Highway runoff treatment by hybrid adsorptive media-baffled subsurface flow constructed wetland

Abstract In this study, a lab-scale baffled horizontal sub-surface flow constructed wetland (HSSF-CW) with adsorptive media/substrate was constructed and operated for one year to assess its performance for highway runoff (HRO) pollution control. Based on the results of isothermal adsorption experiments, a hybrid of zeolite, expanded vermiculite, vesuvianite was chosen out of five candidate media as the optimal combination in terms of adsorption efficiency. The performance of the constructed wetland (CW) with the predetermined hybrid media was tested under different hydraulic loadings (HLs) with continuous and intermittent flow conditions. The results show that ammonia nitrogen (NH 4 + -N) and total phosphorus (TP) adsorption by the media fitted very well with the Langmuir isothermal equation. 2D contour plot analysis is a useful tool, which can give a visible pollutants removal law in CWs and help to understand how such a system works along the horizontal direction. Results from intermittent operation indicate that an average removal efficiency of 86.5%, 68.1%, 78.25%, 95.2% and 64.85% were achieved for total suspended solids (TSS), chemical oxygen demand (COD), total kjeldahl nitrogen (TKN), NH 4 + -N and TP, respectively. The performances during continuous flow under different HLs illustrate that HLs have little influence on COD, NH 4 + -N and TP removal under HLs lower than 0.56 m 3 /m 2  d, while the removal rates are remarkably decreased at a high HL of 1.12 m 3 /m 2  d, especially for TP. Moreover, media/substrates adsorption is the main process for NH 4 + -N and TP removal, while plants uptake plays a limited role. The findings suggest that the baffled adsorptive media HSSF-CW is a promising system for HRO pollution control and shows potential for field application.