(682d) Effects of Interfacial Forces On the Hydrodynamic Behavior of An Anaerobic Sequencing Batch Reactor (ASBR)

Hydrogen is known as a clean and ideal energy source due to its renewable status and green effect on the global environment (Nurtono et al., 2012). It can be obtained through physicochemical and biological routes. The hydrogen production by microorganisms (biohydrogen) is affected simultaneously by biological, physical, and chemical factors (Ding et al., 2010; Wang et al., 2009; Wang et al., 2010). Although its production is complex, with numerous interactions between gas, liquids and solids, current research has focused primarily on the biological and chemical characteristics (Nath and Das, 2004). However, the physical characteristics of the reactors are seldom well described (Cao et al., 2010).

In this sense, CFD tools can be valuable to study the fluid dynamics in bioreactors. Simulations can provide values in any location inside the reactor, and the influence of each force can be analyzed independently. However, there are difficulties when simulating the phenomena occurring in the reactor. The interaction between the dispersed gas phase and the continuous liquid phase, for example, is affected by interfacial forces (drag, lift and virtual mass forces) and the turbulence in the reactor. Therefore, the correct modeling of these forces is of prime importance for capturing the physics correctly (Tabib et al., 2008).

The present work aims to use CFD techniques in order to analyze the influence of interfacial forces on the behavior of a gas-liquid flow in a pilot-scale anaerobic sequencing batch reactor. The reactor has a capacity of 1 m³, operating with a mixture of wastewater and biomass for biohydrogen production.

Numerical simulations were carried out considering gas bubbles and liquid injected at the bottom of the reactor. The phases leave the reactor through different tubes, located at the top of the reactor. The interaction between the disperse bubbles and the liquid phase in the turbulent flow inside the reactor is influenced by the drag, lift and virtual mass forces. Thus, in the present work the sensitivity of these forces has been evaluated through simulations using an Eulerian-Eulerian framework. Each case was calculated to simulate 300 s of flow, with the last 100 s considered to obtain average values.

Results indicates that the interfacial forces have their greatest influence in the bottom part of the reactor. The lift force shifts the maximum of gas volume fraction and axial velocities to the center of the reactor, while the virtual mass force accentuate those peaks. In the middle and top section of the reactor, the lift force has lower influence on the flow, but the virtual mass force still causes higher maximum values in the evaluated variables. References

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