Due to the current aim of the Department of Homeland Security to reduce the usage of chlorine gas, many water-treatment facilities are shifting to hypochlorite solution as an alternative to chlorine gas as a secondary disinfectant. Many of the facilities use a high concentration hypochlorite provided by an external supplier, which is typically 10-12.5% by weight.<br/>Hypochlorite solutions have a potential of introducing oxyhalide disinfection by-products into the drinking water, such as chlorate and perchlorate. Perchlorate is a regulated compound in the states of Massachusetts and California at the MCL of 2 ppb and 6 ppb respectively in water. Chlorate is included in the USEPA Contaminant Candidate list and its proposed action level in the state of California is 200 ppb in water.<br/>In the current study, hypochlorite samples were collected from the tanks right before new chemical was delivered. Samples were also collected from delivery trucks. The objective of the testing was to compare between the levels of chlorine, chlorate and perchlorate in the storage tanks and in the newly delivered chemical. Hypochlorite samples were pre-treated using excess of hydrogen peroxide for chlorine removal and manganese dioxide for removal of residual hydrogen peroxide. Afterwards, the samples were analyzed using ion chromatography.<br/>The results showed that during the summer, delivered hypochlorite was found to already contain chlorate in the range of 500-1000 ppm. Hypochlorite samples collected from the tanks contained chlorate in the range of 6400-8500 ppm, which means 8 to 10 fold increase during the storage period. Considering chlorine dose of 5 mg/L, chlorate concentrations in the tanks are alarming and would cause the concentrations in water to exceed the proposed action level. Perchlorate levels had 2.5 to 38 fold increase, but are not of a concern considering current regulation. Degradation of the hypochlorite solution was found to be 10-20% during the storage period.

Fate of oxyhalide disinfection by-products in hypochlorite solution storage tanks

249th National Meeting (2015)

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