Hydrovida was contacted by a prospect after a Clean-In-Place (CIP) of their Reverse Osmosis (RO) membranes led to concerning results. Before cleaning, the client had noticed a rapid rise in differential pressure and increased salt rejection in the final stage of the RO system—symptoms typically linked to scaling, likely due to a failure in the antiscalant pump or the antiscalant itself. After performing CIP, the increase in differential pressure and salt passage of the tail end vessels were higher than before cleaning.
Upon inspection, significant scaling was found on the interior of the RO pressure vessels and membranes. A membrane from the final stage of the system was removed for foulant analysis to identify the cause and plan an effective cleaning strategy. The membrane was covered in large, well-formed crystals on its casing and anti-telescoping devices, which adhered strongly and were difficult to remove.
Upon inspection, significant scaling was found on the interior of the RO pressure vessels and membranes. A membrane from the final stage of the system was removed for foulant analysis to identify the cause and plan an effective cleaning strategy. The membrane was covered in large, well-formed crystals on its casing and anti-telescoping devices, which adhered strongly and were difficult to remove.
Scale precipitation on membrane cleaned with generic membrane cleaner
Hydrovida’s lab carefully collected and analyzed the scale using a Scanning Electron Microscope (SEM). A SEM bombards a surface sample with beams of electrons to produce a very high resolution image of a specimen up to 3,000,000 times magnification, to allow to see topographical details of the scale crystal morphology, helping identify the specific type of scale present.
SEM imaging (200x magnification) of a scale particle collected from the RO membrane
Hydrovida also employed Energy Dispersive X-Ray Spectroscopy (EDS) in the foulant analysis to identify and quantify elements in the sample. EDS works by bombarding the sample with high-energy electrons or X-rays, causing atoms to emit characteristic X-rays that reveal their elemental composition.
EDS spectra of the particle in the SEM image.
Hydrovida Elemental Mapped Imaging (EMI) is a highly useful analytical technique that combines information from the SEM and EDS techniques to create a spatial distribution of elements present within a sample. The SEM image is taken of a sample, while EDS analysis is simultaneously performed. Using element map imaging software, the overall elemental composition of the sample can be mapped to the exact location of each element present. Each element is assigned a color, and the software reveals the precise location of the element. Increases of intensity of color directly correlate to elevated elemental concentrations in that area. Element map imaging helps tell a more definitive of story of foulant complexes and gives a great overall picture of the identification fouling present and the most probable causes of fouling.
EMI showing calcium (dark blue) complexed with phosphorus (light blue), and calcium complexed with carbon (red)
After confirming the scale was primarily calcium phosphate, Hydrovida investigated the source of phosphorus, as the feed water to the RO was municipal, and did not contain any phosphorus. Phosphorus is typically only present in wastewaters. Hydrovida traced the phosphorus source to the phosphoric acid in a generic RO cleaner, which had been determined to cause the scale to precipitate during cleaning. Using this information, Hydrovida developed a custom cleaning regimen that fully removed the scale, restoring membrane flow and significantly improving salt rejection.
Hydrovida believes that dedicating time and analysis to RO fouling is vital for maintaining consistent, efficient system performance. A membrane autopsy and lab analysis offer critical insights into chemical feed problems, membrane health, and system optimization. Relying on guesswork often leads to increased costs, extended troubleshooting, and unnecessary downtime, making a thorough analysis a smarter, more cost-effective approach.
Hydrovida believes that dedicating time and analysis to RO fouling is vital for maintaining consistent, efficient system performance. A membrane autopsy and lab analysis offer critical insights into chemical feed problems, membrane health, and system optimization. Relying on guesswork often leads to increased costs, extended troubleshooting, and unnecessary downtime, making a thorough analysis a smarter, more cost-effective approach.
