EFFECTS OF DOSING REGIMEN AND AGITATION PROFILE UPON FLOC CHARACTERISTICS

The efficiency of solid-liquid separation processes that employ floccu lation and sedimentation mainly depends upon the characteristics of ag gregates produced by coagulation. Size and density are foremost, howev er, most flocculation processes are designed such that many larger flo cs are formed by floc-floc collisions resulting in the entrapment of l arge amounts of interstitial water. Thus, as particle size increases, flee density generally decreases. Not only does this affect the achiev able rate of sedimentation, but it also contributes to the volume of p rocess sludge that must be dewatered prior to ultimate disposal. The o bjective of the present work is to examine combinations of flocculant dosing and activation along with shear profile or history that can pro duce flocs of unusually compact structure, thereby increasing the effi ciency of separation and reducing the volume of sludge produced. Four types of batch coagulation experiments were conducted, employing both single and intermittent polymer applications as well as periodic episo des of elevated shear to provide more compact constituent hoc structur es. A light obscuration method, in which the increase in diode phototu be output during sedimentation was used to assess mean aggregate densi ty, was employed throughout the study; it provided a convenient means for comparison of the effects of process modifications upon sedimentat ion.