Chlorination of natural organic matter: kinetics of chlorination and of THM formation

The kinetics of the formation of trihalomethanes (THMs) and of chlorine con sumption for the chlorination of natural organic matter with an excess of c hlorine (50 muM > [Cl-2](o) > 210 muM) was investigated. THM precursors cou ld be divided into a fast and a slowly reacting fraction. Long term chlorin e demand and the formation of THM could be described by second order kineti cs. Rate constants were between 0.01 and 0.03 M-1 s(-1) in the pH range 7-9 for surface waters and humic materials extracted from surface waters. A gr oundwater gave a higher rate constant of 0.124 M-1 s(-1). Resorcinol-type s tructures were tested with respect to kinetics and yield of THM formation. They could possibly be responsible for the fast reacting THM precursors, wh ich represent 15-30% of the THM precursors of natural waters. Additional cl asses of compounds that might contribute to the initial THM formation inclu de readily enolizable compounds such as beta -diketones and beta -ketoacids . Experiments with phenol showed that slowly reacting THM precursors may co nsist of phenolic compounds. The influence of pretreatments (UV/visible irr adiation, ozone and chlorine dioxide) on chlorine demand and THM formation from NOM was also studied: UV/visible irradiation does not alter THM format ion but leads to a higher chlorine demand. Preoxidation with ozone leads to a lower THM formation with an unaltered chlorine demand and preoxidation w ith chlorine dioxide reduces THM formation and the chlorine demand. (C) 200 1 Elsevier Science Ltd. All rights reserved.