Using a plug-flow reactor model and literaturevalues for haloacetic acid (HAA)biodegradation kinetic parameters, theauthors evaluated HAA removal efficiency inbiofilters and distribution systems. The simulationsperformed indicated that HAAremoval through bacterial activity is possibleboth within biofilters and along the pipewalls from the distribution system. Becauselarge numbers of bacteria are needed to beable to reduce HAA levels below U.S. EnvironmentalProtection Agency limits, only thebiofilters, where relatively large bacterialdensities can accumulate on the filter media,proved efficient systems for removing HAAs.Although previous research showed thatHAAs could be degraded in biologicallyactive carbon filters and along distributionsystems, none of these studies correlatedHAA degradation efficiency with physicaland biological parameters (e.g., pipe diameter,filter grain diameter, flow velocity,biodegradation kinetic constants). The currentresearch fills in these gaps and demonstrateswhy a biofilter is more efficient thanthe distribution system at removing HAAs.Includes 53 references, tables, figures.