Mechanism of sodium alginate (SA) fouling with the co-existing cations in membrane distillation process

Abstract

The interaction between organic and inorganic membrane fouling has garnered extensive attention. However, the specific roles of co-existing cations in alginate-induced fouling during the membrane distillation (MD) process remain inadequately investigated. This study explored the influence of sodium and calcium ions on the fouling behavior of sodium alginate (SA) in MD. Results illustrate that fouling tendency followed the order: SA (adding Na⁺) group > SA (adding Na⁺ and Ca²⁺) group > SA (adding Ca²⁺) group > pure SA group. Moreover, the addition of salts facilitated the formation of reversible fouling, with Na⁺ contributing to higher reversible membrane resistance due to salt crystal growth. As ionic strength increased, the flux decline rate gradually accelerated in both the SA (adding Na⁺) and SA (adding Na⁺ and Ca²⁺) groups. Conversely, elevating the ionic strength of Ca²⁺ mitigated fouling by forming loose, hydrophilic gel-like structures. Additionally, modified Hermia fouling models, along with the concentration polarization model, were used to gain deeper insights into the mechanisms of membrane fouling.