In this episode of ZwitterCo Unfiltered, Jon Goodman is joined by Scott Brown and Leonid Semenihin to answer customer questions about cleaning programs for membrane systems. The team compares how ultrafiltration, reverse osmosis, and nanofiltration systems are cleaned in North America versus Europe, and discusses why those programs can look so different depending on region, feed stream, and system design.
Cleaning is one of the topics ZwitterCo customers ask about most, and it’s also one of the least standardized parts of running a membrane system. In this episode of ZwitterCo Unfiltered, host John Goodman sat down with Leonid Semenihin, ZwitterCo’s European sales engineer, and Scott Brown, who focuses on dairy in North America, to walk through how cleaning programs actually work for ultrafiltration, reverse osmosis, and nanofiltration, and why those programs look so different depending on where a plant is located.
Temperature and Surfactant Basics
The conversation opened with two questions ZwitterCo hears often. The operating limit for Evolution membranes is 55°C, with cleaning set at 50°C, matching the limits of conventional membranes cast on polyester backings so that Evolution elements can serve as direct replacements. On surfactant selection, the guidance was to avoid anionic surfactants during a full system load and to stay completely away from cationic surfactants, such as quaternary ammonium compounds.
Nonionic surfactants are the preferred choice. One complication customers run into: cut sheets and SDS documents don’t always disclose whether a formulated cleaner or a blended enzyme product contains an anionic or nonionic surfactant, so it’s worth confirming directly with a cleaning chemical supplier.
Why European and North American Cleaning Programs Diverge
Leonid explained that chlorine has largely been phased out of European cleaning programs because reaction byproducts of chlorine-containing agents can be toxic and bioaccumulating, and food-safety limits aren’t set for all of them. In its place, many European customers rely on PHT cleaning, a high pH, high temperature program in which the final alkaline stage is run at 60 to 70°C and a pH between 10 and 12, rather than the standard 50°C. PHT is used almost exclusively on ultrafiltration; reverse osmosis and nanofiltration in Europe follow largely the same cleaning steps as they do in North America, since standard RO elements can’t withstand PHT-level temperatures.
Heat can also serve as a standalone sanitization step. Holding a system at 70°C for 20 to 30 minutes functions as a batch pasteurization with no added chemistry, and some customers combine that hold with the final alkaline stage to sanitize and clean in a single step.
The tradeoff shows up in larger, more complex systems, where controlling temperature evenly across every section of piping becomes difficult. Some customers who ran into that challenge have started shifting their sanitization step from thermal to peracetic acid instead. Peracetic acid is also used in Europe, though more commonly as an oxidizer to boost cleaning performance rather than as a sanitizer. ZwitterCo doesn’t yet have its own data on running Evolution PCM or Evolution SF membranes at 70°C for sanitization, and testing with interested customers is underway.
A Typical North American Program
Scott described a common US cleaning sequence: a production flush and a short precipitation flush, followed by a roughly 15-minute alkaline “junk wash” around pH 10.5 to 10.7 to loosen the bulk of the soil, another flush, then a caustic wash recirculated for 20 to 25 minutes at pH near 11. Many programs then add an enzyme wash at pH 9 to 10, run at a lower temperature to preserve enzyme activity.
That enzyme step tends to be both the most expensive and the longest part of the program. Because Evolution membranes don’t foul the way conventional elements do, some customers have been able to skip the enzyme wash entirely, which Scott estimated can return about 45 minutes of wash time plus another 15 to 20 minutes of flush time and flush water, on top of the chemical cost savings.
On the European side, Leonid noted that plant-protein customers sometimes run as many as three separate enzymatic steps in a single program: one to break down protein fouling, a lipase step for fat fouling, and in some cases a cellulase step for fibrous fouling.
Why No Two Plants Clean the Same Way
Both guests agreed that cleaning programs vary widely even within a single country. Scott pointed to differences in local water hardness, from Idaho to California, Texas, and New Mexico, whether a plant uses polished or softened well water, the age of a plant’s separators, and the tendency of plants to run well beyond their original design capacity. One Northern California customer that switched to a weekly heat sanitize, after adjusting system controls that had originally cut the system off at 122°F, saw its bacteria issues resolve.
For reverse osmosis and nanofiltration specifically, Leonid described the typical European program as a pre-wash with an alkaline solution, a full alkaline wash, an enzymatic cleaner, an acidic step to inactivate the enzyme and remove residual matter, and a final alkaline step. Ultrafiltration adds a thermal sanitization stage after that; RO skips it because the membrane can’t tolerate the temperature. In North America, RO sanitization typically uses peracetic acid at a low temperature around 70°F instead of heat, since heating peracetic acid causes it to off-gas and creates an unsafe environment.
Talk to ZwitterCo About Your Cleaning Program
If you’re trying to figure out where your own cleaning program stands, whether that’s questions about surfactant selection, PHT cleaning, or how far you can go in reducing enzyme steps, reach out to ZwitterCo to talk through your specific system and application.
