374
Discussion
Process," Ph.D. Thesis, University of California, Berkeley, 1970.
3. PATTERSON, J.W., et al., "Measurement and Significance of ATP in Activated Sludge," Env. Sei.
and Techn., 4=7m 569, 1970.
4. ORHON, D., "The Mechanism and Design of the Contact Stabilization Activated Sludge Process,"
Ph.D. Thesis, University of California, Berkeley, 1971.
5. WEDDLE, C.L. and JENKINS, D. "The Viability and Activity of Activated Sludge," Wat. Res., 5:
8,621,1971.
6. WASHINGTON, D.R., "Activity of High Solids Cultures," Proc. 152nd National Meeting, The
Amer. Chem. Soc, Div. of Microbiol. Chem. and Techn., N.Y. 1966.
7. DOWNING, A.L., "Factors to be considered in the design of Activated Sludge Plants" in Advances
in Water Quality Improvement, E.F. Gloyna and W.W. Eckenfelder Jr. eds., University of Texas
Press, Austin, 1968.
8. POSTAGE, J.R., and HUNTER, J.R. "The Survival of Starved Bacteria," /. Gen. Microbiol, 29,
233, 1962.
Reply
Although Dr. Orhon's questions could only be answered by further work it may be stated that
the comparison RA/removed BOD would not give more information than the comparison RA/load, as
the effluent BOD was very low and nearly constant.
The contact time raw water/sludge, the retention time of sludge in the final sedimentation basin,
are comparatively short (1 hr), and cannot be compared to the times obtained in the contact stabilization process.
K.L. Murphy, Canada.
In a completely mixed system the input concentration variation is considerably modified by
mixing with the contents of the aerator. The authors relate the oxygen uptake to the concentrations
of BOD in the influent. The influent concentration is not the concentration in the aerator; thus no
correlation should exist. Rather the author should compare the variation in respiration rate to the
BOD concentration in the aerator which for a completely mixed system is that of the effluent.
Our studies on conventional full scale aeration tanks indicate that neither plug (or piston) flow nor
complete mixing can be obtained in practice. The result of this incomplete mixing causes a smoothing
(reduction in amplitude) of input irregularities and provides a time delay which would cause a shift in
any measured response. Similar results as presented by the authors could be obtained through incomplete mixing.
The authors have mentioned the difficulties associated with these measurements. Further information on the details of these measurements, the location in the aerator and the methodology employed
would clarify the experimental details.
With a model as complicated as that proposed by the authors to explain the observed phenomenon
the use of BOD5 as a measured parameter seems inappropriate. The numerical value of the 5 day
oxygen demand depends on the composition of the waste, the degree of treatment attained as well as
the total amount of pollutants present. Could the authors comment on the use of other more
definitive parameters more in keeping with the complexity of the proposed model in lieu of the 5 day
BOD?
Reply
P.H. Brouzes, France.
The working respirometer is made to show initial fast variations to study samples from a large
plant. The delay between taking the activated sludge sample and putting it in the respirometer, fails to
detect the most important part of the O2 uptake.
The explanation of the lag period between BOD peak load and of oxygen uptake, is not due to
storage of food, but to the growth of sludge mass. The sludge mass is an integration function of the
food. When the food is constant and maximal, the sludge mass growth rate and the endogenous
respiration rate are maximal. When the BOD is minimal and constant, the sludge mass decreases at a
maximal rate due to endogenous respiration (Wastage is assumed to be constant).
Reply by D. Lefort, France:
Mr. Murphy's comments concerning the fact that complete mixing or plug flow are theoretical
cases, are fully justified. In the case of the measurements presented here, we were quite near to the
conditions of complete mixing, due to the retention time of water (1 hr) and the type of basin
Discussion
Process," Ph.D. Thesis, University of California, Berkeley, 1970.
3. PATTERSON, J.W., et al., "Measurement and Significance of ATP in Activated Sludge," Env. Sei.
and Techn., 4=7m 569, 1970.
4. ORHON, D., "The Mechanism and Design of the Contact Stabilization Activated Sludge Process,"
Ph.D. Thesis, University of California, Berkeley, 1971.
5. WEDDLE, C.L. and JENKINS, D. "The Viability and Activity of Activated Sludge," Wat. Res., 5:
8,621,1971.
6. WASHINGTON, D.R., "Activity of High Solids Cultures," Proc. 152nd National Meeting, The
Amer. Chem. Soc, Div. of Microbiol. Chem. and Techn., N.Y. 1966.
7. DOWNING, A.L., "Factors to be considered in the design of Activated Sludge Plants" in Advances
in Water Quality Improvement, E.F. Gloyna and W.W. Eckenfelder Jr. eds., University of Texas
Press, Austin, 1968.
8. POSTAGE, J.R., and HUNTER, J.R. "The Survival of Starved Bacteria," /. Gen. Microbiol, 29,
233, 1962.
Reply
Although Dr. Orhon's questions could only be answered by further work it may be stated that
the comparison RA/removed BOD would not give more information than the comparison RA/load, as
the effluent BOD was very low and nearly constant.
The contact time raw water/sludge, the retention time of sludge in the final sedimentation basin,
are comparatively short (1 hr), and cannot be compared to the times obtained in the contact stabilization process.
K.L. Murphy, Canada.
In a completely mixed system the input concentration variation is considerably modified by
mixing with the contents of the aerator. The authors relate the oxygen uptake to the concentrations
of BOD in the influent. The influent concentration is not the concentration in the aerator; thus no
correlation should exist. Rather the author should compare the variation in respiration rate to the
BOD concentration in the aerator which for a completely mixed system is that of the effluent.
Our studies on conventional full scale aeration tanks indicate that neither plug (or piston) flow nor
complete mixing can be obtained in practice. The result of this incomplete mixing causes a smoothing
(reduction in amplitude) of input irregularities and provides a time delay which would cause a shift in
any measured response. Similar results as presented by the authors could be obtained through incomplete mixing.
The authors have mentioned the difficulties associated with these measurements. Further information on the details of these measurements, the location in the aerator and the methodology employed
would clarify the experimental details.
With a model as complicated as that proposed by the authors to explain the observed phenomenon
the use of BOD5 as a measured parameter seems inappropriate. The numerical value of the 5 day
oxygen demand depends on the composition of the waste, the degree of treatment attained as well as
the total amount of pollutants present. Could the authors comment on the use of other more
definitive parameters more in keeping with the complexity of the proposed model in lieu of the 5 day
BOD?
Reply
P.H. Brouzes, France.
The working respirometer is made to show initial fast variations to study samples from a large
plant. The delay between taking the activated sludge sample and putting it in the respirometer, fails to
detect the most important part of the O2 uptake.
The explanation of the lag period between BOD peak load and of oxygen uptake, is not due to
storage of food, but to the growth of sludge mass. The sludge mass is an integration function of the
food. When the food is constant and maximal, the sludge mass growth rate and the endogenous
respiration rate are maximal. When the BOD is minimal and constant, the sludge mass decreases at a
maximal rate due to endogenous respiration (Wastage is assumed to be constant).
Reply by D. Lefort, France:
Mr. Murphy's comments concerning the fact that complete mixing or plug flow are theoretical
cases, are fully justified. In the case of the measurements presented here, we were quite near to the
conditions of complete mixing, due to the retention time of water (1 hr) and the type of basin