Article written by: Jason Danaher Ph.D.
A protein fractionator, also known as a foam fractionator or protein skimmer, is a water treatment device commonly used in purging systems, growout systems, and effluent/influent treatment to improve water quality. A protein fractionator can be appropriate for freshwater systems ( < 1.0 ppt), but its treatment efficiency improves with salinity concentration encountered in brackish water (1.0 ppt - 30 ppt) and saltwater systems ( > 30 ppt) because salinity increases the water's surface tension and creates more stable bubbles used for the filtration process. A protein fractionator's primary function is to remove dissolved organic compounds (DOCs) and fine particulates before they break down into ammonia and nitrite. By doing so, the fractionator reduces the load on biological filtration, improves clarity of the water, and enhances overall system stability.
How a Protein Fractionator Functions
In large aquatic systems a centrifugal pump delivers untreated water to the protein fractionator. The effectiveness of a protein fractionator depends on the quality of its bubbles, and higher salinity enhances the critical characteristics of these bubbles. The protein fractionator functions by injecting a large quantity of fine air bubbles into the untreated water column within the vessel (Figure 1). Smaller, more numerous bubbles create a far greater total surface area and adhesion for DOCs to bind to. As bubbles rise in the vessel or reaction chamber, their surface tension attracts and adsorbs organic molecules, lipids, proteins, and other hydrophobic compounds. These waste-laden bubbles accumulate at the top of the vessel, creating foam. The foam is then collected in a separate chamber and drained from the aquatic system (Figure 1). Without sufficient surface tension, as is often the case with freshwater, a stable foam cannot form, and the waste-carrying bubbles simply pop and release their contents back into the reaction chamber; thus, never leaving the aquatic system. But rest assured, other synergistic technologies can be incorporated with protein fractionators in freshwater systems to create more stable foam.
Figure 1. Important components of a protein fractionator unit used to improve water quality.
Principles Behind the Venturi Effect
One of the most efficient ways to generate the fine bubbles required is through the venturi effect. This principle states that when a fluid passes through a constricted section of pipe, its velocity increases while pressure decreases. In a venturi injector (Figure 1), water moving at high speed through the narrow throat creates a low-pressure zone that draws in atmospheric air from its surroundings. This mixing of water and air produces a stream of bubbles. Properly designed venturi injectors create extremely small bubbles, maximizing surface area and the efficiency of organics removal.
Water Quality Parameters Improved
Protein fractionators directly and indirectly improve several water quality parameters in aquatic systems:
Dissolved Organic Carbon (DOCs): Fractionators remove organic molecules before microbial decomposition occurs.
Turbidity and Water Clarity: The removal of fine particulates and organic matter increases transparency, which is especially important in display aquariums and research systems. Improved clarity can also lead to better disinfection rates when ultra-violet (UV) light is used because UV light penetration is dependent on the untreated water’s clarity and turbidity concentration.
Foam and Surface Films: By capturing surfactants, fractionators prevent unsightly surface scum and improve gas exchange at the water-air interface.
Oxygen Levels: The aeration process may enhance oxygen transfer, supporting aquatic life and stabilizing dissolved oxygen levels. But more importantly, the removal of organics decreases the biological and chemical oxygen demand required to break down the fine particulate wastes.
Nitrogenous Waste Reduction (Indirect): By stripping organics early, fractionators reduce the secondary ammonification rate at which ammonia and nitrite are produced, lowering the loading on biofilters.
Pathogen Control: Some bacteria, parasites, and spores attach to organic particles or bubbles and can be removed along with the foam, providing a modest biosecurity benefit.
In addition, combining ozone treatment into the protein fractionator’s process flow creates a synergistic effect and can make the treatment process more effective and efficient. Ozone breaks down and flocculates organic particles, making them easier to remove from the untreated water.
Conclusion
Protein fractionators are highly effective tools in aquatic system management, especially where high biomass is present or pristine water clarity is required. By using the venturi effect to generate fine bubbles that capture dissolved and particulate organics, the protein fractionator improves clarity, reduces organic loading, enhances oxygenation, and indirectly stabilizes nitrogen cycling. Protein fractionators play a critical role in maintaining optimal water quality and supporting healthy aquatic organisms for both aquaculture and ornamental display systems. Feel free to email Aquatic Equipment & Design, Inc. staff at info@aquaticed.com or call 407-995-6490 for additional information and tips on protein fractionator technology and its application for your aquatic system.