The Ecological Evaluation Of Nitrogen And Phosphorus Removals Of Domestic Sewage For Constructed Wetland Plants

Ecological functions of domestic sewage N and P removals by wetland plants were evaluated using in situ observation and simulated solution culture expreiments. Seasonal variations of N and P concentrations and N:P ratios in roots, stems and leaves were in situ studied on six wetland plant species including Ponlederia cordata, Iris germanica, Canna indica, Phragmilas communis, Acorus calamus Linn and Vetiveria zizanoides in 2008. The decontaminating effects were studied on ten wetland plant species including Pontederia cordata, Iris germanica, Canna indica, Phragmitas communis, Acorns calamus Linn, Vetiveria zizanoides, Scirpus validus, Zizania latifolia, Cyperus allernifolius, Thalia dealbala, Echinodorus amazonicus using simulated solution culture experiment in 2010, and the influence of roots area, rhizospheric microorganism and N and P concentrations and N:P ratios in roots, stems and leaves on the decontaminaing abilities were analyzed. The main results as follows:(1) All six wetland plants observed in 2008 had strong ability of N and P accumulations. The N-enriched and P-enriched species were Iris germanica and Canna indica, repectively. The N and P storages were higher in Phragmitas communis, Acorus calamus Linn and Vetiveria zizanoides than in Iris germanica and Pontederia cordatais. The N and P concentrations were higher in the aboveground than belowground part except Vetiveria zizanoides (P<0.05). Additionally, the N and P storages per m2 of all plants positively correlated with their biomass and higher in the aboveground than belowground part, which indicated that it is an effective pathway to remove N and P elments with harvesting the plant aboveground parts in domestic sewage.(2) The annual average rates of pollutant removal across ten plants studied in 2010 were between 40% and 70%, and the removal ability showed TP>NH4+-N>TN>COD. The highest TP removal rate was Thalia dealbata being 78%. the highest NH4+-N removal rate was Pontederia cordata being 74%, the highest TN removal rate was Iris germanica being 70%, the highest COD removal rate was Pontederia cordata being 65%.(3) The average TP removal rate across ten species in 2010 showed autum> summer> spring> winter, however NH4+-N, TN and COD removal rate showed summer> spring> autum> winter. Additionally, the removal rate varied with the location with middle> lower> upper level. (4) The rhizosphere microorganism quantity all showed that bacteria> actinomyces> fungus. Bacteria accounted for 95% of the total microorganism amount, and the microorganism amount in summer is higher than in winter. Actinomyces amount in summer positively correlated with TP removal rate.(5) The area of three-level roots was higher than that of the secondary level. The roots area in winter was higher in summer. For the removal rate of four kinds of pollutants, three-level roots area positively correlated with the absorption of roots to N.In sum, the three plants of Phragmitas communis, Acorus calamus Linn and Vetiveria zizanoides were recommended to plant in the domestic sewage treatment. Tthe five plants of Thalia dealbata, Pontederia cordata, Acorus calamus Linn, Iris germanica and Scirpus validus were the five top species to decontaminating N and P pollutants in mid-substropical region according to the comprehensive evaluation.