title: Sunlight inactivation of fecal indicator bacteria in open-water unit process treatment wetlands: Modeling endogenous and exogenous inactivation rates.
abstract: A pilot-scale open-water unit process wetland was monitored for one year and found to be effective in enhancing sunlight inactivation of fecal indicator bacteria (FIB). The removal of Escherichia coli and enterococci in the open-water wetland receiving non-disinfected secondary municipal wastewater reached 3 logs and 2 logs in summer time, respectively. Pigmented enterococci were shown to be significantly more resistant to sunlight inactivation than non-pigmented enterococci. A model was developed to predict the inactivation of E. coli, and pigmented and non-pigmented enterococci that accounts for endogenous and exogenous sunlight inactivation mechanisms and dark processes. Endogenous inactivation rates were modeled using the sum of UVA and UVB irradiance. Exogenous inactivation was only significant for enterococci, and was modeled as a function of steady-state singlet oxygen concentration. The rate constants were determined from lab experiments and an empirical correction factor was used to account for differences between lab and field conditions. The model was used to predict removal rate constants for FIB in the pilot-scale wetland; considering the variability of the monitoring data, there was general agreement between the modeled values and those determined from measurements. Using the model, we estimate that open-water wetlands at 40° latitude with practical sizes can achieve 3-log (99.9%) removal of E. coli and non-pigmented enterococci throughout the year [5.5 ha and 7.0 ha per million gallons of wastewater effluent per day (MGD), respectively]. Differences in sunlight inactivation rates observed between pigmented and non-pigmented enterococci, as well as between lab-cultured and indigenous wastewater bacteria highlight the challenges of using FIB as model organisms for actual pathogens in natural sunlit environments.
authors.affiliation: Engineering Research Center for Re-Inventing the Nation's Urban Water Infrastructure (ReNUWIt), USA; Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710, USA.
authors.forename: Mi T
authors.initials: MT
authors.lastname: Nguyen
authors.affiliation: Engineering Research Center for Re-Inventing the Nation's Urban Water Infrastructure (ReNUWIt), USA; Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710, USA.
authors.forename: Justin T
authors.initials: JT
authors.lastname: Jasper
authors.affiliation: Engineering Research Center for Re-Inventing the Nation's Urban Water Infrastructure (ReNUWIt), USA; Department of Civil and Environmental Engineering, Stanford University Stanford, CA 94305, USA.
authors.forename: Alexandria B
authors.initials: AB
authors.lastname: Boehm
authors.affiliation: Engineering Research Center for Re-Inventing the Nation's Urban Water Infrastructure (ReNUWIt), USA; Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710, USA. Electronic address: karanelson@berkeley.edu.
authors.forename: Kara L
authors.initials: KL
authors.lastname: Nelson
mesh_terms: D001419:Bacteria / Q000528:radiation effects*; D016983:Enterococcus / Q000528:radiation effects; D004926:Escherichia coli / Q000528:radiation effects; D005243:Feces / Q000382:microbiology; D008962:Models, Theoretical; D010865:Pilot Projects; D013472:Sunlight; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000382:microbiology*; D018508:Water Purification / Q000379:methods*; D053833:Wetlands
chemical_list: D062065:Wastewater
keywords: Constructed wetlands; Disinfection; Pathogens; Wastewater treatment