Measurement of the adsorption of 14C-Polyethyleneimine polymers during flocculation of silica,bacteria and algae

¹⁴C-Polyethyleneimine polymers of two different mol. wts have been prepared. These polymers have been used to study the flocculation of silica in water, of the bacterium E. coli in its nutrient and over a range of polymer concentration from about 1 to 1000 ppm. The degree of flocculation, and the amounts of polymer adsorbed on the colloid surface and the corresponding equilibrium concentration of polymer in solution have been measured. The concentration of polymer added to produce flocculation increased in the ratio from 1:30:500 in comparing silica. E. coli and C. ellipsoidia, respectively. However, the amount of polymer adsorbed on the same three colloids labelled with the tagged polymer, increased in the ratio 1:10:20 under comparable conditions. The higher concentrations needed to flocculate the two biocolloids cannot, therefore, be attributed to lack of adsorbed polymer on the surface. It is also true that much higher concentrations of polymer were needed on the surface to reverse the charge on the biocolloids compared with silica in order that flocculation might occur. The results are discussed briefly especially in relation to the need to explain flocculation phenomena in terms of the surface areas of the colloids and surface coverage by the polymers. Experimental results are reported which indicate that interaction of PEI polymers with anions in the algal and E. coli nutrients, and with biopolymers formed in the growth of the latter are important in affecting flocculation.