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

A constructed wetland treatment system consisting of subsurface flow (SSF) wetland cells, sand filters, and final effluent wetlands was found to be effective in removing carbonaceous biochemical oxygen demand (CBOD) and total suspended solids (TSS) to below 30 and 10 mg L^-1, respectively. Removal efficiency 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 wetland cells. In both years, parallel wetland treatment cells had significantly different (p < 0.001) plant densities of broadleaf cattail (Typha latifolia L.) and softstem bulrush [Schoenoplectus tabernaemontani (K.C. Gmel.) Palla], with significantly more TN removed from the more densely vegetated cell. 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 deeply rooted macrophytes is supporting sequential nitrification-denitrification within the anaerobic wetland substrate. More than 99% of the dissolved phosphate (PO₄/^3--P) was removed within the entire system in both years, but removal efficiencies within the wetland cells decreased from 91.2% the first year to 66.1% the second year, indicating that adsorption sites for PO₄/^3--P may be saturated despite increased plant assimilation. Experimental manipulation of waste applied to the sand filters demonstrated that a header-type distribution system promoting horizontal flow was more effective at nitrifying ammonium (NH₄/⁺-N) discharged to the sand filters than the surface application of waste promoting vertical flow.