<p> The thickening and classifying characteristics of small size hydrocyclones were investigatedo Test slurries, consisting of mixed cultures of microorganisms in water. were partitioned into two fractions by hydrocyclones ranginq in size from 2 mm to 10 mm body diameter which operated at inlet pressures ranging from 80 to 200 psi and volume splits ranginq from 1.0 to 3.0. </p> <p> The classtfyino response was defined in terms of the relative magnitudes of the specific growth rate of the two fractions as determined by coincident observation of duplicate batch biological reactors each seeded with one portion of the partitioned slurry. </p> <p> The thickening response was defined by the Rietema-Tenbergen separation efficiency. </p> <p> The biokinetic aspects of this investigation are emphasized in this manuscript. </p> / Thesis / Master of Engineering (MEngr)