Effect of multivalent cations on membrane‐foulant and foulant‐foulant interactions controlling fouling of nanofiltration membranes

Abstract

Insight was gained into the various factors influencing membrane fouling in the presence of different cations. Membrane‐foulant interaction energies were computed from contact angle measurements following the Lifshitz‐van der Waals/acid‐base approach. A unique approach was used to investigate cake‐enhanced concentration polarization (CECP) effects. Calcium worsened organic fouling through organic‐calcium complexation and increasing foulant affinity for the membrane surface, whereas magnesium and lanthanum had less influence on membrane fouling as they moderately decreased the foulants' affinity for the membrane surface. Fouling was facilitated by permeation drag and reduction in membrane‐foulant electrostatic repulsive interactions due to slight neutralization of foulant and membrane zeta potential. Although cake layers formed in the presence of magnesium and lanthanum had low resistance to water flow, the cake layers resulted in severe CECP effects. Initial membrane fouling rates related well to energies of adhesion, whereas later fouling rates did not show clear correlation to energies of cohesion.

Quantitative Assessment of Interfacial Interactions Governing Ultrafiltration Membrane Fouling by the Mixture of Silica Nanoparticles (SiO2 NPs) and Natural Organic Matter (NOM): Effects of Solution Chemistry

“…As shown in Figure 2c, the absolute value of zeta potential gradually decreased with the increase in calcium ion concentration, implying that the SiO 2 NP-NOM mixture will become more unsteady and more accessible for aggregation at higher concentrations. This phenomenon is in agreement with previous studies, which reported that calcium ions could reduce the negative charge of SiO 2 NPs or NOM [27,30,46]. This is attributed partly to double-layer compression and charge screening, and partly to the complexation of calcium ions with the carboxylic groups on the surface of the SiO 2 NP-NOM mixture resulting in charge neutralization.…”

“…The contact angles of the PES UF membrane and the SiO 2 NP-NOM mixture were measured using a contact angle analyzer (JC2000C Contact Angle Meter, Shanghai Zhongchen Experiment Equipment Co. Ltd., Shanghai, China) based on the sessile drop method [23,28,29]. The SiO 2 NP-NOM mixture was first deposited on the PES UF membrane using the deadend stirred-cell filtration system, and then subjected to contact angle measurement [30]. The measurement of contact angle was performed at the time of two seconds after the liquid drop formed on the clean PES UF membranes or the PES UF membranes covered with SiO 2 NP-NOM mixture.…”

“…Although the impacts of solution chemistry on the surface charges of SiO 2 NPs and NOM alone have been well documented in previous studies [30,38,[45][46][47][48], information on SiO 2 NP-NOM mixtures under different solution condition is still lacking. It can be seen in Figure 2a that, with increasing pH, the SiO 2 NP-NOM mixture surface became strongly charged, as reflected in the higher absolute value of negative zeta potential.…”

Tuning nanofiltration membrane performance: OH–MoS2 nanosheet engineering and divalent cation influence on fouling and organic removal

“…The lower impact of Mg 2+ ions on HA fouling could also be linked to the high affinity of Mg 2+ ions for water molecules and its strongly held hydration shell, which weakens its interaction with HA compared with Ca 2+ [ 53 ]. In contrast to many studies reporting a higher fouling impact of HA foulants in the presence of Ca 2+ , studies have also reported a superior charge screening effect and charge density of Mg 2+ to cause more severe fouling compared to Ca 2+ [ 3 , 54 ]. However, cation interactions with NOM and associated fouling are highly dependent on NOM content, feed water chemistry, membrane surface properties, and operating parameters of nanofiltration [ 5 ].…”

Inorganic and Organic Silicon Fouling of Nanofiltration Membranes during Pilot-Scale Direct Potable Reuse

“…Importantly, silicon concentrations in municipal secondary effluents ,,, can be higher than typical surface and groundwaters and seawater, , which in conjunction with proteins and alginates/polysaccharides can amplify fouling of membranes employed for potable reuse. ,, Another consideration is that anthropogenic organosilicon compounds have been identified in wastewater effluents, , whose role in fouling is only beginning to be delineated . Therefore, information derived from seawater and brackish groundwater desalination is not directly applicable to potable reuse because of the extremely high degree of resilience required for DPR, and additional investigations of RO/NF fouling under representative conditions are imperative. ,,− …”