Discussion by E.F. Gloyna and MJ. Gromiec
Similar studies to those of the authors have been conducted at The University of Texas at Austin,
USA, in an effort to examine the application of ORP as a means of evaluating waste stabilization pond
performance. Hermann and Gloyna (1957) reported tests describing ORP measurements made at
two-hour intervals on samples taken from the top, middle and bottom strata of four model waste
stabilization ponds. These experiments showed that the (-) ORP values during the dark period were
markedly higher than during the period of photosynthetic oxygenation, and that there was a rapid
reduction in (-) ORP at the beginning of the light cycle.
Fisher and Gloyna (1963) applied the ORP measurements to evaluate the performance of waste
stabilization ponds when treating excess activated sludge. Three model ponds and one full-scale facility
were used in this study. The surface area of the waste stabilization pond was 85 acres (34.4 ha) and
the average organic loading was 34 lbs BOD/acre/day (38 kg BOD/ha/day). The excess activated sludge
was derived from a typical biosorption activated sludge treatment plant. Diurnal measurements of
ORP, BOD, DO, pH and temperature were made at two stations. Measurements were made at three
depths in the pond. The ORP at both stations varied between +250V and +350 mv.
The model ponds with a surface area of 1.8 sq. ft. (0.17 sq.m) and depth of 1 ft. (0.3m) were
divided into four baffled chambers and had a light intensity at the water surface of approximately 700
foot-candles (7,550 lumens/sq. m). The light was turned on for 12 hours each day. Ponds A and B
were loaded at an average rate of 56 lbs BOD/acre/day (63 kgs/ha/day) and Pond C received an average
organic load of 119 lbs BOD/acre/day (133 kgs/ha/day). In all cases activated sludge was diluted with
water and the waste was then added batchwise. Ponds A and C were dosed every day but Pond B was
dosed only three days during each week. The ORP of effluent samples taken from Ponds A and B
were nearly all in the range of +350 mv to +450 mv, while ORP of effluent samples from Pond C
during the final 22 days of operation decreased from about +450 mv to some negative value. The
diurnal pattern of Pond C reflected the heavy organic loading throughout the pond system, and nearly
all of the ORP values observed throughout Pond C ranged from zero to - 1 0 0 mv. The first obnoxious
odors were noticed when the ORP dropped below +150 mv. From the above results it was concluded
that ORP measurements are more useful indicators of pond conditions than the frequently used pH
measurements.
ORP measurements are also useful in detecting significant changes in sulfide concentrations.
Increases in sulfides can reflect increased demands for oxygen. A significant chemical demand for
oxygen will require additional photosynthetic capacity and this added algal activity must be translated
into increased pond area.
The amount of sulfides released near the bottom of a facultative pond or in an anaerobic pond is
related to the concentration of sulfates, thiosulfates, etc., in the wastewater. The extent to which the
ORP is reduced depends to a large extent on the amount of sulfides generates, but the ORP is also
influenced by the poising capacity of the medium. This poising capacity of the medium depends on all
of the reactions that take place in the pond.
Investigations by Gloyna and Espino (1967) dealt with the release of hydrogen sulfide in a model
facultative pond for which the depth was two meters. Numerous tests were conducted to determine
the influence of individual variables such as influent BOD, detention time, S
= concentration and
S 0 4
= concentration on ROP. Based on these studies, it was possible to detect impending odor
problems. ORP measurements readily showed the progression of sulfides from the bottom to the top
of a pond. Also, it was shown that the sulfide concentration could be related to the BOD surface load,
S 0 4
= , in the influent and detention provided in the pond.
It was concluded that ORP measurements can be useful indicators of biological activity and to a
certain extent this test can be used as a diognostic tool. While the ORP data cannot provide
information on the efficiency of biological treatment process, this test can be of considerable value to
the plant operator on a day-to-day basis.
REFERENCE
1. DRYNAN, W.R., and GLOYNA, E.F. (1959) 'Oxidation - Reduction Potential Measurements in
Waste Treatment Systems, "South-western Water Works Journal, 41, 3, 28-40.
2. FISHER, C.P., and GLOYNA, E.F. (1965) 'Treatment of Activated Sludge in Stabilization
Ponds," Journal Water Pollution Control Federation, 37, 11, 1511-1520.
3. GLOYNA, E.F., and ESPINO, E. (1969) "Sulfide Production in Waste Stabilization Ponds,"
Journal of the Sanitary Engineering Division, ASCE, SA3, 607-628. Also, The University of Texas
at Austin Report, CRWRNo. 26, EHE-04-6802.
Dean, College of Engineering and Joe King Professor, The University of Texas at Austin.
Research Associate, Center for Research in Water Resources, The University of Texas at Austin.
485
Similar studies to those of the authors have been conducted at The University of Texas at Austin,
USA, in an effort to examine the application of ORP as a means of evaluating waste stabilization pond
performance. Hermann and Gloyna (1957) reported tests describing ORP measurements made at
two-hour intervals on samples taken from the top, middle and bottom strata of four model waste
stabilization ponds. These experiments showed that the (-) ORP values during the dark period were
markedly higher than during the period of photosynthetic oxygenation, and that there was a rapid
reduction in (-) ORP at the beginning of the light cycle.
Fisher and Gloyna (1963) applied the ORP measurements to evaluate the performance of waste
stabilization ponds when treating excess activated sludge. Three model ponds and one full-scale facility
were used in this study. The surface area of the waste stabilization pond was 85 acres (34.4 ha) and
the average organic loading was 34 lbs BOD/acre/day (38 kg BOD/ha/day). The excess activated sludge
was derived from a typical biosorption activated sludge treatment plant. Diurnal measurements of
ORP, BOD, DO, pH and temperature were made at two stations. Measurements were made at three
depths in the pond. The ORP at both stations varied between +250V and +350 mv.
The model ponds with a surface area of 1.8 sq. ft. (0.17 sq.m) and depth of 1 ft. (0.3m) were
divided into four baffled chambers and had a light intensity at the water surface of approximately 700
foot-candles (7,550 lumens/sq. m). The light was turned on for 12 hours each day. Ponds A and B
were loaded at an average rate of 56 lbs BOD/acre/day (63 kgs/ha/day) and Pond C received an average
organic load of 119 lbs BOD/acre/day (133 kgs/ha/day). In all cases activated sludge was diluted with
water and the waste was then added batchwise. Ponds A and C were dosed every day but Pond B was
dosed only three days during each week. The ORP of effluent samples taken from Ponds A and B
were nearly all in the range of +350 mv to +450 mv, while ORP of effluent samples from Pond C
during the final 22 days of operation decreased from about +450 mv to some negative value. The
diurnal pattern of Pond C reflected the heavy organic loading throughout the pond system, and nearly
all of the ORP values observed throughout Pond C ranged from zero to - 1 0 0 mv. The first obnoxious
odors were noticed when the ORP dropped below +150 mv. From the above results it was concluded
that ORP measurements are more useful indicators of pond conditions than the frequently used pH
measurements.
ORP measurements are also useful in detecting significant changes in sulfide concentrations.
Increases in sulfides can reflect increased demands for oxygen. A significant chemical demand for
oxygen will require additional photosynthetic capacity and this added algal activity must be translated
into increased pond area.
The amount of sulfides released near the bottom of a facultative pond or in an anaerobic pond is
related to the concentration of sulfates, thiosulfates, etc., in the wastewater. The extent to which the
ORP is reduced depends to a large extent on the amount of sulfides generates, but the ORP is also
influenced by the poising capacity of the medium. This poising capacity of the medium depends on all
of the reactions that take place in the pond.
Investigations by Gloyna and Espino (1967) dealt with the release of hydrogen sulfide in a model
facultative pond for which the depth was two meters. Numerous tests were conducted to determine
the influence of individual variables such as influent BOD, detention time, S
= concentration and
S 0 4
= concentration on ROP. Based on these studies, it was possible to detect impending odor
problems. ORP measurements readily showed the progression of sulfides from the bottom to the top
of a pond. Also, it was shown that the sulfide concentration could be related to the BOD surface load,
S 0 4
= , in the influent and detention provided in the pond.
It was concluded that ORP measurements can be useful indicators of biological activity and to a
certain extent this test can be used as a diognostic tool. While the ORP data cannot provide
information on the efficiency of biological treatment process, this test can be of considerable value to
the plant operator on a day-to-day basis.
REFERENCE
1. DRYNAN, W.R., and GLOYNA, E.F. (1959) 'Oxidation - Reduction Potential Measurements in
Waste Treatment Systems, "South-western Water Works Journal, 41, 3, 28-40.
2. FISHER, C.P., and GLOYNA, E.F. (1965) 'Treatment of Activated Sludge in Stabilization
Ponds," Journal Water Pollution Control Federation, 37, 11, 1511-1520.
3. GLOYNA, E.F., and ESPINO, E. (1969) "Sulfide Production in Waste Stabilization Ponds,"
Journal of the Sanitary Engineering Division, ASCE, SA3, 607-628. Also, The University of Texas
at Austin Report, CRWRNo. 26, EHE-04-6802.
Dean, College of Engineering and Joe King Professor, The University of Texas at Austin.
Research Associate, Center for Research in Water Resources, The University of Texas at Austin.
485