Current problems and countermeasures of constructed wetland for wastewater treatment: A review

Constructed wetland (CW), a green wastewater treatment technology, is extensively used in the world owing to its advantages of less investment, low energy consumption, simple operation and maintenance, and satisfactory purification effect. Currently, with the promotion of CW application, a variety of problems have been gradually exposed. This paper summarizes the common problems of CWs, including poor wastewater purification capacity in cold climate, vulnerability of aquatic plants, clogging risk, greenhouse gases emissions, large land area occupation and inadequate management. In view of the above existing problems, optimized schemes are put forward. At cold temperature, proper thermal insulation, additional aeration, hydraulic condition optimization, and effluent recirculation are recommended to promote pollutants removal by CWs. To strengthen the function of phytoremediation in CWs, it is necessary to choose suitable plant species and reasonable planting patterns. A variety of methods (e.g., solid sampling, hydraulic conductivity test, tracer experiments, bio-electrochemical sensor, geophysical methods) have been developed for monitoring and evaluation of CW clogging. Anti-clogging measures mainly include wastewater pretreatment, replacement of matrix, addition of chemical oxidants, biosurfactants and enzymes, introduction of degrading bacteria or earthworms etc. CWs often emit greenhouse gases (e.g., CH4 and N2O) during wastewater treatment, which can be controlled by conventional methods (e.g., flow patterns, vegetation types, electron receptor supplementation, special filler utilization) and bio-electrochemical method. CW database construction and utilization, appropriate CW type design (e.g., hybrid CW), and strict technical management and supervision are recommended to realize the standardized and efficient operation of CWs.