Towards a Greener Future: Sustainable Membrane Fabrication for Wastewater Treatment
Creators: Mizan, Md Mizanul Haque
Publisher: name: University of Alberta Library
Year: 2024

<pre><code>Large-scale membrane technology has seen significant growth over the past 40 years. Despite its advancements, the industry lacks sustainability and cannot be considered entirely environmentally friendly. Membrane manufacturing primarily depends on nonbiodegradable petroleum-based polymers and hazardous solvents. These materials contribute to the energy crisis, pose disposal challenges and present risks to human health and the environment. Given the increasing energy crisis and environmental pollution concerns, the eco-friendly transformation of this engineering sector is imperative. Consequently, there is growing interest in utilizing bio-based polymers to enhance sustainability in membrane fabrication, with a particular focus on biodegradable materials. In the realm of sustainable and green chemistry, the exploration of greener alternative solvents is underway for membrane fabrication. This PhD research aims to develop a more sustainable approach for producing high-performance membranes using biodegradable materials and green solvents.
The first part of the study focused on developing high-performance poly (sodium 4-styrene sulfonate) (PSS) and polyethyleneimine (PEI) based polyelectrolyte complex membranes using an organic solvent-free aqueous phase separation (APS) process. This work aimed to enhance the pure water permeability (PWP) of the membrane, which is a primary concern for APS-based membranes. In order to achieve this goal, two key parameters—monomer mixing ratio and casting solution temperature—were varied. The results showed that nanofiltration and ultrafiltration membranes with different molecular weight cut-off values could be obtained by controlling these parameters. Optimal PSS/PEI monomer mixing ratios of 1:1.65 and 1:1.70 produced nanofiltration membranes with high pure water permeability and excellent divalent salt retention. On the other hand, PSS/PEI monomer ratios of 1:1.75 and 1:1.80 led to ultrafiltration membranes with high BSA retention and increased PWP. The casting solution temperature was found to be a crucial parameter in controlling the phase separation kinetics, resulting in membranes with different pore sizes and permeabilities. The increase in casting solution temperature from 25 to 60°C resulted in ultrafiltration membranes with high BSA retention and increased PWP. 
In the second part, an eco-friendly and biodegradable electrospun membrane was fabricated using the electrospinning technique. The goal of this study was to enhance the sustainability of the membrane fabrication process by utilizing biodegradable materials and non-toxic green solvents. This was achieved by using biodegradable polycaprolactone (PCL) and sulfonated kraft lignin (SKL) blend as the membrane material. Additionally, using acetic acid as a benign solvent for preparing the PCL/SKL electrospun membrane prevented secondary pollution and contributed to the overall green approach. The influence of SKL content on the surface morphology, chemical composition, and mechanical properties of the electrospun membrane was studied in detail. Membranes modified with SKL exhibited superhydrophilicity and underwater superoleophobicity, with water contact angles of 0° and underwater oil contact angles over 150°. These membranes demonstrated high pure water flux (800-900 LMH) and effective emulsion flux during gravity-driven filtration, with superior anti-oil-fouling performance. Moreover, the SKL-modified membrane showed consistent performance after several cycles and maintained stability across a wide pH range. 
The last part of this research presents a facile and scalable method for fabricating a green and biodegradable PCL/SKL-based ultrafiltration membrane using a nonsolvent-induced phase separation approach. The study examined the impact of SKL content within the PCL matrix using various characterization techniques and evaluated the dye/salt separation performance of the prepared membranes. This is the first exploration of SKL and PCL as compatible materials for preparing biodegradable phase inversion membranes using acetic acid as a green solvent. The proposed method ensures simplicity and scalability in the membrane fabrication process.
The overall findings of this PhD research contribute significantly to advancing sustainability in membrane fabrication processes, offering insights into developing high-performance, eco-friendly membranes with potential applications across various fields.
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