## 3 Results and Discussion
Figure 7: Equilibrium results on the adsorptive removal of acetaminophen from waste water by adsorption onto (**a**) the activated carbon GPP20 and (**b**) the polymeric resin Sepabeads SP207. Experimental results are shown together with fittings to the Freundlich, to the Langmuir and to the Langmuir-Freundlich isotherm models. Error bars stand for the standard deviation of three experimental replications. Note: for a better visualization of fittings, the scale of axis Y has been adjusted to results. According to the fitted Langmuir-Freudnlich isotherms, the average \(Q_{\rm m}\) determined for the adsorption of ibuprofen were larger than for the adsorption of acetaminophen for both of the presently-used adsorbents This is apparently in disagreement with the larger \(q_{\rm e}\) that had been experimentally determined for the adsorption of acetaminophen onto GPP20, as compared with ibuprofen. However, it must be highlighted that large standard deviations were observed for the \(Q_{\rm m}\) values determined for ibuprofen. In fact, although all the isotherms fitted the Langmuir-Freunlich isotherm, those corresponding to the adsorption of acetaminophen onto GPP20 reached a well-defined plateau, which was not the case of ibuprofen. This further supports that, in contrast to ibuprofen, the adsorption of acetaminophen is governed by non-electrostatic interactions. Regarding the \(K_{\rm LF}\), a parameter that is frequently related to the affinity of the adsorbent for the adsorbate, larger values were determined for GPP20 than for Sepabeads SP207. In the case of GPP20, a larger affinity for acetaminophen than for ibuprofen may be inferred on the basis of \(K_{\rm LF}\) values, which agrees with the neutral charge of GPP20 and acetaminophen at the working pH (both in ultrapure and waste water). Meanwhile, Sepabeads, which is positively charged at the working pH, showed larger affinity for ibuprofen (negative form) than for acetaminophen (neutral). It is to be noted that, in this work, neither the \(q_{\rm e}\) nor the \(Q_{\rm m}\) values decreased in waste water as compared to ultrapure water, which points to the applicability of both the activated carbon and the polymeric resin for an adsorptive tertiary treatment of waste water. In the literature, there are published works (ex: [39; 40]) that report the reduction of the pharmaceuticals adsorption uptake by carbonaceous adsorbents in waste water as compared with ultrapure or distilled water, pointing to the competitive effects of dissolved organic matter (DOM). In contrast, there are studies (ex: [41]) that highlight an increased adsorption capacity of organic pollutants in waste water, and relate this increase to the action of microorganisms in waste water, the adsorbent acting as a bearer surface that favors their degrading. In this sense, [PERSON] et al. [42] proved that the formation of a bacterial biofilm on the surface of a commercial activated carbon meant the increase of the adsorption of salicylic acid from water. Therefore, in this work, it may be hypothesized the occurrence of a synergism between microorganisms degradation and adsorption for the removal of pharmaceuticals. Thus, the action of microorganisms may have compensated for the competitive effect by DOM so the pharmaceuticals adsorption capacity remained the same in waste water than in ultrapure water.