The long-term removal of 34 trace organic micropollutants (<1 μg L(-1)) was evaluated and modeled in drinking water biological filters with sand media from a full-scale plant. The micropollutants included pesticides, pharmaceuticals, and personal care products, some of which are endocrine disrupting chemicals, and represent a wide range of uses, chemical structures, adsorbabilities, and biodegradabilities. Micropollutant removal ranged from no measurable removal (<15%) for 13 compounds to removal below the detection limit and followed one of four trends over the one year study period: steady state removal throughout, increasing removal to steady state (acclimation), decreasing removal, or no removal (recalcitrant). Removals for all 19 nonrecalcitrant compounds followed first-order kinetics when at steady state with increased removal at longer empty bed contact times (EBCT). Rate constants were calculated, 0.02-0.37 min(-1), and used in a pseudo-first-order rate model with the EBCT to predict removals in laboratory biofilters at a different EBCT and influent conditions. Drinking water biofiltration has the potential to be an effective process for the control of many trace organic contaminants and a pseudo-first-order model can serve as an appropriate method for approximating performance.
Biologically acclimated sand and granular activated carbon (GAC) filter performance for trace organic contaminant control is compared under variable water quality and operational conditions.
Episodic occurrences of trace organic contaminants may affect their removal by biofilters. Removal of the naturally occurring algal metabolite 2‐methylisoborneol (MIB) and the herbicide 2,4‐dichlorphenoxyacetic acid (2,4‐D) by seven biofilters with an average empty bed contact time (EBCT) of 8.7 min is presented under a range of intermittent exposure conditions with continuous presence of dissolved organic matter. An average 70% removal of both MIB and 2,4‐D was found under constant exposure conditions over seven months. With the use of a pseudo‐first‐order model, much of the variability in removal during this time could be explained by EBCT changes. Microorganisms in the biofilters retained the capacity to biodegrade MIB and 2,4‐D after non‐exposure periods of up to five months. However, after nine months of non‐exposure, the MIB and 2,4‐D removals were lower than with the control biofilter, although the biofilter began to quickly reacclimate to these contaminants.
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