Ultrafiltration and nanofiltration membrane fouling by natural organic matter: Mechanisms and mitigation by pre-ozonation and pH

Abstract

The fouling of ultrafiltration (UF) and nanofiltration (NF) membranes during the treatment of surface waters continues to be of concern and the particular role of natural organic matter (NOM) requires further investigation. In this study the effect of pH and surface charge on membrane fouling during the treatment of samples of a representative surface water (Hyde Park recreational lake) were evaluated, together with the impact of pre-ozonation. While biopolymers in the surface water could be removed by the UF membrane, smaller molecular weight (MW) fractions of NOM were poorly removed, confirming the importance of membrane pore size. For NF membranes the removal of smaller MW fractions (800 Da-10 kDa) was less than expected from their pore size; however, nearly all of the hydrophobic, humic-type substances could be removed by the hydrophilic NF membranes for all MW distributions (greater than 90%). The results indicated the importance of the charge and hydrophilic nature of the NOM. Thus, the hydrophilic NF membrane could remove the hydrophobic organic matter, but not the hydrophilic substances. Increasing charge effects (more negative zeta potentials) with increasing solution pH were found to enhance organics removal and reduce fouling (flux decline), most likely through greater membrane surface repulsion. Pre-ozonation of the surface water increased the hydrophilic fraction and anionic charge of NOM and altered their size distributions. This resulted in a decreased fouling (less flux decline) for the UF and smaller pore NF, but a slight increase in fouling for the larger pore NF. The differences in the NF behavior are believed to relate to the relative sizes of ozonated organic fractions and the NF pores; a similar size of ozonated organic fractions and the NF pores causes significant membrane fouling.

Application of coagulation‐ultrafiltration‐nanofiltration in a pilot study for Tai Lake water treatment

“…Natural organic matter (NOM) is a collective term including proteins, humic acids, fulvic acids, polysaccharides, and other dissolved organic substances (Villacorte et al, 2015;Yu, Liu, Crawshaw, Liu, & Graham, 2018), and they are considered as key contaminants in surface water treatment. The application of combined ultrafiltration (UF) and nanofiltration (NF) for NOM treatment is increasing (Ates, Yilmaz, Kitis, & Yetis, 2009;Kim & Yu, 2005).…”

Effect of pre-coagulation using different aluminium species on crystallization of cake layer and membrane fouling

“…XRD analysis of the sludges without HA, collected with different ages, showed a broad range of peaks and confirmed the presence of amorphous Al(OH) 3 with poorly ordered structure, especially for the polymeric Al (Fig. 5).…”

“…43,44 For ferrihydrite precipitate, the process of crystallization was found to be inhibited by Si. 45 Lin et al 46 confirmed that the crystalline structure of the Al 13 aggregates differed from that of Al(OH) 3 and that the Al 13 aggregates did not have a well-defined crystalline structure.…”

“…Different types of pre-treatment before membrane filtration have been explored for many years, such as adsorption, coagulation, and oxidation. [1][2][3][4] Some materials, such as powdered activated carbon (PAC), 5 heated aluminum oxide particles (HAOPs), 6,7 magnetic ion exchange (MIEX) 8 and synthesized zeolite, 9 have been studied as pre-adsorption materials to mitigate membrane fouling. An anion exchange resin before ultrafiltration can also significantly mitigate irreversible fouling and reduce the dissolved organic carbon (DOC) content of clarified water.…”

Evaluation of the effect of body fluid analogs on the parameters of nanofiltration during the purification of swimming pool water

“…It must be emphasized that the hydrophilic protein fraction also constitutes an important factor that blocks membranes [42]. An increase in the concentration of bivalent cations, a reduction in the pH of the solution, and an increase in the concentration of electrolytes significantly contribute to the contamination of membranes as a result of changes in the intermolecular electrostatic actions [44,45]. Given the presence of cations in BFA solutions, one can expect a reduction in the efficiency of membranes.…”