Studies On Flow Pattern Optimization Of Wastewater Land Treatment System

The hydrodynamic characteristic of the land treatment system would directlyinfluence the removal efficiency of pollutants, which was caused mainly by residencetime. The study in the hydrodynamic characteristic could realize the residence timedistribution(RTD) of the land treatment system, and it would be helpful to provide abase for the design and optimization.With the foundation of RTD theory, the hydrodynamic characteristic of reactor wasanalyzed using tracer-response technology. The effect of the factors, such as the pipelinedistribution, water-layer, bear-layer, and the particle diameter of packing were studied.At the same time, Fluent, which is a software of computational fluid dynamics(CFD),was used to simulation the path way of water in the reactor, comparing to the ruglermothed, and optimize the structure of reactor.The results show Rhodamine B is better than NaCl because when Rhodamine B isused as tracer the reproducibility of experiment results is more accurate. The residencetime distribution theory and the result of CFD model both show that bear-layer andwater-layer have the functions of distributing and collecting water in all water-carryingsection. The effect of degree of pipeline distribution doesn’t have great influence onhydrodynamic characteristic. The efficiency of volume is all above90%. Water-layerand bear-layer have little effect on hydrodynamic characteristic when the pipeline isfully distributed. Attributing to water-layer, the proportion of stagnant volume inineffective volume increases and the degree of axial dispersion is lower. Hydrodynamiccharacteristic of flow doesn’t great change after bear-layer is added. When the watercross-section is half of the pipeline (half distributed), water-layer and bear-layer havethe functions of collecting and distributing water, which could increase the efficiency ofvolume. Water-layer changes the way of water flow and eliminate by-passing and largeportion of stagnant volume. Bear-layer increases the efficiency of volume, anddecreases the proportion of dead volume. The orthogonal analysis show that the impacton the efficiency of volume follow bear-layer>water-layer>pipeline. So the volumeefficiency of “half distribution pipeline-water layer-bear-layer “is the highest, andhydrodynamic characteristic is the nearest to plug flow. The dimensionless meanresidence time is1.093, the degree of dispersion0.037which is low. With the increaseof packing particle diameter, the direction of water changes from upright to slant in the reactor of full-pipe without bear-layer or water-layer. However the packing particlediameter products little effect on hydrodynamic characteristics in the reactor ofhalf-pipe, which directions are all slant.