Efficiency via flow control
Our current research in this field is aiming at a methodology to reveal the potentials of the individual plant and to find and evaluate optimal configurations and operational regimes for high energy efficiency by optimal hydrodynamic and biochemical process conditions based on numerical simulation tools. Furthermore, it is the goal to validate the implemented measures at the plant by means of innovative sensor technologies.
As the current knowledge of the hydrodynamic and biochemical processes in the waste water treatment plants is insufficient, especially due to the complexity of the multiphase flow of the aerated sludge (gas bubbles, particles and liquid), CFD simulations can be helpful for assessment and improvement. However, simulations with existing models show significant deviations from experimental results. Therefore, the demand for improvement of the simulation models is high. The project LEOBEL addresses this problem. LEOBEL ist funded by the Deutsche Bundesstiftung Umwelt (project number AZ30799).
Behaviour of gas bubbles in activated sludge
We investigate gas bubble swarms in activated sludge on different experimental scales regarding gas bubble size distributions, equivalent Sauter mean diameters, gas bubble rising velocities and local gas fractions as well as the oxygen mass transfer. Gas dispersion, bubble rise and oxygen transfer was studied on a bubble column of 3.5 m height by means of an ultrafast X-ray tomography. We investigated two commercial rubber membrane spargers and a novel monolithic membrane sparger for operation in clean water and salty water as well as activated sludge. Experimental results are used as reference data for improvement of simulation models.
Performance tests in a pilot plant
Performance tests of novel gas dispersion regimes and innovative gas injection systems are conducted in two nitrification tanks which are operated in a bypass of a waste water treatment plant. The performance of novel concepts and also commercial state of the art solutions is compared based on the energy consumption and cleaning efficiency. Moreover, the experimental results are used for validation of the optimized simulation models on an intermediate scale before their application in numerical studies of real scale waste water treatment facilities.
Improved oxygen transfer efficiency at baffles
Oxygen transfer efficiency from gas bubbles is improved by an extended residence time of the gas bubbles in the activated sludge which can be achieved by bringing baffles into the bubbly flow. Therefore, fundamental studies of the behavior of gas bubbles sliding along a baffle were conducted. We investigated the change of bubble size distribution, Sauter mean diameter, rise velocity, residence time as well as local and global mass transfer coefficient. Also, the impact of roughness, wettability, mounting angle and length of the baffles were considered. The experimental results show, that hydrophilic baffles with a small mounting angle and a short length have potential to enhance the local oxygen mass transfer. Corresponding mass transfer measurements are being conducted in experimental setups with different baffle configurations.
- Technische Universität Dortmund, Fakultät Bio- und Chemieingenieurwesen, LS Strömungsmechanik
- IWEB Institut für Wasser & Energie Bochum GmbH
- SOWAG Süd-Oberlausitzer Wasserversorgungs- und Abwasserentsorgungsgesellschaft mbH
- Ruhrverband KöR
- Sommer, A.-E., Wagner, M., Reinecke, S.F., Bieberle, B., Barthel, F., Hampel, U.
Analysis of activated sludge aerated by membrane and monolithic spargers with ultrafast X-ray tomography.
Flow Measurement and Instrumentation 53, 2017, 18–27.
- Höffmann, A. K., Ehrhard, P.
Numerical investigations of bubbles rising in water
Proceedings in Applied Mathematics and Mechanics 17, 2017 (in press).
- Sommer, A., Herrmann-Heber, R., Reinecke, S., Hampel, U.
Bafﬂes as means of process intensifcation in activated sludge aeration: an experimental study on bubble residence time.
ProcessNet Jahrestreffen 2017, Dresden (Germany), 14.-17 März 2017.