Evaluating TOC analytical results

Abstract

Tests indicate particulate fraction of total organic carbon in a natural water is more accurately measured by the combustion method than by the ultraviolet–persulfate oxidation method.The Disinfectants/Disinfection By‐products (D/DBP) Rule includes total organic carbon (TOC) as a regulatory compliance parameter with the idea that TOC concentration is a direct indicator of the potential for DBP formation upon chlorination. A comprehensive study was conducted to evaluate the ability of the two most common methods—ultraviolet (UV)–persulfate oxidation and catalytic combustion—to measure the particulate fraction of the TOC in water and determine whether this fraction contributes to DBP formation. Results showed that particulate TOC fraction in a natural water was more accurately measured by the combustion method. Therefore, the method used by a water utility to evaluate TOC removal through a water treatment plant can significantly affect the chemical dosages required for regulatory compliance and treatment cost. Furthermore, chlorination testing results suggest that the DBP formation reactions may not be affected by particulate TOC, leading the authors to propose that dissolved organic carbon rather than TOC is a more appropriate indicator of DBP formation potential in water treatment.