Effect of mixing on the kinetics of polymer-aided flocculation

Polymer-aided flocculation is defined in this study as the coagulation and flocculation process which is accomplished by using alum in conjunction wit h a small dosage of polymer. Polymer is commonly used to improve flocculati on performance; however, few in-depth studies of mixing requirements when u sing polymer as an aid have been reported. Presented is an evaluation of th e effect of mixing on the kinetics of polymer-aided flocculation. The study found that the optimum (G) over bar(f)-values occurred at 70 to 100 s(-1), such that (G) over bar(f) t(b)-values (Camp Number) were in the range of 1 13,000 to 144,000. The limited improvement in kinetics achieved by increasi ng the (G) over bar(f)-value beyond 100 s(-1) will probably not justify the higher energy consumption. Moreover, experimentation has shown that the ma ximum (G) over bar(f)-value recommended for the design is (G) over bar(f)=2 00 s(-1) ((G) over bar(f)t(b)=252,000), and the critical mixing rate occurr ed at (G) over bar(f)=400 s(-1) ((G) over bar(f)t(b)=432,000), beyond which significant flee break-up will occur. The optimum (G) over bar(f)-value de termined from the study suggests that the currently designed flocculators u sing alum alone can be used when polymer is used as a coagulant aid. Thus, the use of polymer as a coagulant aid can improve the coagulation and flocc ulation efficiency in existing systems.