Study On Aquatic Plant Filter Bed System For Purifying Influent To Taihu Lake

Aquatic plant filter bed System is introduced from Japan. It is a new type of constructed wetland without any substrate which purify raw water by absorption and filtration of plant root systems and degradation of symbiotic microorganism, and applied mainly to purification of hyper-eutrophic surface water. Study on aquatic plant filter bed system for purifying influent to Taihu Lake is conduced in this paper. The following results are obtained:1. In winter, the removal efficiency of Oenanthe javanica and Lolium perenne for TN,TP,CODMn is worked in this paper, and they can reach as high as 21.4%,35.87%and 11.48%,while 29.92%,46.97%and 17.38%.2. In summer, the pollution-purified results of the Ipomoes aquatica filter bed system is explored. Under the optimal operation conditions with hydraulic loading rate of 5.0m3/(m2.d) , the removal loading rates of TP,TN,NH4+-N are 0.92 g/(m2?d),2.20 g/(m2?d) and 1.83 g/(m2?d) respectively for all-year average, the removal efficiency are accordingly 44%,20% and 57%. The removal efficiency of TN,NH4+-N,TP and CODMn vary in different month and have obvious regularity, which is highest in August and can reach as high as 34%,75%,48% and 20%.3. The water quality of Zizania latifolia and Nymphaea linn.Sp filter bed are tested all year. We find that the density of nutrients influent evidently the purification of them, which is the main cause that purify-results in winter is better than that in summer. The water-purify abilities of Zizania latifolia and Nymphaea linn.Sp filter bed are better than that of the Ipomoes aquatica and Oenanthe javanica filter bed in transition, so a method that using different plants in series is suggested in this paper,to make sure that the hydrophyte filter bed can work well in transition.4. By the dynamics evaluation of nitrification and denitrification potential for sediment accumulating in the roots of plants and in the bottom of APFB, we find that the maximum nitrification appear in the sediment of roots, and the maximum nitrification and denitrification potential appear in the middle part and front part of APFB separately. This distribution causes unfavorable effect on microorganism denitrification process. N,P are absorbed as the rate of 5 to 1 by Ipomoes aquatica. The maximum amount of NH4+-N,TOC released by sediment appears in the front part of APFB, while the P is not released easily by sediment.5. Analysis of the mass balances of nitrogen and phosohorus in the Ipomoes aquatica planted channel shows that uptake by plant,denitrification and block precipitation contribute nearly equal to each other for removal of TN.