Comparison of operational design criteria for subsurface flow constructed wetlands for wastewater treatment

Many communities are investigating the use of constructed wetlands as a sim ple, viable alternative to poorly operating on-site wastewater treatment. C urrently, the most popular design models in the U.S.A. for subsurface flow units are the US Environmental Protection Agency (EPA) and the Tennessee Va lley Authority (TVA) methods. However, there has been limited data verifyin g if the operating performance is up to design standards. In order to addre ss this problem, this paper documents the performance of such treatment sys tems over a broad range of conditions in North Alabama. The operational dat a is used to determine a best-fit value of reaction rate constant and propo ses improved input parameters for both design models. According to this dat a, 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 m(2)/kg BOD5 per day into the wetland for the TVA method.