| As an important drinking water source for urban and rural life in China,in recent years,with the rapid development of industry and agriculture,the application of a large amount of nitrogen fertilizer and the improper treatment of industrial and domestic sewage have led to the increasingly serious pollution of nitrate nitrogen and ammonia nitrogen in groundwater.At present,most of the groundwater pollutants exceeding the standard in northern China are mainly nitrate nitrogen and ammonia nitrogen.Residents drinking groundwater contaminated with nitrate nitrogen and ammonia nitrogen for a long time will cause an increase in methemoglobin,and in severe cases,it will also lead to cancerous diseases.Groundwater treatment of nitrogen and ammonia nitrogen pollution is of great significance to drinking water safety in Northeast China.In this study,the groundwater source in northern China was polluted by nitrate nitrogen and ammonia nitrogen,and the optimal chitosan modified filter material was selected for dynamic simulation experiments to study its nitrogen removal and filtration efficiency,and to provide theoretical references for practical applications.The main research contents of this thesis include the following four parts:(1)Comparative study on chitosan modified filter materials: Six filter materials(quartz sand,activated carbon,diatomite,ceramsite,natural zeolite,zeolite molecular sieve)were modified by chitosan,and the removal effect of nitrate nitrogen and ammonia nitrogen before and after chitosan modified filter was compared.The results showed that the chitosan modified filter material was better than the unmodified filter material in removing nitrate nitrogen and ammonia nitrogen.The stability of chitosan modified filter was further studied by changing temperature,p H value of raw water and concentration of raw water.The results showed that the removal effect of chitosan modified filter material on nitrate nitrogen and ammonia nitrogen increased gradually within the temperature range of 10~30 ?,indicating that the increase of temperature was beneficial to the adsorption reaction.Chitosan modified filter material had the best removal effect on nitrate nitrogen when the p H value was 4.5~5.0,while chitosan modified filter material had the best removal effect on ammonia nitrogen when the p H value was 6.5~7.0.Nitrate nitrogen concentration of raw water is 40 mg/L,the chitosan modified filter material for best treatment effect of nitrate nitrogen,ammonia nitrogen concentration of raw water for 7 mg/L,the chitosan modified filter material of nitrate nitrogen removal effect is best,and no matter in what kind of influence factor conditions,chitosan modified zeolite molecular sieve of nitrate nitrogen and ammonia nitrogen removal effect is the best,so eventually determine chitosan modified zeolite molecular sieve as the best modified filter material.(2)Experimental study on filtration efficiency of nitrate nitrogen by chitosan modified zeolite molecular sieve: through the study of filter height and filter speed,the optimal process parameters of chitosan modified zeolite molecular sieve for filtering nitrate nitrogen were determined.The test results showed that the optimal process parameters were: the filter height was 70 cm and the filter speed was 4 m/h.The effects of different influencing factors,including temperature,p H value of raw water and concentration of raw water on nitrate nitrogen filtration by chitosan modified zeolite were studied.The results showed that the chitosan modified zeolite molecular sieve had the best filtering effect on nitrate nitrogen,up to 48.43%,at room temperature(25 ?),p H value of raw water was 4.5~5.0 and concentration of raw water was 40 mg/L.(3)Experimental study on the filtration efficiency of ammonia nitrogen modified zeolite molecular sieves: The optimum process parameters for the filtration of ammonia nitrogen by chitosan modified zeolite molecular sieves were determined by the study of filter height and filtration rate.The test results showed that the optimal process parameters were: the filter height was 70 cm and the filter speed was 4 m/h.the effects of different influencing factors,including temperature,raw water p H and raw water concentration on the filtration of ammonia nitrogen by chitosan modified zeolite molecular sieve were studied.The results showed that the chitosan modified zeolite molecular sieve has the best filtering effect on ammonia nitrogen at room temperature(25 ?),p H value of raw water was 6.5~7.0,and raw water concentration was 7 mg/L.(4)The mechanism of chitosan modified zeolite molecular sieve filtration: The kinetic model studies show that the adsorption process of nitrate nitrogen and ammonia nitrogen by chitosan modified zeolite molecular sieves conforms to the Thomas adsorption kinetic model.SEM,EDS,and FTIR were used to analyze the physicochemical characteristics of the chitosan modified zeolite molecular sieve before and after filtration,so as to analyze the filtration mechanism of the chitosan modified zeolite molecular sieve before and after filtration.The results showed that the original uneven structure on the surface of the chitosan modified zeolite molecular sieve filtered with nitrate nitrogen and ammonia nitrogen disappeared,indicating that the nitrate nitrogen and ammonia nitrogen were successfully adsorbed;both the chitosan modified zeolite molecular sieve retained silica aluminoxide before and after filtration Tetrahedron structure.High-throughput sequencing was used to study the filtration mechanism of microorganisms on the filtration of nitrate nitrogen and ammonia nitrogen by chitosan modified zeolite molecular sieves,and the results showed that certain colonies with denitrification function were generated on the surface of the filter material.The research results of filtration performance and mechanism of chitosan modified zeolite molecular sieve can provide technical support for the safe water supply of groundwater drinking water source in northern China. |
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