Membranes for Water and Wastewater Treatment

Inducing Deep Sweeps and Vortex Ejections on Patterned Membrane Surfaces to Mitigate Surface Fouling

Patterned membrane surfaces offer a hydrodynamic approach to mitigating concentration polarization and subsequent surface fouling. However, when subjected to steady crossflow conditions, surface patterns promote particle accumulation in the recirculation zones of cavity-like spaces. In order to resolve this issue, we numerically subject a two-dimensional, patterned membrane surface to a rapidly pulsed crossflow. When combined with cavity-like spaces, such as the valleys of membrane surface patterns, a rapidly pulsed flow generates mixing mechanisms (i.e., the deep sweep and the vortex ejection) and disrupts recirculation zones. In only four pulses, we demonstrate the ability of these mechanisms to remove over half of the particles trapped in recirculation zones via massless particle tracking studies (i.e., numerical integration of the simulated velocity field). The results of this work suggest that when combined with a rapidly pulsed inlet flow, patterned membrane surfaces can not only alleviate concentration polarization and the surface fouling that follows but also reduce the need for traditional cleaning methods that require operational downtime and often involve the use of abrasive chemical agents.

Fabrication and Characterization of Cu2+-Driven PTFE-Reinforced Artificial Muscle Polymer Membrane for Water Purification and Energy Harvesting Applications

Ionic polymer membranes have not yet gained widespread practical application in areas such as water purification and energy harvesting due to their high cost and tendency to swell. The present study involved the fabrication of reinforced textile structures composed of polytetrafluoroethylene (PTFE)-reinforced Nafion membranes coated with non-precious metals, copper and silver, as a surface electrode by applying a chemical decomposition technique. Several mechanical, contact angle measurement and dielectric tests were conducted on membranes to evaluate their mechanical, wettability and conductivity properties. From scanning electron microscopy, it is clear that the formation of surface electrodes with uniform dispersion of metal particles. Scratch test reveals the adhesive strength between the coated metal particles and membrane. The silver-activated copper-coated membrane has a high contact angle of 121°. Thus, the fabricated membranes can have good antibacterial and adsorption properties for water treatment. The copper-coated membrane has a high Young's modulus of 779 ± 80 MPa and a tensile strength of 29.1 ± 8 MPa, whereas the elongation at break is more for silver-activated copper-coated samples recorded as 158 ± 4%. The viscoelastic behavior of the membranes was analyzed through dynamic mechanical analysis (DMA). A sharp rise in the storage modulus (E') value of 4.8 × 1010 Pa at ~80 °C at a frequency of 1 Hz on metal surface electrodes signifies an improvement in the strength of the material in comparison to the initial pure membrane. The successful enhancement of conductivity on the membrane surface via chemical deposition on the silver-activated membrane is 1 × 10-4 (S/cm) and holds great potential for facilitating voltage transmission through the tribolayer in the nanogenerators.

Polyaniline nanofibers, a nanostructured conducting polymer for the remediation of Methyl orange dye from aqueous solutions in fixed-bed column studies

Polyaniline nanofibers (PANI NFs) were synthesized and employed as potential adsorbents in a continuous flow fixed-bed column adsorption study for an organic dye, Methyl Orange (MO) removal from water. These nanostructured adsorbents were characterized using ATR-FTIR, FE-SEM, HR-TEM, TGA, BET, XRD, XPS, and the Zeta-sizer. Morphological representations from SEM and TEM analyses showed that the fibers were nanosized with diameters lower than 80 nm and an interconnected network possessing a smooth surface. The SBET of the PANI NFs was found to be 35.80 m2/g. The impact of column design parameters for instance; influent concentration, flow rate, and bed mass was investigated using pH 4 influent MO solutions optimized through batch studies. The best influent concentration, bed length, and flow rate for this study were determined as 25 mg/L, 9 cm (6 g), and 3 mL/min, respectively. The column information was fitted in Thomas, Yoon-Nelson, and Bohart-Adams models. It appeared that the Thomas and Yoon-Nelson models described the data satisfactorily. The PANI NFs were able to treat 29.16 L of 25 mg/L MO solution at 9 cm bed length. A sulfate peak in a de-convoluted sulfur spectrum using XPS verified the successful adsorption of Methyl Orange.

Transport of Amino Acids in Soy Sauce Desalination Process by Electrodialysis

Soy sauce is a common condiment that has a unique flavor, one that is derived from its rich amino acids and salts. It is known that excessive intake of high-sodium food will affect human health, causing a series of diseases such as hypertension and kidney disease. Therefore, removing sodium from the soy sauce and retaining the amino acids is desirable. In this study, electrodialysis (ED) was employed for the desalination of soy sauce using commercial ion exchange membranes (IEMs). The influence of the current density and initial pH on the desalination degree of the soy sauce was explored. Results showed that the optimal desalination condition for ED was reached at a current density of 5 mA/cm² and pH of 5, with the desalination degree of 64% and the amino acid loss rate of 29.8%. Moreover, it was found that the loss rate of amino acids was related to the initial concentration and molecular structure. In addition, the amino acid adsorption by IEMs was explored. Results implied that the molecular weight and structure affect amino acid adsorption. This study illustrated that the ED process can successfully reduce the salt content of the soy sauce and retain most of the amino acids without compromising the original flavor.