## 3 Results  
The amount of paracetamol adsorbed onto microalgae or activated carbon versus contact time under stirring is shown in Figure 1. For both adsorbents, the amount of adsorbed paracetamol increased with time until becoming stable at the equilibrium, which happened after stirring for 240 min. Although adsorption kinetics onto both adsorbents were similar in terms of \(t_{e}\), the adsorbed paracetamol at the equilibrium was quite higher in the case of the activated carbon than in the case of microalgae. In _Synechocystis_ sp. kinetic experiments, about 10% of the initial amount of paracetamol was absorbed at \(t_{e}\), while, in the case of commercial activated carbon, about 20% of the initial amount of paracetamol was adsorbed at this time. From a practical point of view, these results point to the necessity of a larger adsorbentssolution ratio to attain higher percentages of paracetamol removal under the experimental conditions used here. The fittings of the experimental results to the kinetic models of Lagergren (pseudo first-order) and pseudo second-order are shown together with the experimental results in Figure 1. The kinetic parameters derived from these results are shown in Table 1. As may be seen, both kinetic equations  
Figure 1: Kinetic results on the adsorption of paracetamol onto (**a**) _Synechocystis_ sp. ; (**b**) activated carbon. Experimental results of the adsorbed paracetamol (\(q_{t}\), mg g\({}^{-1}\)) versus time (\(t\), min) are represented together with fittings to the Lagergren and pseudo-second order kinetic equations. Note: Error bars stand for standard deviation. fitted results with similar \(r^{2}\) and Sxy and both \(k_{1}\) and \(k_{2}\) indicated a faster adsorption rate onto _Synechocystis_ sp. The paracetamol adsorption equilibrium isotherms using _Synechocystis_ sp. and activated carbon as adsorbents are shown in Figure 2.  
Although the isotherms show a similar trend, the difference between the adsorption capacities of both adsorbent materials is remarkable. The fittings of experimental results to the Langmuir and Freundlich adsorption isotherms are shown in Figure 2 together with the experimental results. As it may be seen, the Langmuir isotherm well described the adsorption equilibrium of paracetamol onto the commercial activated carbon, which points to the homogeneity of the activated carbon surface. However, in the case of _Synechocystis_ sp., although the quality of [PERSON] and Freundlich fittings \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Kinetic Equations** & **Parameter** & _Synechocystis_ sp.** & **Activated Carbon** \\ \hline \multirow{4}{*}{Pseudo1 st order} & \(k_{1}\) (min\({}^{-1}\)) & 0.014 \(\pm\) 0.002 & 0.017 \(\pm\) 0.001 \\  & \(q_{e}\) (mg g\({}^{-1}\)) & 14.51 \(\pm\) 0.39 & 220.8 \(\pm\) 2.6 \\  & \(r^{2}\) & **0.97** & **0.99** \\  & \(S_{xy}\) & 0.9 & 5.9 \\ \hline \multirow{4}{*}{Pseudo2 nd order} & \(k_{2}\) (mg g\({}^{-1}\) min\({}^{-1}\)) & 0.0012 \(\pm\) 0.0001 & 90\(\cdot\)10\({}^{-6}\) \(\pm\) 8\(\cdot\)10\({}^{-6}\) \\  & \(q_{e}\) (mg g\({}^{-1}\)) & 16.38 \(\pm\) 0.26 & 247.5 \(\pm\) 4.5 \\  & \(r^{2}\) & **0.99** & **0.99** \\  & \(S_{xy}\) & 0.4 & 6.8 \\ \hline
**Equilibrium Isotherms** & **Parameter** & _Synechocystis_ sp.** & **Activated Carbon** \\ \hline \multirow{4}{*}{[PERSON]} & \(K_{F}\) (mg g\({}^{-1}\) (mg L\({}^{-1}\))\({}^{-N}\)) & 0.63 \(\pm\) 0.06 & 40.33 \(\pm\) 12.21 \\  & \(N\) & 1.36 \(\pm\) 0.04 & 2.7 \(\pm\) 0.5 \\  & \(r^{2}\) & **1.00** & **0.90** \\  & \(S_{xy}\) & 0.4 & 23.9 \\ \hline \multirow{4}{*}{[PERSON]} & \(Q_{max}\) (mg g\({}^{-1}\)) & 52.8 \(\pm\) 6.8 & 278.3 \(\pm\) 11.3 \\  & \(K_{L}\) (L mg\({}^{-1}\)) & 0.0055 \(\pm\) 0.0010 & 0.044 \(\pm\) 0.006 \\  & \(r^{2}\) & **0.99** & **0.99** \\  & \(S_{xy}\) & 0.6 & 9.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters from the experimental results fittings to the kinetic equations (pseudo first-order (Lagergren equation) and pseudo second-order equations) and equilibrium isotherms (Langmuir and Freundlich isotherms).