Discussion
501
where Rj = total retention time of n lagoons of equal retention time per lagoon.
For a two lagoon series, equation (6) gives R j - 6 days, for a single lagoon system, Ry = 8 days.
During summer when K = 0,6, say, the percentage BOD 5 remaining will be:
Two lagoon system = 12.8%
Single lagoon system = 17.2%
Under these conditions there is little point using a two series lagoon system. If however, it is
required to have 80% or greater reduction in BOD in winter, the two or three lagoon system has
decided advantages in reducing retention, times over the single lagoon system.
Referring to temperature effects, the Authors accept Θ = 1,035. This value appears to be low.
Analysis by Marais and Capri
2 of data on aerated lagoons in papers by Eckenfelder
1 '
4 for domestic
and papermill wastes give Θ = 1,070 and 1,085 respectively. Similarly data from McKinney and
Benjes
5 on aerated lagoons treating domestic type wastes taking settlement into account gives Θ =
1,080
2 . Mancini and Barnhart
6 found experimentally Θ - 1,065 and state that Θ varies from 1,06 to
1,18. The value found by Bartsch and Randall
3 , Θ = 1,097 is probably on the high side because it is
based on the single instead of series lagoon formulations; this tends to push up the value of Θ.
In lagoons where settlement of organic material occurs there is greater reduction during winter
than to be expected from kinetic considerations assuming a completely mixed lagoon and lesser
reduction during summer due to increased load on the lagoon liquid from fermentation of the
accumulated bottom sludge solids. In general settlement and fermentation effects tend to reduce the
difference between winter and summer BOD when compared to a lagoon in which all the material is
kept in suspension and so load to an apparent low value of Θ.
Wherever the possibility of sludge settlement occurs, with seasonal temperature changes complex
patterns of oxygen consumption and effluent BOD emerge. It seems to the Writer that under such
conditions a simplified kinetic approach
2 which neglects growth and decay functions for the
micro-organism may be more useful at the present time than the more complex but theoretically more
correct approach proposed by the Authors. The situation is different where complete mixing is
assured.
REFERENCES
1. O'CONNOR, DJ. & ECKENFELDER, W.W., (1960). Treatment of organic wastes in aerated
lagoons. J.Wat. Poliut. Control Fed. 32, (4)
2. MARAIS, G.v.R. & CAPRI, M.J., (1970). A simplified kinetic theory for aerated lagoons. 2nd Int.
Symp. for Waste Treatment Lagoons, Kansas City, Missouri.
3. BRATSCH, E.H. & RANDALL, C.W., (1971). Aerated Lagoons - a report on the state of the art.
J.Wat. Pollut. Control Fed. Vol. 43, (4).
4. ECKENFELDER, W.W. (1968). Water Pollution in the chemical industry. Short course sponsored
by the Manufacturing Chemists Association and Univ. of Texas, Austin, Texas.
5. McKINNEY, R.E. & BENJES, H.H. (1965). Evaluation of two aerated lagoons. J.San.Eng.Div.,
Am.Soc.Civ.Engrs., 91.
6. MANCINI, J.L. & BARNHART, E.L. (1968). Industrial waste treatment in aerated lagoons. In
Advances in Water Quality Improvements. Ed. Gloyna, E.F. & Eckenfelder, W.W., Univ. of Texas
Press.
W.J. Oswald
What is the fate of settled organic matter, i.e. is methane fermentation significant? What growth of
blue green algae occurs in second or tertiary ponds?
L. Holmberg, Denmark
Experiments are in progress in Denmark with rotating floating drums filled with hollow plastic
spheres which combine a trickling filter effect and an activated sludge effect giving very high BOD
removal compared to the power input. Built-in pumps lift water and the spheres and release air under
the spheres just moved by the rotation movement.
501
where Rj = total retention time of n lagoons of equal retention time per lagoon.
For a two lagoon series, equation (6) gives R j - 6 days, for a single lagoon system, Ry = 8 days.
During summer when K = 0,6, say, the percentage BOD 5 remaining will be:
Two lagoon system = 12.8%
Single lagoon system = 17.2%
Under these conditions there is little point using a two series lagoon system. If however, it is
required to have 80% or greater reduction in BOD in winter, the two or three lagoon system has
decided advantages in reducing retention, times over the single lagoon system.
Referring to temperature effects, the Authors accept Θ = 1,035. This value appears to be low.
Analysis by Marais and Capri
2 of data on aerated lagoons in papers by Eckenfelder
1 '
4 for domestic
and papermill wastes give Θ = 1,070 and 1,085 respectively. Similarly data from McKinney and
Benjes
5 on aerated lagoons treating domestic type wastes taking settlement into account gives Θ =
1,080
2 . Mancini and Barnhart
6 found experimentally Θ - 1,065 and state that Θ varies from 1,06 to
1,18. The value found by Bartsch and Randall
3 , Θ = 1,097 is probably on the high side because it is
based on the single instead of series lagoon formulations; this tends to push up the value of Θ.
In lagoons where settlement of organic material occurs there is greater reduction during winter
than to be expected from kinetic considerations assuming a completely mixed lagoon and lesser
reduction during summer due to increased load on the lagoon liquid from fermentation of the
accumulated bottom sludge solids. In general settlement and fermentation effects tend to reduce the
difference between winter and summer BOD when compared to a lagoon in which all the material is
kept in suspension and so load to an apparent low value of Θ.
Wherever the possibility of sludge settlement occurs, with seasonal temperature changes complex
patterns of oxygen consumption and effluent BOD emerge. It seems to the Writer that under such
conditions a simplified kinetic approach
2 which neglects growth and decay functions for the
micro-organism may be more useful at the present time than the more complex but theoretically more
correct approach proposed by the Authors. The situation is different where complete mixing is
assured.
REFERENCES
1. O'CONNOR, DJ. & ECKENFELDER, W.W., (1960). Treatment of organic wastes in aerated
lagoons. J.Wat. Poliut. Control Fed. 32, (4)
2. MARAIS, G.v.R. & CAPRI, M.J., (1970). A simplified kinetic theory for aerated lagoons. 2nd Int.
Symp. for Waste Treatment Lagoons, Kansas City, Missouri.
3. BRATSCH, E.H. & RANDALL, C.W., (1971). Aerated Lagoons - a report on the state of the art.
J.Wat. Pollut. Control Fed. Vol. 43, (4).
4. ECKENFELDER, W.W. (1968). Water Pollution in the chemical industry. Short course sponsored
by the Manufacturing Chemists Association and Univ. of Texas, Austin, Texas.
5. McKINNEY, R.E. & BENJES, H.H. (1965). Evaluation of two aerated lagoons. J.San.Eng.Div.,
Am.Soc.Civ.Engrs., 91.
6. MANCINI, J.L. & BARNHART, E.L. (1968). Industrial waste treatment in aerated lagoons. In
Advances in Water Quality Improvements. Ed. Gloyna, E.F. & Eckenfelder, W.W., Univ. of Texas
Press.
W.J. Oswald
What is the fate of settled organic matter, i.e. is methane fermentation significant? What growth of
blue green algae occurs in second or tertiary ponds?
L. Holmberg, Denmark
Experiments are in progress in Denmark with rotating floating drums filled with hollow plastic
spheres which combine a trickling filter effect and an activated sludge effect giving very high BOD
removal compared to the power input. Built-in pumps lift water and the spheres and release air under
the spheres just moved by the rotation movement.