Constituent removal design procedures have developed rapidly in recent years. Three design models were compared in the Water Environment Federation's Manual of Practice (WEF, 2001). All three models are based on analysis of wetland input/output data or mass balance relationships, and they all take the general form of a first-order plug-flow model; however, they do not directly account for the complex reactions and interactions that occur in wetlands but instead use a lumped apparent rate constant to account for the change in concentration or mass between the input and output (Tchobanoglous et al., 2003). Such an approach is the best that can be done with the currently available database and understanding of wetland processes. The models are fundamentally equivalent and should be expected to produce similar results, but unfortunately that is not the case. This is partly due to the fact that the models were not developed from the same sets of data and also partly due to differences in the structure and content of the models. The models can be divided into two types: (1) the volumetric models as developed by Reed et al. (1995) and Crites and Tchobanoglous (1998) and (2) the areal loading models developed by Kadlec and Knight (1996). Some of the major advantages and limitations of these two design approaches are listed below.
Was this article helpful?