| A treatment system,consists of anaerobic process and constructed wetland(CW),could applys to the treatment of decentralized domestic wastewaters, which had the advantages of good treatment, easy to control and cost-effective, a ecological technology. Now the research on CW was mainly focused on how to prevent blocking and to improve the removal rate under low temperature, as well as the removal efficiencies of nitrogen and phosphorus in combination of different type CWs. According to the establishment of 8 CW systems(pilot-scale), the operational stability was monitored systematacially in different plant-substrate CWs and the interaction between plant species and hydraulic loading was also explored. Meanwhile, the pollutant distribution characteristics along the CW were described,and the contribution of plant absorption in nitrogen and phosphorus removal was analyzed specifically. In this way, we could provide theoretical basis with the optimization of substrate and plant in CW and develop rural domestic treatment process. The main content and important conclusions of this work are summarized as follows:(1) In order to research the effects of different types of plants and substrates on removal efficiencies of the system, 8 CW systems(pilot-scale), of which were used to treat decentralized domestic sewage, were established. The results showed that all of these CW systems work well on COD removal. When 8 systems ran stable, the TN removal rates of plant systems were more than 45%, and the differences of TP removal efficiencies were not significant. The TN removal rates of different substrate systems were different significantly.The TP removal rates of different substrate systems from the most to the least were Modified steel slag, Modified zeolite, Ceramsite and Zeolite.(2) To analyze removal rule of pollutant along the direction of flow, water quality change was monitored along the flow. The results showed that the pollutant concentration decreased gradually along the length. Organics could be mainly removed in the first compartment. The removal of nitrogen was not synchronized with the removal of organics, which had the highest removal rate in the third compartment. The main region of phosphorus removal was in the upside of the CW, and phosphorus release phenomenon appeared in the middle to lower part of the CW. Delamination phenomenon of dissolved oxygen(DO) was obvious in the CW,and the value of DO could be described as upper layer > middle layer > lower layer.(3) Plant species were divided into short-root, middle-root and long-root plant based on the length of root. When the system ran stable, the effect of interaction between plant species and hydraulic loading on pollutant removal efficiency was studied. The results showed thatplant species did have significant effect on the removal of nitrogen and phosphorus, but had a little difference with the removal of COD. Moreover, the removal rate of nitrogen and phosphorus could be ranked as long-root, middle-root as well as short-root plant CWs.Hydraulic loading affected the removal of pollutants significantly. The interaction of plant species and hydraulic loading had effect on removal rate of pollutant significantly.(4) To further define the contribution of plant absorption in nitrogen and phosphorus removal, the concentration of nitrogen and phosphorus in different tissue of these plants were measured. The study found that TN concentrations of those plants over ground from the most to the least were Irispseudacorus, Arundo donax var versicolor, Cyperus alternifolius and Cannaindica, and TP concentations were Irispseudacorus, Cannaindica, Arundo donax var versicolor and Cyperus alternifolius. Seasonally, TN of these plants could be described as spring < summer < autumn, which was different with TP. |
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