Led by Professor Juliet Gopinath, a researcher in electrical, computer and energy engineering and physics at the University of Colorado Boulder, a multidisciplinary engineering team has developed a laser-based imaging method that allows scientists to observe desalination membrane fouling as it occurs. The work addresses one of the most persistent operational challenges in large-scale desalination plants and offers a new way to study membrane performance under realistic conditions.
Simmons, Y. L., Andersen, J. M., Zohrabi, M., Bright, V. M., Greenberg, A. R., & Gopinath, J. T. (2025). Stimulated Raman Scattering Microscopy: Real-Time In-Situ Physical and Chemical Characterization of Reverse Osmosis Desalination Membrane Scaling. Environmental Science & Technology. https://doi.org/10.1021/acs.est.5c10405
Desalination plays a growing role in global water supply as freshwater resources face increasing pressure. More than half of the world’s population experiences water scarcity for at least part of the year, and long-term projections suggest this figure will rise as climate variability and demand intensify. Reverse osmosis systems account for the majority of installed desalination capacity worldwide, making their efficiency and reliability central to sustainable water infrastructure.
Professor Juliet Gopinath, from University of Colorado Boulder stated,
“Watching these crystals form as it happens, getting volumetric data and identifying the chemical all at once is pretty exciting. Previously, you could get volume data or chemical identification, but not at the same time.”
Reverse osmosis membranes are thin polymer films designed to allow water molecules to pass while rejecting dissolved salts and contaminants. Over time, minerals, organic matter, and biological materials accumulate on these membranes in a process known as fouling. This buildup reduces water throughput, increases energy consumption, and raises maintenance costs. Despite its importance, fouling is difficult to study directly because it develops at the membrane surface during operation and is typically detected only after system performance declines.
The CU Boulder team addressed this challenge by applying stimulated Raman scattering microscopy, an optical technique that reveals molecular composition by measuring how light interacts with vibrating chemical bonds. Unlike conventional membrane analysis methods that require membranes to be removed and examined after use, stimulated Raman scattering enables real-time, in-situ observation without disrupting operation.
Using this approach, the researchers monitored the formation of calcium sulfate and calcium bicarbonate crystals on reverse osmosis membranes. These compounds are common contributors to mineral scaling in seawater desalination systems. The technique allowed the team to capture three-dimensional volumetric images while simultaneously identifying the chemical nature of the forming deposits.
According to postdoctoral researcher Jasmine Andersen, the ability to combine structural imaging with chemical identification represents a significant advance. Previous tools typically provided either physical information about deposit growth or chemical composition data, but not both at once. Observing these processes simultaneously makes it possible to track how specific compounds nucleate, grow, and interact with the membrane surface over time.
The experiments revealed distinct crystal growth behaviors for different mineral species, underscoring the complexity of fouling mechanisms. These observations suggest that membrane performance is influenced not only by how much material accumulates but also by the structure and chemistry of the deposits themselves. Such insights could inform the design of membranes that are more resistant to scaling or operating strategies that slow fouling before it affects system efficiency.
Professor Emeritus Alan Greenberg, an expert in membrane characterization, noted that even modest reductions in fouling can translate into meaningful improvements in plant productivity. Lower fouling rates can reduce cleaning frequency, extend membrane lifespan, and decrease energy demand, all of which are critical factors in the cost and environmental footprint of desalination.
While the current study focused on inorganic scaling, the researchers indicate that the same imaging method could be extended to more complex fouling scenarios involving organic compounds and biological growth. These mixed fouling conditions are common in both seawater and brackish water treatment systems and are particularly challenging to diagnose using existing monitoring techniques.
As desalination becomes more widespread, tools that improve understanding of membrane behavior under real operating conditions will be increasingly important. The work led by Professor Gopinath demonstrates how advanced optical imaging techniques can bridge the gap between laboratory analysis and industrial application, providing engineers with clearer insight into processes that directly affect water treatment efficiency and sustainability.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
