Membrane fouling study : from fundamental theory to industrial fouling mitigation
Creators: name: Cheng, Yu-Heng
name: 0000-0003-4565-7244
Publisher: name: The University of Texas at Austin
Year: 2021
Subjects: Fouling model
Fouling mitigation
Ultrafiltration membrane

description: Membrane filtration is widely applied to the treatment of sewage, wastewater from the biomedical industry, and flowback water from hydraulic fracturing, but fouling remains a key challenge in these applications. Membrane fouling increases mass transfer resistance and energy consumption. Severely fouled membranes require expensive cleaning or replacement, which increases operating costs and reduces filtration efficiency. Modelling membrane fouling can advance our understanding of filtration processes and improve our ability to predict the onset and severity of fouling. This study focuses on developing fouling models in constant flux crossflow operations, commonly used in industry, and on developing fouling-resistant coatings to mitigate membrane fouling in industrial filtration applications. Two fouling mechanisms from the accepted Hermia’s model, intermediate pore blocking and cake filtration, were modified and combined together to describe fouling in constant flux crossflow ultrafiltration (UF). The model gave a qualitatively good fit to experimental fouling results using rigid latex bead particles and deformable oil droplets. Observations of the model’s accuracy at different fluxes shed light on the physical meaning of the threshold flux: the flux below which cake buildup is negligible and above which cake filtration becomes the dominant fouling mechanism. Although the model that combines intermediate pore blocking (IPB) and cake filtration can qualitatively described fouling by latex beads and emulsified oil, the IPB model fails at high foulant concentrations or high permeate flux. To resolve this issue, the IPB model has been replaced with a complete coverage model (CCM). CCM was combined with the cake filtration model, and then compared to the previous combined IPB/cake filtration model. Constant flux crossflow fouling experiments were conducted using dilute latex bead suspensions and commercial poly(ether sulfone) flat sheet ultrafiltration membranes to investigate the influence of operating conditions (foulant concentration, permeate flux, etc.) on the evolution of transmembrane pressure profile. The CCM/cake filtration combined model provides better agreement with experimental data than does the IPB/cake filtration combined model. To mitigate fouling in oil-water separations, a new approach to preparing hydrophilic membrane coatings based on 1,4-benzoquinone and various commercially available polyetheramines was developed. These coatings, prepared specifically from 1,4-benzoquinone and Jeffamine® EDR 148, poly(benzoquinone-Jeffamine® EDR 148) (p(BQ-EDR 148)), were used to modify polysulfone (PS) ultrafiltration membranes. In fouling experiments using an oil/water emulsion, membranes exhibited comparable fouling resistance to that of a polydopamine (pDA) modified membrane, a commonly used surface-modified membrane. Based on contact angle measurements, p(BQ-EDR 148) and pDA modified membranes have similar levels of hydrophilicity, and both exhibited higher threshold flux values than did their unmodified analogs. Based on their similar threshold flux values, p(BQ-EDR 148) (76 LMH) and pDA modified membranes (74 LMH) should have similar fouling resistance. Moreover, the mean pore size of p(BQ-EDR 148) modified membranes can be tuned, while keeping the pure water permeance constant, by changing the deposition time and molar ratio of benzoquinone to EDR 148 in the modification solution.