Potential for total nitrogen removal by combining vertical flow and horizontal flow constructed wetlands: A full-scale experiment study

To improve total nitrogen removal, a full-scale experimental study was conducted on a hybrid constructed wetlands plant designed for 100 person equivalents. The plant was composed of a first stage of vertical filters (fed with raw wastewater), followed by a second stage of horizontal filters. It was monitored over one year, measuring hydraulic conditions, physico-chemical conditions, gas emission, oxygen levels in the gas phase as well as regular treatment performance by 24-h composite samples. Different vertical filter configurations (media depth, intermediate and passive aeration system) were tested as well as two horizontal filter designs. Nitrogen removal is discussed in terms of the efficiency of each stage in relation to the season and the load applied. This study indicates limits for systems configuration and suggests some design avenues for hybrid systems to reach high and regular levels of nitrogen removal with reasonable surface area per person.