Subsurface flow constructed wetland performance at a Pennsylvania campground and conference center

A constructed wetland treatment system consisting of subsurface now (SSF) w etland cells, sand filters, and final effluent wetlands was found to be eff ective in removing carbonaceous biochemical oxygen demand (CBOD) and total suspended solids (TSS) to below 30 and 10 mg L-1, respectively. Removal eff iciency of total nitrogen (TN) loads improved from 60.1 to 88.5% over the 2 -yr study, primarily due to increased vegetation densities in the SSF wetla nd cells. In both Sears, parallel wetland treatment cells had significantly different (p < 0.001) plant densities of broadleaf cattail (Typha latifoli a L.) and softstem bulrush [Schoenoplectus tabernaemontani (K.C. Gmel.) Pal la], with significantly more TN removed from the more densely vegetated cel l. Overall, the assimilation of N by plants removed less than 25% of the TN load, regardless of plant density, indicating that the primary role of dee ply rooted macrophytes is supporting sequential nitrification-denitrificati on within the anaerobic wetland substrate. More than 99% of the dissolved p hosphate (PO43--P) was removed within the entire system in both years, but removal efficiencies within the wetland cells decreased from 91.2% the firs t year to 66.1% the second year, indicating that adsorption sites for PO43- -P may be saturated despite increased plant assimilation. Experimental mani pulation of waste applied to the sand filters demonstrated that a header-ty pe distribution system promoting horizontal flow was more effective at nitr ifying ammonium (NH4+-N) discharged to the sand filters than the surface ap plication of waste promoting vertical now.