An investigation into the occurrence of nanometer and micrometer range particles in the feedconcentrate channels of operating, production capacity reverse osmosis (RO) and nanofiltration (NF) membrane process was performed. Samples of the feed, permeate and concentrate bulk streams were sampled and submitted for particle analysis. Particle distributions using nanoparticle tracking analysis (NTA) and single particle optical sensing (SPOS) technologies were employed to evaluate the size (average diameter) and concentration of particulates in membrane process feed-concentrate channels. The ability to access commercially available nano-range analytical particle sensing equipment has expanded in recent years, such as nanoparticle tracking analysis (NTA) and single particle optical sensing (SPOS). NTA was first used to initially screen the range of particles in the membrane feed-concentrate channel of a brackish RO facility, then in a follow-up action, both NTA and SPOS were used to evaluate the size and number of nano- and micro-scale particles in the feed concentrate channel of NF membrane process. ? NTA analysis revealed that particles ranging between 300 and 1,300 nanometers (nm) existed in the feed-concentrate RO channel stream that had been pretreated with sulfuric acid, scale inhibitor and 1- micron cartridge filtration. Particle sizes varied widely in the feedwater but averaged approximately 320-nm in the feedwater. However, particle sizes increased in the concentrate which was found to contain particles averaging around 535-nm. ? Unlike the brackish RO process, particles ranging between 50 nm and 70 micrometers (?m) were detected in the feed-concentrate channel of the NF membrane process evaluated. The NF process treated surficial groundwater and employed pretreatment consisting of sulfuric acid, scale inhibitor addition and nominal 5-micron cartridge filtration. Most of the particles identified in the NF feedconcentrate channel had an average diameter of less than 1-?m. Submicron particle content averaged 64 million particles per milliliter (mL), 47 million particles/mL, and 3.5 million particles/mL in the feed, interstage and concentrate streams, respectively. The concentration of particles less than 500-nm exceeded those greater than 500-nm by at least one order of magnitude. However, the less abundant microparticles occupied more of the volume within the feed-concentrate channel than the more concentrated submicron particles. ? Additional note: A companion study that analyzed matter captured after filtering 20-liters of the NF feed, interstage and concentrate streams on 0.2-micron rated silver 47-mm diameter filter pads by energy-dispersive x-ray spectroscopy revealed deposits of calcium carbonate, elemental sulfur, and silts/clays in each stream; however, deposits of organic-based matter were mainly identified in the interstage and concentrate streams (source: Powell & Duranceau, 2021).
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- Steven Duranceau
- University of Central Florida
- AMTA/AWWA Membrane Technology Conference, Las Vegas
- AMTA/AWWA Membrane Technology Conference
- Nanometer, Micrometer, Nanofiltration