Protein skimmer or foam fractionators are used for removal of fine solids and dissolved protein from the water. Protein skimmers remove dissolved particles from a waste water flow by adsorption of the particle at the gas-liquid surface. Water molecules that border an air surface tend to align themselves. Foam fractionators are especially suitable for removal of particles smaller than 30 micron and particles that have an electric charge. The higher the salinity of the water the more effective the skimmers are, because of the formation of finer air bubbles, due to the increased surface tension.

ACE skimmers normally work with counter-current flow where the water enters near the top of the reactor and the air is injected near the bottom by means of venturi injectors. The skimmers can be custom-designed for a wide variety of flows and can be manufactured in rectangular or cylindrical shapes. The preferred choice of plastic can be Polypropylene (PP) or Polyethylene (PE) both are durable, strong and chemically inert materials.