(ii) Centrifugation. It can be effectively used for precipitation of bacterial cells or macromolecules, if the density differs from that of the medium (consult Chapters 40 and 45 for more details). (iii) Flocculation and floatation. These techniques facilitate separation, where filtration and centrifugation are not suitable. For instance, small bacterial cells, can be induced to stick together with the help of inorganic salts, minerals or organic polyelectrolyses. The size of particles thus increases, which facilitates flocculation, so that the flocculated cells can be recovered by centrifugation. It other cases, gas bubbles, which are created in the medium, adsorb to the cells making a foam, which would undergo floatation and can be easily recovered. Flocculation and floatation are most efficient for the recovery of microbial biomass in single cell protein (SCP) production systems (consult Chapter 45 for SCP)