DOM removal is more important than the specific DOM removal pretreatment process for GAC adsorption of TrOCs

Abstract

Granular activated carbon (GAC) is an effective treatment technology for removing dissolved organic matter (DOM) and trace organic contaminants (TrOCs) from drinking water. However, higher DOM concentrations lead to earlier TrOC breakthrough because of competitive adsorption between them. As such, it is imperative to select an appropriate DOM removal pretreatment process. This study investigated the impact of three DOM removal pretreatment processes on the breakthrough of 29 TrOCs in a single raw water source by treating to the same average dissolved organic carbon (DOC) concentration of 2.1 to 2.2 mg L⁻¹. The three pretreatment processes were (1) ozonation following by biofiltration and conventional treatment (O₃/BF/C), (2) magnetic ion exchange following by conventional treatment (MIEX/C), and (3) conventional treatment alone (C). The effect of DOC concentration itself was also evaluated solely for O₃/BF/C treated waters at average concentrations of 2.2, 2.9, and 3.8 mg L⁻¹. Using GAC in rapid small-scale column tests, MIEX/C pretreatment resulted in DOM with the highest absorbability (latest breakthrough) followed by C then O₃/BF/C. In terms of TrOC breakthrough, MIEX/C pretreatment resulted in earlier TrOC breakthrough at higher bed volumes but, on average, bed volumes to 10% TrOC breakthrough (BV_10%,TrOC) were statistically the same between all pretreatments. Only the water with the highest DOC concentration, treated by O₃/BF/C, resulted in lower BV_10%,TrOC values on average. These results suggest that for high levels of TrOC removal by GAC, as defined by BV_10%,TrOC values, influent DOC concentrations are more important than the specific DOM removal pretreatment process.