Organics and nutrients removal in vertical flow wetlands: loading fluctuation and alternative media

Two wetland systems (conventional and structurally modified) were studied for the removal of organics and nutrients from municipal wastewater. Each system consisted of three vertical flow (VF) wetlands, which were filled with agricultural, construction waste materials and planted with Phragmites australis and Canna indica. The wetland units were operated under constant and consecutive shock hydraulic load (HL). Input nutrients and organics load across the wetland units ranged between 4.0-116.0 g N/m²d, 0.5-23.0 g P/m²d, 1.0-527.0 g biochemical oxygen demand (BOD)/m²d and 16.0-686.0 g chemical oxygen demand (COD)/m²d. Nitrification and organic carbon availability controlled nitrogen (N) removals in first and third stage VF wetlands, respectively, during constant load phase; organics removals were influenced by dissolved oxygen concentration of municipal wastewater. Second stage VF wetlands (of both systems) were inefficient in terms of COD removals during shock load periods, which were counter-balanced by first and third stages. First stage VF wetlands achieved higher N removal rates than following stages during shock load periods. Wetland maturation provided a buffer against substantial HL increment and sharp input load decrease in latter shock and recovery phases, respectively. Agricultural waste (sugarcane bagasse) provided carbon to support denitrification; construction materials (recycled brick and crushed mortar) removed phosphorus (P) from wastewater through adsorption. Coliform removal in VF wetlands was achieved through media filtration. Structurally modified system achieved higher removals than the conventional system. BOD, COD, total nitrogen and NH₄-N removal percentage across two systems ranged between 76-79%, 59-63%, 73-77% and 90-95%, respectively. In general, this study enlightens potential application of appropriate waste materials for wastewater treatment.