Experiment And Simulation On Nitrogen And Phosphorus Removal Of Ecological Ditch

In recent years, the agricultural non-point source pollution is increasingly serious, which threatens the water quality and ecological system. To control the agricultural non-point source pollution, the first and most important task is to control the migration and transformation of nitrogen and phosphorus in the agricultural ditches. Therefore, it is of great theoretical and realistic significance to study the transformation mechanism of nitrogen and phosphorus.Based on studies at home and abroad, an ecological ditch with stepped permeable dams was designed, and according to the design a pilot device was built, the plants and packings required were selected through screening tests. Firstly, intercept effects of the blank ditch, the plant ditch and the packing ditch with permeable dam on nitrogen(N) and phosphorus(P) were compared and analyzed. Secondly, the mechanism of N and P removal in ditches under the collaboration of aquatic organisms and hydraulic power was studied through the dynamic and static experiments, in order to find out the specific influences of different environmental factors such as influent concentration, influent flow and water level. Then, orthogonal dynamic simulation test was conducted to explore the significance of four influence factors(influent nitrogen concentration, concentration of suspended solids(SS), influent flow, and water level) on nitrogen removal. Finally, the transport and diffusion of N and P in the ditch was simulated by EFDC, a three dimensional water quality model, and the simulation results and the experimental data were compared.The results suggested that(1) the ditches had intercept effect on nitrogen pollutants, the general change of nitrogen content in different sections presented the downward trend with the hydraulic retention time, and the intercept effect of the packing ditch with permeable dam was much better than that of the blank ditch and the plant ditch;(2) Ammonia and Nitrate were the primary transport forms of nitrogen, and they decreased along the flow direction;(3) the effect sequences of the four factors were as follows: water level, influent nitrogen concentration, concentration of SS and influent flow, and the optimal level combination were high influent concentration, low SS concentration, medium water level and low flow;(4) the simulation results of EFDC model well fitted with the test results, and average relative errors of EFDC model simulated results were all less than 15%, which verified the reliability of the model.