Changes to NSF/ANSI Standard 60 may impact the use of sodium hypochlorite in drinking water systems. New rules are being considered for the contaminates bromate, perchlorate and chlorate, all of which can be traced to sodium hypochlorite.
By Gerald F. Connell
United States drinking water systems are always on the alert for contaminants that are in the chemicals used in the treatment or develop in the treatment process. Many of these contaminants have been identified by researchers and regulators and are regulated under the NSF/ANSI Standard 60. Changes to Standard 60 are always under consideration and new changes that can impact the disinfection process are anticipated to be effective in the year 2013.
Standard 60 covers the chemicals used in the treatment of water, including the disinfection chemicals, in general, and sodium hypochlorite and chlorine, in particular.
Although there may be other changes to Standard 60, those effecting bleach are of importance to the industry. The changes relate to sodium hypochlorite and the contaminants in hypochlorite. These contaminants are bromate, perchlorate and chlorate.
It is important to look at each compound and their sources. Each can be traced to sodium hypochlorite.
Bromate is a potent human carcinogen.. It can come from two separate sources in drinking water. The first is in the hypochlorite manufacturing process itself. Sodium hypochlorite is generally produced for bulk use by the reaction of chlorine gas with sodium hydroxide or can be produced on-site by the electrolysis of brine (salt) solutions. The compounds used in bulk production (chlorine gas and sodium hydroxide) can contain bromine (chlorine gas) or bromide (sodium hydroxide). The reaction of chlorine gas and sodium hydroxide produces sodium hypochlorite.
The bromine in the chlorine gas and bromide in sodium hydroxide are converted to bromate at the pH level of the sodium hypochlorite solution produced by the reaction. The addition of this hypochlorite to water in the disinfection process adds bromate to the finished water. Brine is used to feed on-site generation which also produces hypochlorite with bromated levels.
Bromide ions can be present in the raw water supply, surface or ground water. When water containing bromide ions is exposed to disinfection using the ozonation process, the reaction of bromide with ozone will produce bromate ions.
While the development of bromate in the ozonation process requires testing of the finished water for bromate content, treatment with hypochlorite does not require testing for bromates in the finished water. The quantity of bromate present in the finished water from the hypochlorite disinfection process can be controlled by limiting the bromide concentration in the hypochlorite source or the hypochlorite manufacturing process.
Perchlorate affects the ability of the thyroid gland to take up iodine. This would affect the functions of the thyroid gland and its performance in the body. Perchlorate is a product of sodium hypochlorite decomposition. The longer hypochlorite is kept by the utility before use, the more likely the significant increase in perchlorate. Also, the development of perchlorate’s use in rocket propellants and the improper disposal of wastes from the manufacture of these propellants has been a cause for the appearance of perchlorate in raw water supplies.
Rapid turnover of the hypochlorite and/or a reduction in inventory of the sodium hypochlorite at the treatment plant will aid in the reduction of perchlorate development. Conversion to chlorine gas from hypochlorite would also be of help since perchlorate is not present in chlorine.
Chlorate can affect the health of certain population groups such as senior citizens, children, etc. Chlorate is included in the contaminant candidate list and will probably be included in the unregulated contaminant mandatory rule.
Chlorate is formed when sodium hypochlorite decomposes in a bleach solution. Thermal decomposition of bleach is the primary source of chlorate. Quick turnover of sodium hypochlorite is the best method known to keep the chlorate level low. This could require frequent cleaning of the storage tanks so that a heel of “old” sodium hypochlorite is not kept in the tank. Temperature reduction and/or dilution on receipt from the supplier would also reduce the formation of chlorate.
The following are the current or proposed regulatory actions or regulations for each of the three contaminants or byproducts mentioned above:
1. Bromate – The maximum level of bromine allowed in sodium hypochlorite is expected to be reduced by January 2013 to around a level of 39 ppm. Currently, 69 ppm of bromate is the Maximum Contaminant Level (MCL) allowed in sodium hypochlorite. Since bromated is produced in the ozonation process, ozone’s use in the treatment process could be reconsidered.
2. Perchlorate – Several states have established regulatory limits for perchlorate in drinking water. Standard 60 is expected to have a perchlorate limit established by January 2013. The EPA has an advisory of 15 ppb of chlorate per liter of water but there is no deferral regulation for perchlorate in drinking water at this time. California has a maximum level of 6 ppb and in Massachusetts the maximum allowable is 2 ppb for perchlorate. New Jersey has a proposed MCL of 5 ppb.
3. Chlorate – Limits are being considered for addition to Standard 60 with a target date of January 2013. No current Federal regulations have been issues for chlorate. Currently Canada has guidelines established for drinking water for a MAC of 1 ppm.
About the Author: Gerald F. Connell is an independent consultant with over 35 years in the use and handling of chlorine in water treatment. He is the author of “The Chlorination/Chloramination Handbook” as well as “The Chlorination/Dechlorination Handbook.”