Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 117

Foam fractionation (also known as protein skimming or protein fractionation) is a process that mimics the natural process of wind and wave movement on the ocean surface – this mixing of air with seawater creates a thick foam of surfactant materials, known as spindrift, which blows up onto the shore and so is taken out of the aquatic system. In a foam fractionator, this is accomplished by pushing microbubbles through a venturi injector into the base of a tall cylindrical column. System water flows through the column from top to bottom, countercurrent to the bubbles rising in the column. As the bubbles rise, long‐chained organic molecules stick to them. As the bubbles contact the surface, they coalesce into a thick film, releasing air that then burps the foam up and out of an inverted funnel collection device (Figure A3.6). This collection device is usually auto‐rinsed with potable water to municipal sewer on a regular cycle. When applied correctly, this provides continuous removal of proteins, amino acids, and lipids from the decomposition of organic waste in the aquarium. In addition, this sticky surfactant waste tends to also carry secondary waste products that include trace metals and bacteria through adsorption, coagulation, and microflocculation. Foam fractionators also increase aeration of the system water. Foam fractionators have to be closely managed to maintain the correct flow for efficient operation. They are not effective in freshwater; they typically require a salinity of >15 g/L to provide the necessary surfactant pressure.

Figure A3.4 Sand filter (a), canister filter (b), bead filter (c).

Source: Image (b) courtesy of Catherine Hadfield, Seattle Aquarium.

Figure A3.5 Settling tank.

Figure A3.6 Foam fractionator.

Source: Image courtesy of Catherine Hadfield, Seattle Aquarium.

Relatively small doses of ozone enhance the removal of organics and provide disinfection. This is typically on a side‐stream equivalent to about 20% of the main filtration rate but is fed directly from the aquarium for optimum performance. This combination of foam fractionation and ozone provides increased pH, increased dissolved oxygen concentration, increased oxidation reduction potential (ORP), improved water clarity, and reduced dependency on turnover rate, sand filters, and other traditional LSS components.