Solids removal in freshwater recirculating aquaculture systems.

摘要

The efficient removal of suspended solids from recirculated culture water is essential to maintain water quality in a recirculating aquaculture farm. Poor solids removal will lead to an increased oxygen demand, mechanical clogging of equipment, and fish stress. The objectives of this study were to assess the tandem combination of double drain tanks, swirl separators and rotating microscreen filters for removing solids and to make recommendations for system improvement. The assessment was carried out by complementing field measurements at a commercial fresh water recirculating aquaculture farm producing Atlantic salmon (Salmo salar) smolts with computer simulations. The culture tanks were found to be well mixed however the double drain did not always achieve a high degree of solids separation, but did achieve a separation in terms of particle size. Computer modelling established that the separation efficiency of the culture tanks is determined by two dimensionless groups. Removal efficiencies for the swirl separators varied from 10% to 90% and was found to increase with increasing inlet concentration. Computer models have shown that the dominant mode of removal in the swirl separators is sedimentation and that a tangential inlet does little to improve removal efficiencies. A dimensionless velocity number was found to describe the removal efficiency of the swirl separators taking into account flow rate, solids density, and geometry. The average removal efficiency of the microscreen drum filter was found to be 41%.