WATER POLLUTION CONTROL RESEARCH SERIES 11024 DDK 02/70
Proposed Combined Sewer Control
by
Electrode Potential
U.S. DEPARTMENT OP THE INTERIOR • FEDERAL, WATER QUALITY ADMINISTRATION
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W! T POL]IJTION CO ROL R EARCR S flB
The Water Pollution Control Research Reports describe the results and
progress in the control and abat nent of pollution of our Nation’s
waters. They provide a central source ‘ information on the research,
develo ent and demonstration activities of the Federal Water Q uality
Administration, Department of the Interior, through in-house research
and grants end contracts with Federal, state, and local agencies,
research institutions, and industrial organizations.
Triplicate tear-out abstract cards are placed inside the back cover to
facilitate information retrieval. Space is provided on the card for
the user’s accession number and for additional keywords.
Inqniries pertaining to Water Pollution Control Research Reports should
be directed to the Head, Project Reports System, Room nOB, Plmrning
and Resources Office, Office of Research and Develop ient, Department
of the Interior, Federal Water Quality Administration, Washington, D.C.
2O21 2.
Previous ] y issued reports on the Storm and Combined Sewer Pollution
Control Program:
WP-20-ll Problems of Ccm bined Sever Facilities and Overflows -
1967.
WP-20-15 Water Pollution Aspects of Urban Runoff.
WP-20-16 Strainer/Filter Treatmcnt of Combined Sever Overf1ow .
WP-20-l7 Dissolved Air Floi ati n ‘treatment of Combined Sever
Overflows.
WP-20-18 Improved SeAl ts for Infiltration Control.
WP-20-2]. Selected Urban Storm Water Runoff Abstracts.
WP-20-22 Polymers for Sever Flow Control.
OBD-Ii Combined Sever Separation Using Pressure Severs.
Crazed Resin Filtration of Combined Sever Overflows.
1 S’2. .5 Rotary Vibratory Fine Screening of C nbined Sewer
Overflows.
flAST-6 Storm Water Problems and Control in Sanitary Severs,
Oakl md and Berkeley, California.
DAST-9 Sewer Infiltration Reduction by Zone Pumping.
DAST -13 Design of a Combined Sewer Fluidic Regulator.
I J ..25 Rapid-Flow Filter for Sewer Overflows.
DAST-29 Control of Pollution by Underwater Storage.
I ST-32 Stream Pollution and Abatement from Combined Sever
Overflows - Bucyrus, Cthio.
DAST-36 Storm and Canbined Sever Demonstration Projects -
January 1970.
flA -37 C bined Sever Overflow S nir ’ar Papers.
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PROPOSED COMBINED SEWER CONTROL
BY
ELECTRODE POTENTIAL
FEDERAL WATER QUALITY ADMINISTRATION
DEPARTMENT OF THE INTERIOR
by
Merrimack College
North And over, Massachusetts
Contract No. 217-01-68
11024 DDK
FEBRUARY, 1970
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FWPCA Review Notice
This report has been reviewed by the Federal Water
Pollution Control Administration and approved for
publication. Approval does not signify that the contents
necessarily reflect the views and policies of the
Federal Water Pollution Control Administration.
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ABSTRACT
The objective of the project was to investigate the effectiveness of
electrode potential measurements to modulate discharges from combined and
storm sewer overflows to reduce stream and estuarine pollution. Studies
included varying the composition of sewage, flow rate and examining the
tendency to polarize or coat the electrodes under actual flow conditions.
The analysis of experimental results shows a high degree of correlation
between the electrode potential of the sewage and its strength. Linear
correlation coefficients between electrode potential and the various
sewage parameters measured were found to be as shown below:
Parameter Linear Correlation Coefficient
BOD 0.873
COD 0.852
Sulfides 0.896
Total Phosphorus 0.893
Nitrates 0.807
Chlorides 0.225
These results were obtained using predominantly stale, domestic sewage in
the laboratory and more work should be performed with fresh sewage to
substantiate these findings. This work should be supplemented by a field
demonstration.
The 3/ 8 -in. diameter Ag, AgC1-Pt flow-through cells were found to yield
the most stable, reproducible and accurate readings. It was found that
immersion electrodes do polarize while the Ag, AgC1-Pt flow-through cell
has shown no polarization during the ten months of sewage experimentation.
The response time was instantaneous when flow through the cell was
changed from tap water, or the standard ferricyanide-ferrocyanide solution,
to sewage.
It was found that the potential measures positive or small negative values
when DO levels are above 1 mg/l and drops sharply to measure highly
negative values when DO concentrations fall below 1 mg/i.
In the examination of the effect of flow rate on the electrode potential,
little, if any, effect was noticed when the flow rate was varied from
0.5 liter/minute to + liter/minute. The effect of very high and very low
flow-through velocities should be investigated.
Based on these limited investigations it appears that the addition of a
buffer to sewage may be helpful in stabilizing the potential, although
the influence of a strong reductant may be masked.
It was demonstrated that the potential will be more negative the greater
the S concentration, except when a small amount of DO is present which
exerts an attenuating influence. Flows carrying substantial concentrations
of reducing substances with a detrimental impact on the dissolved oxygen
reservoir of any receiving waters must be kept from exerting their damaging
influence on bathing beaches, tidal estuaries and other water resources.
Controlling the flow from outfalls by the electrode potential should
significantly help to minimize such insults to the environment.
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I. CONTENTS
Page
Abstract I
I. Table of Contents ii
II. List of Figures IV
III. List of Tables v
IV. Summary and Conclusions 1
V. Recommendations 5
VI. Introduction
A. Scope of Problem 7
(a) Characteristics of Combined and Stormwater Flows 8
(b) Quantity of Combined Overflows and Stormwater 9
(c) Damages Due to Stormwater 10
(d) Effect on Streams from Wastewater Overflows 10
B. Overall Purpose of Project 12
C. General Background 13
1. Plan of Operation 13
2. Objectives 13
3. Redox Potential Fundamentals l 4-
D. Breakdown of Fundamental Operations 17
1. Chronology of This Project and Current Status 17
2. Specific Objectives i8
3. Breakdown into Fundamental operations i8
(a) Techniques for Measuring Electrode Potential 21
(b) Conditions Necessary to Establish Reliable
Potential Readings 21
VII. Design of Laboratory Demonstration System and Experiments 23
A. Design of Laboratory Demonstration System 23
B. Synthetic Sewage Experimentation 26
C. Conditions Imposed for Proper Potential Measurement 30
1. Different Types of Electrode Systems and Response 30
2. Types of Monitoring Systems 32
3. Range of Potentials 33
4• Sensitivity of Potential to Sewage Strength 35
5. Effect of Interfering Substances
6. Maintenance of Flow-Through C 1l ‘÷1
7. Characterization of Different Types of Sewage
a. Variables Encountered in Sewage
b. Urban Runoff
c. Agricultural Drainage ‘+2
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CONTENTS (Continued)
Page
8. Effect of SuiCides on Electrode Potenial 42
9. Poising of Electrode Potential
(a) Experiments with Addition of Sulfide to
Phosphate Buffer and Distilled Water
(b) Experiments wit1 Addition of Sulfide to
Sewage with and without Phosphate Buffer added 1 7
D. Comparison of Electrode Potentials Against Conventional
Sewage Parameters
VIII. Discussion 60
A. Response, Sensitivity and Stability of Electrode
System 60
B. Sensitivity of Potential to the Strength of Untreated
Sewage and Waste Effluents 60
C. Effect of Interfering Substances or Predominant
Oxidants; Phosphate Buffer Poising 61
D. Zones of Potentials when Layering Occurs and Possible
Compensation for Such Events 62
E. Effect of Different Cell Systems on the Response 62
IX. Acknowledgements 6 -i-
X. References . 65
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II. FIGURES
Page
Figure 1 O.R.P. Relationship in Waste Treatment 16
Figure 2 Detail of Substrate Loop with Electrode Potential
Cell 2 -
Figure 3 Diagram of Complete Laboratory Demonstration 25
Figure J- Conceptual Design of Electrode Potential
Control Installation 27
Figure 5 Laboratory Demonstration System 28
Figure 6 Cross Section of Flow-Type Cell for Measuring
Oxidation-Reduction Potential 32
Figure 7 Potential Values of Some Sanitary Engineering
Processes 3 4
Figure 8 Polarization of Immersion Electrodes 36
Figure 9 Potential of Clean Immersion Electrodes 37
Figure 10 Record of Temperature of Water Bath 38
Figure 11 Potential Record of Flow-Through Cell (with
electrical interference) 39
Figure 12 Potential Record of Flow-Through Cell (without
interference from electrical heater)
Figure 13 Linear Correlation of Electrode Potential with BOD 50
Figure 1 -i- Exponential Correlation of Electrode Potential
with BOD 52
Figure 15 Linear Correlation of Electrode Potential with BOD 53
Figure 16 Exponential Correlation of Electrode Potential
with Sulfides 5 1+
Figure 17 Correlation of Electrode Potential with Total
Phosphorous 55
Figure 18 Correlation of Electrode Potential with COD 57
Figure 19 Correlation of Electrode Potential with Nitrate
Nitrogen 58
Figure 20 Correlation of Electrode Potential with Chlorides 59
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III.. TABLES
Page
Table I Stream Quality Conditions at Time of Bypassing
Pumping Stations
Table II Schedule and Work Effort 19
Table III List of Conventional Sewage Parameters Against
Which Potentials are to be Compared 20
Table IV Composition of Synthetic Sewage 26
Table V Variation of Electrode Potential of Quinone-
hydroquinone System 30
Table VI Response of Electrode Systems 31
Table VII Effect of Total Sulfide Concentration on Potential
Table VIII Summary Tabulation of Data from Potential Study
(FwPcA) 50
Table IX Correlation Coefficients 56
Table X Summary of Correlation Analysis 56
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IV. CONCLUSIONS AND SUMMARY
1. The average annual overflow from sewerage systems is estimated
to contain 3 to 5% of the untreated sewage and during storms, as much
as 95% of untreated sewage. Stormwater and combined sewer overflows are
responsible for major amounts of polluting material in the Nation’s
receiving waters. Urban runoff and agricultural drainage contribute
significant amounts of pollutional materials to watercourses. These
discharges affect all known water uses adversely.
2. The 3/8_in, diameter Ag, AgC1-Pt flow-through cells were found to
yield the most stable, reproducible and accurate readings. It was found
that immersion electrodes do polarize while the Ag, AgCL-Pt flow-through
cell has shown no polarization during the ten months of sewage experimen-
tation. The response time was instantaneous when flow through the cell
was changed from tap water, or the standard ferricyanide-ferrocyanide
solution, to sewage.
3. In the laboratory, the stationary electrodes polarized when
immersed in sewage at 20°C for a period of seven days, but under the
same conditions a similar problem did not arise using the flow-through
type cell. Potential measurements in sewage using the flow-through type
cell can be obtained with a reproducibility within 1 or 2 millivolts.
ii-. The response of the cell has been instantaneous when changing
the substrate flowing through it from water (+300 my) to stale sewage
(-250 my) at 200 or 25°C. Potential changes in the sewage itself, by
the addition of sulfide ion or aeration have been recorded instantaneously
also, indicating the sensitivity of the cell to changes in the substrate.
5. The analysis of experimental results shows a high degree of
correlation between the electrode potential of the sewage and its
strength. Linear correlation coefficients between electrode potential
and the various sewage parameters measured were found to be as shown
below:
Parameter Linear Correlation Coefficient
BOD 0.873
COD 0.852
Sulfides 0.896
Total Phosphorus 0.893
Nitrates 0.807
Chlorides 0.225
These results were obtained using predominantly stale, domestic sewage in
the laboratory and more work should be performed with fresh sewage to
substantiate these findings. This work should be supplemented by a field
demonstration.
6. Automatic records of the potential demonstrate that continuous
potential recording can be achieved successfully. The response and
sensitivity of the sensing cell have been investigated.
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7. The proposed system, if measuring a potential falling to -30 my
or below (signalling facultative anaerobic waste characteristics with
potentially damaging effects on the receiving waters), would trigger a
solenoid which by telemetering would close a gate in the outfall. Thus,
the flow will be shunted to a pond or tank until the potential rises to
+25 my or +30 my indicating satisfactory characteristics to permit direct
release to the stream.
8. It was found that the potential measures positive or small negative
values when DO levels are above 1 mg/l and drops sharply to measure highly
negative values when DO concentrations fall below 1 mg/i.
9. In the examination of the effect of flow rate on the electrode
potential, little, if any, effect was noticed when the flow rate was
varied from 0,5 liter/minute to liter/minute. The effect of very high
and very low flow—through velocities should be investigated.
10. Based on these limited investigations it appears that the addition
of a buffer to sewage may be helpful in stabilizing the potential, although
the influence of a strong reductant may be masked.
11. From controlled laboratory investigations, the results of which
are seen in Table VIII, it is known that formation of sulfides will start
to depress the potential, especially after the DO in the system has been
exhausted.
12. It was demonstrated that the potential will be more negative the
greater the S= concentration, except when a small amount of DO is present
which exerts an attenuating influence. Flows carrying substantial concen-
trations of reducing substances with a detrimental impact on the
dissolved oxygen reservoir of any receiving waters must be kept from
exerting their damaging influence on bathing beaches, tidal estuaries
and other water resources. Controlling the flow from outfalls by the
electrode potential should significantly help to minimize such insults
to the environment.
In summary, the following additional comments may be helpful:
Although it is recognized that overflow discharges are not necessarily
anaerobic, the flows most detrimental to the oxygen balance of any
receiving waters contain reducing substances in substantial concentration.
Much of the laboratory work was carried out with stale sewage to similate
similar conditions, especially the production of sulfides - long a problem
in large sewerage systems and long outfall lines.
Without wanting to imply that the data from these studies are adequate
to set any operating standards, some preliminary estimates for an
operational potential are possible. F r the present, an operating level
of electrode potential of at least +25 or +30 appears to be a potential
level above which the oxygen balance in any receiving water would not be
damaged. Therefore, discharges much below this potential should not be
tolerated.
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In the examination of the effect of flow rate on the electrode potential
little, if any, effect was noticed when the flow rate was varied from
0.5 liter/minute to 1 -i- liter/minute. The effect of very high and very low
flow-through velocities should be investigated.
The my signal may have to be integrated with a definite time constant
to be determined in each case.
Application of the electrode potential control for the intermittant
flows from combined sewer overflows and storm sewers promises to be an
economical solution as part of the overall pollution abatement program
facing this Nation’s rivers and shorelines. Controlling the flow of
combined sewer and stormwater outfalls by the electrode potential should
definitely help to minimize such insults to the environment.
As water quality requirements or standards change or are upgraded, the
critical potential level can be adjusted readily. This intrinsic
flexibility demonstrates a further advantage of the potential method as
compared with fixed treatment plant capacity or other devices.
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V. RECONMENDATIONS
1. The degree of correlation achieved between the potential and
standard parameters, such as BOD. COD, sulfides, total phosphorous and
nitrate nitrogen, provides a meaningful basis for demonstration of the
laboratory calibrated electrode system. Following additional analysis
of the laboratory model with more dilute combined sewage and stormwater,
pilot studies, including field testing of the electrode system in an
existing outfall, are still needed to substantiate laboratory findings.
During the first year of this study it was demonstrated that a stable
and significant potential response by the electrode s::stem for untreated
sewage can be obtained and that continuous potential recording can be
achieved successfully. Additional data of the t e obtained is necessary
to strengthen and substantiate the present conclusions.
2. Although the effect of strong reducing substances in the form of
sulfides have been investigated, additional studies should be conducted
to establish the effect of other reductants, if any, present in sewerage
systems before flow modulation by potential is practiced. Longer periods
of contact with substrates containing a high concentration of sulfides
should be investigated to examine the effect of these substances on the
electrodes.
3. A limited study of the effect of phosphate buffer to improve the
poising of the substrate medium was undertaken. Based on these limited
investigations it appears that the addition of a phosphate buffer to
sewage may be helpful in stabilizing the potential, under certain
conditions. Further laboratory work, including extension to other buffer
systems, is needed.
4• The effect of the flow-through velocity on the electrode potential
signal from flow-through t e cell systems, especially at very low and
high velocities, is still not entirely clear. Although no appreciable
affecton the potential was found with flow rates varying from 500 mi/mm
to #,ooo mi/mm, a wider range of flow rates should be explored.
5. The effect of temperature and the response of the potential
measuring system under widely varying sewage strengths (dilute storm
sewage) should be further investigated.
6. Following the significant correlation obtained in these studies
between electrode potential and total phosphorous concentration (r = 0.89)
and nitrate nitrogen (r = -0.81), the applicability of the electrode
potential to determine discharges of urban runoff and agricultural
drainage qualities should be investigated. Wastewaters containing urban
runoff and agricultural drainage type pollutants, high in nutrients,
may be prepared synthetically in the laboratory and the response,
sensitivity and stability of the electrode potential to these wastewater
characteristics established before a field demonstration is undertaken.
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7. The potential cell developed by Universal Interloc, Inc., claimed
to have improved characteristics, should be investigated along with the
Fischer and Porter system which has given the most stable, reproducible
and accurate readings. The latter showed especially desirable long-term
stability in the laboratory with a range of untreated sewages, including
concentrations of sulfides up to 30 ppm. This electrode system should be
investigated in an existing outfall, unless the Universal Interloc sensor
proves to be a superior system.
8. A conceptual design of a prototype installation to control the
quality of discharge from a combined or storm sewer was shown in Figure 14•
The my signal was shown as simply transmitted to a potential recorder.
The telemetering of an amplified signal to actuate a solenoid-operated
valve should be investigated in an actual field investigation. The
instantaneous changes in wastewater quality in combined and storm sewers
may produce highly variable potentials. Therefore, the millivolt signal
may have to be integrated with a time constant to be employed as a control.
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VI. INTRODUCTION
A. Scope of Problem
The problems associated with storm sewers, combined sewers and overflows
therefrom discharging drainage and wastewater into the Nation’s water
resources have been found to produce uniformly adverse effects. Waste-
water and storm drainage reaching receiving streams without treatment
originate from combined sewer overflows directly to streams and tidal
basins. Stormwater drains also discharge directly to streams, and
bypasses of wastewater from treatment plants and pumping sbations,
usually occurring during storms, represent additional uncontrolled
discharges to watercourses.
Since the first flush of storm water is likely to move most of the
accumulated sewer deposits, its interception is particularly important.
In the case of intercepting sewers, most of the storm water carried by
the collector tributary to the interceptor must be allowed to overflow
into the receiving body of water that the interceptor is designed to
protect. This overflow contains a proportionate share of the sanitary
sewage that enters the combined system during the period of storm
runoff. As a result, the total amount of polluting material reaching
the “protected” body of water in the course of a year is usually a
significant though small fraction of the total annual volume of sanitary
sewage. The annual average overflow is estimated to contain 3 to 5
percent of the untreated sewage and, during storms, as much as 95 percent
of untreated sewage (1).
The quality of the overflows reflects a high degree of pollutional load
to watercourses as measured by the usual standards of biochemical oxygen
demand, coliform organisms, solids, etc. Fsr example, data from
Buffalo, N.Y. indicate that about one-third of the city’s annual
production of sewage solids overflowed without treatment, although only
2 to 3% of the sewage volume actually overflowed. More important is the
danger to public health from the pathogenic bacteria and viruses that
are present in raw sewage. Stormwater alone was demonstrated to carry
significant amounts of pollutional load, particularly in the early
portions of storms when a flushing action occurs. This phenomenon is
responsible for substantial organic loading of streams during storms.
All types of water uses are affected. The problem is of major importance
and is growing worse with increasing urbanization and water demands.
In view of the seriousness of the problem a preliminary evaluation of the
effectiveness of the electrode potential as a measure of strength of
pollutant, and ultimately as a control device, has been needed. The
activity of the system establishes a potential range which may be used
to modulate the flow into a receiving stream, lake or tidal basin, or
to a holding tank or pond until the effluent quality improves. While
the electrode potential is not related directly to the dissolved oxygen
concentration, it is a measure of the relative concentrations of overall
oxidants to reductants.
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In November 1965 the White House released a report (2) ‘Restoring the
Quality of O ir Environment”, which points out that “two-thirds of the
U. S. population, about 125 million people, are served by domestic
sewers.” Sewage from about one-tenth of these people is discharged raw.
Furthermore, stormwater from heavy rains exceeds the capacity of existing
treatment plants in communities with combined sewers, resulting in
considerable amounts of sewage being discharged raw. In total, sewage
discharges correspond to the raw sewage from almost 50 million people (2).
In Massachusetts alone, there are 37 cities and towns that are served
exclusively by combined sewers, serving a population of almost one million
(0.95 million). In the U. S. there are some 125 million people served by
combined or separate sanitary sewer systems (2)(3), The 59 million
people affected by the combined sewer systems represent 50 percent of the
total sewered population (1). A 1967 survey conducted by the APWA for
FWPCA (3) estimated that there are 1,329 jurisdictions, served in whole
or in part by combined sewers, having a total population of 5 )- i - million.
The cost for replacing the combined sewers with separate sanitary and
storm sewers was estimated to be approximately $30 billion. To effect
total separation, including expenses necessary for plumbing changes,
would increase this cost to approximately $1i -B billion. The report
discloses that the possibility of changing all combined sewers to
separate is remote. Therefore, a more economical solution, such as the
interception of the first surge containing most of the accumulated sewer
deposits, by the electrode potential method, was suggested by the princi-
pal investigator and studied during the past year. The results of this
study form the body of this report.
(a) Characteristics of Combined and Stormwater Flows:
Various investigators (14) (5) (6) (7) have estimated the proportion of
sewage that is diverted to a receiving body of water through overflow
structures for various capacities of the interceptor sewer. Intercepting
sewers generally allow for the collection of the maximum dry-weather flow
and the first surge of storm flow for treatment. Where rainfalls are
intense and of short duration, as in most parts of the North American
continent, it is not possible to discharge a substantial amount of storm-
water through interceptors that are reasonably proportioned. Thus,
interceptors are commonly designed to carry only two or three times the
average dry-weather flow, or from 250 to 600 gpcd. A more informative
measure of the capacity of interceptors in excess of the average dry-
weather flow is the amount of rainfall or runoff that they can carry,
expressed in inches per hour. In 19147 McKee (14) studying overflows from
combined sewers in Boston, Massachusetts, found that when flow in sewers
is twice the average dry-weather flow, approximately 2.7% of the total
annual flow of domestic sewage may be expected to overflow to the
receiving stream. The basic data were developed for low intensity,
prolonged rains but were projected to include high intensity storms.
During storms the percentage of sewage lost by overflow would be quite
high. Thus, for a rainfall intensity of only 0.1 in/hr, it was found
that 82% of the sewage during the storm would overflow from a system
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designed for twice the dry-weather flow, and 73% would overflow if the
system were designed for three times the dry-weather flow. For storms
of 0.5 in/hr, the overflow would be 97 and 9 %, respectively. Even with
interceptors designed to collect up to 9 times the dry-weather flow,
32% of the sewage would overflow from storms of 0.5 in/hr. Thus, even
with relatively small rainfall intensities “significant pollution in
terms of organic load and bacterial contamination will be discharged
directly into the watercourse” (!i).
Similarly, Shifrin and Homer (5) in St. Louis found the sewage discharged
by combined sewer overflows to vary from 2.2% to 3.1% of total annual
flow; while Moorhead (6) estimated for Washington, D.C. an annual average
of 3.3% or 3.6 mgd of sewage, lost by overflows from combined sewers.
In many areas the frequency of storms causing significant discharges of
sewage to the streams is far too high for adequate protection of the
receiving water. For interceptors designed for 1.5 to 3 times average
dry-weather flow, McKee (L ) found that overflows may be expected 5 to 6
times per month in the summer; much too frequent for waters to be used
for bathing or shellfish propagation. Johnson (8) showed that at
several outflow points in Washington, D. C. the average number of over-
flows varied from 5 to 17 per month in the summer and from 3.8 to .7
per month in the winter. Agreeing with these findings are the results
of studies made for New York City (9), Kansas City, Mo. (10) and
Northampton, England (11). A more recent survey (3) indicates that for
the 1 - ,212 overflow points examined, overflows occur an average of 28
times per year and each overflow event lasts for an average of five hours.
(b) Quantity of Combined Overflows and Stormwater:
Complete information is not available on the quantity of discharge from
overflows because the complexities inherent in any collection system.
Accepting that from 3 to 5% of untreated wastewater annually reaches
watercourses from combined sewer overflows and confining the estimate to
the conservative side of the range at 3% annual overflow, almost
60 billion gallons of raw sewage per year enter the rivers, streams and
tidal estuaries of this Nation (1). This amounts to about 200 tons of
BOD per day. Enormous quantities of stormwater of questionable quality
must be added to these figures.
Quantities of stormwater alone discharged by sewers vary greatly in
different areas, depending on the rainfall - runoff pattern. However,
with a few assumptions, an estimate of the amounts of surface runoff
from storms may be obtained. If it is assumed that 1/3 of the total area
is impervious for an urban community served by sewers, the runoff volume
will amount to 5.8 mg/sq.mi. per inch of rainfall. There are some
ii, oo communities of all sizes in the 50 States, having a total area of
1l 3,000 sq.mi. Applying the above criteria, total stormwater runoff will
equal 25 BG for each inch of rainfall. Chicago, with 190 sq.mi. of
sewered area serving 3.5 million people, under these assumptions,
produces a stormwater runoff of 1.1 per inch of rain.
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(c) Damages Due to Storrnwater:
The most frequent problem arises from the surcharge of sewers, flooding
residence and business basements with a combination of untreated sewage
and stormwater. Besides causing a nuisance, it represents a financial
loss and is also a menace to public health. Preliminary results of a
study of the flow and composition of stormwater at three stations in
Northamption, England, suggest that stormwater overflows differ in
character from what might be expected. It was expected that the results
would show a heavy runoff to dilute the sewage, thus creating little
pollution. Instead, the suspended solids concentration increased as the
intensity of runoff increased. With storm flow 3 times that of dry-
weather flow, samples taken in the first five minutes at one station
showed that average suspended solids concentration was 250% of that
found in the sewage. However, samples taken more than 35 minutes later
dropped to a 75% concentration. The British studies also showed that
large deposits of solids accumulated in large, old sewers, especially
those with relatively flat slopes. Apparently, deposits build up in dry
weather and high flows during rainstorms pick them up to produce the high
solids concentration.
(d) Effect on Streams from Wastewater Overflows:
Despite essentially separate collection system, wastewater flows in
interceptors increase substantially during storms. It is not known
exactly how the stormwater reaches the interceptors, but it is presumed
that rising groundwater (infiltration) and flow from connected roof
leaders, catchbasins, basement sumps, and yard drains all contribute.
Because the treatment plant will not accommodate the increased hydraulic
load, it is necessary to bypass the plant during storms. For example,
stormwater-diluted wastewater is by-passed through outfalls to San Fran-
cisco Bay from the East Bay Metropolitan Utility District.
Another way of measuring the effect of stormwaters on watercourses is by
examining conditions at pumping stations when it is necessary to bypass
during storms. Table I presents stream quality data showing the effect
of bypass discharges from pumping stations. Samples were taken upstream
and downstream from, and at, the station. At the same time samples were
taken from a nearby stream which did not receive wastewater overflows.
The organic and bacteriological quality of the water upstream from the
discharge point is about equivalent to the stream not receiving waste;
however, the inorganic load imposed by erosion into the creek is
apparent in the concentrations of solids. The harmful effect on the
stream by the wastewater is clearly demonstrated in Table I by the
increase in B.O.D. and coliform counts.
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TABLE I
Stream Quality Conditions at Time of By-passing Pumping Stations
Another Stream
Point of Not Receiving
Upstream Discharge Downstream Discharge
Determi -
nation Avg. Max. Avg. Max. Avg. Max. Avg. Max .
BOD
(mg/mi) 6.8 21 92 360 25 6o 9.5 16
T. S.
(mg/mi) 1 69 7) 3 385 5 3 918 2, 82 6,026 6,672
Coli form
( N/
100 ml) 1,990 4,250 tj.8,200 70,000 40,500 126,500 2, 35 -i ,250
Generally accepted engineering practice in this country has been to
design combined sewers to handle during storms two to three times the dry
weather flow. By-passing the excess directly to the nearest watercourse
is accomplished by any of several schemes. The surcharging and over-
flowing of combined sewers is more objectionable than the backing up of
drains that carry only storm water. The amount of water entering at the
junctions of the submains in a combined system must be controlled by
admitting only as much water to the interceptor as its capacity permits.
All water in excess of this value must be diverted into storrnwater over-
flows. This diversion can be regulated hydraulically or mechanically.
There are many hydraulic separation divices, such as the side overflow
spiliway weir, leaping (gap) weir, siphon spiliway, perpendicular weir
(diversion dam), tipping-gate regulator and orifice or drop-inlet regu-
lator. Mechanical diversion of storm-water flows is generally regulated
by a float-operated valve which controls the admission of water to the
interceptor, such as the float-operated gate, hydraulic cylinder, manual
or automatic valve which may require changing of position if a slide or
sluice gate type of valve is used. All types of regulators share one
common difficulty - they present operating and maintenance problems
without which they are prone to clogging.
It is established that the overflows from combined sewer systems and the
discharge of stormwater from storm sewers contribute directly to pollu-
tion. As mentioned earlier, the high cost of sewer separation plus the
very significant possible need for separate treatment of stormwater has
been the subject of a recent study (12). Information on combined sewer
service was obtained by direct inverviews of 6 i jurisdictions having a
total population of 51 million. Projected to the entire Nation, it was
estimated that there are 1,329 jurisdictions, served in whole or in part
- II -
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by combined sewer systems, including plumbing, could cost approximately
$1i8 billion. Therefore, electrode potential control for these inter-
mittant flows promises to be a more economical solution as part of the
overall pollution abatement program of this Nation t s rivers and shore-
lines.
B. Overall Purpose of Project
The purpose of this project has been to initiate an investigation of the
effectiveness of electrode potential control to regulate the flow of
untreated sewage and waste effluents to protect the water quality of
receiving streams and tidal basins. Pollution abatement from these
wastewaters may be achieved by diversion of discharges (such as:
bypasses of wastewater by treatment plants and pumping stations and the
flushing of accumulated organic matter during the early flooding from
stormwater) to holding tanks, ponds and/or subsequent exposure to waste
treatment.
Sewer systems with overflows contribute materially to pollution and
particularly during storms. The annual average overflow was estimated
to contain 3 to 5 percent of the untreated sewage and, during storms,
as much as 95 percent of untreated sewage. Stormwater quantities are in
addition to these amounts. These overflows contribute a high degree of
poflutional load to watercourses as measured by biochemical oxygen demand,
coliform organisms, solids, etc. Stormwater alone has been demonstrated
to carry significant amounts of pollution (see Chapter VII, Section 7),
especially during the early part of storms when a flushing action
occurs.
Rather than the entire overflow discharging into a river or estuary,
the ultimate objective of electrode potential control is to program the
amount of overflow held back (especially the early slugs) for additional
treatment. The electrode potential system will sense the effluent quality
and relay the signal to a flow regulator. As the quality of the discharge
improves, the flow will be sent to the stream. This modulation according
to quality leads to smaller sized holding ponds or tanks and thus reduces
the construction cost of the hydraulic structure. Therefore, control by
the electrode potential method will be able to modulate overflows from
combined systems to intercept discharges to a receiving stream or other
watercourse that would otherwise contribute materially to their pollution.
Diverting flows of this nature to a minimum sized pond or tank permi ts
subsequent treatment to any desired degree to be achieved. By contain-
ment of the most offensive and strongest discharge surge, only a
relatively small treatment volume is necessary. Most important, the
water quality of the receiving stream or estuary will be safeguarded
automatically and continuously.
Following the analysis of the electrode system in the laboratory during
the first year, pilot studies, including field testing and demonstration
of the laboratory model in one or more outfalls should be undertaken to
substantiate laboratory findings during the second year.
- 12 -
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C. General Background
1. Plan of Operation
The project plan has been basically a resea ’ch phase leading to a pilot
plant demonstration. The first phase, underway since March 1969, has
been carried out in the laboratory. It consisted of measuring electrode
potentials of untreated or partially treated wastes with which to
modulate the flow. Several electrode systems, their stability, response
and reliability have been investigated and compared. The most reliable
electrode system can be incorporated in an electrolytic control circuit
for control of the effluent quality. Provided the project is continued,
the second year will be devoted to testing the calibrated electrode
system by operating this model under field conditions to evaluate its
response to meet water quality standards.
2. Objectives
The immediate objective of this study has been to investigate the response
and the effectiveness of the electrode potential as a measure of the
strength of wastewater discharges from combined sewer overflows and storm
sewers. Further work is expected to demonstrate the control of harmful
discharges by the electrode potential method. In practice, the potential
will be used to modulate the discharge (especially the early flushings)
from combined and storm sewers by temporarily diverting this flow until
it can receive adequate treatment, following the period of peak flow
through the treatment plant.
A measured potential falling to say -30 my (signalling a polluted
effluent with potentiaily damaging effects on the receiving waters)
triggers a solenoid which by telemetering will close a gate in the out-
fall. Thus, the flow will be shunted to a pond or tank until the
potential rises to say +25 my or +30 my, indicating satisfactory
characteristics to permit release to the receiving stream. The my signal
may have to be integrated with a definite time constant to be determined
in each case.
The proposed system has been investigated initially for effectiveness of
response to a variety of sewage strengths by the operation of a labora-
tory test model. These studies have included: 1) varying the composition
of sewage (synthetic and real sewage), 2) varying the degree of aeration,
3) varying the concentration of sulfides, i-i-) examining the presence of
grease, 5) varying the flow rate, 6) examining the tendency to polarize
or coat the electrodes under actual flow conditions, and 7) investigating
the effect of different cell systems on the response. Following the
analysis of this model in the laboratory, pilot studies, including field
testing of the electrode system in an existing outfall, are necessary to
substantiate laboratory findings.
-13 -
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3. Redox Potential Fundamentals
Many of the chemical and biochemical processes encountered in sewage and
industrial wastes can be described fundamentally as oxidation-reduction
systems. Although determination of the electrode potential does not
itself explain the nature of the systems at work, it is used to evaluate
the magnitude and character of process changes. Measurement of a redox
potential has been facilitated considerably in recent years due to
improvements in potentiometers and metallic electrodes which have resulted
in greater accuracy and convenience. The development of the flow-through
cell system may be regarded as a definite “breakthrough tt , virtually
eliminating polarization of the electrodes.
According to the definition of the oxidatton-reduction process,
oxidation involves a loss, and reduction, a gain, of one or more
electrons. A typical example is the hydrogen electrode, where the
hydrogen gas is the reduced and the hydrogen ion is the oxidized form.
The redox potential is a measure of the tendency for a substance to give
up or to accept electrons. It is a quantitative measure of the free
energy of the reaction (or myriads of reactions) involved in the elec-
tronic transfer. During the metabolic process of microorganisms, a
definite oxidation-potential is maintained in a particular organism-
substrate system, the reduction intensity of which depends on the species,
cultural age, its variation phase, and its environment (13). The value
of redox potentials in characterizing a physiological state in higher
forms of life has been established. The relationships between reduction
intensity and known physiological conditions have already proven of
special value in bacteriology.
Transfer of an electron or electrons from one compound to another is a
result of potential difference between the two reactants. The magnitude
of this potential difference depends upon the ease with which the elec-
trons are lost or gained. The greater the oxidizing or reducing power
of a substance, the greater will be the electrical potential difference.
The oxidation-reduction potential is always referred to the normal
hydrogen electrode, assumed to have zero potential. The more highly
oxidizing a substance (or bio-system), the more positive will be its
electrical potential; the more highly reducing a substance (or bio-
system), the more negative will be its electrical potential.
- l 4. -
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According to Hewitt (13), the Nernst equation as modified by Faraday’s
law is:
Rh - E + in ( )
in which:
Rh = electrode potential with respect to the hydrogen half-cell,
(volts);
E = a standard potential of the system when the aCtivity of all
oxidants and reductants are unity and at 30 C, (volts);
R 8.315 volt-joules coulombs, (the gas constant);
T = absolute temperature, (°K);
F 96,500 coulonThs, (Faraday’s constant);
n = number of electrons participate in the redox potential system.
It is evident from the equation that the greater the relative concentra-
tion of oxidized form the higher will be the potential. With a more
reduced substance, a lower, or more negative, potential will result.
It may be observed that if a system is 50% oxidized, the concentration of
oxidants equals that of the reductants, i.e. (Ox.) = (Red.) and Eh = E 0 .
It follows that Eo is a measure of the oxidation and reduction intensity
level of the system and enables different systems to be graded in the
order of their oxidizing or reducing tendencies. Thus, a system with
+100 my will oxidize a system with E 0 -100 my, but on the other
hand, will itself be oxidized by a system with E 0 +200 my, see
Figure 1.
Although the measurement of oxidation-reduction potential does not itself
explain the nature of the systems at work, the e.m.f. represents their
relative proportions. A number of variables affect the potential of a
biological system such as sewage and the rate of potential change is a
function of: a) kind of organisms present in the substrate; b) condition
of organisms; c) growth phase of the microorganisms; d) nature and
quantities of other constituents in the system providing environment
effects; and e) condition of the process or of the operation.
Practical Application of the Potential and Limitations
It is fair to assume that electrode potential instrumentation in the
future will be further improved and that present techniques may be
compared to the crude hydrogen electrode used at the turn of the century.
Nevertheless, potential measurements in sewage can be obtained with a
reproducibility within 1 or 2 millivolts.
-15-
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U.Ub tUxId.J
Eh=E ÷—Iog
n [ Red.]
> CHLORINATED WASTES
I-
>
OPTIMUM ZONE FOR TRICKLING
FILTER & ACTIVATED SLUDGE
LU OPERATION
I X +400 — ,,- . REDUCING ACTIVITY RANGES
z , [ AEROBES]
>-
If)
z
LU
+200-
w E
If)
LU LU
/
o
0 __
/// FACULTAT lYE
I-
> 0
p / ///jjq
OPTIMUM ZONE OF SLUDGE
w 0
/ DIGESTOR OPERATIONS
—200- ‘ (ANAEROBIC DECOMPOS 1 O
z —
>-
I-
z
LU
—400— #‘ \- REDUCING ACTIVITY RANGES SULFATE REDUC7ION TO
LU [ ANAEROBES]
I’)
LU
0
Figure 1. O.R.P. Relationships in Wastes Treatment
-16 -
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As was recognized by Pomeroy (1)-i-): “Determination of the oxidation-
reduction potential may provide a quick method of determining the
presence or absence of dissolved oxygen or hydrogen sulfide in sewage...
and may be a useful analytical method in estimating the degree of
contamination of sewage.”
The advantage of obtaining an electrode potential of biological systems
over most other standard and non-standard parameters to characterize
pollution is that it describes the instantaneous state of reaction of
the sewage system according to the fundamental electronic concept of
matter. Values for other parameters, such as BOD, N0 2 -N, NO 3 N and
other qualitative chemical determinations, yield only the average rate
and extent of biological oxidation (15). According to Luck (16), who
used redox potential for the determination of chlorine compounds in
water, the potential is an analysis that will provide information
related to the bactericidal strength of the solution. In chlorination,
the electrode potential comes close to attaining this objective because
it measures the effective integrated oxidation strength of the materials
in a solution - similar to the application in the present studies.
D. Breakdown of Fundamental Operations
1. Chrolology of this Project and Current Status
The original two-year proposal, submitted December li-i-, 1966, and
resubmitted to FWPCA on October 25, 1967, contained a plan of operation
which suggested that this research project be conducted in two phases:
a) first phase to be carried out in the laboratory and designed to
evaluate at the laboratory level the feasibility of measuring electrode
potentials of untreated sewage with which to modulate the flow, with the
second phase designed to take a calibrated potential system and operating
this model under field conditions.
At the time of the official approval by the Commissioner FWPCA, on
November 29, 1968, it was clearly stated that the one year project (“to
investigate at the laboratory level the feasibility of utilizing electrode
potential measuring systems to indicate the strength of combined sewage”)
is considered as a complete unit although the findings may demonstrate
the need for further field projects. The feasibility of the potential
method has been clearly demonstrated in the laboratory but additional
data are necessary to further substantiate the limits of applicability
among untreated combined sewage, domestic sewage, urban runoff, agricul-
tural drainage and industrial waste effluents.
At the time of the official approval, it was further stipulated that:
“Subsequent extension into a development field demonstration project
shall be submitted as a separate proposal based upon, and justified by,
the findings of the feasibility demonstration. A proposal for a
Research, Development and Demonstration Contract, dated January 23, 1970,
was submitted to FWPCA on January 26, 1970. It proposes essentially the
further extension of this project into a field demonstration with
-17-
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continuing laboratory back-up and substantiation of the electrode potential
method. The test model should permit in situ study of the effects of film
formation, flow rate, temperature variation and permit evaluation of some
types of industrial waste admixtures. It is apparent that the complexities
and number of variables, viz, intensity and duration of storm, strength of
combined sewage or domestic sewage, stream flow regulation, size and slope
of sewer, etc. and their interactions will require subjecting automatic
electrode potential control to the systems approach. Therefore, the
interdisciplinary team approach, as originally proposed and practiced
during the current investigations, needs to be continued.
2. Specific Objectives
Specifically, the present studies included the following objectives:
1) to determine the sensitivity of redox potential to the
strength of untreated sewage and waste effluents (initially
synthetically prepared mixtures),
2) to establish the transient effect of interfering substances
or predominant oxidants on the performance of the Potential
sensing systems,
3) to investigate the effect of different cell systems on the
response and degree of modulation achieved for operating the
gate value, or equivalent device.
3. Breakdown into Fundamental Operations
Accordingly, a logical breakdown of the project into its fundamental
operations was developed. A schedule of tasks and work effort estimate,
as shown in Table II, were submitted to FWPCA on March JJ- , 1969.
Simultaneously, a list of the standard and non-standard sewage parameters
was prepared against which the electrode potentials were compared to
examine their effect on the electrode, cell system rather than indicating
sewage strength characteristics. The list of parameters is shown in
Table III. The parameters to indicate the strength of the combined
sewage for comparison against potential readings were carefully considered
in conference and discussion with Mr. Warren H Oldaker, Project Officer,
FWFCA. The usual characterization parameters, including BOD, COD, DO,
residue (especially total volatile solids), nitrogenous matter, phosphorous,
chlorides, sulfides, pH, temperature and settleable matter were carried
out throughout the experimental period and the data are presented later
in Table VIII.
-------
TAB lE II
Schedule and Work Effort
A. Schedule . The scheduling of tasks is as follows:
1) Literature Search [ —I
2) Ordering of Electrodes and Recorder L _ I
3) Setting up Laboratory Experiments
1 ) Synthetic Sewage and Nutrients U - ]
Experimentation (Response)
5) Conduct Laboratory Tests with Synthetic _____________
and Real Sewage (Collection of Data)
6) Analysis of Data ___________
7) Prepare Final Report
B. Work Effort . The total work effort has been broken down into
man-days per task, as shown below:
Task
1) Literature Search
2) Ordering of Electrodes and Recorder
3) Setting up Laboratory Experiments
L ) Synthetic Sewage and Nutrients Experimentation
(Response)
5) Conduct Laboratory Tests with Synthetic and Real
Sewage (Collection of Data)
6) Analysis of Data
7) Prepare Final Report
Total Effort:
Task
Time Span ( months )
2 ) 6 8 10 12
I—
T:-
Li
0
10
30
50
20
30
320
- 19 -
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TABLE III
List of Conventional Sewage Parameters Against
Which Potentials are to be Compared
A. Standard Parameters--those involved in the determination of the
strength of the sewage:
1) Dissolved Oxygen
2) B.O.D. (two and five-day values)
3) COD
- ) Residue (total volatile solids)
5) Nitrogen
a. Ammonia and Organic Nitrogen (total Kjeldahl)
b. Nitrate
6) Phosphorous (persulfate digestion)
7) Chloride
8) Sulfides
9) pH
10) Temperature
11) Settleable matter (Imhoff cone)
12) Known redox systems (.OlM Borax buffer at pH 9.22 and)
(acid potassium phthalate buffer at)
(ph = 1i .OO)
B. Non-Standard Parameters--those involved in determining the proper
functioning of the cell system:
i) Ether solubles (polar method)
2) Bacteria (total coliform)
3) Known redox systems (for standardization)
- 20 -
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(a) Techniques for Measuring Electrode Potential
Prior to the initiation of experimentation with sewage substrates it was
necessary to work out a number of details to determine the response of
the potential in the laboratory.
1) Static Measurements: The initial calibrations consisted of immersing
standard electrode systems, (Fischer and Porter, Leeds and Northrup, and
others) for comparison with known potential systems and were contined
throughout the investigations to serve as standard potential measurements;
(2) Short Time Duration Measurements: Various sewage substrates and
substrate strengths (from fresh to stale effluents) were tested. The
purpose of these initial tests was primarily to investigate response, i.e.
testing the capability and the speed of the cell to respond to highly
variable potentials; 3) Long Time Duration Measurements: During these
studies, emphasis was placed on stability of the readings, the effect of
electrode polarization, and coating of the electrodes; ) i ) Short and Long
Duration Measurements in Flow-Through Type Cells: The ultimate application
was by means of a flow-through cell to overcome the problem of electrode
polarization. To examine the validity of the measurements it was necessary
to compare frequently the potentials between a static system immersed in a
known potential solution, a flow-through cell with the known potential
solution circulating through it and a flow-through cell with the substrate
being investigates. If any problems would arise, cross-referencing of’ the
potential was possible by interchanging the flow-through cells.
(b) Conditions Necessary to Establish Reliable Potential Readings
To overcome coating of the stationary electrodes, a weak solution of HC1
was used for primary cleaning followed by scrubbing with a paste of
Alconox powder or Bon-Ami and followed by thorough rinsing with distilled
water.
Although a problem not encountered in the laboratory aspects of this work,
wetting of the electrodes after prolonged dry periods may be necessary.
Wrapping with Mylar, Tedlar, or coating with acrylic sprays may be
satisfactory techniques but a loss in sensitivity may result. Application
of an aerosol spray may overcome any reduction in sensitivity and should
be investigated separately.
Reproducibility of electrode readings, due to a poorly poised system, did
not present a problem. Borchardt, at the University of Michigan, found
that if the electrodes are allowed to age in the substrate for a 2k-hour
period, the electrodes give accurate readings, provided the system is free
from poisoning. Should the reproducibility of results still pose a problem
because of a poorly poised system, it may become necessary to maintain a
base level of potential with a phosphate, or borate, etc. buffer system
and permit the potential of the substrate to float on the basic buffer
potential. Changes in substrate quality would be reflected in a different
range of potential level without impairing the usefulness of the potential
as a criterion for discharge. (Note: This supposition was developed
during the planning stage but the problem never arose during the actual
laboratory investigations).
-21-
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The number of sample specimen taken for analysis was predetermined by
deciding that a once per month sampling frequency would permit sufficient
time to trace a fresh sewage sample to septicity, and allow for clean-up
of equipment and apparatus to get ready for the next run.
The reduction in personnel funds from $26,LiOO originally requested to the
$15,600 granted (a Li.i% reduction) made it necessary that the number of
sewage samples collected and analyses performed be scaled down. Never-
theless, nine (9) major samples (30 gals. each) were collected during the
8_months? experimental period and over 200 analyses were performed, many
of these in duplicate and triplicate. Only their averages are shown in
the summary tabulation, see Table VIII.
Following discussion of the design and construction of the laboratory
demonstration system, the experimental data is presented. The data is
discussed with special reference to support the “Specific Objectives”.
- _
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VII. DESIGN OF LABORATORY DEMONSTRATION SYSTEM AND E) ERI NTS
To simulate field conditions and to provide the necessary flexibility for
experimental purposes, three (3) electrode potential measuring cell
systems were employed. One of tkiese was an immersion-type system, used
at any time as a reference check of the potential against a known
standard potential solution (quinhydrone; Ce(III), ce(IV); ferricyanide,
ferrocyanide system; etc.). The other two electrode systems were identi-
cal flow-through cells. One flow-through cell was employed to measure
the potential of the actual waste (termed “experimental” cell); the
other to make frequent checks against the standard potential solution
(termed “control” cell).
Although each flow—through cell was provided with a separate flow system,
a specially designed valving arrangement permitted the reversal of flows,
i.e. direct measurement and verification of the actual waste potential
by the continuously calibrated “control” cell, and similarly, verifica-
tion of the response (sensitivity and accuracy) of the “experimental”
cell against the standard potential solution.
A. Design of Laboratory Demonstration System
The basic design of the demonstration set-up to perform the laboratory
experiments is shown in Figure 2. It presents a descriptive detail of
the experimental bench-scale model of a flow-through potential cell
and potential recorder, complete with sewage substrate and recirculating
pump. As may be seen in Figure 2, it is a closed system with the
recirculating pump or peristaltic design to prevent any contamination
of the recirculating medium during experimentation. The insulated water
ha:h, made from a 55-gallon drum, surrounded a 30-gallon polyetylene tank
with cover and was used for temperature-controlled storage of the sub-
strate. A paddle wheel mixing device was installed to maintain a uniform
concentration of the substrate during storage. A Warburg refrigeration
bath served as the source of cooling water and the constancy of the water
jacket temperature was tested to a variation within ± 0.5 C.
A diagram of the complete laboratory demonstration system is shown in
Figure 3. It was designed to operate the “experimental” flow-through
potential cell; a separate recirculating system of known standard
potential operating in parallel with the identical, “control” electrode
system; and finally an immersion-type electrode pair, immersed in a
solution of known, standard potential (quinhydrone system or equivalent),
to serve as a primary laboratory standard.
Adequate provisions were made to cross-reference electrode systems with
sewage substrate and standard potential solutions to check on various
operating characteristics, such as electrode fouling, transient effect
of interfering substances, predominant oxidants and/or reductants and
response of different cell systems, besides verifying the strength of
sewage - as needed - during the conduct of the experimental studies.
- 23 -
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Rotor Motor
5 - gal Tank
1\)
-v
Cone tant Temperature
Water Bath
.4
Co
Co
Sewage
Subetrate
Potential
Recorder
Stirrer
I
3/1 - in,
dia.
Flow-through
22.12-tn.
3/8-in.
dia.
Recirc.
Pw
Scale : 1-in. - lO- .in.
Figure 2 Detail of Substrate Loop with Electrode Potential Cell
-------
Performance Standard
pH Li.OO Buffer +
Quinhydrone
Eh 1 j70 my 20C
-gal Reeervoir
Combined or Storm
Sewage Sub$trate
N)
Standard ORP
Electrodea
Potential Cell
(Control)
Potential
Recorder
Recirc.
Pump
Recirc. To Waste To Waste
Pump
Scale : 1-in. ‘ 10—in.
Figure 3 Diagram of Complete Laboratory Demonstration
-------
A conceptual design of a prototype installation in a combined or storm
sewer is shown in Figure 14• For the present, the millivolt signal is
shown simply as transmitted to a potential recorder. The telemetering
of an amplified signal to actuate a solenoid-operated valve will be
investigated at a later stage (although no difficulties are anticipated),
following the successful laboratory demonstration of a stable and
significant potential response by the electrode system. In such a proto—
type installation it may become necessary to make provision for scme
(sewer) upstream flow to wet the electrode system in advance of the
initial slug of combined or storm sewage following a period of prolonged
drought. Aerosol spray application after a period of dryness to rejuve-
nate the electrodes or buoy suspension of the system are other alterna-
tives to maintain the cell system in good operating condition. Details
to provide such an advance flow have been omitted from the present
diagram pending further investigations, not included as part of the first
year phase of these investigations.
A photograph of the complete laboratory demonstration system is shown
in Figure 5.
B. Synthetic Sewage Experimentation
Synthetic sewage substrate was prepared in accordance with the composi-
tion developed by Weinberger and Sawyer (17). The exact composition is
shown in Table iv.
TABLE IV
Composition of Synthetic Sewage
( per liter of North Andover tap water)
Chemical Amount
Nutrient Broth 100 mg
Urea 30 rag
Castile Soap 50 mg
Soluble Starch 100 mg
Diatomaceous Earth 25 rag
Sodium Chloride 30 rag
Potassium Chloride 7 mg
Calcium Chloride 7 rag
Magnesium Sulfate 5 rug
Aluminum Sulfate (18 H 2 0) 5 mg
Disodium Hydrogen Phosphate 25 mg
Sodium Bicarbonate 168 rag
- 26 -
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Potential Recorder
(telemeter to gate)
Combined or Storm Sewer Outfall
I ’ )
Flow-through
Potential Cell
Sewer
Outfall
Figure I Conceptual Design of Electrode Potential Control Installation
-------
L .
I
41
‘ 1 -
Figure 5. Laboratory Demonstration System
c l
9
-------
Considerable delay was experienced in obtaining the Nutrient Broth from
the supplier and therefore it was prepared by mixing its two separate
components on the basis of 3 gms Bacto-Beef Extract with 5 gms Bacto-
Peptone (18). A total of three (3) liters of synthetic sewage was
prepared for the initial BOD run to determine its actual strength.
Sufficient stock solutions were prepared for 30 gallons of synthetic
sewage in accordance with the procedure outlined by Weinberger and
Sawyer (17)
Domestic sewage from Lawrence, Massachusetts, for seeding, was obtained
from the Lawrence Experiment Station, Massachusetts Department of Public
Health, on July 7, 1969. Following its use for seeding of the initial
synthetic BOD run, the remainder of the seed was frozen for replication
in future runs.
The initial BOD run was set up with a 25% dilution of unseeded synthetic
sewage and 0.5%, 1%, 2% and 4% dilutions of seeded synthetic sewage.
The latter four dilutions were seeded with 0.5 ml and 1.0 ml of diluted
(half-strength) settled Lawrence sewage, respectively.
The first BOD run was designed to obttain initial (15 minute), three-
day, five-day, seven-day, ten-day and thirty-day readings. All BOD
samples were run in triplicate. Summaries of the DO and BOD data were
presented in Monthly Progress Letter No. 4 (19).
The data showed that the 25% dilution of synthetic sewage (unseeded) ran
out of DO in less than three days. This pointed to the possibility of
contaminated chemicals and dilution water.
The seeded synthetic sewages (0.5%, 1%, 2% and )- % dilutions), seeded with
0.5 ml and 1.0 ml of half strength Lawrence sewage, respectively,
exhibited a higher BOD for those samples to which less seed had been
added. The seed (settled Lawrence sewage) may have contained toxic or
inhibitory chemicals.
These vagaries in the dissolved oxygen data and difficulties with the BOD
data led to checking the procedure carefully.
The cause of the spurious data was traced ultimately to the use of a
wrong alkaline KI solution and contaminated compressed air, used for the
dilution water.
In the meantime, examination of electrode potential response with real
sewage was initiated rather than a continuation with the synthetic
medium. This departure from the work schedule was mutually agreed upon
with the concurrence of the Project Officer in order to not fall behind
in the fact-finding phase of these investigations.
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C. Conditions Imposed for Proper Potential Measurement
1. Different Types of Electrode Systems and Response
All electrode systems consist of two electrodes: an inert, noble metal
electrode and a reference electrode half cell.
Examination of the response of different types of cell systems (Pt-Cal,
Ag-Cal, Pt-Cu) was undertaken and different types of electrode designs
(immersion and flow-through) calibrated and results compared against
standard potentials from the leterature for such well-defined redox
systems as: quinone-hydroquinone: Fe(II), Fe(III); SO =, So ;
Ce(Ifl), Ce(IV); and the ferricyanide, ferrocyanide sy tem.
Work to develope a non-fouling reference electrode (Cu or Ag plate) a
together with a thin-film Pt-encapsulated electrode has been underway
It was hoped that this system, with the non-fouling reference electrode
continuously immersed and the noble Pt readout electrode alternately wet
and dry (if necessary aerosol sprayed or buoy suspended), would ultimately
‘oduce the permanent potential measuring system; provided the reference
electrode can withstand the bacterial action from growths. The purpose of
the Cu electrode is to provide a more rugged reference electrode, capable
of withstanding the aggressive action of storm and combined sewage and
produce a more dependable, stable electrode potential in prototype
installations. This electrode system was investigated in parallel with
the other systems.
In addition to the regular immersion ty \of electrode systems, the 3/8-yin.
diameter Ag, AgC1-Pt flow-through cells’ / have given the most stable,
reproducible and accurate readings.
Initially, standardization of these electrode systems was by means of
the quinhydrone system. The variation of its potential with pH is
shown in Table V.
TABLE V
Variation of Electrode Potential of Quinone-hydroquinone System
2H + C 6 H 1 0 2 = 2e + C 6 H 1 (OH) 2
Readout, my
1 611.0.7
Li.6 3 .Li.
7 285.1
10 108.8
The equation for a saturated solution of quinhydrone at 25°C is:
= 0.6998 - 0.0591 pH (2)
(a) Manufactured by Delta Scientific Corp., 120 East Hoffman Avenue,
, . Lindenhurst, New York 11757.
Manufactured by Fischer & Porter Company, Warminster, Pennsylvania 189711..
-30
-------
Other potential systems which have teen employed include: Fe(II), Fe(III);
SO 3 , SO) =; Ce(III), Ce(IV); and ferricyanide, ferrocyanide. Some results
obtained during the calibration experiments with the Ce(III), Ce(IV)
system are shown in Table VI. This data shows good agreement between the
Pt-Cal and the thin-film Pt-encapsulated and non-fouling Cu reference
electrode systems(c).
TAB1 VI
Response of Electrode Systems (a)
(Std. potential Ce(III), Ce(IV) = 1217.2 mv at 25°C.)
10 mg of Ce(IV)
mg of Ce(III) Pt-Cal Electrodes (t) Pt-Cu Electrodes (c)
(my) (my)
0 1212 1227
1211 1228
1.0 1210 1227
1208 1226
2.0 1 20 - -
1202 1222
3.0 1200 1221
1198 1220
LLO 1195 1219
1192 1218
5.0 1191 1217
1190 1215
6.0 1189 1213
1188 1212
7.0 1187 1211
ii8 1210
8.0 1182 1210
1181 1209
9.0 1180 1208
1180 1207
10.0 1179 1206
1178
11.0 1177 120 )-t
1176
12.0 1175 1202
1172
13.0 1172 1201
1171
lL .0 1170 1200
2 - -.0 1160 1190
5) Duplicate readings at one minute intervals
(‘0) Manufactured by the Leeds and Northrup Company
(‘c) Manufactured by the Delta Scientific Corporation
- 31 -
-------
Experiences with the Fe(II), Fe(III) system have been less than satis-
factory, the best value acheived was Eh = 76 my as compared to a standard
potential value of 5 2 5 Ji- my at 25°C from the literature. The sulfite-
sulfate system produced no stable value, the potential kept drifting at
a steady rate. Much greater success in determining electrode response
was achieved with the Ce(III), Ce(IV) system, as shown by the values
reported in Table VI. After a number of known redox systems were
evaluated (including quinhydrone), a ferricyanide, ferrocyanide system
[ K 3 Fe ( I’T)6 solution] was chosen ultimately as the standard potential
because of its very stable potential over a long period of time. Data
showing this stability were presented in Progress Letter Number . (20).
The flow-through cell uses the silver-silver chloride half cell which is
similar in construction to the calomel half cell. It consists of a silver
electrode, immersed in a saturated KC1 reservoir connected to the sample
by a salt bridge consisti ig of saturated KCI solution diffusing through a
porous porcelain tube (21). The Ag-AgC1 cell has a half cell potential of
+197 my at 25°C (as compared to 220 my for the standard calomel). This
type of half cell, together with either a gold or a platinum electrode,
was used successfully as the flow-through(a) potential cell in these
investigations.
More recently, while investigating polarization resistance techniques,
another flow-through potential sensor ceJ4, claimed to have a high degree
of accuracy, was developed. This system appears to have an improved
liquid junction and self-pressurization for the Ag, AgC1 reference cell.
An extremely short transmission cable should result in essentially no
transmission leakage from the platinum electrode. Another advantage
claimed is the extremely high impedance of the amplifier which senses the
output of the Pt electrode. One of the disadvantages appears to be the
need of an amplifier which increases the cost of this system appreciably.
2. Types of Monitoring Systems
There are two basic designs of potential cell systems that are of interest:
1) the stationary cell and 2) the flow-through cell. Either of these cell
designs may employ various types of electrode pairs; one a standard half
cell, the other an inert, noble metal electrode (platinum, gold, etc.).
When the electrodes of a stationary cell system are immersed the solution
must be agitated continuously to prevent polarization of the noble metal
electrode. This electrode must also be cleaned periodically to assure
correct response.
(a) Manufactured by Fischer & Porter Company.
(b) Manufactured by Universal Interloc, Inc., l7 -i-01 Armstrong Avenue,
Santa Ana, California 92705.
- 32 -
-------
The flow-through cell consists of a platinum electrode and a standard
silver, silver chloride electrode which is in intimate contact with a
saturated KC1 solution, kept under a guage pressure so that it will
diffuse through the porous membrane and make contact with the liquid in
the flow-through cell. This cell, unlike the stationary cell, presents
no obstruction to the flow as may be seen in Figure 6, and therefore is
not easily plugged by fibrous material or grease present in wastewaters.
1
Polarization of the noble electrode in the flow-through cell has been
avoided by a large paltinum electrode and a rapid flow rate. Earlier
work showed that a flow-through velocity Of at least 1 ft/sec prevents
polarization amost indefinitely (22). The entire electrode assembly is
housed in a Teflon block along with the KC1 reservoir.
Any good potentiometer may be used in conjunction with these cells to
measure the potential difference. In the present experiments three
meters of this type, a Leeds and Northrup pH and my meter, a RCA V.T.V.M.
and a Fischer and Porter recording my meter were used interchangeably.
3. Range of Potentials
As sewage flows through its delivery system, it is treating itself as it
travels. Fresh sewage from a household may exhibit high positive potentials
due to the presence of dissolved oxygen. When introduced into the delivery
system, it is assimilated into a body of water where the conditions are not
always conducive to the retention of an aerobic state. Because of high
oxygen uptake at the water surface, any reaeration is likely to be
cancelled out, leaving only the sewer stream oxygen to be depleted before
anaerobiosis may set in.
While fresh sewage will exhibit high positive potentials (especially in
the present of Do), when introduced into sewerage systems not conducive
to the retention of an aerobic state, the potential will fall significantly.
POTENTIOMETER
YYYYYXXYY)1 N I //////!
N POROUS JUNCTION
L INDER
Fig. —Cross section of a flow-type cell for meosurng oxidat on-reduction-potental
- 33 -
-------
Thus, while pctential drops are small (generally xhihitin positive or
small negative values) when DO levels are above 1 mg/l, sharp drops
(highly negative values) are observed when DO concentrations fall below
1 mg/l. (Note: Compare values in Table VIII). Okey, et al. (23), found
a relatively small decrease of potential below 5 mg/i DO until the DO fell
to below 1.0 mg/i when the rate of potential drop increased sharply with
a drop of +25 my (from - 1-75 my tQ -350 my) as the dissolved oxygen
concentration fell from 1.0 mg/i to approximately 0.1 mg/l. Since
anaerobic conditions are more likely to become established when velocities
are low and detention periods in sewers long, these types of systems are
likely to exhibit low electrode potentials which does not limit the
feasibility of using electrode potential systems in sewage. Thus, the
ultimate objective, to prevent the discharge of sewage exhibiting these
characteristics by continuous potential monitoring, appears feasible to
achieve.
Collection systems which are small may be expected to exhibit higher
potentials because of shorter detention time.
In Figure 7, Dirasian (22 ) has indicated the range of potentials likely to
be encountered. Although a range of 0 my to +1 00 my for wastewater is
shown, it is not ususual to find negative potential values if anaerobic
conditions are impending.
U ’
I d
4’
4
d
I d
4
d
FIG. 7
POTENTIAL VALUES
OF
SOME,
+ 300
SANITARY ENGINEERING PROCESSES
+ 400
U
p 300
+300
7
/
/
/
/
,
/
/
/
/
/
/
/
/
/
I
+ too
0
/
/
/
/
/
/
/
/
/
/
/
/
7,
/
/
/
/
/
/
/
/
/
/
- too
I
I-
U)
(I ,
I-
z
I d
D
-J
4’
I ’
Id
I .,
x
z
z
0
-300
U
U
Id
I-
-j
I ’
2
Id
4
4
0
0
Id
U)
4
2
- 3)4 -
-------
11. Sensitivity of Potential to Sewage Strength
As reported in the literature, the response time of a potential system
varies, depending on the substrate material. The time interval to obtain
fairly steady potentials was found by Henry (25) to vary from 2 to 5 to
10 minutes in sewage. According to Hood (26) the time interval in sewage
is 10 to 30 minutes. However, both authors used immersion electrodes
in their work rather than a flow-through type cell.
Another advantage of the flow-through cell is its greatly improved
response time. The response time of the Fischer and Porter flow-through
cell to the standard ferricyanide, ferrocyanide potential system was
found to be less than one second (19).
5. Effect of Interfering Substances
A major problem that develops when using stationary electrodes to measure
potentials of flowing systems is the accumulation of polarizing substances
on the electrodes. Since stationary electrodes are obstructions in the
flow path, it is likely that non-polar substances such as oils, grease and
sewer slimes deposit themselves on, or coat the electrodes. Figure 8
shows the effect of electrode polarization on a stationary system after it
had been immersed in sewage for approximately ten (10) days without
cleaning. The potential record of the same system for the entire previous
week (starting August 19, 1969 is shown in Figure 9. A record of the sewage
substrate temperature is shown in Figure 10, indicating that temperature
control within 25 ± 0.5°C, or better, was achieved during the controlled
laboratory investigations.
The flow-through cell was also developed to overcome the problem of
polarization, utilizing the inside surface of a pipe as the noble metal
electrode. It presents no longer a flow path obstruction and deposition
of material on the electrode is minimized or eliminated. The potential
record, using a flow-through cell, for the week beginning August 29, 1969,
is shown in Figure 11. Beginning with a potential of approximately -210 my,
the potential gradually rose to -120 my in about 1 I days. When the peristaltic
pump was turned on (l0:1-i-5 a.m. on September 2, 1969) the potential dropped
to -250 my due to the anaerobic substrate being delivered to the cell from
the bottom of the 30-gal tank. The stepwise pattern on the chart is due
to electrical interference from the large heating unit of the thermostated
Warburg respirometer.
A record of the my signal from the flow-through cell without the temperature
bath (holding room and sewage temperature constant at 20°C) is shown in
Figure 12. This seven-day chart, started on September 3, 1969, shows a
fairly steady potential of about -200 my for two days, which then gradually
decreased to -2 40 my at the end of the week. This record of the potential
is considerably smoother and demonstrates that continuous potential
recording can be achieved successfully.
- 35 -
-------
c
Figure 8, Polarization of Immersion Electrodes
- ----- - •+400
I
- 36 -
-------
Figure 9. potential of Clean Immersion Electrodes
‘(
I
- 3 T -
-------
PM
Figure 10. Record of Te pereture of ‘ater Bath
38
-------
PM
Figure 11. o enti i i ecord of Flow-Through Cell
(With electrical interference)
-39
-------
, QI .L ’-I’flrou ti Cell
(without ir.terfere ce fr i electrical heater)
3’
-40-
-------
‘fi
o. taintenance of Flow-Through Cell
A perfectly clean noble metal electrode is essential for proper potential
measurements (25). Various methods for the care and cleaning of
stationary electrodes have been recommended and are practiced.
The cleaning of the flow—through cell assembly is accomplished easily with
a test-tube brush and plenty of water (21). In extraordinary cases, after
prolonged operation of the cell, it may be necessary to use a dilute
solution (1.5%) of HC1 to rejuvenate the noble metal electrode.
7. Characterization of Different Types of Drainage
a) Variables Encountered in Sewage
The chemical and physical components of sewage are many and varied. An
exact characterization of sewage is difficult and probably futile.
Nevertheless, a number of investigators have tabulated concentrations of
certain parameters to characterize a weak, medium or strong sewage,
varying for example in BOD strength from 100 to 200 to 400 ppm,
respectively.
Other variables are also of increasing interest, such as phosphorus,
nitrogen and sulfur compounds. Weibel (27) estimated concentrations of
nutrients in a tcmedium t strength sewage as follows:
Total N (as N) = 1 o mg/i
Total P0) 4 (as P0) 4 ) = 10 mg/i
Estimating the concentrations of nutrients to be found in sewage,
Sawyer (28) reported similar values:
NH 3 - N = 20.0 mg/i
NO 3 - N = 0.0 mg/i
Organic N = 15.0 mg/i
P0 ) 4 - P = 8.0 mg/i
Organic P = 2.0 mg/i
The accumulation of suifides in sewage is a function mainly of the
sewerage system. Such factors as detention time in sewers, flow velocity,
sewer slime composition and other variables have been studied intensively
by a number of other investigators (29)(30)(31)(32)(33)(3 ) 4) and estimation
of concentrations appears to be very difficult. More will be stated later
about the presence of suifides and their effect on the potential.
b) Urban Runoff
Drainage from urban areas is not as clean as it was once thought to be.
The concentration of solids and nutrients, as well as BOD loadings and
other variables encountered in several studies (l)(3)(i2)(35)(36) have
-
-------
indicated that urban runoff should receive increased attention to help
alleviate pollution. Studies of selected areas in Cincinnati; Chicago;
Ann Arbor, Michigan; Stockholm, Sweden; and Pretoria, Union of South Africa
have shown BOB values as high as 185 ppm (Chicago) with a mean value of
about 30 ppm and coilform as high as 2 0,OOO N/lOO ml (i). Total
phosphorus concentration as high as ) i.1 i ppm .was reported recently in the
drainage for a street in Chicago (12). The range of solids concentrations
reported shows that this parameter is entirely dependent upon the topography,
hydrologic and geologic characteristics of the drainage area under
consideration. However, these characteristics must be evaluated in
reference to the pollutional load carried by the early flushing of the
sewerage system into the nearest watercourse.
c) Agricultural Drainage
The superimposed loads of nutrients from the increased availability and
utilization of commercial fertilizers are of a much greater magnitude than
was generally recognized. More intensive land use and farming practices
throughout the world are contributing to increased pollution of streams,
lakes and oceans. The concentration of total phosphorus in Lake Constance
on the German/Swiss border has increased at an alarming rate. In 19 - -5
the total p concentration was 0.5 mg/l, by 1955 this concentration had
risen to 5 mg/i and in 1967 reached a level of 10 mg/l; much of this rapid
increase being ascribed to more intensive farming techniques. At the same
time, several large cities have been vying for the water resources of
Lake Constance as their future water supply.
Sylvester (37) has reported values indicative of the nutrient content of
agricultural drainage which show total phosphorus concentrations of the
order of ppm and total nitrogen as high as 3 and ppm. Irrigation
uses involve enormous quantities of water (as measured by acre-feet;
1 acre-foot = 326,000 gals.). While these concentrations may still appear
small, they represent many tons of nutrients unloaded and being discharged
into this Nation’s waterways.
8. Effect of Sulfides on Electrode Potential
For a better understanding of the effect sulfides on the electrode
potential, some relationships between bacterial growth, sulfides and
electrode potential may be helpful.
The generation of sulfides in sewage takes place as the result of two
biochemical processes: 1) decomposition of S-containing organic compounds
by facultative bacteria, and 2) reduction of sulfates by the bacteria
Sporovibrio desulfuricans . Each requires its special environment to
function properly and sewage and sewer systems provide a viable surrounding
for both. The facultative bacteria populate the stream of the sewer and
produce sulfides as a result of their metabolic processes in which complex
organics in the stream are broken down into more simple forms. The
generation of sulfides in this manner is generally small, except where
unusually long mains or long ocean outfalls are used. In such cases, as
in slow moving gravity flow systems, anaerobic conditions exist in the
- 1 2 -
-------
flowing sewageand sulfide generation may reach considerable proportions.
The second process involves reduction of sulfates by S. desulfuricans.
This strain of obligate anaerobes is found in the waste stream, although
generally in relatively small concentrations (average 258 orgs/ml
according to Eliassen, et al (33). The presence of these sulfate-splitting
bacteria in sewer slimes, however, reaches higher populations ( 6 ,000/ml)
and the most active sulfide generation takes place in the slimes. The
stream acts as a source of sulfates for these sulfur ingesting bacteria.
It is possible to visualize a free-flowing sewer as being composed of two
zones of potential. The surface and upper body of the flow may exhibit
a positive Eh in the presence of oxygen diffusing into this flow. However,
in the lower levels oxygen has already been consumed by the biochemical
reactions. The sewage and slime interface, as well as the slime growths,
exhibit low potentials as indioated. by the presence of S. desulfuricans .
These organisms exist in large quantities only in potential ranges of
-200 my to -300 my, indicating anaerobic conditions generally accompanied
by the active generation of sulfides.
There are two ways in which sulfides and sulfide-producing bacteria may
affect the potential: i) by generation of sulfides in the stream and from
slimes to become factors in the redox level, and 2) by scouring of the
slimes within the sewer, such as during periods of intense rainfall.
From separate studies (30)(38) conducted on force mains in Miami and
Los Angeles, it has been established that sulfide accumulation depresses
the potential level significantly. At Miami, in a four-mile force main
leading to the treatment plant, the potential dropped on the average from
-236 my to -308 my (Ecal), while total sulfides increased from 0.8 mg/i
to 7.0 mg/i. Bargman, et al (30) reported that in the nine-mile stretch
of force main leading to the Hy-perion Treatment Plant in Los Angeles
potential levels dropped from +2L 8 mv to + - -8 my, with an increase of total
sulfides from 0.2 to 1.8 ppm. All other characteristics reported remained
constant. Sulfide production may be expected to be more active in
sluggish sewer systems. If environmental conditions are conducive to the
growth of sulfate reducing slimes, they will contribute directly to the
depression of the potential.
In both cities, the sewage streams were devoid of dissolved oxygen. There
is a possible correlation between the potential drop and depletion of DO;
after that with sulfide concentration in the anaerobic range. The
mechanism of sulfide production requires that dissolved oxygen be depleted
before facultative bacteria begin breaking down complex organics in the
stream to form sulfides. Once anaerobic conditions have become established,
the sulfides formed by the facultative bacteria will depress the potential
level. When sufficiently low levels are reached, serious sulfide
production is started by anaerobic bacteria.
- L 3 -
-------
The effects from scouring of sewer slimes from the interior walls of
sewers presents another major pollutional control problem and one that
lends itself to modulation by potential-controlled flow. The degree of
mixing and the characteristics of the slimes will affect the potential of
the sewer discharge. The hydraulic characteristics of the sewerage
system and the intensity of rainfall will have a great effect upon the
rate at which slimes are scourei and the total amount of scouring which
will take place.
As part of the current laboratory demonstration studies, sulfides were
analyzed along with determinaiions of the potential whenever practicable.
These values are shown in chronological order in Table VII. t is
apparent that beginning with the observations of October 2 #), as the
sulfide concentration increased the potential became increasingly negative.
The sulfide concentration was increased by the addition of Na 2 S9H 2 O during
the last four observations as shown in Table VII, Part A.
To check on the performance of the electrode system and to confirm the
reproducibility of results, the same sewage substrate (30-gals sample)
used previously during the sulfide addition was aerated and the changes
in potential, total sulfide concentration, dissolved oxygen and BOD noted.
The results are shown in Table VII, Part B. These results show fairly
good agreement with those obtained while the substrate became increasingly
anaerobic.
Further experimentation to check the sensitivity and reproducibility of
the electrode potential was conducted with another 30-gallon samble of
sewage. However, in this experiment the sulfide concentration was not
artificially increased. The results are presented in Table VII, Part C.
Again, fairly good agreement between the potential and sulfide concentra-.
tions with the values obtained in the previous parts of this experiment,
was observed.
Although perhaps of questionable value, an effort was made to relate the
dissolved oxygen concentration with the electrode potential in the
presence of sulfides. Okey, et al (23) has reported a drop of potential
from +75 my :.o -350 my as the dissolved oxygen concentration fell from
1.0 mg/i to about 0.1 mg/i. For the data presented in Table VII, Part A,
dissolved oxygen concentrations were zero during the period of 9/8
thorugh l0/2)4(*). A small amount of DO (perhaps 0.1 to 0.5 ppm) was
available in the substrate on 10/26, the day on which the minimum
negative potential was observed (-150 my).
It is extremely difficult to separate the effect of dissolved oxygen and
sulfides on the electrode potential. However, by rearranging the appro-
priate data from Table VII some general facts seem to stand out:
(*)See Table VIII for complete DO data. The DO values were analyzed
and found to be zero for 9/8, 9/10, 9/11, 9/23, 9/29 and l0/21 .
(#)This sewage sample was collected from the Lawrence Experiment Station,
Lawrence, Massachusetts on October 22, 1969.
-------
TABLE VII
Effect of Total Sulfide Concentration on potential
part A:
Date Total S Concentration in Sewage Potential Reading(b )
(1969) (mg/i Total Sulfide as s) (my)
8/29 3.00 -220
9/3 1 L 8 0 -228
9/8 5 .L i -236
9/10 6.12 -2 Q
9/li 0.51 -2 48
9/23 3.28 -232
9/29 0.10 -210
lo/2 ) - 5.60 -300
10/26 -i .35 -150
11/3 7.55 -258
11/3 8.loca -306
11/3 10 0 (a) 357
11/3 2010 (a)
11/3 3010 (a) -511
Note: (a) due to Na 2 S addition
(1) Fischer & Porter Cell at 20°C
Part B:
Time interval Total
of Aeration potentiai(b) Sulfide(C) D.0.(c) B.0.D.(C )
(hr) (my) (mg/i) (mg/i) (mg/i)
0 -511 30.1 0.0
0.5 —250 .03 0.0 220
1 -100 0.5k 2.3 50
2 +95 0.0 5.1 0.0
(c) Average values of duplicate samples.
Part C:
Time interval Total ,. .
of aeration potential Su1fide D.0.( B.0.D.
(hr) (my) (mg/i) (mg/i) (mg/i)
0 —320 6.59 0.0 275
0.5 -i68 3.12 1.8 108
1 0.0 5.7 1 3
2 +157 0.0 6.9 0.0
(c) Average values of duplicate samples.
- 1j5
-------
Electrode Potential Dissolved Oxygen S Concentration
(my)
—150 0.1 to 0.5 L 35
-100 2.3 0.5
+100 5.1 0
±L 3 5.7 0
-168 1.8 3.12
-236 0
-2 -i 0 0 6.1
-2 )- 8 0 0.5
-232 0 3.2
-210 0 0.1
-300 0 5.6
All other factors being equal, i.e, pH, temperature, etc. of the substrate
and environmental conditions (not controlled in these experiments) it
appears that: (i) a similar my range (+100 my to -210 my) as that reported
by Okey, et al (23) exists when very little or no sulfides are present,
(ii) that in the presence of appreciable S concentration a potential of
-150 my to -300 my may be expected, and (iii) the greater the S concen-
tration the more negative the potential will be, except when a small amount
of DO is present which will exert an attenuating influence.
It appears from these controlled laboratory investigations and previous
studies in the field that sulfide production is indicative of a state of
l potential and may be the predominant reductant present in extensive
sewerage systems with small slopes. Certainly, flows carrying reducing
substances of this order will have a detremental impact on the dissolved
oxygen reservoir of any receiving waters and must be kept from exerting
their damaging influence on bathing beaches, tidal estuaries and other
water resources. Controlling the flow from outfalls by the electrode
potential should significantly help to minimize such insults to the
environment.
9. Poising of Electrode Potential
Although the need for poising the substrate system to obtain reliable
potential measurements did not appear necessary throughout the studies
reported herein, there was some discussion about the lack of poising of
the combined sewage and/or stormwater runoff. Therefore, several limited
experiments were conducted to examine the effect of the addition of a
phosphate buffer initially to distilled water and then to the sewage
substrate.
(a) Experiments with Addition of Sulfide to Phosphate Buffer
and Distilled Water
Sulfide ion was added in known amounts to distilled water by itself and
phosphate buffer (as specified in the B.O.D. procedure in Standard Methods)
and the effect on potential observed, using the standard, immersion-type
Leeds and Northrup electrode system at 20°C.
-------
The results are given below:
Sample: 500 ml of Distilled Water
Sulfide
Concentration Potential
( ppm) ( my )
0 +300
5 —85
10 -115
15 -120
20 -135
25 _iLi i
50 -132
Sample: 500 ml of Phosphate Buffer
Sulfide
Concentration Potential
( ppm) ( my )
0 +300
5 -185
10 -200
15 -210
20 -213
25 -222
50 -235
The buffer appears to have reduced the potential range from 100 to 0 rev.
(b) Experiments with Addition of Sulfide to Sewage with and
without Phosphate Buffer Added
A 500 ml sample of sewage was treated with 50 ml of phosphate buffer (as
specified in the B.0.D. procedure in Standard Methods) and the sulfide
concentration increased by addition of known volumes of Na 2 S9H 2 0
solution. The results are summarized below:
- L 7 -
-------
Sample: 500 nil of’ Sewage without added Pho tha e huff’er
Sulfide
Concentration Potential
Added (ppm) ( nay )
0 -200
5 -209
10 -213
15 -221
20 -223
25 -230
50 -258
Sample: 500 ml Sewage with 50 ml Phosphate Buffer Added, (initial
potential without buffer = -200 my)
Sulfide
Concentration Potential
Added (ppm) ( my )
0 -161
5 -2 0
10 -2 40
15 -239
20 -2 0
25
50
The buffer appears to have reduced the range of potential from 4-0 to 5 my.
Based on these limited investigations it appears that the addition of a
buffer to sewage may be helpful in stabilizing the potential, although
the influence of a strong reductant might be masked. Further laboratory
work on this phase is needed.
D. Comparison of Electrode Potentials Against Conventional Sewage
Parameters
Laboratory analyses of both standard and non-standard parameters to
characterize the sewage and for comparison against potential readings
were carried out in accordance with the approved Plan of Operation,
beginning on July 2L , 1969. Initially only BOD and COD values were
determined along with the electrode potentials. As the personnel became
more familiar with the laboratory procedures an increasing number of
- 1 8 -
-------
parameters could be determined simultaneously. Instead of the 13 para-
meters listed in the original Plan of Operation, as shown in Table III,
actually a total of i6 parameters were studied ultimately.
A summary of the laboratory analyses against which electrode potentials
are compared is shown in Table VIII. Most of these data were obtained
in duplicate and triplicate. I: may be observed that a total of nine
different 30-gals. sewage samples were collected and subjected to
analysis between July 23, 1969 and February 9, 1970. The strength of
sewage samples as collected varied with five-day ROD values from 109 mg/i
to 312 mg/i; total solids ranged from 476 mg/i to 857 mg/i, while the
electrode potential ranged from +113 my to -329 my. Therefore, sewages
varying from weak (or dilute) to strong were investigated. The majority
of the samples analyzed exhibited anaerobic conditions as reflected by
the electrode potential and corroborated by the sulfide concentrations.
Little attempt was made to maintain the sewage in an aerobic state once
it had been collected, except continuous gentle stirring. Rather, it was
the intention not to alter the sewage substrate and thus it became
increasingly septic with time. This procedure broadened the experimental
range of the same substrate and permitted investigations of the effect
of sulfide concentration on the potential.
From even a cursory examination of the data summary in Table VIII, it
is apparent that due to the randomness of the data collection (dictated
by the complexities of sample collection, analytical methods and number
of variables), it was Liecessary to apply methods of statistical analysis.
Therefore, the laboratory data was subjected to a correlation analysis
to determine the relationship of each parameter and its significance to
the electrode potential. Linear and curvilinear (exponential) correlation
programs were written in Fortran IV language and the data analyzed on an
IBM 360 and IBM 1130 computer. The output from the program includes
the correlation coefficient, the fiducial limit (± one standard error)
and the graphical presentation based on a separate plotting subroutine.
Linear correlation between the electrode potential and ROD of the
sewage is shown in Figure 13. The constants for the regression equation
were also printed out by the computer and the linear correlation
coefficient was found to be 0.873 which is significant. The computer plot
of an exponential relationship between potential and BOD is shown in
Figure l , which also shows significant correlation between the two
parameters.
Linear correlation between electrode potential and sulfides is shown in
Figure 15. The correlation coefficient is 0.896 which is also significant.
For comparison, the computer plot of an exponential relationship between
potential and sulfides is shown in Figure 16 which is also of interest.
Examination of the relationship between electrode potential and total
phosphorous concentration (by the persulfate digestion method) also
resulted in a significant correlation, r = 0.893, as shown in Figure 17.
-
-------
TARI .E VIII - SUMMARY TARUL .A0203 OF DATA FROM POTEMTIAI STUDY (FWPCA)
8ew.9s
Bsmpi. Anelysie T p.reture
Pat. ( °c )
12 2 12k!
7—23 7—24 25
7—29 25
7—29 25
7—25 8—19 25
8—20 25
8—29 25
9—03 25
9—08 25
9—10 25
9—11 25
8—27 9—22 25
9—23 25
9-24 25
9-26 25
9—29 25
9-30 25
10—02 25
10—03 25
10—06 25
10-08 25
‘Ji 10—16 10-23 20
0 10—24 20
10—26 20
10—27 20
10—29 20
77
379
50 102
225 625
0.0 349
0.0
0.0 138 283
0.0 206
99 191
0.0
0.0 15
49
-329 0.0 312 568 857 358 498
-300 0.0 220 480
-150 107 927 350 577
—148 1.1 231.
— 59 62 114 1068 439 626
2.9 8.02
4.8 8.02
5.4 8.02
6.1 8,02
0.5 8.02
7.52 200
3.3 7.54
410
4.35 8.8
440 8.7
10—31 11—03
11—12
11—18
11—19 11—21
12—02 12—02
12—03
12—05
12-06
12—08
1970
1—07 1—07
1—08
1—09
1—10
1—12
1—13
1-14
1—19
1—20
1—21
2-Os 2—05 20
2—06 20
2—09 20
20
20
—382
-192
1.8
90
20
- 72
3.8
107
20
20
20
20
20
-299
-218
—203
—182
— 93
0.0
0.6
252
165
49
464
838
953
324
417
514
536
20 —205 0.0 221 451 846 410 436
20 -208
20 -180 0.0 156
20 -150 1083 506 577
20 —111 1.2 99 220
20 — 75 2.1
20 — 70 33 102
20 — 58 2.3 31 1039 464 575
20 — 37 2.4 75
20 — 34 2.5 70 1041 469 572
*118 3.5 109 207
+191 4.2 68 132
+230 4.8 86
7.4 7.6
27.8
6.7
16.7 6.5
7.2
28, 4
21.8 7,85 25.7
7,9
20.45 73.85
3.7 106,8
112.0
3.65 100.8
31.7 7.55 9.4
17.2
8.7
2.4
6.90 300
43.2 6.07
7.11 455 10.5
5.4
41.1 7.70
_________ Residue ________ Tot s I Se tt l.—
(a) Total Fixed Volatile Total Phoeporoue able Colifona 100/Ri
ORP 3 DOD COD Solids Solid, Solid, nxxoni. 303 Orgaoic (pxrxulfat.) C1 S Matter Greace
j j j j 11 j jm /jj (ms/fl ( /U ( mg/i ) J_ j ( mg/I) iSSL .L_ 1SldL1 ) AISOL1i j j fl MPN Pecal
355
52
• 31
+ 80
0
- 1 5
+ 56
-220
-228
-236
-240
-248
—225
—231
—235
-230
-210
-190
—112
—125
-110
-110
888 362 526
721 277 444
848 356 492
1056 738 318
32 1048 312 737
20
2.6
6.5
5,6
6,2
6,2 5.6
7.0
20.5 (1.0
7.2 7.7
450
18,5 445
<1.0 7.8
53.4 250
5.2 33
19.0
22.4
160.9 4.8
7.6
7.2 240.9 3.7
150.4 1.3
5.35 147.5
5.0 <1.0
141.9 <1.0
5.7 140.3
145, 5
476 222 255 7.0
2,75
10.35
150
210 9.7 1.1mb 8 1.1x10 8
2.4x10 8 1.1 mb 8
350 10.5
520 2.4mb 8 9 .3mb 6
2 .4mb 8 4.6x10 6
650 7.25 2.4mb 8 4.3x10 6
1 . 1mb 8 4.6e1 13 6
550 8.25
70
100
6.8
6.8
6,8
(a) Fischer and Porter cell.
-------
9.0.0. UA3 ’1_)
390. -
3 .
2’lO . -
180. -
H
120. -
60. -
(BcO) — O.96(-’mv) — 31.Ii,
*
0.959
—31.352
CORRELATION COEFFICIENT * 0.873
c . POTENTI’L (MV)
§
*
*
*
*
*
V - B*X + A
*
A.
8
Fipure 1 Linear Corr€].akicn of Electrode ?oteii al with LCD
-------
B’O.O• (t [ /L)
300.000
240. XXJ
Lfl
N)
i20.
60.000
O.0078(..mv)
(B0D) 26.8 + e
LN(Y) • A + B * X
3.28651
0.00783
CORRELATION COEFFICIEMT • 0.8337
*
8
I €Qi POTENTIAL (MV)
a
*
a
a *
*
*
*
*
*
*
* *
a
a
a
*0
a
*
8 .
Figure 114 Exponential Correlation of Electrode Potential with BOD
-------
SLJLFIOES
30.000
25.000
20.000
15.000
w
iO .000
51000
§
(MEi/L)
0.062
8.563
CORRELATION C0E FIC1ENT • 0.896
NEC3u POTENTIAL (MV)
(S) O.062(—!nv) — 8,S6
0
Y • 5*( + A
*
0
*
*
Au
*
§
Figure iS
Linear Correlation of Electrode Potential with Sulfides
-------
SJLFIOES (M3’L)
30.000
eo .cxx
iO.cXX
* *
*
11.76369
2.39980
--- - ---—--.-. t-.--.- -- -— -I
N
0 C)
Figure 16 Exponential Correlation of Electrode Potential with Sulfides
4
(S) — 7.RxlO” 6 + (, )2.1I
*
**
*
*
4
*
4 *
LN(Y) • A + B * LN(X)
*
B.
*
f a
CORRELATION COEFFICIEMI • 0.7240
• POTENTIAL (MV)
I ’
-------
*
(P) - o.olS(-mv) + LL.3?
Y B*X + A
0.015
CORRELATION COEFFICIENT = 0.393
P (MO/L)
8’
7
7
S
*
*
*
\ S1
E .
5.
§
NED’ POTENTIAL (MV)
Figure 17 Correlation of Electrode Potential with Total Phosphorous
-------
The results of linear correlation between electrode potential and the
COD are shown in Figure 18. The correlation coefficient is 0.852 which
is comparable to the 0.873 value found with BOD.
Similarly, the correlations of potential with nitrates and chlorides are
shown in Figures 19 and 20. Significant correlation between NO 3 -N and
potential was found but not between chlorides and the potential. This
result is not unexpected since high concentrations of chlorides do not
participate in biochemical degradation reactions. A summary of the
correlation coefficients is shown in Table IX.
TABLE IX
Correlation Coefficients Curvilinear
(Exponential)
Parameter Linear Correlation Correlation
BOD 0.873 0.8314
Sulfides 0.896 0.7214
T ta1 Phosphorous 0.893 0.897
COD 0.852 0.726
Nitrates -0.807 -0.7814
Chlorides -0.225 -0.213
For additional information, the equations of best fit and their correlation
coefficients for these five parameters are given below:
TABLE X
Summary of Correlation Analysis
Correlation
Parameters Equation of Best Fit Coefficient
Potential vs. BOD BOD = O.96(-mv) - 31.14 0.873
Potential vs. S S = O.0 6 2(-mv) - 8.56 0.896
Potential vs. p P = O.015(-mv) + 14.37 0.893
Potential vs. COD COD = l. 6 )4(-mv) - 13.1 0.852
Potential vs. N0 3 -N NO 3 -N = -O.00 66 (-mv) + 7.93 -0.807
Potential vs. Cl C1 = -O.22(-mv) + 138.7 -0.225
- 6-
-------
C’O•O’ (MD/L)
600 .000
600 .000
400’ 000
*
1. 644
‘13.080
CORRELATION COEFFICIENT • 0.852
NEt3’ POTENTIAL (MV
* *
*
*
200.000
*
100 .000
•1
/
,
*
V • B*X + A
B
(COD) - i.61i(-mv) — 13.1
N
Figure 18 Correlation of Electrode Potential with COD
-------
JH N (hrvu)
8 .000
7 . - J()
7 .000
B • O0
(No 3 N) - —O.00 6 (..xnv) + 7,93 *
s•cxJo
YSB*X+A
—0.006
7.930
CORRELATION COEFFICIENT - —0.807
_______________ ____- ____ ________- ________- ____ NED. OTENTIAL (MV)
I S
Figure 19 Corre] ition of’ Electrode Potential with Nitrate Nitrogen
-------
CL - (M3/L)
250
* YB*X+A
*
* B —0.217
138.725
130 000
‘ fill
90 000 —0.225
50’ 000
* * **
* *
*
10’OOO ______ 1’€t o pomNTIp (MV)
Figure 20 Correlation of Electrode Potential with Chlorides
-------
VIII. DISCUSSION
A. Response, Sensitivity and Stability of Electrode System
As the result of these laboratory investigations with weak to strong
sewage, it has been demonstrated that the response of certain potential
measuring systems can be instantaneous. Not all systems perform equally
well and the conditions for measurement are important, including proper
electrode maintenance.
The sensitivity of these systems is excellent, a reproducibility
of 1 to 2 my can be expected.
The stability of several electrode systems has been investigated and
found to vary among these systems. The stability of the immersion type
system is questionable in a prototype installation because of electrode
polarization. However, the stability of the potential obtained with
flow-through electrode systems is excellent (no polarization in the presence
of strong sewage solids and normal grease concentrations), provided the
flow through the cell is maintained continuously.
B.. Sensitivity of Potential to the Strength of Untreated Sewage
and Waste Effluents
The sensitivity of the flow-through Fischer and Porter celL to various
sewages varying from 109 ppm to 312 ppm B.O.D. and from 1476 ppm to 857 ppm
Total Solids has been demonstrated in the laboratory. This data is
limited to the extent of nine different sewage samples analyzed from
July 1969 to February 1970. Further substantiating work in the laboratory
for additional support data is necessary, supplemented by a field demon-
stration.
Based on the present laboratory data, it is evident that the redox
potential is sensitive to the B.O.D. concentration (r = 0.85). The
potential is insensitive to chlorides which may be expected since
chlorides do not participate generally in the biochemical reactions or
determine the nature of biotic microenvironments. A relatively high
negative correlation of the nitrates with the negative potential was
found. The negative correlation simply indicates that the higher the
NO 3 -N concentration, or the more stabilized the substrate, the less
negative the potential would be expected. The relatively high degree of
correlation was not expected but is interesting. Similarly, the correlation
of the total phosphorous concentration (as determined by persulfate
digestion) with electrode potential is significant (r = 0.89) and lends
additional emphasis to the concept that the potential will also be useful
in controlling the discharges from urban runoff and agricultural drainage
from storm sewers. Further experimental work is indicated and should be
carried out in the laboratory during the second year, concurrently with
the field demonstration in a combined sewer, as has been suggested in the
renewal proposal dated January 26, 1970.
- 60 -
-------
C. Effect of Interfering Substances or Predominant Oxidants;
Phosphate Buffer Poising
To determine the transient effect of interfering substances on the
electrode potential, several experiments were carried out. On several
occasions, highly anaerobic or stale sewage was aerated and the potential
recorded. An instantaneous and significant rise was observed in each
case. In addition to analyzing for sulfides and measuring the potential,
the sulfide concentration in the substrate was also artificially increased
in the form of Na 2 S and the effect on the potential noted (see data shown
in Table vii).
Thus, the electrode potential system was found to respond immediately to
the presence or sudden change in concentration of an oxidant or reductant.
Further work with other oxidants and reductants should be conducted to
further substantiate these findings before they can be generalized.
As already discussed, the total phosphorous concentration has been found
to correlate to a high degree with the electrode potential. Thus, the
presence of nutrients (at least phosphorous) appears to be amenable to
electrode potential detection rather than interfere with this method for
controlling harmful discharges.
To improve the poising of the substrate medium for a more stable
measurement, the addition of phosphate buffer(*) to various substrates
was examined in the presence of sulfides. A sample of distilled water
to which concentrations of up to 50 ppm of buffer had been added showed
the negative potential to increase by about 100 my as the concentration
of S increased from 5 to 50 ppm. When the same concentrations of sulfide
were added to a sample of phosphate buffer the potential increased only
50 my. Thus, the buffer appears to have improved the poising of the
potential over the distilled water.
A similar set of experiments was carried out on sewage to determine the
degree of poising achieved with phosphate buffer. A sample of sewage to
which concentrations up to 50 ppm of S= had been added, showed the negative
potential to increase by about 50 my as the concentration of S increased
from 5 to 50 ppm. When the same concentrations of S were added to a
sample of sewage, to which 10% by volume of phosphate buffer had been
added, the potential remained unchanged (-2)-iO my) until the maximum of
50 ppm of S were added, at which time the negative potential increased by
5 my (-2Li5 my). These experiments show that (i) distilled water is a
poorly poised system, (ii) domestic sewage is a more poised system, (iii)
the addition of phosphate buffer to sewage tends to completely poise the
system (even in the presence of an interfering system, i.e. a strong
reductant). From these experiments, it would appear that the potential
measurement of dilute sewages (such as combined sewage and stormwater) may
be accomplished withoug the addition of a poising agent, even in the case
of nominal concentrations of a predominant reductant. However, in cases
where particularly strong reductants are present in high concentrations
the addition of a poising agent may be beneficial. Further exploration
of these concepts is necessary before any definite statements can be
supported as valid.
( ) Phosphate buffer as specified for the B.O.D. procedure in Standard
Methods.
- 61 -
-------
D. Zones of Potentials when Layering Occurs and Possible Compensation
for Such Events
It is possible to visualize a free-flowing sewer as being composed of two
zones of potential. The body of the flaw may exhibit even a positive
potential, Eh, in the presence of oxygen diffusing into this flow. However,
the slime growths along the wall will exhibit negative potentials as in
the presence of S. desulfuricans . These organisms exist in large quantities
only in potential ranges of -200 my to -300 my, indicating highly anaerobic
conditions generally accompanied by an active generation of sulfides.
Thus, under certain circumstances, the existence of two zones of potential
in a flowing sewer is possible.
However, the potential method investigated herein is concerned with
controlling the quanity of the flaw that is being discharged. The
discharge from a sewerage system will reflect the conditions of the system,
the dry-weather and wet-weather flows in the case of combined sewers and
the type of storm. If the initial slug contains slimes scoured from the
wall (and this may well be the case after a prolonged drought) or if the
system has small slopes, the solubility of sulfides is such that they will
exert their influence on the potential almost instantaneously. After
the initial scouring of the sewer barrel, if the storm subsides or if the
system carries a fresh sewage, there will be generally no significant
concentration of sulfides and the potential will be less negative or may
be positive and the flow may be discharged directly. In some instances
it may be necessary to install flaw-through cells at different levels and
to telemeter an integrated signal to the flow control device.
E. Effect of Different Cell Systems on the Response
Both Beckman and Leeds and Northrup immersion electrodes were used to
measure the potential of untreated sewage, but these systems do have
the problem of electrode polarization due to the presence of grease and
slime growths. Thus, they are rendered insensitive in a relatively short
period of time.
Investigation of the non-fouling reference electr9r1 (Cu plate) together
with a thin-film Pt-encapsulated electrode system ) showed that the
signal drifted when measuring sewage potentials, although earlier
calibration experiments (see Table VI0 had been most encouraging.
However, during the experimentation with sewage the Cu-Pt electrode
system was found to be relatively insensitive and unstable. Therefore,
evaluation of this immersion electrode system was abandoned during
October 1969.
The Ag, AgCl-Pt flaw-through electrode system(b), used throughout most
of these investigations, has been quite sensitive to variable potentials,
registered changes instantaneously and showed exceflent stability without
polarization. Maintenance of the electrode system has been negligible in
spite of the fact that potentials varying from +200 my to -350 my have
been recorded and sewages with concentrations up to 30 ppm of total
(a) Manufactured by Delta Scientific Corporation, Lindenhurst, New York.
(b) Manufactured by Fischer - and Porter Company, Warminster, Pennsylvania.
- 62 -
-------
sulfides were measured. The cleaning of the flow-through cell assembly
can be readily accomplished with a test tube brush and plenty of water.
In especiallydifficult cases, after prolonged operation of the cell, it
may be necessary to use a dilute (1.5%) solution of HC1 to rejuvenate the
noble metal electrode.
In spite of the successfully demonstrated response, especially with the
3/8-in, diameter flow-through cells, the instantaneous changes in the
wastewater quality from combined and storm sewers may reflect in highly
variable potentials. Therefore, the my signal may have to be integrated
with a definite time constant before telemetering the signal to operate
the flow control device (gate valve or equivalent). From the above
experiments, it appears that a meaningful modulation of the flow can be
achieved.
- 63 -
-------
IX. ACKNOWLEDGEMENTS
The authors acknowledge the assistance of colleagues and assistants who
have been associated with this research project: Dr. Donald A. Kearns
and Messrs. John J. Gall and Phillip W. quinn of Merrimack College.
The authors are also indebted to Messrs. Jereul Magner, Lawrence A. Greenberg
and Leo Carroll of the Fischer and Porter Company for their splendid coop-
eration to provide the necessary instruments, their technical advice and
service in connection with these investigations.
Technical advice and many helpful suggestions by Mr. William A. Rosenkranz,
Chief, and Mr. Francis J. Condon, Project Officer, Storm and Combined Sewer
Pollution Control Branch, Federal Water Pollution Control Administration,
Washington, D.C. and Mr. Warren H Oldaker, Project Officer, New England
Basins Office, FWPCA, U.S. Department of the Interior, assisted in the
guidance of this research program.
The authors are indebted to the staff of the Lawrence Experiment Station,
Commonwealth of Massachusetts, Lawrence, Massachusetts, for conducting
the bacterial density analysis, both MEN and fecal coliform. Without
their assistance it would have been impossible for the laboratory
personnel to carry out all of these analyses under the reduced budget.
This project was supported in part by a Water Supply and Pollution
Control Demonstration Grant No. 11020 DOK from the Division of Research
and Training Grants, Federal Water Pollution Control Administration.
- 65 -
-------
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(28) Sawyer, C.N., “Causes, Effects and Control of Aquatic Growths’ t ,
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of a High Oxygen Demand Sewage”, Sewage and Industrial Wastes , 29,
7,768 (1957). —
(31) Pomeroy, R., “Generation and Control of Sulfide in Filled Pipes”,
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Pollution Control Federation , 1 O, 1, 112 (1968)
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