CONSTRUCTED WETLAND DESIGN AND PERFORMANCE FOR SWINE LAGOON WASTEWATER TREATMENT

Abstract

Although constructed wetlands have been identified as a potentially important component of animal wastewatertreatment systems, their design requirements have been based mainly on municipal systems. The objective of this investigationwas to examine various design approaches for constructed wetlands in relation to the performance of our constructedwetlands for swine wastewater treatment. The free water surface wetlands in Duplin County, North Carolina, investigatedin this study were constructed in 1992 based on the Natural Resources Conservation Service (NRCS) presumptive designmethod. We used four wetland cells (3.6 m 33.5 m) with two cells connected in series; the two series of cells were plantedand predominated, respectively, by either bulrushes or cattails and were studied from 1993 to 1999. The wetlands wereeffective in treating nitrogen with mean total nitrogen and ammoniaN concentration reductions of approximately 85%;however, they were not effective in the treatment of phosphorus. Regression analyses of outflow concentration vs. inflowconcentration and hydraulic loading rate for total N and ammoniaN were reasonably correlated (r 2 > 0.66 and r 2 > 0.65,respectively). Our calculated firstorder plugflow kinetics model rate constants (K20) for totalN and ammoniaN (8.4 and8.9, respectively) were slightly lower than those reported in the limited literature and currently recommended for use inconstructed wetland design. Nonetheless, use of our calculated rate constants would result in about the same size constructedwetland for treating swine lagoon wastewater.