Lead minerals found in drinking water distribution systems increase chlorine dioxide decay to a single inorganic product

Abstract

Chlorine dioxide (ClO₂), an alternative disinfectant to free chlorine, has been used to reduce the formation of organic disinfection byproducts during water treatment. ClO₂ is highly reactive, and its decay is enhanced in the presence of lead oxide (PbO₂), lead carbonate (PbCO₃), and cupric oxide (CuO), minerals commonly found in the corrosion scale on distribution system pipes. Reaction of these corrosion minerals with chlorine dioxide and the byproducts created during said reactions were investigated. In addition to corrosion mineral, initial concentration of ClO₂ and pH were both varied. Reaction took place in a batch reactor, ClO₂ was measured via ultraviolet-visible spectrophotometry, and byproducts were quantified using ion chromatography. Only chlorite is produced from ClO₂ decay when lead minerals are present, whereas both chlorite and chlorate are produced by disproportionation when CuO is present. ClO₂ decay occurs at a significantly higher rate on PbO₂ compared to CuO. The reaction rate for ClO₂ decay, in the presence of PbO₂, peaks at pH 8.3, which corresponds to the point of zero charge of PbO₂. This indicates that surface charge may play a significant role in lead mineral-assisted decay reactions with disinfectants, including ClO₂. The reaction rate dependence for ClO₂ decay on PbO₂ is well described by a pseudo-second-order adsorption kinetic model. These findings highlight the need for chlorite, but not chlorate, byproduct management when ClO₂ is used as a disinfectant in water distribution systems with lead-based pipes. Robust strategies for management of a chlorine dioxide residual must be implemented in both copper and lead-based service lines to ensure a disinfectant persists and protects against microbial contamination in premise plumbing.