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.
US drinking water systems are concerned about disinfection products that might contaminate the water either from 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.
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 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 bromate contamination.
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. Most water system, however do not contain sufficient levels of bromide ions to make this a serious problem.
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.
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.
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.
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.
The selection of a primary and secondary disinfectant is governed by both the requirements for pathogen inactivation and the production of disinfection byproducts. The choice between ozone and other agents such a hypochlorite with respect to bromate formation will depend on source water bromide levels. In areas where bromide levels are low and disinfection requirements are high, ozone will likely be the choice of more drinking water treatment facilities