Preparation Of Chitosan Quaternary Ammonium Salt And Its Influence On Coagulation-ultrafiltration Process

In the field of recycled water reuse,the secondary effluent of urban wastewater treatment plants has gradually become one of the important components of recycled water sources based on factors such as low treatment costs and abundant and stable water volume.However,the secondary effluent of the wastewater treatment plant still faces the problem that the dissolved organic matter pollutants cannot be completely and effectively removed,and the safety and health risks of direct reuse will increase,so it must be advanced treatment to meet the increasingly stringent water quality requirements and Reuse standard.The advanced sewage treatment technology with the precoagulation-ultrafiltration system as the core is of great significance to the regeneration and reuse of the current sewage and alleviation of the water resources crisis.It can not only alleviate the problem of membrane pollution,but also ensure the quality of the recycled water.The choice of coagulant in pre-coagulation is very important for the stable operation of the whole system and the quality of effluent,and it needs to be strictly controlled in actual operation.In this study,in view of the problems of poor solubility and poor coagulation ability of chitosan（CTS）,3-chloro-2-hydroxypropyltrimethylammonium chloride（CTA）was used as an etherifying agent to introduce quaternary ammonium salt groups to its After chemical modification,water-soluble chitosan-chitosan quaternary ammonium salt（HTCC）was prepared.Taking the secondary effluent of WWTP as the treatment object,the prepared HTCC was selected as coagulant,and the basic properties of HTCC,the coagulation performance of HTCC and the effect of HTCC on the secondary effluent of WWTP treated by coagulation-ultrafiltration technology were studied.HTCC was prepared by introducing quaternary ammonium salt groups on CTS.The study found that when the reaction temperature was 70°C,the reaction time was8 h,and the CTS/CTA mass ratio was 1:5,the prepared HTCC had the highest substitution degree of 96.67%;After chemical modification,the soluble p H range of HTCC was greatly broadened,the solubility was increased from 3.23 mg/m L to 17.22mg/m L,the water solubility was significantly improved,and the surface charge was also increased.The solubility and surface potential of HTCC also increased.The flocculation effect of HTCC on the secondary effluent of the wastewater treatment plant is affected by the dosage,p H and HTCC substitution degree.The optimal dosage is 3 mg/L,the optimal p H working range is 5～9,and the HTCC substitution degree reaches 96.7%,the highest removal rates of turbidity and UV₂₅₄were 80.7%and 49.1%,respectively;compared with CTS coagulant,the removal rates of turbidity and UV254 were increased by 24.86 and 21.7 percentage points,respectively,and polyaluminum chloride（PAC）),the removal effects of turbidity and UV₂₅₄are comparable,but HTCC requires less dosage,and HTCC has a wider p H range for coagulation than the two;HTCC has an electrical neutralization effect during flocculation under optimal conditions Just as important as adsorption and bridging,HTCC itself also plays the role of catching and sweeping.Under the optimal coagulation conditions,HTCC can strengthen the removal of organic matter and fluorescent substances by ultrafiltration,effectively reduce the decrease of the flux of the ultrafiltration membrane,and at the same time have a high recovery rate of backwashing.The resistance,reversible resistance and irreversible resistance decreased by 46.07%,59.13%and 68.42%respectively;HTCC coagulation pretreatment can absorb some dissolved organic matter through coagulation on the one hand,and relieve the blockage of membrane pores,on the other hand,the larger flocs can reduce the blockage of membrane pores.The formed loose porous filter cake layer further adsorbs and removes small molecular organic matter,and strengthens the mitigation effect on membrane fouling.In this paper,the pretreatment method of HTCC coagulation is used to systematically study and evaluate the enhancement of ultrafiltration water purification efficiency and the mitigation of membrane fouling,as well as the mechanism of membrane fouling.The research results can be used for advanced sewage treatment technology.And the secondary effluent reuse provides new ideas,and at the same time plays a positive role in the promotion and application of modified natural organic coagulants in the field of advanced sewage treatment.