EFFECT OF PRE-OZONATION ON REMOVAL OF ORGANIC-MATTER DURING WATER-TREATMENT PLANT-OPERATIONS

Pre-ozonation altered removal of organic matter during bench or full-s cale water treatment through two main effects. First, pre-ozonation di rectly removed organic matter by mineralization, volatilization and/or stripping reactions, improving removal in comparison to unozonated sy stems. On the other hand, preozonation decreased the surface charge of floc formed after coagulation with hydrolyzable metal salts, hinderin g adsorptive removal of the anionic organic molecules by floc surfaces and/or inducing stabilized floc formation; changes that decrease remo val in comparison to unozonated systems. The relative importance of th e two effects determined whether pre-ozonation enhanced or hindered re moval of organic matter. In most water treatment plants pre-ozonation is predicted to have an adverse effect on physical removal of organic matter at ozone doses above about 0.7 mg O3/mg TOC, while enhanced rem oval may occur if relatively high concentrations of volatile organic m atter are present. In ancillary results, preozonation hindered turbidi ty removal and increased the concentration of coagulant metal residual s in finished drinking water at low coagulant doses.