| It results in water eutrophication that rural domestic wastewater containing nitrogen and phosphorus is discharged into natural water bodies without any treatment. After comparative studies on several familiar treatment technology of disperse sewage, subsurface flow constructed wetland was chosen to treat rural domestic wastewater. Process research on subsurface flow constructed wetland including treatment effiency, purification mechanism, technology types, influent factors and model establishment was done in the paper. The primary contents and conclusion are as follows.(1) Plant purification experiment by floating bed technology had been done to investigate purification abilities of thermophilous plants and cold tolerant plants.The result showed Iris pseudacorus Linn. and Typha orientalis Presl had greater advantage on purification than others in the spring, Canna indica Linn. did better in the summer, Acorus tatarinowii Schott and Lolium perenne Linn. did better in the winter. Polarography and photosynthesis experiment had been done to disscuss influence of oxygen diffusion rate and photosynthetic rate on purification performance. Oxygen diffusion rate of plant roots was related to root length, root-wall thickness, root diameter, and the maximum of ODR appears on apical zone. Oxygen carring process helped to microorganism growth. It showed significantly linear correlation between photosynthetic rate and transpiration rate that correlation coefficient of them was0.961. Removal efficiencies of CODcr, NH4+-N, TN embodied similar variety regulation with photosynthetic rate. Nitrogen removal efficiency had significant correlation with photosynthetic rate, and ammonia-nitrogen removal efficiency had very significant correlation with transpiration rate.(2) Substrates adsorption test by batch equilibrium method had been done to research phosphorus adsorption characteristics of substrates. The results indicated that Langmuir adsorption isotherm was fit for describing the absorption characteristics of zeolite, coal cinder and anthracite, while Freundlich dsorption isotherm was fit for biological ceramsite. Coal cinder and anthracite had greater advantage on phosphorus adsorption by comparing theoretical saturated adsorption capacity qm and adaorption parameter KF of substrates. Initial phosphorus concertration, substrate dose, pH, organic materials and other anion had different effects on substrates phosphorus adsorption characteristics.The adsorption kinetics curves of the subtrates showed the same trend including quick, medium and slow period, but the reaction time of reaching equilibrium were different. The pseudo second-order kinetics was best to describe the phosphorus adaorption kinetics onto all substrates examined, followed by Elovich and two-constant equations. It indicated the the adsorption reaction of phosphorus was endothermic and spontaneous that thermodynamic parameters ΔH0was positive and ΔG0was negative. The mechanism of phosphorus adsorption on zeolite and biological ceramsite was attributed to physical adsorption, while the mechanism on coal cinder and anthracite included physical adsorption, ligand exchange and chemical adsorption.(3) Dynamic purification experiment of singal and combined substrate, treatment experiment to rural domestic wastewater, optimization test of operation parameters had been done on the device of integrated vertical flow constructed wetland. The result showed removal effiencies of CODcr and TP had no correlation with influent loads, but removal effiency of TN had correlation with influent load of nitrogen. Biochemical treatment performance of biological ceramsite was better than other substrates, nitrogen removal ability of zeolite was better, phosphorus removal ability of anthracite was better. The combined substrates composed by zeolite, coal cinder and gravel with the proportion of1:1:1could remove nitrogen, phosphorus and organics effectively. Pollutants were mostly removed in the down-flow column of IVCW and the major dissolved nitrogen was removed by nitrification and denitrification of microogranism. Suspended-nitrogen in rural domestic wastewater which deposited in filler pore could cause "nitrogen-releasing" phenomenon. The factors including temperature, gas-flow ratio, C/N ratio and nitrogen-source forms had significant influence on TN removal efficiency. Variance analysis and multiple comparisons of orthogonal test datas indicated interaction between hydraulic load and water depth had significant effect on TP removal efficiency, and the optimal plan of the system was hydraulic load of1200mm/d, water depth of80cm and low influent concentration.(4) Rural domestic wastewater treatment experiment by horizontal flow, down-flow, up-flow wetlands had been done to anyalysis the influence of HRT, load ratio and temperature on treatment efficiency. The result showed horizontal flow wetland with HRT of4d was fit to treat wastewater with high load of turbidity and CODcr. Down-flow wetland with HRT of4d-6d was fit to treat wastewater with high load of NH4+-N and TN. Up-flow wetland with HRT of8d was fit to treat wastewater with high load of TP. Temperature had significant effect on CODCr removal speed, and the exponential equation y=A.eBx could describe relationship of temperature and organic substance removal speed. B-value of the wetlands had little difference, so CODcr removal speed of wetlands had insignificant difference. Temperature had significant effect on NH4+-N and TN removal speed, and the sigmoidal equation could describe relationship of temperature and nitrogen removal speed. Temperature had greater effect on NH4+-N removal speed of down-flow wetland and TN removal speed of up-flow wetland. Temperature had less effect on TP removal speed, and the sigmoidal equation could also describe relationship of temperature and phosphorus removal speed. Distribution regularity of pollutants along the water flow in wetlands had been investigated. Concentration of organic substance and phosphorus gradually decreased along the water flow. Concentration of nitrogen generally decreased along the water flow, but different degree of fluctuation was caused by "nitrogen-releasing" phenomenon cause in dow-flow and up-flow wetlands.(5) Features about basic models of construct wetland had been analysised, stock and flow figure of ecological dynamic model had been described by Vensim software of system dynamics, and generalized differential equations of various kinds of wetland models had been discussed. The result showed main development line of wetland models included basic state of system, reaction kinetics and hydrodynamics, but every wetland model had its own characteristics on its standpoint, adapted condition and representation mechanism. Attenuation model concerned to removal efficiency of pollutants, kinetics models reflected removal speed of pollutants, Monod model focused on contribution to removal rate of pollutants by microorganism activities. Based on box-model theory, Ecological dynamic model consisting of six submodules including carbon, nitrogen, water quality, dissolved oxygen, autotrophic microbe and heterotrophic microbe considered reaction mechanism and degradation process in wetlands. From synergistic action of physical, chemical and biological process, generalized differential equations of various kinds of wetland models was dC/dt=-kCn/(K+C)m. |
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