Developing a model to determine the settling velocity of ballasted flocs

Muhammad Qasim, Seongjun Park, Yonggeol Moon, Jong Oh Kim

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Ballasted flocculation is an advanced clarification process capable to treat exceed of colloidal and suspended particles in natural water resources caused by climate change. The settling velocity of aggregated flocs is the most important design parameter in BF facilities. The ballasted flocs exhibit hybrid properties due to solid (ballast) and porous (coagulated suspended particles) fractions of internal structure. Therefore, the transition of ballasted flocs in fluid medium exhibits different phenomenon compared to conventional flocs. Therefore, it is imperative to investigate and model the transition of ballasted flocs in fluid medium using real time camera observations. During the past decade, many attempts have been made to develop models exhibiting settling phenomenon of ballasted flocs. However, the developed models underestimate the settling velocity due to a lack of real-time observations of the settling behavior of ballasted flocs. In this study, real-time observations of the settling velocity of individual floc were conducted by adopting an image analysis method. The observed experimental velocities were used to compare and modify the existing floc density and settling velocity models. The modified velocity models based on existing correlations insufficiently predicted the settling velocity variations of ballasted flocs. Therefore, we propose a model that extends the widely used Stokes' law with the modified Tambo and Watanabe model to precisely predict the settling velocity of ballasted flocs. Statistical analyses (70% correlation) illustrated that the proposed model is the most suitable approach for predicting the settling velocity of ballasted flocs.

Original languageEnglish
Article number104515
JournalJournal of Environmental Chemical Engineering
Issue number6
StatePublished - 2020 Dec


  • AProjected area of floc
  • Abbreviations VFloc settling velocity
  • CDrag co-efficient
  • DFloc diameter
  • Re Reynolds number
  • dDiameter of parent particles in suspension
  • g Gravitational force
  • μ Viscosity of water
  • ρ-ρEffective floc density
  • ρ-ρEffective parent particle density
  • ρDensity of water at room temperature
  • ρFloc density
  • ρParent particle density (kaolin)


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