Understanding of membrane fouling phenomena and fouling characteristics in pharmaceutical separation

• Main Author: Navin Raj S/O Tamilselvam
• Other Authors: Lee Jong-Min
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Chemistry; Earth and Environmental Sciences; Engineering
• Online Access: https://hdl.handle.net/10356/181534
• Institution: Nanyang Technological University

Adopting a circular approach, where water and wastewater are treated and reused, becomes paramount in maintaining an ecologically sustainable balance for our environment. Equally crucial is effective wastewater management, particularly in water-intensive sectors like the pharmaceutical industry, known for its diverse manufacturing processes and substantial cleaning demands. As the pharmaceutical sector acknowledges the significance of sustainability and environmental awareness, driven by its substantial water consumption and high wastewater volumes, it becomes imperative to embrace more efficient water management practices. In this context, the adoption of water recycling, reuse, and advanced wastewater treatment technologies, including membrane filtration, holds great potential in reducing water usage and mitigating wastewater generation during pharmaceutical production. Membrane filtration, with its ability to enhance water treatment processes, emerges as an attractive option for industries seeking eco-friendly practices and water conservation. However, despite its promise, the practical implementation of membrane technology faces a major challenge in the form of membrane fouling. This issue hinders its smooth application in commercial settings. To overcome this obstacle effectively, a comprehensive investigation into the fundamental fouling mechanisms associated with various types of foulant particles is crucial. This deeper understanding will pave the way for refining membrane filtration technology and making it more efficient and sustainable for industrial applications. Membrane fouling stands as a critical challenge in membrane filtration processes, and while the effects of various operating parameters have been extensively studied, the influence of particle shape remains relatively unexplored. To bridge this gap, our study delved into investigating the impact of polystyrene particle sphericity, namely sphere, peanut, and pear shapes, on external membrane fouling. Additionally, we examined the effect of particle charge, including unmodified, carboxylated, and aminated particles. Employing the Direct Observation Through the Membrane (DOTM) technique, we observed fouling behaviors and determined the critical flux of polystyrene particles at different concentrations and crossflow velocities (CFV). The results obtained from DOTM revealed that non-spherical particles, such as peanut and pear shapes, exhibited higher critical flux values compared to spherical particles. This difference was attributed to the looser packing of the cake due to the varied particle orientations in non-spherical shapes. Even at higher CFVs, the distinctions in critical flux values among particles with different surface charges persisted, indicating the persistent impact of particle shapes. In the context of dead-end filtration, non-spherical particles showed lower flux declines than their spherical counterparts, further emphasizing the importance of particle shape in membrane fouling. The shear-induced diffusion model effectively predicted the behavior of all five particle types. To quantify the interaction energies, we applied the Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (XDLVO) models, with XDLVO calculations providing better agreement with the relative critical flux trends of all polystyrene particles. Regarding the flux decline trends, both DLVO and XDLVO results demonstrated good agreement, offering valuable insights into the complex fouling mechanisms associated with particle shape and charge. To harness the advantages of membrane-based separation in the pharmaceutical and chemical industries, a thorough understanding of membrane fouling in organic solvents becomes paramount. Specifically targeting the separation of biocatalysts in pharmaceutical manufacturing, our study focused on investigating membrane fouling by bovine serum albumin (BSA) in various solvent mixtures: 10% v/v isopropanol (IPA), 10% v/v dimethyl sulfoxide (DMSO), 30% v/v IPA, and 30% v/v DMSO, benchmarked against water. The presence of either IPA or DMSO exacerbated the fouling phenomenon, with DMSO showing comparatively worse fouling behavior. To unravel the underlying fouling mechanisms, we employed various analytical techniques. Field Emission Scanning Electron Microscopy (FESEM) images were captured to assess the extent of external fouling, while Evapoporometry (EP) provided crucial information about the pore-size distributions of fouled membranes, aiding in the examination of internal fouling. A fouling model was skillfully applied to extract the fouling parameters, and interfacial interaction energies were derived to gain deeper insights into the fouling process. Our findings revealed that the worst fouling in 30% v/v DMSO resulted from a combination of significant external and internal fouling. On the other hand, the second-worst fouling by 30% v/v IPA was predominantly attributed to internal fouling. Interestingly, the magnitudes of the total interaction energies derived from DLVO and XDLVO models exhibited a weak correlation with the relative flux declines. These results offer valuable insights into the intricate mechanisms governing membrane fouling in distinct solvent environments. By shedding light on membrane fouling in organic solvents, this study opens doors to better exploiting membrane-based separation techniques in pharmaceutical and chemical industries. Understanding the fouling behaviors in different solvent mixtures enables more informed decisions and optimizations in membrane filtration processes, thereby enhancing overall process efficiency and sustainability.