Investigation of the shape change of bio-flocs and its influence on mass transport using particle image velocimetry.
In this laboratory study, an advanced flow visualization technique - particle image velocimetry (PIV) - was employed to investigate the change of shape of activated sludge flocs in water and its influence on the material transport characteristics of the flocs. The continuous shape change of the bio-flocs that occurred within a very short period of time could be captured by the PIV system. The results demonstrate that the fluid turbulence caused the shift of parts of a floc from one side to the other in less than 200 ms. During the continuous shape change, the liquid within the floc was forced out of the floc, which was then refilled with the liquid from the surrounding flow. For the bio-flocs saturated with a tracer dye, it was shown that the dye could be released from the flocs at a faster rate when the flocs were swayed around in water. The experimental results indicate that frequent shape change of bio-flocs facilitates the exchange of fluid and materials between the floc interior and the surrounding water. This mass transfer mechanism can be more important than molecular diffusion and internal permeation to the function and behavior of particle aggregates, including bio-flocs, in natural waters and treatment systems.
Department of Civil Engineering, Environmental Engineering Research Centre, The University of Hong Kong, Pokfulam Road, Hong Kong, China E-mail: xlia@hkucc.hku.hk.
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Ren
Department of Civil Engineering, Environmental Engineering Research Centre, The University of Hong Kong, Pokfulam Road, Hong Kong, China E-mail: xlia@hkucc.hku.hk; Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
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Xiao
Department of Civil Engineering, Environmental Engineering Research Centre, The University of Hong Kong, Pokfulam Road, Hong Kong, China E-mail: xlia@hkucc.hku.hk.
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Sun
Department of Civil Engineering, Environmental Engineering Research Centre, The University of Hong Kong, Pokfulam Road, Hong Kong, China E-mail: xlia@hkucc.hku.hk; Harbin Institute of Technology Shenzhen Graduate School, Shenzhen 518055, China.
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Sun
Department of Civil Engineering, Environmental Engineering Research Centre, The University of Hong Kong, Pokfulam Road, Hong Kong, China E-mail: xlia@hkucc.hku.hk.
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Lam
Department of Civil Engineering, Environmental Engineering Research Centre, The University of Hong Kong, Pokfulam Road, Hong Kong, China E-mail: xlia@hkucc.hku.hk.
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Li
D005427:Flocculation; D057446:Hydrodynamics; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D014874:Water Pollutants, Chemical