454
Discussion
approximately 0.0004 mg/liter; an excellent agreement with that calculated above.
The effect of turbulence on the mass transfer mechanisms from liquid to the floe particle may be
threefold; (1) it may reduce the liquid film resistance, (2) it may reduce the clump resistance, and (3)
it may solubilize a portion of the floe providing additional nutrients for microbiological degradation.
If the concentration of oxygen and substrate is not limiting the metabolic reaction rate of the
organisms in the floe, increased turbulence to reduce the liquid film and clump resistance will have no
effect on the oxygen or substrate utilization rate in the system. However, for low substrate and
oxygen bulk liquid concentrations, an increase in turbulence to shear the floe particles and
significantly reduce the clump resistance will be required to maintain the system at an optimum
metabolic rate. For large floe particles of specific spherical diameter (based on wet volume and surface
area measurements) of 60 microns, oxygen concentrations below 2.0 mg/1 limited the metabolic rate
of Zoogloea ramigera floe. After floe break up in a high speed blender, the maximum metabolic rate
was maintained at concentrations as low as 0.1 mg/1. It is also conceivable that, when high
concentrations of suspended solids are present in biological treatment systems, mechanical bridging or
packing of the cells may occur, thus, reducing the interfacial area available for mass transfer and
effectively increasing clump resistance of the floe particles. Again turbulence of the proper scale would
assist in shearing these bridged clumps, thereby effectively increasing the overall mass transfer rate to
the active cells.
The third effect of turbulence, solubilization of floe material, produced no significant change in
the maximum oxygen uptake rate of the Zoogloea ramigera floe. However, when activated sludge floe
was blended, significant increases in the oxygen uptake rate occurred (Baillod et al 1970).
It is clear from consideration of the current technology that turbulence of a scale consistent with
the size of individual floe or gas particles may affect the apparent mass transfer rates to or from these
particles. Although there is considerable evidence to suggest that this is an important factor under
certain conditions in reactor design, the actual mechanisms are still not well defined.
REFERENCES
BAILLOD, C.R. and BOYLE, W.C, 1970. "Mass Transfer Limitations in Substrate Removal", Jour.
San. Engr. Div. A.S.C.E. 96, SA2, 525.
BERTHOUEX, P.M., 1964. "Factors Affecting Oxygen Transfer in Activated Sludge Mixed Liquor",
M.S. Thesis, State University of Iowa, Iowa City, Iowa.
BORKOWSKI, J.D. and JOHNSON, M.J., 1967. "Experimental Evaluation of Liquid Film Resistance
in Oxygen Transport to Microbial Cells", Applied Microbiology, 15, 1483.
DIENDOERFER, F.H., and GADEN, E.L., Jr., 1955. "Effects of Liquid Physical Properties on
Oxygen Transfer in Penicillin Fermentation", Applied Microbiology, 3, 253.
DOWNING, A.L., 1960. "Aeration in the Activated Sludge Process", Journal of the Institution of
Public Health Engineers, 59, 80.
ECKENFELDER, W.W. & FORD, D.L., 1968. "New Concepts in Oxygen Transfer and Aeration",
Advances in Water Quality Improvement, Water Symp. No. 1, (Ed. by E.F. Gloyna and W.W.
Eckenfelder, Jr.), Univ. of Texas Press, Austin, Texas. 59, 80.
FINN, R.K.,-1954. "Agitation-Aeration in Laboratory and in Industry", Bacteriological Reviews, 18,
254.
LOWENBURG, T.J., 1963. "Factors Affecting Oxygen Transfer in Activated Sludge Mixed Liquor",
M.S. Thesis, State University of Iowa, Iowa City, Iowa.
MANCY, K.H. & OKUN, D.A., 1960. "Effect of Surface Active Agents on Rate of Oxygen Transfer",
Advances in Biological Waste Treatment, (ed. by W.W. Eckenfelder and J. McCabe), Pergamon
Press, New York.
MUELLER, J.A., 1966. "Oxygen Diffusion Through a Pure Culture Floe of Zoogloea ramigera", Ph.D.
Thesis, The University of Wisconsin, Madison, Wisconsin.
MUELLER, J.A., BOYLE, W.C, and LIGHTFOOT, E.N., (1968) "Oxygen Diffusion Through
Zoogloeal Floe", Biotechnology and Bioengineering, X, 331.
TUFFILE and PINHO, 1970. "Determination of Oxygen Transfer Coefficient in Viscous
Streptomycete Fermentations", Biotechnology and Bioengineering, XII, 849.
Discussion
approximately 0.0004 mg/liter; an excellent agreement with that calculated above.
The effect of turbulence on the mass transfer mechanisms from liquid to the floe particle may be
threefold; (1) it may reduce the liquid film resistance, (2) it may reduce the clump resistance, and (3)
it may solubilize a portion of the floe providing additional nutrients for microbiological degradation.
If the concentration of oxygen and substrate is not limiting the metabolic reaction rate of the
organisms in the floe, increased turbulence to reduce the liquid film and clump resistance will have no
effect on the oxygen or substrate utilization rate in the system. However, for low substrate and
oxygen bulk liquid concentrations, an increase in turbulence to shear the floe particles and
significantly reduce the clump resistance will be required to maintain the system at an optimum
metabolic rate. For large floe particles of specific spherical diameter (based on wet volume and surface
area measurements) of 60 microns, oxygen concentrations below 2.0 mg/1 limited the metabolic rate
of Zoogloea ramigera floe. After floe break up in a high speed blender, the maximum metabolic rate
was maintained at concentrations as low as 0.1 mg/1. It is also conceivable that, when high
concentrations of suspended solids are present in biological treatment systems, mechanical bridging or
packing of the cells may occur, thus, reducing the interfacial area available for mass transfer and
effectively increasing clump resistance of the floe particles. Again turbulence of the proper scale would
assist in shearing these bridged clumps, thereby effectively increasing the overall mass transfer rate to
the active cells.
The third effect of turbulence, solubilization of floe material, produced no significant change in
the maximum oxygen uptake rate of the Zoogloea ramigera floe. However, when activated sludge floe
was blended, significant increases in the oxygen uptake rate occurred (Baillod et al 1970).
It is clear from consideration of the current technology that turbulence of a scale consistent with
the size of individual floe or gas particles may affect the apparent mass transfer rates to or from these
particles. Although there is considerable evidence to suggest that this is an important factor under
certain conditions in reactor design, the actual mechanisms are still not well defined.
REFERENCES
BAILLOD, C.R. and BOYLE, W.C, 1970. "Mass Transfer Limitations in Substrate Removal", Jour.
San. Engr. Div. A.S.C.E. 96, SA2, 525.
BERTHOUEX, P.M., 1964. "Factors Affecting Oxygen Transfer in Activated Sludge Mixed Liquor",
M.S. Thesis, State University of Iowa, Iowa City, Iowa.
BORKOWSKI, J.D. and JOHNSON, M.J., 1967. "Experimental Evaluation of Liquid Film Resistance
in Oxygen Transport to Microbial Cells", Applied Microbiology, 15, 1483.
DIENDOERFER, F.H., and GADEN, E.L., Jr., 1955. "Effects of Liquid Physical Properties on
Oxygen Transfer in Penicillin Fermentation", Applied Microbiology, 3, 253.
DOWNING, A.L., 1960. "Aeration in the Activated Sludge Process", Journal of the Institution of
Public Health Engineers, 59, 80.
ECKENFELDER, W.W. & FORD, D.L., 1968. "New Concepts in Oxygen Transfer and Aeration",
Advances in Water Quality Improvement, Water Symp. No. 1, (Ed. by E.F. Gloyna and W.W.
Eckenfelder, Jr.), Univ. of Texas Press, Austin, Texas. 59, 80.
FINN, R.K.,-1954. "Agitation-Aeration in Laboratory and in Industry", Bacteriological Reviews, 18,
254.
LOWENBURG, T.J., 1963. "Factors Affecting Oxygen Transfer in Activated Sludge Mixed Liquor",
M.S. Thesis, State University of Iowa, Iowa City, Iowa.
MANCY, K.H. & OKUN, D.A., 1960. "Effect of Surface Active Agents on Rate of Oxygen Transfer",
Advances in Biological Waste Treatment, (ed. by W.W. Eckenfelder and J. McCabe), Pergamon
Press, New York.
MUELLER, J.A., 1966. "Oxygen Diffusion Through a Pure Culture Floe of Zoogloea ramigera", Ph.D.
Thesis, The University of Wisconsin, Madison, Wisconsin.
MUELLER, J.A., BOYLE, W.C, and LIGHTFOOT, E.N., (1968) "Oxygen Diffusion Through
Zoogloeal Floe", Biotechnology and Bioengineering, X, 331.
TUFFILE and PINHO, 1970. "Determination of Oxygen Transfer Coefficient in Viscous
Streptomycete Fermentations", Biotechnology and Bioengineering, XII, 849.