
121Bubble Production and Foamate Recovery
(7.6) and (7.7), the smaller the bubbles. To produce microbubbles in the
10 to 100 μm range, the impeller speed typically must be as high as 5,000
to 10,000 rpm. This represents very high energy intensity as the energy
consumption of agitation is proportional to the cube of the agitation speed
(McCabe et al., 2001). A reduction in gas–liquid surface tension can par-
tially improve the energy efciency of mechanical agitation because it has
been shown by this method that a lower surface tension results in smaller
bubbles (Shouci Lu and Eric, 2005). However, just as in the case of sparg-
ing, the energ