Simplified process to determine rate constants for sunlight-mediated removal of trace organic and microbial contaminants in unit process open-water treatment wetlands

Unit process, open-water (UPOW) treatment wetlands are a unique type of constructed wetlands that are designed to promote photo- A nd microbiologically mediated natural water treatment processes. A mechanistic understanding of the removal processes for nitrate, trace organic contaminants (TrOCs), and microbial contaminants in UPOW wetlands has been established, and equations have been previously developed to describe removal kinetics. However, the numerical models developed to predict photodegradation rate constants for the removal of TrOC and microbial contaminants involve too many steps to facilitate a practical design approach. In this article, we present a method for predicting rates of phototransformation of representative TrOCs (atenolol, propranolol, sulfamethoxazole, and carbamazepine) and inactivation of microbial indicator organisms (Escherichia coli and MS2) that allows a user to readily design UPOW wetlands to meet different performance goals. Photodegradation rate constants were determined for a range of conditions that influence treatment efficacy (i.e., time of year, pH, latitude, and dissolved organic carbon concentration), and are presented in a series of figures. We illustrate the use of these figures for UPOW wetland design with a representative example of the design process. A spreadsheet containing sample calculations is included in the Supplementary Data.