Adapting direct filtration to increasing source water dissolved organic carbon using clarification and granular activated carbon

Changing source water quality namely through increasing natural organic matter (NOM) concentration challenges surface water treatment, especially direct filtration. We conducted a pilot-scale assessment of various adaptation strategies (e.g., clarification, granular activated carbon [GAC] filtration) for direct filtration facilities under the stress of rising NOM levels. Recognizing that changing source water can impact broader aspects of treatment, we considered the implications of Fe and Mn removal via KMnO₄ pre-oxidation. GAC media showed promise as an adaptation strategy, providing ~60% removal of dissolved organic carbon (DOC), and a significant reduction in disinfection by-product formation potential (DBPfp). However, KMnO₄ pretreatment showed limited Mn and Fe removal, and filters with GAC media released dissolved Mn at up to ~30% of prefilter levels. These data suggest that using GAC may come with the risk of poor Mn removal performance if Mn is not removed during pretreatment. This work highlights the complexities anticipated under emerging climate pressures and emphasizes the need for comprehensive treatment solutions that consider factors beyond NOM.