Effect of Multilayered Structure of Filtration Beds on Sewage Treatment Performance in a Multistage Constructed Wetland

In this research, the performance characteristics of the multilayered filtration bed （ MLF ） and non-multilayered filtration bed （ n-MLF ） in a pilot-scale multistage constructed wetland for treating sewage were compared, and the effect of the multilayered structure on the water purification performance was elucidated. It was confirmed that the effect of the multilayered structure on the aerated treatment performance of, for example, BOD and NH 4+ -N removal was negligible under the vertical flow condition, but not under the hybrid condition comprising both vertical and horizontal flows. MLF was easier to become anaerated than n-MLF, resulting in a lower aerated treatment performance under the hybrid condition. Furthermore, the effect of a lack of vegetation on MLF manifested as a lower nitrogen removal performance. Although the specific removal unit for BOD and phosphorus under the vertical flow condition in MLF increased 1.5fold compared with that in n-MLF, the removal performance of nitrogen could not be improved. The specific energy consumption for sewage treatment by the constructed wetland in this work was low at 0.32 kWh m -3 , demonstrating the effectiveness of the constructed wetland in accomplishing the decarbonization of sewage works.