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SR-2003-013

Disinfection Devices: Field Experiences

Richard W. Weaver, Amanda Y. Richter

Wastewater that is to be surface applied must first be disinfected to remove odors and disease-causing microorganisms. We are conducting a study, funded by an EPA 319 grant, determining the ability of subsurface flow constructed wetlands to treat wastewater on-site. When 10 of our 21 wetlands were installed with sprinklers for surface application, we got into the activity of effluent disinfection. Currently, there are two basic methods of disinfection for on-site wastewater treatment systems: chlorination and ultraviolet (UV) light disinfection. Both chlorination and UV disinfection have a dose and time relationship. The longer wastewater is exposed to chlo rine or UV light, and/or the stronger the chlorine concentration or light intensity, the greater the potential of disinfection (White, 1999).

Optimal disinfection occurs with high quality effluent. Poor wastewater quality, water with total suspended solids (TSS) over 50 mg/L or turbidity over 12 NTU, can contribute to UV unit failure (Petrasek, et al., 1980). Total suspended solids and turbidity are two wastewater parameters that quantify the presence of particles in wastewater. Both disinfection methods require the removal of large particles that may contain or shield microorganisms from the disinfectants (Johnson & Qualls, 1984). Organic matter and nitrogen compounds in effluent increase the amount of chlorine that must be added to achieve disinfectio n (White, 1999, Tchobanoglous & Burton, 1991).

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