Land saving and promising seasonal performance in novel spiral wetland

Abstract

Constructed wetlands have been widely employed as an ecological treatment technology. However, compared to conventional wastewater treatment methods, constructed wetlands require a larger land area, which is incompatible with the limited urban land resources where every inch is valuable. To address this issue, this study proposed and constructed a space-saving spiral constructed wetland. Through optimized structural design, the spiral wetland effectively reduced land occupation and maximizes the utilization of each elevation space to 70 %−80 %. Under the same wetland plane area, spiral wetland only uses 1/3 and 2/3 of the land resources of traditional wetland and the slope wetland, respectively. By utilizing high water head, it resolved dynamic issues faced by traditional wetlands. Additionally, aeration and re-aeration occurred during the transfer of rainwater between each layer of the wetland, enhancing its treatment performance. During summer, the average purification rate of COD is 82 %, and the purification efficiency of ammonia nitrogen is almost 100 % in the spiral wetland where it can accommodate large volumes of stormwater resulting from short-term heavy rainfall events while handling greater pollution loads, which challenges associated with significant amounts of storm runoff and instantaneous water flow during summer periods. In winter seasons, overflow from the spiral wetland combined with multi-stage purification alleviated clogging issues commonly encountered by traditional wetlands and enhanced treatment efficiency which remained above 90 %. The spiral wetlands provided a novel approach to resolving conflicts related to land use in urban areas.