Contaminant Removal in a Pilot Drinking Water Treatment Plant by Pre-oxidation Followed by Biological Activated Carbon Filtration: Spiking versus Ambient Studies

Advanced drinking water treatment including biological activated carbon (BAC) filtration, ozonation, and advanced oxidation processes (AOPs) can improve trace organic contaminant removal compared to conventional processes. Contaminant removals through a pilot-scale lime-softening drinking water treatment plant (pH > 8.5 after recarbonation) using BAC alone and parallel ozone and ozone/hydrogen peroxide (AOP) treatment units followed by BAC were compared. The BAC filters contained aged media (∼14 years) harvested from the full-scale facility. Taste and odor compounds, 1,4-dioxane, neonicotinoids, antibiotics, and other contaminants of emerging concern were spiked into the water ahead of the ozone contactors at concentrations ranging from 26 ng L^-1 to 7.3 μg L^-1. Removal by BAC filtration varied from 19 ± 11% for 1,4-dioxane to 77 ± 40% for geosmin. Ozone and hydroxyl radical exposures ranging over 0.49-1.27 × 10^-2 M s and 0.19-4.67 × 10^-10 M s, respectively, improved removal of all spiked contaminants compared to BAC filtration alone, especially for 1,4-dioxane (85 ± 16%). When evaluating contaminant removal at ambient concentrations, however, concentrations of many contaminants rebounded after ozone or AOP treatment due to desorption from the BAC media. Our findings suggest that contaminants may be released from aged BAC unless the material is replaced upon addition of ozone or AOPs to an existing treatment facility.