| Rural domestic wastewater is one of the main pollution sources which lead to serious environmental problems of Taihu Lake. Proper selection of rural sewage treatment process to achieve nitrogen and phosphorus utilization is the focus of the study. Southeast University proposed a combination system of biological and ecological, which was called "anaerobic-anoxic-water dropping aeration bio-contact oxidation-vegetated construcated wetland", in this paper, wetland was the main focus of the study. Using the aquatic plant filter bed-horizontal subsurface constructed wetland technology, planting a variety of pollution-purrifying wetland crops to realize the sustainable development of rural sewage treatment.Different aquatic plants exsited the different ability for nitrogen and phosphorus removal of wetland system. The root ion absorption kinetics results showed that, there was a big difference among the maximum absorption rate (Imax) and minimum affinity (Km) of different plants. Water spinach owned the maximum Imax and minimum Imax, was suitable for wastewater with broad range of N, TSP concentration. Taro, to the contrary, had both weak affinity and low absorption rate of wastewater with N, TSP; Leek had higher absorption rate of N and TSP, Water bamboo was on the contrary; Burclover was more fit for high TSP、NH4+-N and low NO3-N concentration wastewater remediation, while potherb mustard was just the opposite.Ion kinetic parameters (Michaelis constant Km and maximum absorption rate Imax) explain the plants absorption of a certain kind of ion comprehensively. The bigger the Imax value, the plants have much more potential absorption ability to some kind of ion.1/Km indicates the affinity of the uptake system of plants roots, the smaller the Km value, the higher the affinity of the plants to some kind of ion. Different ammonium nitrate ratio wastewater of construced wetland affected the removal of nitrogen and phosphorus. TN removal efficiency decreased with the increasing concentration of nitrate nitrogen after the first increase, that meaned there was a place for the nitrogen removal efficiency of the saturation point. When NO3--N/NH4+-N was 2:1, the wetland of TN and TP removal efficiency got the highest. While NO3--N/NH4+-N was 1:1, the aquatic plant filter bed had the best removal efficiency. Experimental data showed that Water spinach and Leek were suitable for ammonium, which could be used for the wetland that lacked of oxygen.With the increase of water depth, the nitrogen and phosphorus removal efficiency presented different changing trends even the opoosite of the hibird constructed wetland; With the increase of hydraulic load, N and P removal continue to reduce, ramoval load first increased then decreased; Running a whole year, different hybrid wetland plants on N and P removal presented seasonal variation. The results showed that, the undercurrent’s best water depth of water spinach bed-water bamboo wetland and water spinach bed-zizania aquatic wetland was 35cm, the other wetlands were 45cm; the removal efficiency of nitrogen and phosphorus by the constructed wetland decreased with the increase of hydraulic, while the removal of load creased first then decreased.1# (leek-pepper, leek-water bamboo, spinach-lettuce) average removal efficiency of TPand TN all over the year were 23.41%、 35.61%、86.46%、19.84 and 22.26%、68.21%、65.20%、24.08%; 2#(cress-water bamboo, water spinach-water bamboo, water spinach-taro) average removal efficiency of TPand TN all over the year were 35.89%、76.26%、 76.24% and 33.81%、53.80%、50.60%; 3#(water spinach-zinania, chrysanthemum-ryegrass&lettuce) average removal efficiency of TPand TN all over the year were 56.23%,89.08%,82.85%,52.39% and 36.96%,54.57%, 58.89%,30.51%; 4#(leek-water spinach, leek-potherb mustardd) average removal efficiency of TPand TN all over the year were 43.83%,87.90%,50.15%,40.75% and 32.02%,43.04%,33.71%,28.35%;5#(water spinach-leek, burclover-leek) average removal efficiency of TPand TN all over the year were 46.29%,79.38%,64.63%,51.17% and 31.17%,43.04%,41.41%,30.30%;6#(leek-pepper, leek-chrysanthemum, cress-chrysanthemum) average removal efficiency of TPand TN all over the year were 66.99%,51.40%,41.81%,56.95%'64.05%,31.27%, 28.14%,47.62%.The TN, TP and NH4+-N test data were processed by the least aquare method, using the optimal principle could obtain the optimal hydraulic load and the optimal remomal efficiency, which procided the theoretical basis for selecting the parameters of the constructed wetland.The laboratory drainage and construction site drainage of Southeat University Wuxi branch resulted in high As、Cr and Hg values in the water, which leaded to heavy metal content in lettuce and salting technic exceeding the national standards. Sinach had stong ability of heavy metal absorption, a small amount of trace elements in water could lead to metal exceeds bid in spinach.In summary, according to the seasonal variation, hydraulic load, water depth, sewage water quality to collocate the economical crops, can guarantee the nitrogen and phosphorus effluent water quality of hybrid constructed wetland, rural sewage became resource utilization. |
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