Water Research Foundation Report Series

Cometabolism of Trihalomethanes in Nitrifying Biofilters

by Gerald E. Speitel, L. Katz, D. Wahman, and J. Fairey

Published 30 June 2006

Many utilities find themselves trying to satisfy simultaneously the disinfection and disinfection by-product (DBP) regulations. The proposed Stage 2 rules will only make this task more difficult. Chlorine disinfection remains quite popular in the United States, although many utilities now use combinations of chlorine and chloramines to avoid excessive THM and haloacetic acid (HAA) formation. The objectives of this project were to: 1) determine cometabolism kinetics and the significance of enzyme competition and by-product toxicity for ammonia and the four THMs with Nitrosomonas europaea and mixed-culture nitrifiers encountered in drinking water treatment; 2) demonstrate THM cometabolism in continuous-flow biofilters receiving only ammonia and THMs in the influent; 3) study monochloramine removal in GAC beds to identify the influence of GAC type and operating conditions on removal rates and service life; and (4) demonstrate THM cometabolism in continuous-flow biofilters receiving ammonia, monochloramines, and THMs in the influent.