| In order to solve the traditional constructed wetland problems of low efficiencyand plant species is lack in winter and spring in north.The study used the Cannaindica L. and Lolium perenne L. as the cultivated plant of the hydroponic ditch and theconstructed wetland. In this paper, the growth status of two cultivated plant and theeffects of them to purification of water quality during the summer were compared.Meanwhile, to confirm the feasibility of Lolium perenne L. as the cultivated plant ofthe hydroponic ditch and the constructed wetland for year-round use, the growth statusand the effects on wastewater treatment of Lolium perenne L. during the spring andwinter were observed. These ecological wastewater treatment systems located in thefourth wastewater treatment plant in Xi’an, and the effluent from the primary clarifierin the wastewater treatment plant was intermittently conducted to the experimentalsystems. The depths of water in the hydroponic ditch and the substrate of thehorizontal and vertical constructed wetland were0.10m,0.30m and0.60m,respectively. The supplemental water loading in the Canna indica L. system graduallyincreased from150L/d、300L/d to450L/d while the Lolium perenne L. system wasalways150L/d. The main results are shown as follows:(1) The Canna indica L. growed well in the Hydroponic Ditch and the HybridConstructed Wetland. The removal efficiencies of COD and SS in0.10m series,0.30m series and0.60m series were70%and90%above and the increase ofsupplemental water loading have little influence on the COD and SS removal.When the supplemental water loading was low, the TN removal efficiency ofevery series reached80%above. When the supplemental water loading washigh, the TP removal efficiency of0.10m series and0.60m series reached80%above. The pollutant concentrations in the effluent from hybrid process werelower than the second class specified in Integrated Wastewater DischargeStandard（GB18918-2002）.(2) In winter the Lolium perenne L. in Hydroponic Ditch and the HybridConstructed Wetland were into dormant state, in spring it began to growquickly and in summer as the temperature increased it stopped growth. In spring and summer the0.10m series had a better removal effect on COD, SSand NH4+-N while for the P removal the three series were not ideal. In winterthe effluent concentrations of COD,SS and the NH4+-N,TP berore the systemiced were lower than the second class specified in Integrated WastewaterDischarge Standard（GB18918-2002）.(3) The difference of plant species had an important effect on pollutant removal.When planted Canna indica L. in every series the content of DO was abundant,while planted Lolium perenne L. in0.30m series and0.60m series the contentof DO were lack. The Canna indica L. system had a better removal effect ofNH4+-N and TP. The Lolium perenne L. system for0.30m series and0.60mseries the NH4+-N removal efficiency was low and or the P removal the threeseries were not ideal.(4) The water depth and the depth of substrate were important parameters toinfluence the removal efficiency of pollutants in hydroponic cultivation andconstructed wetland. The experimental results showed that, regardless ofplanting Canna indica L. or Lolium perenne L. the concentration of DO in0.10m series was always higher than the0.30m series and0.60m series. Theabundant DO in0.10m series could solve the problem of DO shortage intraditional wetlands, and also strengthen the removal of nitrogen andphosphate in the wetland. When planted Canna indica L. for0.10m series theremoval efficiencyies of TN and TP could reach90%and70%above. Whenplanted Lolium perenne L. the0.10m series also had a better removal effect onTN.(5) To improve the removal effect of N and P were the main problem ofconstructed wetland. When planted Lolium perenne L. in the condition ofabundant DO the emoval efficiency of TN in0.10m series wassummer(65.1%)>spring(49.3%)>winter(37.0%). As in0.30m series and0.60mseries the content of DO were lack, the TN removal effect was determined bythe DO concentration in different season. The emoval efficiency of TN in0.30m series and0.60m series were both winter (31.9%,36.5%)>summer(28.2%,33.8%)>spring(17.0%,13.5%). The emoval efficiency of TP in0.10mseries was spring(56.2%)>summer(36.7%)>winter(24.7%), in0.30m series wasspring(47.9%)>winter(38.0%)>summer(34.4%) and in0.60m series wassummer(49.8%)>spring(44.7%)>winter(33.4%). It showed that in spring whenthe plant growed fast the plant absorb had an active function for the TP removal.The Canna indica L. had a good removal effect of N and P as the develop root.So it was better to choose large plant as the hydrponic ditch and constructedwetland cultivated plant.(6) The Lolium perenne L. could choose as the cultivated plant of the hydroponic ditch and the constructed wetland for year-round use, it could reduce thetrouble for plant exchange and it was economy to obain. The0.10m serieshydroponic ditch and the constructed wetland not only obtain better ofpollutants, but also greatly reduced the construction cost. When the influentpollutant concentration was high,it should reduce the water load to ensure theremoval effect of pollutants. In winter it was better to take preservationmeasures to prevent the system iced. At the same time, the Lolium perenne L.should harvest timely to strengthen the plant uptake function of phosphorus. |
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