Settling velocity characterization of aquacultural solids

A top-loading settling column is described and used to characterize the settling properties of the solids in the discharge water from a commercial rainbow trout production facility. Mass-based and phosphorus-based settling curves are presented. The median settling velocity on a mass-basis for the settleable solids was 1.7 cm s(-1). The median settling velocity for the settleable phosphorus was 1.15 cm s(-1). Manually stripping fecal material from rainbow trout resulted in settleable solids with a median settling velocity of 0.7 cm s(-1). Examination of the settling velocity curves show that halving the overflow rate (OFR) from 2 to 1 cm s(-1) changes the removal efficiency from 0.61 to 0.73, an increase of about 20%. Halving the OFR again to 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 facility to facility. The methods described in this paper can be used to perform a similar type of analysis at other aquacultural sites, which may be growing other species under different management regimes. (C) 2000 Elsevier Science B.V. All rights reserved.