Effect of Coagulation and Applied Breakage Shear on the Regrowth of Kaolin Flocs

摘要

A computer-controlled digital camera was used to examine the formation, breakage, and regrowth of flocsnformed by kaolin or the mixture of kaolin and humic acid with aluminum sulfate (alum) at different intensities ofnapplied shear, as well as for continuous optical monitoring (Photometric Dispersion Analyzer). The computercontrolledndigital camera could record the flocs size and morphology. There was full regrowth of flocs in kaolinnsuspension when their zeta potential was close to zero, regardless of intensity of the applied shear, whichnindicated a significant reversibility of the floc break-up process. However, such a process displayed a distinctnirreversibility at higher alum dosage when the flocs were positively charged as the intensity of applied shearnincreased, though there was full reversibility of floc breakage at low applied breakage shear. Addition of humicnacid weakened the reversibility of broken flocs in all cases, especially at high breakage shear. Two-dimensionalnfractal dimension (D2) of regrown flocs in kaolin suspension coagulated under condition of charge neutralizationnwas not influenced by the applied shear except at high applied shear (400 rpm), whereas at a higher alum dosagenthe D2 decreased as the applied shear increased. The D2 was lower in the presence of humic acid. Further, the D2nof regrown flocs with charge neutralization was higher than that with higher alum dosage, whether the modelnwater contained humic acid or not. Without humic acid in water, the residual turbidity and particle number afternbreakage and regrowth were both decreased as the applied shear increased up to 250 rpm. Higher breakagenshear, such as 400 rpm, gives higher residual turbidity (or residual particle number). This work gives newninformation and a better understanding of the regrowth of broken flocs, a subject which is of considerablenpractical importance in water and wastewater treatment.