Recirculating aquaculture systems (RAS) and bio-floc systems (BFS) for the production of shrimp are a potentially sustainable alternative to traditional culture systems in terms of water conservation and reduced impact on receiving water quality. RASconsist of an integrated set of unit processes that treat water for reuse in the culture tank. RAS require unit processes, external to the culture unit, to remove particulate waste solids, biological filters to oxidize toxic ammonia-nitrogen and nitrite-nitrogen, and aeration of the water to remove carbon dioxide and increase oxygen concentrations (Ebeling, 2000). In contrast, BFS were developed to manage water quality by stimulating the growth of heterotrophic bacteria within the culture unit (Avnimelech, 2003; Burford et al, 2003); therefore, BFS are similar, in principle, to activated sludge wastewater treatment systems. In BFS microbial breakdown of organic matter, along with a nitrogen source for protein synthesis, leads to the production of new bacterial cell material; consequently, inorganic nitrogen is immobilized into bacterial proteins (Avnimelech, 1999). Both RAS and BFS can be operated at or near zero water exchange, i.e., no water discharge during a cropping cycle and are suitable for indoor and outdoor culture. Long-term operational stability of these systems depends on the ability of microorganisms to remove toxic nitrogen species (e.g., ammonium and nitrite) and on the use of natural biota, which includes bacteria and algae, as a supplemental feed source (Burford et al, 2003; Burford et al, 2004; Avnimelech, 2007).
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