Factors affecting the rejection of organic solutes during NF/RO treatment—a literature review

https://escholarship.org/content/qt50r1b9sg/qt50r1b9sg.pdf?t=ok16ag

Engineered nanomaterials for water treatment and remediation: Costs, benefits, and applicability

The removal mechanisms of four natural steroid hormones-estradiol, estrone, testosterone, and progesterone-by nanofiltration (NF) membranes were investigated. Two nanofiltration membranes with quite different permeabilities and salt retention characteristics were utilized. To better understand hormone removal mechanisms, the membrane average pore size was determined from retention data of inert organic solutes of various molecular weights and a pore transport model that incorporates steric (size) exclusion and hindered convection and diffusion. Results indicate that, at the early stages of filtration, adsorption (or partitioning) of hormones to the membrane polymer is the dominant removal mechanism. Because the adsorptive capacity of the membrane is limited, the final retention stabilizes when the adsorption of hormones into the membrane polymer has reached equilibrium. At this later filtration stage, the overall hormone retention is lower than that expected based solely on the size exclusion mechanism. This behavior is attributed to partitioning and subsequent diffusion of hormone molecules in the membrane polymeric phase, which ultimately results in a lower retention. Hormone diffusion in the membrane polymeric matrix most likely depends on the size of the hormone molecule, hydrogen bonding of hormones to membrane functional groups, and hydrophobic interactions of the hormone with the membrane polymeric matrix.

/pdf/removal-of-natural-hormones-by-nanofiltration-membranes-30uewa1db4.pdf

Removal of Natural Hormones by Nanofiltration Membranes: Measurement, Modeling, and Mechanisms

https://www.dora.lib4ri.ch/eawag/islandora/object/eawag%3A18122/datastream/PDF3/Rizzo-2019-Consolidated_vs_new_advanced_treatment-%28accepted_version%29.pdf

Consolidated vs new advanced treatment methods for the removal of contaminants of emerging concern from urban wastewater.

The ability of a variety of nanofiltration and reverse osmosis membranes to retain the natural hormone estrone are examined here as a function of solution conditions. While size exclusion dominates retention with the tighter membranes, both size exclusion and adsorptive effects appear to be instrumental in maintaining high retention on nanofiltration membranes that otherwise exhibit relatively low ion retentions. These adsorptive effects may be driven by hydrogen bonding between estrone and the membrane. Electrostatic attraction appears to aid retention with an apparent slight decrease in retention at high NaCl concentrations. Deprotonation of estrone leads to a significant decrease in retention, most likely as a result of the effect of strong electrostatic repulsive forces decreasing the proximity of the negatively charged estrone to the negatively charged membrane surface and thus lowering the potential for adsorptive retention. This deprotonation effect is absent for tight RO membranes. The results rep...

/pdf/removal-of-the-natural-hormone-estrone-from-aqueous-2s9jqfizlg.pdf

Removal of the Natural Hormone Estrone from Aqueous Solutions using Nanofiltration and Reverse Osmosis

Predictive reverse osmosis (RO) models have been well-developed for many systems. However, the applications to dilute organic−water systems require the modification of transport models and the understanding of solute−polymer interactions. Studies with various substituted, nonionized phenolic compounds showed that these could cause substantial membrane water flux drop, even in dilute solutions with negligible osmotic pressure. Further, the organics could significantly adsorb on the cross-linked aromatic polyamide active layer. In some cases, even concentrations as low as 0.2 mM, 2,4-dinitrophenol (solution in particle-free, double-distilled water) can cause as much as a 70% flux drop with an aromatic polyamide membrane. Two models are presented in this paper:  a modified steady-state solution diffusion model and an unsteady-state diffusion adsorption model which are able to predict flux and permeate concentrations from a single RO experiment. Further, the development of these models allows for the understa...

C. N. Smothers

Papers

Separation of organic pollutants by reverse osmosis and nanofiltration membranes: Mathematical models and experimental verification

Nanofiltration of Charged Organic Molecules in Aqueous and Non‐aqueous Solvents: Separation Results and Mechanisms