MIXING IN DISTRIBUTION-SYSTEM STORAGE TANKS - ITS EFFECT ON WATER-QUALITY

Nearly all distribution systems in the United States include storage t anks and reservoirs. They are the most visible components of a water d istribution system but are generally the least understood in terms of their impact on water quality. Long residence times in storage tanks c an have negative impacts on water quality in drinking water distributi on systems, including the loss of chlorine residuals and the regrowth of microorganisms. It is generally accepted that complete mixing maxim izes water quality but little is understood about mixing regimes in ge neral. This paper demonstrates the use of compartment models to charac terize mixing in three tanks. It was found that the mixing regimes in these tanks were well characterized by compartment-type models and tha t these tanks were not completely mixed, contrary to conventional wisd om. It is clear that much more research is needed in order to truly un derstand mixing regimes in tanks and reservoirs and that this understa nding, if properly applied, can have a positive impact on water qualit y.