ABSTRACT
Dworshak National Fish Hatchery, located along the Clearwater River in north central Idaho, was constructed as a reuse hatchery in order to produce a steelhead trout smolt in 1 year. This hatchery is unique as water temperature can be controlled through recirculation, similar to an aquarium. The results, which achieved effluent ammonium concentrations of 0.1 mg/L consistently, showed promise for use at the hatchery where the reuse water quality should be less than 1 mg/L NH3-N. As the hatchery water also contains much less Biochemical Oxygen Demand and could reach temperatures of 50°F or less, it was decided to run a pilot study. Fluidized beds are high-rate biological processes which utilize the surface area provided by very small media. The operation of the fluidized bed consists of introducing the wastewater with a velocity sufficient enough to impart motion, or fluidize the bed. After the bed becomes activated with nitrifying bacteria, a biomass will begin to grow on the sand particles.
