| With the development of industrial production and the improvement of living standards,the random discharge and treatment results of rural domestic sewage are not up to standard,resulting in increasingly serious environmental pollution and damage.In order to strengthen the treatment effect of the constructed wetland system on total phosphorus,ammonia nitrogen and COD in rural domestic sewage,and speed up the solution of the serious problem of rural domestic sewage polluting the surrounding environment.In this thesis,the clinoptilolite is used as the matrix material of the constructed wetland,and the composite modified zeolite is obtained by the modification of sodium hydroxide and ferric chloride as the adsorption material.Factors such as particle size,zeolite dosage,p H value and modification method are studied The effect on the treatment effect was discussed,and the adsorption mechanism of the compound modified zeolite in the treatment of rural domestic sewage was discussed.After determining the optimal process conditions for the removal of pollutants by the composite modified zeolite,the composite modified zeolite was applied in the pilot-scale reaction of the constructed wetland to study the operation effect of the composite modified zeolite in the actual project.The result obtained is as follows:(1)The comparative experiments of corn stover and clinoptilolite in the treatment of pollutants in sewage show that the clinoptilolite removal effect is better.The dosage of compound modified zeolite in the sewage is 20g/L,the particle size is 0.2-0.4mm,and under the condition of p H=7,when the reaction reaches equilibrium,the removal rate of total phosphorus is 84.12%,and the removal rate of ammonia nitrogen is 81.89%.The removal rate of COD was 83.41%.(2)The adsorption isotherms and adsorption kinetics of the composite modified zeolite for the adsorption of total phosphorus,ammonia nitrogen and COD were studied.The results show that,for the three pollutants,the Langmuir equation fits better than the Freundlich equation.It shows that the adsorption process is mainly in the form of monolayer adsorption;the quasi-second-order rate equation can better reflect the adsorption process of pollutants being removed by the composite modified zeolite than the quasi-first-order rate equation.The basic principle of zeolite adsorption of pollutants in sewage is mainly as follows: chemical adsorption.The maximum adsorption capacity of the composite modified zeolite for total phosphorus was 3.934mg/g,the maximum adsorption capacity for ammonia nitrogen was7.163mg/g,and the maximum adsorption capacity for COD was 9.768mg/g.(3)The characterization analysis of the zeolite showed that the silica-alumina ratio of clinoptilolite was reduced after alkali modification,and the pore size and pore volume were increased.Further iron ion modification could form more iron hydroxides inside the zeolite.The composite modified zeolite not only has ion exchange and adsorption removal of pollutants in water,but also has complex precipitation reaction between phosphate ions and iron hydroxide;the pollutant removal effect is further improved than that of natural clinoptilolite.(4)The pilot-scale reaction of composite modified zeolite used to simulate the treatment of rural domestic sewage by artificial wetlands shows that under the optimal experimental conditions,the average total phosphorus concentration in the effluent of the artificial wetland system during the reaction period is 75 days after the composite vertical flow constructed wetland.The parameter is 0.9716mg/L,the total phosphorus removal rate is 86.96%,the average ammonia nitrogen concentration parameter of the effluent is 12.8424mg/L,the ammonia nitrogen removal rate is 85.27%,the average COD concentration parameter of the effluent is 67.124mg/L,and the COD removal rate is 86.29%;good effect on pollutant treatment,laying a good foundation for the application of composite modified zeolite in practical engineering projects. |
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