Effect of Water Level Fluctuations on Nitrogen Removal and Plant Growth Performance in Vertical Subsurface-Flow Wetland Mesocosms

ABSTRACT

The effects of Typha orientalis and water level fluctuation on nitrogen and organic carbon removal were studied in vertical subsurface flow mesocosm columns over a six month period. The treatments were control (U1, without plants); conventional (U2, no fluctuation); drawdown (U3, daily removal of wastewater from the upper 5 cm layer); and, drained (U4, removal of all pore water once every 10 days). Synthetic wastewater containing 20 mg L⁻¹ of total nitrogen (TN) and 10 mg L⁻¹ of total organic carbon (TOC) was used as the influent water. Influent and effluent waters were sampled every two weeks; T. orientalis was sampled at six-week intervals to evaluate biomass, shoot density, cumulative height and root porosity. The U3 system outperformed the U2 and U4 treatment systems (P < 0.05) in nitrogen removal, and the U4 system outperformed U3 and U2 in TOC removal. Estimated plant biomasses under treatments systems U2, U3, and U4 were 2.43, 2.19 and 2.49 kg/m², respectively. T. orientalis that were grown under treatment U2 had the highest root porosity.