Settling velocity characterization of aquacultural solids

A top-loading settling column is described and used to characterize the set tling properties of the solids in the discharge water from a commercial rai nbow trout production facility. Mass-based and phosphorus-based settling cu rves are presented. The median settling velocity on a mass-basis for the se ttleable solids was 1.7 cm s(-1). The median settling velocity for the sett leable phosphorus was 1.15 cm s(-1). Manually stripping fecal material from rainbow trout resulted in settleable solids with a median settling velocit y of 0.7 cm s(-1). Examination of the settling velocity curves show that ha lving the overflow rate (OFR) from 2 to 1 cm s(-1) changes the removal effi ciency from 0.61 to 0.73, an increase of about 20%. Halving the OFR again t o 0.5 cm s(-1) increases the removal efficiency to 0.81, an improvement of about 11%. Settling characteristics of aquacultural solids will vary from f acility to facility. The methods described in this paper can be used to per form a similar type of analysis at other aquacultural sites, which may be g rowing other species under different management regimes. (C) 2000 Elsevier Science B.V. All rights reserved.