Hp4750

Membrane performance was characterized by using the Sterlitech HP4750 stirred cell to perform convective studies. Water permeability was determined for each membrane by measuring the volumetric flux of deionized ultrafiltered (DIUF) water at 1.4, 2.76, and 4.14 bar respectively. Methylene blue (5 mg/L) and neutral red (5 mg/L), as well as various molecular weights (5 kDa and 10 kD at concentrations of 100 mg/L) of Blue Dextran, were filtered through the membrane. The permeate was collected and dye concentration for the feed, permeate, and remaining retentate was analyzed using the VWR UV-6300PC Spectrophotometer.
For cellulose–lignin composite membranes, antifouling properties were analyzed by testing permeability of 100 mg/L humic acid solution at pH of 5.6 in a crossflow system.

Membrane performance was examined by dead-end filtration system (Sterlitech, HP4750, Auburn, WA, USA), where the effective area was 14.6 cm². The membrane at the beginning was cut and put in according to the size of the dead-end cell. After that, the membrane was pre-compacted at 1.5 bar for 30 min with feed solution (DI water). The permeate flux was tested for all membranes at 1 and 2 bars (ultrafiltration) for 30 min. All experiments were performed three times, then the average values were calculated.
The permeation flux (J₀) is derived from the following Equation (2): $$\mathrm{flux}\left({\mathrm{J}}_0\right)=\frac{W}{A.t}$$
where W is the weight of filtrated solution (grams), A is the membrane surface area (meter cubic) and t is the experiment time (hour).
To determine the phenol rejection efficiency, a synthetic OMW with concentration around 75 ppm was prepared. The OMW was filtered through the system and the concentration of phenols was analyzed by UV/Vis spectrophotometer according to the Folin-Ciocalteu method at a wavelength of 750 nm. Phenol’s rejection efficiency was calculated using the measured feed and permeate concentrations following Equation (3): $$\mathrm{Rejection}(\%)=\frac{{\mathrm{C}}_{\mathrm{f}}-{\mathrm{C}}_{\mathrm{p}}}{{\mathrm{C}}_{\mathrm{f}}}\ast 100\%$$
where C_f and C_p are the concentrations of the feed solution and permeate, respectively.

Permeance measurements for all membranes were conducted in methanol (HPLC-grade, Fisher Chemical) with an electronically controlled pressure-driven membrane testing cell (Sterlitech HP4750). The 25 mm diameter membranes were soaked in methanol for 24 hours prior to permeance testing. After equilibrium soaking, the membrane was transferred to the Sterlitech membrane cell and 100 mL of fresh methanol for permeance testing was added. The cell was slowly pressurized to 150 psig at a controlled rate of 25 psi/min with an electronically controlled gas manifold and the permeate flow rate was measured by recording the mass of permeated methanol over time. Once 80 mL of methanol permeate had been collected, the experimental run would end.
Membrane permeance was calculated from the average mass flow rate of permeate ( $\stackrel{°}{M}$ ), geometric membrane area (A) and pressure (P) with the following equation (Eq. (3)): $Permeance=\frac{\stackrel{°}{M}}{A*P}$

Membrane filtration was carried out in a dead-end filtration cell (HP 4750, Sterlitech, Kent, Washington, DC, USA). Membrane pieces with an effective filtration area of 14.6 cm² were cut and placed in a stainless metal plate. Nitrogen gas was used as the driving force, and a stirrer was used to minimize the concentration polarization at a stirring rate of 300 rpm. The membrane was pre-conditioned with DI water until a steady flux was achieved. Methods for determining flux and rejection using DI water or polyethylene glycols (PEGs) mixtures (of PEG 1000, 1500, 2000, 3000, 4000 and 6000) have been described in the previous study [30 (link)]. Permeate from the filtration was collected and recorded by a digital mass balance. High-performance liquid chromatography (HPLC) coupled with an evaporative light scattering detector (ELSD) were used for the identification of individual PEG oligomers in the feed, permeate and retentate [30 (link)].

The OSN tests were performed at room temperature using a commercial permeation cell (HP4750, Sterlitech^®). The feed chamber has a suspending stir bar to keep the solution homogeneous. It was further connected to a solution tank to increase the total volume to be around 2.5 L to ensure the concentration change in the feed side during the permeation test is negligible. The pressure of the feed side was set to 1 bar, while the permeate side was open to the atmosphere. A series of dye solutions with a concentration of 100 ppm was used as feed solutions. The permeate was collected and the weight was monitored by a digital balance. The permeate collected in the first 2 h was decanted to allow the system to approach the steady state. The dye concentration was measured by a UV-vis spectrophotometer. The solvent permeance P (LMH/bar) was calculated by Eq. (1), $P=V/\left(A\cdot \mathrm{\Delta }t\cdot \mathrm{\Delta }P\right)$ where, V (L) is the volume of the permeated solvent collected during a certain time period ∆t (h) under the pressure different ∆P (bar), and A is the membrane area (m²).
The dye rejection R (%) was calculated by Eq. (2), $R=\left(1-C_P/C_F\right)\times 100\%$ where, C_P and C_F are the dye concentrations in the permeate and feed solutions, respectively.

The water permeation and salt rejection were assessed in a stirred cell (Sterlitech HP4750 Stirred cell, Kent, WA, USA). The GO‐based membrane was fixed at the bottom of the stirred cell with the active area of 14.6 cm². The stirred cell was filled with 300 mL of aqueous NaCl or MgSO₄ solution. The stir‐rate for the stirred cell was set as 60 rpm. Pressure was applied using nitrogen gas from 8 to 16 bar. The solution permeated through the membrane was collected in a small plastic vessel. The volume of permeated solution was measured by weighing the solution at every 12 h. The test was conducted at least 3 days and all tests were at least triplicated for reproducibility.

A dead-end cell (HP4750, Sterlitech Corp., Kent, UK), as illustrated in Figure 2, with an effective area of 14.6 cm², was used to evaluate the RO membrane performance. Specifically, a circular membrane disc was cut and mounted in a permeation cell. A porous stainless-steel brace was used as membrane supporter and tightened by rubber O-ring. At 16 bar, the membrane was compacted to achieve a steady water permeability for 30 min. Then, at 15 bar, the membrane was stabilized with RO water for 15 min. After that, the 1 mL of RO water was collected and time taken was recorded. The filtration was repeated using 2000 ppm NaCl as feed water. The time taken to collect 1 mL of permeate was recorded. Water permeability of salt (A_w,s) and salt rejection (R_s) were calculated using Equations (5) and (6), respectively:
where V is the total amounts of the collected permeate (L), A is the cross-sectional area (m²) and t is duration of treatment (h).

C_f,s is salt concentrations of feed and C_p,s salt concentration of permeate by a conductivity meter.