Pumping effect on particle sizes in a recirculating aquaculture system

Abstract

Centrifugal pumps are widely used to continuously move water to and from filtration devices in recirculating fish culture systems. The smaller the particle size, particularly below 60–100 μm, the more difficult and costly it is to remove particulate materials. Minimizing the production of small particles reduces the overall amount of filtration needed. The high rotational speed of a centrifugal pump impeller and the organic composition of suspended solids in recirculating systems suggest that particle size might be affected by pumping. The hypothesis that pumping culture water causes the waste particle sizes to decrease was tested. Water samples were taken from four hybrid striped bass recirculating aquaculture systems before and after a centrifugal pump. Sampling occurred at the pump intake and outflow sections through ball values. The samples were gently agitated to keep particles in suspension until they were analyzed using a light scattering particle analyzer. Eight samples were taken at each sampling site (64 samples total). Particle size was analyzed on both a differential volume and differential number basis in a range of 0.4–900 μm. Pumping was found to have a significant effect on particle size ( P<0.05) when judged on differential volume but it did not significantly ( P<0.05) affect differential number. The results suggest that the pumps were breaking up the larger particles into moderately smaller particles based on volume. However, this did not affect the number of very small particles (ca. <60 μm) that dominated the samples.