Ozone is one of the most powerful water treatment compounds available to systems managers today. It is a technology that has been in continual commercial use for over 100 years and has distinct properties that allow disinfection of even heavily compromised water streams.
With the 1996 reauthorization of the Safe Drinking Water Act, Ozone was named as among Best Available Technology (BAT) for small system compliance to National Primary Drinking water Regulations as overseen by the US Environmental Protection Agency.
DISINFECTION TREATMENT TECHNOLOGIES LISTED IN THE U.S. ENVIRONMENT PROTECTION AGENCY=S SURFACE WATER TREATMENT RULE (SWTR)
Ozone is a powerful oxidant with high disinfectant capacity. A study found that within a pH range of 6 to 10, at 3 to 10 EC, and with ozone residuals between 0.3 to 2.0 mg/L, bacteriophage MS-2 (a surrogate test organism) and Hepatitis A virus were completely inactivated. Inactivations ranged from >3.9-log to >6-log, and occurred within very short contact periods (i.e., 5 seconds). A 1992 research report describes treatment studies conducted on MS-2, poliovirus, and Giardia cysts. It found that MS-2 in natural waters are very sensitive to ozone in comparison to poliovirus type 3. In addition, Giardia muris and enteric viruses may be inactivated by ozone (as the primary disinfectant) with 5 minutes contact time and ozone residuals of 0.5 to 0.6 mg/L to 3-log and 4-log removals, respectively. The report concludes that design of ozone as a primary treatment should be based on simple criteria including ozone residual, competing ozone demands, and a minimum contact time to meet the required cyst and viral inactivation requirements, in combination with USEPA guidance recommendations. Viral inactivation CT values for ozone were published in the original USEPA guidance manual for the SWTR.
The EPA has reviewed survey data submitted by the International Ozone Association and found that ozonation has been applied at many drinking water treatment facilities in the U.S. with capacities greater than 100,000 gal/day and some smaller facilities, for disinfection as well as for other water treatment objectives. Applications at the smallest water system size category (i.e., systems serving <500) are not plentiful. However, ozonation technology for even the smallest public water system applications is available from a number of suppliers, and is found to be currently in use in relevant systems. Ozone treatment, therefore, is a listed technology for all categories of public water systems.
Ozone Small Potable Water Systems
Ozone, the strongest oxidant and disinfectant in commercial use has been employed in over 3,000 large scale municipal plants world-wide. In August 1997, and again in August 1998, the U.S. EPA identified ozone as a Small System Compliance Technology for existing National Primary Drinking Water Regulations related to revisions in the 1996 Safe Drinking Water Act. Survey data developed to support the inclusion of ozone as a “Compliance Technology” identified that over half of the more than 260 U.S. municipal ozone installations known to be operating in early 1998 are in systems treating less than 1 MGD (e.g., plants that serve less than 10,000 persons). An additional 363 community, non-community and single family ozone installations using ultraviolet generation and filtration process also were identified.
Ozone Treatment of Potable Water
Ozonation has been in continuous use in Nice, France since 1906, to ensure disinfection of mountain stream water. Because ozone is both the strongest oxidant and strongest disinfectant available for potable water treatment, this unique material can be utilized for a number of specific water treatment applications, including disinfection, taste and odor control, color removal, iron and manganese oxidation, H2S removal, nitrite and cyanide destruction, oxidation of many organics (e.g., phenols, some pesticides, some detergents), algae destruction and removal, and as a coagulant aid.
Even though ozone is the strongest chemical disinfectant available for water treatment, there are some refractory organics that it will not oxidize, or will oxidize too slowly to be of practical significance. In such cases, ozone can be combined with UV radiation and/or hydrogen peroxide to produce the hydroxyl free radical, HO*, which is an even stronger oxidant than is molecular Ozone, O3. Deliberate production of the hydroxyl free radical starting with ozone has been termed “Ozone Advanced Oxidation”. Some groundwaters that are contaminated with chlorinated organic solvents and some refractory hydrocarbons are being treated successfully by ozone advanced oxidation techniques.