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The impact of local hydrodynamics on high-rate activated sludge flocculation in laboratory and full-scale reactors

(2020) Processes. 8(2).
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Abstract
High rate activated sludge (HRAS) processes have a high potential for carbon and energy recovery from sewage, yet they suffer frequently from poor settleability due to flocculation issues. The process of flocculation is generally optimized using jar tests. However, detailed jar hydrodynamics are often unknown, and average quantities are used, which can significantly differ from the local conditions. The presented work combined experimental and numerical data to investigate the impact of local hydrodynamics on HRAS flocculation for two different jar test configurations (i.e., radial vs. axial impellers at different impeller velocities) and compared the hydrodynamics in these jar tests to those in a representative section of a full scale reactor using computational fluid dynamics (CFD). The analysis showed that the flocculation performance was highly influenced by the impeller type and its speed. The axial impeller appeared to be more appropriate for floc formation over a range of impeller speeds as it produced a more homogeneous distribution of local velocity gradients compared to the radial impeller. In contrast, the radial impeller generated larger volumes (%) of high velocity gradients in which floc breakage may occur. Comparison to local velocity gradients in a full scale system showed that also here, high velocity gradients occurred in the region around the impeller, which might significantly hamper the HRAS flocculation process. As such, this study showed that a model based approach was necessary to translate lab scale results to full scale. These new insights can help improve future experimental setups and reactor design for improved HRAS flocculation.
Keywords
BIOMATH, water resource recovery facility, sludge settling, flocculation state, jar test, CFD

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MLA
Balemans, Sophie, et al. “The Impact of Local Hydrodynamics on High-Rate Activated Sludge Flocculation in Laboratory and Full-Scale Reactors.” Processes, vol. 8, no. 2, MDPI, 2020.
APA
Balemans, S., Vlaeminck, S., Torfs, E., Hartog, L., Zaharova, L., Rehman, U., & Nopens, I. (2020). The impact of local hydrodynamics on high-rate activated sludge flocculation in laboratory and full-scale reactors. Processes, 8(2).
Chicago author-date
Balemans, Sophie, Siegfried Vlaeminck, Elena Torfs, Leonie Hartog, Laura Zaharova, Usman Rehman, and Ingmar Nopens. 2020. “The Impact of Local Hydrodynamics on High-Rate Activated Sludge Flocculation in Laboratory and Full-Scale Reactors.” Processes 8 (2).
Chicago author-date (all authors)
Balemans, Sophie, Siegfried Vlaeminck, Elena Torfs, Leonie Hartog, Laura Zaharova, Usman Rehman, and Ingmar Nopens. 2020. “The Impact of Local Hydrodynamics on High-Rate Activated Sludge Flocculation in Laboratory and Full-Scale Reactors.” Processes 8 (2).
Vancouver
1.
Balemans S, Vlaeminck S, Torfs E, Hartog L, Zaharova L, Rehman U, et al. The impact of local hydrodynamics on high-rate activated sludge flocculation in laboratory and full-scale reactors. Processes. 2020;8(2).
IEEE
[1]
S. Balemans et al., “The impact of local hydrodynamics on high-rate activated sludge flocculation in laboratory and full-scale reactors,” Processes, vol. 8, no. 2, 2020.
@article{8649629,
  abstract     = {{High rate activated sludge (HRAS) processes have a high potential for carbon and energy recovery from sewage, yet they suffer frequently from poor settleability due to flocculation issues. The process of flocculation is generally optimized using jar tests. However, detailed jar hydrodynamics are often unknown, and average quantities are used, which can significantly differ from the local conditions. The presented work combined experimental and numerical data to investigate the impact of local hydrodynamics on HRAS flocculation for two different jar test configurations (i.e., radial vs. axial impellers at different impeller velocities) and compared the hydrodynamics in these jar tests to those in a representative section of a full scale reactor using computational fluid dynamics (CFD). The analysis showed that the flocculation performance was highly influenced by the impeller type and its speed. The axial impeller appeared to be more appropriate for floc formation over a range of impeller speeds as it produced a more homogeneous distribution of local velocity gradients compared to the radial impeller. In contrast, the radial impeller generated larger volumes (%) of high velocity gradients in which floc breakage may occur. Comparison to local velocity gradients in a full scale system showed that also here, high velocity gradients occurred in the region around the impeller, which might significantly hamper the HRAS flocculation process. As such, this study showed that a model based approach was necessary to translate lab scale results to full scale. These new insights can help improve future experimental setups and reactor design for improved HRAS flocculation.}},
  articleno    = {{131}},
  author       = {{Balemans, Sophie and Vlaeminck, Siegfried and Torfs, Elena and Hartog, Leonie and Zaharova, Laura and Rehman, Usman and Nopens, Ingmar}},
  issn         = {{2227-9717}},
  journal      = {{Processes}},
  keywords     = {{BIOMATH,water resource recovery facility,sludge settling,flocculation state,jar test,CFD}},
  language     = {{eng}},
  number       = {{2}},
  publisher    = {{MDPI}},
  title        = {{The impact of local hydrodynamics on high-rate activated sludge flocculation in laboratory and full-scale reactors}},
  url          = {{http://dx.doi.org/10.3390/pr8020131}},
  volume       = {{8}},
  year         = {{2020}},
}

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