Removal of pharmaceuticals from municipal wastewater
3617
0 1 2 3 4 5 6 7 8 9 10
(b)
25
(a)
20
15
10
Experimental data
Experimental data Freundlich Langmuir Sips
Freundlich
5
Langmuir
0
0
20
40
60
80
100
0
20
40
60
80
100
C e (μg L
-1 )
C e (μg L
-1 )
16
16
(d)
(c)
14
14
12
12
10
10
8
8
6
6
Experimental data
Experimental data Freundlich Langmuir Sips
Freundlich
4
4
Langmuir
2
2
Sips
0
0
0
20
40
60
80
100
0
20
40
60
80
100
C e (μg L
-1 )
C e (μg L
-1 )
Figure 3 Equilibrium results on the removal of (a) diclofenac, (b) salicylic acid, (c) ibuprofen, and (d) acetaminophen from a secondary effluent of a STP by adsorption onto PS800-150. Experimental results are shown together with fittings to the Freundlich, to the Langmuir and to the Sips isotherm models. Note: error bars stand for standard deviation of three experimental replications.
Finally, the shape of the adsorption isotherms revealed a favor- able process, with n > 1, which points to the fact that the adsorbents are efficient not only removing high but also low concentrations of these pharmaceuticals. In any case, higher n values were determined for the adsorption of these pharma- ceuticals from ultrapure water than from the STP effluent. With respect to salicylic acid, the Freundlich isotherm parameters in Table 5 will be used for the comparison of its adsorption from the two different aqueous matrixes. In terms of adsorption affinity, a higher salicylic acid adsorption coefficient K F was obtained for the adsorption from ultrapure water. In the case of n , it was larger than 1 either from ultrapure water or from the STP secondary effluent, but a larger value was determined for the adsorption from ultrapure water. Therefore, some matrix effects must have affected the salicylic acid adsorption from the STP effluent. In any case, as it was for the rest of the pharmaceuticals, the adsorption capacity remained the same from both ultrapure water and the STP secondary effluent, which is a key issue for the application of the charcoal here produced for an adsorptive tertiary treatment of wastewater.
is the one that better fits experimental results, except for salicylic acid. In this last case, the best fittings were obtained by the Freundlich isotherm model. Parameters in Table 5 sup- port these remarks, as it may be seen by the Q m and the R 2 and S yx obtained for each pharmaceutical. When comparing the equilibrium isotherms obtained for the adsorption of the considered pharmaceuticals from the STP secondary effluent and ultrapure water, differences are not out- standing. Focusing on the Sips isotherm model parameters (Table 5) for comparing the adsorption of diclofenac, ibuprofen and acetaminophen, several remarks may be made. First, considering the associated deviations, the Q m values determined for the adsorption from the STP effluent and from ultrapure water are equivalent. In the case of the K LF , which is usually related to the affinity of the adsorbent toward the adsorbate, each pharmaceutical showed a different pattern. Equal K LF were determined for diclofenac while higher values were determined in ultrapure water than in the STP secondary effluent for ibuprofen and acetaminophen. Therefore, it may be inferred that the adsorption affinity for these last pharmaceuti- cals may be affected by the complex matrix of the STP effluent.
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