MIB and geosmin removal during adsorption and biodegradation phases of GAC filtration

Biologically active carbon (BAC) filtration is a robust process for removal of many contaminants of concern. In this study, the effectiveness of BAC filtration to remove natural organic matter (NOM) and taste and odor (T&O) compounds was investigated by long-term (7 months) bench-scale filtration experiments. Filters contained fresh granular activated carbon (GAC) and a 2-year-old BAC which were fed with ozonated water from a full-scale water treatment plant spiked with 2-methylisoborneol (MIB) and geosmin. The study aims to evaluate T&O removal of GAC transitioning from its adsorptive to biological state, and to determine the effects of changing hydraulic loading during T&O episodes and its effect on dissolved oxygen (DO) consumption. Sequencing of microbial communities in the BAC revealed that 20% of the identified bacteria were of genus Nitrospira. Based on nitrate formation and dissolved organic carbon (DOC) removal of the 2-year-old BAC, the fresh GAC turned biological after approximately 32,000 bed volumes. DOC removal of the GAC decreased from the initial 80% to 17%, however, the removal of MIB and geosmin remained > 90% throughout the experiment (i.e., from adsorption to biodegradation). The 2-year-old BAC showed 9% lower MIB removals than the transitioned GAC filter indicating a contribution of remaining adsorption sites on MIB removal. When challenging the filters at different hydraulic loadings, higher T&O removal was achieved at higher empty bed contact times, which correlated well with increased DO consumption.