Effect of the type and concentration of multivalent cations on the durability of polymeric media for degrading quorum sensing signaling molecules in membrane bioreactors

Quorum quenching (QQ) techniques have been applied to membrane bioreactors (MBRs) to inhibit biofouling in the form of polymeric media entrapping QQ bacteria, called QQ media. However, concerns about the durability of QQ media during long-term operation have been raised. To address this, the degree of cross-linking in QQ media was enhanced by either increasing the Ca²⁺ concentration in the 1st cross-linking solution or changing the type of multivalent metal cation in the 2nd cross-linking solution. The QQ beads fabricated under these conditions were compared to those of previously developed conditions in terms of physical durability and biological QQ efficiency. The improved QQ beads demonstrated greater durability, as confirmed by measurements of hardness, swelling ratio, and alginate leakage. In addition, they showed higher QQ efficiency, which was verified through bioassay and analysis of internal microorganisms. The results indicated optimal performance when the 1st cross-linking solution had 16 % w/v CaCl₂, or when the 2nd cross-linking solution contained Al³⁺ as the metal cation, with 0.1 M Al₂(SO₄)₃. Finally, the lifespan of the improved QQ beads was estimated using an experimentally derived formula, suggesting that the lifespan of 16 % w/v CaCl₂ and 0.1 M Al₂(SO₄)₃ QQ beads indicated an increase by factors of 2.71 and 3.35, respectively, when compared with the conventional QQ beads.