Study Of Flocculation Performance Of Quanternary Ammonium Salt Of Chitosan

Quanternary ammonium salt of chitosan is synthesized on the base of former researches,with water solution of 2,3-epoxypropyltrimethyl ammonium chloride added at trice. The obtained quanternary ammonium salt of chitosan lays foundation for the following flocculation experiments.The effect of quanternary ammonium salt of chitosan on the treatment of domestic sewage from Tuandao sewage plant is studied.The optimum dose,stirring conditions and pH value on the flocculation performance are ascertained. The results indicate that, the optimum flocculation performance is achieved at dosage 16～18 mg/L and pH between 5～9;the highest turbidity and CODCr removal efficiency are 93.9%and 48.3%respectively. The flocculation performance of quanternary ammonium salt of chitosan is compared with that of chitosan and other flocculants in the documents.The results indicate that,the flocculation effect of quanternary ammonium salt of chitosan is much better than that of chitosan: turbidity and CODCr removal efficiency are higher,and the optimum flocculation range of dosage and pH are wider.Compared with other flocculants,HACC is more efficient in turbidity removal.Kaoline, one of the suspended granules is chosen as flocculation object.The flocculation performance of quanternary ammonium salt of chitosan is studied.Influence of dosage and stirring conditions under different initial turbidities on residual turbidities is investigated.The results indicate that the flocculant dosage increases slowly with increasing initial turbities. There is no distinct increase of stirring time, while turbitiy removal efficiency increases sharply as initial turbidities increases.The configuration of floc of different time are observed by SEM and theories of flocculation are studied. The results indicate that the dominating theroies are charge neutralisation and bridging: some quanternary ammonium of chitosan is adsorbed on suspended granules firstly, decreasing the surface potential,then through the bridging of the residual flocculant,the dimension of the floc increases and the configuration turns denser.The effects of the combination of quanternary ammonium of chitosan and PAC on improving turbidity and aluminum removal efficiency , the optimal dosage of them and stirring conditions, are studied. With the aid of SEM, the flocculating aid theroy of quanternary ammonium of chitosan is studied. The results showed that, in the treatment of kaoline with tubidity of 22NTU,the optimum dosage of PAC is15mg/L and HACC is 0.015mg/L,50% of PAC ang 70% of HACC is economized when use HACC as flocculation aid. Within PACdosage among 14 to16mg/L,pH among 5 to 9,residual turbidity and alminum are below 3NTU and 0.2mg/L respectively. The optimum rapid strring conditions are 350r/min ,12s(for PAC),200r/min 70s(for HACC)and slow strring at 50r/min,20min.The flocculating aid theroy of quanternary ammonium of chitosan is concluded to be bridging.