Controlling the Formation of Chlorate Ion in Liquid Hypochlorite Feedstocks

Abstract

Experiments were carried out to confirm the presence of chlorate ion (ClO3−) in the treated water of utilities that use hypochlorination. Sixteen commercially produced, concentrated liquid hypochlorite feedstocks were analyzed for ClO3−, and levels as high as 158 g percent ClO3− relative to hypochlorite ion were measured. Finished‐water samples from the utilities surveyed contained as much as 0.30 mg ClO3−/L, primarily the result of decomposition of the liquid hypochlorite feedstocks. Although both dilution and lower temperatures can be effective in minimizing ClO3− formation, it was observed that diluting the initial liquid hypochlorite concentration by a factor of 2 is more effective than decreasing the temperature from 24 to 10°C. A methodology is proposed that predicts the dilution or temperature reduction (or both) required to avoid significant ClO3− formation in the feedstock solutions.

Perchlorate, bromate, and chlorate in hypochlorite solutions: Guidelines for utilities

“…The major factors affecting perchlorate formation parallel those previously described for reducing the decomposition of bleach: temperature, ionic strength, concentration, and pH (Gordon & Bubnis, 2000; Gordon et al, 1997; Gordon et al, 1993). The information gathered during this study provided the basis for several hypothetical hypochlorite solution storage scenarios, which led to a number of quantitative and qualitative recommendations.…”

“…Transition metal ion concentrations measured for this study were below detection in most of the bulk hypochlorite and OSG samples (data not shown), although utility 1A had nickel present at 0.2 mg/L, copper at 0.1 mg/L, and iron concentrations approaching 10 mg/L in the hypochlorite solution. Given that metal ions have been demonstrated to have a catalytic effect on the decomposition of hypochlorite (Adam, 1994; Gordon et al, 1993), the presence of iron and nickel may have been a factor (in addition to age) in the low FAC concentration at utility 1A. Regarding the OSG hypochlorite, most brine samples showed higher levels of metal ion contamination relative to the hypochlorite product from the OSG (data not shown).…”

“…The majority of utilities in the United States use chlorine gas during treatment, but approximately one third of all US drinking water treatment plants use bulk hypochlorite for disinfection, and around 8% use onsite hypochlorite generators or onsite generators (OSGs) during treatment (Routt et al, 2008a, 2008b). Hypochlorite solutions contain many regulated and unregulated contaminants, including bromate, chlorite, chlorate, and perchlorate (Asami et al, 2009; Greiner et al, 2008; Weinberg et al, 2003; Gordon et al, 1993).…”

Chlorate Challenges for Water Systems

“…Utilities using chlorine dioxide can reduce approximately 35% of the chlorate in their distribution systems by altering chlorine dioxide generation (Gallagher et al, 1994), though substantial amounts of chlorate will still be formed during degradation of the chlorine dioxide. The formation of chlorate ion in hypochlorite solutions is directly influenced by storage methods and handling techniques at utilities using bulk hypochlorite (Stanford et al, 2011; Gordon et al, 1995, 1993). Dilution of bulk hypochlorite with softened water and pH control in the 12–13 range, or careful temperature control, can help minimize the amount of chlorate formed during storage.…”

Using Chlorine Dioxide for Drinking Water Disinfection by the Application of the Chlorite/Chlorine Process

“…The reaction of chlorine with the by-product of chlorine dioxide, chlorite, is described by Equations (9) and (10). The short lifetime product [Cl 2 O 2 ] is formed [9,10]. In drinking water, there are two possibilities for [Cl 2 O 2 ]-decomposition: the re-formation of chlorine dioxide (cf.…”