MAT Freshwater Protein Skimmers for Salmon & Trout Hatcheries

MAT-Kuling Product Catalog

Freshwater does not foam the way seawater does. Lower ionic strength means bubbles coalesce faster and the foam column collapses, which is why a standard marine skimmer underperforms on a hatchery. The MAT PSF series is engineered specifically for fresh and brackish water, carrying roughly three times the installed power and several times the air suction of the marine equivalent at the same body diameter.

Fresh by Design supplies, installs and commissions the MAT freshwater range across Australia, New Zealand and the Pacific — nine current sizes from the PSF-22 through to the PSF-1500 at 1,500 m³/hr.

The PSF series was developed at the request of salmon farmers for pre-smolt tanks and is now used across freshwater and brackish RAS generally — salmon and trout hatcheries, land-based grow-out, and any recirculating system where dissolved organics are limiting stocking density.

The skimmer is an add-on to an existing filtration train rather than a replacement for any part of it. Removing dissolved organics upstream reduces the load on the biofilter and improves clarity, which is what allows more biomass and more feed in the same tank volume.

Water is drawn into the skimmer body by a high-head venturi feed pump. The venturi draws air into the flow as very fine bubbles, which rise through the water column in a controlled cyclone. Proteins and other surface-active compounds collect at the bubble surface and are carried upward, along with fine particulate material below about 40 microns that attaches to the foam. The foam thickens near the top of the body, collects in the cup and discharges through the effluent line.

MAT spent over twelve months testing venturi injectors and body geometries against the freshwater foaming problem, feeding the skimmer at higher pressure to force enough air into the cyclone to hold a workable foam. That energy difference is the engineering, and it is why a marine skimmer cannot simply be run on fresh water.

In 2020 the Norwegian Institute for Water Research (NIVA), Norway’s leading independent research institute for marine and freshwater science, carried out an independent, unpaid field trial on MAT freshwater protein skimmers at a Norwegian salmon farm. Water was sampled before installation and for a month afterwards with the pre-smolt pool at full capacity. Removal rose with particle size across the trial, and several water quality chemical parameters improved. View the published NIVA results.

Percentage of Particles Removal Diagram in MAT Freshwater Protein Skimmers Tested by NIVA

Freshwater foam is less stable than marine foam, so the collector level needs closer control to run efficiently without wasting water. Automated foam level control is available as an option from the PSF-220 upward, and is the option to specify for any farm running to a controlled process rather than a daily manual adjustment.

Purpose-built for fresh and brackish water, not a marine unit run on fresh water.
Removal of fine particulate material ( < 40 micron ) that attaches to the foam.
Reduced load imposed on downstream biological and mechanical filtration.
Maximises oxygen saturation in the water while it mixes and dissolves oxygen.
Upgraded body, high-efficiency foam cap collector and purpose-designed freshwater venturi.
Auto-wash system for inner and for outer tube.
Optional automated foam level control.
Food-grade polypropylene body — fully corrosion resistant, no coatings to fail.
Resistant and robust fabrication.
Nine sizes from PSF-22 to PSF-1500, covering 7 to 870 m³/hr at two-minute dwell.
Custom sizes available on request.