Multiscale analysis of floc formation for in situ optimized coagulation in algae-laden water: Integrating PSD monitoring, DLCA modeling, and MD simulations.

An in situ enhanced coagulation-flocculation-sedimentation (CFS) system coupled with online particle detection was developed for algal removal in drinking water treatment. Particle size distribution (PSD) dynamics, molecular dynamics (MD) simulations, and DLCA modeling were integrated into a multiscale framework to characterize floc growth dynamics and reveal the mechanisms governing CFS performance. PSD analysis suggested that 2-3 μm particles were important intermediate indicators of floc development and removal. Moderate pre-oxidation with FeCl2-KMnO4 achieved 95.7% algal removal. DLCA simulations showed that pre-oxidation accelerated floc growth and increased the radius of gyration (Rg) to 10.18-12.44. Sequential Fe/Al dosing with secondary coagulant addition at 90 s achieved comparable algal removal (94.4%). MD simulations indicated that Fe3+ formed strong electrostatic interactions with natural organic matter (-3000 to -4000 kJ mol-1). The DLCA model was validated by experimental floc images and morphological analysis, which yielded an Rg of 10.41 and a growth rate of 0.0362 under sequential Fe/Al dosing. Both pre-oxidation and sequential Fe/Al dosing increased floc fractal dimensions, generating more compact and stable aggregates. These findings established a multiscale mechanistic framework for optimizing enhanced CFS processes in algae-laden drinking water treatment systems.