Protein skimmers, or foam fractionators, are gaining interest in large RAS, both for freshwater and saltwater . The function of the protein skimmer may serve different purposes when elaborating on detailed water quality parameters and will most often be used to ‘improve water quality’. Protein skimmers can have positive effect on water quality parameters linked to removal of organic matter and particles – mostly related as Total Suspended Solids (TSS ), dissolved organic matter (DOM) or Biological Oxygen Demand (BOD) . Removing organics can lead to a reduced competitive advantage of heterotrophic bacteria and reduce free swimming bacteria, while also reduce off flavor issues – which can have huge implications for RAS growing fish directly for consumption.
To understand protein skimmer function in RAS better and dimension larger skimmers into RAS removal metrics and dynamics should be understood along the chemical and physical properties inside the foam chamber and the interconnections to usage of ozone in the skimmer. Ozone can severely improve skimmer performance with partial oxidation of dissolved organic molecule, activating potential for removal in the foam cloud, and can be integrated in protein skimmer air stream.
Practical observations point towards a general lower ozone usage compared to industry standards or applied in traditional ozone side streams in RAS – potentially due to the combination of partial oxidation, removal of organics in the foam and the high-water volume in contact with the ozone.
Studies and practical experience also point towards reducing retention time in skimmers from the traditional 1,5-2 minutes, and rather inject ozone into a larger water stream, ultimately gaining better treatment results in the system from the same volume as earlier intended.
Dimensioning large protein skimmer into RAS from an early phase gives the opportunity to direct large water flows into the reaction chamber by gravity, which in combination with lower ozone/oxygen consumption will pose a possibility to reduce both OPEX, footprint and system complexity with pumps, pipes, and automation.