Removal of pharmaceuticals from municipal wastewater
3615
In order to describe the adsorption equilibrium results, dif- ferent non-linear models were tried. First of all, fittings to the main two parameter isotherms, namely the Freundlich iso- therm (Freundlich, 1906) and the Langmuir isotherm (Langmuir, 1918), which are described by Eqs. (5) and (6), were determined. Then, the Sips isotherm (Sips, 1948), which is a combined form of Langmuir and Freundlich and a three parameter model, as described by Eq. (7), was also tried. q e ¼ K F C 1 = n e ð 5 Þ
3. Results and discussion
The parameters analyzed on the secondary effluent used in this work (Table 3) showed typical values of a municipal STP effluent and accomplished with European regulations on the discharge of this sort of effluents (35 mg L 1 TSS, 25mgL 1 BOD 5 and125mgL 1 COD as established by the EU Council Directive 91/271/EEC). The kinetic experimental data on the adsorption of diclofe- nac, ibuprofen, salicylic acid and acetaminophen from the sec- ondary effluent of a STP and from ultrapure water are shown in Figs. 1 and 2, respectively, together with fittings to the pseudo-first order and the pseudo-second order kinetic equa- tions. Parameters determined from these fittings are depicted in Table 4. As it may be seen in Fig. 1, under identical experimental conditions, when the equilibrium is reached, the adsorbed mass of each pharmaceutical on PS800-150 from the secondary effluent was different. Clearly, the drug showing the lowest adsorbed mass is salicylic acid. Furthermore, it is evident that the adsorption of acetaminophen is slower than that of the rest of drugs. Mostly, experimental results are better fitted
Q m K L C e 1 þ K L C e
q e ¼
ð
6 Þ
1 = n e
Q m K LF C
q e ¼
ð 7 Þ
1 = n e
1 þ K LF C
where K F is the Freundlich adsorption constant (mg g 1 (mgL 1 ) 1/ n ); n is the degree of non-linearity; Q m is the maximum adsorption capacity (mg g 1 ); K L (Lmg 1 ) and K LF (mgg 1 (mgL 1 ) 1/ n ) are the Langmuir and Langmuir– Freundlich affinity coefficients, respectively.
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Experimental data pseudo-first order kinetic equation pseudo-second order kinetic equation
Experimental data pseudo-first order kinetic equation pseudo-second order kinetic equation
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Experimental data pseudo-first order kinetic equation pseudo-second order kinetic equation
Experimental data pseudo-first kinetic equation pseudo-second kinetic equation
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Figure 2 Kinetic results on the removal of (a) diclofenac, (b) salicylic acid, (c) ibuprofen, and (d) acetaminophen from ultrapure water by adsorption onto PS800-150. Experimental results throughout time are shown together with the corresponding fittings to the pseudo-first and to the pseudo-second order kinetic equations. Note: error bars stand for standard deviation of three experimental replications.
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