Effects of pollutant speciation in treatment wetlands design

This paper reports on observed and potential effects of distributions of detention times and first order removal rate constants. Rate constants are distributed across the species that make up a grouped class of contaminants, such as total suspended solids (TSS) and biochemical oxygen demand (BOD). The existence of these distributions is shown to invalidate the plug flow (PF) model assumption in almost all cases. The tanks-in-series (TIS) model is shown to offer a better platform to accommodate distributed parameters. Detention time distributions (DTDs) and k-value distributions (kVDs) are shown to both lead to TIS models. Discrete, uniform and gamma distributions for detention and k-values are explored. The greater the variance, the more important the impacts on performance modeling. Data for the reduction of TSS are analyzed from the perspective of particle size distributions, and shown to result in the appearance of TIS behavior for the lumped TSS measure. The retarded rate constant concept is shown to be subsumed by the idea of a weathering mixture with a distribution of rate constants. [Copyright &y& Elsevier]