In a typical recycled aquaculture system, the oxidation of ammonia in the biofilters will cause nitrate to build up to the point of being detrimental to animal health. The general solution to this problem is a water change, but regulations in locations affected by drought now limit the amount of water available. In addition, regulations limit nitrate discharge concentrations under many conditions. These discharges to control nitrate concentrations also discharge any salts that have been added to the recycle system water, as well as alkalinity added to neutralize the nitrate being created.
Aquaneering Denitrification System
Enter the denitrification system. Denitrification systems have been in use for several decades, primarily in wastewater treatment, but have not been traditionally used in aquaculture and aquatic filtration systems.
Dallas Weaver, Ph.D. and the Aquaneering
production team testing the denitrification system
The denitrification system currently being developed by Aquaneering reduces nitrate to nitrogen gas and then uses an aerobic fluidized bed to oxidize any residuals from the anaerobic denitrification reaction. This system will be used to process and recycle the high nitrate wastewater for a striped bass hatchery in Ensenada, Mexico. The system will support brood stock and fingerlings for production, which will be released to pens in the Pacific at a certain age and size for grow-out.
The unique design is a collaboration between Dallas Weaver, Ph.D., of Scientific Hatcheries, and Mark Francis of Aquaneering. The system will process 60 to 120 tons of water per day, providing nitrate-free return water and eliminating an equal volume of total water demand.
The main anaerobic reactor is a specially designed fluidized bed bioreactor (FBB) with an atmosphere controlled packed column for removing the nitrogen produced, without
adding oxygen to the water. Bacteria growing on the sand media will reduce the nitrate to nitrite and then to nitrogen gas. As some potentially toxic compounds and residual ammonia are often formed under anaerobic microbiological conditions, this anaerobic system discharge will be treated with a high-performance aerobic fluidized bed biofilter and “protein skimmer” to control colloidal solids and surface active agents. The overall system is tied into a SCADA system for alarming and remote notifications. This particular design is skid mounted for easy installation.
The Ensenada hatchery will have recirculating water and zero discharge in an environment with a very limited water supply. The end result: protecting precious resources and supporting fish hatcheries through technological innovation.