New solution to build constructed wetland in cold climatic region.

Constructed wetland is an efficient and convenient wastewater treatment technology that has been widely used in China and elsewhere. However, seasonal frozen soil is easily formed in the cold regions of northern China. The local wetlands are in the frozen soil layer, causing the pollutants from wastewater not to be removed well. Therefore, a new constructed wetland structure that uses shallow geothermal energy to keep the wetland not frozen in the winter is proposed in this paper. The results of the experiment show that the average removal rates of total nitrogen, ammonium ion, and total phosphorus in the multistage constructed wetland system are 54.8%, 44.5%, and 77.7%, respectively. This performance is substantially better than that of conventional wetlands in winter. The proposed wetland structure can be applied to conventional wetlands and avoid the conventional wetlands being idle during cold seasons, which is conducive to the popularization of constructed wetlands (CWs) in cold regions.