Causes of membrane fouling: three main groups

Fouling is not one single thing

When membrane performance falls, the first reflex is to clean it. Yet a clean carried out with the wrong chemical can damage the membrane instead of removing the fouling. To intervene correctly you first have to know which group the fouling belongs to.

The fouling we encounter in the field largely falls under three headings.

The three main groups

Each group has its own symptoms and its own remedy.

• Precipitation-related: silica and scale form a hard layer on the membrane surface
• Particle-related: suspended solids such as silt, clay and fines coat the surface
• Biological: bacterial growth forms a biofilm on the membrane

The cause is sought in the pretreatment

For all three groups the source usually lies not in the membrane itself but in the stages ahead of it. Precipitation points to an inadequate antiscalant choice or dose, particle fouling to what the filtration is letting through, and biological fouling to a gap in the disinfection arrangement.

So if fouling keeps recurring, the answer is not to clean more often but to review the pretreatment.