Advective transport in activated sludge flocs

Li, Dahong; Ganczarczyk, Jerzy J.

doi:10.2175/wer.64.3.7

Cited by 61 publications

(42 citation statements)

References 15 publications

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“…In support of this result, Li and Ganczarczyk (1992) stated that sludge flocs may be permeable, depending on their size and the plant operating conditions. They also suggested that advective transport through channels in the sludge flocs could be the main mass transfer mechanism, which could explain the absence of transport limitations in the flocs.…”

Section: Physicochemical Phenomena: Diffusion Of Substrate Into Activmentioning

confidence: 85%

Transient response of aerobic and anoxic activated sludge activities to sudden substrate concentration changes

Vanrolleghem¹,

Sin²,

Gernaey³

2004

Biotech & Bioengineering

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The state-of-the-art understanding of activated sludge processes as summarized in activated sludge models (ASMs) predicts an instantaneous increase in the biomass activity (which is measured, e.g., by the corresponding respiration rate OUR, NUR, etc.) under sudden substrate concentration changes. Experimental data (e.g., short-term batch respiration experiments under aerobic or anoxic conditions) collected for the calibration of the dynamic models (ASMs) often exhibit a transient phenomenon while attaining maximum activity, which cannot be explained by the current understanding of the activated sludge process. That transient phenomenon exhibits itself immediately upon addition of a substrate source to an endogenously respiring activated sludge sample and it usually takes a few minutes until the activated sludge reaches its maximum possible rate under given environmental conditions. This discrepancy between the state-of-the-art model and the experimental data is addressed in detail in this investigation. It is shown that the discrepancy is not caused by an error in the experimental set-up/data but it is rather due to model inadequacy. Among the hypotheses proposed, it appears that this transient response of the activated sludge most likely results from the sequence of intracellular reactions involved in substrate degradation by the activated sludge. Results from studies performed elsewhere with pure cultures (S. cerevisae and E. coli) support the hypothesis. The transient phenomenon can be described by a dynamic metabolic network model or by a simple first-order model, as adopted in this study. The transient phenomenon occurring in short-term batch respiration experiments is shown to interfere severely with parameter estimation if not modeled properly (2.8%, 11.5%, and 16.8% relative errors [average of three experiments] on Y(H), micro(maxH), and K(S), respectively). Proper modeling of this transient phenomenon whose time constant is on the order of minutes (1 to 3 min) is expected to contribute fundamentally to a better understanding and modeling of Orbal, carousel, and SBR-type treatment plants with fast-alternating process conditions, although such studies are beyond the scope of this report.

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Section: Physicochemical Phenomena: Diffusion Of Substrate Into Activmentioning

confidence: 85%

Transient response of aerobic and anoxic activated sludge activities to sudden substrate concentration changes

Vanrolleghem¹,

Sin²,

Gernaey³

2004

Biotech & Bioengineering

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“…Theoretical work has been conducted to characterize the permeability and the reduction factors (Brinkman, 1947;Happel, 1958;Dullien, 1992;Alder, 1981;Veerapaneni and Wiesner, 1996;Vanni, 2000). In addition, many conventional column experiments (Li and Ganczarczyk, 1992;Li and Logan, 1997;Li et al, 2003) have been carried out to elucidate the inherent relationship between the reduction factor and the permeability of the particles. However, these experiments only predicted the floc permeability from the floc terminal velocity and other factors and could not provide detailed information about the hydrodynamics in the creeping flow field.…”

Section: Discussionmentioning

confidence: 99%

Investigation of the hydrodynamic behavior of diatom aggregates using particle image velocimetry

Xiao

Lam

et al. 2012

Journal of Environmental Sciences

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The hydrodynamic behavior of diatom aggregates has a significant influence on the interactions and flocculation kinetics of algae. However, characterization of the hydrodynamics of diatoms and diatom aggregates in water is rather difficult. In this laboratory study, an advanced visualization technique in particle image velocimetry (PIV) was employed to investigate the hydrodynamic properties of settling diatom aggregates. The experiments were conducted in a settling column filled with a suspension of fluorescent polymeric beads as seed tracers. A laser light sheet was generated by the PIV setup to illuminate a thin vertical planar region in the settling column, while the motions of particles were recorded by a high speed charge-coupled device (CCD) camera. This technique was able to capture the trajectories of the tracers when a diatom aggregate settled through the tracer suspension. The PIV results indicated directly the curvilinear feature of the streamlines around diatom aggregates. The rectilinear collision model largely overestimated the collision areas of the settling particles. Algae aggregates appeared to be highly porous and fractal, which allowed streamlines to penetrate into the aggregate interior. The diatom aggregates have a fluid collection efficiency of 10%-40%. The permeable feature of aggregates can significantly enhance the collisions and flocculation between the aggregates and other small particles including algal cells in water.

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“…Aggregates formed by bacteria are known to be highly fractal (Meakin, 1988;Li and Ganczarczyk, 1989;Jiang and Logan, 1991), with fractal dimensions depending on the type of floc, physical conditions such as fluid shear rate, and the mechanism of floc formation (Logan and Wilkinson, 1991;Zahid and Ganczarczyk, 1994;Li et al, 2003). The open structure of highly porous and fractal aggregates can allow intra-aggregate flow through the flocs, resulting in their settling velocity being appreciably faster than that predicted for impermeable spherical particles (Li and Ganczarczyk, 1992;Johnson et al, 1996;Li and Yuan, 2002). Biological flocs produced in activated sludge reactors are highly porous and fractal (Li and Ganczarczyk, 1990;Lee et al, 1996;Li and Yuan, 2002), but the flow through the floc is not large enough to affect their settling behavior.…”

Section: Introductionmentioning

confidence: 99%

“…Biological flocs produced in activated sludge reactors are highly porous and fractal (Li and Ganczarczyk, 1990;Lee et al, 1996;Li and Yuan, 2002), but the flow through the floc is not large enough to affect their settling behavior. However, floc permeability can affect mass transport rates to bacteria inside the floc, even under conditions where it does not affect settling velocity (Logan and Hunt, 1988;Li and Ganczarczyk, 1992;Tsou et al, 2002;Li et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Physical and hydrodynamic properties of flocs produced during biological hydrogen production

Zhang¹,

Li²,

Oh³

et al. 2004

Biotech & Bioengineering

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Dense flocs readily form in continuous culture bioreactors used for hydrogen production, but the fractal and hydrodynamic properties of these flocs have not been previously analyzed. We therefore examined the size distribution, fractal dimension, and hydrodynamic properties of flocs formed in a continuous flow, well-mixed reactor treating synthetic wastewater at a fixed condition of a 4.5 h hydraulic detention time (23jC, pH 5.5). The reactor was operated for a total of 3 months at three different organic loading rates (27, 53, and 80 g-COD/L-d) with influent glucose concentrations of 5, 10, and 15 g-COD/L. At all three loading rates the removal of glucose was nearly complete (98.6 -99.4%) and biomass was produced in proportion to the organic loading rate (0.86 F 0.11, 2.40 F 0.26, and 4.59 F 1.55 g/L of MLVSS in the reactor). Overall conversion efficiencies of glucose to hydrogen, evaluated on the basis of a maximum of 4 mol-H 2 /molglucose, increased with organic loading rates in the order 17.7%, 23.1%, and 25.6%. The gas contained 56.1 F 4.9% hydrogen, with the balance as carbon dioxide. No methane gas was detected. Under these conditions, flocs were produced with mean sizes that increased with organic loading, in the order 0.12 cm (5 g-COD/L), 0.35 cm (10 g-COD/L), and 0.58 cm (15 g-COD/L). As the average floc size increased, the flocs became on average denser and less fractal, with fractal dimensions increasing from 2.11 F 0.17 to 2.48 F 0.13. Floc porosities ranged from 0.75 -0.96, and resulted in aggregate densities that allowed little intra-aggregate flow through the floc. As a result, average settling velocities were not appreciably larger than those predicted by Stokes' law for spherical, impermeable flocs. Our results demonstrate that dense, relatively impermeable flocs are produced in biohydrogen reactors that have settling properties in reasonable agreement with Stokes' law. B 2004 Wiley Periodicals, Inc.

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Advective transport in activated sludge flocs

Cited by 61 publications

References 15 publications

Transient response of aerobic and anoxic activated sludge activities to sudden substrate concentration changes

Transient response of aerobic and anoxic activated sludge activities to sudden substrate concentration changes

Investigation of the hydrodynamic behavior of diatom aggregates using particle image velocimetry

Physical and hydrodynamic properties of flocs produced during biological hydrogen production

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