[Paper Review] Fouling in thin film nanocomposite membranes for power generation through pressure retarded osmosis

Arvin Shadravan, Mahmood Amani+2 more|arXiv (Cornell University)|Dec 5, 2021

Membrane Separation Technologies7 citations

TL;DR

This study develops thin film nanocomposite (TFN) membranes with enhanced hydrophilicity via nanomaterial integration to improve fouling resistance and osmotic power generation in pressure retarded osmosis (PRO). The TFN membranes exhibit higher flux and better fouling tolerance than conventional TFC membranes due to their optimized porous structure and surface hydrophilicity, demonstrating promise for sustainable salinity-gradient energy recovery.

ABSTRACT

Osmotic energy (or salinity-gradient energy) is the energy released when water with different salinities is mixed, such as rivers and oceans. By employing a semipermeable membrane to control the mixing process, the osmotic pressure gradient energy can be generated in terms of electrical power via pressure retarded osmosis (PRO) without causing adverse environmental impacts. This work presents the fabrication of thin film nanocomposite (TFN) membranes which are customized to offer high flux in forward osmosis (FO) and high osmotic power in PRO. In this study, the TFN membrane was fabricated by forming a polyamide thin film on the polysulfone substrate through the interfacial polymerization process. One of the challenges in this process is the fouling of PRO membranes. Fouling is one of the major characteristics that results in the decline in the water flux of the membrane. The hydraulic pressure during PRO processes is less than RO processes so membranes that are used for PRO are less likely to foul. Experiments show that TFN membranes are more tolerant of fouling than TFC membranes because of the nanomaterials which has higher surface hydrophilicity. The structure of the membrane is a very significant characteristic that has an influence on fouling. Especially, the structure of porosity that is coherent to the thickness.

Motivation & Objective

• To develop thin film nanocomposite (TFN) membranes with improved performance for osmotic power generation via pressure retarded osmosis (PRO).
• To reduce membrane fouling— a major limitation in PRO—by enhancing surface hydrophilicity through nanomaterial incorporation.
• To investigate the influence of membrane structure, particularly porosity and thickness, on fouling behavior and flux performance.
• To compare the fouling tolerance of TFN membranes with conventional TFC membranes under PRO operating conditions.

Proposed method

• Fabrication of TFN membranes via interfacial polymerization of polyamide on a polysulfone substrate, incorporating nanomaterials to enhance hydrophilicity.
• Use of nanomaterials within the membrane matrix to improve surface properties and reduce fouling propensity.
• Characterization of membrane structure, including porosity and thickness, to correlate structural features with performance.
• Evaluation of water flux and fouling resistance under PRO conditions, comparing TFN and TFC membranes.
• Assessment of hydraulic pressure effects on fouling, noting that lower pressures in PRO reduce fouling severity compared to RO.
• Analysis of surface hydrophilicity as a key factor in enhancing membrane tolerance to fouling.

Experimental results

Research questions

• RQ1 How does nanomaterial integration in TFN membranes affect their fouling resistance in PRO processes?
• RQ2 What is the role of membrane porosity and thickness in influencing fouling and water flux in PRO?
• RQ3 How does the surface hydrophilicity of TFN membranes compare to TFC membranes in mitigating fouling?
• RQ4 To what extent do lower hydraulic pressures in PRO reduce fouling compared to reverse osmosis (RO) systems?
• RQ5 What structural and material features of TFN membranes lead to higher osmotic power generation and better flux retention?

Key findings

• TFN membranes exhibit higher water flux and improved osmotic power generation compared to conventional TFC membranes due to enhanced surface hydrophilicity from nanomaterials.
• The incorporation of nanomaterials significantly increases membrane surface hydrophilicity, reducing the adhesion of foulants and improving fouling resistance.
• TFN membranes demonstrate greater tolerance to fouling than TFC membranes, attributed to their optimized porous structure and hydrophilic surface characteristics.
• Membrane structure, particularly the coherence of porosity relative to thickness, plays a critical role in determining fouling behavior and flux performance.
• Lower hydraulic pressures in PRO processes reduce fouling severity, making membranes less prone to flux decline compared to RO systems.
• The study confirms that structural design and surface chemistry are key determinants of long-term performance and fouling resistance in PRO membranes.