Fabrication of Functionalized Mixed Matrix Biodegradable PLA Based Membranes for Efficient Oil/Water Separation

Abstract

Global concerns over water scarcity and environmental pollution have raised awareness towards advanced and sustainable technology developments for wastewater treatment. With the scope of this work, we focused on oily wastewater. Industries such as oil and gas, petrochemicals, food processing, and metal manufacturing generate huge amounts of oily wastewater, with varying concentration of oil and grease based on the source producing it. The treatment of such wastewater is challenging, especially when oil droplets are emulsified, making conventional separation methods inefficient. Hence, membrane filtration emerged as a superior treatment technology due to its selectivity, efficiency, and potential for modification to address specific separation needs. Polymeric membranes such as polyvinylidene fluoride (PVDF) and polyether sulfone (PES) are widely adopted in wastewater treatment due to their high chemical resistance and durability. However, their long-term environmental footprint remains a growing concern. These polymers are typically derived from non-renewable petroleum sources and are non-biodegradable, contributing to solid waste accumulation at end-of-life stages. With increasing regulatory and societal pressures to reduce plastic waste and adopt circular economy practices, the development of biodegradable alternatives has become essential, particularly for applications where membrane replacement is frequent, or disposal is unavoidable.

This thesis focuses on the development of biodegradable polylactic acid (PLA)-based mixed matrix membranes (MMMs) incorporating functionalized nanoparticles to enhance hydrophilicity, anti-fouling properties, and oil-water separation performance. PLA is an attractive alternative to conventional petroleum-based polymers due to its biodegradability, biocompatibility, and adequate mechanical strength, aligning with current sustainability goals. However, its inherent hydrophobicity limits its performance in water treatment applications. To overcome this challenge, functionalized multi-walled carbon nanotubes (MWCNTs) were introduced into the PLA matrix with amino-silica (Amino-SiO2) and titanium dioxide (TiO2) functionalization to improve membrane hydrophilicity, permeability, and oil rejection efficiency.

Results revealed that the incorporation of 0.5 wt.% Amino-SiO2 functionalized MWCNTs enhanced water permeability by 75% and achieved 99% oil rejection, while 2 wt% TiO2 functionalized MWCNTs led to an 89% increase in water permeability and 99.4% oil rejection. Moreover, the UV induced-cleaning capabilities of the TiO2-functionalized membranes demonstrated excellent anti-fouling performance, maintaining total organic carbon (TOC) levels within EPA standards even after five filtration cycles, with a 100% flux recovery rate. The study further examined the integration of these membranes into dual-membrane systems to evaluate their effectiveness in mitigating fouling and removing contaminants from synthetic oily emulsions and sewage oil-spiked wastewater. Two configurations were tested: PLA/M1 (Amino-SiO2), followed by PLA/M2 (TiO2), and vice versa. The latter configuration exhibited superior durability, antifouling properties, and higher removal efficiencies, achieving 99% oil removal, 86.3% COD removal, and 92.4% total bacterial count reduction over an extended operation period when wastewater was the feed.

These findings prove the potential biodegradable PLA-based MMMs has as a sustainable alternative to the non-biodegradable polymeric membranes, addressing both the environmental impact of membrane disposal and the efficiency of oily wastewater treatment. Furthermore, by integrating advanced nanomaterials and other advanced treatment techniques such as UV radiation, sonication, etc., the membrane cleaning process can become more sustainable with minimal chemical interventions. This research contributes to the development of sustainable, high-performance membrane technologies for oily wastewater treatment, supporting global sustainability goals, sustainability visions of countries, and fostering eco-friendly technological advancements.

Date of Award	13 May 2025
Original language	American English
Supervisor	Shadi Hasan (Supervisor)