Enzymes-enabled Bio-catalytic Fouling Resistant Membranes for Wastewater Treatment

Abstract

This dissertation presents a comprehensive study on enzyme-enabled biocatalytic membranes along with 2D nanomaterials to overcome conventional methods struggle with trace contaminants, membrane fouling and selectivity issues. The first study explored the immobilization of horseradish peroxidase (HRP) and laccase (L) enzymes, along with the hydrophilic zwitterionic compound L-DOPA, on nano-filtration (NF) membranes. The objective was to evaluate the effectiveness of the enzymatic-modified membrane (HRP-NF) towards degrading colors (methyl orange and methylene blue) in wastewater and improving its resistance to organic fouling. The HRP-NF membrane showed significant removal of colors (97%) and TOC (68%). These membranes also demonstrated improved antifouling properties, with an 8% decrease in flux for HRP-NF and a 6% decrease for HRP-L-NF, attributed to their enhanced hydrophilicity and biocatalytic effects. A coumarin-based radical scavenger was also used to confirm the formation of protein radicals through enzyme and H2O2 reaction. Therefore, biocatalysis and membrane technology effectively removed industrial dyes and reduced fouling, offering dual benefits of degradation and separation. The second investigation focused on using the laccase enzyme on chitosan-based membranes to enhance fouling mitigation. A composite chitosan/MXene/GO (CMG) membrane was fabricated and coated with laccase to form a laccase-coated CMG (LCMG) membrane. Laccase significantly improved the catalytic and antifouling properties of the LCMG membrane, resulting in minimal flux decline (5%) and a flux recovery rate of 92 % after cleaning, outperforming the uncoated CMG membrane. In addition, reactive oxygen species (ROS) generation by the combined effect of laccase and MXene reduced microbial fouling by 83%, as confirmed by EPR analysis. These findings demonstrated the effectiveness of laccase enzyme-enabled biocatalytic membranes in reducing fouling and advancing sustainable water treatment. The third study targeted the removal of persistent pharmaceutical pollutants (paracetamol and ibuprofen), using four chitosan-based nanocomposite membranes - neat chitosan (CS), chitosan/MXene (CM), laccase-coated chitosan/MXene (LCM) and MnO₂/chitosan/MXene (MCM), and compared with commercial NF membrane. The LCM membrane, enhanced with laccase, demonstrated exceptional performance, achieving up to 99% removal of ibuprofen and 93% of paracetamol. The MCM membrane, which incorporated MnO₂, showed slightly lower but impressive removal rates of 98.5% for ibuprofen and 91% for paracetamol. In comparison, the CM membrane showed moderate performance, and the CS and NF membranes exhibited only 32% removal. Additionally, antifouling tests revealed a minimum flux decline and high flux recovery rates of over 93% for both LCM and MCM. Enhanced hydrophilicity, catalytic degradation, and ROS production contributed to the superior performance of LCM and MCM membranes, further supporting them as robust solutions for pharmaceutical wastewater treatment.

Hence, this thesis advances membrane technology by integrating enzymatic biocatalysis and nanotechnology to tackle EMPs and fouling. These biocatalytic membranes offer a sustainable wastewater treatment solution, combining separation, catalytic degradation, and antifouling properties for potential large-scale applications.

Date of Award	8 May 2025
Original language	American English
Supervisor	Constantinos Chrysikopoulos (Supervisor)