How the CENTS-RAS is working???

A system where the water (in fish rearing tank) , instead of being discharged to the outside environment, is reused after undergoing filtration in a settling pond or water treatment process.

Biofiltration.

As we mentioned earlier, the biological filter (biofilter) is the heart of the RAS. As the name implies, it is a living filter composed of a media (corrugated plastic sheets or beads or sand grains) upon which a film of bacteria grows. The bacteria provide the waste treatment by removing pollutants.

The two primary water pollutants that need to be removed are

(1) fish waste (toxic ammonia compounds) excreted into the water and

(2) Uneaten fish feed particles. The biofilter is the site where beneficial bacteria remove (detoxify) fish excretory products, primarily ammonia.Ammonia and Nitrate Toxicity:Ammonia and nitrite are toxic to fish.

Ammonia in water occurs in two forms: ionized ammonium (NH4+) and unionized (free) ammonia (NH3). The latter, NH3, is highly toxic to fish in small concentrations and should be kept at levels below 0.05 mg/l. The total amount of NH3 and NH4 remain in proportion to one another for a given temperature and pH, and a decrease in one form will be compensated by conversion of the other. The amount of unionized ammonia in the water is directly proportional to the temperature and pH. As the temperature of pH increases, the amount of NH3 relative to NH4 also increases.In addition to ammonia, nitrite (NO2) poisoning of fish also is an imminent danger in RAS. Nitrite levels should be kept below 0.5 mg/l. Brown blood disease (methemoglobinemia) occurs in cultured salmon and channel catfish when hemoglobin is oxidized by nitrite to form methemoglobin (a respiratory pigment of the blood that cannot transport oxygen). The disease can occur at nitrite concentrations of 0.5 mg/l or greater. As the name implies, the blood has a characteristic chocolate brown color. Adding salt (NaCl) at a rate of 1 pound per 120 gallons of water (a chloride to nitrite ratio of 16:1) will suppress this disease in soft water; a ratio of 3:1 is effective in hard water.