This work estimates the interior permeability of waste activated sludge flocs by observing the motion of individual flocs moving vertically toward an impermeable flat plate. Through a comparison of experimental data with theoretical predictions in the literature, floc permeabilities of original sludge and freeze–thaw‐conditioned sludges are found to be 0.7 × 10−7 to 5 × 10−7 m2 and 0.9 × 10−9 to 6 × 10−9 m2, respectively. Moreover, incorporating inertial effect delays the influence of the flat plate, thereby causing the creeping‐flow‐based correlation to fail.
We monitored the changes in concentrations, zeta potentials, sizes and capillary suction times of the solids flocs in the clarified water from eight floc blanket clarifiers of PingTsan Water Works of Taiwan Water Supply Company with low (< 10 NTU) and high (> 100 NTU) turbidity raw water. For the former, one-stage coagulation-sedimentation treatment was adopted which yielded a rather unstable blanket. Complete washout was noticeable when the PACl dosage was insufficient. On the treatment of high-turbidity raw water, on the other hand, the Works adopted the combined treatment process, that is, the raw water was first coagulated and settled in a pre-sedimentation tank, afterwards, its effluent was coagulated again and clarified in the clarifiers. The resulting flocs could form a networked blanket that was relatively stable to the shock load in raw water turbidity.
The random replacement interaction-by-exchange-with-the-mean (IEM) model, which was proposed previously as a numerically more preferable IEM scheme, had been employed for investigating the micromixing effects on the steady-state multiplicity and the relative stability of the oscillatory and stationary state of the Gray-Scott model (Gray, P.; Scott, S. K. Chem. Eng. Sci. 1983, 38, 29). In the bistable region, incomplete micromixing tends to largely reduce the attraction basin for the thermodynamic branch, while in the region where the stable limit cycle exists, it tends to weaken the relative stability of the oscillatory states. Owing to the random replacement nature of the present micromixing model, a stochastic response behavior is observed for the resulting limit cycle attractor and the attraction basin boundary on the parameter space.
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