418
Discussion
Reply to W. Torpey, H. Heukelekian, A.J. Kaplovsky and R. Epstein
Dr. W.A. Pretorius made certain assumptions about the author's work which were not entirely
correct, resulting in a somewhat incomplete assessment.
Initially, this was an in-depth research effort to develop new fundamental information to enhance
removal of pollutants employing biological slimes on rotating discs. The study was not intended to
repeat or duplicate the state of the art.
Secondly, so that the wrong impression does not remain as portrayed by the discussant's
comments, the following re-emphasis appears warranted.
This is not an activated sludge process and, therefore,
(1) we were not concerned with suspended cultures or recycling
(2) we were not using submerged bubbles for solution of oxygen
(3) nor were we dealing with differences of dissolved oxygen across a biological interface.
We dealt with exposing attached biological growth to atmospheres enriched with oxygen. Our
findings showed:
(1) that this enrichment affected a marked acceleration in oxidation of both carbon and nitrogen as
compared with the acceleration formally achieved by exposing to ambient air and reported
previously by the authors.
(2) we have maximized reactor velocity by concentration of self regenerated biological surface. The
following examples are pertinent for comparison:
sq. ft./cu. ft.
(a) activated sludge (by Schropher)
=
4
(b) trickling filter
=
13
(c) synthetic surfaces
=
25
(d) the authors' original ambient air studies
total surface
_
1 n o
volume of reactor
(e) with enriched atmosphere
=
150
The authors were thoroughly familiar with the discussants referenced literature, which was deemed
irrelevant to our studies except the basic experiments by Hartmann.
The discussant makes reference to increasing rotational speed as a means of increasing D.O. This
approach would be contra-indicated in that the power requirements vary as the cube of the rotating
velocity (in excess of 1 ft. per second speed).
The system was not operated as an extended aeration unit as indicated by the discussant because
the biological growths were prevented from accumulating on the rotating discs in order to negate
anaerobic conditions. However, as the paper emphasized, such conditions were not present and slime
control was rarely needed or practiced.
With regard to costs the authors re-emphasize the objective of the study namely to develop
fundamental process information from which a consulting engineer could initiate the design and
reduction to practice. Understandably, the latter would entail such inputs as cost of materials, labor,
structural, electrical and mechanical design all of which were beyond the scope of this investigation.
Certainly we were concerned with the economics as to the capital and operating charges with regard to
comparison of rotating disc treatment with respect to other forms of biological treatment in addition
to economics of the use of atmospheres enriched with oxygen. It was the considered opinion of the
authors that any costs should not be evaluated by University research personnel but such evaluation
should be delegated to those who specialize in such matters. Hopefully, someone interested in the
findings would undertake a complete cost analysis and thereby make a further contribution.
Discussion
Reply to W. Torpey, H. Heukelekian, A.J. Kaplovsky and R. Epstein
Dr. W.A. Pretorius made certain assumptions about the author's work which were not entirely
correct, resulting in a somewhat incomplete assessment.
Initially, this was an in-depth research effort to develop new fundamental information to enhance
removal of pollutants employing biological slimes on rotating discs. The study was not intended to
repeat or duplicate the state of the art.
Secondly, so that the wrong impression does not remain as portrayed by the discussant's
comments, the following re-emphasis appears warranted.
This is not an activated sludge process and, therefore,
(1) we were not concerned with suspended cultures or recycling
(2) we were not using submerged bubbles for solution of oxygen
(3) nor were we dealing with differences of dissolved oxygen across a biological interface.
We dealt with exposing attached biological growth to atmospheres enriched with oxygen. Our
findings showed:
(1) that this enrichment affected a marked acceleration in oxidation of both carbon and nitrogen as
compared with the acceleration formally achieved by exposing to ambient air and reported
previously by the authors.
(2) we have maximized reactor velocity by concentration of self regenerated biological surface. The
following examples are pertinent for comparison:
sq. ft./cu. ft.
(a) activated sludge (by Schropher)
=
4
(b) trickling filter
=
13
(c) synthetic surfaces
=
25
(d) the authors' original ambient air studies
total surface
_
1 n o
volume of reactor
(e) with enriched atmosphere
=
150
The authors were thoroughly familiar with the discussants referenced literature, which was deemed
irrelevant to our studies except the basic experiments by Hartmann.
The discussant makes reference to increasing rotational speed as a means of increasing D.O. This
approach would be contra-indicated in that the power requirements vary as the cube of the rotating
velocity (in excess of 1 ft. per second speed).
The system was not operated as an extended aeration unit as indicated by the discussant because
the biological growths were prevented from accumulating on the rotating discs in order to negate
anaerobic conditions. However, as the paper emphasized, such conditions were not present and slime
control was rarely needed or practiced.
With regard to costs the authors re-emphasize the objective of the study namely to develop
fundamental process information from which a consulting engineer could initiate the design and
reduction to practice. Understandably, the latter would entail such inputs as cost of materials, labor,
structural, electrical and mechanical design all of which were beyond the scope of this investigation.
Certainly we were concerned with the economics as to the capital and operating charges with regard to
comparison of rotating disc treatment with respect to other forms of biological treatment in addition
to economics of the use of atmospheres enriched with oxygen. It was the considered opinion of the
authors that any costs should not be evaluated by University research personnel but such evaluation
should be delegated to those who specialize in such matters. Hopefully, someone interested in the
findings would undertake a complete cost analysis and thereby make a further contribution.