Studies On Pollutants Removal Performance And Flow Pattern Optimization Of Land Treatment System

Recently, land application as alternative technology of secondary sewage treatment process and advanced treatment technology, have developed rapidly, for low capital investment, low operating expense and good treatment effect.The traditional wastewater land application system uses soil as medium, which has the problems of lower hydraulic loading, easy to jam and so on. In order to solve these problems, ceramiste and rubble were used as fillers to replace the soil, and then pollutants removal performance was studied. It was found that the biodegradability was the main factor of land application system for COD removal efficiency and with the reduction of biodegradability, COD removal efficiency decreased. The removal of TP and NH3-N mainly depended on the adsorption of filler, and when adsorptions reach to saturation, removal rates decreased.Hydraulic characteristics of wastewater land application system directly affects the the treatment efficiency, which mainly caused by the different residence time. Studying the hydraulic characteristics of the land application system, which is the basis of design parameters choice and structural optimization, can strengthen the understanding of the residence time distribution of land application and the physical form of the system.Hydraulic characteristics of land application system were studied by tracer experimental methods. The first phase, accuracy of test methods and applicability of instruments were discussed from static tests and dynamic tests, to find the appropriate test method and matching test apparatus for the study of the hydraulic characteristics of the land application system. The second phase, from four parameters of media height, flow direction, inflow way and outflow way, we use the method of orthogonal to optimize structure of land application system, ultimately to improve the efficiency of land application system and provide theoretical support and technical parameters for design and in-depth study. It was found that the flow direction and media height were the main factors of hydraulic characteristics of the land application system. The average residence times of the upward flow were closer to the theoretical values, the percentage of dead was smaller and flow patterns were closer to plug flow. So upward flow was the initial way. With the increase in height of the media, percentage of dead zone tends to decrease and volume efficiency of the plug flow increased, so media height of 54cm was better than 34cm. Other factors had little effect. Finally, it was determined that optimal schemes were 54cm media height - upward flow - horizontal inflow way - longitudinal outflow way and 54cm media height - upward flow - longitudinal inflow way - longitudinal outflow way.Based on the study of tracer test, it is necessary to look for the non-ideal flow model which could reproduce the flow pattern of land application system.It was found that the simulation goodness of fit of dispersion model and CSTR in series model was different with the case, so they could not simulate well the flow pattern characteristics of land treatment system. On the basis of dispersion model, I have introduced shift delay parameter and established two-parameter model. Researching on the two-parameter model and the shift of the log-normal distribution model, it was found that the two models under the different conditions of flow properties of land application systems had a good simulation effect.