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Constructed wetlands have recently gained popularity as an alternative method for wastewater treatment. This paper compares two design methodologies currently used for constructed wetlands; Tennessee Valley Authority (TVA) and the Environmental Protection Agency (EPA) methods. A discussion of parameters for both methods is given and a wetland treatment system is designed for an individual residence with typical BOD5 loads and flow rates. Calculation results revealed significant discrepancies in the required constructed wetlands volume, and thus detention time, stemming from inherent differences in the design methodologies. The EPA method relies heavily on plug flow kinetics, and is therefore sensitive to changes in the reaction rate constant and media porosity. Conversely, TVA determines the surface area by sizing in accordance with a recommended hydraulic loading criterion and is affected only by the hydraulic flow rates. This study concluded that a constructed wetland is a viable option under design considerations that are not favorable for traditional on‐site wastewater treatment methods. However, it is recommended that conservative values for flow and loading rates be assumed to assure complete treatment for either of the design methods.

Many communities are investigating the use of constructed wetlands as a simple, viable alternative to poorly operating on-site wastewater treatment. Currently, the most popular design models in the U.S.A. for subsurface flow units are the US Environmental Protection Agency (EPA) and the Tennessee Valley Authority (TVA) methods. However, there has been limited data verifying if the operating performance is up to design standards. In order to address this problem, this paper documents the performance of such treatment systems over a broad range of conditions in North Alabama. The operational data is used to determine a best-fit value of reaction rate constant and proposes improved input parameters for both design models. According to this data, the average plug-flow reaction rate constant was calculated to be 0.70 d-1 for the EPA method, while the recommended organic loading criterion is 11.4 m2/kg BOD5 per day into the wetland for the TVA method.