Fractal Aggregates Evolution During Flocculation

Abstract

A temporal analysis of fractal aggregates during water flocculation is presented. Water was prepared using kaolin solution and a non-intrusive image-based analysis method was used for two-dimensional fractal dimension assessment (d F). The d F values were determined for aggregates larger than 270 µm from 100 images taken in each combination of velocity gradients (G f) and flocculation times (T f). The G f values of 20, 30, 40, 50 and 60 s-1 and T f values of 2 to 180 minutes were studied, with a ΔT f of 1 minute for 2 ≤ T f ≤ 10 minutes and a ΔT f of 5 minutes for 10 ≤ T f ≤ 180 minutes. Results showed that d F tends toward stability from a T f of 40 minutes, with distinct levels in each G f. Further, d F values decrease from 1.80 to 1.35 for G f from 20 to 60 s-1 .

Simultaneous In Situ Characterization of Turbulent Flocculation and Reactor Mixing Using Image Analysis and Particle Image Velocimetry in Unison

“…Temporal D 2 variations for both CC and EC exhibited a trend toward a higher D 2 , indicating a shift toward a more spherical, compact, and less porous floc throughout flocculation, 1,7,68 possibly due to cyclical floc breakage and regrowth. 37 Our observations agree with other reports of more compact flocs forming over time for lower G̅ values, 24,73,74 whereas contrasting trends are also available. 7,22,24,68 3.2.3.…”

“…For the CC and EC experiments, a vertical cross section of the reactor was illuminated using a 15 W Millennia eV TM CW diode-pumped solid-state (DPSS) laser operated at 10 W combined with optics to convert the concentrated laser beam into a light sheet approximately 2.3 mm thick and situated approximately 3 cm from the reactor wall, as shown in Figures a and . Images were captured using a Phantom Miro M340 charged couple device high-speed camera with a 25.6 mm by 16.0 mm 12-bit complementary metal oxide semiconductor sensor with an output image size of 1600 horizontal pixels by 1600 vertical pixels, offering a higher total pixel count and dynamic range compared to similar studies. ,,− High-speed image data were acquired by software Phantom Camera Control supplied by the camera manufacturer. A CAT-6 Ethernet cable was used to communicate with the camera and transfer image data.…”

“…37 Our observations agree with other reports of more compact flocs forming over time for lower G̅ values, 24,73,74 whereas contrasting trends are also available. 7,22,24,68 3.2.3. Mean and Maximum Floc Sizes.…”

“…Given the importance of these characteristics, many laboratory-scale investigations have explored the role of mixing hydrodynamics on orthokinetic flocculation and found that higher mixing intensities result in smaller steady-state floc sizes. − Spatial variations in floc size distributions, mean size, and morphology have been reported to be highly dependent on overall reactor size and baffle widths, providing important insights into the viability of applying results obtained from laboratory-scale experiments to full-scale facilities. , In contrast, the influence of mixing on floc morphology is unclear, with higher shear rates reportedly yielding more compact flocs in some cases, , more branched flocs in other instances, and even having no effect in yet other experiments . The impacts of mechanical mixing choices, which directly tie to hydrodynamic conditions, have also been explored, with a paddle mixer generating more compact flocs compared with a rolling cylinder .…”