Study On Vertical Flow Constructed Wetlands To Decontaminate Wastewater

As a biological wastewater treatment technology, constructed wetland is high efficiency, low investment, cheap operational fee, low energy, wild field of application and so on, so it apparently is adapt to the situation of our country and the wastewater treatment in country and town. This paper was background on "Hun River Landscape constructions-ecological restoration project of Shenfu irrigation canal along Fushun Development Zone". The vertical flow constructed wetland's pollutants removal effect when treating sewage from the irrigation canal was studied, at the same time, to further strengthen and stabilize the long-term phosphorus removal in the wetland, phosphorus adsorption properties of three kinds of substrates included limestone, beans stone and steel slag were also studied. The experiments results indicated that, the best hydraulic loading in the vertical wetland was 0.15 m3·m-2·d, total phosphorus adsorption capacity in the theory was as follows:limestone> steel slag> beans stone, and therefore, limestone and steel slag can be considered to replace part of the beans stone substrate when filling the wetland to make sure a long-term excellent phosphorus removal efficiency.In the second phase of study, four different low hydraulic loadings were applied to study the impact of hydraulic loading on the effectiveness of wetland's decontamination. Meanwhile, the distribution state of dissolved oxygen in wetland and pollutants removal efficiency of different substrate layers ware analyzed to understand wetland system's processing mechanism and to provide research basis for further enhancing the pollutant removal efficiency. The experiments results indicated that:(1)Under the low hydraulic loadings, the two experimental wetland systems'COD removal efficiency were impacted great with hydraulic loading, COD removal rate decreased as the hydraulic loading was increased. NH3-N removal rate was affected less by hydraulic loading, NH3-N removal rate in two sets of wetlands was steady at a good level, the rate remained at 86%-90%. TP removal rate was most affected by hydraulic loading, the removal rate decreased by 20% when hydraulic loading increased from loading q1 to loading q4. (2) Under different hydraulic loadings, dissolved oxygen content and distribution in the wetlands were much similar. Hydraulic loading affected the distribution of dissolved oxygen little. Appropriate increase in hydraulic loading can increase the atmosphere reaeration rate and plants'oxygen transitions rate, and improve with the hypoxic environment in the wetlands. (3)Different layers showed unlike decontamination effectiveness. The main place for COD removal was from substrate surface to 20 cm, the rate was greater than 70%. The main place for NH3-N removal was from substrate 20 cm to 40 cm, the rate was greater than more than 58%. TP was mainly removed in the substrate 20 cm-40 cm and 40 cm-55 cm.