| In the rural areas of south China, water resources are rich, as well as the output of domesitic sewage. However, the vast majority of the sewage is discharged into the environment directly without treatment, which not only pollutes the river nearby and the phreatic water, but also threatens the drinking water safety and the health of rural residents. Therefore, after analyzing domestic sewage quality and emission characteristics, a constructed wetland system for southern rural areas was designed on the basis of many designs and operating experience of constructed wetlands. The system contains two wetland beds in series, and between which there is an adaptor adjusting the water flow of the latter bed. The main substrates of the system are river sand and dolomite. Under the circumstances of no plants and two plants (canna and cattail) planted in the system, the following points were studied:1. the different removal efficiency of the non-plant-system with different flow;2. the removal efficiency of the system after planting two plants;3. the removal efficiency of the plant-system in the cases of high concentration;4. the change of series of parameters in influent, effluent and along the substrates, as well as the growth status of two plants, their absorption of nitrogen and phosphorus in the sewage, and the influence of removal efficiency of substrates and plants on the expected life of the system. The main results are as follows:1. The elimination capacity of TP (total phosphorus) by the system without plants was high, with a removal rate of68.29%, while the removal rate of TN (total nitrogen) was low, only23.34%, and the removal efficiency of NH4+-N was limited. The removal efficiency of pollutants was affected by the temperature to some extent, and the removal ability of COD (chemical oxygen demand) and TN were improved while the environment temperature was high. The substrates had good buffering capacity on water quality. pH of the effluent stablilized in a neutral range after the treatment of two wetland beds even if pH of the influent fluctuated greatly.2. There was little influence of water flow in the two beds on the removal efficiency of TN, NH4+-N and TP, but the removal rate of COD went up by13%from down-down flow to down-up flow. The adsorption capacity of substrates could be partly recovered by changing the water flow.3. The aboveground biomass of the two selected plants increased fastly, and the root elongation could improved DO (dissolved oxgen) concentration in every substrates layer. Moreover, the quantity of microbes went up significantly because of two plants. The removal rates of TN, NH4+-N and TP rised by60%,80%and30%separately after planting vegetation. The removal rate of COD went up only by5%, but the value was stable compared with no plants. Besides, the adsorption capacity of substrates was also partly recovered after planting. Cattail can assimilate more nitrogen and phosphorus than canna, and it was more obvious in the case of high pollutant concentration.4. Most pollutants were removed in the first wetland when the concentration was low, while most were removed in the second wetland when the concentration was doubled. After the concentration increasing, the purification effect of COD, TN and NH4+-N were also good, and the removal rate of TP even increased5%in contrast with that in low concentration. Almost every parameter of effluent was stabe. The two wetland beds havd particular advantages when treating sewage with different concentration. These results indicated that the designed constructed wetland had a good adaptability and tolerance with high pollutant concentration.5. According to the removal efficiency of selected substrates and two plants, the expected lifespan of the system is2.64year. This can meet the need of the treatment of domestic sewage of southern rural areas, and the market prospect of this kind of constructed wetland is hopeful. |
PDF Full Text Request