The improvement of pollutant removal efficiency in saturated vertical flow constructed wetlands by tubifex tubifex.

Pilot-scale saturated vertical flow constructed wetlands (VF-CWs) were established to identify whether T. tubifex has the similar performance in saturated VF-CWs to that in surface flow CWs in improving pollutant removal efficiency (RE). The saturated VF-CWs with T. tubifex achieved REs of 67.3% total nitrogen (TN) and 39.8% chemical oxygen demand (COD), which were significantly higher than treatments without T. tubifex (42.2% TN and 31.4% COD). There existed significant interactions between macrophytes and T. tubifex. T. tubifex greatly improved the dissolved oxygen by increasing the connectivity between layers, and enhanced dehydrogenase activity and fluorescein diacetate. Adding T. tubifex improved the bacterial diversity and relative abundance of both N-cycle bacteria and fermentation bacteria in the biofilms. The improvements of ammonia oxidation and anammox were the main pathways for the increased nitrogen removal by T. tubifex. Therefore, T. tubifex is a useful tool for improving pollutant REs in saturated VF-CWs.