Constructed wetland as one of technique in phytoremediation, combined and utilized green plants, soil and microorganism in reducing the pollutants in wastewater. Plant selection and types of a substrate are among the factors that contribute to the greater performance of pollutant removal. Gravel and sand are the commonly substrate used in sub-surface constructed wetland because they have acceptability with the hydraulic condition and capable to increase the removal of pollutants in wastewater treatment. In this study, the gravel and sand combination were used to increase pollutant removal. Three (3) sets of experiments were set up as treatment of palm oil mill effluent (POME) which is POME only (PO) as control and, POME with gravel (PG), and POME with gravel-sand (PGS) bed. The POME samples were recirculated through the sub-surface flow constructed wetland for 30 days of treatment. The PGS systems contributes higher performance rather than single gravel or sand with 66% COD, 97% suspended solid, 98% turbidity, 98% ammonia-nitrogen and 99% TN removal and 74% of TP removal. Therefore, the use of gravel-sand substrate is very promising for sub-surface flow constructed wetland treatment systems for POME.
