1 Nitrogen Removal Assessment by Multivariable Statistical Technique in Free Surface Wetland Reza MOHAMMADPOUR * , Aminuddin AB GHANI, Shafiq SHAHARUDDIN, Chun Kiat CHANG, Nor Azazi ZAKARIA River Engineering and Urban Drainage Research Centre (REDAC), Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Penang, Malaysia * Corresponding author Email: reza564@gmail.com ABSTRACT The free surface constructed wetland (FSCW) is considered to be a low-cost alternative to remove a high portion of the nitrogenous components from the wastewater. To assess nitrogen removal in FSCW, 11 water quality variables were collected twice a month from 17 sampling stations for 13 months. The hierarchical cluster analysis classified the FSCW into three clusters with similar characteristics. A discriminant function analysis was employed to develop linear discriminant functions among the clusters. The result showed that the Cluster-I with less area and high load of nitrogenous components didn’t remove the nitrogen significantly, whereas the Cluster-II with higher concentration of plants reduced a significant portion of nitrite (48%). Due to combination of nitrification and denitrification processes, the Cluster-III with no emerged plants removed a high portion of nitrate (47%) and ammoniacal nitrogen (38%). The wetland removed a high percentage of nitrite (80%), nitrate (62%) and ammoniacal nitrogen (51%). KEYWORDS Free surface wetland, nitrogen removal, cluster analysis, discriminant analysis, pollution removal INTRODUCTION Due to low concentration of plant and vegetation in municipal area, the industrial runoff with high pollution discharge into natural water. The Free Surface Constructed Wetlands (FSCW) is recognized as low energy green-technique with a high ability to decrease various nutrients and pollution in wastewater (Kadlec and Wallace, 2008; Vymazal, 2007). The FSCW closely is similar to natural wetlands with a combination of open water and emergent plants rooted in the soil as macrophyte area. In the Malaysia, the FSCW is recommended as a part of Storm water Management Manual for treatment of storm water runoff (Zakaria et al. 2003; Asmaliza et al., 2013). Generally, three parts can be recognized in the FSCW, the inlet, macrophyte and open water area or micropool (Zakaria et. al, 2003). The FSCW reduces the different kind of contaminants such as organic matter, inorganic matter, trace organics and pathogens (US EPA, 2000). The wastewater is treated by a combination of several processes such as sedimentation, oxidation, adsorption, filtration, digestion, reduction, and precipitation (US EPA, 2000). The macrophyte is a main part of FSCW with a large number of processes, i.e. retention of pollutants, control of water flow, biochemical transformations and stimulation of microbial activity (García-Lledó et al., 2011). 13 th International Conference on Urban Drainage, Sarawak, Malaysia, 7–12 September 2014