## 3 Results and Discussion
### Effect of DES-Lignin on Membrane Performance  
The pure water flux of the reference and DES-lignin modified membranes at different operating pressure as well as their related PEG solution rejection (35 kD) and contact angles are presented in Table 2. It can be seen that the pure water flux increases as the dosage of DES-lignin in the dope solution increases, which is in accordance with the improvement of hydrophilicity, i.e., the lower contact angle of the modified membranes, and the bulk porosity of the fabricated membranes (Table 1). The better hydrophilicity in the membranes incorporated with DES-lignin can be ascribed to the presence of different hydrophilic functional groups in the DES-lignin structure, such as hydroxyl and carbonyl groups, as evidenced by a higher amplitude at wavenumbers of 3200-3600 and 1735 cm\({}^{-1}\), respectively (Figure 2). These results are in line with the findings of [PERSON] et al., which show a slight reduction of contact angles as a result of using alkali lignin as an additive in the modification of polysulfone membranes. Furthermore, the TOC results of pure water after 10 min (leakage) for each experiment was very low (below 1 mg/L), indicating no leakage of DES-lignin from the membrane structure. This trace of leakage can be attributed to the residual solvents remaining in the membrane structure, which could be seen in the reference membrane as well. In general, the inherent trade-off between permeability and rejection was obviated, and the PEG rejection for modified membranes remained almost the same as that of the reference membrane. Interestingly, in the low dosage of lignin content in the dope solution (0.25 wt %), a membrane with better performance in terms of pure water flux and PEG solution rejection was achieved. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Membrane**} & **PES** & **Lignin Content** & **Conact Angle** & \multicolumn{3}{c}{**Pure water Flux**} & \multirow{2}{*}{**Permeability**} & **Leakage** & **Rejection (\%)** \\  & **(\%)** & **(\%)** & & **(\(\downarrow\)) bar** & **2 bar** & **(\(\downarrow\)/m’h bar)** & **(mg/L)** & **(PEG 35 kDa)** \\ \hline \#1 & 20 & - & \(51.9\pm 0.4\) & \(67.7\pm 1.8\) & \(137.9\pm 0.7\) & \(210.0\pm 0.9\) & 74.9 & 0.9 & 85.7 \\  & & & & \(75.9\pm 1.7\) & \(151.1\pm 0.5\) & \(233.3\pm 0.8\) & 0.6 & 82.8 \\ \hline \#2 & 20 & 0.25 & \(486.6\pm 0.3\) & \(85.9\pm 2.0\) & \(71.2\pm 1.7\) & \(254.8\pm 1.4\) & & 0.5 & 88.7 \\  & & & \(78.8\pm 1.9\) & \(154.5\pm 1.6\) & \(235.8\pm 0.9\) & & 0.4 & 84.9 \\ \hline \#3 & 20 & 0.5 & \(46.9\pm 0.4\) & \(94.2\pm 1.7\) & \(189.9\pm 0.7\) & \(286.0\pm 0.7\) & 91.5 & 0.4 & 75.7 \\  & & & & \(86.4\pm 0.9\) & \(181.2\pm 0.8\) & \(260.8\pm 0.7\) & & 0.4 & 83.6 \\ \hline \#4 & 20 & 1 & \(45.6\pm 1.2\) & \(105.6\pm 1.3\) & \(206.0\pm 1.0\) & \(309.4\pm 0.9\) & 0.6 & 86.6 \\  & & & \(104.6\pm 1.4\) & \(183.7\pm 0.4\) & \(288.5\pm 0.5\) & & 0.8 & 81.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Polymer solution condition, contact angle (\(\pm\)95% confidence Interval), pure water flux at different pressures, leakage (TOC results of pure water after 10 min), and PEG 35 kDa rejection of fabricated membranes.