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Protein Skimmers/Fractionators

Protein skimming or foam fractionation is the process by which dissolved and particulate organic carbons are removed from a liquid, in this case the fish culture water, by adsorbing them onto the surface of fine bubbles rising in a closed contact column against a counter-current water flow.

The bubbles burst and form stable foam at the top of the water column and the accumulated organic wastes are discharged from the column along with the foam produced.

The removed substances are called "surfactants" because they are surface active or "charged"

Benefits of Protein Skimming include:-

  • Removal of suspended solids.
  • Removal of proteins and high molecular weight compounds.
  • Increased water clarity through removal of humic and phenolic compounds.
  • Increased oxygenation of the culture water.
  • pH stabilisation through removal of organic acids.
  • Performance is defendant on:

  • Air to water ratio
  • Air bubble diameter
  • Column height
  • Air/water contact time
  • Use of ozone

Bubble size is the most important of these and within the control of the design of the protein skimmer.

An efficient air diffuser or venturi plays an important part in generating a swarm of bubbles that are as small as possible, ensuring maximum surface area for the adsorption of the organic compounds. Smaller bubbles also rise more slowly, allowing more contact time with the process water.

Generally it is difficult to generate a small enough bubble size in freshwater to achieve effective foam production (except in cases of very high organic loading) and therefore protein skimming is mainly only recommended for seawater or brackish applications where the salinity is more than 16 ppt. However, a number of freshwater skimmers are available for use in ponds.

Protein skimming is further enhanced by the application of ozone into the air mixture, which further oxidises and breaks down complex organic compounds as well as providing a degree of disinfection, depending on the quantity used.


Below you will see the links to the various sections on this very large subject covering all the
type of Filtration Systems we recommend.



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