Recirculating Aquaculture Systems

Consumer demand for fish continues to rise and, whilst this is good news for the aquaculture industry, it puts increasing pressure on traditional farming methods.

aquaculture1 Pond and open cage systems occupy large areas in already overcrowded sites, require huge volumes of water, and allow little control over the growing environment. This raises questions about the long-term sustainability of this approach and increasing numbers of fish farmers are turning to recirculating aquaculture system (RAS) technology. In RAS stock grows in tanks requiring make-up as low as 2% of the total tank water volume per day, and this can be drawn from a borehole or even a municipal water supply. RAS provides a high level of biosecurity and environmental control, so stock health is significantly improved even with high stock densities. However, fish excrete metabolites which contribute to the carbonaceous biological oxygen demand (BOD) and the ammonia concentration of the circulating water. In order to ensure healthy stock, treating the recirculating water to remove these contaminants is crucial. The process of choice is the aerobic moving bed biofilm reactor (MBBR). In this process, bacteria grow on the surface of the media, using the contaminants in the water as a food source, and form a deposit on the media surface, called a biofilm, which removes the contaminants. Within the biofilm, carbonaceous BOD is oxidized into carbon dioxide and ammonia into nitrate. The media is free to move within the aeration reactor and, unlike a fixed bed filter, is self-cleaning so backwashing is not required. A high protected surface area is needed to provide a range of micro-environments conducive to the growth of different bacteria to ensure efficient removal of both BOD and ammonia. Biopipe+ and Bioflo+ media are widely used for this application.

Advantages of Warden Biomedia

  • Low water losses
  • Efficient removal of ammonia and BOD
  • Small footprint
  • High protected surface area optimises bacterial growth
  • Reduced media blockages and fouling problems and lower maintenance costs
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