Catalytic Membranes for Water Quality Engineering

Potable and non-potable water recycling from wastewater has become a key element of water infrastructure, particularly in regions where urbanisation, industrialisation, and climate change are placing considerable stress on the hydrological cycle. Pressure-driven membrane processes such as reverse osmosis (RO) are central to advanced wastewater treatment schemes, given their high removal of colloidal and dissolved contaminants. In Scotland alone, 45% of the water treatment infrastructure is underpinned by membrane processes. Nonetheless, state-of-the-art RO membranes do not achieve sufficient removal of small (molecular weight < 150 Da) neutral molecules. Among this class of compounds, nitrosamines such as N-nitrosodimethylamine (NDMA), a by-product of chlorination of wastewater effluent, is significantly concerning due to its carcinogenicity and genotoxicity. Removal of NDMA and other nitrosamines thus requires post-treatment and conversion to less hazardous end-products. Among post-treatment processes, UV photolysis is effective in degrading nitrosamines to less harmful amines, but involves high energy costs, while advanced oxidation by ozone or H2O2 is inefficient due to scavenging of hydroxyl radicals by natural organic matter and bicarbonate ions.

Reductive post-treatment has emerged as an alternative strategy for remediation, with catalysts such as Pd and Ru exhibiting extremely high activity for the H2 reduction of ­N-nitrosamines to ammonia and secondary amines, both of which are much less harmful compounds. Notwithstanding their high activity and stability, Pd and Ru-catalysed remediation still involves a separate unit operation downstream of the RO stage, requiring disposal of reduction products, and continuous H2 dosage to observe quantitative nitrosamine removal. If Ru/Pd catalytic NPs could be integrated into the RO membrane material, it would eliminate the requirement of costly post-treatment of the RO permeate (see scheme). Moreover, use of a membrane process would decrease the dose of H2 that would otherwise be needed for nitrosamine reduction, as the boundary layer formed near the membrane surface would yield a locally high concentration of contaminants and chemisorbed H2, thereby speeding reaction kinetics. Finally, a membrane process would decrease the concentration of reaction end-products in the treated water. This PhD studentship will demonstrate, for the first time, the integration of hydrogenation-metal-based catalytic NPs into polyamide RO membranes for the physicochemical removal of nitrosamines and other micropollutants.