| Constructed Rapid Infiltration system(CRI system), a wastewater treatment technology aiming mainly at the wastewater from small towns or residents, is a kind of brand-new biological wastewater treatment method, which is becoming the hot spots of research and application. Related research shows that CRI system is good at removing the ammonia nitrogen, organic, SS and so on, but the removal efficiency is bad for TP and TN. On account of many reasons, the research of pollutant removal mechanism and basic theory is quite deficient, there are few reports on pollutant removal dynamics, hydraulic load, operation mode and engineering design are depended on experience in practical engineering application. Therefore, adopted site investigation, testing analysis and theoretical research methods, this subject study the migration rule and characteristics of pollutants in the CRI system, clarify removal mechanism of organic, nitrogen and phosphorus in the CRI system, explore pollutant removal kinetic process, constructing the dynamic model of removing pollutants in CRI system, filter layer height calculation model in constructed rapid infiltration system and relation curves between fill concentration, water concentration and hydraulic load in CRI system, optimization CRI pool body structure, filter material composition and operation mode, improve the removal efficiency of pollutants in CRI system.Through prospecting phoenix river CRI system engineering in Chengdu, it shows that CRI system is good at removing the ammonia nitrogen, organic, SS and so on, effluent water is stable in CRI system, and the CRI system has strong resistance to load impact ability, the ammonia nitrogen, organic, SS of ultimate effluent is qualified to Standard A of "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant" (GB18918-2002). But the removal efficiency is bad for TP and TN and the ultimate effluent is not qualified to Standard A of "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant" (GB18918-2002). When improving the CRI process, it must consider changing pool filter layer structure, filter material composition and operation mode to improve the removal efficiency of TN and TP in CRI system.Through constructing simulation column 1 of CRI system for treating sewage in lab, this paper further investigates the pollutant migration, transformation, degradation rule in CRI system, masters the degradation mechanism of pollutants especially N and P, analyses the reasons of lower removal for TN and TP. The result in this paper will make a good foundation for optimizing pool body structure, filter material composition and operation mode, improving the removal efficiency of pollutants especially nitrogen and phosphorus in CRI system, guiding designation of CRI systems engineering and further applying CRI technology.In order to improve the denitrification efficiency of CRI system, this paper optimizes CRI system by changing the filter material composition, filter structure and operation mode to construct CRI system model column which can remove nitrogen better. Test results show that when added 25% of charcoal into the filter material of CRI system (simulation column 2 of CRI system), the removal rate of TN increases 5.5%.When added anaerobic section at the lower part of simulation column 2 of CRI system (simulation column 3 of CRI system, the removal rate of TN increases 3.8%% than simulation column 2 of CRI system, but the removal rate of TN is still low. Because when simulation column 3 treats wastewater, although saturated zone is set as denitrification section at 100-150cm of the pond, organic matter at 0-100cm of the pond is removed effectively and organic concentration entering into the saturated zone is low that cannot provide enough carbon sources for the denitrifying reaction. It restrains the denitrifying reaction and makes the denitrifying bacteria can't change nitrate into gaseous nitrogen completely. When added moderate carbon into the filter simulation column 3 of CRI system (filter simulation column 4), TN removal rate reaches 59.1% in filter simulation column 4 which increased 15% or so than the filter simulation column 3. It shows that the existing CRI system has the low removal rate for TN because of lack of anaerobic environment and organic carbon sources.The mechanism of phosphorus removal in CRI system shows that it should begin from developing new type filler and improve phosphorus adsorption and chemical deposition of infiltration mediums to improve phosphorus removal rate of CRI system. Iron and sands(normal substrate of CRI system) are closed as research objects, the isothermal adsorption characteristics of iron and sands adsorbing phosphorus in the wastewater are researched, dynamic process iron and sands adsorbing phosphorus in the are analyzed by first order reaction kinetic model and pseudo-second-order kinetics model, rule and performance of adsorbing phosphorus are investigated. Researches show that isothermal adsorption characteristics of both iron and sand adsorbing phosphorus conform to Langmuir equation, absorption reaction can be spontaneous, spontaneous degree, adsorption ability and stability of iron adsorbing phosphorus are better than sand, the maximum amounts of iron adsorbing phosphorus is 7.56 times than sand, therefore, adding some amount of iron into the substrate of CRI, CRI can remove more phosphorus. Adsorption kinetic of iron adsorbing phosphorus in the wastewater is closer to the first order reaction kinetic model, while sand is closer to the pseudo-second-order kinetics model by analyzing standard errors of first order reaction kinetic model and pseudo-second-order kinetics model, relative errors between parameter (Qo) of Langmuir equations and parameter (w) of first order reaction kinetic model and parameter (qe) of pseudo-second-order kinetics model synthetically. Research results enrich and develop water pollution control and remediation theory of CRI system and provide new ideas for constructing dynamic model of matrix adsorbing solute. When adding moderate iron into the filter simulation column of CRI system (filter simulation column 5), TP removal rate reaches 84.2% in filter simulation column5 which increased 40% or so than the filter simulation columnl.In order to further understand CRI system theoretically, this paper constructs the pollution degradation dynamics model of CRI system using reaction-diffusion theory from the standpoint of degradation speed of aerobic microbes to matrix, diffusion process of Matrix from liquid to biological membrane and biological membrane growth and oxidation process. A data analysis software, is applies to analyze the test data to calibrate dynamic model parameters. The significance of model parameters is researched by combining mathematical theory and test results.Simulation column of CRI system is applied to treat domestic wastewater and organic matter degradation kinetics characteristics are studied on the basis of Monod equation, research of Mann A.T. and the Chemical Oxygen Demand (COD) degradation law. Then the mathematics calculation model of filter layer height is built based on COD degradation kinetic equation in CRI system. Through experimental verification, it shows that within a certain range, this model could precisely calculate the economic and appropriate height of filter layer in line with the requirement of influent COD concentration, hydraulic load and effluent quality in CRI system. Rule curve between water concentration and hydraulic loading is constructed based on the mathematics calculation model of filter layer height. Hydraulic loading can be calculated by rule curve due to water concentration and effluent water requirements. It provides a scientific quantitative calculation method for calculating hydraulic loading of CRI system. However, since these models are derived within a certain range, when hydraulic load or influent concentration is beyond the applicable scope, there will be a certain deviation between models calculated values and actual results. Therefore, in actual project, the parameters of models must be ascertained or revised according to the characteristics of specific filter and reactor itself.
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