Improving Winter Performance of Constructed Wetlands for Wastewater Treatment in Northern China: A Review

Constructed wetlands are engineered systems relying on natural microbial, biological, physical and chemical processes to treat wastewater. Treatment performance tends to decrease in colder temperatures, so that ways to enhance the performance in northern climates has been sought. In China, the first constructed wetland was built in China in 1987 and since then, about 450 systems have been constructed throughout the country. At least 67 constructed wetlands are located in northern China and have reported significant seasonal changes of treatment efficiencies. This paper reviews current engineering practices including case studies showing ways to increase winter treatment effectiveness in cold climates. These measures include: (1) internal improvement of system design and setup of the system, (2) optimization of winter operation, and (3) external incorporation of pre- and post-treatment technologies. Various measures to raise the temperatures of these systems in the winter were compared in several constructed wetlands (40 and 50 degrees N). For example, plastic film mulch can be used with thermal insulation; however, the operators of constructed wetlands often use ice to cover the system due to lower cost and maintenance. This review demonstrates that the effectiveness of constructed wetlands in cold climates can be improved through better operation strategies.