Treatment of total petroleum hydrocarbon by free water surface constructed wetland: Effects of different combinations of submerged and free-floating plants

Submerged and free-floating plants in free water surface constructed wetland (FWSCW) play a crucial role in pollutant removal, but their combined effectiveness for total petroleum hydrocarbon (TPH) removal remains unclear. In this study, four lab-scale FWSCWs with different combinations of submerged and free-floating plants (CW1: E. crassipes and V. natans , CW2: E. crassipes and M. aquaticum , CW3: L. laevigatum and V. natans , and CW4: L. laevigatum and M. aquaticum ) were established to investigate the TPH removal of FWSCW. CW4 achieved satisfactory removal of TPH and other contaminants, with a 3.15–12.5 % TPH removal efficiency improvement compared to other FWSCW. The TPH concentration in plants and total biomass in CW4 were significantly higher than those in other FWSCW (p < 0.05), which was attributed to the strong TPH bioaccumulation capacity of M. aquaticum . Further analysis showed the correlation between TPH removal efficiency and the TPH concentration in M. aquaticum (p < 0.05), which may be caused by the outstanding TPH bioaccumulate and transport ability of M. aquaticum . TPH removal was also correlated with the removal of TP, COD and NH 4 + -N (p < 0.05). Abovementioned results provided scientific basis to selection and combination of submerged and free-floating plants during TPH removal in FWSCW. • TPH removal efficiency of FWSCW was 78.57 % to 91.07 %. • M. aquaticum increased TPH removal in FWSCW. • Bioaccumulation capacity and plant biomass affected the removal of TPH.