Empirical model for disappearance of free oxidants in natural water with wide salinity and ammonia ranges

Abstract

An empirical model for the disappearance rates of chlorine-induced free oxidants was developed. Both in seawater and river water, the disappearance of free oxidants occurred in two stages (stage I and II). The disappearance of free oxidants in stage II was considered to be the consumption by organic substances in natural water. The disappearance rate could be empirically explained by a second-order reaction of oxidants. The observed rate constant was decreased with the increase of the oxidant concentration after subtracting the decrease in stage I from the chlorine dose in natural water. Especially in seawater, the maximum persistence of oxidants could be estimated by the self-decomposition rate of hypobromite which was the disappearance rate in artificial seawater, and the rate constant was obtained as a function of bromide concentration. The disappearance in stage I, which was very rapid, was considered to be the reactions with reactive inorganic and organic substances in natural water. The minimum decrease, which was led to the maximum persistence in stage II, could be approximately expressed as the consumption by ammonia. Using our proposed model, the maximum persistence of free oxidants in natural water with wide salinity and ammonia ranges could be estimated.