EFFECTS OF MACROMOLECULAR CONFORMATION UPON SOLID-LIQUID SEPARATION AND WATER-TREATMENT PLANT RESIDUALS

The efficiency of solid-liquid separation in coagulation -sedimentatio n processes depends greatly upon the performance of the coagulant with respect to the production of suitable flee properties. When high-mole cular weight polymers (that function primarily by bridging between pro ximate primary particles) are used as coagulant-aids, the dynamic proc esses of polymer adsorption and macromolecular rearrangement figure pr ominently in the success of flee formation. Ideally, one would like to have the macromolecule adsorb quickly upon the primary particle surfa ce in an extended, rod-like conformation; this configuration should pe rsist throughout the collisional process to produce rapid flee growth. A period of macromolecular relaxation would then ensue, with the form ation of additional affiliations between functional groups and surface sites. Recently, there have been speculations that the relative speed s of these processes may not necessarily conform to the common percept ion that sorption is quick and that the rearrangement of the sorbed ma cromolecule is fairly slow. These questions are critical with respect to the optimal design of coagulation processes that minimize water tre atment plant residuals. It is the purpose of the present work to quant itatively assess the dynamic behavior of polymer coagulant-aids in the flocculation of colloidal kaolin. This has been accomplished through use of an unique settling experiment in which the characteristic time associated with reduction of size of the pendant polymer loops can be determined; in this procedure, macrovideography is used to continuousl y record flee size, and light obscuration is used to produce phototube output profiles that directly reflect characteristics of both flee gr owth and the sedimentation process. Additional confirmation of these r esults was sought with a series of simple filtration experiments.