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The tubular flocculation reactor is a new and efficient device for treating algae-containing wastewater. The introduction of bubbles during the reaction process can effectively shorten the time required for floc separation. However, the impact of bubbles on floc formation and removal in the tubular flocculation reactor is not well understood. To further clarify the effect of bubbles on the reactor’s operation, this study employed a uniform experimental design, varying the flow rate, chemical dosage, bubble reaction distance, and bubble injection rate in the reactor to examine the influence of bubbles under different operating conditions. The results indicated that as the bubble reaction distance increased from 0 m to 7.6 m, the removal efficiency increased from 60% to 70%, the floc size increased from 160 μm to 165 μm, and the fractal dimension decreased from 2.1 to 1.9. When the bubble volume increased from 5% to 30%, the removal efficiency increased from 50% to 80%. Under constant bubble conditions, the rising speed of the flocs increased from 0.4 mm·s⁻¹ to 1.2 mm·s⁻¹, while the removal efficiency increased from 30% to 90%. A logarithmic correlation was observed between the rising speed and removal efficiency. A linear relationship was found between the floc rising speed and the floc size, with floc size increasing from 200 μm to 800 μm and the rising speed increasing from 0.4 mm·s⁻¹ to 2.3 mm·s⁻¹. An exponential relationship was found between the fractal dimension and the rising speed, with the rising speed decreasing from 2.3 mm·s⁻¹ to 0.4 mm·s⁻¹, while the fractal dimension increased from 1.93 to 2.02. Full article

A study was undertaken at Lake Apopka in Florida to assess the minimum water depth required to contain a wind-induced episodic rise of fluid mud. In a year-long investigation, measurements were made at the mean water depth of 1.3 m to record the variation of suspended sediment concentration due to bed erosion and settling of the flocculated matter. The height of rise is defined as the elevation above the bed at which the mud floc volume fraction is at the threshold between the so-called flocculation settling and hindered settling regimes. The rise, which is considered significant when fluid mud occupies the 0.2 m high benthic boundary layer (BBL), occurs when the threshold wind exceeds about 9 m s⁻¹ corresponding to a 4% cumulative probability of occurrence. Predictive modeling suggests that in 2 m water depth the required wind would be about 14 m s⁻¹ with a low probability of 2%. Moreover, a transition occurs from wave-dominant resuspension at low depths to current-dominance in deeper water, which likely influences BBL dynamics with potential effects on the benthic biota. Provided a higher than present depth can be sustained in the large lake, the deduced relationship between fluid mud rise, wind speed, and water depth makes it feasible to select the depth at which the frequency of fluid mud occupying the BBL remains acceptably low. The developed protocol is general enough to be applicable to other similar shallow lakes where fluid mud rise must be contained. Full article