Determining Foulants & How to Clean Them - Part 1

Determining Foulants

Fouling can be caused by a few things. This can be from either particles like clay, organics and bacteria, or from inorganic deposits. Often times, it’s a combination of many different foulants as they form layers on the surface of the membrane. The best way to determine the correct cleaning procedure is to Autopsy the membrane. There are techniques that can be used to determine where most of the fouling occurs, which can help determine what the foulants may be. These two techniques are profiling and probing.


Profiling involves using the sample ports for each vessel to check the water’s conductivity and pressure drop. Once the conductivity is checked for each vessel, they should be compared to each other. If one vessel has a higher conductivity than the others, then the vessel should be probed. This will provide further information.


Probing allows you to determine the problem by isolating it within the vessel without removing the elements while the system is still online. Probing entails inserting a 1/4 inch plastic tube through the length of the pressure vessel. As the tube is pulled back to the permeate manifold, you can monitor the conductivity. This is what tells you whether the first stage is fouled (typically particles) or the second stage (inorganic deposits).

Cleaning Steps

Although RO permeate water must be used in all cleaning procedures, there are different cleaning procedures necessary to rid the membrane of biological, inorganic, and particulate fouling.

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