[Effect of constructed wetland on the purification of industrial zone rainfall runoff contaminated with phenanthrene].

According to the water characteristics of industrial rainfall runoff in the catchment of Tongsha Reservoir, Dongguan City, a subsurface-flow constructed wetland (SSFCW) was used to treat simulated rainfall and the spatial variation of removal efficiency of contaminants in the wetland bed was analyzed. The longitudinal and vertical variation of removal efficiency of COD, NH4(+) -N, TN, TP and phenanthrene were examined. Enzyme activity of polyphenol oxidase (PPO) and nitrate reductase (NR) along the wetland bed were analyzed as well, meanwhile, four biogeochemical indexes of the wetland system, including DO, pH, ORP and water temperature, were monitored and their influences on the removal efficiency of contaminants and enzyme activity were analyzed. Results showed that DO, pH, ORP, water temperature all presented a decreasing tendency along the wetland bed, and the removal of COD, TP and phenanthrene occurred mainly in the front quarter of the wetland system; in the vertical direction, DO and ORP in the upper wetland bed were significantly higher than those in the ground floor, suggesting that the horizontal subsurface system was in an anaerobic or anoxic condition. The removal rates of COD, TP, TN, NH4(+) -N and phenanthrene were 1.17-1.36, 2.04-2.11, 1.40-1.92, 1.37-2.30, and 1.07-1.36 times higher than those at the bottom, respectively. Therefore, the vertical variation of purification efficiency was more significant than the longitudinal variation. A significant positive correlation was determined between the enzyme activity of NR and the NO3(-) -N concentration, but the longitudinal variation in the enzyme activity of NR and PPO was not obvious.