RO Membrane Scaling and Fouling

RO Membrane Scaling and Fouling

When using a membrane-based water treatment system, fouling of membranes can create quite an issue for water operators. Reverse osmosis (RO), microfiltration (MF), nanofiltration (NF) and ultrafiltration (UF) are all membrane-based water treatment technologies and therefore are prone to fouling. Membrane fouling will at the very least decrease production and use more energy and can even lead to much more costly equipment replacements. However, measures can be taken to prevent fouling and knowing some of the warning signs can help to assist your water treatment operations. There are even systems today that can act to prevent fouling simply by their process design such as Closed Circuit Reverse Osmosis.

Signs of Membrane Fouling:

Poor Water Quality

A decline in your water quality is generally a sign of membrane fouling. If your membrane-based water treatment system starts to produce low quality permeate, check the composition of the foulant which may give you some more details about what could be causing the issue. If the foulant is colloidal, you may need to check your pretreatment or install a new pretreatment system if you do not have one. If your membranes are showing poor salt rejection and an increase in transmembrane pressure simultaneously, your membranes could be scaling.

Odd Smells, Strong Smells or Mold

Strange and strong smells can be a sign of biological growth on your membranes. If you have pretreatment such as carbon filters before your membrane-based water treatment system, check the filters for a slime like substance or mold growth. This can usually be counteracted by an adjustment in temperature and a biocide may be a necessary addition.

Build Up on Membrane Edges

This is a very obvious sign of your membranes fouling. If you see an actual build up of solids on your membranes, it’s usually foulants collecting into a solid mass. It’s always important to check the composition of this build up forming on the membranes. Occasionally, it can be harmless, however knowing the composition can inform your next move on combating the issue if there is one. A possible clean-in-place (CIP) may be necessary and some chemical additions to the water from your chemical provider may do the trick.

When and Why to Clean Fouling Membranes

If you have membrane fouling, you may need to replace your membranes if the problem has been compounding for a while. However, you may be able to simply clean the membranes and get back into water production in no time. A preventative approach is always best to help avoid a shut down or the need to replace membranes earlier than necessary. A membrane cleaning schedule is a great place to start. If you don’t already have one, schedule a consultation with a chemical provider to see how they can help. If you are seeking to clean your membrane-based water treatment system on your own, it is recommended that the membrane system operator thoroughly investigate the signs of fouling before they select a cleaning chemical and a cleaning protocol. Cleaning should generally occur when the normalized flux has decreased 10% to 15%, the normalized salt content of the permeate has increased by 10%.

There are also certain membrane-based systems that actually counter act fouling and scaling. Closed-Circuit based RO (CCRO) prevents fouling because the CCRO process provides a constantly changing membrane environment. The plug flow sequence found in the CCRO process also helps to purge the membranes of foulants several times per hour. 

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