| In recent years, water environment problems are becoming increasingly prominent in China, which consist not only a lack of total water resources volume, but also the deterioration of water quality, decreased water function, and the destruction and decline of aquatic ecosystem in structure and function. Within the span of the "Eleventh Five-Year Plan", although a large number of sewage treatment plants have been constructed, urban sewage treatment rate still remains low and treated water quality cannot fully meet the requirements. There is an urgent need to introduce some efficient wastewater treatment technologies for disposing the polluted water contribution to restoring ecological, landscape and consumption function of water in a short time.Constructed Rapid Infiltration System (CRI system for short) is a new biological wastewater treatment systems, which is developed on the basis of the traditional Land Treatment System (RI system for short). Natural sands, ceramic, steel slag and cinder, which have the advantages of better penetrability, cheap and easy accessibility, are as filler materials to construct the CRI system. It shows that in engineering application and related research, CRI system apt to remove the ammonia nitrogen and organics, but its removal effect of TP and TN is not very good. Because of many reasons, research and basic theory focus on nitrogen and phosphorus removal mechanism are quite deficient. In the meantime, the theoretical basis of hydraulic load, operation mode and engineering design in practical engineering application is not adequate.Through researching Feng Huang River CRI system in Chengdu, and systematically analyzing the project construction and effects of sewage treatment, it shows that CRI system is good at removing the ammonia nitrogen and organic, whose effluent meets Standard A of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002). While the removal effect of TP and TN fails to reach the same standard.By constructing simulation column A of CRI system for wastewater disposal in lab, a future study concentrating on migration, transformation, and degradation of pollutant phosphorus in CRI system in this paper, as well as degradation mechanisms of phosphorus and partial reasons of lower removal effects of TP have been carried out. Pollutant phosphorous in CRI system can be removed by function of physical chemistry and biological effect. In physical chemistry removal mechanism, phosphorous is removed by ways of absorption and precipitation of filter; while in biological removal mechanism, the removal of phosphorous mainly depends on the accumulation of phosphate accumulation bacterial and the synthesis of phosphate by microorganism to create in guaranteeing nutrients and energy for reproduction in wastewater. However, due to a less amount of element iron, aluminum, magnesium and calcium in natural sands as traditional filter material in CRI system, it has lower phosphorus removal effect through absorption and precipitation. Meanwhile, the excessive accumulation capacity and assimilation of phosphorus by microorganism is small so that system always remains a relatively low phosphorus removal rate in traditional CRI system.To set Iron and sands (common substrate of CRI system) as comparison objects in this paper. Through researching and comparing the isothermal adsorption characteristics of iron and sands in adsorbing phosphorus in the wastewater, and analyzing the dynamic process of iron and sands in adsorbing phosphorus by first order reaction kinetics model and pseudo-second-order kinetics model, the discipline and performance of phosphorus adsorption are studied. The analysis of feasibility of using iron as the filter material for phosphorus removal in the CRI system is conducted at the same time. The research results indicate that using iron as enhanced filter material in CRI system has great advantages in phosphorus absorption. Results from isotherm tests show that theoretical maximum phosphorus adsorption capacity of iron-constructed filter is 7.56 times larger than that of sands-constructed filter material. The equilibrium adsorption capacity of iron in absorbing phosphorus is 1.6449 mg/g by calculation of pseudo-second-order kinetics model, while the sand's is 0.1627 mg/g. When adding moderate iron into the simulation column of CRI system (column B), TP removal rate reaches 84.2% in filter simulation column B which is 40% higher than that in column A. |
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