Floc characteristics, including their size distribution,
mean size,
and fractal dimension, are impacted by mixing intensity and duration,
coagulant dosing method, dose, type, and pH. Herein, we directly employ
flocs inherently generated during treatment to determine instantaneous
velocity fields, which were further utilized to estimate local velocity
gradients and turbulent kinetic energy dissipation (TKED) rates. This
novel non-intrusive methodology, which combines particle image velocimetry
(PIV) and an imagery-based sizing scheme, was examined through the
characteristics of reactor mixing and flocculation from in
situ measurements for conventional FeCl3 chemical
coagulation and iron electrocoagulation (EC). Our first-of-its-kind
procedure avoids the need to externally add artificial seeding particles
for PIV analysis, automatically reducing the number of experiments,
and simultaneously improves both accuracy and precision by linking
fluid dynamics and particle characteristics with only a single experiment.
The TKED rates estimated using flocs were largely similar with conventional
artificial seeding at the early stage of flocculation when flocs were
smaller. However, the new method is expected to estimate turbulence
more accurately in the flocs’ microenvironment during the later
stages of tapered flocculation when particle sizes are similar to
dissipation eddy dimensions, especially at high particle concentrations
(i.e., highly turbid waters). Measured size distributions,
mean sizes, and fractal dimensions confirm the robustness of the present
imagery-based sizing scheme and showed that EC produced numerous and
more compact flocs than conventional coagulation.