Biofiltration was found to be a possible process for humic acid removal once filters had been acclimated to a synthetic feedwater for 12–16 months. The biofilters were exposed to a synthetic feedwater with influent TOC concentrations ranging from 1.6–4.5 mg L‒1 and a composition of 65% humic acid, 15% formate, 10% acetate and 10% formaldehyde on a carbon mass basis. TOC removals improved from 19 ± 13% (n = 15) to 49 ± 10% (n = 20) in one biofilter and from −11 ± 25% (15) to 51 ± 7% (n = 20) in another biofilter. These increases were found to be statistically significant at the 5% level. The increase in removal was due to an increase in removal of both the readily biodegradable carbons and humics in the biofilters. The humic removal increased from 10 to 36% in biofilter #1 and from 0 to 35% in biofilter #2. At the end of the experiments, formate removals were between 91–94%, acetate removals ranged from 83–87%, and formaldehyde was completely removed in the biofilters. SUVA was not found to be a good indicator of humic removal in the biofilters.

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