EPA-670/2-75
June 1975
Environmental Protection Technology Series
CONTROLLING SULFIDES IN
SANITARY SEWERS USING
AIR AND OXYGEN
Office of ieseareti anil Development
-------
EPA-670/2-75-060
June 1975
CONTROLLING SULFIDES IN SANITARY SEWERS USING AIR AND OXYGEN
By
R. Joe Sewell
City of Port Arthur
Port Arthur, Texas 77640
Project No. 11010 DYO
Program Element No. 1BB043
Project Officers
Charles L. Swanson and John N. English*
*Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
REVIEW NOTICE
The National Environmental Research Center--Cincinnati
has reviewed this report and approved its publication.
Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental
Protection Agency, nor does mention of trade names or
commercial products constitute endorsement or recommen-
dation for use.
-------
FOREWORD
Man and his environment must be protected from the adverse
effects of pesticides, radiation, noise and other forms of pollution,
and the unwise management of solid waste. Efforts to protect the
environment require a focus that recognizes the interplay between
the components of our physical environment—air, water, and land.
The National Environmental Research Centers provide this multi-
disciplinary focus through programs engaged in
• studies on the effects of environmental contaminants on
man and the biosphere, and
• a search for ways to prevent contamination and to recycle
valuable resources.
As part of these activities, the study described here investi-
gated the applicability of using air and pure oxygen entrainment
devices to control sulfides in sanitary sewers.
A. W. Breidenbach, Ph.D.
Di rector
National Environmental
Research Center, Cincinnati
-------
ABSTRACT
This report documents ambient sulfide conditions and corrosion rates
in a sanitary sewerage system, and presents the results of a study
that demonstrated that the use of air or pure oxygen were effective
in controlling sqlfides. The three techniques used to entrain the
gases in the sewage included injection, U-tubes, and pressure tanks.
Sulfide control was evaluated at eight separate locations involving
lift stations, force mains, and receiving gravity lines. The entrain-
ment techniques studied were not optimized. However, odor and corrosion
problems were abated. Preliminary cost data indicated that air
injection into force mains, and the use of air with the U-tube were
the least costly sulfide control measures.
This report was submitted in fulfillment of Project Number 11010 DYO,
by the City of Port Arthur, Texas, under the partial sponsorship of
the Office of Research and Development, U.S. Environmental Protection
Agency.
IV
-------
CONTENTS
Page
Abstract 1v
List of Figures vi
List of Tables viii
Acknowledgments x
Sections
I Conclusions 1
II Recommendations 2
III Introduction 3
IV Description of Sewerage System, Port Arthur, Texas 14
V Description of Control Methods 23
VI Sulfide Problems and Control Results 32
VII Evaluation of Oxygen Sources and Entrainment Methods 94
VIII Summary of Sulfide Control Methods 100
IX Economic Analysis 104
X References 108
-------
FIGURES
No. Page
1 Hydrogen Sulfide Development 1n a Sanitary Sewer 11
2 Principal Components of the Sanitary Sewerage System - 16
City of Port Arthur, Texas
3 Total Sulfide Levels in the Port Arthur Sanitary Sewerage 22
System
4 Force Main Piping Arrangement 25
5 Typical Diffuser Arrangement for 24" Cast Iron Pipe 26
6 Pressure Tank Air Injection 29
7 Typical U-Tube Installation 31
8 Lakeshore System 33
9 Deterioration of Lakeshore Interceptor 34
10 Deterioration in the Lake Charles Lift Station 35
11 Grannis Avenue Pump Station 42
12 Railroad Pump Station 44
13 Total Sulfide and Dissolved Oxygen Levels During Oxygen 47
Injection Optimization Study - Railroad Ave.-Thomas Blvd.
Pump Station
14 Total Sulfide and Dissolved Oxygen Levels During Air 50
Injection Optimization Study - Railroad Ave.-Thomas Blvd.
Pump Station
15 Sulfide Levels, Lakeshore Interceptor, by Temperature 53
Groupings
16 Stillwell System 55
17 Total Sulfide and Dissolved Oxygen Levels During Gaseous 60
Oxygen Injection Optimization Study - 19th Street-Still well
Blvd. Lift Station
vi
-------
No..
18 Average Total Sulfide and Dissolved Oxygen Levels During 63
20-Hour Sampling Program Evaluating Pressure Tank - 19th
Street-Stillwell Blvd. Lift Station
19 Smith-Young System 66
20 Profile of Smith-Young Force Main 67
21 Total Sulfide Levies in the Smith Young System 70
22 Smith-Young Pump Station 72
23 Pear Ridge System 76
24 Pioneer Park Lift Station - U-Tube Configuration 79
25 15 Minute Oxygen Demand vs. Air:Water Ratio & 30 Second 85
IDOD vs. A1r:Water Ratios at Pioneer Park Lift Station
26 Mainline System 86
27 Lake Charles Lift Station 88
vn
-------
TABLES
No.
1 Deterioration Rates of Concrete Sewer Pipe 18
Port Arthur, Texas
2 Sewage Characteristics 37
Grannis Avenue Pump Station - Force Main
3 Sewage Characteristics 3&
Railroad Avenue-Thomas Blvd. Pump Station - Force Main
& Houston Avenue-Lakeshore Blvd. Lift Station
4 Sewage Characteristics 40
Lakeshore Interceptor
5 Optimization of Oxygen Injection 43
Grannis Avenue Wet Well - Force Main
6 Optimization of Oxygen Injection 46
Railroad Avenue-Thomas Blvd. Pump Station - Force Main
7 Optimization of Air Injection 49
Railroad Avenue-Thomas Blvd. Pump Station - Force Main
8 Sewage Characteristics 52
Lakeshore Interceptor
9 Sewage Characteristics 56
19th Street-Stillwell Blvd. Lift Station
10 Sewage Characteristics 57
19th Street-Stillwell Blvd. Lift Station - Force Main -
Gravity Line
11 Optimization of Oxygen Injection 59
19th Street Lift Station - Force Main
12 Sewage Characteristics 62
Pressure Tank Test Program
19th-Street-Stillwell Blvd. Lift Station - Force Main
13 Sewage Characteristics 65
Pressure Tank Test Program
19th Street-Stillwell Blvd. Lift Station - Force Main
-------
No.
14 Sewage Characteristics 69
Smith-Young Pump Station - Force Main - Gravity Line
15 Sewage Characteristics 73
Smith-Young Pump Station - Force Main
16 Sewage Characteristics 78
Pear Ridge Lift Station - Pressure Tank Installation
17 U-Tube Operation - Constant Air:Water Ratio (8.1) 82
Pioneer Park Lift Station
18 U-Tube Operation - Variable Air-.Water Ratios 84
Pioneer Park Lift Station
19 Sewage Characteristics ^
Lake Charles Lift Station
20 Sulfide Levels 92
Mainline (Lakeview) Pump Station
21 Oxygen Requirements for Sulfide Control 102
22 Cost Comparisons for Hydrogen Sulfide Control 107
IX
-------
ACKNOWLEDGEMENTS
The contributions to the project by Mr. C.L. Swanson, EPA Project Officer,
from the design to the final report preparation are gratefully acknowledged.
Mr. Marvin E. Need, P.E., Sou-Tex Engineers, was responsible for the design
of all aeration facilities used in the study and participated in the testing
program. He also served as Project Director in the initial grant.
The full cooperation of all personnel of the Port Arthur Sewer Department
is gratefully acknowledged with particular thanks to:
Mr. Leon Holtzclaw, Superintendent
Mr. Tony W. Humphery
Mr. John Gautherie
There were several students at Lamar University who worked on the project
with significant contribution. These are:
Mr. Thomas J. Rolen
Mr. Rudolph S. Sarich
-------
SECTION I
CONCLUSIONS
1. Injection of air or pure oxygen into force mains reduced sulfide
concentrations to acceptable levels. A minimum feed rate for these
sources of oxygen was found to exist for the reduction of existing
sulfides and prevention of further generation. The cost of air in-
jection was less than pure oxygen for the conditions of the study.
The ability to obtain a dissolved oxygen residual with air injection
was not demonstrated and the amount transferable using pure oxygen
appeared to be limited.
2. The U-Tube proved effective in the control of sulfides for the air:
water ratios evaluated. Reductions of sulfide in the U-Tube were equal
to other systems tested, and sufficient oxygen was entrained to permit
continued oxidation in downstream gravity sewers.
3. The pressure tank as a means of controlling sulfides was demonstrated;
however, the applied oxygen required under operational conditions was
excessive. For the conditions of the study, this was the most costly
method of sulfide control.
4. The net effect of the aeration program was the reduction of sulfide
levels downstream of control points. Further, the severe odor problems
at various locations have been eliminated and have been reported only
during periods where control equipment was inoperative.
5. At the control points of the study, the recirculation of aerated
sewage to the wet well proved to be effective in the reduction of sulfides
in the wet well and reduced odor problems.
6. The force main proved to be the major generator of sulfides in the
system. The sewage transfer station was shown to be an effective point
at which existing sulfides can be controlled using oxygen and the oxygen
serves to prevent additional sulfide generation in force mains.
-------
SECTION II
RECOMMENDATIONS
The use of air or pure oxygen for sulfide control should be considered
both in the design of new systems and for existing systems. The sewage
transfer station can be an effective point of control with optional
methods of injection available for economic evaluation. There are
several factors which must be considered in designing control systems.
These include: (1) physical configuration of the system; (2) sewage
characteristics; and (3) the ability to conduct field studies.
The first step is to identify the physical configuration and constraints.
These include the force main gradient, length and diameter. Equally
important is pumping capacity and available heads. Changes in grade,
depressions or other restrictions can prevent the system from functioning.
The choice of equipment for oxygen injection will be governed by these
parameters.
Sewage characteristics that are significant include temperature, bio-
chemical oxygen demand and sulfide levels of incoming sewage. The
immediate dissolved oxygen demand of the incoming sewage can provide
information on the magnitude of oxygen required.
Design parameters should consider the oxygen application in mg/1 in lieu
of air:water ratios, or in air feed rates expressed as a function of
force main diameter. The applied oxygen in this manner relates oxygen
demand of the sewage to system hydraulics.
The field testing of air injection should be performed in addition to
testing for sewage characteristics. This can be accomplished by the use
of a mobile air compressor with a self contained power supply. A
necessary requirement is a flow measuring device capable of measuring
anticipated flow rates. In addition to this, discharge pump pressures
should be monitored and flow measurements made or estimated. The per-
formance of these preliminary evaluations will assist in the decisions
that must be made.
-------
SECTION III
INTRODUCTION
In 1967 the City of Port Arthur, Texas, following recommendations from
its Water and Sewer Study Committee, initiated studies dealing with the
deterioration of the City's concrete sanitary sewer lines. These studies
revealed that the sewerage system was under serious attact by hydrogen
sulfide corrosion. After careful consideration of the various recommen-
dations for bringing the deterioration under control, the control method
recommended by the Committee was the injection of air and/or pure oxygen
into the principal force mains identified in the preliminary evaluations.
The City implemented the control methods recommended by the Committee at
three locations in December, 1968. On March 25, 1969 the City of Port
Arthur accepted a Demonstration Grant from the Environmental Protection
Agency to expand the work to additional locations in the sewerage system.
A supplemental grant was awarded on June 24, 1970 to install and evaluate
other control measures including U-tube aerators at two lift stations.
PURPOSE AND SCOPE
The purpose of the study was to demonstrate and evaluate the effectiveness
of oxygen in controlling hydrogen sulfide in sanitary sewerage systems.
The oxygen sources utilized were air and pure oxygen. Various methods of
entrainment were also evaluated.
The scope of the project was extensive in that its goal was to place the
entire sewage collection system under the proposed methods of hydrogen
sulfide control, thereby affording protection to the entire system. An
ancillary function of the study was to ascertain what effects the entrain-
ment of oxygen, at levels required for hydrogen sulfide control, had on
sewage characteristics.
The demonstration project consisted of two separate phases; the initial
grant award, Phase I; and the supplemental grant, Phase II. The first
Phase of the study consisted of the evaluation of hydrogen sulfide
control measures at four locations (Railroad Avenue-Thomas Boulevard
Pump Station, Grannis Avenue Pump Station, Smith-Young Pump Station, and
19th Street-Stillwell Boulevard Life Station). Each station and its
respective control measure is an integral part of a system, and thus will
be discussed as a part of that system. A system is here defined as the
lift station(s), force main(s), and receiving gravity lines which form a
specific physically related unit. The physical nature of the system was
an important consideration in the selection of control methods to be
evaluated in the system.
Control measures were evaluated at four additional stations during the
-------
second phase of the project. Two of the additional stations, the Pear
Ridge (abandoned sewage treatment plant) Lift Station and Pioneer Park
(Hospital) Lift Station, are part of the Pear Ridge System. The remain-
ing two stations, Lake Charles Lift Station and Mainline Pump Station,
are located on the major interceptor that parallels the Sabine-Neches
Ship Channel. The wet well of the Lake Charles Lift Station receives
sewage from the Lakeshore and Stillwell Systems. The Mainline Station,
which is the final pump station in the City's collection and transmission
system, receives sewage from all systems within the central portion of
the city.
HISTORY
The City of Port Arthur began construction of its sanitary sewerage
system in 1910 with construction of the main sewage treatment facilities
in 1959. Since its initial construction, the system has continually been
extended to provide service to unsewered areas as well as meeting the
population growth of the contiguous areas. In addition, the City of Port
Arthur has effectuated, to a limited extent, regionalization of sewage
treatment. The City has contracted with neighboring cities to treat their
sewage, thereby eliminating smaller treatment plants serving these
communities.
The City of Port Arthur has experienced all of the problems associated
with hydrogen sulfide gas in sewerage systems. The most severe was the
loss of life of two workmen at the sewage treatment plant in 1962. The
cause of death was attributed in part to hydrogen sulfide gas (1).
By 1967, the city had experienced numerous structural failures in the
sanitary sewer system in the form of cave-ins (2). The structural failures
were associated with the reduction of the load carrying capacity of the
pipe, which in turn was caused by the deterioration of the pipe wall by
the attack of sulfuric acid. Sulfuric acid is one of the oxidation pro-
ducts in the hydrogen sulfide cycle evidenced in sanitary sewage collection
systems.
Odor problems have been reported throughout the city with varying degrees
of intensity. Two methods have been employed to control odor, venting
and masking. Venting has been tried in Port Arthur with only limited
success. Masking does not really solve the odor problem, but merely
substitutes a new odor. This method is only partially successful and
is very expensive.
Major hydrogen sulfide corrosion problems have also occurred above ground.
This is prominently evidenced by the corrosion of equipment at the sewage
treatment plant, which is directly related to the release of hydrogen
sulfide gas from the raw sewage. At one location in the city, where
serious odor problems and structural failures have been reported, gal-
vanized chain link fences have been reduced to a series of rusty wires
by the gas.
-------
The construction of sanitary sewage collection systems represents a
significant capital investment to a city, and due to their character
are normally designed for a fifty year period. One of the common forms
of financing these systems is by selling bonds with a maturation date
of thirty years. There are documented instances in Port Arthur of fail-
ure of sanitary sewers within six years after construction, leaving
twenty-four years of bonded indebtedness for facilities that no longer
exist. Equally important is the additional economic burden imposed by
replacement costs which are considerably greater than initial construction
costs due to surface improvements and inflation.
During the summer of 1967, based upon recommendations by the Water and
Sewer Study Committee, the City Council authorized a television survey
of selected sanitary sewer lines in the city. This survey demonstrated
extensive damage to the major trunk lines which was attributed to
hydrogen sulfide corrosion. At that time it was estimated that the
annual loss due to this corrosion was $600,000 per year or $10 per capita.
Based on 1967 material and construction prices, replacement of these lines
would cost approximately ten million dollars (3). This loss could be
prevented if the deterioration could be brought under control. Thus, the
City Council authorized additional studies to isolate the principle points
of hydrogen sulfide generation within the system and to evaluate various
methods of hydrogen sulfide control. This work led to the subject study
as reported herein.
SULFIDE GENERATION AND CONTROL
Corrosion problems encountered in sanitary sewers are generally attributable
to the presence of hydrogen sulfide. Since hydrogen sulfide is intimately
associated with the problems, it is apropos to review the properties of
hydrogen sulfide. Hydrogen sulfide is a colorless gas with a foul odor
(rotten eggs); is slightly heavier than air; is moderately soluble in water;
and small amounts in air cause headaches while higher concentrations cause
paralysis in the nerve centers of the heart and lungs which results in
fainting and death (4). Further, concentrations of the gas of 0.2 percent
are toxic to humans after a few minutes exposure (5). Another significant
property of hydrogen sulfide is that it is explosive at concentrations of
4.3 percent (6). Hydrogen sulfide is soluble in water to the extent of
3000 to 4000 mg/1 at the normal temperatures found in sewers (7). The
corrosion potential of sulfuric acid, the oxidation product of hydrogen
sulfide, will be discussed later in this report.
The properties of hydrogen sulfide noted above clearly indicate the concern
over the presence of this gas in a sanitary sewerage system. It is
intuitively obvious that sewers are not designed to generate hydrogen
sulfide gas, rather the gases are generated as a function of the environ-
ment of the sanitary sewer and the material transported. Germane to the
discussion is the consideration for the potential of hydrogen sulfide
generation in sanitary sewers.
-------
Potential for Hydrogen Sulfide Generation
A widely accepted theory that describes the presence of hydrogen sulfide
in sanitary sewers is its generation from sulfate-reducing bacteria which
use the sulfates as their hydrogen acceptor. The reaction is abbreviated
in symbolic form as follows where C is used to designate organic matter:
SO^ + 2C + 2H20 bacteria > 2HCO~ + H2S
_ • u c
S" + 2H ^ V
The sulfate-reducing bacteria associated with this reaction are classified
as obligate anaerobes (8). "One of the most interesting aspects of the
sulfate-reducing bacteria is the highly specific character of these
bacteria, especially in view of the fact that most of the common bacteria
reduce sulfates to sulfide in their protoplasm" (8). The significance of
the presence of sulfate on sulfide generation in sanitary sewers is there-
fore apparent. In many instances, where natural occurring sulfates are of
minor concentrations they are added to the water supply when it is chemically
treated by the use of a coagulation aid such as alum. It has been reported
in other studies that when sulfates in the sewage are below a concentration
of 25 mg/1, the generation of sulfides is inhibited under certain conditions
(6). This would imply that sulfide generation is almost assured when
concentrations are in excess of a limiting value. Pomeroy and Bowl us have,
however, referenced areas in Southern California where sulfates ranged from
200 to 400 ppm yet sulfides were not generated in sanitary sewers. They
also pointed out that areas in Southern California and Arizona have
experienced sulfide problems with low sulfate concentrations (9).
Neel, in work in southeast Texas, reported that significant hydrogen sulfide
has been generated from sewage where the carrier water of the waste had an
initial sulfate concentration of less than three milligrams per liter (10).
Sulfur in sewage occurs in two forms, organic and inorganic (11). Sulfate
ions represent the major portion of inorganic sulfur and as indicated,
occur in varying amounts in carrier wa-ter. Organic sulfur in sewage has
been reported to be low and in the magnitude of 0.2ppm (12). A value
of 1-2 ppm (of sulfur) has also been reported for domestic sewage, reach-
ing 5-10 ppm in industrial wastes (13). There are many organic compounds
that contain sulfur with protein being one readily recognized. The
elementary composition of all proteins contains approximately 0.2 percent
sulfur (14).
The generation of hydrogen sulfide can result from the reduction of organic
sulfur, inorganic sulfur or combinations thereof depending upon concen-
trations (13). Further, it has been pointed out in other studies that it
is feasible for hydrogen sulfide production from organic sulfur compounds
to precede its production from sulfates in sewage that contains both sources
of sulfur (15). Thus, it is obvious that sanitary sewage, regardless of
-------
the quality of the carrier water, does have an inherent potential for
the generation of hydrogen sulfide. This potential will continue until
such time that all sulfate and other sulfur bearing compounds have been
completely reduced.
Sewage strength, or the concentration of the biological nutrients pres-
ent, is a measure of sulfide generating potential. The greater the
sewage strength or amount of organic matter infers a higher concentra-
tion of sulfur with the potential for reduction to sulfides. The most
common measure of sewage strength is the BOD (Biochemical Oxygen Demand)
Test. Therefore, the greater the BOD the higher the sulfide potential.
The potential for hydrogen sulfide generation, based upon presence of
sulfur bearing compounds, exists universally in sanitary sewers. However,
this potential for sulfide generation fails to explain the condition
whereby sulfides and hydrogen sulfide are found in large quantities in
some sewers while appearing in only trace amounts in others. It soon
became apparent that while the sulfur compounds provide the potential
for conversion to sulfides, other factors control the generation of
the gas. This has been the subject of several studies, which have
contributed to the fundamental understanding of sulfide generation, the
principal factors affecting generation and subsequent control of the
generation.
Factors Effecting Hydrogen Sulfide Generation
The location or point within the sanitary sewer where the gas is generated
must be determined before control measures can be considered. Pomeroy
and Bowlus (9) reported that "In free flowing sewers, sulfides are pro-
duced only by slimes on the submerged surface of the sewer and by
deposited sludge." This was not validated by later studies; however,
the slimes remain the primary generator of sulfides in gravity sewers
(21).
In gravity lines, the slime develops in the invert and sides which are
inudated at all flows. It therefore follows that the magnitude of the
sulfide generation is a function of the active area of contact. Unlike
the gravity sewer, the total inside surface area of force mains is
covered with an active biological mass.
The factors that control the magnitude of sulfide generation are strength
of sewage, temperature, retention time or velocity-length function, and a
surface area factor. Under normal conditions, there is no opportunity
for aeration in force mains and the sulfide generation continues. Thus
the force main has proven itself as a major sulfide generator. This fact
has been reported in studies performed in the Gulf Coast Plain of Texas
(6) (23).
Studies have indicated the significance of temperature on sulfide generation,
In these studies the rate of generation was found to increase about 7
percent per degree rise of temperature up to 30° Centigrade (16). The
-------
rates of generation at 30° and 37° were similar, indicating a possible
optimum in that range. There exists a minimum temperature, regardless
of other conditions, for which sulfides will not be generated.
The first published work relating sulfide buildup to sewage strength (BOD)
and velocity of flow also included temperature effects. The temperature for
the Standard BOD is 20° Centigrade. For any other temperature it is cor-
rected by a factor based on the condition that biological activity increases
(geometrically) seven percent per degree change in temperature from the stan-
dard. This is based upon work by Baumgartner in 1934 (16).
The formula for converting a Standard BOD to the effective BOD at any
temperature is given by the following:
Effective B.O.D. = Standard B.O.D. x (l.O?)*"20 [1]
Using this formula data was presented in 1946 (9) relating the Effective
B.O.D. to the velocity required to prevent sulfide build-up. This data
may be expressed in equation form as follows:
Marginal E BOD = 55V2 [2]
in which V is the velocity in feet per second and is applicable only
where flow is not greater than one half full. If the actual velocity
is below that given, sulfide buildup could be expected (9).
Use of the equation and table for the prediction of sulfide build-up
requires the following data to be used:
a) peak summer temperatures
b) daily peak BOD values
c) maximum effective BOD calculated
-d) actual velocity during these peak flow conditions is also
determined.
The pH (negative log of the hydrogen ion concentration) of the sewage
is also a factor affecting hydrogen sulfide generation. However, Pomeroy
once stated "pH is not likely to have much effect on the rate of
generation in sewers within tne range from 6 up to 8 or perhaps 9 (9)."
Perhaps a more significant affect of pH on sulfide in sewers than_that
of generation is the form in which it occurs, i.e. sulfide ion (S~),
hydrosulfide ion (HS~) or un-ionized hydrogen sulfide (H^S). The in-
soluble portion of sulfides is of no concern as these are not available
to be released as a gas. The dissolved sulfide is the form from which
the gas develops. At a pH=6, 83 percent of the dissolved sulfide is
un-ionized while at a pH=7, 33 percent is un-ionized. Concentration
greater than a pH=8 becomes insignificant as only 4.8 percent is un-
ionized (24) (25). Thus, the lower the pH, the greater the potential
for evolution of the gas to the sewer atmosphere.
The retention or residence time of the sewage, sometimes referred to as
sewage age, in the collection system is often alluded to as a contributing
-------
factor in sulfide buildup. Again reference is made to the work of Pomeroy
and Bowlus in which they state, "Actually the age of the sewage is of
minor importance. It is not the age that matters; It is how rapidly
the sewage flows" (9). This is further explained by the following,
"The rate at which sewage flows through a sewer does not affect the rate
of output of sulfide by the slimes on the sides of the sewer, until
velocities are reached which scour the sides and which keep the stream
in a well-aerated condition. This scouring effect is probably not of much
consequence until the velocity exceeds 3 feet per second" (9). This
is applicable only to free flowing sewers.
One additional factor related to velocity is the effect it has upon
absorption of oxygen. Research reported by Streeter et al, indicated
that the rate of absorption of oxygen by a free surface stream varies
in proportion with the 1.75 exponent of the velocity (17). Additional
work on this subject was done by Kehr in 1938 (18). This clarifies the
previous conditions whereby the generation of sulfides is limited in the
flowing portion of a sewer. The reaeration would inhibit the growth of
strict anaerobes while at the same time oxidize the sulfides released
by facultative organisms.
The above referenced material, although explaining the transfer of oxygen
across a liquid-gas interface, does not directly relate to the condition
found in sanitary sewers. Recent research performed on aeration rates
in sewers provides more specific information on the subject. More
important than providing a mystical number to be erroneously used as
a panacea, the research provides an equation for predicting the exchange
coefficient for specific conditions (19) (7). This work has provided
the subject of hydrogen sulfide control with a new tool for future use
that should result in more rational designs.
Research has continued to pursue the generation of sulfide in both gravity
lines and force mains, with the biochemical oxygen demand, temperature,
velocity and pipe geometry the principal factors evaluated. In 1950,
Davy presented work in which the Pomeroy and Bowles relationships between
BOD, temperature and velocity had been tested for local conditions as
found in Melbourne, Australia (22). This work oriented sulfide pro-
duction to being a function of velocity. The work by Davy was later
modified by Pomeroy for gravity sewers resulting in more simplified
equations for predicting sulfide buildup (21).
Mechanisms of Hydrogen Sulfide Corrosion
Hydrogen sulfide will ionize in water to form a weak diprotic acid, hydro-
sulfuric acid, which yields hydrogen and hydrogen sulfide ions. The
hydrosulfide ion will then ionize to form hydrogen and sulfide ions (4).
This would represent one form of acid formation on the crown and walls of
-------
the pipe. There is one other form of acid formation associated with the
hydrogen sulfide that is generally recognized to be the predominant form
as found in sanitary sewers. This is the oxidation of hydrogen sulfide
to sulfuric acid by aerobic bacteria. Sulfuric acid is a strong acid
whereas hydrosulfuric acid is a weak one. Sulfuric acid, being more
reactive, explains more clearly the reduction of the cement binder (insol-
uble in water) to water soluble salts, primarily sulfates (26) (13). The
complete cycle with chemical equations is shown in Figure 1. The unique-
ness of the cycle is the role played by oxygen (27).
Therefore, it is not the hydrogen soiiHde gas, but rather sulfuric acid,
the product of the oxidation of the gas, which attacks the concrete sewer
pipe. After being generated, primarily in the slimes, the sulfides and
gas enter the flowing sewage. The gas that is not oxidized may then be
released to the sewer atmosphere. The release of the gas in gravity lines
occurs primarily at points of turbulence such as improperly constructed
joints, manholes, etc. Large amounts of the gas are released at wet wells
where the inflow line is not submerged. The turbulence at the discharge
point of the force mains is another major point of release of the gas.
The humidity of the sanitary sewer atmosphere is very high and the exposed
walls of the pipe are normally moist with water of condensation. This
water serves as a receiver of the liberated hydrogen sulfide gas and
provides a harbour for bacteria. Ventilation of the sewer permits oxygen
to enter the sewer which is also absorbed by the moisture. The oxygen
permits the bacteria that develop to be aerobic. It is at this stage
that another facet of the uniqueness of the hydrogen sulfide generation pro-
cess in a sewer is manifested. Although the gas is initially generated
under anaerobic conditions, an aerobic environment is required for the
final oxidation to sulfuric acid.
Control of Hydrogen Sulfide
The significance of hydrogen sulfide in sanitary sewer systems has been
stated and the need for control of the gas identified. Researchers have
essentially two basic approaches to control hydrogen sulfide. The first
approach employs methods which prevent generation while the second permits
the generation to occur with the subsequent rendering of the gas harmless
by chemical reactions. Prior to any discussion of specific techniques
employed and reported, a review of the most significant factors involved,
i.e. basic properties, and how they can give insight into control tech-
niques is appropriate.
Bacterial Action - - Bacterial action as found in gravity sewers is the
first factor to be reviewed as it is applicable to control of sulfides
from either inorganic (sulfate ion) or organic sources of sulfur. In
the former, the attack of the sulfate ions is by strict anaerobes that
utilize the combined oxygen and the sulfur becomes a hydrogen acceptor.
This alludes to several methods of control. First, an alternate combined
oxygen source could be provided that would be more readily available to
the bacteria. Secondly, the maintenance of a residual dissolved oxygen
10
-------
"2s
H^SO. + cement >CaSO.
24 4
Water
Droplets
Resultant
Corrosion
Figure 1. Hydrogen Sulfide Development in a Sanitary Sewer
11
-------
would restrict the growth of obligate anaerobic bacteria as well as
oxidize the sulfides released by facultative bacteria. Free oxygen has
the same effect on anaerobic bacteria as that achieved by injecting a toxic
material. The use of toxic materials serves as an additional method of
control.
Organic compounds containing sulfur present an entirely different problem.
The common bacteria that utilize organic matter are responsible. These
organisms secrete sulfides from the breakdown or organic compounds while
undergoing aerobic metabolism. If the dissolved oxygen is depleted, they
will seek a combined oxygen source. If the combined oxygen source should
be sulfates, the magnitude of sulfides released would be increased. One
method of control would be to take steps to assure the presence of oxygen
to oxidize sulfides released to the environment. A second method, under
anaerobic conditions would be the provision of an alternate combined
oxygen source, such as nitrates, in lieu of sulfates. The addition of
toxic chemicals to kill the bacteria would be an alternative method of
biological control.
Chemical Action -- There are several ramifications to the use of chemicals.
Under the discussion of bacterial action, the use of toxic chemicals
represents one form of control. Second, is the addition of chemicals to
provide an alternate combined oxygen source as previously discussed. Pro-
vided the sulfides have already been produced, these could be precipitated
by addition of heavy metals that form insoluble metallic sulfides. The
adjustment of pH to either extreme, i.e. acid or base, will inactivate the
slime layer. The addition of chemicals, for example chlorine, would
oxidize the sulfides in lieu of forming insoluble metallic salts. The
addition of oxygen would also serve to oxidize any ionized sulfides and
facilitate the dual purpose of maintaining aerobic conditions.
Physical Controls -- Physical control of sulfides could be accomplished
by designing the system for velocities equal to or greater than the
scour velocities. There are two types of scour involved and these should
not be confused. A sediment scour velocity is one in which the inorganic
material, such as sand that enters sewers, will be transported. This
velocity has been reported to be from 1.6 to 2.0 feet per second (28).
A slime scour velocity is one in which slimes are prevented from develop-
ing on the walls and invert of the pipe. There has been very little in-
formation reported on the magnitude of this velocity. One sewer which
had a velocity of 4.9 feet per second was found to be relatively free of
slime (29). This velocity would be expected to greatly exceed the
sediment scour velocity and would not be practical.
A method applied in isolated instances has been flushing or dilution
during low flows. In the latter, creek waters have been diverted to sani-
tary sewers to increase the flow and also provide additional dissolved
oxygen (30) (31). Infiltration has provided the extra water in many in-
stances. The advent of rigid water quality standards and the high cost
12
-------
of construction of sewage facilities has made these methods undesirable.
"Other methods to minimize odors and other sulfide nuisances are:
a) Minimize points of high turbulence withfn the system
b) Design pump station wet wells in a way which precludes the
surcharge of tributary lines
c) Provide air jumpers across large siphons and around lift
stations
d) Provide forced draft ventilation if there is a point where
air may be depleted seriously of its oxygen content (7)."
The most frequently referenced methods of control that have been used are
as follows:
Method
Chi orination
Nitrate
(Sodium or Calcium)
Iron Salts
Zinc Salts
Lime (Caustic Soda)
Oxygen (Aeration)
Action
References
destruction of sulfide (9)(32)(38)(21)(34)(7)(35)
alternate oxygen source (9)(7)(21)(36)(37)
precipitation of sulfides (9)(7)(21)
precipitation of sulfides (9)(7)(21)
pH adjustment (9)(7)(21)
oxidation (9)(7)(38)(23)(39)(40)
(41)01)
Other methods that have been proposed and applied are directed primarily
to the extension of useful life of the conduit and not control of the
sulfides. There are two approaches to the problem, one is the use of
sacrificial concrete and secondly the use of limestone aggregates (21).
The major shortcomings of these methods, as in the case of using inert pipe
materials, is that they do not control odor problems.
Hydrogen sulfide presents an odor problem that has brought about serious
problems that have warranted control. The odor problems have varied from
the sewerage system to the sewage treatment plant. Many of the plant odor
problems result from sewage arriving at the plant with high levels of hydro-
qen sulfide. The treatment process releases these and creates nusiances.
A comprehensive treatise of odor control at treatment plants was presented
by Wisely (30)(31)(32). Most of the methods employed for odor control in
sanitary sewers are the same as for sulfide control. Masking of odors by
substitution has in some instances abated the odor problem; however this
approach has two major shortcomings. First, the method is very expensive
and second, the masking of the odor will not prevent corrosion.
13
-------
SECTION IV
DESCRIPTION OF SEWERAGE SYSTEM
PORT ARTHUR, TEXAS
The City of Port Arthur, Jefferson County, Texas is located in the extreme
southeast corner of the state approximately 90 miles east of Houston. With
a maximum elevation of only 10 feet above sea level, the city is located
within the flat, rolling terrain of the Gulf Coastal Plains.
The climate of the area may be best described as sub-tropical. This is
evidenced by an annual mean temperature of 68.8° Fahrenheit, with the
monthly mean temperature ranging from a high of 82.9° F in August to a
low of 52.8° F in January.
The mean annual rainfall for the area is 52.38 inches. The rainfall is
distributed fairly uniformly throughout the year, with July having the
highest monthly mean rainfall, 6.32 inches, and March the lowest, 3.04
inches. The maximum rainfall of record for a month is 18.71 inches, while
the minimum is zero.
The City of Port Arthur, with a 1970 population of 66,676, is a center for
petroleum, petrochemicals, rice milling, and other industrial activities.
One of the major activities is derived from the port facilities which are
located on the intercoastal waterway. The proximity to the coast accounts
for the extensive commercial fishing which serves the area,
WATER AND SEWER SYSTEM
The City of Port Arthur initiated construction of its water distribution
system in 1910. The demand for water continued to increase with the growth
of the city necessitating expansion of the water supply system. The water
treatment plant was constructed in 1926 with a major expansion of these
facilities in 1950. The most recent improvements to the plant occurred in
1972 with the conversion from a dry chemical to a liquid chemical feed
operation. The plant has continuously provided the users with potable
water that is well below the limiting criteria of the Texas State Depart-
ment of Health (43).
Construction of the sanitary sewage collection system was initiated in 1910 with
the construction of 9,350 feet of 6, 8, and 10 inch diameter sewers The sew-
erage system has grown continually until now the system contains 729,000 feet
of sewers, with 42 inch diameter pipe being the largest. Of the total
length of sewers in the city, 596,000 feet is 12 inch diameter or less
?™hn™3*'°?° I66- °f 1S in? dl'ameter or larger. The system contains
594,000 feet of pipe made of acid resistant materials, the major portion
of which is 6 and 8 inches in diameter. Over 60 percent of the pipe over
14
-------
15 inches in diameter is made of concrete. A skeleton diagram of the
principal components of the sanitary sewerage system is shown in Figure
2 with the subsystems utilized in the study identified.
The Texas State Department of Health in their "Design Criteria for Sewer-
age Systems" specify a design velocity of 2 feet per second for sanitary
sewers^flowing one-half full (44). Under given conditions and where justified,
a minimum velocity of 1.6 feet per second flowing one-half full is
acceptable. The minimum velocity 1s applicable to the Gulf Coastal Plain
where the 2 feet per second requirement would result in high construction
costs. The very flat topography of the Port Arthur area has resulted in
a total of 28 lift stations using the lower velocity criteria. If the 2
feet per second requirement would have been maintained throughout the city,
a considerably larger number of lift stations would have been required.
The cost of construction of the sewerage system, exclusive of the lift
stations and treatment plants through 1967, was $4,214,000. The estimated
present worth of the system is $5,704,000. The present worth of the sewage
system (structure, equipment, wet well, etc.) lift stations, which origi-
nally cost $820,000 is estimated at $1,115,000,
The city did not construct sewage treatment facilities to serve the central
area until 1961. Prior to this time the sewage was discharged directly
into the Sabine-Neches Canal without treatment. The first of several small
sewage treatment plants to serve the outlying or peripherial areas was com-
pleted in 1957. In addition to serving the city proper, the main sewage
treatment plant treats sewage from the communities of Pear Ridge, Griffin
Park, Lakeview and a small area of Groves.
The original cost of sewage treatment facilities, including improvements
and additions was $2,103,000. The estimated present worth of these facilities
is $2,805,000.
WATER AND SEWAGE CHARACTERISTICS
The City of Port Arthur obtains its water supply from the Neches River via
a canal system owned and operated by the Lower Neches Valley Authority.
The canal system is an unlined canal that extends from the northern part
of the county. The canal serves several cities and industries in addition
to the City of Port Arthur. The city maintains two large raw water storage
reservoirs that receive water from the canal. The water from the reser-
voirs is carried by pipeline to the water treatment plant.
The water treatment plant uses chemical coagulation, pH adjustment, sand
filters and chlorination. Prior to 1972, the city used dry alum for their
coagulation aids and lime for pH adjustment. During 1972, facilities were
Installed that will use liquid alum and caustic. This should provide a
greater control in the chemical treatment.
There are two water quality parameters that are related to the study that
15
-------
cr>
LEGEND
O Lift Station
0 Pump Station
Gravity Line
Force Main
A Sewage Treatment Plant
Pear Ridge
Smith-Young
P
I
I
O 3rd Avenue
1
I
Smith-Young
System
19th Street-Stillwell Blvd.
P (Alligator Bayou)
Railroad Ave.-Thomas Blvd.
Pear Ridge
System
Pioneer Park
(Hospital)
Stillwell System
l Grannis
I Ave.
Lakeshore
System
I
Lewis Drive
Q
L
8th Avenue
<3
I ----- ,'
Houston Ave.-Lakeshore Dr.
Mainline
Lake Charles
Figure 2. Principal Components of the Sanitary Sewerage System, City of Port Arthur, Texas
-------
are Important to consider. These are sulfates and hydrogen ion concentra-
tions. For a period of 13 years, data indicated an average sulfate content
of 21.8 mg/1 and a pH of 7.22 for the raw water supply. During this same
period the treated water had a sulfate content of 36.1 mg/1 and a pH of
7.5. The chemical treatment of water increased the sulfate content of the
water by 14.3 mg/1 (45). The sulfate level of the treated water is well
below acceptable levels (43).
The wastewater treated by the sewage treatment plant is a combination of
domestic and commercial wastewater. Although the area is highly indus-
trialized, industrial wastes were not handled by the city prior to 1972.
The average biochemical oxygen demand of the influent to the plant for a
five year period was 152 mg/1, while the highest single month average for
the same period was 308 mg/1.
SEWERAGE SYSTEM FAILURES
Although failures had occurred in the system before 1951, it was not until
that year that significant data were recorded on failures within the system.
These failures have occurred throughout the entire collection system and have
not been isolated to a specific area of the city. Most of the recorded
failures have occurred in pipe of fifteen inch diameter or larger.
The records of the city were reviewed for the purpose of evaluating the
deterioration rates experienced in the city. The rates were established
by dividing the total wall thickness of the pipe by the time period in
years between installation and complete structural failure. The rates
obtained in this manner will be lower than the actual rate of deterioration.
Deterioration rates observed are shown in Table 1.
In many instances the wall thickness reached a critical thickness if not
total deterioration prior to complete structural failure. During the in-
spection survey several pipes were observed in which the crown of the pipe
had disappeared without a cave-in. The fact that the line did not cave-in
can be partly explained by the arch action of the soil Overlying the pipe.
Further, the over burden on the pipe when considering this action was not
of sufficient magnitude to cause failure. Several unique modes of sulfuric
acid attack, which were observed both prior to and during the study, will
be discussed later.
Discription of Deterioration
At the initiation of the study, a survey was made of the collection system
to access the condition of the sewers and obtain information concerning
the character of failures. Throughout the entire study these character-
istics were noted to complete the failure descriptions. The surveys of the
sewerage system provided valuable information concerning the mode of failure
of concrete sewer pipe attributable to hydrogen sul fide.
The very old sewers that demonstrated severe deterioration were character-
17
-------
Table 1
DETERIORATION RATES OF CONCRETE SEWER PIPE
PORT ARTHUR, TEXAS
LOCATION
19 & Stillwell Lift Station to
Lake Charles Lift Station
3rd Avenue Lift Station — south
Smith-Young Force Main Discharge to
25th Street
West of Lake Charles Lift Station
oo Along West Thomas Blvd.
Pioneer Park (Hospital Lift Station) to 5th
Stillwell Blvd.
Pioneer Park
El Vista
El Vista
Port Acres
(1) Some failures actually occurred earlier but were not reported until the date shown
(2) Most recent failure
(3) Standard Strength — non-reinforced
Pipe Diameter
(inches)
24
18
15
30
15
i 30
24
30
8-15
18
15
Year in
Service
1951
1951
1957
1961
1957
1951
1951
1951
1956
1957
1956
Year of w
Failure
1967
1966
1967
1966
1967
1967
1965
1970
1967
1969
1971 (2)
Years of
Service
16
15
10
5
10
16
14
19
11
12
15
Wall Thickness v ' Deterioration Rate
(inches) (inches/year)
21/8
1 1/2
11/4
23/4
1 1/4
23/4
21/8
23/4
3/4 to 1 1/4
11/2
11/4
0.133
0.100
0.125
0.55
0.125
0.172
0.133
0.144
0.114
0.125
0.083
-------
istic of most published or observed conditions. The crown of the pipe
showed the greatest magnitude of loss of wall thickness. From the crown
of the pipe the thickness tappered to no loss of material at the minimum
flow line. In most cases, at the point of contact with the low flow line,
a second point of severe deterioration was observed; however, the loss of
material was less than at the crown and represented only a small band
parallel with the water line. Below the flow line or pipe invert, no
deterioration of the concrete was observed. In all instances, the
deterioration appeared to be uniform throughout the entire length of the
sewer. Most of these sewers had a series of ripples at the crown. This
rippling effect was created by the reinforcing steel imbedded in the
concrete pipe. The concrete on either side, i.e. up-or-downstream, was
recessed from the location of the steel. There were several instances in
which all traces of the steel at the crown had been removed.
Concrete sewers installed in the 1960's provided a different view of the
mode of failure. One major trunk line was entered at every manhole and
observed. The deterioration observed was quite different from that ob-
served in older sewers. First, there was only a very minor trace, if any,
of deterioration observed upstream from the manhole. Downstream from each
manhole various conditions were observed that are worthy of note.
Where the manhole was installed in a straight segment of the sewer, severe
deterioration was observed immediately downstream. This was characterized
by exposed aggregate where the mortar had been destroyed by the sulfuric
acid attack and washed away during peak periods leaving the aggregate ex-
posed. Closer investigation revealed the most severe damage appeared to
occur on only the first two or three joints downstream. In some of the
manholes, the attack at the manhole was of such a degree that the steel
was exposed; however in the second or third joint downstream the steel
was not exposed. The conditions noted prompted an investigation of the
same sewer at a point between manholes. An excavation was made exposing
the pipe and a segment of the crown was removed for observation. The
crown of the pipe at this point had lost less than one-half inch and a
good cover was still provided for the steel.
As previously cited, one of the unusual facets of hydrogen sulfide attack
of concrete pipes is that two distinct systems are required, one void of
free oxygen and one requiring free oxygen. The oxygen required for the
aerobic cycle and final conversion of the hydrogen sulfide to sulfuric
acid comes from manholes in the sewer. Apparently, the movement of the
air entering the sewer at manholes tends to move downstream. This con-
dition coupled with the turbulence at the manhole which releases the
hydrogen sulfide gas provides the proper percentages for the reaction to
be continuous. The hydrogen sulfide released is also apparently swept
downstream. The explanation for the movement of air downstream is that
the sewage tends to move the air by friction at the interface. This is
not to imply a strong movement of air but a movement of sufficient mag-
nitude to force a downstream movement of both air and gas. The implications
of the character of failure described and apparent cause are quite signifi-
cant and should perhaps be given consideration in future designs.
19
-------
The same trunk!ine as previously described changes direction at several
points. The line between manholes remains straight. At each point where
a change in direction existed, the manhole was entered and observations
noted. As in the straight sections, the line upstream was essentially
free from deterioration. Downstream of the manhole a most unusual attack
of the pipe was observed.
The crown of the pipe downstream of these manholes although demonstrating
deterioration, was not the point of most severe attack. The most serious
attack was near the water line and occurred primarily in the area of the
spring line and the upper quadrant tapering to the crown and opposite quad-
rant. This deterioration occurred only on the outside radius of the change
in direction. At these changes in direction, the momentum of the sewage
was carried up the sides of the pipe on the outer radius while being de-
pressed on the inner radius. No deterioration was observed on the inner
radius of the pipe at the change in direction. Hydraulic action on the
face of the pipe at the outer radius is greater than normally experienced
in a straight pipe thereby maintaining a continuous washing of the surface.
The only explanation for the character of failure observed is that the high
degree of moisture found in this area tends to absorb more hydrogen sulfide
and oxygen than other quadrants of the pipe. The opposite side as well as
the crown of the pipe at these points was relatively dry compared to the
side where severe damage had occurred. The major damage was observed on the
first joint of pipe downstream with the second joint of the pipe demonstrating
a similar but lesser degree of deterioration. Further downstream the attack
on the concrete appeared to occur in the crown of the pipe.
Throughout the entire sewerage system one zone of distinct hydrogen sulfide
attack was always noted. This was the gravity line immediately downstream
of the force main or lift station discharge, with the degree of severity
always being greater near the discharge point and decreasing downstream.
This contributes to the general philosophy that the force mains are the
principle hydrogen sulfide generators in a sewage collection system. In
all lines observed, the magnitude of attack and the distance downstream
where deterioration was observed appeared to be a function of the sulfide
levels measured at the discharge points.
The preliminary work performed in selecting sampling points and treatment
locations revealed an additional area of concrete deterioration. This was
the mortar in manholes and the wet wells at lift stations. In most instances,
the degree of attack at wet wells was much more severe than at manholes.
The damage at lift stations appeared to be uniform at the cover with less
severe attack on the walls. This is not to infer that damage to the walls
was not reaching critical proportions. A report submitted to the City
Council concerning the condition of wet wells in the sewerage system noted
that the cover of several wet wells and the walls of one particular station
had experienced an alarming degree of deterioration and that failure was
imminent (47). While plans were made to either rebuild or abandon these
wet wells, guard rails were installed to prevent excessive loads from
being imposed on the structure.
20
-------
Although not directly related to the descriptions of deterioration, a
result of the deterioration was noted and deserves mention. During the
Initial survey and throughout the course of the study, a condition was
observed in gravity lines which created many problems and contributed to
undesirable flow conditions in the sewers. The continued deterioration
of the mortar binder of the concrete pipe resulted 1n the freeing of
aggregate which dropped to the invert of the pipe. The low velocities
permitted by the Texas State Department of Health were insufficient to
flush the debris to the wet wells where It could be removed. The
aggregate formed traps which hold the sand and grit from the mortar result-
ing in an ever increasing buildup of materials on the bottom. This buildup
results 1n two undesirable conditions. First, the invert is changed from a
smooth, circular shape to an irregular flat bottom. This has the effect of
altering the flow characteristics by changing both the hydraulic radius and
the roughness. The net effect of the debris is to further reduce flow
velocities which were inadequate to begin with. In addition to the un-
desirable effect on flow characteristics, the irregular rough surface traps
large amounts of organic matter. The material removed from the invert was
very granular and black 1n color. After washing and allowing to lay on the
ground for several days, the material took on the appearance of sand and
gravel.
One cubic centimeter of this material was carried to the laboratory for
analysis. Upon dewaterlng, it was placed in a liter of distilled water.
After mixing, the solution was tested for sulfides and C.O.D. The sulfide
content, which was primarily dissolved, reached 16 parts per million. The
C.O.D. of the material approached levels characteristic of industrial
waste water.
The sampling of the gravity lines and manholes was very difficult due to
this buildup of material, particularly during low flows. During these
periods of low flow it was almost impossible to obtain a sample that did
not contain some of the debris.
SULFIDE LEVELS IN SANITARY SEWERAGE SYSTEM
The continuing collapse of sanitary sewers, led to an Investigation to
ascertain the level of sulfides that exist in the sanitary sewerage system.
Although the study was not comprehensive, it did report sulfide levels (2).
The study only reported total sulfides and did not give values for dissolved
sulfides and pH which are necessary to determine hydrogen sulfide content of
the sewage (25). Sulfide levels in mg/1 that have been observed are shown
in Figure 3 and identified by the referenced source listed in Section XIII.
Pomeroy reported a dissolved sulfide concentration of 0.1 m g/1 would be
expected to cause corrosion at a rate of one inch per decade (21). Hydrogen
sulfide concentrations of 0.2 mg/1 have been reported as the level at which
corrosion begins (55). The total sulfide levels for the sanitary sewerage
system as shown in Figure 3 would explain the high rate of corrosion pre-
iously reported for Port Arthur. Additional information concerning sulfide
levels will be presented in SECTION VI, DISCUSSION OF INDIVIDUAL SYSTEMS.
21
-------
Pear Ridge
LEGEND
0 Pump Station
O Lift Station
— Gravity Line
— Force Main
A Sewage Treatment Plant
Il.8l3.ol54
3.0 |5. 2|54
O 3rd Avenue
|l.2|2 1 | 22 J
' ' Reference
Ave. Max. No.
19th Street - Stillwell Blvd.
(Alligator Bayou)
J4.9 I?.5 I 54
|5.9 J7.0 I 54^
Railroad Ave.-Thomas Blvd.
|3.2|4.6|54
Stillwell System
54
I
u.
Houston Ave.
Lakeshore Dr.
U.3l6.ll54 I
8th Avenue
Lake Charles
Smith-Young
|2.9|4.0|54
| Smith-Young System
Ridge
em
\
11.6 15.8 54
10.7 14.0 55
er Park
)ital)
Lewis Drive
Q
H3.6I5.5 154 1
1
^~- —
;
Figure 3. Total Sulfide Levels in the Port Arthur Sanitary Svwerage System
5.314.8 I 54
.3l64
-V)
^
Mainline
-------
SECTION V
DESCRIPTION OF CONTROL METHODS
The City of Port Arthur's Water and Sewer Study Committee considered var-
ious methods to control the odor and concrete corrosion problems caused
by hydrogen sulfide. After reviewing the various methods of control, the
Committee recommended the use of oxygen as a possible control method.
Two sources of oxygen were to be used: air, provided by blowers, and
pure oxygen, initially delivered at the site in trailers and later pro-
vided by higher capacity cryogenic tanks. Special considerations were
given to each source of oxygen and injection method evaluated, and a
general discussion of these will be given.
OXYGEN GAS INJECTION - FORCE MAIN
Oxygen gas was first selected for use in force mains and was later used in
conjunction with U-Tubes. There were several reasons for the selection of
pure oxygen. First, the total volume of gas injection would be consider-
ably less than with air which contains only 21 percent oxygen. Not only
would the total volume be less but all of the gas would be available for
chemical oxidation or biological action.
There have.feeen several studies, involving the.injection of air, hut they
considered chemical-biological actions without regard to head losses. The
age of the pumps in the Port Arthur Sewerage System and the marginal avail-
able head was of concern in the selection of the oxygen source. It was
felt that the lower gas volume that resulted from using pure oxygen would
create less system losses and minimize the potential of air locking.
Previous studies using blowers for air injection reported conditions of
excessive noise associated with the compressors. The sites selected for
control in the Port Arthur Sewerage System were all located in residential
areas where the sound of the blowers would be undesirable. Also, the dry pits
of the lift stations were space limited and could not accomodate the air
compressors. The use of gaseous oxygen represents a noiseless operation
with no serious problems associated with aesthetics.
The decision to use gaseous oxygen brought about one serious concern. This
was the potential for explosions as expressed by several concerned citizens.
The potential for explosion is real when oxygen is mixed with combustible
gases and the presence of hydrogen sylfide accentuated this. This
question was presented to a chemist who acknowledged the fear, however not
without qualifications (47). Sewer gases when mixed with air (oxygen)
in a dry or nearly dry condition, will explode when sparked by some source
of fire or catalyst. The presence of water or water vapor serves as a
stabilizing factor thereby reducing the potential for an explosion. The
injection of oxygen into the liquid stream would not create a hazardous
condition. The gases present would be oxidized and further generation of
combustible gases would not be possible under aerobic conditions.
23
-------
There is always a fear of gasoline and other combustible materials being
discharged into the sewerage system. Most of these are of a lower specifi
gravity than water and would therefore be trapped in the wet wells. Only
in a vary unusual circumstance would these materials be drawn into the
force main.
The concern in the use of oxygen was not completely dispelled and special
precautions were taken. The construction specifications required that all
piping, valves, and other equipment be throughly cleaned and be free from
oil or grease prior to installation. Further, all joints were to be seal-
ed by use of a special teflon tape.
The oxygen from the tank passed through a control valve for flow regulatio
a rotameter for flow measurement, and a solenoid valve prior to entering
the diffusion equipment. The solenoid control valve was set to open ten
seconds after the pump cycle starts and to close when the pump stops. Thi
measure was taken to assure that the oxygen would always be injected direc
into the sewage.
There were three methods of injection utilized at various stages in the
study. The initial installations utilized an enlarged section of pipe out
side the lift station with three diffusers installed. The piping arrange-
ment is shown in Figure 4, and the diffuser arrangement shown in Figure 5.
The use of the diffusers raised a serious question concerning operation an<
maintenance. It was felt that the piping and diffusers would serve to tra
rags and other debris which would block the flow. After one year of opera
tion, one of the sections was opened and found to contain only a minor amo
of debris that would not interfere with flow conditions. The original des
did not provide a manway for access to the diffusers which should be insta
Blockage of the flow in the original configuration would represent a major
task for removal for maintenance purposes.
Two other methods of injection were later tried in the study. The first o-
these consisted of drilling and tapping with the oxygen injected without
diffusers. The next was insertion of a curved copper tube with the bend
in the downstream direction. The reason for this was to prevent the colle<
tion of rags. Each copper tube had a series of small diameter holes along
the length in two rows with the end of the tube closed. The purpose was
to reduce the bubble size.
AIR INJECTION - FORCE MAIN
The application of air injection has been used with success in various
locations in the control of hydrogen sulfide. Air injection was planned
at one location after a period of operational experience with oxygen.
This would permit an economic evaluation of the oxygen sources for
hydrogen sulfide control as well as provide operation and maintenance
experience.
The methods of injection at the first installation was identical to that
24
-------
Concentric Reducer
rvs
en
Oxygen or Air
Supply
I See Figure 5 for
I Diffuser Details
\
Style 38 Dresser
Coupling
\
Expanded 24 Section
Existing Force Main
Note: Not to scale
Figure 4. Force Main Piping Arrangement
-------
Solenoid Valve
From Oxygen or
Air Source
24 Cast Iron Pipe
I I
I I
I I
~T
Center Line of Pipe
I "
!
Diffusers
Figure 5. Typical Diffuser Arrangement for 24' Cast Iron Pipe
-------
first used with oxygen. This was the expanded section with dlffusers as
shown 1n Figures 4 and 5. The expanded section had the effect of reducing
the velocity and Increasing the pressure. The increased pressure would
Increase the solubility while the diffuser would provide greater surface
area for the air bubbles thereby increasing the potential for oxygen transfer.
The system was designed in a manner that would permit either continuous
air feed or air feed only during pump operation. The blowers selected for
the original installation were oil-free to prevent the Introduction of oil
and grease into the sewage.
A second method for injecting air into a force main was selected and
evaluated during the study. This method involved a straight pipe flush
with the crown of the force main. Air injection was also used in
conjunction with a U-Tube aeration device. This represents a special
condition and discussion will be found in the section dealing with
this method.
OPEN TANK AIR INJECTION
A sewage lift station as opposed to a sewage pump station require a
different approach to the hydrogen sulfide problem. The two types are
differentiated as follows: (a) The lift station serves to lift the sewage
from a lower elevation to a higher elevation for gravity flow or employs
a very short force main and (b) the sewage pump station is associated with
force mains of considerable length. The sewage lift stations that had a
history of hydrogen sulfide problems did not serve as generators but served
to release previously generated hydrogen sulfide gas in the vicinity of the
turbulence created at the discharge point.
Consideration was given to the application of a large circular aeration tank
with diffusers at the periphery of the tank. The tank would serve to provide
detention time for the oxidation of the sulfides and permit conversion of the
sewage to an aerobic condition. The major problem as previously stated was
the arrival of perviously generated sulfides and not additional generation.
Upon careful consideration of the problem, this method of air injection was
abandoned in favor of the pressure tank. The basic reason for elimination
of this method was that there was no assurance that the sulfides would be
oxidized and that the tank would merely serve to strip out the gas. In
this instance, severe odor problems could be anticipated at the installation,
PRESSURE TANKS
The application of a pressure tank of air injection is based upon Henry's
Law. Henry's Law may be stated as follows: "The weight of a gas that
dissolves in a definite volume of liquid is directly proportional to the
27
-------
pressure at which the gas 1s supplied to the liquid" (4). This means
that if one gram of gas dissolves in a liter of water at one atmosphere,
then two grams will dissolve at two atmospheres.
There are three factors that control the solubility of a gas in a liquid
and these are: (a) the nature of the gas and the solvent, (b) the
pressure at which the gas is applied (Henry's Law) and (c) the tempera-
ture. It 1s therefore obvious the role pressure plays for a system of air
injection into sewage. One additional comment concerning pressure 1s
Important. The effect of pressure does not follow Henry's Law when a
reaction takes place with the solvent. In the application of oxygen,
there is no reaction with the solvent (water); however, reaction will occur
with the sulfides.
The basic concept applied for pressure tank air injection was for a con-
tinuous flux of sewage with a controllable detention time. The air would
be continuously Injected at an elevated pressure through diffusers, with
a blowoff at the top of the tank with excess air piped to the discharge
line. The sewage would flow from the bottom of the tank to the top and
discharge through an overflow. The flow schematic is shown in Figure 6.
This installation was selected to meet the needs of certain lift station
configurations in the Port Arthur Sewerage System. There were several
lift stations with records of hydrogen sulfide problems. The sulfides
were found to exist in the wet wells and the turbulence at the discharge
released the gas. These stations operate strictly as a 11ft station (no
force main) or they operate with a very short force main with only minor
generation of additional sulfides. In these instances, it was felt that
air/oxygen injection would not be successful primarily as a function of
detention of contact time. A more serious shortcoming was found 1n the
stations with short force mains where oxygen Injection was applied. This
was a complete separation of the oxygen and sewage resulting in two phase
flow. This will be more fully discussed under Data Collection and Analysis.
The pressure tank for air injection therefore had two basic purposes. It
increased the solubility of oxygen in the sewage by operating above atmos-
pheric pressure. The second factor was that the high degree of mixing,
by using variable spaced diffusers, and the detention time, would assure
that the sulfides would be oxidized prior to discharge. (The mixing also
served to prevent short circuiting through the pressure vessel).
U-TUBE AERATION DEVICE
The application of the U-Tube aeration device represents a recent develop-
ment for oxygen transfer. The first reported work was by Bruijn and
Tuinzaad in 1958 (48). Additional work on U-Tubes was reported by Speece,
Adams and Wooldridge in 1969 (49), and by Speece and Orosco in 1970 (50).
Concurrent with this work was a separate study of U-Tube aeration by
Rocketdyna for the Environmental Protection Agency (51). The work by
Rocketdyne served as the basis for design of the U-Tubes used in this study.
28
-------
Blowoff Valve
To Force Main or
Gravity Sewer
Air Header -•
Air Supply
Diffuser •
Access La*8er
Drain and Recirculation
Line to Wet Well
Air Header
Air Line
Flow Meter
Valve
Pump
Figure 6. Pressure Tank Air Injection
-------
There are two basic elements of the U-Tube aeration process. Air is en-
trained in the liquid flow by an aspirator device (venturi) or by com-
pressed air. Following air entrainment, the flow regime is changed to
increase the pressure and provide additional residence time. The con-
figuration of the U-Tube and the method of air entrainment can take
various forms, however the basic configuration is shown in Figure 7-
The U-Tube application in Port Arthur was at sewage lift stations and
located within the dry pit although several other applications have
been demonstrated (52). There were two sources of oxygen employed with
the U-Tubes in the Port Arthur Sewerage System. One design called for
compressed air while the second utilized pure oxygen.
30
-------
Expander
Pump Discharge
Aeration Device
Aspirator
Compressed Air -
Gaseous Oxygen
Discharge to
Gravity Sewer
• Up-leg
Expanded Section
Down-leg
Expander
Figure 7. Typical U-Tube Installation
31
-------
SECTION VI
SULFIDE PROBLEMS AND CONTROL RESULTS
LAKESHORE SYSTEM
The Lakeshore System involves three lift or pump stations, two of which have
sulfide control measures installed. The three stations are Grannis Avenue
Pump Station, Railroad Avenue-Thomas Boulevard Pump Station and the Houston
Avenue-Lakeshore Drive Lift Station. All three stations discharge into a
common point, a junction box, which is an integral part of the Houston
Avenue-Lakeshore Drive Lift Station. From the junction box, the sewage
flows by gravity to the Lake Charles Lift Station, the terminal point of
both the Lakeshore and Stillwell Systems. Details of the system are shown
in Figure 8.
Protection of the gravity line in this system was a major concern. This
line is approximately 10 years old and consists of 21 and 24 inch diameter
concrete pipe, a significant capital investment. Although there are not
any large sections of this line in imminent danger of failure, short sections
downstream of those manholes where the line changes direction are approaching
critical condition. Photographs of portions of this line are shown in Figure
9.
In addition to the corrosion of the pipe, odor problems have also persisted
along this gravity sewer. This problem has been most severe at the Lake
Charles Lift Station. As seen in Figure 10, the wet well at this station
has undergone severe deterioration and its structural stability would be
classified as critical with a potential for failure at any time. The
desirability of bringing the hydrogen sulfide problem in this system under
control is obvious.
Sulfide Levels
Sulfide levels were monitored at sampling stations located at wet wells,
discharge points (junction box) and selected points in the interceptor.
The results of the monitoring program will be discussed in sequence from
the upstream stations to the end of the gravity line at the Lake Charles
Lift Station wet well.
Grannis Avenue Pump Station
This station is characterized as a low capacity station in which the sewage
has a long detention period in the wet well. The station is equipped with
two pumps that alternate. During one test period, the pumps operated for
an average of ten minutes per hour. During high flow periods, these pumps
cycle frequently due to pump capacity and wet well storage. The reverse
is true during low flow periods. The station receives sewage*with high
levels of sulfides and has a history of odor complaints
32
-------
Grannis Ave. Pump
Station
P.C. -2 @ 600 gpm each
S.A. = 68 acres
, L=3150
Railroad Ave.-Thomas Blvd.
Pump Station
P.C. -1 @ 1200 gpm, 1 @ 2400 gpm
. = 512 acres
0, L=3850
Houston Ave.-Lakeshore Dr.
Lift Station
P.C. -1 @ 2400 gpm, 1 @ 700 gpm
1 @ 400 gpm
S.A. = 598 acres
21 0
L=500
LEGEND
D Pump Station*
O Lift Station*
— Gravity Line
"• — Force Main
O Manhole*
P-C. Pump Capcity
S.A. Service Area**
0 Diameter
L Length
Sampling Point
Indirect Service Area, areas whose sewage has
been pumped at least once prior to entering
station, are shown in parenthesis
Note: not to scale
Lake Charles Ave. Lift
Station
P.C. -3 @ 1500 gpm, 1 @ 3000
S.A. = 636 (2253) acres
24 0, L=7200
Figure 8. Lakeshore System
-------
View downstream; left side. First joint downstream at manhole. Sewer
changes direction at this location.
View downstream: right side. First joint downstream at manhole. Sewer
changes direction to left at this location.
Figure 9. Deterioration at Manholes - Lake Charles Interceptor
34
-------
Deterioration at the top of the Lift Station. Note exposed rebars.
•*
•mm
Deterioration of wet well wall. Note line traces. These are due to
rust along tracing rebars in wall.
Figure 10. Deterioration in the Lake Charles Lift Station Wet Well
35
-------
Samples were obtained from the wet well and at the point of discharge.
Data collected for the station are given in Table 2. The first two sample
periods indicated a decrease in sulfides which is contrary to what would
be expected. This decrease can partly be explained by the fact that some
hydrogen sulfide gas was released, apparent by odors of the gas, by tur-
bulence in the junction box.
The samples obtained on July 21, 1969, during a period of high infiltration,
provide a good example of the sulfide generation in this force main. The
level of total and dissolved sulfide in the wet well effluent which had a
trace of dissolved oxygen increased by 4.3 mg/1 and 3.0 mg/1, respectively.
The generation potential was much more dramatically indicated by the samples
collected on July 30, 1969 where there was an increase of 9.5 mg/1 of total
sulfides and 7.4 mg/1 of dissolved sulfides.
Railroad Avenue & Thomas Boulevard Pump Station
The city has not received as many odor complaints on this station as it has
on other stations within the Lakeshore System; however, the exposed aggregate
on the inside walls of the wet well evidence sulfuric acid attack.
In 1969, Wright reported some average values for total sulfides at this
station (53). As seen in Table 3, Wright reported the average increase
in total sulfides to be 2.2 mg/1. Samples taken on July 2, 1969 indicated
a higher sulfide level than had been previously reported. The sulfide level
increased from 0 to 15 and 14.6 mg/1 respectively for total and dissolved
sulfides.
The significance of oxygen in control ing sulfide generation was indicated
by samples collected July 17, 1969. The sample at the wet well contained
4.09 mg/1 of dissolved oxygen and 0.3 mg/1 of total sulfides. The discharge
contained only 0.9 mg/1 total sulfides and the dissolved oxygen had de-
creased to 1.82 mg/1.
Houston Avenue - Lakeshore Boulevard Lift Station
The Houston- Lakeshore Station is important in evaluating the Lakeshore
System because it's effluent mixes with the discharge from the previously
mentioned force mains. The combined flows then enter the Lakeshore
Interceptor. As the station is only a lift station and not recognized as
sulfide generator, only.discharae data were collected.
Data were collected from June until November, 1969. The summary data are
presented in Table 3. The most undesirable characteristic of this sewage,
which comes primarily from the downtown area, is the temperature. Average
sulfide levels were generally acceptable especially when considering the
pH levels. The pH levels would be considered an asset as they were generally
in the basic range.
Lakeshore Boulevard Interceptor
The Lakeshore Interceptor was sampled at two intermediate locations and at
36
-------
6-29-69
Table 2
SEWAGE CHARACTERISTICS
GRANNIS AVENUE PUMP STATION - FORCE MAIN
PARAMETER
Date I!
7-2-69
CO
-•J
7-21-69
7-30-69
pling Point
WW*
D
WW
D
WW
D
WW
D
Temp.
C°c)
29
29
28
28
29
30
29
29
pH
7.0
7.0
6.9
7.0
6.8
7.0
5.7
5.9
Total Sulfides
(mg/1)
4.1
3.4
5.0
2.4
0.6
4.9
2.2
11.7
Dissolved Sulfides
(mg/1)
3.4
3.0
3.4
1.6
0.5
3.5
1.6
9.0
Dissolved Oxygen BOD
(mg/1) (mg/1)
0
0
0
0
0.5
0.4
0
0
137
198
150
174
211
245
154
318
* WW-Wet well
D - Force main discharge
-------
Table 3
SEWAGE CHARACTERISTICS
(a) Railroad Ave. - Thomas Blvd. Pump Station - Force Main
[Test Period December 5,1968 to January 29,1969]
Parameter
Sampling Point Total Sulf ides Dissolved Oxygen
(mg/1) (mg/1)
Wet Well
Discharge
Ave.
Max.
Min.
Ave.
Max.
Min.
2.8
6.0
1.3
5.0
6.2
3.0
0
0
0
0
0
0
(b) Houston Ave. - Lakeshore Blvd. Lift Station
[Test Period June 27 to Nov. 29,1969]
Parameters
Ave.
Max.
Min.
Temp.
(•C)
32.7
37
21
pH
7.8
10.0
6.7
Total Sulfides
(mg/1)
0.4
1.5
0
Dissolved Sulfides
(mg/1)
0.3
1.3
0
DO
(mg/1)
1.2
4.2
0
BOD
(mg/1)
218
418
65
COD
(mg/1)
586
1620
76
38
-------
the terminal point of the interceptor, the wet well at the Lake Charles Lift
Station. The sampling points (manholes) are indicated in Figure 8.
Due to the sulfide corrosion in gravity sewers previsously described on
page 21, there were significant debris and sludge deposits in the invert of
the interceptor. Consequently, it was very difficult to obtain character-
istic samples of the flowing sewage without disturbing these solids.
During the low flow periods, sampling was not possible.
The data, as shown in Table 4, indicate that the high sulfide levels
generated in the force mains are reduced as the sewage moves from the
junction box at the Houston-Lakeshore Station to the Lake Charles Lift
Station. The reduction is due to the evolution of hydrogen sulfide gas
which is evidenced by the corrosion found in the line.
For any condition of flow less than one-half full, the sulfide generation
increases as the flow decreases. There were many periods observed in which
the flow was less than one-half full. However, because of the release of
gas at the points of turbulence further buildup of sulfides in the sewage
did not occur.
System Design
The installation of aeration equipment to oxidize the sulfides in the
junction box, would have been the most desirable approach for several reasons-
First, all three flows could have been treated assuring that the sewage enter-
ing the interceptor would be at an acceptable sulfide level; second, control
at a single point would have meant equipment installation at one location in
lieu of two or three; and lastly, the economics, capital costs, maintenance
and operational costs, etc., of one control point would have been more favor-
able. However, the design of the junction box was such that major renovation
would be required to allow such an installation.
Since the Houston-Lakeshore Station was not considered a sulfide generator,
the system sulfide control measures would have to be provided at the two
pump stations, the principle sulfide contributors. Further, consideration of
flows from the two pump stations indicated that the major amount of excess
oxygen would have to be added at the Railroad-Thomas Boulevard Station. The
flow from this station is approximately ten fold greater than the Grannis
Station. Control at the Grannis Avenue Station would be primarily aimed at
preventing sulfide buildup in the force main, with the maintenance of a
dissolved oxygen residual being secondary. By eliminating the majority of
the sulfides from entering the Lakeshore Intercepter and increasing the
residual dissolved oxygen of the flows, it was felt that the surface aeration
in the sewer would be adequate to oxidize additional sulfides generated in
the interceptor. Ideally, the total oxygen supplied would be sufficient to
actually retard sulfide generation.
Grannis Avenue Pump Station
The proximity of houses at this station required that noise be kept at a
39
-------
Table 4
SEWAGE CHARACTERISTICS
Lakeshore Interceptor
[Test Period June 27 - July 31,1969]
Sampling Point
Temp. pH
Parameters *
Total Sulfides Dissolved Sulfides
(mg/1) (mg/1)
DO BOD
(mg/1) (mg/1)
Lakeshore Blvd.
& Waco Ave.
28.5 7.4
1.9
1.5
trace 111
Lakeshore Blvd. &
Stillwell Blvd.
28.5 7.1
1.7
1.4
0
138
Lake Charles
Lift Station
29
6.6
1.9
1.1
0
184
* Weighted Average Values
-------
minimum. Secondly, the dry pit configuration would not permit the in-
stallation of equipment inside. The force main diameter is; 8 inches and
length is 3150 feet. Pumping capacity during dry weather is 600 gpm.
pure oxygen was the sulfide control measure used at this station. The
oxygen equipment was Installed adjacent to the pump station. The oxygen
equipment and the diffuser arrangement installed for oxygen entrainment
are shown in Figures 4 and 5. Details of this installation are shown in
Figure 11.
After a period of operational experience, the installation was modified.
The force main was tapped downstream from the dlffusers and a four inch
diameter recirculation line was installed to permit oxygenated sewage to
be returned to the wet well. This was done to control odors and corrosion
in the wet well.
Operation and Data Analysis
There were no taps provided for sampling directly from the force main and
samples of the discharge had to be taken at the junction box which also
received the discharge from the two other stations. These two stations
could be turned off for only short periods of time as their flow was signif-
icantly greater than the Grannis Station. During the pumping cycles of the
two stations it was virtually impossible to differentiate flow from the
Grannis Avenue Force Main. In addition to these problems associated with
sewage flows, there was an objective to maintain as high a level of D.O.
as possible at the sacrifice of optimization of the system.
The data collected for various oxygen feed rates are provided in Table 5
One concluding factor of this data is that the force main served as a sulfide
generator and this generation can be controlled by injecting pure oxygen.
For those oxygen feed rates where data were obtainable, the control of sulfldes
was accomplished and a residual dissolved oxygen maintained. It appears that
the same degree of control would be possible at a lower feed rate.
Railroad Avenue & Thomas Boulevard Pump Station
The location of the station provided more flexibility in the selection of
methods for sulfide control. This factor coupled with the length of the
force main and its sulfide generation history provide a good opportunity to
compare two methods of sulfide control by oxygen on the same system. The
injection of pure oxygen was first studied followed by an evaluation of
air injection. Details of this installation are provided in Figure 12. The
force main diameter is 16 inches and the length is 3850 feet. The pump
station capacity during dry weather flow is 1200 gpm.
Either pure oxygen or air could be injected in the sewage through the
diffuser system designed for the project (Figures 4 and 5). This station
required six dlffusers, in lieu of three installed at other locations, to
facilitate both oxygen and air injection. This permitted the change of
equipment, i.e. from pure oxygen to air,with only minor modifications.
41
-------
Grannis Ave.
Proctor Street
Harry Danbo Ave.
171 Gravity Sewer
ill
I I
Wet Well
Manway
DRY PIT
Force Main
Expanded Section
with Diffusers
(see Fig. 4 & 5)
\
Note: not to scale
Chain Link
Fence
X
Converter
Liquid Oxygen
Storage
Figure 11. Grannis Ave. Pump Station
42
-------
Table 5
OPTIMIZATION OF OXYGEN INJECTION
Grannis Avenue Wet Well - Force Main
[Test Period June 23 - Sept. 9,1969]
Sampling Point
Parameter
Wet Well
-ps.
to
Sulfides
(mg/1)
Total
Dissolved
Dissolved Oxygen
(mg/1)
Biochemical Oxygen
Demand (mg/1)
Chemical Oxygen
Demand (mg/1)
Ave.**
Max.
Min.
2.3
5.0
0.6
1.9
3.4
0.5
0.05
0.47
0
266
402
137
529
826
296
02 =0cfm
6.4
11.7
2.4
4.6
9.0
1.6
0.06
0.44
0
256
346
174
538
815
401
Force Main Discharge
02 = 5cfm
0.9
2.2
0.3
0.5
1.9
0.2
4.9
8.2
2.4
313
401
240
541
694
386
02 = 6cfm
0.5
2.1
trace
0.3
1.4
0.0
6.5
11.7
2.8
336
342
318
725
970
553
7cfm
0.6
0.7
0.5
0.3
0.3
0.2
4.9
6.9
3.0
457
581
333
687
787
588
* 02 (Oxygen) Injection Rate into Force Main
** Weighted average
-------
•a
2
'3
03
Diffuser Installatio
Force Mi
Oxygen Feed Line
OxygenTrailerLocation
Blower
Manway
Chainlink Fence
Thomas Blvd.
Figure 12. Railroad Pump Station
44
-------
The oxygen feed system was equipped with a rotameter that would permit flow
variation from zero to 14 cfm. The air compressor was installed without
flow measuring equipment which presented some problems in optimization.
Variation in air feed was achieved by varying the amount of waste air.
This provided a means of varying air flow. However, calculation of accurate
ainwater ratios was not possible. A rotameter was installed at a later
date and more accurate air feed rate data were obtained.
The installation was modified during the study in an effort to control the
sulfides in the wet well. A recirculation line downstream of the diffuser
returns flow to the last manhole on the gravity line prior to entering the
wet well. The return flow, high in dissolved oxygen content, is mixed with
the incoming sewage, which contains sulfides except during periods of high
infiltration.
Oxygen Injection
Oxygen was injected in the force main from June until September, 1969.
During this period, the oxygen feed rate was varied to determine the op-
timum rate for sulfide control and residual dissolved oxygen. After an
oxygen feed rate was set, the station was permitted to operate a minimum
of 24 hours to allow the system to adjust. Longer periods between changes
in oxygen feed rate and sampling appeared to have little, if any, effect
on test results.
The oxygen feed rates at the station were varied from zero to six cfm.
Data at one cfm were not obtainable as the rotameter would not stabilize
at that rate. The feed rates used would represent an oxygen to water
volume ratio of 1.24 to 3.72 percent on an oxygen application of 14 to
43 mg/1. The design of the system did not permit the evaluation of head
losses. However based upon pump cycling times, the injection of oxygen
did not appear to have any adverse effect on the hydraulics of the system.
The data collected during the optimization study are presented in Table 6.
For each parameter listed, the average value of all samples, the maximum
value and the minimum observed values are recorded for each oxygen feed
rate. The Table includes data for the wet well and force main discharge.
The data for total sulfides and dissolved oxygen are plotted in Figure 13.
The effect of dissolved oxygen on sulfide levels is clearly shown by the
plot of the data. There are several conditions indicated by the plot of
these data that require additional comment. First, although dissolved
sulfides were completely oxidized at all oxygen feed rates studied, it was
not possible to reduce total sulfides to zero. Sulfides, in the form of
metallic sulfides, would appear as total sulfides, but are not dissolved
sulfides. In the insoluble metallic sulfide form, they are not involved
in the undesirable reactions associated with dissolved sulfides. This
clearly points out the necessity of measuring both dissolved and total sul-
fides. The temperature during the test period was near the maximum observed
for the sewage. This high temperature increased the oxygen demand and
45
-------
Table 6
OPTIMIZATION OF OXYGEN INJECTION
Railroad Ave. - Thomas Blvd. Pump Station - Force Main
[Test Period: June 23 - September 9,1969]
Parameter
Oxygen Injection Rates (cfm)
3.0 4.0 4.5
5.0
6.0
Temperature (°C)
pH
Total Sulfides
(mg/1)
Dissolved Sulfides
(mg/1)
Dissolved Oxygen
(mg/1)
Biochemical Oxygen
Demand (mg/1)
Chemical Oxygen
Demand (mg/1)
*WW - Wet Well, D - Force Main Discharge
Ave. 29
Max. 29
Min. 28
29
29
28
7.0
7.1
6.9
7.1
7.1
7.0
0.5
1.8
0.3
1.2
2.1
0.9
0.4
1.1
0.2
1.1
2.1
0.3
-
-
-
-
-
-
203
372
102
282
350
170
487
602
217
527
578
467
30
31
29
30
31
29
7.2
7.2
7.1
7.1
7.2
6.9
1.5
2.1
1.0
0.1
0.3
0
0.9
1.4
0.6
0
0.2
0
0.4
0.4
0.4
1.1
3.2
0
269
332
215
252
353
209
417
527
278
412
604
282
30
31
30
31
31
30
7.1
7.1
7.0
7.0
7.2
6.9
1.7
2.1
1.3
0.1
0.2
trace
0.8
0.9
0
0
trace
0
-
—
-
2.1
3.8
0.8
264
310
232
272
302
250
428
508
381
441
627
353
30
30.5
29
30
31
28
7.0
7.2
6.6
7.0
7.5
6.6
1.0
1.8
1.0
0.2
2.5
0
0.7
1.6
0.1
0.1
2.0
0
0.6
0.6
0.6
3.5
12.0
0
202
250
67
189
343
55
388
480
126
382
712
59
30
31
30
30
31
29
7.0
7.0
6.7
7.1
7.3
6.8
0.8
0.9
0.3
0.2
1.3
0
0.5
0.6
0.3
0
1.3
0
_
_
-
_
-
-
173
337
90
189
342
49
480
594
408
480
608
283
30
31
29
31
33
29
6.9
7.2
6.8
6.9
7.2
6.5
1.9
3.3
0.6
0.1
0.3
0
1.3
2.1
0.4
0
0.2
0
_
_
-
2.0
3.2
0.6
180
270
30
231
510
30
404
557
148
437
895
138
30
32
29
30
33
30
6.7
7.3
5.9
6.8
7.3
5.6
2.0
3.0
0.5
0.1
0.2
0
1.2
2.0
0.3
0
0
0
_
_
-
2.3
3.2
1.0
326
436
174
312
508
174
740
1680
254
597
2070
110
46
-------
Wet Well
& & Force Main Discharge
Note: Average Values
I1
G
I
73
234
Gaseous Oxygen Injection Rate (cfm)
12
0- - -0 Maximum
Q - (3 Average
& Minimum
BA
s
K,
Note: Samples taken at Force
Main Discharge
Gaseous Oxygen Injection Rate (cfm)
Figure 13. Total Sulfide and Dissolved Oxygen Levels During
Oxygen Injection Optimization Study - Railroad
Ave.- Thomas Blvd. Pump Station
47
-------
sulfide generating potential of the sewage. The ability to control sul-
fides under the most severe conditions meant that control could be effectu-
ated under all other conditions observed.
The injection of pure oxygen into a liquid stream should allow almost
any level of saturation or super-saturation to be attained, and the mag-
nitude of dissolved oxygen in the force main discharge increased with
increased feed rates; however saturation values were equalled or exceeded
for only one oxygen feed rate during the study period. This was for only
one individual sample and not an average condition. It should also be
pointed out that the highest average residual dissolved oxygen level was
also measured at this rate and it represented only 46 percent of saturation. How-
ever, oxygen data at this point cannot be considered as an optimal value, because
other parameters indicated a much weaker sewage during the test period.
The optimum feed injection rate for dissolved oxygen residual was four cfm,
an oxygen:water ratio of 2.48 percent. Observations of the force main
discharge provides in part an answer to this condition. At lower oxygen
feed rates, the discharge from the force main was smooth and undisturbed.
At the higher feed rates, the flow was highly turbulent. The turbulence
was caused by the release of large air (oxygen) bubbles. This would imply
that the oxygen either degases or collects into bubbles after being
initially dispersed and failing to dissolve. After bubbles form at the
crown, they are moved downstream where they are released to the atmos-
phere at the discharge point.
BOD and COD tests were performed in conjunction with the optimization study.
As seen in Table 6, the data were erratic and inconclusive.
Air Injection
Air injection at the Railroad Ave.-Thomas Blvd. Pump Station began in
September, 1969 and has operated continuously until the present time.
Optimization studies began September, 1969 and continued to August, 1970. The
air feed was varied from zero to 100 cfm. At the completion of each series of
tests at a fixed air injection rate, the feed rate was changed and the system
permitted to adjust before conducting additional tests.
The test data obtained for the selected parameters are given in Table 7.
The two prime parameters, total sulfides and dissolved oxygen, are plotted
in Figure 14. Based on the sulfide plot, it would appear that the optimum
feed would lie between 36 and 60 cfm for the 16 inch diameter force main.
This would represent an air:water ratio of 17,39 to 37.50 percent. The
data also indicates a possible second optimum point to occur at higher
feed rates. However, this should be viewed with caution. At the air feed
of 66 cfm, the BOD was almost twice the value as that at 60 cfm, indicating
a higher potential for sulfide generation during the test period. The data
obtained for dissolved oxygen exhibited changes that corresponded in gen-
eral to the changes in sulfides. Dissolved oxygen residuals were high
when sulfide levels were low and low when sulfide levels were high.
48
-------
Table 7. OPTIMIZATION OF AIR INJECTION
Railroad Ave.-Thomas Blvd. Pump Station - Force Main
[Test Period Sept. 25,1969-Aug. 19,1970]
PARAMETER
Temperature
pH
Total Sulfides
(mg/1)
Dissolved Sulfides
(mg/1)
Dissolved Oxygen
(mg/1)
Biochemical
Oxygen Demand
(mg/1)
Chemical Oxygen
Demand (mg/1)
Sampling
Point
WW*
D
WW
D
WW
D
WW
D
WW
D
WW
D
WW
D
0
Ave. 28
Max. 29
Min. 27
26
26
26
7.0
7.0
7.0
H
7.0
1.4
1.9
1.2
2.3
3.0
1.5
1.1
1.5
0.7
2.0
3.0
1.3
0
0
0
0
0
0
269
278
253
251
291
186
472
496
445
500
511
480
12
30
31
27
30
30
29
6.9
6.9
7.2
6.7
1.4
2.0
0.6
0.7
2.5
0.1
1.2
2.0
0.5
0.5
2.0
0
0
0
0
0.2
1.0
0
116
300
80
136
350
90
543
726
449
600
722
464
24
33
Air Injection Rate (cfm)
36 48
60
66
100**
100
§9o
29
28
29
27.5
6.7
6.9
6.6
6.9
7.0
6.8
1.7
2.4
1.4
§j
A
0.4
1.5
2.2
1.2
1.6
3.0
0
0
0
0
0
0.2
0
185
252
156
183
234
150
449
625
223
493
610
402
27
27
27
26
26
26
6.8
O.o
6.7
6.8
O.o
O.o
1.4
2.2
0.9
2.7
5.0
1.8
1.2
2.2
0.9
2.3
3.5
1.8
0
0
0
0
0
0
294
343
269
251
269
242
446
463
438
503
524
491
30
31
26
29
30
28.5
6.7
7.0
6.4
?:i
6.3
1.4
2.4
0.4
0.6
2.4
0
1.2
2.2
0.3
0.5
1.9
0
0
0
0
0.4
2.0
0
133
210
102
148
276
90
553
890
372
fie
435
30
30
29
30
31
29
6.8
6 9
6.7
6.9
u
1.4
2.0
0.8
0.3
1.6
0
1.2
1.8
0.7
0.2
1.0
0
0
0
0
0.7
1.8
0
181
310
95
171
228
75
737
1288
494
192
1234
419
27
27
27
26
28
26
6.8
O.O
O.o
6.9
7.0
6.8
2.0
2.7
1.5
1.5
2.1
1.2
1.8
2.0
1.4
1.0
1.7
0.6
0
0
0
0
0
0
303
329
260
280
287
265
485
542
445
539
627
472
29
29
29
27
27
27
6.5
6 6
&'A
fc?
6.5
2.0
2.0
1.5
0.5
0.6
trace
1.6
1.6
1.6
0.3
0.6
trace
0.9
0.9
0.9
2.4
2.8
2.0
227
280
180
173
260
110
435
458
415
502
481
24
31
16
24
21
16
7.1
7.5
6.7
7.3
9.6
6.6
1.0
1.8
0
0.1
1.4
0
0.8
1.8
0
0
0.2
0
0.4
2.2
0
2.1
6.0
0
261
466
132
271
495
120
522
1122
314
610
1000
282
* WW - Wet Well, D - Force Main Discharge
** Aerated Sewage recirculated back into wet well
-------
3 r-
O—Q Wet Well
A- -»& Force Main Discharge
Note: Average Values
10
80
90
100
Air Injection Rate (cfm)
Force Main Discharge
Q—0 Ave.
O--Q Max.
w>
20 30 40 50 60 70 80
Air Injection Rate (cfm)
90 100
Figure 14. Total Sulfide and Dissolved Oxygen Levels during Air Injection Optimization
Study - Railroad Ave.-Thomas Blvd. Pump Station
50
-------
Consideration of optimum air flow rates must include the .effects on the
hydraulics of the system. This was not a consideration in the original
project and no provisions were made for accurate flow measurements or
evaluation of head losses for the various air rates. Attempts were made
to predict pumping rates from wet well levels. However, the large
variations in the levels and their failure to follow a consistent pattern
made it necessary to abandon this method. Considering the failure to
adequately evaluate the system hydraulics, the use of air flow rates
should preempt the use of air:water ratios.
The discharge of the force main at the junction box cycled between
smooth flow and highly turbulent flow. The periods of high turbulence
were characterized by splashing and foaming accompanied by the sound of
escaping air. As the air flow rate was increased, the magnitude and frequen-
cy of turbulence increased. This would indicate that the air collects at the
crown of the pipe and is carried downstream as bubbles. An air flow rate
where there was complete separation of air and sewage did not occur.
Lakeshore Interceptor
The evaluation of changes in sulfides and dissolved oxygen in the gravity
portion of the Lakeshore System could not be correlated with specific air
or oxygen feed rates. There were several factors that contributed to this.
Foremost was the inability to measure flow rates and the lack of facilities
for continuous sampling.
The data collected from July, 1969 to February, 1970 were grouped according
to temperature. These data are shown in Table 8. The average sulffde levels
are plotted in Figure 15 for each temperature grouping. The average total
sulfide levels entering the gravity system for the selected time periods
could not be evaluated due to the system operation. Considering the pre-
viously reported data on sulfide levels from the three stations, it could
be assumed that the weighted average would have been low with periodic
slugs of higher concentration.
The plotted data indicated an increase in sulfide levels at each down-
stream sampling point and for all temperatures with only two exceptions noted.
As mentioned in the earlier discussion along this line, significant sludge
deposits were present. An analysis of this sludge revealed sulfide concen-
trations of 80 mg/1. Considering these facts it is very possible that the
sewage flowing over this material could leach sulfides from the debris as
it moves downstream. This continual leaching of the sulfides plus genera-
tion in the slime layer would react with residual oxygen or oxygen from
reaeration in the line downstream. Dissolved oxygen was found in only
trace amounts for individual samples, and never observed consistently
for any period of time.
STILLWELL SYSTEM
The system as defined for the study has one lift station and a long gravity
51
-------
TABLE 8
SEWAGE CHARACTERISTICS
Lakeshore Interceptor - Oxygen Injection at Both Grannis Avenue
and Railroad Ave. - Thomas Blvd. Pump Stations
Sampling Point Test Period
en
r\)
Lakeshore Drive
&
Waco Ave.
Lakeshore Drive
&
Stillwell Blvd.
Lake Charles
Lift Station
August 1969
September 1969
Oct.-Nov. 1969
Jan.-Feb. 1970
August 1969
September 1969
Oct.-Nov. 1969
December 1969 -
April 1970
August 1969
September 1969
Oct.-Nov. 1969
December 1969 -
February 1970
31.5
30.5
24.0
18.0
31.5
30.5
26.0
19.0
31.5
30.0
24.0
18.0
7.0
7.6
7.3
7.4
7.4
7.4
7.5
7.7
7.0
7.2
7.1
6.8
0.4
1.5
0.3
trace
1.8
3.4
2.5
0.6
2.5
2.6
1.3
0.8
PARAMETER *
Temp. pH Total Sulfides Dissolved Sulfides
(°C) (mg/1) (mg/1)
0.2
1.4
0.2
0
1.5
3.2
1.8
0.3
2.1
2.3
0.8
0.5
ed Oxygen
S/l)
0
0
0
0.3
0
0
0
BOD
(mg/1)
292
411
246
-
356
366
307
trace
0
0
0
187
313
371
197
203
* Average values
-------
Note: Abscissa not to scale
I
£
en
I
Lakeshore Dr.
& Waco Ave.
Lakeshore Dr.
&StillwellBlvd.
Lake Charles
Life Station
Figure 15. Sulfide levels, Lakeshore Interceptor, by temperature
grouping
53
-------
line. The gravity system upstream from the lift station serves a large
area in which the gravity lines are very long with flat slopes. The lift
station, identified as the 19th Street-Still well Boulevard (also Alligator
Bayou), has a dry weather flow capacity of 2400 gpm and a 16 inch diameter
force main approximately 600 feet in length. The force main discharges
into a 24 inch diameter gravity sewer which transports the sewage to the
Lake Charles Lift Station. The gravity sewer changes to 30 inch diameter
pipe 2700 feet upstream of the wet well. The lift station and gravity line
were constructed in 1951. Details of the system are shown in Figure 16.
Strong odors have always been associated with the wet well of this lift
station, however, complaints have been minimized due to its location. The
most persistent area of complaints has been in the vicinity of the manhole
where the force main discharges. Sections of the downstream gravity line
have failed due to deterioration. The pipe that has not been replaced was
found to be in critical condition with failure possible at any time.
Sulfide Levels
Data collection was started in June, 1969 to evaluate system sulfide levels.
The amount of base data collected was limited as this was one of the first
sites to receive oxygen injection. It was necessary, because of operating
conditions, to change sampling locations during the study to obtain samples
unaffected by oxygen injection. The amount of sulfide data on untreated
sewage at the lift station 1s more complete than for the gravity system.
Lift Station - Wet Well
The sampling points are located in Figure 16. Initially, all samples were
taken from the wet well for evaluation of sewage characteristics. After
recirculation of treated sewage was started, 1t was necessary to sample
the gravity line entering the wet well to ascertain characteristics of the
untreated sewage. The data are shown 1n Table 9 for sewage characteristics
from manholes Immediately upstream of the station or from the wet well.
Additionally, the sulfide levels at the point of discharge from the force
main are shown.
The sulfide levels entering the wet well and in the wet well are shown to
be near the same-level as the force main discharge. The major problem
of the station was the release of hydrogen sulfide gas due to turbulence
in the wet well and at the discharge manhole. The short force main did not
serve as a major sulfide generator.
Gravity Line
The gravity line was observed to have large quanities of debris deposited
in the pipe. This hampered sampling of the line, particularily during the
low flow periods. Data collected for the gravity system are shown in Table
10. The sulfide level of the sewage from the force main discharge is
shown to Increase downstream with the exception of the last station. There
are changes 1n direction which create turbulence prior to this sampling
54
-------
LEGEND
D Pump Station* P.O. Pump Capacity
— Gravity Line S.A. Service Area**
Force Main 0 Diameter
O Manhole* L Length
O Lift Station*
* Sampling Point
* * Indirect Service Area, areas whose sewage has been
pumped at least onee prior to entering station, is
shown in parenthesis
19 St.-Stillwell Blvd.
(Alligator Bayou)
Lift Sfotinn
P.C. -2 @ 2400 gpm
each
S.A. = 1075 acres
24* 0, L=5320'
Note: not to scale
16 "0 Concrete Pipe
L=600X
Lake Charles Ave.
Lift Station
P.C. -3 @ 1500 gpm
1 @ 3000 gpm
S.A.=636 (2253) acres
Figure 16. Stillwell System
55
-------
Table 9
SEWAGE CHARACTERISTICS
19th Street - Stillwell Blvd. Lift Station - Force Main
PARAMETER *
en
en
Sampling Point
Manhole No. 1
Manhole No. 2
Wet Well
19th Street Man-
hole (Force Main
Discharge)
Test Period
Jan. - March, 1970
Feb.-March, 1970
June-July, 1969
June-July, 1969
Temp.
18.9
19.1
29.4
29.9
PH
6.8
6.8
6.9
6.8
Total Sulfides
(mg/1)
2.12
0.84
2.64
2.59
Dissolved Sulfides
(mg/1)
1.82
0.54
2.21
1.97
BOD
(mg/1)
168
129
260
176
COD
(mg/1)
481
284
486
412
-------
Table 10
SEWAGE CHARACTERISTICS
Stillwell System
[Test Period: June 24 - July 7,1969]
Sampling Point
PARAMETER*
Temp. pH Total Sulfides Dissolved Sulfides
(°C) (mg/1) (mg/1)
Dissolved Oxygen
(mg/1)
BOD COD
(mg/I) (mg/1)
19th Street Lift Station
Wet Well 29.5
19th Street Force
Main Discharge
30.0
Gillham Circle Manhole
No. 1 30.0
Gillham Circle Manhole
No. 2 28.0
Stillwell Blvd. & 5th
Avenue 27.5
Vickburg Avenue &
5th Avenue 28.0
7.0
6.8
-
7.1
7.2
6.5
2.6
2.6
1.4
3.4
4.2
2.4
2.2
2.0
0.6
2.8
2.9
1.4
0
0
-
0
0
0
260
176
-
160
160
143
486
412
-
464
427
378
* Average Values
-------
point.. This would permit the release of hydrogen sulfide thereby lowering
the sulfide level. The pipe in this area has been severely damaged indi-
cating the release of gases for a long period.
The increase in sulfide levels downstream would indicate that the gravity
line serves as a sulfide generator. The sludge was sampled to determine
if this material would have affected the test results if some of it was
inadvertently included in the sample. Dewatered samples of the debris
were placed in distilled water and the supernatent tested for sulfides.
The sludge was found to contain sulfides as high as 80 mg/1. Thus, the
increases in sulfides shown could have been influenced significantly if
samples had included this material.
System Design & Operation
The high sulfide level entering the wet well of the lift station was the
major problem at this site and not generation through the short force main.
The downstream gravity line appeared to be a major generator of sulfides;
however, this should not be considered conclusive due to sampling problems
encountered with sludge deposits. These two conditions established criteria
for control at this site: oxidation of existing sulfides and maintenance of re-
sidual dissolved oxygen in the sewage. The length of the force main was consid-
ered to be inadequate for air injection. However, the injection of pure oxygen
was to be employed for the interim period prior to fabrication of a pressure
tank, the preferred technique for sulfide control with air at this location.
r
Oxygen tanks (truck trailers) were moved to the site and necessary piping
installed. Diffuser tubes in an expanded pipe section as shown in Figures
4 and 5 were to be used for gas entrainment. A solenoid valve was used in
conjunction with a timer to control the oxygen feed. The valve was set to
open 10 seconds after the pump started to assure that oxygen would be in-
jected into a liquid stream. The oxygen injection system was operated
and tested from June, 1969 until September, 1969. The data collected for
this test period are shown in Table 11.
The data for sulfides and oxygen at the various oxygen feed rates are plotted
in Figure 17. A slight reduction in sulfides was obtained but they were not
reduced to acceptable levels for the oxygen feed rates tested. The oxygen
transfer was equally disappointing for the system. There was only one
oxygen feed rate at which any significant amount of dissolved oxygen was
found in the force main discharge. This would indicate that the optimum
would occur at a feed rate in excess of the 10 cfm tested. Interpretation
of this data at the higher feed rate should be viewed with caution, parti-
cularity in view of the failure to oxidize any significant amount of sulfides.
Observations of the force main discharge during the testing offer an ex-
planation for the failure of the system to achieve a higher oxygen transfer.
At all oxygen feed rates the force main discharge was characterized by a
high degree of turbulence and foaming, the magnitude of which increased with
increased feed rates. This was not observed when there was no oxygen feed.
The flow could be described as a liquid carrying large bubbles of oxygen down-
58
-------
Table 11
OPTIMIZATION OF OXYGEN INJECTION
19th Street Lift Station - Force Main
[Test Period June 24 - Sept. 12,1969]
PARAMETER
Temperature (° C)
pH
Total Sulfides
(mg/1)
Dissolved Sulfides
(mg/1)
Dissolved Oxygen
(mg/1)
Biochemical Oxygen
(mg/1)
Chemical Oxygen
Demand (mg/1)
Sampling
Point
Ave.
WW Max.
Min.
D
WW
D
WW
D
WW
D
WW
D
WW
D
WW
D
0
30
32
28
30
31
27
7.0
7.2
6.9
6.9
7.1
6.4
1.6
2.0
1.0
2.5
2.6
0.8
1.6
2.0
0.8
2.0
2.2
0.2
0
0
0
0
0
0
177
186
164
176
200
141
415
522
214
412
557
231
4.0
29
29
29
32
33
29
7.2
7.2
7.2
7.0
7.2
6.9
2.2
2.2
2.2
2.0
3.4
0.4
1.8
1.8
1.8
1.4
3.3
0.4
_
_
-
0.2
0.2
0
_
-
-
269
385
192
557
557
557
429
605
207
Oxygen Injection Rate (cfm)
6.0 7.75
30
31
29
31
34
28
6.9
7.0
6.8
7.0
7.2
6.8
3.8
5.0
2.0
3.1
3.8
0.9
3.4
4.8
2.0
2.3
3.7
0.6
0.3
1.8
0
388
500
101
282
445
85
440
846
300
454
636
223
29
31
24
29
31
28
7.1
7.1
7.1
6.9
7.0
6.8
1.7
2.4
0.2
1.6
2.9
0
1.6
2.2
0.2
1.3
2.7
0
188
323
156
130
182
60
604
897
251
445
661
234
9.75
30
30
30
29
29
29
7.1
7.1
7.1
7.1
7.1
7.1
2.0
2.0
2.0
1.7
1.7
1.7
2.0
2.0
2.0
0.9
0.9
0.9
194
194
194
160
160
160
846
846
846
697
697
697
10.0
30
32
29
30
32
28
6.9
7.2
7.2
6.9
3.2
4.1
2.2
2.1
5.7
0.7
2.4
3.3
1.5
1.3
2.6
0.5
1.4
6.1
0
681
1590
334
508
676
427
59
-------
0 0 Wet Well
& Force Main Discharge
Note: Average Values
6 3
(A
I
s 2
3
_L
_L
J_
34 567
Gaseous Oxygen Injection Rate (mg/1)
10
OB
1
i
0 Q Average
Q- — -Q Maximum
Note: a) Samples taken at force main discharge
b) Minimum value (for all rates) = 0
34567
Gaseous Oxygen Injection Rate (mg/1)
10
Figure 17. Total Sulfide and Dissolved Oxygen Levels During Gaseous Oxygen
Injection Optimization Study - 19th Street - Stillwell Blvd. Lift Station
60
-------
stream with the bubbles erupting at the point of discharge. Samples taken
at the force main discharge and placed in glass containers had the appear-
ance of boiling water for a few minutes due to the degassing of the entrained
oxygen bubbles and not the evolution of dissolved oxygen. Testing for
sulfides and dissolved oxygen was performed after degassing was completed.
For practical purposes, a two phase (liquid - gas) flow regime existed which
separated immediately when a free surface was created in the gravity line.
The result, as indicated by the data, was to add oxygen to the sewer
atmosphere and not increase the dissolved oxygen content of the sewage or
oxidize sulfides.
The installation of the pressure tank was completed and placed in operation
during November, 1969. The original installation called for a variable
detention time of 17 to 30 minutes and operating pressures of from one to
two atmospheres. Air to water ratios could be varied from zero to 35 per-
cent. Details of the pressure tank are shown in Figure 6. The air was
injected through diffusers installed perpendicular to the tank wall at two
levels and equally spaced around the tank periphery.
The pressure tank was designed to handle the low flow of the station under
normal condition, i.e. no excessive infiltration, at a detention time of
approximately 20 minutes. During the peak hourly flows, the pumps at the
station would operate, by-passing the pressure tank and discharging directly
into the gravity line. At the peak hourly flow, approximately 50 percent
of the flow through the station is bypassed. This condition, based upon
pump time evaluations, would occur approximately nine periods per day. The
total sewage bypassed would represent approximately 30 percent of the total
flow through the station.
Sampling began in November, 1969 with the start-up of the pressure tank and
continued until February, 1970. During this initial start-up period for the
equipment, numerous problems were encountered which prohibited a continuous
sampling program from being carried out. Most of the problems experienced
were mechanical problems with equipment and not performance problems with
one exception. There was a significant decrease in the quality of the
effluent from the tank. The dissolved oxygen level began to decrease and
the sulfide content began to increase. The tank was inspected and a solids
buildup was found in the bottom of the tank. A drain line was installed
from the bottom of the tank that would permit either continuous or inter-
mittent draining of the tank back to the wet well. Continuous recirculation
that returned an oxygen enriched stream to the wet well appeared to offer
the best operational characteristics.
During March, 1970, a twenty-hour sampling program was conducted to cover
the flow ranges and variation in sewage characteristics. The data collected
during this period are shown in Table 12. The average sulfide and dissolved
oxygen levels are presented in Figure 18. A reduction in total sulfides
of 94 percent is shown across the system; however the effect of recirculation
is significant with a reduction of 74 percent demonstrated. The important
factor is that both total and dissolved sulfides in the wet well were below
the recognized level for deterioration due to sulfides. The dissolved
oxygen leaving the pressure tank was 67 percent of saturation while the
force main discharge was 51 percent of saturation. Thus, a loss of dissolved
61
-------
Table 12
SEWAGE CHARACTERISTICS
Pressure Tank Test Program
19 Street - Stillwell Blvd. Lift Station - Force Main
20-Hour Sampling Program
PARAMETER
Composite
Temperature
( C)
Composite pH
Average
Total Sulfides
(mg/1)
Average
Dissolved Sulfides
(mg/1)
Average
Dissolved Oxygen
(mg/1)
Composite BOD
(unfiltered)
(mg/1)
Composite BOD
(filtered)
(mg/1)
Composite COD
(mg/1)
Sampling
Period
1*
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Composite Suspended 9
Solids (mg/1)
3
4
Manhole at
New Orleans
19
19
19
19
6.7
6.8
6.8
6.7
2.5
1.9
2.8
1.9
2.4
1.5
2.4
1.9
0
0
0
0
270
195
165
130
205
135
125
120
613
578
362
392
167
07
u 1
37
130
Sampling Point
19th Street L.S. Pressure Tank
Wet Well Effluent Line
20
19
19
19
6.9
6.9
6.9
6.8
0.8
0.7
0.5
0.4
0.6
0.6
0.4
0.3
1.0
1.8
2.8
2.7
270
185
135
140
225
160
120
95
513
528
419
426
220
110
67
157
20
19
19
19
6.9
7.9
7.2
6.8
0.4
0.4
0.3
0.1
0.3
0.3
0.2
0.1
6.4
5.7
6.4
6.7
300
95
150
135
210
105
125
100
498
410
370
355
180
147
50
133
19th St. Force
Main Discharge
19
19
19
18
6.8
6.8
6.9
7.0
0
0.4
0.1
0
0
0
0
0
4.5
4.2
5.3
5.2
325
130
145
115
225
95
115
85
632
494
400
373
280
123
67
300
* 1 - March 26,1970, 1:00-5:00 p.m.
2 - March 26,1970, 6:00-10:00 p.m.
3 - March 27,1970, 12:00-4:00 a.m.
4 - March 27,1970, 6:00-10:00 a.m.
62
-------
BJ>
£
c
QJ
T3
I 2
Note: Abscissa not to scale
Manhole at
New Orleans
19th Street L.S.
Wet Well
Pressure Tank
Effluent Line
19th Street Force
Main Discharge
Figure 18. Average Total Sulflde and Dissolved Oxygen Levels during 20-hour sampling
program evaluating pressure tank - 19th Street - Stillwell Blvd. Lift Station
63
-------
oxygen occurred in the force main and at the discharge manhole. Perhaps
the most important aspect of the twenty hour sampling program is the high
dissolved oxygen level found in the wet well.
The initial period of testing indicated a reduction in BOD and this period
of concentrated testing gave an excellent opportunity to evaluate changes.
A reduction in BOD would indicate the development of a biological floe and
for this reason a biochemical oxygen demand test was run on filtered and
unfiltered samples. The unfiltered samples for all sample locations
averaged 28 percent greater than filtered samples. A reduction was shown
in the BOD across the system for both filtered and unfiltered samples.
Suspended solids at all locations increased over the raw solids indicating
the development of a biological floe. The maintenance of a residual dis-
solved oxygen level in the wet well could contribute significantly to this
floe development.
Sampling was continued at the installation from March, 1970 until November,
1970. The sampling during this period was conducted at various times of
the day. The sewage characteristics observed for the period are shown in
Table 13.
Sulfide levels were reduced by 90 percent to a concentration of 0.3 and
0.1 for total and dissolved sulfides respectively. The dissolved oxygen
level of the pressure tank effluent averaged 61 percent of saturation
dropping to 28 percent at the discharge manhole. The pressure tank demon-
strated a 16 percent reduction of the wet well influent BOD while the
force main discharge had only a 13 percent reduction. It is significant
to note that for the period, the COD of the wet well, pressure tank dis-
charge and force main discharge were essentially unchanged.
SMITH-YOUNG SYSTEM
The Smith-Young System consists of a single pump station that discharges
into a gravity sewer that connects with the Lakeshore Interceptor near
the Mainline Pump Station. Dry weather pumping capacity is 350 gpm. The
pump station serves 164 acres and the gravity sewer serves an additional
1800 acres between the pump station and the interceptor.
The force main, the longest in the Port Arthur Sewerage System, is 8 inches
in diameter and 5,427 feet in length. The gravity sewer is 12,600 feet
from the force main discharge to the Lakeshore Interceptor. The pipe
diameter increases from 15 inches to 30 inches in diameter. Details of
the system are shown in Figure 19. The profile of the force main is shown
in Figure 20. The changes in slope up to the point where the force main
goes under the drainage ditch proved to be a significant factor in the
system operation.
Sulfide Levels
Since the construction of the pump station in 1956, odor problems and
64
-------
Table 13
SEWAGE CHARACTERISTICS
Pressure Tank Test Program
19th Street - Stillwell Blvd. Lift Station - Force Main
[Test Period June 26 - Nov. 27,1970]
Sampling Point
Parameter
Temperature (°C)
PH
Total Sulfides
(mg/1)
Dissolved Sulfides
(mg/1)
Dissolved Oxygen
(mg/1)
Biochemical Oxygen
Demand (mg/1)
Chemical Oxygen
Demand (mg/1)
New Orleans man-
hole and manhole
at trailor
Ave. 23.0
Max. 29.0
Min. 18.5
6.8
7.0
6.6
4.3
7.4
1.1
4.1
6.9
0.8
0
0
0
209
474
100
423
651
107
19th Street L.S.
Wet Well
24
30
19
6.8
6.9
6.6
1.5
3.6
0.3
1.3
3.0
0.1
1.0
7.0
0
174
270
120
457
528
378
Pressure Tank
Effluent Line
24
30
18
7.0
7.2
6.6
0.4
1.0
0.1
0.2
0.5
0.1
5.2
7.0
2.4
175
300
80
440
660
355
19th Street
Force Main
Discharge
24
29
17
6.9
7.0
6.6
0.3
1.5
0
0.1
0.8
0
2.4
6.0
0.2
181
325
72
429
623
203
Note: A portion of the aerated sewage from the pressure tank was being recirculated back into the
wet well
65
-------
LEGEND
is
D Pump Station
— Gravity Line
-- Force Main
O Manhole*
9 Manhole
P.C. Pump Capcity
S.A. Service Area**
S Sampling Point
0 Diameter
L Length
Smith-Young Pump Station
P.C. -2 @ 350 gpm each
S.A. = 164 acres
I
I
I
I
I
8" 0,L=542?'
30/>0, L=3200/
* Sampling Points
* * Indirect service area, areas whose sewage has been
pumped at least once prior to entering station,
is shown in parenthesis
Note: not to scale
Figure 19. Smith-Young System
66
-------
1
106
105
104
103
102
§ 101
1001
99
98
97
I
1000 2000 3000 4000
Distance from Point of Force Main Discharge (feet)
Figure 20. Profile of Smith-Young Force Main
5000
6000
-------
deterioration have gradually intensified. The most severe odor problems
have occurred at the point where the force main discharges into the gravity
system (Sunken Court manhole). Large segments of the gravity system have
failed with the most recent in December, 1971. The failure required the
replacement of 800 feet of 15 inch diameter pipe.
Sewage characteristics were observed throughout the system from June until
September, 1969. Sampling stations were established at the wet well, the
force main discharge and points along the gravity line. The locations of
these sampling stations are shown in Figure 19.
Smith-Young Pump Station (39th Street)
The sewage characteristics found in the wet well were not unusual for domestic
sewage. Sulfide levels and BOD values were low. Extreme care was required
in sampling the wet well as a thick mat of grease and other materials was
found to be floating on the sewage. BOD values in excess of 800 mg/1 were
observed when this material was inadvertently picked up in the sample. The
presence of this mat of grease can be explained by the fact that most of
the houses in the subdivision have garbage grinders. It is also significant
to note that sewage temperatures during this period averaged 29.5°C. Sulfide
levels observed at the force main discharge were the highest observed for a
sustained period of sampling. The increase in sulfide levels was the most
dramatic and clearly establishes this as the principle sulfide generator of
the system. The average increase in total sulfides was 9.75 mg/1 and 9.0
mg/1 of dissolved sulfides. Based on the average hydrogen ion concentration,
approximately 40-50 percent of the sulfides were in the form of hydrogen
sulfide gas. Data for the wet well and force main discharge are included
in Table 14.
Gravity Line
The gravity line was sampled during the same period as the pump station.
The data collected at the three sampling stations are included in Table
14 and sulfide data are plotted in Figure 21.
The plot of sulfides indicates a significant decrease in sulfides from the
force main discharge to the downstream stations. Part of this decrease
could be attributable to dilution with fresh sewage, infiltration or a com-
bination of these. A second consideration would be the reduction in sulfides
by the evolution of hydrogen sulfide gas by degassing at points of turbulence.
Considering the history of odors and corrosion, the latter would appear to be
the most reasonable assumption. This is further reinforced by the average
hydrogen ion concentrations observed which establishes a relatively high
percent of sulfides to be in the form of hydrogen sulfide gas. Considering
the sulfide generation in the gravity line, which could not be determined
the changes would have been even more radical.
System Design and Operation
The selection of air or oxygen gas injection at this station had to take
several factors into consideration. The proximity of houses to the pump
68
-------
Table 14
SEWAGE CHARACTERISTICS
Smith Young System
[Test Period June 21 - Sept. 12,1969]
Sampling Point
Temp.
PH
vo
Total Sulfides
(mg/1)
Smith-Young
Pump Station
Wet Well
Smith-Young
Force Main
Discharge
Manhole behind
Thomas Jefferson
High School
Manhole at Intersec-
tion of Dry den Ave.
& Williams Street
Manhole at north-
east end of Lewis
Avenue
Ave. 29.5
Max. 31.0
Min. 27.5
29.1
30.0
27.5
28.1
29.0
27.5
29.2
30.0
28.5
29.3
32.0
28.0
6.8
7.0
6.4
6.9
7.1
6.8
7.0
7.0
6.9
7.1
7.5
7.0
7.1
7.2
6.9
0.9
1.8
0.4
10.7
14.0
3.0
3.2
4.1
2.2
2.7
4.0
1.6
0.7
1.3
0
PARAMETER
Dissolved Sulfides
(mg/1)
0.8
1.6
0.1
9.8
13.0
2.1
3.0
3.8
2.0
2.4
4.0
1.3
0.6
1.3
0
Dissolved Oxygen
(mg/1)
0
1.0
0
0.7
0
0
0
0
0
0
0
0
1.2
0
BOD
(mg/1)
184
190
165
266
531
140
155
201
89
342
625
218
283
563
117
COD
(mg/1)
876
1992
400
366
563
222
301
377
247
410
599
311
409
590
334
-------
Average
© -0 Maximum
& & Minimum
Note: Abscissa not to scale
Smith-Young
Pump Station
Wet Well
Smith-Young
Force Main
Discharge
Manhole behind
Thomas Jefferson
High School
Manhole at inter-
section of Dryden
Ave. & Williams St.
Manhole at
northeast end of
Lewis Ave.
Figure 21. Total Sulfide Levels in the Smith-Young System
-------
station imposed a noise constraint. The length of the line, coupled with
the depression at the drainage ditch, indicated a potential air locking
problem. Calculations indicated a velocity of from 2 to 3 fps, depending
on roughness characteristics. The final decision was to use oxygen gas
and to inject it without the use of diffusers. The oxygen was to be
injected at three points, one in the bottom of the pipe and one in each
of the bottom quadrants. The details of the original installation and
later modifications are shown in Figure 22.
The installation of the equipment was completed and oxygen injection was
started November 14, 1969. The initial oxygen feed rate of 10 cfm was
set and a continuous monitoring program was scheduled for 48 hours. The
principal goal was to see if the stripping of solids from the force main
would occur as had been reported in the literature. The data collection
was started and continued for approximately 24 hours. During this period,
the sulfides in the discharge were low and the dissolved oxygen of the
sewage was gradually increasing. The settleable solids at the discharge
point were very erratic.
During this sample period, the length of the pump cycle was steadily in-
creasing until a point was reached where the discharge was continuous. At
the point of discharge, the force main was flowing less than one-half full
and with a low velocity. The oxygen was turned off and a sample port on
the force main before the oxygen injection point was opened. Oxygen was dis-
charged from this line until sewage began to flow. The valve was closed
and the oxygen was again injected at a rate of 10 cfm. In approximately two
to four hours, the discharge was again severely restricted. After bleeding
the oxygen from the line the second time, the pumps were permitted to
operate without oxygen injection, and the pump cycle returned to normal.
The oxygen feed rate was then set at four cfm and in approximately six
hours, the previously described condition developed. The oxygen was once
again bled from the system and an oxygen feed rate of one cfm was found to
work without an undesirable effect on pumping rates. The data for this
period of sampling were discarded due to flow conditions being atypical.
There are two possible explanations for failure of the system to operate.
The most obvious one being that the depression in the force main resulted
in the formation of a block and trapped oxygen on the upstream side. The
second would be that due to the downward slope of the force main the oxygen
was trapped in the vicinity of the pump station, the highest point in that
section of pipe. Due to the ability to bleed off large volumes of oxygen
at the pump station it would infer that the latter was the case.
Further testing revealed that at an oxygen feed rate of one cfm the system
flow characteristics would not be seriously impeded. The system operated
from December, 1969 until March, 1970 under this condition. Some degree
of control was effectuated as the average total sulfides at the force main
discharge was held to 2.2 mg/1. Considering the average temperature of
18.5°C for the period, it was felt that this would not be adequate during
periods of elevated temperature. The data obtained during this period are
provided in Table 15.
71
-------
Drainage Ditch
^J
r\3
Note: Not to scale
•x x
X
<
d
Gravity
Line
f
Manway
DRY PIT
Converter
V
(~) Manway Liquid Oxygen
^~^ Storage
WET WELL
Spigot & Bleed-
off valve
Tin
x — -ii
i!
in
ill
"-^/ D/i
— ^ we
Gravity Line
^- Force
Main
lation
Line
Chain Link Fence
To Stadium Road (S.H. 347)
39th Street
To 9th Avenue
Figure 22. Smith-Young Pump Station
-------
Table 15
SEWAGE CHARACTERISTICS
Smith Young Pump Station - Force Main
[Test Period Dec. 13,1969 - March 6,1970]
Sampling Point
Temp.
pH
Wet Well
Force Main
Discharge
Ave. 17.6
Max. 23.0
Min. 12.0
18.5
20.0
13.0
6.8
7.1
5.4
6.9
7.2
6.5
1.2
2.6
0
2.2
5.0
0
PARAMETER
Total Sulfides Dissolved Sulfides
(mg/1) (mg/1)
1.0
1.7
0
1.7
4.4
0
Dissolved Oxygen BOD
(mg/1) (mg/1)
0.4
2.2
0
1.3
9.0
0
296
600
130
Note: O« (oxygen) injection rate of 1 cfm
-------
A decision was made to provide a recirculation line to the wet well and in-
ject oxygen into this line. Details are shown in Figure 22. The ability
to achieve a high level of dissolved oxygen in sewage as it left the station
was clearly demonstrated as the average value was 140 percent of saturation.
Sulfide control was not demonstrated as the sulfide level at the force main
discharge was greater than when the oxygen feed was directly into the line.
Further consideration of the data reveals that the sulfides were controlled
at a point approximately 3000 feet downstream from the pump and across the
depression. The sulfides were then generated in the remaining 2500 feet to
an undesirable level.
The ability to control sulfides and obtain a dissolved oxygen residual at
the mid-point of the force main, a distance of approximately 2700 feet, was
congruous with other locations. This indicated that the problem was one of
system hydraulics and an excessive oxygen demand. The accumulation of oxygen
gas in the crown of the pipe between the pump station and discharge was de-
monstrated by the large volumes of gas that could be released at the pump
station. The force main in this section is relatively flat and after passing
the depression, the force main has an overall positive slope to the final
point of discharge shown in Figure 20. The force main configuration coupled
with the apparent trapping of gas in the first section indicated a possible
solution.
A jumper was installed across the depression to permit passage of the gas.
Oxygen feed rates of one to four cfm continued to have adverse effects upon
the system performance. This indicated that the oxygen gas was not being
carried to the jumper. The oxygen feed was then increased to 10 cfm and
oxygen gas was released at the discharge manhole. Under this condition the
system hydraulics appeared to operate in a normal manner. Once the gas
passed the point of depression it appeared to aid the flow condition in
this section of the pipe indicating that the system will function properly
provided the gas could be moved downstream of the depression. At the oxygen
feed that this was achieved, the operation cost would be prohibitive.
The conditions observed for this system alluded to a means of solving the
problem. Injection of air or gaseous oxygen immediately downstream of the
depression would not appear to restrict normal flow conditions. Secondly,
the remaining length of 2700 feet would provide adequate contact time to
oxidize sulfides and prevent further generation of sulfides. The force main
easement in this area is limited which imposes restrictions for the in-
stallation of gaseous oxygen or air compressor equipment.
PEAR RIDGE SYSTEM
The Pear Ridge System as defined for the study consists of three lift stations
and a long gravity system. This system begins at the abandoned sewage treat-
ment plant of the City of Pear Ridge. When the city abandoned wastewater
treatment in favor of contracting with the City of Port Arthur for this
service, the existing wet pit and lift station were used to divert the
flow into the Port Arthur Sewerage System. Flow from the station is by
74
-------
gravity to the Third Avenue Lift Station, thence to the Pioneer Park Lift
Station. Flow then continues by gravity until it joins the interceptor
between the Lake Charles Lift Station and the Mainline Pump Station. The
map of this system is shown in Figure 23.
The primary problems of this system have been the odors at the Third Avenue
Lift Station, corrosion of the downstream gravity line, and odor and corro-
sion downstream of the Pioneer Park Lift Station. Venting with a high stack
at the Third Avenue Lift Station removed the odor from the houses adjacent
to the station only to have the houses one block downwind experience the odor.
Attempts were made to mask the odor with equally disappointing results. A
major shortcoming of masking by substituting a new odor is that it fails to
abate corrosion of the concrete structure and pipe. The most recent failure
of pipe due to corrosion occurred immediately downstream of the Pioneer Park
Lift Station in 1971. The failure required the replacement of 150 feet of
30 inch diameter pipe.
Sulfide Levels
The evaluation of sulfide levels in this system, prior to the installation
of control equipment, was conducted for only a brief period during the
summer of 1969. High infiltration during most of the period influenced the
data obtained and sulfide levels found were not compatible with sulfide
problems evidenced downstream of the station. The principle problem was
the generation of sulfides in the Pear Ridge collection system and sub-
dequent release at the lift station and in the downstream gravity line.
Sulfide levels found in the wet wells of the Pear Ridge and Pioneer Park
Lift Stations will be found in the data presented in the Design and Operation
section to follow.
SYSTEM DESIGN AND OPERATION
Two sites were selected in this system for the installation of sulfide con-
trol equipment. These installations, Pear Ridge Lift Station and Pioneer
Park Lift Station, were included in Phase II of the project. These two
stations were serving to create turbulence thereby releasing hydrogen sulfide
and not serving as sulfide generators as in the case of force mains. This
condition defined the basic design concept for control equipment, the ox-
idation of existing sulfides and providing a dissolved oxygen residual in
the sewage to retard sulfide buildups downstream.
Pear Ridge Lift Station
The site of the former sewage treatment plant had adequate space available
and thereby did not impose any size or location restrictions for equipment
that would be installed outside the station; however space inside the
station was limited. The length of the force main being only 100 feet
imposed restrictions on choice of equipment. The experience at the
Nineteenth Street-Stillwell Boulevard Lift Station ruled out the injection
of gaseous oxygen or air into the force main. The use of U-Tubes was also
75
-------
L - 100' I 0 = 12'
Pear Ridge Lift Station
S.A. = 507 acres
L = 5200
0=15"
O Lift Station* P.O. Pump Capcity
• Lift Station S.A. Service Area**
- gravity Line 0 Diameter
— Force Mam T T onath
O Manhole* L Length
Pioneer Park Lift Station
P.G. -2 @ 14QQ gpm
S.A. = 287 (873) acres
* Sampling Point
* * Indirect Service Area, areas whose sewage has
been pumped at least once prior to entering
station, is shown in parenthesis
Note: Drawing not to scale
L = 6480
0=30*
L
8th Ave. Lift Station
Figure 23. Pear Ridge System
76
-------
eliminated due to the configuration of the station. Considering all
these factors, a decision was made to install a second pressure tank.
Details of the station and pressure tank installation are shown in Figure
4. Following the installation of the pressure tank, a concentrated sam-
pling program was conducted from June 16, 1970 until July 28, 1970 to
evaluate the equipment performance. The data collected during this period
are shown in Table 16. The four sampling points are identified in Figure
23.
The total sulfide concentration coming into this station for the test
period averaged 3.88 mg/1. The effect of recirculation on the reduction
of sulfides was demonstrated; however, the reduction was not of the same
magnitude as previously observed for the other pressure tank locations.
The pressure tank effluent was clearly at an acceptable sulfide concen-
tration. The dissolved oxygen content of the sewage leaving the tank was
approximately 66 percent of saturation. Sulfide in the discharge of the
force main was found to increase slightly while the dissolved oxygen level
was decreased by about one mg/1. During the test period and operation of
this equipment through 1971, odor complaints downstream were eliminated.
On one or two occasions, odor complaints were reported and these were
associated with periods at which the pressure tank was not operating.
The noise generated by the blower and air release valve at the top of the
tank, although not anticipated to be a problem, proved troublesome.
Mufflers were added and a wall was erected between the equipment and the
nearest houses. The noise was then at an acceptable level.
Pioneer Park Lift Station
The second phase of the study included the Pioneer Park Lift Station in
the sulfide control program. The recent development of the U-Tube aeration
concept offered a potential method for control. Installation requirements,
which included space in the dry pit and pump characteristics, were evaluated
and it was found that U-Tubes could be installed. The use of compressed air
in lieu of a venturi aspirator was selected. This was the first prototype
installation in the United States using a U-Tube with compressed air in a
sewer system.
The station consisted of two 1400 gpm pumps that alternate at low flows.
Both pumps operate during peak flow periods. The station operation there-
fore required the installation of two U-Tubes. The U-Tube configuration
after the installation is shown in Figure 24.
Air to the two U-Tubes was supplied by a single blower located outside
the station with piping and controls arranged to alternate distribution
to each tube. Injection was accomplished by drilling holes around the
periphery of the expanded section and welding a distribution collar over the
holes. Air was regulated by using a valve and rotameter. The blower was
set to come on ten seconds after the pump started and stopped with the
pump cycle. Continuous operation of the blower was not considered de-
sirable for fear of air-locking the system.
77
-------
Table 16
SEWAGE CHARACTERISTICS
Pressure Tank Test Program
Pear Ridge Lift Station - Force Main
[Test Period June 16 - July 28,1970]
Sampling Point
Temp.
PH
Total Sulfldes
(mg/1)
PARAMETER
Dissolved Sulfides
(mg/1)
Dissolved Oxygen
(mg/1)
BOD (mg/1) COD
Unfiltered Filtered (mg/1)
00
Pear Ridge
Lift Station
Wet Well
Pressure Tank
Influent
Pressure Tank
Effluent
42nd & Eunice
(Force Main
Discharge)
Ave. 28.5
Max. 30.0
Min. 27.0
29.1
30.5
27.0
29.5
31.0
28.0
28.7
30.0
27.0
6.8
7.4
6.6
6.8
7.3
6.6
6.9
7.2
6.6
6.6
7.4
6.7
3.9
6.3
1.8
1.1
2.7
0.1
0.1
0.2
0
0.2
3.0
0
3.1
6.0
1.0
0.89
2.2
0
0
0
0
.05
1.5
0
0
0
0
0.1
1.2
0
4.9
7.0
4.0
3.9
5.0
0
253
360
192
241
350
170
269
390
162
225
310
130
185
250
120
180
310
24
210
380
126
166
240
90
531
681
413
505
631
372
519
707
353
500
736
328
-------
Notes:
1. Mean Sea Level is
Elevation 100.00
2. Stations are measured
along pipe ceoterline.
3. - Manometer
Location
4.1 - Manometer
Number
5. A - Sample Port
Elev. 86.63 P
Sta. 0 + 00 -
To Pump
Elev. 83.50
.Elev. 101.60
Sta. 0 + 74.4
Elev. 100.29
' Sta. 0 + 32
• Air Injection Collar
Elev. 93.09
Sta. 0 + 39.4
-18 in. diameter downleg
10 in. diameter upleg
Elev. 86.09
Sta. 0 + 46.4
.Elev. 84.20
Sta. 0 + 57.0
Figure 24. U-Tube Configuration at
Pioneer Park Lift Station
79
-------
U-Tube system design was based on pilot data developed by Rocketdyne for
a 2-inch diameter prototype installation (51) and on data from a full-
scale installation at Jefferson Parish, Louisiana (52). Downleg velocity
should be in the range from 1.5 to 2 ft/sec to maximize bubble contact
time. Velocity in the return bend and upleg should be in the range from
4 to 6 ft/sec to prevent solids deposition. The basis of design was as
follows:
Flow Rate I400 9Pm
Air Injection Rate 40 cfm
Air/Water Ratio (Volume) 21 %
Downleg
Pipe Diameter 18 inches
Velocity 1.8 fps
Upleg
Pipe Diameter 10 inches
Velocity 5.7 fps
Downleg Length - injection
collar to return bend 14 feet
The evaluation of the U-Tube was to incorporate hydraulic characteristics,
sulfide control and oxygen transfer characteristics. To enable proper
evaluation, sampling ports were placed at the pump and discharge point
with provisions for connecting manometers at six points. The manometer
locations are shown in Figure 24.
The evaluation of the U-Tube hydraulic characteristics required measure-
ment of both liquid and air flow rates. The liquid flow was controlled
by a gate valve located immediately downstream of the pump and measured
downstream in the gravity sewer by velocity-area measurements. Velocities
were measured by means of a pygmy current meter in the first manhole
downstream in the gravity sewer. When three successive measurements were
obtained for a fixed time in which the revolutions did not vary by more
than one percent, the flow was taken as the mean of the three velocity-
area measurements recorded. The only problem encountered with this
method of measurement was the frequent cleaning of the current meter due
to debris such as hair interfering with the cup rotation.
The most .important hydraulic characteristic pertinent to U-Tube operation
is system pressure losses. For the purpose of the study, system
losses were measured from the gate valve to the discharge
(as shown in Figure 24). The original configuration of the lift station
was not evaluated hydraulically prior to the installation of the U-Tube
and comparisons of system losses under actual conditions was not possible.
Calculation of system losses for the original system would indicate that
these would be minor, i.e. less than one psi or 2.3 feet for all conditions
of flow. This represents the friction and minor losses designed into the
station.
The losses through the U-Tube configuration were first evaluated without
air injection. Head loss at design flow and no air was 715 feet of water
or 3.25 psi.
80
-------
The compressor could actually only inject a maximum of 15 cfm for airrwater
ratio of 8.1 percent. Operations at maximum air flow or air:water ratio
resulted in an average system loss of 6.6 feet of water or 2.86 psi. It
was possible to vary the air:water ratio from 3.4 to 8.1 percent at the
design liquid flow, but system head losses measured in this range were
inconclusive.
The ability to inject a greater amount of air to alter the air:water ratio
would have permitted optimization of this device using compressed air. In
addition to finding an optimum airrwater ratio, it would have permitted a
more valid comparison with other installations. Air flows of 43 cfm have
been obtained at installations using aspiration devices with U-Tubes.
This is three times the air flow obtained with the U-Tube in this study
due to equipment limitations.
The second aspect of the U-Tube operation was that of oxygen transfer
characteristics and its ability to function as a sulfide control device.
Prior to any detailed testing, the system was operated for a period of
approximately one month. During this period sewage temperatures were
low and the sulfide levels found were not representative of the system
when sewage temperatures are higher. Data obtained during this period
are shown in Table 17.
Sewage passing through the U-Tube was characterized by minor reductions in
both total and dissolved sulfides. The dissolved oxygen residuals found
in the discharge were found to increase significantly. These tests were
performed at a constant air:water ratio of 8 percent which represented an
oxygen equivalent of 19 mg/1.
The injection of air or oxygen into sewage during this study had as a
primary objective the control of hydrogen sulfide and not the evaluation
of total oxygen transferred. It was felt desirable to evaluate the oxygen
transfer characteristics of the U-Tube using compressed air to permit com-
parisons with other studies. A period of intense testing on the U-Tube
provided the opportunity for an expansion of the standard testing to in-
clude additional oxygen evaluations.
Sewage void of oxygen usually has a deficit that must be satisfied before
a dissolved oxygen residual can be obtained. The test most frequently
used to describe this is the Immediate Dissolved Oxygen Demand (IDOD).
The test yields the amount of oxygen consumed in fifteen minutes. The
ability to obtain a dissolved oxygen residual upon aerating sewage would
imply the immediate oxygen demand was satisfied and the total oxygen
transferred would be represented by the sum of the IDOD and the residual.
The initial procedure for the extended testing of the U-Tube called for
the standard IDOD test to be run only on the U-Tube influent. Tests were
performed on this basis for a short time and then the IDOD was added to
the effluent analysis. The next modification was to determine the oxygen
demand for a 30 second incubation period on both the influent and effluent
of the U-Tube. This was to provide data that would be more representive
81
-------
Table 17
U-Tube Operation - Constant Air.Water Ratio (8.1)
Pioneer Park Lift Station
[Test Period Oct. 30 - Nov. 28,1970]
03
ro
Sampling Point
Wet Well
Station Discharge
Temp. pH Total Sulfides
("0 (m8/D
Ave.24.9 7.0 1.1
Max. 26.0 7.1 4.3
Min. 21.0 6.6 0.1
23.7 7.0 0.9
25.0 7.1 5.0
21.0 6.8 0.0
PARAMETER
Dissolved Sulfides
(mg/1)
1.0
4.3
0.0
0.7
4.0
0.0
DO
(mg/1)
0.2
5.0
0.0
2.7
9.0
0.0
BOD
(mg/1)
187
265
130
198
390
50
COD
(mg/1)
471
636
242
461
700
180
-------
of the contact time in the U-Tube which was 17 seconds at design conditions.
The period of extended testing was during July when sewage temperatures are
near the maximum and when sulfide levels are highest. The data collected
for this period are shown in Table 18. Sulfide levels were reduced by only
a small amount and the residuals were in excess of desirable limits. Dis-
solved oxygen residuals were lower than anticipated; however, when considering
reductions in the IDOD, the total oxygen transferred varied from 1 to 40
percent. The 15 minute and 30 second oxygen demand tests are plotted in
Figure 25.
There were several conditions observed during the testing of this system
that should be noted. First, as long as the blower was operating, odors
were not observed at the station. There was a high degree of turbulence
at the discharge point resulting in a foam collecting on the surface of
the gravity flow. This foam was usually gone or only trace amounts ob-
served at a point approximately 400 feet downstream of the station. Although
not routinely checked, the sulfide level at this location was generally
found to be at an acceptable level. This would indicate that the sulfides
were either released or oxidized in the gravity line. The absence of odor
would indicate that the latter was probably the case. Prior to the in-
stallation of the U-Tube, odors were severe downstream from the station.
MAINLINE SYSTEM
The Mainline System as defined for purposes of the study consists of the
two largest sewage transfer stations in the city. The two stations are
the Lake Charles Lift Station and the Mainline (Lakeview) Pump Station.
Both stations are located on the Lakeshore Interceptor with the Mainline
Station making the final transfer of sewage from the collection system
to the sewage treatment plant. The two stations were included in Phase
II of the project. Details of this system are shown in Figure 26.
Lake Charles Lift Station
The Lake Charles Lift Station is the second largest sewage lift station
in the Port Arthur Sewerage System and handles the flow from the Lakeshore
and Stillwell Systems. The major problem at this location is the sulfides
arriving at the station and their subsequent release and not generation.
Sulfide levels were studied indirectly at the station as a part of other
systems and not in terms of the station serving as a sulfide generator.
There was sufficient evidence that excessive amounts of hydrogen sulfide
gas were being released as it had a history of odor problems and deter-
ioration of concrete in the wet wells and in the downstream sewer. Sulfides
were released in the wet well and at the discharge point of the lift pumps.
System Design and Operation
The criterion for sulfide control at this location was the oxidation of
sulfides and development of a dissolved oxygen residual. The methods
previously employed for sulfide control at lift stations, i.e. pressure
tanks and air-injection into U-Tubes, had several limitations at this
site. Aesthetic considerations related to land use and equipment noise
83
-------
Table 18
U-Tube Operation - Variable Air:Water Ratios
Pioneer Park Lift Station [Test Period July, 1971 ]
oo
Sampling
Point
I*
D* *
I
D
I
D
I
D
I
D
I
D
I
D
I
D
Pump discharge
gpm
1317
1319
1325
1300
1314
1264
1300
1274
Air:Water
Ratio %
3.4
4.5
4.5
5.7
6.3
7.1
8.1
8.2
Oxygen
Applied
(mg/1)
8.2
10.9
10.9
13.8
15.3
17.2
19.6
19.8
Temp.
(°C)
30
30
30.7
33.7
30
32
29
29.6
pH
6.9
6.9
7.1
7.2
6.9
7.2
6.9
7.2
Total
Sulfides
4.3
2.6
5.3
2.7
1.7
0.9
2.3
1.5
5.0
2.8
1.8
1.5
4.2
3.8
2.4
1.7
Dissolved
Sulfides
4.0
2.4
4.2
2.3
1.6
0.6
2.1
1.1
4.8
2.3
1.5
1.1
3.8
3.0
2.0
1.2
DO
(mg/1)
0
0
0
0
0
1.6
0
1.1
0
0
0
1.5
0
0
0
1.2
15 min.
IDOD
(mg/1)
10.2
9.4
10.2
10.1
6.3
3.5
7.9
6.2
10.2
8.8
10.6
6.4
10.2
7.6
9.5
6.8
30 sec.
IDOD
(mg/1)
7.6
7.0
7.6
7.1
_
-
8.2
8.1
_
7.6
7.1
-
Head Li
Across Sj
(»)
6.4
6.5
6.5
6.6
6.6
-
7.1
-
* Pump Discharge
* * U-Tube Discharge
-------
oo
en
"3
«•
-------
Lake Charles Lift Station
P.C. -3 @ 1500 gpm
1 @ 3000 gpm
S.A. = 636 (2253) acres
0 - 36"
L = 7330'-
= 42
L = 9160'
LEGEND
O Manhole P.C. Pump Station
O Lift Station S.A. Service Area
Q Pump Station 0 Diameter
Gravity Line L Length
Force Main
<3 Main Port Arthur Wastewater Treatment Plant
Mainline Pump Station
P.C. -2 Variable Speed
3000-5500 gpm
S.A. = 1079 (6651) acres
= 60
L = 1260'
0= 30'
- L = 4400'
Figure 26. The Mainline System
86
-------
eliminated the two previous methods employed. Further, the station con-
figuration and available pump heads would not permit consideration of the
other control methods.
The station has four lift pumps that discharge into a common discharge box
located outside the station with each pump having a separate discharge
pipe. Two of the pumps alternate during low and normal flows with the
extra pumps operating only during periods of excessive infiltration. As
the most severe sulfide problems were associated with low flows, it was
felt that the installation of U-Tubes on the low lead pumps would provide
the sulfide control desired. The design called for use of gaseous oxygen
in lieu of an aspiration device or compressed air. Details of the Lake
Charles Lift Station are shown in Figure 27. The U-Tubes were essentially
the same as shown in Figure 24 for the Pioneer Park Station. The major
exception was the depth of tubes, diameter, and method of oxygen injection.
The choice of U-Tube aerators presented a problem due to pump character-
istics. The available depth and space was adequate for U-Tube installation;
however> the pump head was inadequate to handle the anticipated head losses
of a diffused air U-Tube. The liquid level in the wet well could have been
raised to obtain better hydraulic characteristics, but was not considered
desirable. Increasing the operation level in the wet well would result
in flooding of the gravity lines and increasing the detention time. These
factors led to the choice of injecting gaseous oxygen in the U-Tube. This
was the first installation of a U-Tube aeration device employing gaseous
oxygen. The basis of design was as follows:
Flow Rate 750 gpm
Oxygen Injection Rate 0.4 cfm
0 to 48 mg/1
Downleg
Pipe Diameter 14 inches
Velocity 1.6 fps
Upleg
Pipe Diameter 10 inches
Velocity 3.1 fps
Down!eg Length - injection
collar to return bend 15.3 feet
The pump capacity of 750 gpm was used for design; however* it was later
learned that the actual pump capacities were 1400 to 1500 gpm. This
error resulted in a less than optimum design and oxygen transfer efficiency.
The system was designed to achieve 80 to 90 percent oxygen transfer based
on projections made from air injection studies on a pilot system by
Rocketdyne (51). Oxygen transfer efficiencies attained were lower because
of the reduction of 50 percent in bubble contact time as will be discussed
later.
The oxygen was initially injected through a straight tap at one location
at the beginning of the expanded section of the U-Tube. This was later
changed to four straight tap injection points. Problems were still
87
-------
Lakeshore Drive
Gravity Sewer
Gravity Sewer
Mar
iwa;
'
Wet Pit
Dry Pit
Oi_
Or
O-t
X
*
Cryogenic Tank
-Converter
Discharge Box
~ Gravity
Sewer
Chainlink Fence
Note: Oxygen injection into U-Tubes located in the Dry Pit.
U-Tube configuration similar to Figure 7 and Figure 24.
Figure 27. Lake Charles Lift Station
88
-------
experienced in achieving oxygen transfer and it was felt that the oxygen
was short circuiting. Finally, copper tubes with a series of holes along
the length with a plugged end were inserted at each injection point. The
tubes were given a radius that pointed downstream to prevent rag build-up
on the diffusers.
During the period of study it was discovered that the major problem was
not with the methods of injection but with the methods of sampling. Samples
were obtained by opening the sampling ports and after a short period, collect-
ing the sample. This method failed to yield any dissolved oxygen, regardless
of the oxygen feed rate. Later, it was found that by permitting the sample
ports to remain open with a continuous flow a dissolved oxygen residual was
found in the samples.
There were several problems encountered with this installation that pre-
vented a long range sampling program to be effectuated. In addition to
the sampling problem, operational problems were encountered. Oxygen
appeared to be collecting in the upper section of the U-Tube which re-
stricted the flow. The effect was to completely block the flow when the
wet well was low. This condition resulted from the minimal operational
head of the pumps due to excessive impeller wear. The pumps were rebuilt
prior to additional testing.
A concentrated period of sampling was conducted during July and August,
1971 on this installation. This sampling was restricted to the sewage
characteristics of sulfides and dissolved oxygen transfer. Head losses
due to oxygen injection were considered to be minimal with the major losses
resulting from the U-Tube piping design. Sewage flow rates were taken at
the rated capacity of the pumps for purposes of calculating applied oxygen
rates. It was felt that errors introduced by this assumption for purposes
of calculating the oxygen:water ratios would not be significant. The
station configuration prevented any reasonable measurement or estimation
of flow without major renovations or aquisition of special flow measuring
equipment. These items were not originally scheduled for the project and
therefore not provided for in the evaluation phase.
Data obtained from the period of intense study are given in Table 19. Four
oxygen feed rates were applied starting at 6.27 milligrams-per-liter and in-
creased in equal intervals to 25.1 milligrams-per-liter. The complete oxida-
tion of sulfides was not accomplished at any oxygen feed; however, the amount
oxidized increased with increased oxygen. Reduction to acceptable levels was
never achieved because of the error in pumping capacities.
The oxygen transfer of the system increased with increased oxygen feed.
This held for the reduction in the IDOD and also for the magnitude of
dissolved oxygen in the U-Tube discharge. The increased reduction plus
the increased level of dissolved oxygen are misleading when considered
with the amount of oxygen applied. At the oxygen feed of 6.3 milligrams
per liter, sixty two percent of the oxygen was transfered. The percentage
of oxygen transfered decreased with increased oxygen feed reaching a
minimum of 38 percent for the ranges tested.
89
-------
Table 19
SEWAGE CHARACTERISTICS
U-Tube Operation with Oxygen Injection
Lake Charles Lift Station
[Test Period: July - August, 1971]'
PARAMETER
Sampling
Point
I*
E
I
E
I
E
I
E
Oxygen Applied Temp
(mg/1)
6.3
12.5
18.8
25.1
Temp.
28.3
28.3
28.1
28.1
28.3
28.3
28.3
28.3
pH
7.1
7.1
7.1
7.1
7.1
7.1
7.1
7.1
Total Sulfides
(mg/1)
2.8
2.1
3.2
2.3
3.2
2.1
3.5
2.2
Dissolved Sulfides
(mg/1)
2.5
1.8
2.9
2.1
2.9
1.8
3.2
1.8
DO
(mg/1)
0
1.7
0
3.6
0
4.4
0
5.5
IDOD
(mg/1)
4.6
2.4
4.5
2.1
5.1
1.9
5.4
1.3
* I - U-Tube Influent, E - U-Tube Effluent
90
-------
Because of the error in pump capacity, the average detention time at this
installation was 17 seconds as compared with 30 seconds at the Pioneer
Park Station. With a 2-fold increase in detention time, it can be
reasonably projected that oxygen transfer efficiency would have been
nearly 100 percent at the lower injection rates and approximately 70
percent at the higher rates tested.
Mainline (Lakeview) Pump Station
This pump station receives the combined flows of all the systems described
in the study. The station was erected in 1961 under the same bond program
that built the sewage treatment plant. The station contains two variable
speed pumps that operate to provide a minimum flow of 3000 gpm to the
plant. A 30-inch diameter force main connects the pump station with the
sewage treatment plant. This line is 4,400 feet in length.
The force main discharges into an open channel at the sewage treatment
plant. The sewage then passes through Barminutors thence to a Parshall
flume and Detriters. Corrosion of this equipment has been a continuing
process and protective coatings have failed to check the corrosive attack
attributable to hydrogen sulfide. The odor around these inlet facilities
was of such intensity that the entire sewage treatment plant was considered
to be operating improperly.
Only a limited amount of data was obtained for sulfide conditions at the
wet well and force main discharge prior to installation of sulfide control.
The data obtained from the wet well and at the force main discharge are
shown in Table 20. As indicated in the table, the sampling occurred
during the months when the sewage temperature was low with an average
value of twenty-one degrees Centigrade. The presence of total and dissolved
sulfides in significant quantities during this period serves to emphasize
the sulfide problem experienced in this sewerage system. The force main
served as a sulfide generator at this location by increasing both total
and dissolved sulfides by an average amount that exceeded two mg/1.
The need to install sulfide control measures at this location was apparent
when considering the corrosion and odor problems at the plant. The
existence of only one pipe to the treatment plant from the station and
its handling of all the city's sewage imposed special considerations for
installation and operation of sulfide control facilities. A pressure
release valve located outside the pump station provided access to the
force main without interrupting operations. There were doubts expressed
as to the effectiveness of injecting air at the top of the pipe and with-
out the use of diffusers as called for in the original design of the
other installations. The blower and necessary piping were installed and
equipment placed in operation November 21, 1971.
The first blower installed was set to deliver fifty cfm and was operated
at this rate while tests were performed to evaluate the effects of
91
-------
Table 20
Sulfide Levels
Mainline (Lakeview) Pump Station
NO AIR INJECTION
PARAMETER
Date
Nov. 12-18, 1971
Nov. 25, 1971
Sampling
Point
WW*
D
WW
D
Temp.
<°c)
22.6
22.7
22.0
22.0
pH
7.0
7.0
7.0
7.0
Total Sulfides
(mg/1)
2.5
5.1
3.3
6.1
Dissolved Sulfides
(mg/1)
2.4
5.0
3.1
6.0
DO
(mg/1)
0
0
0
0
AIR INJECTION
PARAMETER
Date
November 21,1970
December 19,1970
July 13-16,1971
Sampling
Point
WW*
D
WW
D
WW
D
Temp.
(C-)
22.4
22.2
22.0
22.0
—
28.9
pH
7.0
7.0
7.0
7.0
_
7.1
Total Sulfides
(mg/1)
0.8
1.4
2.6
2.3
_
0.5
Dissolved Sulfides
(mg/1)
1.0
1.3
2.2
2.2
0.4
DO
(mg/1)
0
0
0
0
0
* WW-Wet Well; D - Force Main Discharge
92
-------
aeration. The sewage temperature during this period was approximately
22° Centigrade. Data collected during this period are shown in Table
20. The incoming sulfides during this period were low and although the
temperature of the sewage was low, the air injection failed to prevent
additional sul fides from being generated. The blower was replaced by
one capable of delivering 110 cfm. This increased the air feed from 1.7
to 3.67 cubic-feet-per-minute per inch diameter and increased the applied
oxygen from 27.3 to 66.7 milligrams-per-liter based on the minimum pump-
ing rate for the station. The temperature of the sewage during this
period was approximately 29° Centigrade indicating a high sulfide gener-
ating potential in the force main. Data collected during July, 1971
shown in Table 20 indicate control of the sulfides at the increased air
feed. After installation of the larger blower, sulfide odor problems
at the sewage treatment plant were eliminated.
93
-------
SECTION VII.
EVALUATION OF OXYGEN SOURCES
AND METHODS OF INJECTION
The study proposed to evaluate the effectiveness of controlling hydrogen
sulfide through the use of oxygen. Two sources of oxygen were utilized,
pure oxygen and airr and three basic methods were used for entrainment.
Minor modifications were made to the original designs when conditions
dictated the need to meet an individual station requirement or configuration.
There were a total of eight control sites used during the course of the
study with two sites using both air and pure oxygen. One site utilized both
sources of oxygen for injection into a force main providing a unique oppor-
tunity for comparison and evaluation.
The use of oxygen, regardless of its source, can effectively control
sulfides in sanitary sewage by one of two mechanisms. The first is the
oxidation of existing sulfides to acceptable limits and second, is the
inhibition of sulfide generation. There were several methods used for the
entrainment of air or oxygen gas into the sewage which proved to be effec-
tive. Each method had its own distinct or unique features which should
be utilized in design. The critique of the operation experience will be
discussed as follows: methods of injection; oxygen; air; pressure tank; and
U-Tube. Consideration wj.11 be given to effectiveness., op.erati.onal problems,
.maintenances sits requirements, and other special features where applicable.
Methods of Gas Injection in Force Mains
The original design for air and oxygen injection called for the installation
of rather elaborate diffusion facilities as shown in Figures 4 and 5. It
was anticipated that diffusers installed in force mains would collect rags
and other debris thereby impeding flow and creating additional maintenance
problems. This problem did not materialize during the period of study;
however the potential for flow restriction must be recognized. At two
sites the expanded diffuser section was installed in the force main where
either air or oxygen achieved sulfide control. One site used air injection
through a straight tap at the pipe crown which proved equally effective in
sulfide control. Considering these two methods of air injection into force
mains, there does not appear to be any significant difference when consider-
ing only sulfide control, as both were effective.
A second consideration of air or oxygen injection is the amount of oxygen
transfered and the maintenance of a residual dissolved oxygen at the force
main discharge. Oxygen transfer was not the primary objective of the
study; however, the data obtained throughout the study would appear to
favor the diffuser tubes over straight taps.
The diffuser installation required 2.25 cfm per inch diameter to control
sulfides and obtain a dissolved oxygen residual. This represented a
volumetric air to water ratio in the range of 17 to 38 percent. The
94
-------
diffusers were applying oxygen on a weight basis of 60.4mg/1. These
compare with the straight tap where air was applied at 3.66 cfm per
inch diameter with sulfide control achieved, but without obtaining a
dissolved oxygen residual. The volumetric air to water ratio at this
site was 27 percent. This represented an application of oxygen on a
weight basis in the range of 16 to 36 mg/1.
The preceeding discussion clearly indicates the importance of parameter
selection when evaluating air or oxygen injection for sulfide control.
In the instance cited, selection of air feed on the basis of pipe diameter
would indicate the diffuser as being the most effective method of air or
oxygen entrainment. The major limitation to this form of expression is the
failure to relate the gas feed rate to fluid flow. Expressing the air or
oxygen feed on a weight basis clearly indicated that injection through a
straight tap as the most effective for sulfide control and that the
additional cost of diffusers is not warrented.
PURE OXYGEN INJECTION
Gaseous oxygen was used at a total of five locations in the city. Three
of the sewage pump stations had force mains of significant length while a
forth transfer station had a very short force main and should be classified
as a lift station. The fifth location was a lift station where oxygen was
injected into a U-Tube. Discussion of the U-Tube as a sulfide control
device using gaseous oxygen will be deferred to a later section. Details
of these stations are given below which indicates their physical variations.
Force Main
Diameter
Inches
8
Station
Grannis
Railroad Ave.-
Thomas Blvd. 16
19th Street-Stillwell
Blvd. (Alligator Bayou) 16
Smith-Young
(39th Street) 8
Lake Charles Lift
Station 8
Length
Feet
3150
3850
600
5427
U-Tube
Pump
Capacity
gal/min
600
1200
2350
350
1500
Detention Time
(normal flow)
Minutes
13.8
33.4
2.6
41.3
1.0
The configuration of the junction box prevented a complete evaluation of
the Grannis Station operation; however, the data obtained indicated that
sulfide control was being accomplished. Operation of the 19th Street
95
-------
Lift Station demonstrated that the injection of gaseous oxygen into short
force mains is ineffective at low oxygen feed rates, and at higher oxygen
feed rates the oxygen is wasted to the atmosphere. The latter results
from the creation of a two phase flow regime. This short force main was
equipped with diffusion facilities as shown in Figures 4 and 5. The ability
to diffuse the oxygen by small bubbles was without benefit for the system
configuration and operation.
Injection of oxygen at the Smith-Young Pump Station never achieved the
desired level of performance for either sulfide control or oxygen trans-
fer. Failure to achieve sulfide control is attributable to the physical
configuration of the force main. The radical change in the force main
profile where it was depressed to pass under a drainage ditch resulted
in a blockage that trapped oxygen in the upstream pipe. The importance
of the force main profile becomes manifest when oxygen or air is planned
for sulfide control. The severity of the problem would have been intensi-
fied if air had been used in lieu of oxygen.
It was possible to inject oxygen at one cfm without adversely affecting
pumping characteristics and at this rate sulfides were reduced but not
completely controlled. This rate represented a volumetric oxygen to
sewage ratio of 2.14 percent or an applied oxygen of 24.6 mg/1. It is
significant to note that sulfides were controlled at the midpoint of the
force main.
The most comprehensive data for oxygen injection were obtained at the
Railroad-Thomas Boulevard Pump Station. At this location an optimum
feed rate for both sulfide control and dissolved oxygen residual was
obtained. The optimum feed rate was 2 cfm and represented a volumetric
oxygen to sewage ratio of 1.25 percent. This represented an oxygen
application of 14.4 mg/1. The data indicated an average oxygen residual
at the force main discharge of 0.4 ppm which would indicate that 14 mg/1
of oxygen was either consumed in the oxidation of sulfides, used in
meeting the oxygen demand, wasted to the atmosphere, or utilized by a
combination of these mechanisms.
The Smith-Young and Railroad-Thomas Boulevard Pump Stations have very
similar velocities and detention times although their diameters and
flow rates are different. The sewage strength as measured by BOD was
not significantly different during tlie respective test periods and the
other sewage characteriestics were similar. The ability to control
sulfides using oxygen was demonstrated in each instance although the
amount of oxygen required was different as well as the degree of con-
trol. The conditions observed clearly indicate that additional param-
eters are involved in the overall problem of sulfide generation and
control.
Air Injection
Atmospheric oxygen was used at a total of five locations in the city.
The applications were force main injection, pressure tanks and LJ-Tubes.
96
-------
The injection of atmospheric oxygen into force mains will be discussed here
and its use in the other applications will be deferred to a later section.
Atmospheric oxygen, when injected into force mains, can be effective in
the oxidation of existing sulfides and prevention of additional sulfides
from being generated.
The stations where atmospheric oxygen was injected into force mains are
given below with information pertinent to the study.
Force Main Detention
Pump Capacity Diameter Time
Station gpm Inches Length (minutes)
Railroad Ave.-
Thomas Blvd. 1200 16 3850 33.4
Mainline
(Lakeview) 3000* 30 4040 53.9
* design minimum flow conditions
Certain physical aspects, of these two stations, are similar, such as force
main length and detention times, while others, such as force main diameter
and pumping capacity are widely divergent. The sewage characteristics
at the two locations were also similar.
The air requirement to control sulfides at the Railroad Pump Station was
equivalent to 2.5 cfm per inch diameter while at the Mainline Station it
was 3.7 cfm per inch diameter. This corresponded to a volumetric air:
water ratio of 25 percent at Railroad and 15 percent at Mainline. Com-
parison is difficult as the feed rate per inch of pipe diameter is higher at
the Mainline Station while the volumetric air to water ratio is lower.
This dilemma is resolved by consideration of the amount of oxygen applied.
At the Railroad Station this was equivalent to 60 mg/1. At the Mainline
Station with a constant air feed and variable sewage flow the oxygen
applied ranged from 36 to 67 mg/1. On this basis the data obtained would
indicate compatible oxygen requirements for the control of sulfides in
raw sewage independent of other parameters. There are insufficient data
over a sufficiently broad range to substantiate the use of applied oxygen
at a uniform rate; however the potential should be recognized as it would
provide a better design parameter for sulfide control than for air feed
rates expressed as a function of pipe diameter.
PRESSURE TANKS
There were two pressure tank aeration devices designed for the project
97
-------
to be used at locations with short force mains. These were installed at
the Nineteenth Street-Stillwell Boulevard Lift Station and at the site
of the former Pear Ridge Sewage Treatment Plant. The former had a force
main of 600 feet and the latter approximately 100 feet. The major pro-
blem at these locations was the high sulfides arriving at the wet well
and not sulfide generation in the short force main.
The pressure tank proved to be effective in the oxidation of the existing
sulfides and the entrainment of air in the sewage. The volumetric air to
water ratio of this aeration device was 391 percent at nominal con-
ditions, representing an oxygen application of 949mg/l. The nominal
retention time of the sewage in the pressure tank was 17 minutes at
design conditions.
One of the problems that developed during the operation of this aeration
device was the build-up of solids in the tank. The solids that collected
in the bottom of the tank were found to affect circulation patterns thereby
reducing oxygen transfer. To eliminate this problem, the drain line was
opened and permitted to flow continuously as a return flow to the wet
well. The oxygen content of this return flow was found to be effective
in the oxidation of sulfides entering the wet well. This solved one of
the problems encountered throughout the study and that was the problem
of the control of sulfides in wet wells and minimizing corrosion.
There exists an additional problem associated with the pressure tank
aeration device as designed and utilized in the project. The operation
of the pump to the pressure tank was continuous and designed to handle
the average flow through the station. This means that the peak flow
will bypass the unit without receiving treatment. This will not present
a serious problem if the peak sulfide levels do not occur simultaneously
with the peak sewage flows.
It was anticipated in the system design that the residence time in the
pressure tank in conjunction with the excess air would result in a BOD
reduction thereby adding to the benefits of this device. Further, the
retention time in the pressure tank coupled with the recirculation
offered the potential for the development or initiating the growth of
a biological floe, a necessary condition for a BOD reduction. This was
evaluated by performing BOD tests on both filtered and unfiltered samples
taken from various sampling points. Suspended solids determinations were
also made.
Data collected during a continuous twenty hour sampling period yielded
changes in the two primary parameters as anticipated. Suspended solids
increased an average of 41 percent whereas the BOD was decreased by an
average of 6 and 11 percent for unfiltered and filtered samples. Although
a BOD reduction was demonstrated it was not of significant magnitude to
be reliable for predictions. The data collected for this system would
have been more significant provided the actual flows and recirculation rate
could have been quantified. In the absence of flow rates and retention
98
-------
times it is impossible to differentiate between oxygen applied and utilized
in the pressure tank and wet well.
U-TUBE AERATION DEVICES
U-Tube aerators were installed at two locations using compressed air and
pure oxygen in lieu of aspiration devices. The compressed air applica-
tion was effective in reducing sulfide levels but was not capable of
complete oxidation at the air:water ratios studied. Additionally, the
device was effective in the transfer of oxygen which served to oxidize
the sulfides in the downstream gravity sewer. The use of gaseous oxygen
did achieve high levels of sulfide reduction and the oxygen transfer was
below design levels. The dissolved oxygen residual increased with oxygen
application rates; however saturation was never obtained.
The hydraulic performance of the U-Tube aeration devices demonstrated
that these can be used without excessive energy losses across the system.
Considering these losses and the level of oxygen transfer, the U-Tube
proved itself to be an effective method in the role of sulfide control.
The failure of the pure oxygen to obtain a higher degree of control
was a function of improper information on the system hydraulics used in
the design of the U-Tube.
99
-------
SECTION vrir
SUMMARY OF SULFIDE CONTROL METHODS
The objectives of the study were to demonstrate the effectiveness of oxygen
in the control of sul fides and to evaluate various means of entrainment.
These objectives were achieved with minor exceptions. The scope of the
study was of such magnitude that quantifiable results were not always obtain-
able, particularly with the constraints imposed by the system configuration
and operation. The major purpose of the study was to reduce the sul fides
and not to study the efficiency of oxygen transfer; however, the ability
to control sul fides is related to oxygen transfer.
The information developed is limited to applications where energy is im-
parted to the sewage by mechanical pumps. In the study the sewage was
either lifted or lifted and pumped to a distant point in the sewerage system.
The evaluation will first consider air or oxygen injection into force mains
followed by U-T.ub.es. and pressure tanks.
Injection
The first consideration is the application of the expanded diffuser sections
as shown in Figures 4 and 5 as compared to the use of a straight tap for
air or oxygen injection. The installation at the Railroad Station where
diffusers were installed will be compared with the straight Injection at
the Mainline Station using air injection. Information pertinent to the
study is given below.
Force Main
Pump Capacity Diameter Detention
Station gpm (in.) Length Time
120° 16 385° 33'4
(Lakeview) 3000-5500 30 4040 53.9
1- variable speed pump
The Railroad Station required 2.5 cfm-per-inch diameter to control sulfides
as compared to a value of 3.7 at the Mainline Station. The volumetric air
to water ratios were 24.9 as compared to 14.8 to 27.4 percent. The
applied oxygen concentrations on a weight basis were 69.6 at Railroad as
compared with 45.9 to 76.6 at Mainline. The air to water ratios and applied
oxygen for these installations are very close with air feed as a function
of pipe diameter having the greatest variation. There are several ob-
servations relative to these values that should be made. The diffusers
100
-------
at the Railroad Station, although not appearing to restrict flow, could
have had their performance restricted by rags accumulating on the piping
or the diffusers.. Ct was, not possible to determine an optimum air feed
at Mainline due to the variable speed pumps, for the air feed and range
of sewage pumping rates, it was only possible to ascertain that the sulfide
levels were reduced to acceptable levels and that odors that were common
prior to the aeration failed to he observed during the test program.
These data are shown in Table 21.
The analysis of the data under these prescribed conditions fail to establish
a significant advantage for either the diffusers or the straight tap for
air injection. In the absence of more detailed data for specific conditions
it does not appear that the expense incurred with the diffusers and the
potential maintenance problem are warranted.
The Railroad Station provided the opportunity to evaluate air and oxygen
gas under similar conditions with the noted variations in sewage flow.
During the periods of optimization, the average BOD and sulfide values
were approximately the same. Under the conditions of the testing and at
the minimum sulfide levels in the force main discharge, a concentration
of pure oxygen of 16.5 mg/1 was required to control sulfides compared to
an equivalent oxygen concentration from the applied air of 69.6 mg/1.
The oxygen from the air was 4.3 times the amount of pure oxygen gas
required to effectuate control.
The remaining stations where pure oxygen was injected into the force main
required significantly greater magnitudes of oxygen than that found at
the Railroad Station. In each instance it was not possible to optimize
the oxygen feed and the values reported in Table 21 for the Grannis Station
and for the Smith-Young Station are for the best conditions found. The
sulfide levels at Grannis were at acceptable levels for the oxygen applica-
tion indicated, however this oxygen feed would be expected to be excessive.
Sulfide levels in the discharge from the Smith-Young Station were reduced,
but not to acceptable levels. The levels at the mid-point were acceptable.
However, the sulfides were regenerated in the remaining portion.
U-Tubes
The two U-Tube installations enabled comparisons of their performance using
compressed air and oxygen. It was not possible to optimize these aeration
devices due either to equipment restrictions or design based on erroneous
hydraulic characteristics. The information provided in Table 21 is based
upon projected performance from the data obtained for the conditions of
design without the described limitations. It is significant to note that
oxygen required from air is 4.5 times greater than when using oxygen gas.
This compares to a 4.2 ratio found for force mains. A further observation
is that the applied pure oxygen for the Pioneer Park U-Tube is very similar
to that found for the Railroad force main. The volumetric air to water
ratios were also found to be similar for compressed air at the Pioneer Park
U-Tube and the Railroad Avenue force main.
101
-------
Table 21
Oxygen Requirements for Sulfide Control
Application
Station
Applied O2
(Oxygen gas)
mg/1
Applied O2
(Air)
mg/1
Air or Oxygen to Water
Volumetric Ratio
Percent
Air or Oxygen Feed
per inch diameter
cfm/in. dia.
o
ro
Force Main —
Oxygen
Force Main —
Air
Pressure Tank -
Air
U-Tube - Oxygen
Air
Grannis
Railroad
Smith-Young
Railroad
Mainline
Stillwell
Pear Ridge
Lake Charles
Pioneer Park
82.9
16.5
56.9
-
-
13.2
69.6
45.9 - 76.6 *
1093
964
59.7
6.2
1.25
4.27
24.9
14.8 - 27.4
391.3
345.2
2.0
21.4
0.625
0.125
0.250
2.5
3.7
N.A.
N.A.
N.A.
N.A.
* constant air with variable pumping rate
-------
Pressure Tanks
The two pressure tanks were very similar In their design and the operation
of these aeration devices produced very similar operating characteristics.
The requirements for sulfide control were very similar in that the sewage
arriving at the wet well had a rather high sulfide level resulting from a
rather extensive gravity system.
The flow through these aeration devices was continuous resulting in a
continuous operation of both pumps and blowers. It was not possible to
optimize the air requirements at these installations due to the config-
uration and operational requirements.
The volumetric air to water ratios for the two installations was in excess
of 300 percent resulting in an applied oxygen equivalent of 964 and 1093
mg/1 for the Pear Ridge and Stillwell pressure tanks. These values are
excessive when compared with the other methods of sulfide control utilized
in the study.
103
-------
SECTION XI
ECONOMIC ANALYSIS
The control of sulfTdes was demonstrated using alternate sources of oxygen
and variable methods of entrainment. A major factor in the decision to
enter into a sulfide control program is that of economics. An economic
evaluation of sulfide control must include the cost of alternatives, with
the alternatives being different for a new system than for an existing
system. This study was conducted on an existing system with results
applicable to a new system.
The alternative to sulfide control for a new system will be the use of
inert materials in the sewerage system. This eliminates the corrosion
problem but will fail to abate other associated problems such as odors.
The difference in cost between inert materials and materials susceptible
to corrosion can be applied to the cost of sulfide control where the extra
benefit of odor control is derived. In the case of an existing system,
the alternative to implementing a control program will be replacement,
where the structural integrity of the system has not reached a critical
point with failure being imminent, the cost for replacement can be applied
to a sulfide control program to preserve the system. It is therefore
important to be able to evaluate the economics of the alternatives of
sulfide control. This constituted a principal component of the study.
The economic evaluation of alternative methods of sulfide control is contingent
upon the ability to optimize each method. There are two objectives that could
be met when using oxygen for control. First, the control of sulfides independ-
ent of oxygen residuals and second, the control of sulfides with a resulting
dissolved oxygen residual. In the latter case the goal would be to assure
aerobic conditions downstream from the point of control. The constraints im-
posed by the system studied negated the ability to evaluate the second objec-
tive of maintenance of a dissolved oxygen residual. This was attributable to
the accumulation of debris in downstream gravity sewers which had a high oxygen
demand in the principle interceptors. The system optimizations and economic
considerations are therefore based upon sulfide control.
An economic evaluation of sulfide control should include the cost of
alternatives for it to serve as a quantitative aid in decision making. It
was beyond the scope of the study to make a comprehensive evaluation and
the analysis developed is restricted to the sulfide control component.
The principle components to be included are source of oxygen, air or pure
oxygen, and the method of entrainment. The methods of entrainment are
injection into force mains, pressure tanks, and U-Tubes. These are
evaluated as to their applications at sewage transfer stations where a
force main is involved and where only a lift occurs.
The principle components of the cost of sulfide control equipment are con-
struction, equipment, operation, maintenance and replacement. The magnitude
of cos,t associated with each, component can be expected to vary over a large
104
-------
range and will be contingent upon existing facilities and station con-
figuration. A general discussion relative to oxygen source and entrain-
ment equipment will provide the basis for additional analysis.
Initially oxygen was delivered to the station in trailers which were
rented from the supplier. This was an economical approach to preliminary
investigations but prohibitive for long term operation. If oxygen gas is
to be considered for sulfide control, it is recommended that this equip-
ment be installed at the site to determine oxygen requirements prior to
the design of a permanent installation. Cryogenic tanks and converters
were installed at locations scheduled to use oxygen gas for extended
periods. A special concrete foundation was required at one site whereas
at other locations it was possible to install the equipment tin either the
dry or wet pit of the sewage transfer station. There are two alternate
sources that should be considered that can potentially reduce the unit
cost of oxygen. In some instances it would be possible to pipe gaseous
oxygen to the site provided a plant is nearby and an existing easement
available. If oxygen requirements are of sufficient magnitude, consider-
ation should be given to the installation of a small oxygen plant. The
major costs associated with the use of oxygen gas is the cost of oxygen.
Operation and maintenance costs are minimal when using gaseous oxygen.
Air injection by blowers or compressors can usually be installed on existing
concrete structures; however, if space is not available, a small concrete
foundation will suffice. Consideration should be given to installing the
blowers in the dry pit where space is available. The use of blowers requires
a higher degree of maintenance than oxygen facilities and the principle
operating cost is power. The cost of operation can be significantly re-
duced by operating only during pumping cycles. Other cost factors include
replacement of both blower and motor and the use of silencers on the intake
and discharge to reduce noise levels.
The use of elaborate diffusion equipment for either air or oxygen in force
mains did not produce any significant benefit when considering the cost of
installation and periodic maintenance that would be required.
The U-Tube as a means of oxygen entrainment in sewage can be used either
with aspirators, compressed air or oxygen injection. Of these, only
compressed air and oxygen gas were evaluated. The costs associated with
compressed air and oxygen have been discussed in general terms. The
operation and maintenance of the ll-Tube itself is negligible as there
are no moving parts and the only upkeep required would be periodic
painting. The capital cost will be a function of where they are installed.
In this study the costs to be given are for the installation of the U-Tube
inside the dry pit. Other points where the device could be installed are
outside the transfer station or at the end of force mains. A principal
advantage of using venturi aspirators is the elimination of operation and
maintanance costs associated with compressors.
The pressure tank as an aeration device requires a larger area outside the
station than other types of aeration devices. The design of this device
105
-------
requires a continuous operation of both sewage pumps and air compressors
thereby increasing power and operation costs. The continuous operation
also requires more maintenance than the other aeration methods evaluated.
All costs Incurred in the study will not be reported as they would not
be representative of an operating facility. Foremost of these that
would not be applicable are operating and maintenance costs. The cost
for maintenance has been eliminated; however, the cost to be reported
for operation is based upon optimum conditions for air and oxygen feeds
as determined from the study. The capital cost for each facility is
given as well as power or oxygen cost.
Cost comparisons for the various aeration facilities are given in Table
22. Amortized capital cost is based upon an interest rate of 6 percent
and an expected life of 30 years. The total annual cost is given and
this in turn is given as a cost per million gallons treated, per pound
of oxygen applied and per pound of oxygen transferred.
The most favorable aeration facilities for sulfide control, excluding
maintenance costs, can be categorized for sewage transfer facilities
where a lift only is involved and where a force main is required. For
a station where a lift only is required, the most favorable cost found
was for a U-Tube using compressed air followed by a U-Tube using oxygen
gas. The most favorable cost for force main installations was air
injection into force mains followed by oxygen gas injection. These
proved to have a lower cost than the U-Tube, which could also be used
in conjuction with a force main. The cost of a U-Tube in conjunction
with a force main could be reduced by use of an aspirator in lieu of
compressed air or oxygen gas thereby reducing the operating cost which
was significant. The pressure tank resulted in the highest annual cost
and the cost per pound of oxygen transferred. In each instance the cost
reported should be considered with the previous discussions presented
for each type of equipment.
106
-------
Table 22
Cost Comparisons for Hydrogen Sulfide Control
Application
Force Main
Oxygen
Injection
Force Main
Air Injection
Pressure Tank
U-Tube -
Oxygen
Air
Station
Grannis
Railroad
Smith-Young
Railroad
Mainline
Stillwell
Pear Ridge
Lake Charles
Pioneer Park
Capital Amortized Annual Operating Cost Total Cost/Million
Cost Capital Cost (Power or Oxygen) Annual Cost Gallons treated
$ $ $ $ $/MG
3,554.00
3,554.00
3,554.00
2,187.15
2,187.15
12,500.00
12,500.00
10,000.00
8,448.45
258.20
258.20
258.20
227.90
227.90
908.13
908.13
726.50
613.78
2,495.
1,080.
1,080.
678.
2,875.
3,713.
2,875.
575.
678.
20
00
00
24
56
40
56
60
24
2,753
1,338
1,338
906
3,103
4,621
3,783
1,302
1,292
.40
.20
.00
.14
.46
.53
.69
.10
.02
17.46
4.24
14.55
2.87
1.96
27.05
22.15
6.60
3.51
Cost/lb.
O% Applied
3
3
3
.06
.22
.07
0.49
0.31
0
0
5
0
.30
.28
.97
.71
Cost/lb.
used &/or
(f/lb. '
2.8
3.44
3.41
1.98
1.29
14.51
13.48
6.63
4.21
-------
SECTION XIII
References
1 Holtzclaw, Leon V., Personal Interview, March 24, 1970.
2 Neel, Marvin, Report to City Council, August 29, 1967.
3 Holtzclaw, Leon V., Report to City Council, August 24, 1967-
4 Nebergall, W.G., F.C. Schmidt, and H.F. Holtzclaw, Jr., College
Chemistry. D.C. Heath and Company, Boston, (1963) 2nd Edition.
5 "Safety in Wastewater Works" Manual of Practice No. 1, Water
Pollution Control Federation, Washington, D.C. 1959.
6 Santry, I.W., "Hydrogen Sulfide in Sewers" JWPCF, 35, 12 (1580)
December 1963.
7 ASCE Manual of Practice No. 37, Design and Construction of Sanitary
and Storm Sewers 1969 Rev. Ed.
8 McKinney, Ross E., Microbiology for Sanitary Engineers, McGraw Hill
Book Company, Inc. 1962 (p. 100).
9 Pomeroy, R.D., and F.D. Bowlus, "Progress Report on Sulfide Control
Research," Sewage Works Journal Vol. 18, 1597 (1949)
10 Neel, Marvin, Report to Water and Sewage Study Committee, Nov. 18, 1968.
11 Heukelekian, H. and Ruby Lassen, "Oxidation of Reduced Sulfur Compounds
in Sewage," Sewage Works Journal Vol. 19, No. 6, p. 989 (Nov. 1947).
12 Elder, A.L. and A.M. Buswell, "Changes of Sulfur Compounds During
Sewage Treatment", Ind. and Eng. Chemistry, 21, 560 (1929)
13 Parker, C.D., "Mechanics of Corrosion of Concrete Sewers by Hydrogen
Sulfide," Sewage and Industrial Wastes Vol. 23, No. 12, 1477 (Dec. 1951),
14 Noller, Carl R., Structure and Properties of Organic Compounds. W.B.
Saunders Company, Philadelphia (1962).
15 Eliassen, R., A.N. Heller and G. Kisch, "The Effect of Chlorinated
Hydrocarbons on Hydrogen Sulfide Production," Sewage Works Journal,
21, 3, 457 (May, 1949).
16 Baumgartner, W.H., "Effect of Temperature and Seeding on Hydrogen
Sulfide Formation in Sewage," Sewage Works Journal 6. 3, 399 (1934).
108
-------
17 Streeter, H.W., C.T. Wright and R.W. Kehr, "Measurement of Natural
Oxidation in Polluted Streams, An Experimental Study of Atmospheric
Reaeration Under Stream - Flow Conditions," Sewage Works Journal. 8,
2, 282 (1936).
18 Kehr, R.W., "Measures of Natural Oxidation in Polluted Streams, IV.
Effect of Sewage on Atmospheric Reaeration Rates Under Stream Flow
Conditions," Sewage Works Journal. 8, 2, 282 (1936).
19 Parkhurst, J.D., and R.D. Pomeroy, "Oxygen Absorption in Streams,"
Journal of the Sanitary Engineering Division, ASCE, Vol. 98, No. SA
1, Proc. Paper 8701, Feb., 1972, pp. 101-124.
20 Pomeroy, Richard, "Generation and Control of Sulfide in Filled Pipes,"
Sewage and Industrial Wastes. Vol. 31, No. 9, 1082 (Sept. 1959).
21 Pomeroy, Richard, "Sanitary Sewer Design.for Hydrogen Sulfide Control,"
Public Works, pp. 93-96 & 130, October, 1970.
22 Davy, W.I., "Influence of Velocity on Sulfide Generation In Sewers,"
Sewage and Industrial Wastes. Vol. 22, 1132,(Sept. 1950)
23 Sewell, R. Joe, and R. H. White, "Progress in Controlling HgS Corrosion
in the Southwest," presented at the 42nd Annual Conference of the Water
Pollution Control Federation, Dallas, Texas, Oct. 8, 1969.
24 American Public Health Association, Inc., Standard Methods for the
Examination of Water and Wastewater, 1965.
25 Pomeroy, Richard, "Hydrogen Sulfide in Sewage," Sewage Works Journal.
Vol. 13, No. 3, 498 (May 1941).
26 Heukelekian, H., "Some Bacteriological Aspects of Hydrogen Sulfide
Production from Sewage," Sewage Works Journal. Vol 20, No. 3, 490
(May, 1948)
27 McKinney, R.E., "The Role of Chemically Combined Oxygen in Biological
Systems," Journal.Sanitary Engineering Division, ASCE, 82, SA 4,
1053 (August, 1956)
28 Pomeroy, R.D., "Flow Velocities in Small Sewers," Journal W.P.C.F.,
39, 9 Sept., 1967, pp. 1525-1548.
29 Pomeroy, Richard, "The Determination of Sulfides in Sewage and 1n
Sewer Atmospheres," Sewage Works Journal, 13, 3, 502 (1941).
30 Wisely, W.H., "Experiences in Odor Control," Sewage Works Journal,
Vol. 13, No. 6, 1230 (November, 1941).
109
-------
31 Wisely, W.H., "More Experiences in Odor Control," Sewage Works Journal.
Vol. 13, No. 6, 1230 (November, 1941).
32 Nelson, Myron K., "Sulfide Odor Control," Journal W.P.C.F.. Vol. 35,
No. 10, 1255 (October, 1963).
33 Choppin, A.R., and Faulkenberry, L.C., "The Oxidation of Aqueous Sulfide
Solutions by Hypochlorites," Journal American Chemical Society, 59,
2203 (1937).
34 Black, A.P., and J.B. Goodson, "The Oxidation of Sulfides by Chlorine
in Dilute Aqueous Solutions," Journal AWWA, Vol. 44, No. 4, pp. 309-
316, April, 1952.
35 Appel, A.A., "Chemical Treatment of Los Angeles Sewage to Retard
Slimes and Sulfides," Sewage Words Journal, Vol. 19, No. 3, 494
(May, 1947).
36 Carpenter, W.T., "Sodium Nitrate Used to Control Nuisances," Water
Works and Sewerage, 79, 175 (1932).
37 Heukelekian, H., "Effect of the Addition of Sodium Nitrate to Sewage
on Hydrogen Sulfide Production and BOD Reduction," Sewage Works
Journal, 15, 2, 255 (1943).
38 Ullrich, A.H., "Forced Draft Ventilation Protects Concrete Sewer Pipe,
Controls Odor," Water and Wastes Engineering, April, 1968.
39 Laughlin, James E., "Studies in Force Main Aeration," Journal of the
Sanitary Engineering Division, ASCE, 90, SA 6, Proceedings Paper 4150
(December, 1964).
40 Mahlie, W.S., "Removal of Hydrogen Sulfide in Sewage by Aeration,"
Sewage Works Journal, 7, 1, pp. 91-95 (1935).
41 Chen, K.Y., and J.C. Morris, "Oxidation of Sulfide by 03: Catalysis
and Inhibition," Journal of the Sanitary Engineering Division, ASCE,
Vol. 98. SA 1, Proceedings Paper 8710, February, 1972, pp. 215-227.
42 Pomeroy, Richard D., "Cakareous Pipe for Sewers," Journal W.P.C.F.,
Vol. 41, No. 8, 1941 (Aug., 1969).
43 Texas State Department of Health, Chemical Analyses of Public Water
Systems. 1970, Rev.
44 Texas State Department of Health, Design Criteria For Sewerage Systems,
Sept. 1968.
45 Personal Correspondence, Robert A. Bowers, P.E., Director of Planning,
City of Port Arthur, Texas, March 7, 1968.
110
-------
46 Sewell, R. J., "Condition of -Wet Wells Sanitary Sewage Lift Stations,
Port Arthur, Texas," A Report to the Water and Sewer Committee and
to the City of Port Arthur, October 24, 1968.
47 Personal Correspondence, Ewin A. Eads, Ph.D., Professor of Chemistry,
Lamar State College of Technology, Beaumont, Texas, August 23, 1968.
48 Bruijn, J. and H. Tuinzaad, "The Relationship Between Depth of U-Tubes
and the Aeration Process," J.A.W.W.A., SO, 879-883 0958).
49 Speece, R.E., J.L. Adams, and C.B. Wooldridge, "U-Tube Aeration
Operating Characteristics," Journal of the Sanitary Engineering
Division. ASCE, 95, SA 3, pp. 563-574 (1969).
50 Speece, R.E., and Rudolph Orosco, "Design of U-Tube Aeration Systems,"
Journal of the Sanitary Engineering Division, ASCE, 96, SA 3, 715,
(June, 1970)
51 Mitchel, R.C., "U-Tube Aeration," Environmental Protection Technology
Series; EPA 670/2-73-031, September, 1973; U.S. Environmental Protection
Agency, Washington., D.C.
52 Condon, R.L., R.A. Cooper, Jr., and A.J. Englande, Jr., "Instream
Aeration to Control Dissolved Sulfides in Sanitary Sewers"; EPA
670/2-73-024, July 1973; U.S. Environmental Protection Agency,
Washintn-on, D.C.
53 Wrigh obert L., "Force Main Aeration Using Gaseous Oxygen,"
Unpubl d Thesis - Lamar State University, June, 1969.
54 Neel, M • i, "Hydrogen Sulfide Levels in Sanitary Sewerage System,"
A Report to the City Council, City of Port Arthur, Texas, Nov. 1, 1967-
55 Santry, I.W., Jr., "Sanitary Sewers in Port Arthur, Texas," A Report
to the American Concrete Pipe Association, December 1967-March 1968.
Presented to the Water and Sewer Study Committee, November, 1968.
56 Bowl us, F.D. and A.P. Banta, "Control of Anaerobic Decomposition in
Sewage Transportation," Water Works and Sewerage; 79; 11; 369; (1932).
Ill
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-670/2-75-060
3. RECIPIENT'S ACCESSIOWNO.
4. TITLE AND SUBTITLE
CONTROLLING SULFIDES IN SANITARY SEWERS USING
AIR AND OXYGEN
5. REPORT DATE
June 1975 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
R. Joe Sewell
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
City of Port Arthur, Texas
Port Arthur, Texas 77640
10. PROGRAM ELEMENT NO.
1BB043 (ROAP 21ASW, Task 008)
11. dOWWttfOcX/GRANT NO.
11010 DYO
12. SPONSORING AGENCY NAME AND ADDRESS
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report documents ambient sulfide conditions and corrosion rates in a sanitary
sewerage system, and presents the results of a study that demonstrated that the use
of air or pure oxygen were effective in controlling sulfides. The three techniques
used to entrain the gases in the sewage included injection, U-Tubes, and pressure
tanks. Sulfide control was evaluated at eight separate locations involving lift
stations, force mains, and receiving gravity lines. The entrainment techniques
studied were not optimized. However, odor and corrosion problems were abated.
Preliminary cost data indicated that air injection into force mains, and the use of
air with the U-Tube were the least costly sulfide control measures. This report was
submitted in fulfillment of Project Number 11010 DYO, by the City of Port Arthur,
Texas, under the partial sponsorship of the Office of Research and Development, U.S.
Environmental Protection Agency.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
*0dor control
Corrosion prevention
Hydrogen sulfide
*Aeration
Oxygen
Sewers
Force mains
Diffusers
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*Sulfide control
U-Tubes
Pressure tanks
Lift stations
13B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
122
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
112
•A-U.S. GOVERNMENT PRINTING OFFICE: 1975-657-59't/5|t07 Region No. 5-1
------- |