30 YEARS OF EXPERIENCE USING OZONE IN THE UNITED STATES DISINFECTING WASTEWATER
Abstract:This paper reviews the use of ozone as a disinfectant for wastewater over the last 30 years. A historical usage profile of ozone disinfection by Publicly Owned Treatment Works (POTWs) is presented along with some insights focused on the evolution of ozone generation equipment and ozone transfer and contactor design.
The historical usage profile was developed from the literature and work performed by a project team of Kennedy/Jenks Consultants, Los Angeles County Sanitation Districts, and the California State University, Fullerton that was awarded the Water Environment Federation Research Foundation Project, Disinfection of Wastewater Effluent — Comparison of Alternative Technologies (04-HHE-4) in August 2005. One of the project tasks to accomplish this goal was to perform a survey of disinfection practice by major POTWs.
For this study, the USEPA definition of a major POTW was used and is defined as a sewage treatment facility that is owned by a state or municipal agency and has an average dry weather design flow treatment capacity of at least 1 MGD. Using several databases that included the US Census and two USEPA databases (one called the Clean Water Needs Survey (CWNS), and the other called Envirofacts that is used by the NPDES system), approximately 4,450 major POTWs were identified in the 50 US states and the District of Columbia.
The historical use pattern by the wastewater industry is constrasted to the drinking water treatment industry. The comparison shows that wastewater was an early adapter of ozonation, but quickly stopped its use whereas the opposite is true of the water treatment industry. It is estimated that 25 percent of all the surface drinking water treatment plant ≥ 1 MGD in the US use ozone today.
Historically, as many as 50 wastewater treatment plants (POTWs), including 32 major POTWs were equipped to use ozone as a disinfectant as well as to meet additional treatment goals. In 1989 15 major POTWs had the equipment, but were not operating their ozone facilities whereas 17 major POTWs were using this technology. In 2006 this number has dropped to seven POTWs using ozone. During the project survey, three POTWs indicated that they are planning replace their original ozone generators to continue using ozone and four others are in design or planning stages to change to using ozone as their disinfectant.
A telephone survey of the POTWs that have or are using ozone indicate that there were various reasons that POTWs have and are selecting ozone as a disinfectant. Generally, there are site specific reasons that include, but are not limited to the following:
Improving dissolved oxygen (DO) in a receiving water
Providing an additional treatment barrier for reuse
Removing endocrine disruptors and pharmaceutical active agents
Many of the early ozone systems experienced premature equipment failures and problems associated with what were then a developing ozone generation technology. The paper will discuss the extensive increase in the use of ozone in the water treatment industry during the same 30 year period, and significant advances in ozone generator design and operating efficiency, as well as advances in ozone transfer efficiency and ozone contactor design. These improvements will provide significant benefits to POTWs considering use of ozone as their disinfectant.
Document Type: Research Article
Publication date: January 1, 2007
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