Membrane fouling analysis of air-gap membrane distillation (AGMD) for recovery of water and removal of antibiotics from a model wastewater containing antibiotics and humic acid.

The study investigates the efficiency of air-gap membrane distillation (AGMD) in water recovery and antibiotics removal from wastewater, focusing on high-concentration scenarios. Experimental findings reveal enhanced membrane performance with increasing the feed temperature, resulting in vapor permeate fluxes of up to 5 kg/m2.h at higher temperatures. Despite experiencing flux reduction caused by fouling from humic acid (HA) in the feed antibiotics solution, the antibiotics consistently maintain near-complete rejection rates (>99%) over 48 h. The foulant on the membrane surface was illustrated by SEM imaging. To know the temperature polarization and the fouling resistance, mathematical modeling was used, and it validates experimental results, elucidating temperature polarization effects and mass transfer coefficients. An increase in feed flow rates reduced thermal boundary layers, enhancing heat flux. Higher temperatures reduced HA fouling resistance. Therefore, AGMD proves effective in water recovery and antibiotics removal, with mathematical models aiding fouling understanding for future research and detailed computational fluid dynamics (CFD) models.

Fouling Analysis in One-Stage Ultrafiltration of Precipitation-Treated Bacillus subtilis Fermentation Liquors for Biosurfactant Recovery.

Primary recovery of surfactin from precipitation-pretreated fermentation broths of Bacillus subtilis ATCC 21332 culture by one-stage dead-end and cross-flow ultrafiltration (UF) was studied. Dead-end experiments were first performed to select suitable conditions, including the amount of added ethanol-a micelle-destabilizing solvent (0-70 vol%), type (polyethersulfone, polyacrylonitrile, poly(vinylidene fluoride)) and molecular-weight cut-off (MWCO, 30-100 kDa) of the membrane in the surfactin concentration range of 0.25-1.23 g/L. Then, the cross-flow UF experiments were conducted to check the recovery performance in the ranges of feed surfactin concentration of 1.13-2.67 g/L, flow velocity of 0.025-0.05 m/s, and transmembrane pressure of 40-100 kPa. The Hermia model was also used to clarify membrane fouling mechanisms. Finally, three cleaning agents and two in situ cleaning ways (flush and back-flush) were selected to regain the permeate flux. As for the primary recovery of surfactin from the permeate in cross-flow UF, a polyethersulfone membrane with 100-kDa MWCO was suggested, and the NaOH solution at pH 11 was used for membrane flushing.

Performance study of fouling resistant novel ultrafiltration membranes based on the blends of poly (ether ether sulfone)/poly (vinyl pyrrolidone)/nano-titania for the separation of humic acid, dyes and biological macromolecular proteins from aqueous solutions.

This study explains the use of a ultrafiltration membrane made of polyvinyl pyrrolidone (PVP) and poly(ether ether sulfone) (PEES)/Nano-titania (n-TiO2) for the separation of organic compounds. The results of the tests for porosity, water content, surface chemistry, membrane morphology, and contact angle demonstrated that the developed membranes have more hydrophilicity than PEES membranes due to the redundant hydrophilic nature of PVP and n-TiO2. The membrane pure water flux, which contains 5 wt% PVP and 1.5 wt% n-TiO2, was 312.76 Lm-2h-1, about three-fold higher than that of pristine membrane (95.71 Lm-2h-1). Employing bovine serum albumin as a model foulant, the fouling resistance of the PEES/PVP/n-TiO2 membrane was examined. According to the analysis of flux recovery ratio and irreversible resistance, modified membranes were less likely to foul, and the PEES/n-TiO2 membrane with 5% PVP addition was recommended as optimal. The fabricated membranes effectively removed more than 95% of various organic compounds such as humic acid, safranin O, egg albumin, pepsin, and trypsin from aqueous solution. Permeability of safranin O and humic acid of PEES/PVP/n-TiO2 membranes was about 118 Lm-2h-1 and 138 Lm-2h-1, respectively.

Cross-Flow Microfiltration of Glycerol Fermentation Broths with Citrobacter freundii.

This paper reports the study of the cross-flow microfiltration (MF) of glycerol fermentation broths with Citrobacter freundii bacteria. A single channel tubular ceramic membrane with a nominal pore size of 0.14 µm was used. It has been demonstrated that the MF ceramic membrane has been successfully applied to bacteria cell removal and to effectively eliminate colloidal particles from glycerol fermentation broths. However, due to fouling, the significant reduction of the MF performance has been demonstrated. In order to investigate the impact of transmembrane pressure (TMP) and feed flow rate (Q) on MF performance, 24 experiments have been performed. The highest steady state permeate flux (138.97 dm3/m2h) was achieved for 0.12 MPa and 1000 dm3/h. Fouling analysis has been studied based on the resistance-in series model. It has been found that the percentage of irreversible fouling resistance during the MF increases with increasing TMP and Q. The permeate flux regeneration has been achieved by membrane cleaning with 3 wt % NaOH and 3 wt % H3PO4 at 45 °C. The results of this study are expected to be useful in industrially employing the MF process as the first step of glycerol fermentation broth purification.

Impact of Membrane Pore Size on the Clarification Performance of Grape Marc Extract by Microfiltration.

The influence of membrane pore size on the permeate flux, fouling mechanism, and rejection of soluble and suspended solids, as well as of phenolics and anthocyanins, in the clarification of grape marc extract by microfiltration (MF) was studied. MF was operated by using three monotubular ceramic membranes with a pore size of 0.14, 0.2, and 0.8 µm, respectively, according to a batch concentration configuration in selected operating conditions (2.25 bar as operating pressure, 4.93 L/min as feed flow rate, and 25 °C as operating temperature). No significant differences in the permeate flux values were appreciated despite the difference in pore size. The mathematical analyses of the flux behavior revealed that intermediate pore blocking is the predominant mechanism for 0.14 and 0.2 µm membranes, whereas complete pore blocking prevails for the 0.8 µm membrane. Differences in the fouling mechanism were associated with differences in the total phenols rejection: the highest rejection was observed for the 0.8 µm membrane followed by 0.2 and 0.14 µm membranes. All selected membranes showed low rejection of sugars, with values lower than 10%, and no retention towards anthocyanins. All the clarified extracts showed a turbidity lower than 4.87 NTU. Based on the experimental results, the 0.14 µm membrane appeared as the best option for the clarification of grape marc extract.