Effects of chemical preservation on flux and solute rejection by reverse osmosis membranes

Abstract

a b s t r a c tThis study investigates the impacts of chemical preservation on the performance of polyamide reverse osmosis membranes with respect to water permeability and solute rejection. Three preservative chemicals, namely formaldehyde, sodium metabisulfite, and 2,2-Dibromo-3-Nitrilopropionamide, were evaluated for membrane preservation at pH 3 and 7. Experimental data show that chemical preservation may change the membrane surface properties, and consequently water permeability and solute rejection efficiency of the membrane are negatively impacted. The impacts of preservation on boron rejection and sodium rejection are similar in magnitude and more significant than those on water permeability. The results indicate that the impact of chemical preservation on the membrane depends on both the preserving chemicals used and the solution pH value. More importantly, the undesirable impacts of chemical preservation can be minimised by appropriate selection of the preservatives and by preserving the membrane in a reducing condition. A near-neutral pH (i.e., pH 7) is necessary to avoid any significant negative impacts on membrane performance due to chemical preservation using either formaldehyde or sodium metabisulfite. Results reported here suggest that the previously recommended minimum pH value of 3 of the preservative solution may be inadequate.Crown

Chlorination disadvantages and alternative routes for biofouling control in reverse osmosis desalination

“…Therefore, pH of the added solution should be maintained to avoid bad impact on the performance of PA RO membrane, as exhibited in RF. 58 Adding SBS with pH close to 7 was not detrimental for the RO membrane and its permeability, however, it impacted the rejection performance.…”

Customizing the surface charge of thin-film composite membranes by surface plasma thin film polymerization

“…In addition, the decrease of the hydroxyl density initially, may be therefore directly attributed to the physical etching by the plasma of that very thin preservative layer 32 . It is possible that the presence of the preservative materials 33 , which was not washed away in these tests, may have been reacted within the first few minutes of the plasma treatment.…”

Reverse osmosis membrane composition, structure and performance modification by bisulphite, iron(III), bromide and chlorite exposure

“…The methodology used for 153 data fitting was analogous to the one described in Saenz de Jubera et al (2012). 154 RO membrane performance variability is a concern in membrane degradation studies; some 155 works have encountered permeation discrepancies up to 20 % between elements of the same 156 membrane name (Tu et al, 2014). Four virgin membrane coupons were initially characterised 157 obtaining low variability in terms of water and chloride permeation coefficients: A parameter 158 did not differ more than 6 % and B, 11 % between them.…”