Operation Parameters Optimization Of Multi-stage Riverine Constructed Wetland

In the study, the multi-stage constructed wetlands consists of grit chamber, oxidation pond, subsurface flow wetland, surface flow wetland. In order to study the change rule of removal rate of each water treatment unit, the conditions of water flow and coagulation were be changed. The maximum removal content and optimization method of each unit could be got. Some results had be showed.(1) The results of physical and chemical properties of waste water in each unit showed that water pH and nitrate content of all units were qualified, all of the DO were Ⅴ class or worse than Ⅴ class, all of the TN were worse than V, all of the NH4+-N were worse than Ⅴ, all of the NO3--N were qualified, all of the TP were Ⅴ class or worse than Ⅴ class, all of the CODMn were Ⅴ class or Ⅳ class. In a word, the water quality categories of waste water in all units were classified as worse than V class. The changes of water indexes in entrance and exit of each unit were different. Overall, pH and T had no changed. The EC value declined 4.28%. The DO value declined 23.40%. The SD value increased 134.35%. The removal rates of SS, TN, NH4+-N, NO3-N, TP, PO43--P and CODMn were 88.13%,36.18%,53.18%,1.46%, 51.93%,54.64% and 7.93% on average.(2) The results of comprehensive pollution index evaluation showed that the sequence of over standard rate of all units were TN>NH4+-N>TP>CODMn. The sequence of single pollution index of all units were TN>NH4+-N>TP>CODMn. TN was the main pollution factor in all units. When hydraulic load increased, the single pollution index of each unit would be lower or higher. Overall, the removal rate of the comprehensive pollution index I was 39.31%. The water quality categorie of waste water in total entrance was very serious pollution, the others were serious pollution.(3) The results of removal rate of each unit under different hydraulic load showed that the change trends of the removal rate of pollutants and pollution index under different hydraulic load and coagulation were different. Under the same hydraulic load, the pollutants had be best removal by each unit were different. Overall, under low, medium and high three kinds of hydraulic load, when not for coagulation, the removal effect of I, NH4+-N and TP by the multi-stage constructed wetlands were better. When on the coagulation, the removal effect of TN, TP and TP were better.(4) The results of the removal efficiency of different pollutant showed that, the surface flow constructed wetland was best on remove pollutants in all units.