Abstract
Type of metal and metal-oxide NPs added to modify Thin-Film Composites Reverse Osmosis Membranes (TFC-RO) can alter their anti-biofouling properties by changing the dissolution process. The development of a mathematical model can facilitate the selection of these NPs. This work consists of a mathematical and experimental methodology to understand copper-based NPs dissolution of three copper species incorporated into TFC-RO membranes: Cu-NPs, CuO-NPs and Cu-Oligomer complexes formed in situ during the polymerization process. Biocidal capacity of copper species into the membrane was evaluated using colony forming unit method (CFU) over E. coli. In addition, copper ion release kinetics for both NPs and modified membranes were determined. A model based on the shrinking core model (SCM) was validated and applied to determine the limiting rate step in the dissolution process and simulate the ion release kinetics. Fitted curves reached a good adjustment with the experimental data, demonstrating the SCM can be applied to predict ion release process for copper-based NPs in suspension and the modified membranes. All membranes reached similar inhibition rate >50%, however, differences in the dissolution level of copper-based NPs in membrane were noted, suggesting a dual-type effect that defined the copper toxicity into the membrane, associated to the dissolution capacity and ROS production.
Highlights
Thin film composite (TFC) membranes are the best-known polymer membranes for reverse osmosis (RO) with applications in the desalination of seawater
The shrinking core model (SCM) model was applied and evaluated to predict and simulate the ion release kinetics of three copper species incorporated into Thin-Film Composites Reverse Osmosis Membranes (TFC-RO) membranes: Cu-NPs, CuO-NPs and Cu-Oligomer complexes formed in situ during the polymerization process
The linearization of the experimental dates by the SCM method showed that the diffusion though porous shell is the control step for all cases, both copper-based NPs in suspension and for the modified TFC-RO membranes with them, showing a diffusional control over the dissolution reactions with correlation coefficient R2 around of 0.95
Summary
Thin film composite (TFC) membranes are the best-known polymer membranes for reverse osmosis (RO) with applications in the desalination of seawater. TFC-RO membranes typically consist of an ultrathin polyamide (PA) layer obtained from the reaction between diamine in water phase and acyl chloride in organic phase. TFC membranes are the most used membranes in the RO process because of their excellent water flux and solute rejection [1,2,3], but they are susceptible to fouling issues [4]. Organic and inorganic fouling are major concerns in the desalination by RO membrane process industry worldwide [5]. Attached bacterial growth on the membrane surface forms a biofilm, which increases the pressure drop in the system by creating additional resistance in the feed channel [6,8]. Regeneration capacity of some biofilms makes traditional treatments such as chlorine or backwashing ineffective where repeated treatments are needed, increasing operational costs and limiting the lifetime of the membrane [6,10]
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