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OWML: Completed Projects

Project Title: Evaluating the effectiveness of chlorine dioxide as a wastewater disinfection agent.

Project chief:  Christopher Kephart

Project support:  Don Stoeckel

Cooperators:  The Ohio State University, Columbus, Ohio

Project duration:  2006-2009

Introduction and problem: 
As communities in Ohio continue to work toward eliminating pollutant discharge to streams to meet to goals of the Clean Water Act, wastewater reuse through onsite wastewater treatment followed by use for irrigation is an important option. It has been estimated that only 6.4% of Ohio soils are suitable for traditional leach-line or mound septic systems (Mancl and Slater 2002). Consequently, it has been estimated that 27% of all existing on-site household sewage treatment systems (HSTS) are failing to adequately treat sewage effluent (Mancl 1990). A solution to this problem may be to collect and disinfect HSTS effluent thereby permitting possible reuse for irrigation. 

After its introduction in the 1950’s, chlorine dioxide has recently re-emerged as a disinfection agent. Chlorine dioxide has different activity than free chlorine or hypochlorite. Unlike free chlorine and hypochlorite, chlorine dioxide is active over a wide range of pH and its use does not result in the creation of byproducts such as trihalomethanes. Microbial disinfection with chlorine dioxide has been shown to be just as effective or superior to free chlorine – inactivation of viruses is much more effective with chlorine dioxide than free chlorine. A dry-packet delivery system developed by Avantec Technologies Inc., has recently made the chemistry behind chlorine dioxide generation economically and safely available to small systems. Widespread use of a newly developed chlorine dioxide disinfection system would depend, in part, upon its ability to effectively kill pathogenic microorganisms in a sewage effluent matrix.

Goals and objectives: 
The overall goal of this proposed study is to measure the ability of a novel chlorine dioxide delivery system to inactivate pathogens in on-site residential wastewater and thereby render the treated wastewater more suitable for reuse as irrigation water. 

The specific objectives of this study are to (1) develop the Ct relation at bench scale against fecal indicator bacteria and viruses which will describe the inactivation kinetics of chlorine dioxide against multiple targets in a wastewater matrix, and (2) determine the effectiveness of the chlorine dioxide system against indicator organisms in a field-scale operational setting – an onsite, single-family household sewage treatment system.

The capability of the chlorine dioxide system was tested in artificial septic tank effluent against three bacteria (Escherichia coli, enterococci, and Clostridium perfringens) and one virus (coliphage). The inactivation capability was described by the relation between chlorine concentration (C) and contact time (t) required for a specific percentage of microorganism death and is expressed as a constant (Ct).

An initial, bench-scale recovery control experiment was done in the absence of chlorine dioxide treatment in order to calculate the natural die-off or reproduction rates of the indicator organisms in the artificial effluent. The Ct relation was then developed at bench-scale by exposing the artificial effluent to a single concentration of chlorine dioxide. Indicator organism concentrations were plotted versus time so that a dose response curve could be constructed. The dose response was normalized to accommodate the natural die-off and a Ct relation was developed. A final experiment was done to confirm the chlorine dioxide Ct relation when applied in a large-volume field setting. This experiment was done in an onsite septic tank/wastewater stabilization pond/spray irrigation system at the OSU Molly Caren Agricultural Center.

A USGS Open-File Report documenting the results of this study is planned to be completed in 2009.