Settling and coagulation characteristics of fluorescent particles determined by flow cytometry and fluorometry

The new technique of flow cytometry (FC) to count and size fluorescent particles (FP) and the laboratory application to characterize settling and coagulation of model particles are described. Suspensions of FP and sewage particles (SP) in different ratios were coagulated and settled under stirred or quiescent conditions. Coagulation efficiency of FP with SP was less than 0.0005. Non-interactive settling (NS) accounted for most particle removal in laboratory experiments, although thermal convection currents caused dispersion. Decrease in particle numbers of well mixed suspension was first order. Decrease in total suspended particles was higher order because of differences in settling rates among particles. Systems where NS predominated represented systems where coagulation was important. FC analysis of particles removed by NS showed that fluorescent emission for individual particles was proportional to particle surface area. When applied to field studies, FP would represent the limiting case of low interaction behaviour.