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Abstract Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are now widely found in aquatic ecosystems, including sources of drinking water and portable water, due to their increasing prevalence. Among different PFAS treatment or separation technologies, nanofiltration (NF) and reverse osmosis (RO) both yield high rejection efficiencies (>95%) of diverse PFAS in water; however, both technologies are affected by many intrinsic and extrinsic factors. This study evaluated the rejection of PFAS of different carbon chain length (e.g., PFOA and PFBA) by two commercial RO and NF membranes under different operational conditions (e.g., applied pressure and initial PFAS concentration) and feed solution matrixes, such as pH (4–10), salinity (0‐ to 1000‐mM NaCl), and organic matters (0–10 mM). We further performed principal component analysis (PCA) to demonstrate the interrelationships of molecular weight (213–499 g·mol⁻¹), membrane characteristics (RO or NF), feed water matrices, and operational conditions on PFAS rejection. Our results confirmed that size exclusion is a primary mechanism of PFAS rejection by RO and NF, as well as the fact that electrostatic interactions are important when PFAS molecules have sizes less than the NF membrane pores. Practitioner PointsTwo commercial RO and NF membranes were both evaluated to remove 10 different PFAS.High transmembrane pressures facilitated permeate recovery and PFAS rejection by RO.Electrostatic repulsion and pore size exclusion are dominant rejection mechanisms for PFAS removal.pH, ionic strength, and organic matters affected PFAS rejection.Mechanisms of PFAS rejection with RO/NF membranes were explained by PCA analysis. 

Recently, a mixture of hemoglobin (Hb) and bovine serum albumin (BSA) was separated into two highly purified fractions with high recovery via internally staged ultrafiltration (ISUF) having a stack of three identical flat 100 kDa ultrafiltration (UF) membranes in a stirred cell. Selectivities as high as 1000–4000+, and high recoveries of individual species were achieved. Successful separation and purification of IgG from a BSA-IgG mixture was also achieved in a stirred cell using a modified ISUF technique with two 100 kDa membranes on a 70 kDa membrane; here BSA was a model for host cell proteins (HCPs) in post-protein A eluate. We explored here separation and purification of the Hb-BSA system in a developmental cassette of 88 cm2 membrane surface area, having a stack of three 100 kDa membranes on each side of the channel. The channel gap was smaller than that in regular cassettes resulting in higher flow pressure drops. The Hb-BSA separation was studied over a diavolume (DV) range of ~0–6. The Hb-BSA selectivity was as high as 1600 and remained above 300 till 6 DV. Lower feed pressure and a particular permeate collection mode leading to reduced transmembrane pressure drop were crucial for higher performance. Species recoveries were lower for the DV range used especially compared to those in a stirred cell. Successful separation and purification of BSA-IgG system was also demonstrated with similar limitations. Increased flow pressure drop due to flow channel height reduction in existing cassette frames and lower flow rates leading to higher concentration polarization suggest modification of the cassette frame for high performance ISUF for difficult-to-separate protein mixtures in biopharmaceutical separation processes. 

In porous hollow fiber membrane (HFM) based anti-solvent crystallization (AsCr) technique, the anti-solvent is injected from HFM bore into the active pharmaceutical ingredient (API) containing solution flowing in the shell side. Conventionally, shell-side feed solution flows along the HFM. In our compact module design, the shell-side liquid flows perpendicular to the HFMs; the mean flow length is ~ 3 cm reducing considerably the residence time (tres) which strongly influences crystal growth. We investigated AsCr of griseofulvin (GF) from its acetone solution using anti-solvent water injected through HFM pores. The range of tres was 5–30 s; the volume flow rate ratio (FRR) of acetone/water ranged between 0.35 and 1.66; griseofulvin concentration was varied between saturation (3.73 g/100 g acetone) to 0.4 g GF in 100 g of solution having 50 wt% acetone in the total solution. Low tres yielded nanocrystals < 100 nm. The average API crystal size (Davg) remained around 230 nm in a three hour- long experiment. At a fixed mass FRR of 1.34 ±0.1, Davg increased linearly from 48 to 280 nm as tres increased from 5 to 28 s. For two HFM modules in series with the nanocrystal suspension from one module fed to the next module independently fed with anti-solvent water, GF crystallization yields as high as 98 % were achieved. AsCr of L-glutamic acid in water with anti-solvent acetone in the same device illustrated continuous nanocrystal production and similar behaviors vis-`a-vis variations of tres and FRR. The cross-flow HFM based continuous AsCr technique can continuously produce nanocrystals of APIs. 

An air gap membrane distillation (AGMD) module was developed by incorporating a poly(etheretherketone) (PEEK) hollow fiber membrane (HFM) having a nonporous wall. This PEEK HFM was placed inside a polyvinylidene fluoride (PVDF) hydrophobic porous wall HFM with a larger bore diameter. The outside diameter (OD) of PVDF HFM is 925 μm, small enough to be capable of achieving a high surface area packing density of 1297 m2/m3. The air gap thickness was very small, 121 μm. Hot brine flowed on the outside of the PVDF HFM; the colder liquid was passed through the lumen of the PEEK-based condenser hollow fibers. Water vapor condensed in the air gap formed between the inner surface of the porous PVDF HFM and the outer surface of the nonporous condenser PEEK fiber. With 85o C hot brine flowing at 40 mL•min􀀀1 and 5o C coolant flowing at 8 mL•min􀀀1, the water vapor flux was 9.05 kg/m2•h with a salt rejection of 98.7 %. Simulation by COMSOL Multiphysics predicted water flux and interfacial temperature of HFM, which supported the experimental observations. Moreover, the influence of module geometry, membrane characteristics and internal flow configuration on permeate flux, thermal efficiency, gained output ratio (GOR), and temperature and concentration polarization were evaluated. Principal component analysis (PCA) was used to illustrate the interconnections among various parameters and their respective contributions to water flux and other performance indicators. Air gap thickness had the strongest influence on temperature polarization. 

Membrane distillation (MD) can treat high-salinity brine. However, the system’s efficiency is hindered by obstacles, including salt scaling and temperature polarization. When properly implemented, surface patterns can improve the mass and heat transfer in the boundary layer, which leads to higher MD efficiency. In this work, the performance of direct contact membrane distillation (DCMD) using Sharklet-patterned poly (vinylidene fluoride) (PVDF) membranes is investigated. Both non-patterned and patterned PVDF membranes are prepared by lithographically templated thermally induced phase separation (lt-TIPS) process with optimized conditions. Sharklet patterns on the membranes improve the DCMD performance: up to 17 % higher water flux and 35 % increased brine-side heat transfer coefficient. The scaling resistance of the membranes during DCMD is tested by both saturated CaSO4 solution and hypersaline NaCl solutions. Patterned PVDF membranes show an average of 30 % higher water flux and up to 45 % lessened flux decline over time compared with non-patterned membranes when treating high-concentration brines. Post-mortem analysis reveals that Sharklet-patterned membranes display less salt-scaling on surfaces with smaller-sized CaSO4 and NaCl crystals, maintain a relatively cleaner surface, and exhibit better retention of hydrophobicity. 

Purification of IgG from residual host cell proteins (HCPs) in post-Protein A chromatography is important since some HCPs bind with Protein A and elute with the monoclonal antibody (mAb); removal of HCPs from CHO cell lines is essential. To that end, an advanced separation and purification technique in biopharmaceutical manufacturing, namely, internally staged ultrafiltration (ISUF), is investigated here. Choosing BSA as a model for HCPs in post-protein A eluate, separation of a binary mixture of IgG and BSA containing 1.0 mg/ml IgG and 0.1 mg/ml BSA is successfully demonstrated here using a modified ISUF technique: two Omega 100 kDa membranes on top followed by one Omega 70 kDa membrane at the bottom. This modified configuration demonstrated exceptional performance with almost complete rejection, 99 % purity, and 99.5 % retention of IgG, along with 96.5 % recovery of BSA over 10 diavolumes. This modified membrane stacking resulted from strategic considerations of membrane stacking and careful selection of molecular weight cutoffs and materials, and performance analysis of different membranes and stacking configurations using rejection behaviors, purity levels, and recovery rates under varying diavolume and pressure differential. The approach adopted here enhances flexibility in membrane choices in ISUF and provides valuable insights for optimizing membrane-based biopharmaceutical separation techniques.