| Constructed wetland (CW) is a newly developed eco-friendly wastewater treatment technology. It has high efficiency of removal rate of pollutants, and the outflow water quality is stable. Besides, CW resists to high pressure, and it’s easy to maintain. Therefore, this system has gain increasing attentions worldwide and has been widely applied in the treatment of sewage, agricultural point/surface source pollution and the eutrophic water bodies. However, researches regarding CW were limited to its mechanisms in China, the long-term monitor of the efficiency of CW were seldom conducted. In the present study, we focused on three constructed pilot-scale eco-wetlands (Jiaokou and Tangpu Eco-wetlands are located along reservoir area of water source, Lin’an Eco-wetlands are aimed at secondary effluent of sewage treatment plant) for a year to study the seasonal dynamic of water quality and the effects of above wetlands on water purification. The main results were as follows:1. Jiaokou Complex Eco-wetlands were efficient in removing nitrogen (N) and phosphorus (P). The average removal rate of total phosphate (TP) and total nitrogen (TN) were48.3%and40.5%respectively. The removal of NO3--N and NH4+-N also exceeded40%. In the plant growth season from May to July, the average removal efficiency of NO3--N, NH4+-N, TN, COD and TOC could reach80.3%,56.1%,78.7%,42.0%and38.0%respectively. However, in cold seasons as spring and winter, less than20%of COD and TOC were reduced. The relatively low temperature in these seasons might depress microbes actively and plant growth, which would affect the water purification process. Thus, the effects of CW was affected by seasons, and summer is the best season for this system to gain the highest efficiency. By modules analysis, it was shown that the eco-filter modules with filler were effective in removing TP, while the intensive plant resource system were efficient for removing TN and organic matters.2. Tangpu Surface Flow Wetlands exhibited the highest purification effects in May. The wetlands showed high performance in N and P removal, especially in the Iris pseudacorus surface flow system and the Jussiaea stipulacea Ohwi artificial floating island systems. During the monitor period, we noticed that the wetlands were flooded in July with most plants totally submerged, and the purification rate was badly affected. Therefore, it should be pointed out that the design and construction of C Ws should fully consider the local terrain, climate and other factors. Compared with Jiaokou Complex Eco-wetlands, the pollutant removal was more stable higher in Jiaokou wetlands than Tangpu wetlands.3. Lin’an Complex Eco-wetlands could remarkably remove pollutants in Summer. The average removal efficiency of NO3--N, NH4+-N, TN reached61.5%,57.6%and52.2%respectively. But in other seasons, TN removal rate was low due to the relatively poor removal efficiency of NO3--N. However, NH4+-N was consistently well removed in all seasons with the best performance in spring, which reached88.55%. The influent concentration of TP was between0.95-2.042mg/L, while the effluent was0.79-1.71mg/L. The removal rate of TP in four seasons was unsatisfactorily below25%. For COD, the removal rate was proportional to the influent concentration with the best removal rate as60.6%in spring and the worst13.9%in autumn. The removal effects on TOC were similar to those on COD, but to a smaller extent. The highest removal rate was reached in spring, but only27.5%. Overall, Lin’an wetlands showed the best performance in removing pollutants in spring, while the effects in other seasons were relatively low. By module analysis, it was shown that the eco-filter system was most effective for phosphorus removal in summer and autumn, in which the temperature is suitable for plant growth. While, the nutrients intensive system and self-purification system contributed more for N and COD removal. |
PDF Full Text Request