Agricultural drainage is one of important contributors of non-point source pollution, and it is difficult to treat in practice due to its dispersed nature. Constructed wetland system has been proved to be feasible way to improve drainage water quality. A constructed wetland was built in this study, and its purification efficiencies for artificial wastewater that was simulated agricultural drainage were analyzed under different operating conditions.
The results revealed that:
1. The wetland environment was generally under anaerobic state. The values of pH were reduced, however, the alkaline wastewater did not transform to be acidic.
2. The concentrations of ammoniac nitrogen (NH4 ＋－N), total nitrogen (TN) and total phosphorus (TP) of artificial wastewater were reduced prominently shortly after going
into wetland. In different operation conditions, the removal rates of NH4 ＋－N and TP were 42.2~84.6% and 46.2~88.4%. But the removal rates of TN were only 35.9~63.7%.
3. Hydraulic retention time (HRT) which is either too long or too short might reduce the removal efficiency, and the best HRT was found to be 3 days in the system.Results also show that deeper water level was beneficial for the removal of pollutants. The concentration of inflow had little effect on the efficiencies. The removal rates of nitrogen and phosphorus in vertical-flow wetlands were higher than in horizontal-flow wetlands.
4. After running for several months, the organic matter in wetland was decreased. It iv was the result of water flushing, physiological activities of microorganism and aerobic
5. The equation of reaction dynamics in wetland was set up to describe the process of reaction in wetland.
The study showed that these constructed wetland system can intercept and purify the pollutants of non-point source pollution, and it has best lasing-resistant ability. But the aerobic condition must be meliorated to increase the removal rates of TN.
Key words: wetland, nitrogen, phosphorus, organic matter, rate of removal, reaction
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