Control of Brominated and Iodinated DBPs within a Drinking Water Distribution System with Granular Activated Carbon and Biological Filtration

This study evaluated the effectiveness of parallel field-scale granular activated carbon (GAC) and biological activated carbon (BAC) filters for removing brominated and iodinated disinfection byproducts (Br-/I-DBPs) from a drinking water distribution system and associated changes in calculated additive toxicity (CAT). Over an 11 month period, 23 of 37 monitored DBP species were detected in the feedwater, with Br-/I-DBPs constituting 72% of trihalomethanes (THMs), 20% of haloaldehydes (HALs), 67% of haloacetonitriles (HANs), and 48% of haloacetic acids (HAAs). GAC effectively decreased all ambient HANs, HALs, and HAAs to below method reporting limits and completely removed THMs up to 3000 bed volumes, resulting in a 99% reduction in CAT. BAC removed all HANs, HALs, and HAAs but showed limited THM removal; however, CAT was reduced by 99%. Following GAC or BAC treatments, supplemental chlorination led to the formation of THMs, HALs, and HAAs─though no HANs─restoring 30-55% of the original CAT, primarily driven by brominated HALs. Microbial analysis revealed taxa, (e.g., <i>Sphingomonas</i>, <i>Rhodospirillales</i>, and <i>Nitrosomonadales</i>) capable of DBP/precursor degradation, alongside taxa associated with opportunistic pathogens underscoring the need for post-treatment disinfection. Overall, GAC and BAC are effective strategies for mitigating Br-/I-DBPs in distribution systems, though rechlorination partially offset treatment benefits.