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A granular activated carbon (GAC) adsorption simulation methodology using the observed trace organic contaminant mid-point breakthrough and the pore diffusion model is presented, validated, and used to model adsorption and concentration gradient driven desorption. Trace organic contaminant adsorption was well-simulated by this approach; however, desorption from GAC adsorbers was found to occur at lower concentrations than predicted by either pore or surface diffusion model calculations. The observed concentration profiles during desorption yielded a lower peak concentration and more elongated attenuation of contaminants after intermittent loading conditions than predicted by the models. Hindered back diffusion caused by irreversibly adsorbed dissolved organic matter on the GAC surface is hypothesized to be responsible for slowing the desorption kinetics. In addition, laboratory test results indicate a negligible impact of simulated backwashing the GAC media on trace organic contaminant breakthrough., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

While it is known that resorcinol- and phenol-type aromatic structures within natural organic matter (NOM) react during drinking water chlorination to form trihalomethanes (THMs), limited studies have examined aliphatic-type structures as THM and haloacetic acid (HAA) precursors. A suite of aliphatic acid model compounds were chlorinated and brominated separately in controlled laboratory-scale batch experiments. Four and two beta-dicarbonyl acid compounds were found to be important precursors for the formation of THMs (chloroform and bromoform (71-91% mol/mol)), and dihaloacetic acids (DXAAs) (dichloroacetic acid and dibromoacetic acid (5-68% mol/mol)), respectively, after 24 h at pH 8. Based upon adsorbable organic halide formation, THMs and DXAAs, and to a lesser extent mono and trihaloacetic acids, were the majority (> 80%) of the byproducts produced for most of the aliphatic beta-dicarbonyl acid compounds. Aliphatic beta-diketone-acid-type and beta-keto-acid-type structures could be possible fast- and slow-reacting THM precursors, respectively, and aliphatic beta-keto-acid-type structures are possible slow-reacting DXAA precursors. Aliphatic beta-dicarbonyl acid moieties in natural organic matter, particularly in the hydrophilic fraction, could contribute to the significant formation of THMs and DXAAs observed after chlorination of natural waters.