1. Supervisors: John Chew, Jannis Wenk
Understanding small scale bubble generation and their applications in wastewater treatment
Levke Ortlieb
Supervisors: John Chew, Jannis Wenk
22/06/2017

2. Aeration of activated sludge
Motivation
Removal of organic waste: aerobic biological treatment
Typical bubble size for aeration: 2-5mm
Aeration: 45-75% of energy consumption
How can aeration efficiency be improved?
Aeration of activated sludge
Image source:

3. Image source: Garcia-Ochoa, 2010
Transport Mechanism
Oxygen has to be transferred from the gas bubble to the cell
Rate limiting steps:
diffusion through liquid film around bubble and
stagnant liquid around solid particles
Liquid film
Liquid-solid-interface
Cell
Bulk liquid
Gas-liquid interface
Gas film
Gas bubble
Image source: Garcia-Ochoa, 2010

4. Behaviour of different bubbles in water
Small scale bubbles
Advantages:
Long residence time
Large surface area per volume
Improved mixing
Better mass transfer
Behaviour of different bubbles in water
Image Source: Khuntia, 2012

5. Image source: Muroyama, 2013
Research Questions
Improved oxygen transfer?
Retrofitting to existing plants?
Energy and resource savings?
Smoother process control?
Computational model and experiments
Microbubbles
Macrobubbles
Image source: Muroyama, 2013

6. Thank you for your attention!

7. References In case there is a question on why microbubbles –
Nanobubbles are not within our consideration because it is not good for mixing (nanobubbles remain stagnant in liquid).
Macrobubbles – buoyancy plays a larger role than surface tension, hence it rises rapidly.
Microbubbles (in the region of microns) – this is a balance between increased surface area, low buoyancy effect vs. surface tension, still induce a reasonable level of mixing