Membrane Fouling

Inorganic fouling at the membrane surface occurs when components filtered from the feed-stream collect near the membrane/fluid interface.
Biologically associated fouling (commonly referred to as ‘biofouling’), generally involves the concentration of biotic organic matter on the surface of the membrane. Viable bacteria accumulating on the surface may begin to colonize in the boundary layer at the membrane surface and ultimately form a biofilm that will make the bacteria less susceptible to biocides added to the feed water.
The categories of fouling are:
  • Inorganic/scaling
  • Particle/colloidal
  • Microbiological
  • Organic/biomaterial
All membrane fouling has a deleterious effect on membrane performance by:
  • Increasing the pressure that must be applied to the feed-stream in order to maintain flux. This increases energy costs and/or reduces the recovery performance of the plant
  • Increasing salt passage through the membrane with consequential reduction in permeate quality
Membrane Fouling

Membrane Fouling

Increased concentration of dissolved salts, particularly calcium salts, on the membrane surface can lead to precipitation and crystal growth on the membrane, known as scaling. Chemicals designed to retard crystal growth are customarily added to the feed before it reaches the membrane. Other inorganic fouling is treated by means of periodic chemical clean-in-place (CIP) treatments, requiring the train to be taken off-line for the duration of the treatment. Biofouling is treated by combinations of filtration and other pre-treatments together with additions of biocidal chemicals to the feed and CIP’s.