| Landscape water refers to the water body bringing people aestheticfeelings naturally formed or artificially built, which was located in cities,villages or tourist attractions. At present, eutrophication of landscape water isvery severe due to poor recharge water quality, less quantity and inferiorfluidity. Thus, it is imperative to restore the heavily eutrophicated waterbodies with appropriate technique methods. The constructed wetland is anecological wastewater restoration technology, which is easy to integrate withthe landscape construction, treating sewage and enhancing the sight at thesame time. Based upon their merits, constructed wetlands are widely appliedin the repair of eutrophied landscape waters in recent years. However, studieson the lectotype, design and operation of constructed wetlands treatinglandscape waters are deficient and dissatisfactory. Based on this, researchwork was made on the related issues in this article, and main results weresummarized as following aspects:(1) Experimental simulation study.Three experimental devices with the same size were developed as ahorizontal subsurface flow constructed wetland（HFCW), a integrated verticalflow constructed wetland (IVCW) and a integrated baffle constructed wetland(IBCW), respectively. Their removal efficiencies of chemical oxygen demand(COD), nitrogen and phosphorus were studied under the condition of differentpollutant concentrations of influent, still, the top inflow to bottom inflow ratio(top-inflow/bottom-inflow) was adjustied from1/1to1/2to explore theinfluence of this parameter on the removal effects. It was founded that COD,nitrogen and phosphorus could be removed effectively by the three wetlands;The effluent TP concentrations were positively responsive to influent TP concentrations；IVCW and IBCW showed better total nitrogen (TN) removalperformance than HFCW under high concentration condition, however, itreversed under low concentration condition. The average TN removalefficiency of HFCW showed a significant difference under different pollutantconcentrations of influent；COD, phosphorus and NH+4-N were removed byIBCW a little lower with top-inflow/bottom-inflow of1/2compared to theratio of1/1, but the removal rate of TN was significantly improved.(2) Engineering application study.A demonstration project of ecological restoration based on constructedwetlands was conducted in a constructed lake at Beijing Conference Center tostudy and evaluate the effects of wetland anti-clogging design, aquatic plants,filter materials and hydraulic loading rates on the removal of pollutants. Twoprinciples of design based on total water volume balance and total phosphorusbalance were innovatively applied to guiding the process design. Resultsshowed that suspended solid (SS) and chlorophyll a (Chla) of influent couldbe removed effectively by sand rapid filter and specially designed distributiontrench filter system, which was very beneficial to stable the operation of theconstructed wetland. COD, nitrogen and phosphorus could be all removedeffectively by constructed wetland1#(HFCW, gravel as filter material,Phragmites australis as wetland plant) and Constructed wetland2#(HFCW,gravel and steel slag as filter material, Canna generalis as wetland plant).Hydrodynamics analysis of wetland1#and2#showed that hydraulic gradientin wetland might be affected by filter material. The hydraulic gradient ofwetland1#was obviously higher in front section than back section, andhydraulic gradient of wetland2#was affected by front section and backsection. Nitrogen removal efficiency was higher in gravel wetland than steelslag one, but lower in gravel one for phosphorus. When hydraulic loading rateof wetland2#was increased from1.03m/d to1.37m/d, removal efficiencies of COD, nitrogen and phosphorus decreased slightly, but their total removalamounts were still increased. Therefore, higher hydraulic loading rate meantlarger pollutant removal amount on condition that the hydraulic loading ratedid not exceed the wetland’s ecological capacity.(3) Study on process design methods of constructed wetlands for theecological restoration of landscape waters.Design ideas which were different from traditional monomer processdesign ideas were elaborated systematically according to the particularity ofthe restoration of the landscape water, in which constructed wetlands wereregarded as integral parts of the water ecological system, therefore thephysical boundary of the water body was broadened. The ecological capacitycalculation method proposed above matched the design ideas, and it wascompared with the other two traditional calculation methods. Key factors oflandscape water ecological restoration with constructed wetlands such aslectotype, selection of design parameters and other important issues ofwetlands were also summarized. |
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