Although graphite is not effective as an adsorbent in water treatment, it provides a homogenous, non-porous, carbonaceous structure that is ideal for studying fundamental adsorption mechanisms. High-purity graphite powder (C content 99.5%) was oxidized in an ozone stream, producing a near-surface oxygen content of 5.9 at.%, and was used together with the virgin material to establish adsorption isotherms for organic compounds in aqueous solutions. We examined how the aromaticity and substituents of the adsorptives affect adsorption on the model-activated carbon surface. For both virgin and oxidized graphite, the adsorption capacity for the aromatic compounds decreased in the order 1-naphthol > 2-methoxynaphthalene > naphthalene > anisole > phenol, with significant differences in the adsorption capacities of the two graphite species observed only for anisole, naphthalene, and 1-naphthol. The Freundlich constants (KF) for the five compounds on virgin graphite were 23.9, 10.3, 5.5, 1.4, and 0.8 (nmol mg−1 )/(µmol L−1) n, respectively. Naphthalene and 1-naphthol were slightly more adsorbed on the virgin material, whereas oxidized graphite had marginally better adsorption properties for anisole. The results underline the importance of dispersive and π– π interactions in the adsorption of organic compounds on carbonaceous adsorbents; a second aromatic ring in 1-naphthol and 2-methoxynaphthalene greatly increased the adsorption capacity for these compounds compared with their one-ring counterparts phenol and anisole. Differences were also observed in the adsorption of compounds containing hydroxyl or methoxy substituents, which have electron-donating properties (a resonance effect) but different electron-withdrawal characteristics (caused by induction). Two amino acids occurring as zwitterions, l-tryptophan and l-tyrosine, were also tested as adsorptives. l-Tryptophan, which has a larger aromatic system, achieved higher loading on graphite, suggesting an adsorption mechanism primarily governed by dispersive and π– π interactions for these two ionic compounds as well.

In many drinking water treatment facilities with an activated carbon (AC) purification step, polar and hydrophilic molecules are substances of concern. Many of the current test methods for AC do not really reflect AC's adsorption capacity for these substances. To develop a fast and economically reasonable parameter that characterizes AC's ability to remove these compounds, three substances, namely diclofenac, nitrobenzene, and diatrizoate were investigated as test substances. A test set of different AC samples was created by reactivating an exhausted AC in three different ways. Additional AC samples were obtained by sampling different depths of a full-scale AC filter at regular intervals during the operation time of the filter. Several adsorption tests were performed with the three test substances, including adsorption isotherms in the concentration range mg/L, single-point adsorption tests in the concentration range μg/L, and pilot-scale fixed bed filter experiments. The results suggest that diatrizoate allows for a sensitive comparison of different AC samples. A characteristic figure, the 'diatrizoate number' was developed. This diatrizoate number allows for a sensitive, cheap, and quick comparison of different ACs. A similar survey with special focus on problematic substances present on site is recommended for other water treatment facilities.

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