AN ASSESSMENT OF THE ROOT ZONE METHOD OF WASTE-WATER TREATMENT

An evaluation of existing systems provides evidence that the root zone method can meet secondary treatment standards if properly designed and operated. The use of coarse media is recommended to avoid the common operational problem of overland flow. Additionally, the use of bulrushes as the wetland plant is recommended because their deep root zone reduces the surface area required for the root zone bed. Using data from existing systems, the value of the temperature-dependent rate constant for BOD removal (K20) is evaluated and found to be lower than the value implicit in a prevailing design equation. Design guidelines to determine required root zone bed volume and length and width configuration are developed assuming first-order kinetics, plug flow, and Darcy's law. A design example is presented based on guidelines developed from existing systems. Additional design considerations of temperature, flow variation, service life, and cost are discussed.