Pollutant Removal Efficiency of Vertical Sub-surface Upward Flow Constructed Wetlands for Highway Runoff Treatment

Four small-scale cylindrical, vertical upward flow constructed wetland units were installed and evaluated to determine the effectiveness of these units to treat highway runoff. The highway runoff was collected during various rainfall events in the year 2009 from Lukou Viaduct section of Nanjing airport express highway. The natural zeolite and gravel were used as filter substrates and all four units were planted with common reed (Phragmites spp.). These four units were subjected to similar hydraulic retention time (6 h HRT) with different hydraulic loads. Water samples were collected from the influent and effluent of vertical flow constructed wetlands, and were analyzed for determination of total suspended solids, COD, ammoniacal nitrogen, total nitrogen and total phosphorus. The results show that vertical flow constructed wetlands with zeolite-gravel substrate combination achieved the best performance between all systems with mean removal efficiency of 57 % TSS, 45 % COD and 78 % ammoniacal nitrogen. The average ammoniacal nitrogen decreased by approximately 65 % in all wetland units, suggesting that this design had the highest nitrification rate. The study also revealed that the use of substrate materials with specific characteristics, such as zeolite and gravel, can enhance the removal of nutrients. However, the overall performance of vertical upward flow constructed wetlands was not effective.