An investigation of the factors involved in the decomposition of sodium hypochlorite

Chlorine is the most commonly used oxidizing agent for the disinfection of drinking water in the United States. Common sources of chlorine include chlorine gas, aqueous sodium hypochlorite, and solid calcium hypochlorite. Hypochlorite ion (OCl{dollar}sp-{dollar}) is known to undergo decomposition to form chlorate ion (ClO{dollar}sb3sp-{dollar}). Prior to 1991, there was very little concern given by utilities to ClO{dollar}sb3sp-{dollar} formation in hypochlorinated drinking water. It appears to have been the general belief of water utility personnel that observed decreases in the concentration of OCl{dollar}sp-{dollar} were due to the decomposition of OCl{dollar}sp-{dollar} to form oxygen. As high as 0.3 mg/L ClO{dollar}sb3sp-{dollar} may be present in hypochlorinated drinking water.; The primary objective of this work was to determine how various experimental variables affect the kinetics and mechanism of decomposition of concentrated OCl{dollar}sp-{dollar} and the formation of ClO{dollar}sb3sp-{dollar} and O{dollar}sb2{dollar}. The concentrations of OCl{dollar}sp-{dollar}, ClO{dollar}sb3sp-{dollar}, ClO{dollar}sb2sp-{dollar}, and OH{dollar}sp-{dollar} have been measured as a function of time for a variety of experimental conditions. Various analytical methodologies were developed in order to measure these species. An extensive series of decomposition experiments has been carried out by varying the following experimental parameters: OH{dollar}sp-{dollar} concentration, OCl{dollar}sp-{dollar} concentration, temperature, Cl{dollar}sp-{dollar} concentration, presence of common matrix ions.; A second objective of this work was to simulate (and thus predict) the decomposition of OCl{dollar}sp-{dollar} while taking into account the effect of each experimental variable studied. A Predictive Chemical Model has been refined with this task in mind. Accomplishing this objective has lead to a protocol to minimize OCl{dollar}sp-{dollar} decomposition and ClO{dollar}sb3sp-{dollar} formation when concentrated OCl{dollar}sp-{dollar} solutions are used as a source of free available chlorine for drinking water disinfection. From a practical point of view, this allows drinking water utilities to minimize the loss of oxidizing strength during OCl{dollar}sp-{dollar} storage (a cost ultimately passed on to the consumer). This also makes it easier for utilities to comply with any future ClO{dollar}sb3sp-{dollar} regulation that may be established by the USEPA.; The decomposition of OCl{dollar}sp-{dollar} in the pH 9 to 14 region has been applied to a simulation technique based on numerical integration. This simulation has allowed the straight forward investigation into some of the mechanistic detail of OCl{dollar}sp-{dollar} decomposition.