Solids removal from a coldwater recirculating system—comparison of a swirl separator and a radial-flow settler

Solids removal across two settling devices, i.e., a swirl separator and a radial-flow settler, and across a microscreen drum filter was evaluated in a fully recirculating system containing a single 150 m ‘Cornell-type’ dual-drain tank during the production of food-size Arctic char and rainbow trout. The flow through the culture tank was 4500–4800 L/min. Approximately 92–93% of the system flow exited through the Cornell-type sidewall drain. The remaining 7–8% of the flow, approximately 340 L/min, exited through a bottom–center drain and an external standpipe and then to the settling tank. The surface-loading rate applied to both settling tank designs was 0.0031 m/s per square meter (4.6 gpm/ft) of settling area. The swirl separator and the radial-flow settler were evaluated over a range of feeding rates to evaluate the relationship between inlet TSS concentration and TSS removal efficiency. There was a highly significant difference (P < 0.001) in mean TSS removal efficiency of the swirl separator and radial-flow settler, ( S.E.) 37.1 3.3% and 77.9 1.6%, respectively. Also, TSS removal efficiency of the radial-flow settler was less variable than removal efficiency of the swirl separator. The trend in TSS removal efficiency was consistent over a broad range of inlet TSS concentrations to the separator. A mass balance indicates that the swirl separator only removed approximately 23% of the total mass of TSS removed from this recirculating system. However, when the radial-flow settler was operated in the same recirculating system, it accounted for approximately 48% of the mass of TSS removed from the system daily. The mass balance calculations also indicate that the microscreen drum filter accounted for approximately 40–45% of the mass of TSS removed daily from the recirculating system when using either settling device. In either case, these results www.elsevier.com/locate/aqua-online Aquacultural Engineering 33 (2005) 47–61 * Corresponding author. Tel.: +1 304 876 2815; fax: +1 304 87