Closed RAS

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Land-based Closed Recirculating Aquaculture System (Closed RAS)

The land-based closed recirculating aquaculture system FRD Japan’s land-based closed recirculating aquaculture system treats the water using bacteria, making it possible to farm fish in a completely closed water recirculating system* using artificial seawater made from a municipal water supply. *Daily replacement rate: Approx. 0.2% (replaced water/retained water per day)

Three distinguishing features of the Closed RAS

1.Nitrification filters

During nitrification, highly toxic ammonia generated by living things is broken down by bacteria into nitrates that are low in toxicity. FRD Japan uses nitrifying bacterial biofilm carriers that it developed for complete, high-capacity, high-speed denitrification.

2.Denitrification filters

Denitrification uses the action of denitrifying bacteria to deoxidize nitrates and release harmless nitrogen into the atmosphere. The fully automated denitrification system developed by FRD Japan creates conditions that promote the activation of denitrifying bacteria within the system.

3.Electrolysis system

In addition to ammonia and nitrates, organic substances that are difficult to break down build up in water that is not replaced. So FRD Japan developed technology that promotes the decomposition of those substances, using gaseous chlorine generated through the electrolysis of seawater. Compared to a conventional system, this system is cheaper and easier to operate and control.


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