DESIGN METHODS FOR RESIDENTIAL WASTE-WATER TREATMENT

Constructed wetlands have recently gained popularity as an alternative method for wastewater treatment. This paper compares two design metho dologies currently used for constructed wetlands; Tennessee Valley Aut hority (TVA) and the Environmental Protection Agency (EPA) methods. A discussion of parameters for both methods is given and a wetland treat ment system is designed for an individual residence with typical BOD5 loads and flow rates. Calculation results revealed significant discrep ancies 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 wet land is a viable option under design considerations that are not favor able 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 .