Hydraulic Characteristics And Mathematical Simulation Of Horizontal Flow Constructed Wetlands

As a kind of biology sewage disposal technology, constructed wetlands system takes advantage of easy building, low-energy, simple working maintain and good ecological benefits and has extremely wide application prospect. This dissertation focused on horizontal flow constructed wetlands (HFCWs) and the effect of different hydraulic condition on wetland system hydraulics and treatment was studied by situ real-time monitoring self-build laboratory small HFCWs. The behavior of hydraulics and transport of pollutant of HFCWs was analyzed using mathematic model. The main results are shown as follow:1. The packing property of HFCWs:It was concluded that the optimum filling order of six kinds of packing from the surface to the bottom in HFCWs was:yellow sand, fine sand texture, fine sand huangyan, coarse sand huangyan, coarse sand texture and riverstones by hydraulics parameters text. The porosity of packing was about 40%, the hydraulic conductivity was large and the permeability was good.2. The effect of different hydraulic condition on hydraulics and treatment efficiency of constructed wetlands system:(1) The ratio of water yield losses increased while the inflow rate decreased, when the inflow rate of wetland system between 13.5mL/min-332mL/min, water yield losses of system changed from 0.6% to 6.9%;(2) When outfall sited at superstratum of wetland system, the hydraulic efficiency recovery could be improved, the short flow and dead zone reduced. The recovery got up by 2.8%, λ enhanced by 0.194 and S dropped down by 0.261;(3) Lengthen the hydraulic retention time to improve wetland system hydraulic efficiency. When hydraulic retention time was 73 h, the recovery was 98.8, λ was 1.048, S was 0.447;(4) HFCWs inflow and outflow from superstratum and hydraulic retention time was 73 h, hydraulic loading was 0.065 m3/(m2·d) and average maximum temperature was 15, while COD, NO3--N, TN and TP was 76.4,92.1%,81.1% and 50.9%. The removed pollutant mainly focus on first half of horizontal flow artificial wetlands system, the removal efficiency was increased while lengthen the sewage plug flow distance.3. The simulation of hydraulics behavior and pollutant migration and transformation rule of HFCWs:the hydraulics behavior of laboratory horizontal flow artificial wetland was simulated by Visual MODFLOW according to experimental parameters. The simulated result was preferable fitting with actual measurement, the model had a high reliability; The model could reflect the inner flow rule of artificial wetland and pollutant migration and transformation, excellently; The simulation result of different hydraulic loading showed that the reduction of hydraulic loading and lengthen hydraulic retention time could improve the pollutant removal efficiency.