General Model of Chlorine Decay in Blends of Surface Waters, Desalinated Water, and Groundwaters

Management goals for many distribution systems include maintaining a minimum level of free chlorine and limiting disinfection by-products. As water resources become scarce and quality deteriorates, blends are often required, so achieving these goals becomes increasingly difficult. The augmented two-reactant (2RA) model describes chlorine decay in a single water, for various dosing levels and water temperatures. However, it is not known whether there is any effect on chlorine decay (either synergistic or antagonistic) arising from blending waters of distinctly different quality. Linked 2RA models of source waters were used to determine whether bulk decay in blends of various source waters could be accurately and generally modeled. Results showed that chlorine decay in blends of various waters could be described accurately without synergistic or antagonistic effects, implying that each water’s reactants reduced chlorine independently. This held for pairs of surface waters, groundwaters, and raw or treated surface water blended with desalinated water, for various initial chlorine doses and temperatures. Linked models can be incorporated immediately into system models, to predict bulk chlorine decay and trihalomethane (THM) formation in distribution systems supplied from several water sources.