Charge-induced modifications for enhanced membrane performance in water treatment

Abstract

To ensure sufficient water purification resources amidst the current water crises, existing treatment methodologies should be improved on. The focal methodology of this work, membrane technology, is a comprehensive way of purifying drinking water or wastewater or both simultaneously. Commonly used commercial membranes do, however, have fundamental issues related to their inevitable fouling that eventually gives them end-oflife status. One way of mitigating this problem is to use more fouling-resistant membranes made of cellulose, for example, but these are quite prone to hydrolytic damage.

This thesis explores possibilities for expanding the lifetime of polyamide and cellulosic membranes. End-of-life polyamide membranes are reconditioned into working order and cellulosic membranes are made more durable to extend their lifespan. The joint strategy is to perform a charge-enhancing pretreatment, which is followed by charge-driven coating procedures using materials like polyelectrolytes. The treatments are studied stepby-step, and both types of improved membranes are subjected to water purification application tests to examine the benefits of the modifications.

Firstly, charge enhancement was found to be useful for improving the quality and adhesion of coatings. Secondly, the coating systems could be designed so that they have different properties. For instance, a thin and rather sparse polyelectrolyte coating was applied on a cellulosic ultrafiltration membrane to protect it from enzymatic degradation. While acting as a shield, the modification sustained the desired native properties of the underlying membrane. Moreover, in a reconditioning protocol for end-of-life polyamide membranes, the coatings were successfully used to fine-tune the filtration characteristics, even inside a spiral wound element. The properties of the reconditioned membrane were even competitive compared to state-of-the-art commercial membranes.

Ultimately, the water treatment applicability of commercially available membranes was improved by straightforward charge-induced modifications. By applying such methods on a larger scale, it would be possible to increase the availability of water treatment methods, potentially leading to more widespread access to clean water.