Different aeration techniques
are available, such as diffuser aeration, mechanical
aeration and packed column aeration. For turbulent fluids,
the mean shear rate G is determined from the power input
to the fluid per unit volume of the fluid. In intensive
aquaculture systems the average power input to the fluid is
around 1–10 W/m3=101–102 cm2/s3 or 10bGb100 s−1
(Boyd, 1998; McGraw et al., 2001; Schuur, 2003). At
these moderate mixing rates, cells growing in permeable
aggregates can profit fromadvective flow and grow better
than single dispersed cells (γN1). One can calculate that
the relative growth rate of aggregated cells in this energy
regime is greater than the growth rate of free cells (Logan
and Hunt, 1987, 1988). When more intense aeration is
applied, the advantage of growing in flocs disappears and
cells growing solely show higher growth.