Research On Nitrogen And Phosphorus Removal Efficiency Of Synthetic Effluent From Wastewater Treatment Plants By Integrated Ecological Floating-bed

Nowadays,the pollutants concentrations in the effluent of municipal wastewater treatment plants in China are usually treated to be consistent with the Pollutants Discharge Standard for Municipal Wastewater Treatment Plant and then discharged into the receiving water body.However,due to the fact that the above-mentioned standard does not meet the Standard for the Surface Water Environmental Quality,the effluent might cause water eutrophication if there isn't any further treatment for it before discharge.Therefore,the removal of nitrogen and phosphorus in the effluent shows great importance in water environment protection.Compared with traditional constructed wetlands,the ecological floating-bed gains increasingly attention in recent years because of its outstanding characteristics such as abilities of adapting changing water levels and in-situ water treatment,lower construction and operation costs,etc.In order to improve the water purification efficiency of conventional floating-bed,this research constructed an integrated ecological floating-bed?IEFB?which has combined an Iris floating-bed and biofilm carriers,and then studied the nutrient removal efficiencies of the IEFB under different water retention time and different inlet NH₄⁺-N and NO₃^--N ratio.Based on the former results,the contribution of plants and sediments to water purification are also evaluated.The results show that:?1?Extension of hydraulic retention time brought higher removal rate and lower area load for both TN and TP.The TN and TP removal rates and removal efficiencies of IEFB are 22.23%±6.79%,638.97±178.97 mg·m^-2·d^-1 and 76.10%±24.31%,61.71±15.12 mg·m^-2·d^-1 under 2 day's HRT;when the HRT of the IEFB is 3d,the corresponding removal rates and removal efficiencies of TN and TP are20.67%±2.72%,395.61mg·m^-2·d^-1 and 91.58%±5.51%,45.17±0.17mg·m^-2·d^-1.?2?Existence of plants in IEFB greatly improved nitrogen and phosphorus removal efficiencies.The contribution of plants on TN and TP removal are 47.22%⁷4.87%and 38.07%⁶1.57%during the experiment.?3?The removal rate of TN changed as the inlet NH₄⁺-N/NO₃^--N ratio was altered,while no obvious change on TP removal rate occurred.When the inlet water quality consists of 15.00mg/L±0.96 mg/L TN,14.00 mg/L±1.31 mg/L NO₃^--N,0.45 mg/L±0.04 mg/L TP,the TN and TP removal rates of IEFB are 25.61%±5.72%and 94.50%±3.66%,respectively;when the inlet water quality consists of 16.19 mg/L±0.55 mg/L TN,13.03 mg/L±0.50mg/L NH₄⁺-N,0.45 mg/L±0.01mg/L TP,the TN and TP removal rates of IEFB are 60.03%±7.00%and 94.82%±2.51%,respectively.?4?The sediments at the bottom of the IEFB contributes a lot to the removal of nitrogen and phosphorus in IEFB.After covering the sediments with polyethylene membrane,the TN and TP removal rates of IEFB decreased from 27.86%±5.53%,58.77%±6.20%to 14.78%±4.97%,33.51%±25.52%,respectively.According to the analysis results of the long-term operation,integrated ecological floating-bed consists of Iris pseudacorus L.and biofilm carriers shows efficient and steady removal efficiency on NH₄⁺-N,TN and TP.