Practical And Theoretical Exploration On Constructing Urban Wetland Park With Constructed Wetlands Engineering

Wetland park is an important component of wetland protection systems. The wetland park construction has become an important means for effective wetland protection, and one of the effective way to maintain or expand wetland area. The constructed wetland engineering will be applied to the urban wetland park construction, which is not only an effective way and the main mode for wetland restoration, but also a powerful tool full of economic, ecological and social benefit, considering either from the aspect of economic effect or of treatment efficiency. This paper focused on practical research on constructed wetland engineering. Starting from the bio-remediation study with the application of the strong reoxygenation tidal flow constructed wetland and Aixi Lake semi-constructed wetland system, it discussed practical and theoretical applications of constructed wetland engineering to the urban wetland park construction, by analyzing wetland plant's purification efficiency on COD, TN, TP and DO, which has a theoretical and practical significance on the development of urban wetland park.This research studies in following two aspects:1. The bioremediation study with the application of strong reoxygenation tidal flow constructed wetland:(1) All different mix of plants combination had a certain COD removal ability. The best combination of COD removal was Azolla imbricate + Salvinia natans + Colocasia tonoimo, when the cleaning cycle was 10 days, the removals of COD could achieve 96.12% respectively; Azolla imbricate + Hydrocharis dubia + Iris pseudacorus and Hydrocharis dubia + Iris pseudacorus came next, its removal rate could reach 90~94% when the purification cycle was 8 days or more.(2) By comparing the trend of TN removal change for different plants combination, it showed that there was no big difference for each plants combination when the purification period was 1 to 6 days. When the purification period was 10 days, Azolla imbricate + Zizania latifolia had maximum COD removal efficiency of 71.98%, and Azolla imbricate + Salvinia natans + Colocasia tonoimo come next with a maximum of 70.12%.(3) Different plants combination had a certain removal effect on TP removal. In 7 combinations, Nymphoides peltatum + Azolla imbricate was the worst on the dephosphorization, obviously lower than the other six combinations, Ceratophyllum demersum + Azolla imbricate + Triarrhena lutarioriparia was Second. The rest five had a relatively high dephosphorization without distinct difference.(4) All different plants combination showed a stable DO ability which were all distributed in 2~4 mg/L, but when cleaning cycle was 6 or 7 days, the water samples in most plants combination all reached DO peak. The Azolla imbricate + Zizania latifolia was the most obvious. Different plants had a certain ability of radial oxygen. The DO in water were increased with processing time increasing, eventually reaching saturation.2. The bioremediation study with the application of Aixi Lake Semi-constructed wetland:(1) Water quality in sample area was tested and results were all inferior Grade V in terms of COD value.(2) In the sample area of this experiment, the efficiency of COD removal for plants was low. Instead the COD value was higher in some plant area, which was possibly because the weather in Nanchang city continued cold and wet long time before sampling and water plant growth was not strong, resulting that COD removal efficiency was not that obvious. Meantime, many damaged leaves decayed into particles presenting in the water, which were then sampled and measured as organic pollutants, so the COD value was high.(3) By comparing the TN content in vegetation zone and non-vegetation zones, it could be seen that the presence of plants had an obvious effect for TN purification in water, and there were certain gaps in different plant's purification efficiency. The water quality and purification ability in Thalia dealbata, Colocasia tonoimo, Arundo donax zone was much better; Phragmites australis, Typha orientalis, Zizania latifolia also showed a certain degree of purification ability, while Iris pseudacorus area was at the high nitrogen water quality and purification ability was weak.(4) Different plants had big differences on TP purification in water. Rumex japonicus, Zizania latifolia, Phragmites australis, Typha orientalis, Thalia dealbata and Colocasia tonoimo had good purification efficiency, but it was not satisfactory in some Phragmites australis and Iris pseudacorus area, which may be correlated with its growing season, species and quantities. Generally, the TP content in area with aquatic plants was lower than that of non-aquatic plants. Plants take important role on phosphorus absorption, but different plants has different absorption ability. The above studies showed that, with the physical, chemical and biological triple coordination of matrix-microbiology-plant in this complex ecosystem, constructed wetland engineering achieved efficient waste water purification through filtration, adsorption, coprecipitation, ion exchange, plant uptake and microbial decomposition, which had a unique and complex purification mechanism to maintain high biological diversity and to increase the city's waterscape. In future the constructed wetland engineering will be widely used in research and development of urban wetland park construction and will be more focused on close combination of wetland park planning with constructed wetland engineering, to make it an effective way and the main mode for wetland restoration.