Ozone and the Safe Drinking Water Act Rip G. Rice, Ph.D. and Paul K. Overbeck Presented at 24th Annual WQA Convention Ft. Lauderdale, FL March 20, 1998 Courtesy of: Mazzei Injector Corporation | 500 Rooster Dr. | Bakersfield, CA 93307 USA | Phone: 661-363-6500 Visit us online: http://www.mazzei.net 1 Ozone and the Safe Drinking Water Act Abstract Since the initial passage of the Safe Drinking Water Act in 1973, the use of ozone to treat drinking water in the United States has been encouraged increasingly by EPA’s evolving drinking water regulations. The evolution of these regulations is traced and their impact on the uses of ozone in potable water treatment in the United States. is discussed Some statistics are included, in particular a current listing of over 250 U.S. municipal drinking water utilities currently using ozone. A second listing of 140 “small” water plants using ozone – defined by the EPA as serving less than 10,000 persons (producing less than 1 mgd) also is included. A surprising number of additional installations (> 400) are in single family homes and small businesses. Introduction With the identification of halogenated organic compounds formed in drinking water as a result of chlorination (Rook, 1974; Bellar et al., 1974), the U.S. Congress quickly enacted the Safe Drinking Water Act in 1973. This original SDWA charged the U.S. EPA to develop and promulgate a number of regulatory initiatives. Subsequent SDWA amendments (1986 and 1996) have added additional regulatory mandates to the EPA, many of which encourage the use of ozone. Those regulatory developments which encourage the use of ozone will be discussed in this paper. The Safe Drinking Water Act of 1973 One of the major regulations which resulted from the original 1973 SDWA, from the standpoint of ozone, is the so-called “THM Regulation”, promulgated in 1979. This regulation requires large utilities (those serving > 10,000 persons) to meet a maximum contaminant limit (MCL) of 0.010 mg/L (= 100 µg/L) of the total of the four trihalomethanes (chloroform, chlorodibromomethane, bromodichloromethane, and bromoform). Prior to promulgation of the THM Regulation in 1979, the U.S. EPA had surveyed waters produced at 80 U.S. water utilities, sampling their finished waters and analyzing for the four THMs. The only two U.S. ozone plants operating with ozone at that time (Whiting, IN and Strasburg, PA) were included in this National Organics Reconnaissance Survey (the NORS). Significantly, the levels of THMs found at the two ozone plants were the lowest of the other 78 plants. These results, as might be expected, caught EPA’s regulatory attention. As a result, EPA sponsored two projects which involved surveying selected European and Canadian drinking water treatment plants using ozone and also those using chlorine dioxide. In the first survey, a U.S. team of experts, operating under an EPA grant to a municipally-oriented not-for-profit organization, was assembled consisting of an ozone technologist (the senior author), a consulting engineer, a public health professional, and several water treatment experts. With the cooperation of the International Ozone Association, contacts were established with 2 European water research institutes and water utilities. During May, 1977, this survey team spent 30 days visiting water plants using ozone (and some using chlorine dioxide as well) in France, Germany, Belgium, and Switzerland, two water research institutions, and attended five days of technical conferences on ozone which were held in Paris and Berlin. In the Fall of 1977, the survey team visited about a dozen Canadian water treatment plants, all in the Province of Québec, using ozone and chlorine dioxide, and then several U.S. plants using chlorine dioxide. It was during this initial EPA-sponsored European plant survey project that the survey team observed the process of combination of ozonation followed by sand filtration then filtration through granular activated carbon (GAC). Both the Germans and the French had discovered and pilot tested this process about the same time, and several full-scale European plant were operating the process in the mid-1970s. In essence, during ozonation, some of the biorefractory organics are converted to more biodegradable materials by chemical oxidation. Polar oxygen groupings are added to some of the dissolved organics, and some of the larger dissolved organic molecules are cleaved into smaller oxygenated fragments by the oxidative action of ozone. At the same time, dissolved oxygen levels in the water are increased as a side-benefit of the ozonation process. Regardless of the specific mechanisms involved, when these now much more readily biodegradable organic molecules pass through the GAC columns, they encounter natural microorganisms, which develop in virgin GAC after only a few weeks of operation and which thrive in the GAC macropores in the absence of a residual disinfectant (chlorine, chlorine dioxide, or chloramine). These aerobic microorganisms are capable of rapidly mineralizing the biodegradable organics, converting them to carbon dioxide and water in a few minutes of empty bed contact time (5-10 min EBCT). This particular combination of ozonation followed by GAC filtration was termed Biological Activated Carbon (BAC), and was of such interest to EPA regulators that the survey team was sent back to Europe the following year (1978) specifically to study this process combination in more detail. By such water treatment combinations of ozone/biofiltration, Europeans were found to be lowering the levels of THM precursors prior to terminal chlorination or addition of chlorine dioxide. A key to success of the BAC and other ozone/biofiltration processes (involving sand or sand/anthracite rather than GAC medium) was the elimination of chlorination prior to ozonation and biofiltration. This avoids the formation of halogenated organics in the early treatment stages which are neither readily biodegradable nor readily oxidized, even by ozone. Compliance with the THM rule was required by 1981, and during the period between 1981 and 1986, the Congress was busy developing the first amendments to the 1973 SDWA. In the interim, the U.S. drinking water industry had available two reports written by the survey team (Miller et al., 1978; Rice et al., 1982), the first describing European and Canadian experiences with ozone and chlorine dioxide, and the second describing the BAC process as practiced in Europe. Additionally, the survey published a paper pointing out the many applications of ozone in drinking water treatment (Rice et al., 1981). 3 The Safe Drinking Act Amendments of 1986 Whereas the 1973 SDWA had attracted the attention of the U.S. water treatment industry to ozone and chlorine dioxide, it was the SDWA Amendments of 1986 that caused the U.S. water industry to focus on these two oxidants/disinfectants. In implementing the Congressional mandates of the 1986 Amendments, EPA notified the water industry that it would be regulating three new microorganisms present in surface waters, Giardia lamblia cysts, enteric viruses, and Legionella bacteria. In addition, the Standard Plate Count microorganism group underwent a name change to Heterotrophic Plate Count (HPC). THE SURFACE WATER TREATMENT RULE (the SWTR) Beginning in early 1987, EPA published an Advanced Notice of Proposed Rulemaking for a Surface Water Treatment Rule (SWTR), by which systems treating surface waters and serving greater than 10,000 persons would be required to show that they were able to attain primary disinfection of these new microorganisms (primary meaning in the treatment plant). At the same time, the term secondary disinfection was introduced which applies to treated waters in distribution systems. It is not practical for a water treatment system to monitor Giardia cysts, enteric viruses, or any microorganism, for that matter, in real time on-line -- only after the fact. Recognizing this, the EPA developed the “CT” concept, which is the arithmetic product of the concentration (C, in mg/L) of a disinfectant multiplied by the time (T, in minutes) that the disinfectant is in contact with the water. As long as the product of C x T equals or exceeds a specific number set by the agency for the Giardia cysts, the inactivation of a certain percentage of these microorganisms which might be present in the waters being disinfected would be ensured. Each microorganism specified in the SWTR (U.S. EPA, 1989) and its Guidance Manual (U.S. EPA, 1990) has a specific set of CT values, which also are a function of pH (particularly for chlorine), and temperature. The lower the required CT value, the more effective is the specific disinfectant, meaning that a specific level of microorganism inactivation can be guaranteed with lower concentrations and/or shorter contact times for the more effective disinfectants. EPA also presented the disinfecting efficiency of any disinfectant in terms of logarithms of microorganism inactivation, or log-inactivations. If a water containing a viable microorganism concentration of 10,000/mL is treated with a disinfectant such that the number of viable microorganisms is reduced to 1,000/mL (90% inactivation), then 1-log inactivation has been attained. If the level is reduced to 100/mL (99% inactivation), two-logs of inactivation have been attained; if reduced to 10/mL (99.9% inactivation), 3-logs, etc. In publications leading to the SWTR itself, EPA presented a series of CT tables for the four disinfectants in use: chlorine, chlorine dioxide, ozone and chloramine. Table I shows the CT values to attain 99.9% (3-logs) inactivation of Giardia cysts for the four disinfectants mentioned above. Note that the values for ozone are significantly lower than for any of the other disinfectants. 4 With respect to viruses, EPA advised that if sufficient primary disinfectant is added to ensure 3- logs of Giardia cyst inactivation, credit would be allowed for at least 4-logs of simultaneous enteric virus inactivation.