Experimental and computational investigations of the interactions between model organic compounds and subsequent membrane fouling

- Biopolymers UV254 adsorption indicative of organic acid and biopolymer associations.
- Protein-humic acid aggregate due to electrostatic, hydrophobic and hydrogen bonding.
- Divalent ion mediated associations between humic acid and polysaccharides.
- Protein-humic acid associations result in more significant fouling.
- Increased rejection of organic acids due to associations with biopolymers.

The formation of aggregates of sodium alginate and bovine serum albumin (BSA) (as representative biopolymers) with humic acid were detected by Liquid Chromatography (LC) UV254 response in the biopolymer region for mixture solutions. BSA interaction with humic acid showed that aggregation occurred both in the presence and absence of calcium, suggesting that multivalent ions did not play a part in the aggregation process. Similar analyses of the alginate interaction with humic acid also showed a positive interaction, but only in the presence of calcium ions. The fouling characteristics for the BSA-humic acid mixture appeared to be significantly greater than the fouling characteristics of the individual solutions, while for the sodium alginate-humic acid mixture, the fouling rate was similar to that of the sodium alginate alone. The effectiveness of hydraulic backwashing, 10-15% reversibility, was observed for the BSA-humic acid mixture, while the % reversibility was 20-40% for the sodium alginate-humic acid mixture. Increased humic acid and DOC rejection were observed for both BSA-humic acid and sodium alginate-humic acid solutions compared to the individual solutions, indicating that the biopolymer filter cakes were able to retain humic acids. When compared with BSA-humic acid mixture solution, greater removal of humic acid was observed for alginate-humic mixture, suggesting that sodium alginate may have a greater capacity for associations with humic acid when in the presence of calcium than BSA. Complementary molecular dynamics simulations were designed to provide insights into the specific mechanisms of interaction between BSA and humic acid, as well as between alginate and humic acid. For the BSA-humic acid system; electrostatic, hydrophobic and hydrogen bonding were the dominant types of interactions predicted, whilst divalent ion-mediated bonding was not identified in the simulations, which supported the LC-results. Similarly for the alginate-humic acid system, the interactions predicted were divalent ion-mediated interactions only and this was also supported the LC results. This work suggests that LC-UV254 might be used to identify aggregated biopolymers, and that combined with current characterisation techniques, be used to better explain performance variations between water sources.