Highway runoff treatment by lab-scale horizontal sub-surface flow constructed wetlands

In this study, lab-scale horizontal sub-surface flow constructed wetlands were experimented to assess their removal efficiency of highway runoff pollutants under different hydraulic conditions. Constructed wetland units with cobble-stone and broken-stone material as filter media were planted with common reed (Phragmites spp.) plants. Water samples collected from inlets and outlets of the wetland units were analyzed to determine total suspended solids, COD, ammonia-nitrogen, total nitrogen and total phosphorus. The results show that removal efficiency was quite low with cobble-stone filter media, whereas constructed wetland units with broken-stone filter media led to higher removal efficiency for SS (73.54%), COD (55.48%), NH3-N (81.89%) and TP (57.08%), respectively, but had a TN removal of −29.29% (increase in effluent). Results indicate that overall broken-stone filter media demonstrated better performance than cobble-stone filter media because broken-stone has larger specific surface area.