Characterization, Treatment, and Improvement of Aquacultural Effluents
During the water quality and sludge characterization phase, average effluent quality over the course of a day was not found to be impaired during a 7-month sampling and monitoring study at the three trout farms. However, effluent quality was found to change significantly during times of high farm activity (i.e. feeding, harvesting, cleaning, etc.). Normalized Total Suspended Solids (TSS) concentrations were found to be as high as 115 mg/l during harvesting and 63 mg/l during feeding. Solids characterization studies proved farm waste solids degrade over time and that their particle size distributions are a function of the feed size and activity of a certain raceway. Waste solids accumulation studies proved that the solids removal efficiency of farm sediment traps were very low, and after a certain period of time, they reached capacity due to particle scouring.
A pilot plant was constructed in the water and sludge treatability phase to prove a baffled settling scheme was sufficient to treat average and peak TSS concentrations during a normal workweek. The study found optimal TSS removals at detention times of 15-20 minutes, and overflow rates of 77.4 – 48.9 m3/m2·d. Given economic, spatial, and operational constraints, sedimentation was found to be the most feasible treatment technology for raceway-system trout farms.