Removal and structural changes in natural organic matter in a Spanish water treatment plant using nascent chlorine

Concentrations of humic substances were measured in different water treatment plants. Resin adsorption with ionic (DEAE) and polymeric (DAX) resins was carried out to fractionate natural organic matter into humic and non-humic fractions. Fractions were characterized in terms of the formation potential of trihalomethanes (THMFP) and haloacetic acids (HAAFP). The effect of oxidation with a mixture of chlorine, chlorine dioxide and ozone on the nature and removal of NOM throughout treatment was also investigated. In general, DOC, UV and final THM formation potential (THMFP) values showed up-and-down trend along treatment plant. However, THMFP measured at 3 h chlorination time showed to progressively increase with the highest value of 38 μgTHM/L at plant outlet stream. This behavior coincided with an increase in the hydrophilic fraction of NOM throughout treatment. Chlorination tests were carried out at different temperatures. From these experiments similar activation energy values were calculated for THMs and HAAs formation reaction. Greatest differences were measured in disinfection by products (DBPs) formation from the chlorination of hydrophilic fraction. Values varied in the range between 2.7 and 14.5 kcal/mol, being the lowest values for the hydrophobic fraction.