Monochloramine destruction by GAC—effect of activated carbon type and source water characteristics

Abstract

This research evaluated the effect of granular activated carbon (GAC) type and source water characteristics on steady‐state monochloramine reduction in fixed‐bed reactors (FBRs) under drinking water treatment conditions. Five commercially available GACs and two background waters were used to study monochloramine reduction in laboratory‐scale column studies. Steady‐state monochloramine destruction increased with decreasing water pH (over the range likely in chloramination, i.e., pH 7–9) regardless of GAC type or source water. A previously developed finite element model was verified experimentally for monochloramine influent concentrations of interest in drinking water (2 mg/L as Cl2). Simulation of steady‐state process performance with GAC particle sizes used in practice was performed using the model after it was calibrated to results from the monochloramine FBR studies. These steady‐state simulations indicate that with at least one of the GACs tested, < 8 min of empty bed contact time (EBCT) was required to meet the monochloramine standard for kidney dialysis water (0.1 mg/L as Cl2). Despite a required EBCT as long as 20 min, use of more‐traditional GACs may also be feasible for kidney dialysis, provided that benefits gained by steady‐state operation (i.e., never having to replace the filter media) outweigh filter size and portability considerations.