UCLA

Biofouling in membrane technologies accounts for up to 50% of operational costs; its main effects include flux decline, increased required pressure, expensive pretreatment requirements, cleaning-related production interruptions and accelerated membrane replacing. Despite the efforts, current biofouling control strategies, such as feed water disinfection and chemical cleaning have not entirely solved the problem. Therefore, new approaches are being developed. Since biofouling is a biofilm based phenomena, which starts from an initial reversible bacterial adhesion, followed by irreversible attachment, cell reproduction and finally biofilm formation; it is hypothesized that preventing the initial bacterial adhesion would stop biofouling. This research exploits this idea by creating cross-linked polyvinyl alcohol (PVA) coating films with low bacterial adhesion propensity, which are subsequently embedded with antibacterial cation-exchanged zeolites (LTA), forming antibacterial nanocomposites able to inactivate bacteria from replication.

A combinatorial array of PVA films and nanocomposites were prepared with varying degree of polymerization, hydrolysis and cross-linking, as well as, different cross-linking agents, zeolite loadings and antibacterial ion utilized. Then, model bacteria reversible-irreversible adhesion and inactivation rates were analyzed, utilizing a high throughput based assay, in several aquatic matrices.

Determined free energy of adhesion and cohesion showed that most PVA films were hydrophilic and had low propensity to bacterial adhesion. Less cross-linked PVA films prepared from less hydrolyzed PVA produced more adhesion resistant films. PVA molecular weight or cross-linking agent did not affect significantly the outcomes. Overall, the bacterial attachments decreased with increasing free energies, but correlations were low because of large adhesions variability. This leaded to concluded that physical heterogeneity of the films, like nanoscale features formation, were significant in the biofouling propensity.

The effect of embedded zeolites on bacterial adhesion varied with the type of antibacterial ion and zeolite loads. Nanocomposites with Ag-LTA (10%) or Zn-LTA and the combined AgCuZn-LTA had lower irreversible adhesion than corresponding PVA films. While, Cu-LTA worsened the antiadhesive properties, because of a higher surface roughness and a higher rate of inactivation; that left more dead cells, which are more prone to adhesion, on the nanocomposite surface. Overall, irreversible adhesions correlated more strongly with surface roughness than free energy of adhesion.