## 2 Advancements in Ultrafiltration for Protein and Peptide Separation
### Electroultrafiltration (EUF) and Electrodialysis with UF Membrane (EDUF)  
While separating specific protein fractions, concentration polarization may hinder the full potential of an operation unit. To tackle this issue, mechanical interventions require complex control system, but are harder to scale up. Another approach exists which is to elaborate the electrokinetic phenomena comprising of electrophoresis, electroosmosis, and electrolysis into ultrafiltration, namely electroultrafiltration (EUF). Overall, EUF could provide an intriguing basis to ameliorate concentration polarization and foulant deposition without applying shear rate in UF owing to detachment of charged molecules in the form of a gel layer from the membrane surface [76]. In EUF, the maximum component flux at given TMP, \(J_{max}\), can be estimated by [87]:  
\[J_{max}=\mu e\,E_{c} \tag{6}\] \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Process** & **Feeds** & **Membrane and/or Protocols** & **Remarks** & **Ref** \\ \hline \multirow{6}{*}{EDBM} & \multirow{2}{*}{Soy protein hydrolysate} & \multirow{2}{*}{CA (100 kDa), membrane active area: 32 cm\({}^{2}\), 3-20 A m\({}^{-2}\), 170–800 V m\({}^{-1}\)} & \multirow{2}{*}{[78]} & \multirow{2}{*}{[79]} \\  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \hline \multirow{6}{*}{Dynamic UF} & \multirow{2}{*}{Mungbean wastewater} & \multirow{2}{*}{15 kDa (eff membrane area: 360 cm\({}^{2}\)), TMP 1.2 bar, 1403 rpm, and VRF 5.0 (optimum)} & \multirow{2}{*}{[83]} \\  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \hline \multirow{6}{*}{Dynamical UF} & \multirow{2}{*}{UHT milk} & \multirow{2}{*}{VSEP: PES 10 kDa, effective area: 503 cm\({}^{2}\), 60.75 Hz, 45 \({}^{\circ}\)C} & \multirow{2}{*}{[84]} \\  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \hline \multirow{6}{*}{HPTFF} & \multirow{2}{*}{Chicken egg white} & \multirow{2}{*}{30 kDa PES, 2100 rpm, pH 10–11, and NaCl 100 mM} & \multirow{2}{*}{[85]} \\  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \hline \multirow{6}{*}{HPTFF} & \multirow{2}{*}{Chicken egg white} & \multirow{2}{*}{30 kDa PES, 2100 rpm, pH 10–11, and NaCl 100 mM} & \multirow{2}{*}{[86]} \\  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \hline \multirow{6}{*}{Monoclonal antibody} & \multirow{2}{*}{PPS 300 and 100 kDa, PVDF} & \multirow{2}{*}{Only PVDF 100 kDa gave 93.3\% purity for monomer (155 kDa) after one-staged diafiltration} \\  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \hline VRF, volume reduction factor \(=\frac{V_{0}}{V_{0}-V_{0}}\), where \(V_{0}\) is initial feed volume, \(V_{a}\) is average permeate over filtration, and \(V_{p}\) is final permeate volume; EUF = electroultrafiltration; EDWT = electrodialysis with ultrafiltration; EDBM = electrodialysis with bipolar membrane; HPTFF = high-performance tangential flow filtration. & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._Here, the maximum flux depends on critical electrical potential (\(E_{c}\)) and the electrophoretic mobility of the component (\(\mu\)e). The effect of electrical field strength is then introduced to the gel layer model, leading to a new equation for estimating the flux of molecule toward the UF membrane [87]:  
\[J=k\left\{(c_{w}-c_{p})/(c_{b}-c_{p})\right\}+\mu e\,E \tag{7}\]  
Electrophoretic effect mainly governs EUF along with ion association, ion adsorption, or ion dissolution and serves the gradient of electrical field to induce protein mobility. Meanwhile, the movement of solution through porous material under this driving force is called electroosmosis. Although electroosmosis increases the permeate flux, this does not chiefly regulate the process [88; 89]. In contrast, electrolysis is a breakdown phenomenon of organics under electrically driven chemical reaction on the electrodes.