Nitrogen, phosphorous, and organic carbon removal in simulated wetland treatment systems

Effects of vegetation, wastewater drawdown, hydraulic retention time (HRT), and media depth on removal of nitrogen, phosphorous, and organic carbon in microcosms were investigated. Synthetic wastewater was added daily to 28 microcosms, and effluent was sampled every 12 days for 132 days. Effluent was analyzed for ammonium (NH(4)(+)-N), nitrate (NO(3)(-)-N), orthophosphate (PO(4)(3-)-P), and total organic carbon (TOC). Average percent removal of NH(4)(+)-N was significantly greater in microcosms containing plants (67%) than in those without plants (29%). Percent removal of PO(4)(3-)-P was also significantly greater in microcosms with plants (42%) than in microcosms without plants (20%), but no significant difference was found for TOC removal between microcosms with plants (67%) and those without plants (74%). Average removal was significantly lower in microcosms with wastewater drawdown than in those without wastewater fluctuation for both NH(4)(+)-N (51% versus 83%) and PO(4)(3-)-P (14% versus 71%). Percent NH(4)(+)-N removal was significantly greater in microcosms with a 6-day retention time (80%) than in those with a 2-day retention (53%), and PO(4)(3-)-P removal was also significantly greater with a 6-day retention time (55%) than a 2-day retention (29%). No differences were seen in TOC removal due to any of the treatments but HRT, where removal was greater microcosms with a 2-day HRT (76%) than in those with a 6-day HRT (60%). Media depth did not have a significant effect on nutrient removal. Results of this study demonstrate that required design parameters are different depending on the nutrient being removed in systems simulated by these microcosms.