Land-based aquaculture gets a boost from denitrification technology

Raising ocean fish in land-based tanks on a commercial scale is usually uneconomical – while coastal aquariums can simply pump seawater into their tanks, this negates some of the advantages of being land-based for a commercial operation, such as eliminating parasites and water-borne diseases, and keeping fish wastes out of the environment.

If seawater is not used, then salt must be added to freshwater with care to pH levels and temperature. When the price of the fish is quite high—as for pufferfish in Japan—the numbers may work out. But the amount of water consumed and discharged can be very high.

Such a technique can have success for larger firms. For example, Atlantic Sapphire, a salmon operation now under construction near Homestead, Florida, has a license to pump both freshwater and saltwater from wells and to inject up to 20 million gallons per day of waste water into a disposal well. The company plans U.S. output of about 9,500 metric tons (MT) by 2021 in their first stage building plan.

On a smaller scale, FRD Japan, Co., headquartered in Saitama City, has announced that in July it will scale up from a small hatchery facility for rearing trout in land-based tanks to a larger pilot plant in Chiba Prefecture, near Tokyo, with a target output of 30 metric tons (MT) per year. The firm aims to complete a commercial plant in Chiba capable of producing 1,500 MT of sushi-ready salmon slices by 2020. 

However, FRD Japan does not have the nearly unlimited water and disposal route of Atlantic Sapphire, and instead plans to utilize ordinary tap water. As such, it will employ a recirculating aquaculture system (RAS). The technology was developed in 2008 for city sewage disposal systems. It was next used at Shinagawa Aquarium in Tokyo, and is now being applied to salmon farming. The daily replacement rate of the water with new tap water is only 0.2 percent.

Trading company Mitsui & Co., Ltd. acquired 80 percent of venture company FRD's shares for an investment of JPY 900 million (USD 8.4 million, EUR 6.7 million) in April 2017. The other shareholders, with 10 percent each, are Taiyousuiken Inc. and KGC, Ltd.

Taiyousuiken Inc. is a maker of water treatment systems essential to recirculating aquaculture systems (RAS). As FRD’s land-based system uses tap water with salt added, it would be overly expensive to continually replace the water. Additionally, adjusting the water temperature of newly added water takes a lot of energy. In order to reduce water exchange, biofiltration is required to reduce ammonia toxicity. 

Fish wastes include NH3 (ammonia), which is a gas and is sometimes called “toxic” or “free” ammonia. NH4 (ammonium), the ionized form of ammonia, is a nontoxic salt. NH3 and NH4 together are often referred to as total ammonia nitrogen (TAN). 

Taiyousuiken makes a biofilm carrier, “high-speed nitrification carrier Ocean Cleaner No. 3 (OCNO 3)” made of polypropylene foam. While it is common that a biofilter must be seeded and cultured months in advance to allow the growth of a sufficient volume of bacteria, the OCNO 3 is pre-seeded can be used immediately. Though the focus in biofilm design for such carriers is usually on increasing surface area, Taiyousuiken asserts that the shape of the biofilm must also be optimized for holding bacteria. Though the surface area is one-hundredth or less than that of such heavy substrates as coral sand or porous ceramic material, the amount of water it can treat is between 50 to 80 percent that of those materials.

Nitrification of ammonia is followed by converting it into nitrogen gas by denitrifying bacteria so that it can be safely released into the atmosphere. Taiyousuiken also makes the “Ocean Cleaner N2,” an automated system to provide ideal conditions for denitrifying bacteria. The ideal environment is anaerobic, has a temperature between 35 and 38 degrees Celsius, and has a steady supply of nutrients. While Atlantic Sapphire’s system relies on the unique combination of aquifers available in South Florida, FRD’s system could be replicated anywhere.

Land-based systems are increasing worldwide. Swiss Alpine Fish AG in Lostallo, Switzerland— which also utilizes RAS technology — has a current capacity of 600 MT in the round, or 480 MT head-on gutted. The operation started with trout, which are more robust than salmon, and after that succeeded, switched over to Atlantic salmon.

CEO Julian Connor said that he is considering the Japanese market for future expansion. Though he may be playing catch up to FRD’s operations in Japan, he said: “It’s a huge market. I’m not worried about that at all.”