidic condition is lower than that under alkaline condition.CS-CTA was used as the coagulant to study the treatment effect of coagulation-microfiltration process on simulated water samples of humic acid-kaolin,and the effect of CS-CTA as the coagulant on membrane fouling of microfiltration membrane.The results showed that the optimal dosage and pH of coagulation-microfiltration process for simulated water samples were 4mg/L and pH=5.With the increase of dosage,the specific flux of the membrane first increased and then decreased,and reached the maximum value of 43.8%when dosage was3mg/L.With the increase of pH,the specific flux of the membrane first increased and then decreased,reaching the maximum at pH=5(57.3%).Moreover,under acidic conditions,the specific flux of the membrane was higher than that under basic conditions.With the increase of dosage,irreversible resistance,total membrane resistance and MFI of the microfiltration membrane all decreased first and then increased,reaching the minimum at dosage of 3mg/L.Membrane fouling at different pH decreases first and then increases with the increase of pH,and reaches the minimum when pH=5.When CS-CTA was added,the specific flux of the final membrane was higher than that when it was not added,and the calculated irreversible membrane resistance,total membrane resistance and MFI were all lower than that when it was not added,indicating that CS-CTA could alleviate the pollution of microfiltration membrane.According to the fitting results of Hermia formula,the filter cake layer model has the best fitting results,indicating that the formation of filter cake layer is the main reason for the decline of membrane flux of the microfiltration membrane.