Computational study of aeration for wastewater treatment via ventilated pump-turbine

• Published in: The International journal of heat and fluid flow 2018-02, Vol.69, p.43-54
• Main Authors: Daskiran, Cosan, Riglin, Jacob, Schleicher, W. Chris, Oztekin, Alparslan
• Format: Article
• Language: English
• Subjects: Aeration; Large eddy simulation; Mixture multiphase model; Multiphase flow; Oxygen dissolution; Wastewater treatment
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/j.ijheatfluidflow.2017.11.006

•Characteristics of oxygen dissolution for wastewater treatment is investigated.•Large eddy simulations are conducted by employing mixture multiphase model.•Sufficient level of oxygen dissolution for wastewater treatment can be achieved.•Dissolution rate is higher in regions with higher vortical activities.•Power generation of the turbine is hardly influenced by aeration. Large eddy simulations were performed on a modular pump-turbine to study oxygen dissolution inside the draft tube. Air injection was applied over the runner cone surface during turbine operation. Data regarding bubble size, void fraction and interfacial area concentration were presented to understand their influence on oxygen dissolution. Transient single phase and multiphase flow simulations were carried out to investigate the influence of air injection and dissolution within the flow field and turbine performance. Multiphase simulations were conducted by using the mixture multiphase model. The mathematical modeling of oxygen dissolution employed was validated by comparing predicted oxygen dissolution against experimental measurements performed by Zhou et al. (2013). The averaged dissolved oxygen concentration in the range of 1.2–1.4 mg/l was obtained; which is sufficient for an active aerobic microorganism activity for wastewater treatment processes. Dissolution efficiency and the amount of averaged dissolved oxygen inside the draft tube were sensitive to the inlet bubble size. The efficiency of the dissolution increases strongly as the inlet bubble size was reduced. The obtained results revealed that vortex suppression was achieved through air admission within multiphase flow simulation. Moreover, the power generation of the turbine was hardly influenced by the aeration through the runner cone.