Should I focus on soaking or circulation during a Clean-in-Place (CIP)? Which one is more important?

Both soaking and circulation steps are important for an effective cleaning. A well-designed CIP procedure alternates between these two steps to achieve the best cleaning results. While soaking is relatively straightforward, the circulation step requires more attention to ensure it delivers its full cleaning effect. One common industry mistake is to perform only brief circulation followed by long overnight soaks, often overlooking how critical proper flow during circulation is for removing fouling and maintaining cleaning performance.

Why Circulation Supports Membrane Cleaning

• Promotes Turbulence and Physical Cleaning: Circulating at high flow rates creates turbulence, which helps physically dislodge suspended solids and loosen foulants from the membrane surface. This scouring effect also improves how quickly foulants dissolve, similar to how sugar dissolves faster when you stir your tea.
• Replenishes Depleted Cleaning Chemicals: Circulation helps maintain chemical strength by constantly bringing fresh solution into contact with the membranes. This is especially important in fast reactions, such as low pH cleanings used to dissolve calcium carbonate, where the active ingredients can be quickly consumed.
• Flushes Dissolved Foulants: Circulation helps carry away the dislodged foulants, such as scale or biofilm, that were loosened during the soak step. Without circulation, these deposits can settle back onto the membrane surface and reduce cleaning effectiveness.

Best Practices for Effective Circulation Steps

To maximize cleaning effectiveness and minimize the risk of damage, it’s important to follow a few key circulation guidelines:

• Start Slowly and Watch Pressure: Begin circulation at a low flow rate to avoid putting stress on the system. Blockages in the membrane’s feed channels can cause high differential pressure (∆P), often higher than what’s seen during normal operation. Monitor ∆P closely: if it’s within a safe range, gradually increase the flow to the recommended rate.
• Let the ∆P Guide You: If ∆P is high at first, be patient. As circulation begins clearing blockages in the feed channels, pressure will gradually drop, signaling that flow can be safely increased. Continue adjusting the flow in small steps as long as ∆P remains within safe limits.
• Achieve & Maintain Recommended Flow Rates: For 8” membrane elements, aim for 40–45 gallons per minute (gpm) per pressure vessel. Flow rates below this range may not generate enough turbulence for effective cleaning, while higher flows can increase differential pressure and risk membrane damage.
• Clean Each RO Stage Separately: During CIP, isolate and clean each stage of a multi-stage RO individually, preferably while soaking the other stages. Since each stage has a different number of pressure vessels, if you circulate through all stages at once, you’re forced to choose between under-cleaning the first stage (to avoid exceeding differential pressure in later stages) or risking damage to later stages by using the correct flow for the first. Cleaning each stage individually avoids this tradeoff and ensures proper flow through all elements.

Protecting the Membrane from Damage

To avoid issues like telescoping or permanent damage during cleaning, it’s critical to stay within safe pressure limits:

• Never Exceed ∆P Limits: Keep ∆P below 10 psi per 8” element and under 70 psi per pressure vessel. High ∆P during cleaning usually means the flow path is blocked. Exceeding these limits can damage membranes and spacers. Stop circulation and investigate immediately if pressures rise unexpectedly.

AWC’s Approach to Smarter Membrane Cleanings

At American Water Chemicals (AWC®), we provide industry-leading membrane cleaning solutions designed to optimize cleaning effectiveness while extending membrane life. AWC combines advanced cleaning formulations with real-world system expertise, ensuring not just proper flow and chemicals, but the right strategy for each unique cleaning challenge.

Need help with your next membrane cleaning? Contact AWC® here to get expert support.