Design and management of conventional fluidized-sand biofilters

Fluidized-sand beds are an efficient, relatively compact, and cost-competitive technology for removing dissolved wastes from recirculating aquaculture systems, especially in relatively cool or coldwater applications that require maintaining consistently low levels of ammonia and nitrite. This paper describes several types of flow injection mechanisms used in commercial fluidized-sand biofilters and provides criteria for design of flow distribution mechanisms at the bottom of the fluidized bed. This paper also summarizes the most critical aspects of sand selection, as well as methods for calculating or experimentally measuring fluidization velocities and pressure drop for a given filter sand size distribution. Estimates of nitrification rate, ammonia removal efficiency, carbon dioxide production, and oxygen consumption across fluidized-sand biofilters are also provided for various conditions. Fluidized-sand biofilter operational and management practices are also described.