Purification Of Small-scale Stagnant Water In Urban Regions: Human-powered Water Lift And Bank-based Constructed Wetland

There are often many small-scale stagnant bodies of water in the urban regions of China. Due to a lack of fresh water supplies and circulation, they can be a source of a variety of pollutants and diseases by breeding harmful microbes and insects, producing algal blooms, and volatilizing offensive odors, thus causing a series of environmental and public health problems. Therefore, it is necessary to find a new purification technology to solve urban stagnant water bodies’ problem. The research proposed an innovative stagnant water purification system which consisted of a human-powered water lift and a small-size bank-based constructed wetland. The information gathered from this research could provide much help for carrying out better management and purification proposal of landscape water in urban regions.The experimental plots were established in an artificial lake near Yi Tong River of Changchun City in Jilin Province, China. The bank-based constructed wetland was filled with two absorption substrates, clinker and scoria, after which yellow iris(Iris pseudacorus L.) was planted in. The purpose of this study was to evaluate the feasibility of the system for purifying the stagnant water in urban regions, and the results were as follows:(1) The SEM results showed that scoria with better surface porosity have superior adsorption effect compared with the clinker with rough surface. And the aperture of clinker was bigger than scoria. Clinker and scoria were mainly composed of C, Si, Al, Fe, Ca, Na, Mg elements. N and P were detected in the samples of clinker and scoria after absorption. N and P in the samples of clinker were 2.57%, 1.16%, and the samples of scoria were 2.74%, 1.05% respectively. This showed that the clinker and scoria had certain absorptive capacity of nitrogen and phosphorus in sewage, the difference wasn’t significant. Considering from the aspects of resource recovery, availability and cost, we could have clinker instead of scoria during the construction of constructed wetland.(2) The system can effectively circulate stagnant water, increase dissolved oxygen(DO) by more than 45%, outlet DO content reached 8 mg/L, and decrease chemical oxygen demand(COD) by 20%-45%, but it showed lower nitrogen and phosphorus removal rate(<10%).The experiment demonstrated that this type of ecological system is technologically feasible for treating and purifying stagnant water.(3) Yellow iris can grow fast in the bank-based constructed wetland. At the mature plant stage, the aboveground and root dry biomass of yellow iris growing in clinker reached 10.1 g and 8 g, respectively, the aboveground and root dry biomass of yellow iris growing in scoria reached 8 g and 4.1 g, the aboveground biomass have grown more than the root biomass. So we could directly harvest the aboveground part of the plant. The bank-based constructed wetland could not only play the role of landscaping but also offer greater convenience for cutting plants compared with traditional constructed wetlands.(4) After 90 days, nitrogen accumulation in the total plant reached 244.3 mg and 170.7 mg in clinker and scoria, respectively, significantly higher than the phosphorus accumulation. This demonstrated that the ability of plants to remove nitrogen is far greater than that of the removal of phosphorus. The nitrogen accumulation in the aboveground part of plants was 13.3 times and 9.9 times of the original plants in clinker and scoria, respectively. Phosphorus accumulation increased by 21.5 times and 10.5 times in the aboveground parts of plants after 90 days in clinker and scoria, respectively, while only slightly in the plants’ root parts. So we could remove the nitrogen and phosphorus in water by trimming and harvesting the plants.(5) In this study, we reduced the water pollution by means of the bank-based constructed wetland and provided a human-powered device to recycle the stagnant water. The integrated ecological system which was composed of recreation, water purification, landscaping, and environmental education was formed. And it was also of significance for residents in acquiring environmental knowledge, participating in environmental protection, and improving green awareness.