Conditions necessary for low level measurements of reactive oxidants.

摘要

Chlorine dioxide and ozone are considered to be the alternatives to chlorine for the disinfection of drinking water supplies and also for the treatment of wastewaters prior to discharge.; Chlorine dioxide, under normal circumstances, is reduced to chlorite ion which is toxic. The recommended seven-day suggested no-adverse-response levels (SNARL's) of chlorite ion is 0.007 mg/L (7 ppb). Chlorite ion at these low levels cannot be satisfactorily determined by existing methods, and so, it became necessary to develop an analytical method for determining ppb levels of chlorite ion. Such a method can be developed using differential pulse polarography (DPP).; The electrochemical reduction of chlorite ion has been studied between pH 3.7-14 and in an ionic strength range of 0.05-3.0 M. The optimum conditions are pH 4.1-4.4 and an ionic strength of 0.45 M. The current under these conditions is a linear function of chlorite ion concentration ranging from 2.77 {dollar}times{dollar} 10{dollar}sp{lcub}-7{rcub}{dollar} to 2.80 {dollar}times{dollar} 10{dollar}sp{lcub}-4{rcub}{dollar} M (19 ppb to 19 ppm). The imprecision is better than {dollar}pm{dollar}1.0% and {dollar}pm{dollar}3.4% at concentrations of 2.87 {dollar}times{dollar} 10{dollar}sp{lcub}-5{rcub}{dollar} M and 1.74 {dollar}times{dollar} 10{dollar}sp{lcub}-6{rcub}{dollar} M, respectively, with a detection limit of 1 {dollar}times{dollar} 10{dollar}sp{lcub}-7{rcub}{dollar} M (7 ppb). The application of this method for determining chlorite ion in actual drinking water samples is carried out through a sample treatment using Chelex 100. The method is shown to be the method of choice for chlorite ion at the SNARL's level recommended by the National Research Council Safe Drinking Water Committee.; The rate of ozone decomposition has been studied in highly basic solutions (8-15 NaOH), where ozone becomes stable. This is due to the dissociation of the OH radical, which is a chain carrier in mildly basic solution, and to the formation of O{dollar}sb2sp-{dollar} all of which are involved in the regeneration of ozone. The mechanism of ozone regeneration was proposed to explain the observed kinetics and to clarify the contradiction concerning the very slow observed rate of ozone decomposition in basic solution.