c/EPA
United States
Environmental Protection
Agency
Municipal Environmental Research EPA-600/2 79 098
Laboratory August 1979
Cincinnati OH 45268
Research and Development
Comparison of
Ozone
Contactors for
Municipal
Wastewater Effluent
Disinfection
Packed Column
Versus Jet Scrubber
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Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1 Environmental Health Effects Research
2 Environmental Protection Technology
3 Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution-sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-79-098
August 1979
COMPARISON OF OZONE CONTACTORS FOR
MUNICIPAL WASTEWATER EFFLUENT DISINFECTION
Packed Column Versus Jet Scrubber
by
Albert D. Venosa, Edward J. Opatken
and Mark C. Meckes
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U. S. Environmental Protection Agency, and approved for publi-
cation. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
11
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solu-
tion and it involves defining the problem, measuring its impact, and
searching for solutions. The Municipal Environmental Research Laboratory
develops new and improved technology and systems for the prevention, treat-
ment, and management of wastewater and solid and hazardous waste pollutant
discharges from municipal and community sources, for the preservation and
treatment of public drinking water supplies, and to minimize the adverse
economic, social, health, and aesthetic effects of pollution. This publica-
tion is one of the products of that research; a most vital communications
link between the researcher and the user community.
As part of these activities, this report was prepared for use by design
engineers whose responsibility is to design the most efficient, cost-
effective ozone contacting system for achieving a specified bacteriological
quality of wastewater effluent.
Francis T. Mayo
Director
Municipal Environmental
Research Laboratory
111
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PREFACE
In January 1974, a U. S. Environmental Protection Agency (USEPA) Task
Force was formed to review USEPA policy on wastewater disinfection and the
use of chlorine. The Task Force recognized that chlorine and chlorine-based
compounds were being used almost exclusively for the disinfection of waste-
water. While chlorine was considered an effective disinfectant with respect
to meeting bacteriological standards and was adequately protecting public
health, there were potential dangers associated with the use of chlorine.
Disinfection of wastewater with chlorine could result in the formation of
halogenated organic compounds which have been identified as potential
carcinogens. Considerable data also existed that chlorination of wastewater
could result in residual chlorine or chloramine levels that could be toxic
to aquatic life. The Task Force concluded that, in view of the fact that
existing regulations inadvertently encouraged the use of chlorine, a
national regulation requiring disinfection would further compound the
potential problems associated with the chlorination of wastewater.
The Agency recognized that protection of public health from disease
continues to be the primary objective under the present system of regulation
of disinfection of municipal wastewater by means of State standards. It
also recognized that continuous disinfection in some localities was not
necessary to insure public health protection. The exclusive use of chlorine
for disinfection should not be continued where protection of aquatic life
is of primary consideration. Alternate means of disinfection or disinfectant
control (i.e., dechlorination) must be considered where public health hazards
and potential adverse impact on the aquatic or human environments exist.
Consequently, on July 26, 1976, USEPA amended the Secondary Treatment
Information regulation contained in 40 CFR Part 133^ Section 304(d)(l) of the
Federal Water Pollution Control Act Amendments of 1972. The amendment
deleted the fecal coliform bacteria limitation from the definition of
secondary treatment. Reliance on water quality standards for establishment
of disinfection requirements for publicly owned treatment works was selected
by the Agency.to replace the limitations in 40 CFR Part 133.
The USEPA Municipal Wastewater Disinfection Program is intensively
pursuing development of alternative disinfection technology which could
reliably achieve any specified bacteriological limitation without adversely
affecting the environment. Ozonation appears to be the most promising
alternative process presently under investigation. However, ozone is both
cost and energy sensitive. Generation of ozone by corona discharge is only
about 10 percent efficient from a power consumption standpoint. Thus, it
becomes imperative that all or most of the ozone produced on-site must be
utilized in the most efficient manner to prevent needless loss of energy and
resources.
iv
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An in-house research program was initiated at USEPA-Cineinnati's
experimental pilot plant located in the Robert A. Taft Laboratory building.
The purpose of the project is to compare and evaluate various types of gas-
liquid contacting devices in parallel on the same wastewater effluent so
that the conditions necessary for microorgansim reduction efficiency and
mass transfer efficiency can be properly defined and quantified. The
ultimate goal is to optimize ozone contacting to achieve the desired bac-
teriological quality and reduce operational costs of ozonation by eliminating
excessive loss.
This report is the first of a series on the comparative performance of
ozone contactors. It discusses the results of a study comparing a packed
column with a jet scrubber operating in parallel on conventional activated
sludge effluent.
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ABSTRACT
This research effort was initiated with the overall objective of deter-
mining which engineering and microbial operating parameters must be controlled
with respect to municipal effluent disinfection and ozone utilization for
various generic contactors.
Pilot scale investigations were made comparing two ozone contactors, a
jet scrubber and a packed column, for ozone utilization and coliform reduction
efficiency. These investigations were conducted in three phases: (1) batch
operation phase - both contactors were operated separately under identical
conditions using a batch sample of activated sludge effluent; (2) parallel
operational phase both contactors were operated in parallel on the same
activated sludge effluent; and (3) continuous operational phase - both
contactors were operated in parallel to achieve a three log reduction of
coliform bacteria on the same activated sludge effluent. The effluent was
characterizied by determining COD, TOC, SS, NH4~N, N03-N, N02-N, pH and
turbidity.
Bacterial enumerations included total and fecal coliforms, fecal
streptococci, and Salmonella spp. Ozone gas concentrations, before and
after contacting, were determined iodometrically, and ozone residual was
determined by amperometric techniques.
Results showed that the packed column significantly outperformed the
jet scrubber with respect to microorganism reduction and efficiency of ozone
utilization. Wastewater effluent quality interfered with disinfection in
both contactors, the most important variables being chemical oxygen demand
(total and soluble) and organic carbon. Initial bacterial density and ozone
residual were also important factors affecting log reduction of coliforms
and fecal streptococci in both contactors.
VI
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CONTENTS
Page
Foreword iii
Preface iv
Abstract vi
Figures ix
Tables xi
Abbreviations and Symbols xiv
Acknowledgements xvi
1. Introduction 1
2. Conclusions , 3
3. Recommendations 5
4. Materials and Methods
Sources of wastewater effluent 6
Description of equipment 7
Sample collection 11
Ozone concentration 12
Chemical and physical characterization of wastes 13
Bacteriological methods 13
Statistical data handling and experimental design 13
5. Results and Discussion
Ozone generator output 16
vn
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CONTENTS (Continued)
Phase 1 - batch operational mode 18
Wastewater effluent characteristics 19
Determination of mass transfer coefficients 19
Ozone utilization 23
Effect of packing size on packed column
performance 24
Contactor performance 25
Regression analysis 31
Phase 2 - parallel operational mode-factorial
experiment 38
Characteristics of wastewater effluent 38
Total coliform log reduction 38
Fecal coliform log reduction 41
Percent ozone utilization 43
Actual ozone utilization 43
Ozone residual 47
Ozone consumption 50
Linear regression analysis of data from factorial
experiment 54
Phase 3 continuous operation-pilot plant effluent 65
References 67
Appendices
A. The Modified Kenner-Clark Procedure for Enumerating
Salmonella spp 69
B. Mass transfer calculations 71
C. Safety precautions used in the ozone test facility 75
Vlll
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FIGURES
1. Flow schematic of ozone pilot plant system 7
2. Mass balance on ozone pilot plant 8
3. View of packed column 10
4. View of jet scrubber . 10
5. Jet action of scrubber (removed from contactor) . . . . 11
6. View of ozone gas decomposer 11
7. View of gas analysis work station 12
8. Relationship between power consumption and ozone
concentration 17
9. Effect of gas flow rate on ozone production 17
10. Effect of gas flow rate on power consumption 18
11. Variation of Henry's Constant with temperature 20
12. Effect of gas flow rate on mass transfer coefficient 22
13. Effect of ozone dosage on percent ozone utilization 23
14. Effect of G/L ratio on percent ozone utilization at a
constant dosage of 8.0 mg/£ 24
15. Total coliform log reduction as a function of ozone
dosage in the packed column and jet scrubber 40
16. Total coliform log reduction at all dosage levels as a
function of effluent total chemical oxygen demand in the
packed column and jet scrubber 41
17. Percent ozone utilization as a function of ozone dosage
in the packed column and jet scrubber 45
18. Percent ozone utilization as a function of effluent
total chemical oxygen demand in the packed column and
jet scrubber 45
ix
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FIGURES (Continued)
19. Ozone utilization as a function of ozone dosage in the
packed column and jet scrubber 48
20. Ozone utilization at all dosage levels as a function of
effluent total chemical oxygen demand in the packed
column and jet scrubber 48
21. Ozone residual as a function of ozone dosage in the
packed column and jet scrubber 51
22. Ozone residual as a function of effluent total chemical
oxygen demand in the packed column and jet scrubber 51
23. Ozone consumption as a function of ozone dosage in the
packed column and jet scrubber 53
24. Ozone consumption as a function of effluent total chemical
oxygen demand in the packed column and jet scrubber 53
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TABLES
1. List of Equipment and Specifications 9
2. Summary of Muddy Creek Effluent Characteristics 19
3. Effect of Packing Size on Overall Mass Transfer
Coefficients (kgVa) of the Packed Column at
Various Gas Flow Rates 25
4. Difference in Total Coliform Log Reduction (TCLR)
Between the Packed Column and Jet Scrubber as a
Function of Applied Dosage (MCWTP Effluent) 26
5. Difference in Fecal Coliform Log Reduction (FCLR)
Between the Packed Column and Jet Scrubber as a
Function of Applied Dosage (MCWTP Effluent) 27
6. Difference in Fecal Streptococcus Log Reduction (FSLR)
Between the Packed Column and Jet Scrubber as
a Function of Applied Dosage (MCWTP Effluent) 28
7. Densities of Salmonella spp. Before and After the
Ozone Contactors (MCWTP Effluent) 29
8. Difference in Ozone Utilization Between the Packed
Column and Jet Scrubber as a Function of Applied
Dosage (MCWTP Effluent) 30
9. Difference in Ozone Consumption Between the Packed
Column and Jet Scrubber as a Function of Applied
Dosage (MCWTP Effluent) 30
10. Difference in Ozone Residual Between the Packed Column
and Jet Scrubber as a Function of Applied Dosage
(MCWTP Effluent) 31
11. Correlation of Total Coliform Log Reduction (TCLR) in
the Packed Column with Ozone Dosage, Utilization,
Consumption, Residual, and Initial Total Coliform
Density (MCWTP Effluent) 33
XI
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TABLES (Continued)
12. Correlation of Fecal Coliform Log Reduction (FCLR)
in the Packed Column With Ozone Dosage, Utilization,
Consumption, Residual, and Initial Fecal Coliform
Density (MCWTP Effluent) 33
13. Correlation of Fecal Strep Log Reduction (FSLR) in the
Packed Column with Ozone Dosage, Utilization, Consump-
tion, Residual, and Initial Fecal Strep Density (MCWTP
Effluent) 34
14. Correlation of Total Coliform Log Reduction (TCLR) in
the Jet Scrubber with Ozone Dosage, Utilization, Con-
sumption, Residual, and Initial Total Coliform Density
(MCWTP) Effluent) 34
15. Correlation of Fecal Coliform Log Reduction (FCLR) in
the Jet Scrubber with Ozone Dosage, Utilization, Con-
sumption, Residual, and Initial Fecal Coliform
Density (MCWTP Effluent) 34
16. Correlation of Fecal Strep Log Reduction (FSLR) in the
Jet Scrubber with Ozone Dosage, Utilization, Consumption,
Residual, and Initial Fecal Strep Density (MCWTP
Effluent) 35
17. Characteristics of the Pilot Plant Effluent Prior
to Ozonation 38
18. Split-Split-Plot Layout for Total Coliform Log
Reduction Data 39
19. ANOVA for Total Coliform Log Reduction 39
20. Split-Split-Plot Layout for Fecal Coliform Log
Reduction Data 42
21. ANOVA for Fecal Coliform Log Reduction Data 42
22. Split-Split-Plot Layout for Percent Ozone Utilization Data ... 44
23. ANOVA for Percent Ozone Utilization Data 44
24. Split-Split-Plot Layout for Ozone Utilization Data 46
25. ANOVA for Actual Ozone Utilization Data 46
26. Split-Split-Plot Layout for Ozone Residual Data 49
27. ANOVA for Ozone Residual Data 49
XII
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TABLES (Continued)
28. Split-Split-Plot Layout for Ozone Consumption Data 52
29, ANOVA for Ozone Consumption Data 52
30. Correlation of Total Coliform Log Reduction (TCLR)
in the Packed Column at Different Applied Ozone
Dosage Levels with Effluent Quality Parameters 56
31. Correlation of Fecal Coliform Log Reduction (FCLR)
in the Packed Column at Different Applied Ozone
Dosage Levels with Effluent Quality Parameters 58
32. Correlation of Total Coliform Log Reduction (TCLR) in
the Jet Scrubber at Different Applied Ozone Dosage
Levels with Effluent Quality Parameters 58
33. Correlation of Fecal Coliform Log Reduction (FCLR) in
the Jet Scrubber at Different Applied Ozone Dosage
Levels with Effluent Quality Parameters 59
34. Correlation of Ozone Utilization in the Packed Column
at Different Applied Ozone Dosage Levels with
Effluent Quality Parameters . 59
35. Correlation of Ozone Utilization in the Jet Scrubber
at Different Applied Ozone Dosage Levels with
Effluent Quality Parameters 62
36. Correlation of Ozone Residual in the Packed Column
at Different Applied Ozone Dosage Levels with
Effluent Quality Parameters 62
37. Correlation of Ozone Residual in the Jet Scrubber
at Different Applied Ozone Dosage Levels with
Effluent Quality Parameters . 63
38. Correlation of Ozone Consumption in the Packed Column
at Different Applied Ozone Dosage Levels with
Effluent Quality Parameters 63
39. Correlation of Ozone Consumption in the Jet Scrubber
at Different Applied Ozone Dosage Levels with
Effluent Quality. Parameters 64
40. Continuous Operation of Packed Column and Jet Scrubber
for the 100-hour Period of February 28, 1977 to
March 3, 1977 64
Xlll
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LIST OF ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS
ANOVA
COD
df
F
FC
FCLR
FS
FSLR
kg
kg/d
kg/h
kPa
kW
kWh/kg
m3/d
MCWTP
mgA
mg/min
mm Hg
MS
n
r
T2
SCOD
S.D.
t
TC
TCLR
TKN
TOC
TSS
VSS
analysis of variance
chemical oxygen demand
degree of freedom
F-statistic
fecal coliform
fecal coliform log reduction
fecal streptococci
fecal streptococci log reduction
kilogram
kilogram per day
kilogram per hour
kilopascals pressure
kilowatt
kilowatt hour per kilogram
litre per minute
cubic meter per day
Muddy Creek Wastewater Treatment Plant
milligram per litre
milligram per minute
millimeter mercury
mean square
number of observations
correlation coefficient
coefficient of determination
soluble chemical oxygen demand
standard deviation
"t"-statistic
total coliform
total coliform log reduction
total Kjeldahl nitrogen
total organic carbon
total suspended solids
volatile suspended solids
SYMBOLS
a
Ck
Co
-- probability of error
-- contactor designation (i.e., packed column or jet scrubber)
-- ozone consumption (U R0J
xiv
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LIST OF ABBREVIATIONS AMD SYMBOLS (Continued)
°C -- degree centigrade
D.J -- dosage level
D0 -- applied ozone dosage
AY, -- log mean concentration difference of ozone in the gas phase in
equilibrium with ozone in the liquid phase
Fe -- iron
G -- gas flow rate
G/L -- ratio of gas flow rate to liquid flow rate
H -- Henry's Constant
HC1 -- hydrochloric acid
H2S04 -- sulfuric acid
KgV -- mass transfer coefficient
KgVa -- overall mass transfer coefficient
KI — potassium iodide
L -- liquid flow rate
Mn — manganese
N -- ozone transferred from the gas phase into the liquid
Na2S203 -- sodium thiosulfate
NH.+-N -- ammonium nitrogen
NO--N -- nitrite nitrogen
NO_-N -- nitrate nitrogen
ORG-N -- organic nitrogen
03 — ozone
R^ -- replicate
RQ -- ozone residual
Sj -- standard deviation of the difference
U0 -- ozone utilization
X -- total coliform density after ozonation (no./100 m£)
X -- initial total coliform density (no./lOO m£)
X -- mean
X, -- difference between means
x -- ozone concentration in the effluent (mols 0_/mol liq)
Y -- fecal coliform density after ozonation (no./lOO m£)
Yo -- initial fecal coliform density (no./lOO m£)
Y, -- ozone concentration in the inlet gas (mg/£)
Y2 -- ozone concentration in the exhaust gas (mg/£)
y* -- partial pressure of ozone gas in equilibrium with dissolved ozone
Z -- fecal streptococci density after ozonation (no./lOO m&)
Z -- initial fecal streptococci density (no./lOO mJl)
xv
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ACKNOWLEDGEMENTS
The able efforts of Messrs. Glenn Gruber, Leo Fichter, and Burney
Jackson in constructing the ozone disinfection system are gratefully
acknowledged.
Messrs. Richard Butler and William McErlane and Ms. Karen Hoskins
conducted the sampling and assisted in the performance of the ozone mass
balances. Assays of the samples for pathogenic microorganisms were per-
formed by Messrs. Harold Clark and Harold Sparks. Chemical analyses
were performed by the Waste Identification and Analysis Section, Wastewater
Research Division, Municipal Environmental Research Laboratory, USEPA,
Cincinnati, Ohio.
We are indebted to Mr. Joseph Santner for his invaluable guidance in
planning the factorial experiments. The above assistance of Mr. E. J.
Madison in computer data handling is gratefully acknowledged.
xvi
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SECTION 1
INTRODUCTION
Ozonation is rapidly gaining ground in the U.S. as a viable wastewater
disinfection process alternative to chlorination. However, the relatively
high capital and operating costs of ozone generating equipment, as compared
to chlorination, have hampered progress in attainment of widespread accepta-
bility. Any process development which offers promise in reducing the overall
costs of ozonation will accelarate that acceptability.
Ozone is a potent oxidizing agent and its reaction with oxidizable
materials is non-selective. The demand exerted by organic matter in effluents
can have a marked influence on the disinfection efficiency and reliability
of ozone. Care must be exercised in making certain that the ozone produced
is utilized in the most efficient manner; otherwise, the operating costs of
ozonation may be needlessly high due to excessive use of energy resources.
Detailed evaluations on gas-liquid contacting devices are needed so that ozone
utilization can be optimized, reliability established, and operating costs
identified.
Several studies are reported in the literature describing either the
disinfection performance or the mass transfer capability of different con-
tacting devices (8,14,15,18,19). Ghan et al. (8) evaluated three commercially
available contacting devices: a bubble diffuser, a positive pressure injector,
and a multi-stage mixing pump. The authors based their evaluation on ozone
utilization, defined as the difference in the ozone concentration between the
feed gas and exhaust gas. Ozone utilization was converted to a percent by
dividing the difference by the inlet gas concentration and multiplying by 100.
Percent ozone utilized in each contactor was plotted as a function of applied
ozone dosage. Results indicated 90 percent ozone utilization in the mixing
pump up to 50 mg/£ applied ozone, while the percent utilization in the other
two contactors decreased markedly with increasing dosage. They concluded that
the higher utilization in the mixing pump was due to the splitting of the
ozone gas stream into four injection points, thus maintaining a low ozone
dosage at each addition point. Later studies with a multi-stage,sparged system
confirmed that a 90 percent utilization efficiency could be readily achieved.
Masschelein et al'. (13,14) examined the ozone utilization efficiency of
various contacting devices. Systems studied included: (1) a multi-stage,
porous-pipe diffuser system operating in a countercurrent flow configuration;
(2) an injection system, similar in principle to a commercially available
positive pressure injection system; and (3) different types of single-stage
or multi-stage stirred turbine reactors. Comparisons were made on ozone
utilization in water and on total energy consumption. No bacteriological data
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were gathered, nor were parallel studies performed.
Nebel et al. (18) evaluated the rate of phenol oxidation in various ozone
mixing devices. They found that an important consideration in determining
the economic feasibility of a given mixer was whether extensive pumping of
the liquid to be treated is necessary. Parallel studies were not performed.
In 1974, Rosen et al. (19) postulated a conceptual model for ozone dis-
infection. Their model assumes that the rate of reaction of ozone with
bacteria is virtually instantaneous and that ozone disinfection occurs by
direct cell lysis. It was further assumed that lysis would result from
direct contact of a microorganism and an ozone gas bubble. Thus, they sug-
gested that disinfection is independent of dissolved ozone concentration and
that the rate of disinfection is not limited by the bulk mass transfer rate
of ozone into solution. This concept formed the basis for design of the
positive pressure injection system.
Recently, Farooq et al. (7) tested this hypothesis by observing the
different responses of yeasts and acid-fast bacteria to ozone under different
experimental conditions: (1) in the presence of both ozone bubbles and ozone
residual; (2) in the presence of ozone residual alone; and (3) in the presence
of ozone bubbles alone. They found that the primary microbicidal effect
occurred as a result of dissolved ozone. The presence of bubbles enhanced
microorganism reduction slightly, but the enhancement was not of such a
magnitude to affirm the validity of the bubble hypothesis. Since the primary
effect was due to dissolved ozone, disinfection efficiency would not be
independent of dissolved ozone concentration.
The project reported herein was initiated to evaluate various types of
ozone contacting devices operating in parallel on the same wastewater effluent,
so that the disinfection efficiency of ozone can be optimized and operating
costs evaluated. The types of contactors to be used in the study were
selected as representative of a variety of standard gas-liquid mixing
principles in the chemical engineering field and were not necessarily the most
efficient for wastewater effluent disinfection. The thrust of the study was
not achievement of a specified microbial density in the effluent, but rather
comparative log reductions under controlled conditions with definition of the
process variables most effectively influencing disinfection. The total waste-
water flow available at the experimental pilot facility (described in the
next section) is approximately 150 £/min. Thus, only two contactors, each
with a design capacity of 75 £/min, can be evaluated at any one given time.
A packed column is serving as the base unit, the performance of which will be
compared individually with all other contacting units. Other contacting
systems to be investigated in the future include: (1) a positive pressure
injector, (2) a bubble diffuser, and (3) a stirred turbine reactor. This
report concerns the comparison of the packed column with the jet scrubber.
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SECTION 2
CONCLUSIONS
Results of this ozone contactor evaluation have indicated that a jet
scrubber type contactor is not efficient for effluent disinfection with ozone.
The most important factor affecting microorganism reduction in the jet
scrubber was ozone residual. As the ozone residual levels increased, the
exhaust gas concentrations, by necessity, increased. Maintenance of an ozone
residual in the jet scrubber, which operated in a concurrent flow configur-
ation, was predicated upon maintenance of a high concentration of ozone in
the gas phase in equilibrium with the liquid phase. Performance of the jet
scrubber was further hampered by the exceedingly short residence time
(<3 seconds at 75 £/min liquid flow rate). Thus, microorganism reduction in
in the jet scrubber was poor.
The packed column, which was operated in a countercurrent mode, exhibited
a higher mass transfer driving force. Consequently, more ozone was utilized,
higher residuals were achieved, and microorganism reduction was better.
The packed column significantly outperformed the jet scrubber with
respect to microorganism reduction and efficiency of ozone utilization.
Wastewater effluent quality interfered with disinfection in both contactors,
the most important variable being chemical oxygen demand (total and soluble)
and organic carbon. Initial bacterial density was also an important factor
affecting log reduction of coliforms and fecal streptococci in both contactors.
The packed column was superior to the jet scrubber with respect to percent
ozone utilization, regardless of effluent quality and the magnitude of
applied dosage. This superiority was significant at all dosage levels
employed. With respect to actual ozone utilized, the packed column was
superior to the jet scrubber regardless of effluent quality, but the
difference between the contactors increased with increasing dosage.
An analysis of variance of the ozone utilization data from a factorial
experiment indicated that effluent quality did not significantly affect
overall ozone utilization in both contactors. However, linear regression
analyses of the data from each contactor at each individual dosage level
revealed that organic demand measured by TCOD, SCOD, and TOC significantly
affected ozone utilization in both contactors at high but not at low dosage
levels. Coliform reduction was adversely affected in both contactors by
TCOD, SCOD, and TOC at applied ozone dosage levels <13.1 mg/Ji and by TKN and
organic-N at 19.5 mg/£ applied ozone. It was concluded that at low doses
(i.e., 4.9 and 9.7 mg/& ozone), ozone utilization was mass transfer limited,
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while at higher dosages (i.e. >9.7 ing/5, ozone) it was reaction rate limited.
Coliform reduction was reaction-rate limited at all dosage levels.
Ozone residual and ozone consumption (i.e., the difference between ozone
utilization and residual) were significantly affected by effluent quality in
both contactors.
Coliform reductions in the pilot plant effluent to levels less than
100 total coliform/100 mi were achieved in the packed column only at an
applied dosage of 19.5 mg/&. Fecal coliform levels less than 200/100 m£ were
approached in the packed column at 19.5 mg/Ji applied ozone, but not in the
jet scrubber at any dosage.
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SECTION 3
RECOMMENDATIONS
(1) Studies with other contactors should be conducted in a manner
similar to that described in this report. It is essential that gas-
liquid contacting be optimized to eliminate inefficient utilization of
the ozone generated.
(2) Since ozone residuals are so transient and short-lived, more
accurate methods of measurement of such residuals should be devised so
that disinfection control by residual monitoring can be made possible.
(3) In this study, applied dosage was varied by maintaining a constant
ozone gas concentration and varying the gas flow rate. In subsequent
studies, dosage should also be varied by changing the ozone gas concen-
tration and maintaining a constant gas flow rate. This will enable a
better determination of the optimum operating conditions for a specific
contactor.
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SECTION 4
MATERIALS AND METHODS
SOURCES OF WASTEWATER EFFLUENT
Muddy Creek Wastewater Treatment Plant Effluent
During the first few months of the project, secondary effluent from the
Muddy Creek Wastewater Treatment Plant served as the wastewater source for
the ozone disinfection studies. This plant, operated by the Metropolitan
Sewer Board of Greater Cincinnati, is a conventional activated sludge system
treating approximately 57,000 m^/day of domestic wastewater.
On the day of an experiment, 20 m3 of Muddy Creek effluent were drawn
into a tank truck and transported to the experimental pilot plant located at
the Robert A. Taft Laboratory building. The effluent was pumped from the tank
truck through a magnetic flow meter and split into two lines. Both lines
were suitably valved to allow for any desired flow configuration. One line
passed through a rotameter and control valve and finally into the top of the
packed column. The second line was fed into a pump, where the pressure was
boosted to 380 kPa. The wastewater then flowed through a rotameter into the
jet scrubber.
Using the above mode of operation, an entire series of experiments was
performed on each contactor separately. This experimental arrangement, which
was essentially a batch operation, permitted the same effluent to be pumped
to each ozone contactor without the need for parallel, simultaneous operation.
Pilot Plant Effluent at Robert A. Taft Laboratory
Secondary effluent was also obtained from the conventional activated
sludge pilot plant located at the Robert A. Taft Laboratory building. The
raw wastewater entering the plant was of mixed industrial and domestic origin.
Effluent from the final clarifier was pumped through a magnetic flow meter,
and the flow split between the two contactors. An optional mixed media
pressure filter was available for removing suspended solids from the effluent
prior to splitting the flow. Data obtained under this arrangement were
collected with both contactors operating in parallel.
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DESCRIPTION OF EQUIPMENT
General
All experimental work was performed at the USEPA pilot plant facility
located at the Robert A. Taft Laboratory building, Cincinnati, Ohio. The
ozonation system consisted of ozone generation equipment and two generic
type contactors. A flow schematic of the ozone pilot system is shown in
Figure 1. A block diagram is presented in Figure 2 showing a mass balance
for ozone and effluent during a typical pilot run.
Nominal design flow capacity for each ozone contactor was 75 £/min of
secondary effluent. The ozone generator was capable of producing ozone at
a. maximum rate of 3500 mg/min. Since the pilot facilities were designed
for evaluating two contactors in parallel, the maximum applied dosage per
contactor was approximately 23 mg/£.
oo o
TANK TRUCK
FROM MUDDY CREEK
TREATMENT PLANT
PILOT PLANT
CLARIFIERS
Ozone Generation
AIR, OZONE
FLOW SCHEMATIC OZONE CONTACTORS SECONDARY EFFLUENT
Figure 1. Schematic of Ozone Pilot Plant System
Service air from the Robert A. Taft Laboratory building, supplied at a
pressure of 600 kPa, served as the source of air for ozone generation. A
standby 4 kW compressor was available for air supply in the event of failure
in the service air system.
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SERVICE AIR
Q,i flow rate of air
QSE = flow rate of secondary effluent
DP Dew Point
Q,=76 l/min
T=23°C
P=0.5tPo
Ol=745mg/min
QsE=76 l/min
T=20°C
Oj-lSmg/min
Figure 2. Mass Balance on Ozone Pilot Plant
The air was filtered for removal of particulates and lubricants, then
dried by adsorption of water vapor on activated alumina. The dryer con-
sisted of two parallel dryer beds, each containing 7.7 kg of activated alumina.
The process air was passed through one of the dryer beds, where the dew point
was lowered to -78 °C. Approximately 15 percent of the dried air was returned
for regenerating the alumina in the other dryer bed. The dryers then auto-
matically reversed their function, placing the regenerated bed on line for
drying air while the other bed underwent regeneration. The dried air was then
filtered for removal of any carry-over adsorbant and continuously monitored by
an in-line dew-point meter.
The dried air was reduced in pressure from 600 kPa to 55 kPa and then
split into two lines, each equipped with a rotameter and valve for flow con-
trol between 75 and 500 £/min. The gas then entered the dual ozonator, which
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was air-cooled and contained six plates per unit. Power was applied between
200 and 2000 watts, depending upon the ozone concentration and air flow
desired for the particular experimental run. The temperature of both ozone-
enriched gas streams was measured upon exiting the ozonator. The two streams
were recombined to obtain a homogeneous mixture and then split before entering
rotameters with a range between 20 and 130 A/min. After the rotameters,
seperate gas lines fed the packed column and the jet scrubber. An equipment
description for pilot items is shown in Table 1.
TABLE 1. LIST OF EQUIPMENT AND SPECIFICATIONS
Description
Manufacturer
Model no.
Capacity
Prefilter
Dryer
Afterfilter
Dew point monitor
Ozonator
Pall Trinity Micro Corp.
Pall Trinity Micro Corp.
Pall Trinity Micro Corp.
Shaw
Computerized Pollution
MCC1001SV160
25HA1
MCC1101EC12
Mini Hygrometer
OZ-180-G
-
700 I/rain 6 -40
-
-20 °C to -80 °C
4 kg 0,/d
°C
Packed column
Abatement Corp.
Corning Glass
230 mm D X 3.1 m
Intalox Packing, Size:
13 ram 5 25 mm
Jet scrubber
Decomposer
Multi-media filter
Ozone gas analyzer
Ozone residual
analyzer
R. P. Industries
Chromalox
Baker Filtration Co.
Dasibi Environmental Corp.
Fischer f, Porter
Dynactor Model
DY 12-10
GCII330
HRC-30D
1003-AH
17L2112A1
76 1/min
100-350 °C
370 1/min
-
0 - 2.5 rag 03/1
Packed Column
The packed column was a 230 mm diameter glass column 3.1 m in length.
The packing consisted of either 13 mm or 25 mm ceramic intalox saddles. A
teflonredistrubutor plate was located midway in the column to redirect the
liquid towards the center of the column. The packing rested on a ceramic
support plate at the bottom of the column. Secondary effluent entered the
top of the column (Figure 3) and exited at the bottom. The residence time
of the secondary effluent was 20 seconds at a flow rate of 75 £/min. Ozone
was injected at the bottom of the column, flowed upward and countercurrent
to the secondary effluent, and exited at the top. Pressure taps were located
in the gas lines at the bottom and top of the column for determining the
differential gas pressure during an experimental run. A photograph of the
entire packed column is shown in Figure 3.
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Figure 3. View of Packed Column
Figure 4. View of Jet Scrubber
Jet Scrubber Contactor
The jet scrubber was a stainless steel liquid-gas contactor in which
secondary effluent was pumped at a pressure of 280 kPa through an orifice
into a 300 mm diameter chamber. The resulting pressure drop caused minute
droplets to form. The ozone entered near the orifice and both components
(secondary effluent and ozone) flowed concurrently down the chamber. The
combined stream then flowed to a bottom outlet where the contacting gas was
separated from the effluent. A portion of the gas was aspirated back into
the upper chamber by the liquid flowing through the orifice and recycled to
the inlet area. A photograph of this contactor is shown in Figure 4.
Figure 5 shows the action of the jet orifice producing droplets.
Ozone Decomposer
The exhaust gas from each of the contactors was directed to an ozone
decomposer. An electric heater was used to increase the exit gas temperature
to between 260 °C and 290 °C to insure destruction of the ozone in the off-
gases. Figure 6 is a photograph of the decomposer.
10
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Figure 5. Figure 6.
Jet Action of Scrubber View of Ozone Gas Decomposer
(removed from contactor)
SAMPLE COLLECTION
Gas Samples
Ozone gas sampling ports were located at the outlet of the ozone
generator, the exhaust gas line from each contactor, and the exit gas line
following the ozone decomposer. Prior to sample collection the gas line was
purged for approximately one minute to insure equilibrium conditions.
All gas samples were analyzed for ozone by the standard iodometric
method, based on the report of Birdsall, Jenkins, and Spadinger (6). A
specified dosage condition was set by collecting a grab inlet gas sample
and measuring the ozone concentration iodometrically. Continuous measurement
of ozone in the gas stream was made subsequent to the grab analysis to provide
assurance of a steady state ozone concentration. The continuous monitoring
for operating control was accomplished by a Dasibi Environmental Corporation
(Glendale, California) ozone analyzer. Recalibration of the latter instrument
was performed at the start of each day.
Exhaust gas samples from the ozone contactors were collected and analyzed
iodometrically immediately after collection of ah effluent wastewater sample.
Wastewater Effluent Samples
Valved sampling ports were located on the influent and effluent lines
of both ozone contactors. Prior to actual sample collection, the sample
11
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lines were flushed for approximately 30 seconds to make certain that any
build-up of solid materials or microorganisms would be eliminated.
All samples were grab samples. Coliform MPN tubes were inoculated and
ozone residuals were measured immediately after sample collection. Samples
taken for physical-chemical characterization and for pathogen enumeration
were preserved by refrigeration for no more than one hour, according to
Standard Methods (1). Samples for chemical oxygen demand (COD) and total
organic carbon(TOC) analyses were preserved by acidification with sulfuric
acid and hydrocloric acid, respectively.
Samples were collected approximately 30 minutes after start-up or a
change in experimental conditions. The sampling schedule was based on the
flow rate such that sample collection followed the flow of a single slug of
liquid through the treatment process.
OZONE CONCENTRATION
Ozone Gas Analysis
Ozone concentration in the inlet and exhaust gas was determined
iodometrically (6). The ozone-air lines were first purged by allowing the
gas to flow into a solution of approximately 1 N potassium iodide (KI).
Following purging, the gas stream was then directed through a series of
two 500 ml gas washing bottles, each containing approximately 400 ml of a
1 percent KI solution. The exit gas from the second gas washing bottle passed
through a wet test meter for determination of the gas sample volume (Figure 7),
The solutions in the gas washing bottles were transferred to a 1500 ml beaker
and acidified to a pH of less than 2 by the addition of 20 percent sulfuric
acid. This solution was titrated to the starch end point with 0.050 N sodium
thiosulfate (Na2S203). The titrant was standardized daily against
potassium dichromate (6).
Figure 7. View of Gas Analysis Work Station
12
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Ozone Residual Analysis
A modification of the amperometric titration method for total residual
chlorine (1) was used for determination of effluent residual ozone. Samples
were collected at the effluent lines of both contactors in a 200 ml sample
bottle containing 1 ml of a 1 percent KI solution and 4 ml of pH 4 acetic
acid-sodium acetate buffer. The sample was immediately transferred to the
titration cup and titrated with 0.0050 N Na2S203 to the amperometric end point.
The titrant was standardized daily against a standard iodine solution.
CHEMICAL AND PHYSICAL CHARACTERIZATION OF WASTES
Total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD)
after filtration through a Whatman glass fiber filter, total organic carbon
(TOC), total suspended solids (TSS), volatile suspended solids (VSS), ammonia
nitrogen (NHj-N), total Kjeldahl nitrogen (TKN), manganese (Mn) , iron (Fe) ,
pH, and turbidity were determined according to the USEPA Methods Manual (15).
Nitrate nitrogen (N03-N) and nitrite nitrogen (NC^-N) were determined by the
automated hydrazine reduction method (10).
BACTERIOLOGICAL METHODS
Samples collected for bacteriological analysis, both before and after
ozonation, were mixed with sodium thiosulfate (1) . Total and fecal coliforms
were enumerated by the 5-tube, 4-dilution most probable number (MPN) technique
(1). Presumptive medium was lactose broth (Difco), and confirmatory medium
for total coliforms was brilliant green bile broth (Difco). EC broth was used
as confirmatory medium for fecal coliforms. Fecal streptococci were enumerated
by the membrane filter technique (1) using KF streptococcus agar (Difco).
Isolation and enumeration of Salmonella spp. were performed using a modifi-
cation of the Kenner and Clark Method (11) (see Appendix A for a detailed
description of the method.)
STATISTICAL DATA HANDLING AND EXPERIMENTAL DESIGN
Testing of the pilot plant ozonation process was performed according to
predetermined factorial arrangement. The arrangement, called a split-split-
plot design, was modelled according to Anderson and McLean (4).
Secondary effluent was pumped to each ozone contactor at a rate of
75 J?,/min, while ozone gas, generated from air at a constant concentration of
9.7 mg ozone/£ air, was fed to both contactors at various gas flow rates.
Dosage was determined by multiplying the concentration of ozone in the inlet
gas by the ratio of the gas to liquid flow rates. Four different pre-selected
dosage levels were used, and grab samples of ozonated effluent from both con-
tactors were taken for bacteriological and chemical analysis. Both contactors
received the same dosage at any given time, but the order in which the four
dosage levels were applied in any given experiment was randomized by referring
to a random number table. Each entire experiment was considered a "whole
plot" and was replicated on six different days (R^). The "split-plot"
consisted of four dosage levels (D-)within a replicate experiment, and the
"split-split-plot" consisted of the two contactors (C^) compared at each
dosage level within each replicate experiment.
13
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Separate analysis of variance (ANOVA) were performed to compare the two
contactors on the basis of six dependent variables (performance criteria) as
a function of one independent variable (applied ozone dosage) .
The performance criteria were log total coliform reduction, log fecal
coliform reduction (log Ng/N, where NQ = the initial number of coliform
bacteria and N = the number remaining after treatment) , percent ozone
utilization, total ozone utilized (mg/#), ozone residual (mg/£), and ozone
consumtion (mg/£).
Applied ozone dosage was defined as follows:
D0 = y^/L (1)
where DQ = applied dosage (mg OT/^
y, = ozone concentration in the inlet gas (mg 0,/jl )
i j gas
G = gas flow rate (& /min)
gas
L = liquid flow rate (jL . /min).
Percent ozone utilization was defined as follows:
y - y
(100)
where y2 = ozone concentration in the exhaust gas (mg 0 / g ) .
Total ozone utilization was defined as follows: (3)
^1 " y2
U = Dosage x fraction utilized = y (G/L) - = G/L (y1 - y-) ,
y~i
where U = total ozone utilized (mg/&).
Ozone consumption was defined as follows:
' Co = Uo - Ro> C4)
where Co = consumption (mg/A) , and R0 = ozone residual (mg/£) .
In each analysis of variance (ANOVA) there were three "main effects"
(i.e., Cj. D . , and R.) under investigation, and two "interaction effects"
(i.e., R^C^ and DjC^J. The contactor main effect (C^) tested the difference
in performance (i.e., total or fecal coliform log reduction (TCLR or FCLR)
ozone utilization, etc.) between the two contactors. The dose main effect
(Dj) tested the effect of ozone dosage on the performance of both contactors.
14
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The replication main effect (RjJ tested the effect of different days on the
performance of both contactors. Since the only variable which was not
controlled from day to day was effluent quality, R^ actually tested the effect
of effluent quality on contactor performance. The contactor-dosage
interaction effect (CkDj) tested whether the difference in performance
between the two contactors was consistent or changed at each dosage level.
Finally, the contactor-replication interaction effect (C^R^ tested whether
the difference in performance between the two contactors was consistent or
changed from day to day.
In addition to the ANOVA's described above, data were subjected to
linear and stepwise multiple regression analyses to evaluate the effects of
different wastewater parameters individually or in concert on the selected
performance criteria. Data analyses were facilitated by an IBM 370 computer,
using Biomedical Computer Programs BMD02V (Analyses of Variance for Factorial
Design) and BMD02R ( Stepwise Regression) (5).
15
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SECTION 5
RESULTS AND DISCUSSIONS
OZONE GENERATOR OUTPUT
The ozone generator was designed to deliver 4 kg 0,,/d. Initial evalu-
ation of ozone output revealed that less than 2 kg/d were being generated.
A dew point monitor was inserted into the conditioned air line following the
dryer and indicated that the dew point of the air was above -20 C. The
purge rate to the dryer was increased and the dew point subsequently fell
below -40 °C. This caused the ozone output from the generator to rise to the
specified 4 kg/d level. No further problems were experienced in either main-
taining a dew point below -40 C or achieving the desired ozone output.
Mapping of Ozone Generator
Before initiating the contactor evaluation phase of the investigation,
it was necessary to establish the relationship between electrical power, gas
flow rate, and ozone concentration in the gas to permit evaluation of the
ozone generation efficiency of the CPAC ozone generator under various experi-
mental conditions. This was accomplished by mapping the ozone generator,
using only one module of the dual unit to insure accurate gas flow control.
Ozone concentration in the gas was measured as a function of electrical
power at various gas flow rates. Power was ajusted from 0.25 to 2.0 kw at
0.25 kw increments. Results are shown in Figure 8. At a constant gas flow
rate, ozone concentration increased with power until a plateau was reached.
After this point, further increase in power actually resulted in a reduction
in ozone concentration.
The data from Figure 8 were rearranged to illustrate ozone production,
in terms of kg/h, as a function of gas flow at various power levels. Results
are shown in Figure 9. It is evident that ozone production increased with
gas flow rate, followed by a declining production as optimum gas flows were
exceeded, except at the 0.25 kw power level.
The data were again rearranged to demonstrate the power requirements
necessary to produce a unit weight of ozone as a function of gas flow rate
at specified power levels. Results are presented in Figure 10. It is clear
that, at low gas flow rates, considerably more energy was required to
generate a unit weight of ozone than at higher flow rates.
The above mapping experiment can provide useful information to the
16
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G = GAS FLOW (l/min)
01
E
<
-------
50
40
30
20
10
0.25 ft*
I
I
20
40
60 80 100 120 140
GAS FLOW (l/min)
Figure 10. Effect of Gas Flow Rate on Power Consumption
design engineer in sizing ozone generator equipment and to the plant operator
in selecting an operating condition that would deliver the required ozone
capacity at the minimum power requirement per unit weight of ozone. Thus,
to maximize ozone production (kg per unit time) higher gas flows are needed
(Figure 9), resulting in improved power efficiency (Figure 10). However,
higher power levels are also needed (Figure 9), thereby offsetting the
improved production efficiency by a greater energy usage per kg ozone (Figure
10). Conversely, to maximize the ozone concentration, lower gas flows are
needed (Figure 8), resulting in increased power per kg ozone produced (Figure
10) and lower ozone production in terms of kg per unit time (Figure 9).
PHASE 1 BATCH OPERATIONAL MODE
In this phase of the investigation, experiments were performed on waste-
water effluent which was transported by truck from the Muddy Creek Wastewater
Treatment Plant (MCWTP). Since the effluent was a batch source not subject
to continual change in quality, experiments were conducted on each contactor
separately rather than in parallel.
18
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Wastewater Effluent Characteristics
Table 2 summarizes the mean, standard deviation, and range of the efflu-
ent characteristics of the Muddy Creek effluent from August 2, 1976, to Novem-
ber 2, 1978, the experimental period for this phase of the study.
It is evident that the levels of TSS, turbidity, and TOC were low, and
there was very little difference between TCOD and SCOD. Most of the TKN
was composed at NH^-N. In general, the MCWTP effluent quality was excellent.
TABLE 2. SUMMARY OF MUDDY CREEK EFFLUENT CHARACTERISTICS
Parameter
Temperature (C)
TCOD, mg/£
SCOD, mg/£
TOC, mg/£
TSS, mg/£
TURB, JTU
TKN, mg/J,
NHj-N, mg/H
ORG-N, mg/Jl
Log total coliform
density
Log fecal coliform
density
Log fecal streptococci
density
Mean
21
30
24
10.3
6.7
3.8
8.3
7.2
1.6
5.77
5.38
4.19
Standard
Deviation
3
10
9
5.2
3.8
1.5
8.2
7.6
1.0
0.51
0.64
0.71
Range
14-24
18-56
15-49
4.4-25.5
2.4-20
2.3-7.6
1.9-37.8
0.1-34
0.2-3.8
4.90-6.73
4.36-6.54
2.70-5.23
Determination of Mass Transfer Coefficients
Mass transfer coefficients in the packed column and jet scrubber were
determined using MCWTP effluent. Gas flow rates were varied between
35 and 150 Vmin. Ozone was measured in the inlet and exhaust gases and in
the liquid emerging from the contactors.
The quantity of ozone that could be absorbed by the secondary effluent
was limited by the inlet ozone gas concentration as related to Henry's law.
This relationship is described by the following equation:
y* = Hx
where y* = partial pressure of ozone in the gas in equilibrium with the
dissolved ozone in the liquid (mm Hq)
(5)
19
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H = Henry's constant (mm Hg/mol fraction of ozone in the liquid)
m = mol fraction of ozone in the secondary effluent
(moIs 03/mol liquid).
Henry's constant defining the relationship between the partial pressure
of ozone and the concentration of ozone in the liquid can be obtained from
the International Critical Tables (16). Since the units of the terms in
equation 5 were tedious to manipulate, they were converted to the following
more useful terms by incorporating relationships defined in the gas laws:
y* = concentration of ozone in the gas in equilibrium with ozone in
the liquid (rag Gig/litre gas),
H = litres of liquid/litre of gas,
x = concentration of ozone in the liquid (mg Oy'litre liquid).
The magnitude of Henry's constant is substantially affected by temper-
ature, as shown in Figure 11. As temperature increases, the value of
Henry's constant increases.
8.0,
7.0
6.0
5.0
4.0
c/> 3.0
2.0
1.0
I
10 20 30 40
TEMPERATURE (°C)
Figure 11. Variation of Henry's Constant with Temperature
20
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The mass transfer coefficients for the packed column were determined
using the following equation:
N = G (7l y2) - KgVa (A ylm) (6)
where N = ozone transferred from the gas phase into the secondary
effluent (mg/min) ,
G = gas flow rate (litres gas/rain) ,
y1= ozone concentration in the inlet gas (mg/£),
y2= ozone concentration in the exhaust gas (mg/£) ,
KgVa = overall mass transfer coefficient (litres gas/minj ,
A/-, = log mean concentration difference of ozone in the gas phase
across the entire column (mg/£)
The term Ay1 is defined by the following equation:
(71 - 71*) - (72 - 72*)
= -
1m
= - (7)
In
(72 - 72*)
where y, * = ozone concentration (mg/£ ) in the gas phase in equilibrium with
the ozone residual in the liquid at the bottom of the column, as
defined by Henry's Law (equation 5),
and y2* = ozone concentration (mg/&) in the gas phase in equilibrium with
the ozone residual in the liquid at the top of the column.
In the packed column, y->* - 0 because there was no ozone residual in the
liquid entering the top of the column. Thus, equation 7 simplifies to:
(/! - 7!*) 72
7lm = - ( *5 (8)
In
72
The mass transfer coefficients for the jet scrubber were computed in the
same manner. However, since the flow configuration in the jet scrubber was
concurrent rather than countercurrent, yj* = 0 because the liquid entering
the contactor contained no ozone residual. Thus, for the jet scrubber,
equation 7 simplifies to :
y-,- (77 y/)
A/lrn = - ~ - (9)
111 (72 - 72*)
21
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Detailed results from these experiments are given in Appendix B. The
mass transfer coefficients for both contactors at various flow rates are
illustrated in Figure 12. The data indicate that the mass transfer coeffi-
cients for the packed column were more than twice the value determined for
the jet scrubber at the gas flow rates studies.
Henry's Law states, by definition, that as ozone residual increases,
ozone concentration in the gas phase in equilibrium with the residual also
increases. This means that transfer is inhibited by high ozone residuals.
A countercurrent flow configuration, such as in the packed column, has the
advantage not only of contacting the liquid containing the highest ozone
residual with the gas containing the highest ozone concentration (i.e., at
the bottom of the column), but also of contacting the liquid containing the
least ozone residual with the gas containing the lowest concentration of
ozone (i.e., at the top of the column). This tends to equalize the concen-
tration driving force and mass transfer rate across the entire length of the
column.
200
150
100
50
PACKED COLUMN
I
Figure 12.
50 100 150
GAS FLOW RATE (l/minj
Effect of Gas Flow Rate on Mass Transfer Coefficient
In contrast, the jet scrubber, which operates in a concurrent flow
configuration, maintains a high concentration gradient at the inlet end. As
the residual increases, the exit gas concentration, which must be in equi
librium with the residual, also increases. This substantially limits the
concentration driving force in the jet scrubber and explains the lower mass
transfer coefficients relative to those of the packed column.
22
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Both contactors had relatively short contact times (approximately
20 seconds for the packed column and 3 seconds for the jet scrubber, at a
liquid flow rate of 75 £/min). This tended to hinder both mass transfer and
ozone utilization. Longer contact times would permit the dissolved ozone to
react with oxidizable constituents in the secondary effluent, lowering the
ozone residual and increasing the overall ozone concentration driving force.
Ozone Utilization
Ozone utilization, as defined earlier, was evaluated in both contactors
from the same data base used to compute the mass transfer coefficients.
The quantity of ozone that can be absorbed by water is limited by the
temperature of the water and the concentration of the ozone in the gas stream.
Thus, the maximum ozone residual that can be obtained in water is fixed by
Henry's Law (equation 5). However, the results from experiments with secon-
dary effluent revealed that ozone transfer was greater than could be predicted
by Henry's Law. The demand of the secondary effluent created by the presence
of oxidizable organic and inorganic compounds enabled more ozone to be
transferred to the wastewater.
Figure 13 summarizes the percent ozone utilization data in both
contactors as a function of applied ozone dose. Results indicate that the
percent ozone utilized by the packed column was substantially greater than
the jet scrubber. Thus, the packed column was superior to the jet scrubber
from the standpoint of mass transfer efficiency and percent ozone utilization
efficiency.
80
- 60
20
PACKED COLUMN
JET SCRUBBER
4 8 12 16
OZONE DOSAGE (mg/I)
Figure 13. Effect of Ozone Dosage on Percent Ozone Utilization
23
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Ozone Dosage
Dosage was defined earlier in equation (1): DQ = y1G/L.
There are two ways to vary ozone dosage: (1) change the G/L ratio while
maintaining a constant gas concentration, or (2) change the ozone gas
concentration while maintaining a constant G/L ratio. However, utilization
can be changed by maintaining dosage constant and increasing the concentra-
tion of ozone in the gas (i.e., increase y^ and decrease G/L). Figure 14
illustrates the change in percent ozone utilization in both contactors as
a function of G/L at a constant dosage level. It is clear that as G/L
increased (or y decreased), percent ozone utilization decreased, even though
the applied dosage was constant. Caution must be exercised in using these
data, because increased y-, values require increased power input per unit
weight of ozone when the dosage is constant (see Figures 8 and 9). Thus,
power must be factored into any evaluation to establish optimum performance
criteria. The most cost-effective operating condition for ozone disinfection
does not necessarily comprise the lowest ozone dosage.
100
80
BO
LU 40
20
Figure 14,
0.5 1.0 1.5 2.0
RATIO OF GAS FLOW RATE TO LIQUID FLOW RATE (G/L|
Effect of G/L Ratio on Percent Ozone Utilization
at a Constant Dosage of 8.0 mg/£
Effect of Packing Size on Packed Column Performance
After completing Phase I of the investigation, it was necessary to switch
from the MCWTP effluent to the R.A. Taft Laboratory building pilot plant
effluent so that both contactors could be operated in parallel. The overall
quality of the latter effluent was inferior to the MCWTP effluent. This
factor resulted in excessive pressure drops in the packed column when the
system was operated at a liquid flow rate of 75£/min.
24
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To compensate for the increased pressure drops in the packed column, it
was necessary to increase the packing size from 13 mm to 25 mm ceramic inta-
lox saddles. This modification, in effect, lowered the surface area of the
packing and consequently enabled operation of the column at more reasonable
pressure drops (i.e., <300 mm H20). However, this also affected the mass
transfer efficiency of the column. Table 3 demonstrates the effect of packing
size on the overall mass transfer coefficients of the packed column at.various
gas flow rates.
The overall mass transfer coefficient (KgVa) consists of the product of
the mass transfer coefficient (KgV) and the surface area per unit volume
of packing (a). Although the KgVa did not substantially change with packing
size, the total .mass transfer of ozone into the liquid over the entire column
decreased as a direct result of the decrease in surface area of the packing.
TABLE 3. EFFECT OF PACKING SIZE ON OVERALL MASS TRANSFER
COEFFICIENTS (Kg Va) OF THE PACKED COLUMN AT VARIOUS GAS FLOW RATES
Gas flow
rate, £/min
Kg Va, & gas/min
13 mm packing
(KgV, £/min/m)
25 mm packing
(KgV, fc/min/m)
37
74
110
147
84
(0.135)
163
(0.261)
175
(0.280)
205
(0.329)
46
(0.180)
66
(0.258)
73
(0.285)
86
(0.336)
Contactor Performance
Total Coliform Reduction--
During the three month period between August 2, 1976, to November 2, 1976,
a total of 40 experiments were performed with MCWTP effluent to evaluate the
total coliform reduction efficiency of the packed column and the jet scrubber.
The data were grouped into three segments according to the magnitude of the
applied ozone dosage (i.e., low, moderate, and high). All observations were
taken in matched pairs to facilitate direct comparison between the two
contactors. The t-test for matched pairs was performed according to Natrella
(17) after confirming that the data were normally distributed. A significance
level (2) of 0.05 was chosen for all tests. The data are summarized in
Table 4.
25
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TABLE 4. DIFFERENCE IN TOTAL COLIFORM LOG REDUCTION (TCLR)
BETWEEN THE PACKED COLUMN AND JET SCRUBBER AS A
FUNCTION OF APPLIED DOSAGE (MCWTP EFFLUENT)
NJ
CT)
Ozone
Level
Low
Mod-
erate
High
All
dosage, mg/£
Range Mean
2.4- 4.6 3.6
5.9-10.0 7.5
11.8-18.6 13.9
2.4-18.6 7.4
Number of
data points
(n)
14
18
8
40
Mean TCLR
(Std. dev.)
Packed column Jet
1.99
[0. 63)
2.77
CO. 59)
2.41
CO. 96)
2.43
CO. 76)
scrubber
1.36
CO. 87)
2.32
CO. 64)
2.21
CO. 92)
1.96
(0.89)
Mean
difference
(Std. dev.)
0.63
(0.77)
0.45
CO. 52)
0.21
CO. 53)
0.46
CO. 62)
t
t (a=0,05)
3.06 2.16
3.67 2.11
1.12 2.36
4.69 2.02
-------
The t-statistics in Table 4 and subsequent tables were calculated from
the following equation (17):
t = xd"
(10)
where x, = mean difference in TCLR between contactors, S, = standard deviation
of the difference, and n = number of data points. It is clear that total
coliform reduction was significantly greater in the packed column than in the
jet scrubber at the low and moderate dosage levels but not at the high dosage
level. When considering all dosage levels combined (n = 40), TCLR in the
packed column was significantly greater than that in the jet scrubber.
Fecal Coliform Reduction--
The fecal coliform data were analyzed similarly and summarized in Table 5,
The fecal coliform data reflect the same trends as the total coliform data.
The packed column significantly outperformed the jet scrubber with respect to
fecal coliform reduction at low and intermediate dosage levels but not at the
high dosage level. When considering all dosage levels, the packed column was
significantly better than the jet scrubber with respect to FCLR.
TABLE 5. DIFFERENCE IN FECAL COLIFORM LOG REDUCTION (FCLR)
BETWEEN THE PACKED COLUMN .AND JET SCRUBBER AS A
FUNCTION OF APPLIED DOSAGE (MCWTP EFFLUENT)
Number of
Ozone dosage, mg/l data points
Level Range Mean (n)
Low 2.6- 4.6 3.6 13
Mod- 5.9-10.0 7.5 17
erate
High 11.8-18.6 14.0 8
All 2.6-18.6 7.5 38
Mean FCLR
(Std.
Packed column
2.28
(1.27)
3.27
(1.12)
3.09
(1.33)
2.89
(1.27)
dev. )
Jet scrubber
1.42
(1.15)
2.76
(1.09)
2.53
(0.90)
2.25
(1.21)
Mean
difference
(Std. dev/
0.86
(1.10)
0.51
(0.86)
0.56
(0.98)
0.64
(0.98)
t
) t (o=0.05)
2.82 2.18
2.45 2.12
1.62 2.36
4.02 2.03
Fecal Streptococcus Reduction--
The difference in efficiency between the two ozone contactors with
respect to fecal streptococcus reduction are presented in Table 6. It is
clear that the packed column significantly outperformed the jet scrubber with
respect to fecal streptococcus reduction at all dosage levels studied.
27
-------
TABLE 6. DIFFERENCE IN FECAL STREPTOCOCCUS LOG REDUCTION (FSLR)
BETWEEN THE PACKED COLUMN AND JET SCRUBBER
AS A FUNCTION OF APPLIED DOSAGE (MCWRTP EFFLUENT)
Number of
O'one dosage, m°/i data points
Level Range Mean (.n)
Low 2.6- 5.S 3.4 10
Mod- 6.0-8.6 ".3 13
erate
High 10.0-14.6 12.7 6
All 2.4-14.6 7.1 29
Mean FSLR
(Std. dev.)
Packed column
1.
to.
->
10.
3 .
(.0.
T
10.
63
40)
65
67)
12
48)
.39
.SO)
Jet scrubber
1.
(0.
-)
to.
-1
to.
1 .
to.
36
S7)
,28
86)
.17
65)
.94
S3)
Mean
difference t
(Std.
0.
(0.
0.
to.
0.
to.
0.
to.
dev.) t (a=0.05)
27 3.05 2.26
28)
.37 4.04 2.18
33)
95 3.S8 2.57
60)
.45 5.39 2.05
.45)
Salmonella Reduction--
Attempts were made to quantify the density of Salmonella spp. before and
after the ozone contactors to evaluate the disinfection efficiency of both
contactors with respect to enteric pathogens. The method involves a 3-tube
MPN procedure (see Appendix A) and is limited in precision and accuracy. A
total of 20 samples were analyzed for Salmonella spp. in the MCWTP effluent
entering the ozone contactors, plus an additional 39 matched pair samples
exiting the contactors. The geometric mean Salmonella density in the 20 samples
of MCWTP effluent entering the' contactors was only 180 organisms/10 liters.
Many of the samples from the ozone contactors contained too few numbers to
measure. The data are summarized in Table 7.
Of the 39 total samples from each contactor analyzed for Salmonella spp.,
28 from the packed column and 24 from the jet scrubber contained insufficient
numbers to quantify as signified by the "<" symbol. Thus, it is virtually
impossible to quantitatively assess the Salmonella reduction efficiency of
either contactor.
Ozone Utilization--
Ozone utilization data were analyzed in the same manner as the bacteri-
ological data. Results are summarized in Table 8.
It is clear from Table 8 that ozone utilization in the packed column was
significantly higher than the jet scrubber at all dosage levels studied. In
addition, the difference in utilization appeared to increase with increasing
dosage. Thus, the packed column was a more efficient ozone contactor than
the jet scrubber with respect to total ozone utilized, and the relative
efficiency increased with increasing dosage.
28
-------
TABLE 7. DENSITIES OF SALMONELLA SPP. BEFORE AND AFTER
THE OZONE CONTACTORS (MCWTP EFFLUENT)
03 Dose,
mg/&
2.5
2.8
3.0
3.6
3.6
3.6
3.6
3.8
3.8
6.0
6.0
6.4
6.9
7.2
7.4
7.4
7.5
7.5
7.6
7.8
7.9
7.9
7.9
8.0
8.6
10.0
11.2
12.0
12.0
12.4
13.2
13.5
14.2
14.2
14.2
14.5
14.5
14.8
17.7
Influent
No./lO liters
18.2
280
280
7.2
7.2
7.2
2300
86
18.2
7.2
86
1900
780
2300
730
15000
7.2
1280
7.2
480
480
1280
1900
480
480
780
360
2300
15000
42
920
42
7.0
46
150
7.0
46
150
920
Effluent
No./lO liters
Packed
column
<6
7.2
<6
<6
<6
<6
<300
7.2
<6
<6
<6
18.2
6
<300
<300
360
<6
7
<6
<6
46
<4
<6
7.2
<6
<6
<300
<300
<300
<3.6
920
<3.6
<6
<6
<6
<6
<6
72
186
Jet
scrubber
7.2
7.2
480
<6
<6
<6
360
<6
7.2
<6
<6
18.2
18.2
<300
<300
<300
<6
18
<6
<6
<6
7
86
7.2
<6
18.2
<300
<300
<300
7.2
2200
18
<6
<6
<6
<6
<6
<6
420
29
-------
TABLE 8. DIFFERENCE IN OZONE UTILIZATION BETWEEN THE PACKED COLUMN AND
JET SCRUBBER AS A FUNCTION OF APPLIED DOSAGE (MCWTP EFFLUENT)
Number of Mean ozone utilization, mg/£
Ozone dosage, mg/J. data points (Std
Level Range Mean (n)
Low 2.4- 4.6 3.6 14
Mod- 5.9-10.0 7.5 18
erate
High 11.9-18.6 13.9 8
All 2.4-18.6 7.4 40
Packed column
2.9
(0.6)
5.3
(1.0)
7.4
(1.6)
4.9
(2.0)
. dev.)
Jet scrubber
1.7
(0.3)
3.1
(1.0)
4.0
(1.2)
2.8
(1.2)
Mean
difference
(Std. dev.)
1.2
(0.6)
2.2
(1-1)
3.4
(1-8)
2.1
(1.4)
t
t (a=0.05)
8.1 2.16
8.3 2.11
5.2 2.36
9.6 2.02
Ozone Consumption--
The contactors were also evaluated with respect to ozone consumption
(i.e., utilization minus residual). Table 9 summarizes these data.
It is evident that ozone consumption in the packed column was signifi-
cantly higher than in the jet scrubber at all dosage levels studied. Also,
the difference in consumption between the contactors increased with dosage,
just as did the difference in utilization (Table 8). The pattern expressed
by the change in ozone utilization and consumption as a function of dosage
was consistent.
TABLE 9. DIFFERENCE IN OZONE CONSUMPTION BETWEEN THE PACKED COLUMN AND
JET SCRUBBER AS A FUNCTION OF APPLIED DOSAGE (MCWTP EFFLUENT)
Number of
Ozone dosage, mg/5, data points
Level Range Mean (n)
Low 2.4- 4.6 3.6 14
Mod- 5.9-10.0 7.5 18
erate
High 11.8-18.6 13.9 8
All 2.4-18.6 7.4 40
Mean ozone consumption, mg/(t
(Std. dev.)
Packed column Jet scrubber
2.0
(0.5)
3.6
(0.9)
5.2
(1.4)
3.4
(1.5)
1.3
(0.4)
2.3
(1.0)
3.0
(1.3)
2.1
(1.1)
Mean
difference
(Std. dev.
0.7
(0.7)
1.4
(1.4)
2.2
(1.9)
1.3
(1.4)
t
) t (a=0.05)
3.8 2.16
4.2 2.11
3.3 2.36
6.0 2.03
30
-------
Ozone Residual--
Table 10 summarizes the differences between the two contactors with
respect to ozone residual as a function of dosage. Not only was the ozone
residual in the packed column significantly higher than the corresponding
residual in the jet scrubber at each dosage level, but also the difference in
residual between the two contactors increased with higher dosages.
TABLE 10. DIFFERENCE IN OZONE RESIDUAL BETWEEN THE PACKED COLUMN AND
JET SCRUBBER AS A FUNCTION OF APPLIED DOSAGE (MCWTP EFFLUENT)
Numer of Mean ozone residual, mg/£ Mean
Ozone dosage, mg/£ data points (Std. dev.) difference t
Level Range Mean (n) Packed column Jet scrubber (Std. dev.) t (q=Q.Q5)
"Low 2.4- 4.6 3.6 14
Mod- 5.9-10.0 7.5 18
erate
High 11.8-18.6 13.9 8
All 2.4-18.6 7.4 40
0.8
(0.4)
1.7
(0.5)
2.2
(0.6)
1.5
(0.7)
0.3
(0.2)
0.8
(0.6)
1.0
CO. 5)
0.7
(0.5)
0.5
(0.3)
0.8
(0.6)
1.2
(0.3)
0.8
(0.5)
6.4 2.16
5.8 2.11
11.4 2.36
9.6 2.02
Summary of Contactor Performance--
From the foregoing data analyses, it is clear that the packed column
significantly outperformed the jet scrubber with respect to coliform
reduction efficiency and mass transfer efficiency. Total coliform density,
fecal coliform density, and fecal streptococcus density were all reduced to a
significantly greater extent in the packed column than in the jet scrubber.
When considering each individual dosage level, the packed column was superior
to the jet scrubber with respect to total and fecal coliform reduction at low
and intermediate dosages but not at the high dosage. However, fecal strep-
tococcus reductions were significantly higher in the packed column at each
dosage level studied.
Ozone utilization, consumption, and residual were significantly higher
in the packed column than in the jet scrubber at all dosage levels studied,
and these differences increased in magnitude with increasing dosage.
Regression Analyses
The data from the above experiments were subjected to linear regression
analyses to determine which factors in the effluent contributed to the varia-
tion in the microorganism reduction efficiency data and mass transfer ef-
ficiency data. One parameter, such as log total coliform reduction, was
chosen as a dependent variable and regressed individually against a number
of independent variables (i.e., TCOD, SCOD, TOG, TSS, turbidity, TKN, NH -N,
and organic-N). This was also done for log fecal coliform reduction, log
fecal streptococcus reduction, ozone utilization, ozone consumption, and ozone
residual as the dependent variables. No correlations were found between the
31
-------
dependent variables and any of the independent variables mentioned. It was
concluded that the effluent quality was sufficiently constant that the
variation observed in any of the dependent variables could not be accounted
for by the variation of the individual physical-chemical characteristics
of the wastewater effluent.
Attempts were then made to determine whether bacterial reduction (TCLR,
FCLR, and FSLR) could be correlated with ozone dosage, utilization, consump-
tion, and/or residual in each contactor. A fifth variable, initial bacterial
density, was also included as an independent variable. Tables 11 to 16
summarize the correlation matrices resulting from these analyses.
Tables 11 to 13 summarize the correlation between total coliform log
reduction (TCLR), fecal coliform log reduction (FCLR), and fecal strep log
reduction (FSLR), respectively, in the packed column and the various indepen-
dent variables mentioned above. Correlations among the variables themselves
are also presented.
In Tables 11, 12, 14, and 15, a correlation coefficient greater than
0.275 or less than -0.275 is significantly different from zero at the
95 percent confidence level (as determined by the t-test). In tables 13 and
16, an r-value greater than 0.33 or less than-0.33 is significantly different
from zero.
As expected, significant positive correlations existed among the four
ozone variables. Weak but statistically significant correlations existed
between TCLR, FCLR, or FSLR and ozone dosage, residual consumption, and
utilization. Thus, as any one of the latter variables increased in magnitude,
there was a corresponding increase in bacterial reduction. Finally, there
was statistically significant correlations between TCLR and initial total
coliform density, FCLR and initial fecal coliform density, and FSLR and initial
fecal streptococcus density. Thus, the higher the initial bacterial density,
the higher was the resulting log reduction.
Several regression equations for the packed column were derived from the
data used to construct Tables 11 to 13 and are given as follows:
CQ = 0.3 DQ + 1.1 (11)
U0 = 0.4 D0 + 1.7 (12)
R0 = 0.1 Do + 0.5 (13)
where C = ozone consumption (mg/£), Uo= ozone utilization (mg/£), R = ozone
residual (mg/£), and D = ozone dosage (mg/£).
Tables 14 to 16 summarize the correlations between TCLR, FCLR, and FSLR,
respectively, in the jet scrubber and the various selected independent
variables.
The most significant trends observable in the jet scrubber are quite
different from those seen in the packed column. For example, among the ozone
32
-------
variables, residual did not correlate at all with consumption. This was
because the residual was very low most of the time and thus most of the ozone
utilized in the jet scrubber was consumed by the effluent. The strongest
correlations with bacterial reductions were initial bacterial densities and
ozone residuals. Ozone dosage weakly correlated with microorganism reduction,
but neither ozone consumption nor ozone utilization correlated at all. Thus,
it appears that the only time significant microorganism reduction occurred in
the jet scrubber was when an ozone residual was present.
A relationship derived from the data used to construct Tables 14 to 16 is
given as follows:
R0 = 0.07 DQ + 0.1
(14)
TABLE 11. CORRELATION OF TOTAL COLIFORM LOG REDUCTION (TCLR)
IN THE PACKED COLUMN WITH OZONE DOSAGE, UTILIZATION, CONSUMPTION, RESIDUAL,
AND INITIAL TOTAL COLIFORM DENSITY (MCWTP EFFLUENT)
Correlation coefficient (r)*
0^ Dose Residual Utilization Consumption
Dose 1,000 0.725 0.869 0.823
Residual 1.000 0.806 0.608
Utilization 1.000 0.960
Consumption 1.000
Initial TC
density
TCLR
Initial TC
density
0.299
0.22S
0.380
0.403
1.000
TCLR
0.319
0.339
0.519
0.535
0.541
1.000
40 data points used to derive each r-value
TABLE 12. CORRELATION OF FECAL COLIFORM LOG REDUCTION (FCLR)
IN THE PACKED COLUMN WITH OZONE DOSAGE, UTILIZATION, CONSUMPTION, RESIDUAL, AND
INITIAL FECAL COLIFORM DENSITY (MCWTP EFFLUENT)
Dose
Residual
Utilization
Consumption
Initial FC
density
FCLR
Correlation coefficients (r)*
Dose Residual Utilization Consumption
1.000 0.718 0.866 0.821
1.000 0.800 0.603
1.000 0.961
1 000
Initial FC
density
0.322
0.302
0.476
0 . 494
1.000
TCLR
0.326
0.414
0.543
0.531
0.596
1 .000
*3S data points used to derive each r-value
33
-------
TABLE 13. CORRELATION OF FECAL STREr LOG REDUCTION (FSLR) IN THE PACKED COLUMN
WITH OZONE DOSAGE, UTILIZATION, CONSUMPTION, RESIDUAL, AND INITIAL FECAL
STREP DENSITY (MCWTP EFFLUENT)
Dose
Residual
Utilization
Consumption
Initial FS
density
FSLR
Correlation coefficients (r)*
Dose Residual Utilization Consumption
1.000 0.763 0.888 0.827
1.000 0.817 0.605
1.000 0.953
1.000
Initial TC
density
0.374
0.286
0.332
0.309
1.000
FSLR
0.713
0.597
0.706
0.664
0.845
1.000
29 data points used to derive each r-value
TABLE 14. CORRELATION OF TOTAL COLIFORM LOG REDUCTION (TCLR) IN THE JET SCRUBBER
WITH OZONE DOSAGE, UTILIZATION, CONSUMPTION, RESIDUAL, AND INITIAL TOTAL
COLIFORM DENSITY (MCWTP EFFLUENT)
Dose
Residual
Utilization
Consumption
Initial TC
density
TCLR
Correlation coefficients {r)*
Dose Residual Utilization Consumption
1.000 0.5S3 0.732 0.54S
1.000 0.440 0.007
1.000 0.901
1.000
Initial TC
density
0.297
0.549
0.108
-0.146
1.000
TCLR
0
0
0
-0
0
1
360
519
212
015
649
000
40 data points used to derive each r-value
TABLE 15. CORRELATION OF FECAL COLIFORM LOG REDUCTION (FCLR)
IN THE JET SCRUBBER WITH OZONE DOSAGE, UTILIZATION, CONSUMPTION,
RESIDUAL, AND INITIAL FECAL COLIFORM DENSITY (MCWTP EFFLUENT)
Dose
Residual
Utilization
Consumption
Initial FC
density
FCLR
Correlation coefficients (r)*
Dose Residual Utilization Consumption
1.000 0.543 0.728 0.546
1.000 0.432 -0.001
1.000 0.901
1.000
Initial FC
density
0.316
0.608
0.232
-0.035
1.000
FCLR
0.418
0.620
0.254
-0.016
0.708
1.000
*38 data points used to derive each r-value
34
-------
TABLE 16. CORRELATION OF FECAL STREP LOG REDUCTION (FSLR) IN THE JET SCRUBBER
WITH OZONE DOSAGE, UTILIZATION, CONSUMPTION, RESIDUAL, AND INITIAL FECAL
STREP DENSITY (MCWTP EFFLUENT)
Dose
Residual
Utilization
Consumption
Initial FS
density
FSLR
Correlation coefficients (r) *
Dose Residual Utilization Consumption
1.000 0.568 0.672 0.483
1.000 0.525 0.080
1.000 0.890
1.000
_ _ _ _ — _ _ _ __ _ __ _ _ — _ . _. _ — _ _ —
Initial FS
density
0.370
0.605
0.054
-0.261
1.000
FSLR
0.332
0.707
0.268
-0.065
0.851
1.000
29 data points used to derive each r-value
-------
Stepwise Multiple Regression--
The linear regression analyses discussed above provided insight in
determining which factors were responsible for the variation observed in the
data. Further refinement in quantifying these effects was possible by
performing stepwise multiple regression analyses in which ordered, linear
models were developed to predict the overall net effect of all variables
on contactor performance.
The procedure involves re-examination, at every stage of the regression,
of the variables incorporated into the model in previous stages. A variable
which may have been the best single variable to enter at an early stage may,
at a later stage, be superfluous because of the relationships between it and
other variables not in the regression. A judgement on the contribution of
each variable is made after each step of the analysis, as though it had been
the most recent variable entered, irrespective of its actual point of entry
into the model. Any variable which provides a nonsignificant contribution
is removed from the model. This process is continued until no more variables
will be admitted to the equation and no more are rejected. The final result
is a multiple regression equation including all variables contributing to the
effect under examination.
A total of six equations resulted from this analysis, three for the
packed column and three for the jet scrubber. The dependent variables under
examination were TCLR, FCLR, and FSLR. The independent variables were
initial TC, FC, or FS density, ozone dosage, utilization, consumption, and
residual. The three equations for the packed column are given as follows:
XG
Log —x = 0.61 Log X0 + 0.34C0 - 1,77 (r = 0.671) (15)
where X0 = initial total coliform density, X = total coliform density.after
ozonation, C0 = ozone consumption (mg/£), and DQ = ozone dosage (mg/£).
Yo
Log y =0.82 Log Y0 + 0.47U0 - 0.14DO - 2076 (r = 0.698)(16)
where YQ = initial fecal coliform density, Y = fecal coliform density after
ozonation, and UQ = ozone utilization (mg/£).
Z0
Log — = 0.78 Log Z0 + 0.21U0 - 1.76 (r = 0.958) (17)
where ZQ = initial fecal strep density and Z = fecal strep density after
ozonation.
The multiple correlation coefficients (r) were significant at the
cKO.05 level.
36
-------
It is clear from these equations that initial bacterial density was an
important contributing factor to the variation in the data. Thus, when
predicting the effect of ozone on the microorganism reduction efficiency of
a packed column, one must account for the initial bacterial numbers in the
overall model.
It was previously shown that ozone utilization, consumption, and residual
in the packed column were mathematically related to applied dosage (equations
11 to 13). If these relationships are substituted into equations 15 to 17
so that log microorganism reduction is expressed in terms of initial bac-
terial density and dosage alone, the latter equations simplify to:
TCLR = 0.04 DQ + 0.6 log Xo - 1.4 (18)
FCLR = 0.06 DQ + 0.8 log Y - 2.0 (19)
FSLR = 0.09 D0 + 0.8 log Zo - 1.4 (20)
Thus, if the initial total coliform density were 10^/100 ml, the ozone dosage
needed to achieve a 3 log reduction in the packed column would be 20 mg/fc.
The equations for the jet scrubber are given as follows:
TCLR = Log -^- = 0.39RQ + 0.99 Log XQ - 4.01 (r = 0.678) (21)
FCLR = Log -^°— = 0.68R0 + 1.07 Log YQ 3.95 (r = 0.747) (22)
FSLR = Log -|°— = 0.46RQ + 0.79 Log YQ - 1.55 (r = 0.884) (23)
The multiple r-values were significant at the a<0.05 level.
It is clear that, aside from initial bacterial density, the only factor
significantly affecting microorganism reduction efficiency in the jet scrubber
was ozone residual. Substituting equation 14 into equations 21 to 23 so that
microorganism reduction is given in terms of initial bacterial numbers and
applied dosage, the relationships become:
TCLR = 0.03D + log XQ 4.0 (24)
FCLR - 0.05D + 1.1 log YQ - 3.9 (25)
FSLR = 0.03D + 0.8 log ZQ - 1.5 (26)
Thus, to achieve a 3 log reduction of total coliforms in the jet scrubber,
assuming an initial density of 106/100 ml, the applied ozone dosage would be
33 mg/&. This is considerably higher than in the packed column.
It should be pointed out that the above data were obtained at a constant
ozone gas concentration of 10 mg/£ and varying gas flow rates. According to
Henry's Law, mass transfer depends on the difference between the ozone
concentration in the gas and in the liquid. Increasing the concentration of
37
-------
ozone in the gas stream would enable operation of the contactors at lower gas
flow rates and thus improve mass transfer efficiency. This would presumably
improve microorganism reduction efficiency as well, since more ozone would be
added to the liquid. Work is presently underway to verify this hypothesis
experimentally.
PHASE 2 - PARALLEL OPERATIONAL MODE - FACTORIAL EXPERIMENT
During this phase of the investigation, both contactors were operated in
parallel on effluent from the Robert A. Taft Laboratory pilot plant facility.
The experimental arrangement described in Section 4 enables the investi-
gator to test the significant differences in performance between the two
ozone contactors with minimum bias. Moreover, if the resulting analyses of
variance (ANOVA) indicate significant interactions between the various levels
of one factor and those of another, the data can be easily subjected to linear
and stepwise multiple regression analyses to determine which physical-
chemical characteristics of the effluent contribute to such interactions and
to quantify the extent to which each parameter is involved.
Characteristics of the Wastewater Effluent
Table 17 summarizes the mean, standard deviation, and range of the physical-
chemical characteristics of the filtered pilot plant effluent used in this
phase of the study. Effluent was generally poorer than that of the MCWTP
effluent (Table 2).
TABLE 17. CHARACTERISTICS OF THE PILOT PLANT
EFFLUENT PRIOR TO OZONATION
Parameter
Temperature (C)
TCOD
SCOD
TOC
TSS
TURB (JTU)
TKN
" NH4-N
ORG-N
Mean*
mg/l
14
76
65
19.9
6
11.3
16.1
8.6
7.4
Standard deviation
mg/l
0.5
20
23
6.3
3
12.4
7.9
3.0
6.9
Range
mg/l.
13
41
34
8.2 -
2
1.6 -
6.5 -
3.6 -
2.2 -
14
106
105
30.
11
40
27
14.
30.
5
1
5
* 24 data points
Total Coliform Log Reduction (TCLR)
Table 18 illustrates the split-split plot layout as described in Section 4
and summarizes the data for log total coliform reduction in both contactors.
Analysis of the data from Table 18 is shown in Table 19. Examination of the
geometric mean total coliform densities (after ozonation) in Table 18 reveals
38
-------
that a coliform reduction to a level less than 1000 TC/100 ml was achieved
in the packed column only at a dosage of 19.5 mg/£. Such a level of disin-
fection was not achieved in the jet scrubber.
If the computed F-statistic in Table 19 with the appropriate degrees of
freedom is greater than the corresponding F-value from the F-distribution
table (5 percent significance level), the effect under examination is signi-
ficant. The various F-statistics were computed as follows: (1) Dose main
effect (Dp -- the Mean Square (MS) for doses was ratiod against the MS for
the I^Dj interaction; (2) Replication main effect (R-jJ -- the MS for
replication was ratiod against the MS for the ^D- interaction; (3) CkD.=
interaction effect -- the MS for the CkD- was ratiod against the MS for the
RiDiCk interaction; (4) C^ interaction effect -- the MS for the C,R.
interaction was ratiod against the MS for the R-D-Ck interaction. To1test
for a significant difference between the two contactors (contactor main
effect), a Pseudo-F test was performed in which the mean square (MS) for
contactors (Ck) was ratiod against the MS for the R^ interaction plus the
MS for theD-Ck interaction minus the mean square for the R^D-C^ interaction.
TABLE 18. SPLIT-SPLIT-PLOT LAYOUT FOR TOTAL COLIFORM LOG REDUCTION DATA
Replicates
1
2
3
4
5
6
Mean
Standard
deviation
Effluent geometric
mean, TC/100 mfc
Source
of variation
Contactors (C, )
Doses (D.)
Replicates (R. )
CkD.
CkRi
R.D.
l J
RiDjCk
Total
Packed column ,_ TCLR
0- dose, mg/£
4.9 9.7 13.1 19.5
2.03 3.09 4.15 3.14
1.00 2.15 2.22 2.00
2.00 2.46 3.35 2.86
1.00 3.02 3.22 3.31
0.03 0.85 1.35 4.02
0.24 1.16 1.27 3.43
1.05 2.12 2.59 3.13
0.84 0.94 1.17 0.67
9.9.X104 8.7xl()J 2.2xlOJ 5.5x10"
TABLE 19. ANOVA OF TOTAL COLIFORM
Degrees of Sums of
freedom squares
1 16.70
3 19.14
5 17.92
3 1.20
5 0.79
15 12.07
15 3.54
47 71.36
4.9
1.00
1.00
0.14
0.16
0.00
0.07
0.40
0.47
4.7x10
LOG REDUCTION
Mean
squares
16.70
6.38
3.58
0.40
0.16
0.80
0.24
Jet scrubber, TCLR
0 dose, mg/£
9.7 13.1 19.5
1.86 3.00 2.52
0.30 0.07 0.31
1.79 2.54 2.27
0.81 0.91 2.16
0.03 0.00 2.48
0.43 0.03 1.16
0.87 1.09 1.82
0.78 1.35 0.89
)
5 1.6xl05 8.9xl04 1.6xl04
DATA
F
F (a = 0.05)
51.80 37.0
7.90 3.29
4.45 2.90
1.70 3.29
0.67 2.90
39
-------
Results from Table 19 indicate that the difference between the two ozone
contactors (C, ) with respect to TCLR was significant at the 5 percent signifi-
cance level. It can also be seen that the dosage effect (D.) on the combined
TCLR in both contactors was significant at the 5 percent significance level*
This is not unexpected, since an increase in ozone dosage should cause a
corresponding increase in coliform reduction. Significant differences in
TCLR for both contactors were observed among replicate experiments (R^),
indicating that effluent quality varied from day to day and that these
variations affected coliform reduction efficiency in both contactors.
The interaction between contactor and dosage (C,D.) was not significant
(Table 19). This means that the difference between the two contactors with
respect to TCLR was consistent at all dosage levels studied. The interaction
between contactors and replication (C^R.) was also not significant. This
indicates that the differences in TCLR observed between the two contactors
were the same regardless of effluent quality.
The relationship between TCLR and applied ozone dose in each contactor
is depicted graphically in Figure 15. Each point is the mean of the six
replicate experiments. It can be seen that TCLR was better in the packed
column than in the jet scrubber (significant contactor main effect) and that
TCLR was directly proportional to dosage (significant dosage main effect).
The fact that the two lines are nearly parallel illustrates the lack of a
significant contactor-dosage (C.D^) interaction. The replication main effect
(i.e. effect of effluent quality) is illustrated in Figure 16, where the
average TCLR in each contactor at all dosage levels is plotted against total
chemical oxygen demand in the pilot plant effluent. Each point is the mean
TCLR at the four dosage levels. It is evident that an increase in TCOD (a
variable representative of effluent quality) corresponded to a decrease in
TCLR in both contactors. Moreover, the lack of a significant contactor-
replication interaction (Ci,R-) is evidenced by the parallel nature of the two
lines. Thus, effluent quality adversely affected overall TCLR efficiency in
both contactors. The packed column significantly and consistently outper-
formed the jet scrubber with respect to total coliform reduction at all dosage
levels s'tudied and under varying conditions of effluent quality.
s
PACKED COLUMN
- IET SCRUBBER
OZONE DOSE , mg/l
Figure 15. Total Coliform Log Reduction as a Function of Ozone
Dosage in the Packed Column and Jet Scrubber
40
-------
S: 4
©
A
-PACKED COLUMN
IET SCRUBBER
I
I
I
"40 50 60 70 80 90 100
EFFLUENT TOTAL CHEMICAL OXYGEN DEMAND , mg/l
Figure 16. Total Coliform Log Reduction at all Dosage Levels
as a Function of Effluent Total Chemical Oxygen Demand
in the Packed Column and Jet Scrubber
Fecal Coliform Log Reduction (FCLR)
Table 20 summarizes the data for log fecal coliform reduction in both
contactors. Analysis of the data from Table 20 is presented in Table 21.
Results from Table 21 are similar to those depicted in Table 19. All
main effects were significant, and both interactions were not significant.
Thus, as with total coliform reduction, the packed column outperformed the
jet scrubber with respect to fecal coliform reduction at all dosage levels
studied and at all conditions of effluent quality.
Examination of the geometric mean fecal coliform densities (after
ozonation) in Table 20 reveals that a mean FC reduction to a level of less
than 200/100 ml was almost achieved in the peaked column at the highest
dosage level but not even approached in the jet scrubber. These results are
comparable to the total coliform data.
41
-------
TABLE 20. SPLIT-SPLIT-PLOT LAYOUT FOR
FECAL COLIFORM LOG REDUCTION DATA
Replicates 4.9
1 2.35
2 0.49
3 1.29
4 0.15
5 0.0
6 0.31
Mean 0.76
S.D. 0.90
Effluent 4.6x10
geometric
mean,
FC/100 ml
Packed column
FCLR
Dose, mg/5,
9.9 13.1
3.15 5.33
2.17 1.27
3.00 1.52
2.95 3.93
0.31 2.65
0.66 3.15
2.04 2.64
1.26 l.OS
3.6xl03 5.7x10
Jet scrubber
FCLR
19.5
3.21
2.71
3.00
3.02
3.33
3.52
3.13
0.28
2 2.2xl02
Dose, Mg/l
4.9 9.7 13.1 19.5
1.07 2.06 2.54 2.60
0.50 0.84 0.14 0.00
0.29 2.81 1.87 2.00
0.15 1.15 1.35 1.43
0.18 0.0 0.0 2.17
0.14 0.14 0.0 0.66
0.39 1.17 0.98 1.48
0.36 1.10 1.09 0.99
1.2xl05 2.9xl04 3.7xl04 7.3xl03
TABLE
Source of
variation
Contactors (C . )
J
Doses (D.)
Reps (Ri)
C. D.
k 3
C. R.
k i
R.D.
i j
R.D.C.
Total
21. ANOVA FOR FECAL COLIFORM LOG REDUCTION DATA
Degrees of
freedom
1
3
5
3
5
15
15
47
Sums of Mean F
squares squares F (a=0.05)
15.62 15.62 13.93 13.50
19.03 6.34 8.46 3.29
15.48 3.10 4.13 2.90
3.56 1.19 2.64 3.29
1.92 0.38 0.85 2.90
11.25 0.75
6.75 0.45
73.60
42
-------
Percent Ozone Utilization
Table 22 illustrates the split-split-plot layout and summarizes the data
for percent ozone utilization as a function of ozone dosage. Analysis of the
data from Table 22 is given in Table 23.
Results indicate that the difference between the two ozone contactors
(C^) with respect to percent ozone utilization was significant. In addition,
percent ozone utilization in both contactors was significantly different at
all dosage levels studied (D-). Replication (R.^ did not significantly affect
percent ozone utilization in either contactor. Thus, variation in effluent
quality did not bring about a corresponding variation in percent ozone utili-
zation at the four dosage levels studied.
Neither the contactor-dosage (C,D.) interaction nor the contactor-
replication (C, R,) interaction with respect to percent ozone utilization were
significant in this experiment. This means that the differences observed
between the contactors were consistent at all dosage levels studied and at
all conditions of effluent quality experienced.
The relationship between percent ozone utilization and applied ozone
dose in each contactor is depicted graphically in Figure 17. Each point is
the mean of six replicate experiments. It can be seen that percent ozone
utilization was better in the packed column than in the jet scrubber (signifi
cant contactor main effect) and that percent ozone utilization was inversely
proportional to dosage (significant dosage main effect). The fact that the
lines are parallel illustrates the lack of significant contactor-dosage
(CiD-) interaction. The lack of a significant replication main effect (i.e.,
effect of effluent quality) is illustrated in Figure 18 where the average
percent ozone utilization in each contactor at all dosage levels is plotted
against TCOD in the influent wastewater. Each point is the mean percent ozone
utilization at the four dosage levels. It is evident that an increase in
TCOD was not accompanied by any significant overall change in percent ozone
utilization in both contactors. In addition, the lack of a significant con-
tactor-replication interaction (C, R-^) is evidenced by the nearly parallel
nature of the two lines. The packed column significantly and consistently
outperformed the jet scrubber with respect to percent ozone utilization at all
dosage levels studied and under varying conditions of effluent quality. How-
ever, effluent quality did not significantly affect overall percent utili-
zation in either contactor.
Actual Ozone Utilization
Table 24 illustrates the split-split-plot layout and summarizes the data
for ozone utilization. Analysis of the data from Table 24 is given in
Table 25.
Results indicate that the difference between the two ozone contactors
(Cv) with respect to ozone utilization was significant. In addition, ozone
utilization in both contactors combined was significantly different at each
dosage level (D:) studied. The replication main effect (R^ was not signifi-
cant. This means that overall ozone utilization in both contactors was not
43
-------
TABLE 22. SPLIT-SPLIT-PLOT LAYOUT FOR
PERCENT OZONE UTILIZATION DATA
Replicates
1
2
3
4
5
6
Mean
S.D.
Packed column,
ozone utilized, percent
4.9 9.
78 57
67 49
78 52
73 56
61 58
68 63
71 56
6.7 4.
Dose mg/Ji
7 13.1
42
49
46
43
49
53
47
9 4,1
19.5
34
49
40
35
43
43
41
5.6
ozone
4,9
45
57
52
53
61
65
56
7,1
Jet scrubber
utilized, percent
Dose
9.7
32
32
26
34
41
43
35
6.3
rag/Jl
13.1
23
32
25
27
32
35
29
4.7
19.5
20
37
25
21
27
27
27
6,1
TABLE 23. ANOVA FOR PERCENT
OZONE UTILIZATION DATA
Source of Degrees of Suras of
variation freedom squares
Contactors (C, )
Doses (D.)
Reps (R^
C, D.
k J
C. R.
k i
R.D.
i 3
R.D.C,
i j k
Total
1
3
5
3
5
15
15
47
3570,
6159.
384,
81,
191
467
291
11,145
,75
.08
,67
,42
.00
.17
.76
.84
Mean
squares F
3570.
2053.
76.
27.
38.
31.
19
75 77.81
03 65.92
93 2.47
.14 1.40
,20 1.96
.14
.45
F
(a=0.05)
7.60
3.29
2.90
3.29
2.90
44
-------
70
60
50
- 40
30
S 20
10
I
I
PACKED COLUMN
JET SCRUBBER
8 10 12
OZONE DOSAGE mg/l
14
16
18
20
Figure 17. Percent Ozone Utilization as a Function of Ozone Dosage
in the Packed Column and Jet Scrubber
3.0
2.0
0 PACKED COLUMN
A -JET SCRUBBER
A A
_J | | | | | | | | |_
10 20 30 40 50 60 70 80 90 100
EFFLUENT TOTAL CHEMICAL OXYGEN DEMAND , mg/l
Figure 18. Percent Ozone Utilization as a Function of Effluent Total
Chemical Oxygen Demand in the Packed Column and Jet Scrubber
45
-------
TABLE 24. SPLIT-SPLIT-PLOT LAYOUT FOR
OZONE UTILIZATION DATA
Packed
column
ozone utilized,
Replicates
1
2
3
4
5
6
Mean
S
D.
4.9
3.8
3.2
3.7
3.5
2.9
3.3
3.4
0.3
dose
9.
5.
4.
S.
S.
5.
6.
5.
0.
mg/£
7
5
8
0
5
6
1
4
5
mg/£
13.1 19.5
5
6
5
5
6
6
6
0
.5 6.6
.4 9.6
.9 7.8
.7 6.9
.5 8.4
.9 8.4
.2 8.0
.6 1.1
Jet
scrubber
ozone utilized
mgA
dose mg/£
4.9
2.2
2.7
2.5
2.5
2.9
3.1
2.7
0.3
9
3
3
2
3
3
4
3
0
.7
.1
.1
.5
.3
.9
.2
.4
.6
13.1
3.0
4.2
3.2
3.6
4.2
4.6
3.8
0.6
19.5
3.9
7.2
4.8
4.2
5.3
5.3
5.1
1.2
TABLE 25. ANOVA FOR OZONE UTILIZATION DATA
Source of
variation
Contactors (C, )
Doses (D.)
Reps (R..)
C D.
k ]
CkRi
R.D.
i ]
R.D.C,
1 J k
Total
Degrees of Sums of
freedom squares
1
3
5
3
5
15
15
47
47
75
7,
7
0.
11.
0.
151.
.9
.7
.8
.3
.8
,2
.9
5
Mean
squares
47
25
1
Z •
0.
0.
0,
.9
.2
.6
.4
.2
.7
.1
F F
(a=0. OS)
19.0 9.1
33.8 3.3
2.1 2.9
38.9 3.3
2.5 2.9
46
-------
significantly affected by changes in effluent quality.
The contactor-dosage (CjD.) interaction with respect to ozone utilization
was significant at the 5 percent level (Table 25) . This contrasts with the
lack of interaction between contactor and dosage with respect to log total and
fecal coliform reduction (Tables 19 and 21) and percent ozone utilization
(Table 23) . This means that the difference in actual ozone utilization be-
tween the packed column and the jet scrubber at some dosage levels was not the
same at other dosage levels.
Finally, the contactor-replication (C^R^) interaction with respect to
ozone utilization was not significant. This means that the difference in
performance of the two contactors with respect to ozone utilized was the same
regardless of effluent quality. This effect was also observed for log total
and fecal coliform reduction and percent ozone utilization.
These effects are clearly visualized by examining Figures 19 and 20.
The relationship between ozone utilization and applied ozone dose in each
contactor is depicted graphically in Figure 19. Each point is the mean of
six replicate experiments. It can be seen that ozone utilization in the packed
column was better than in the jet scrubber (significant contactor main effect)
and that ozone utilization in both contactors was proportional to dosage
(significant dosage main effect) . The fact that the two lines are not par-
allel illustrates the significant contactor -dosage interaction (CkD.). As
dosage increased, the increase in ozone utilization in the packed column was
greater than in the jet scrubber. The lack of a significant replication main
effect is illustrated in Figure 20, where the average ozone utilization in
each contactor at all dosage levels is plotted against TCOD in the pilot plant
effluent. Each point is the mean ozone utilization at the four dosage levels.
It is evident that an increase in TCOD was not accompanied by any significant
overall change in ozone utilization in either contactor. Moreover, the lack
of significant contactor-replication interaction (C^R.:) is evidenced by the
nearly parallel nature of the two lines. Thus, the packed column significantly
outperformed the jet scrubber with respect to actual utilization. Effluent
quality did not significantly affect overall ozone utilization in both con-
tactors; however, it will be seen later that ozone utilization in each con-
tactor was affected by effluent quality at certain individual dosage levels.
Ozone Residual
Table 26 illustrate the split-split-plot layout and summarizes the data
for ozone residual. Analysis of the data from Table 26 is given in Table 27.
Results indicate that the difference between the two ozone contactors
(C, ) with respect to ozone residual was significant at the 5 percent level.
In addition, ozone residual was significantly different at each dosage level
(D.) studied. This is expected, since ozone residual should increase with
increasing dosage. Finally, Table 27 indicates that effluent quality (rep-
lication) significantly affected the magnitude of ozone residual in the
effluent from both contactors. Thus, as effluent quality deteriorated, ozone
residual decreased at the same applied dosage level.
47
-------
© PACKED COLUMN
A JET SCRUBBER
15
20
OZONE DOSE , nig/1
Figure 19. Ozone Utilization as a Function of Ozone Dosage
in the Packed Column and Jet Scrubber
I
© PACKED COLUMN
A JET SCRUBBER
I
I
10 20 30 40 50 60 70 80
EFFLUENT TOTAL CHEMICAL OXYGEN DEMAND . mg/l
90 100
Figure 20. Ozone Utilization at all Dosage Levels as a Function
of Effluent Total Chemical Oxygen Demand in the Packed
Column and Jet Scrubber
48
-------
TABLE 26. SPLIT-SPLIT-PLOT LAYOUT
FOR OZONE RESIDUAL DATA
Packed column
ozone residual,
rag/£
Jet scrubber
ozone residual,
dose, mg/£
Replicates
1
2
3
4
5
6
Mean
S.D.
4.
0.
0.
0.
0.
0.
0.
0.
0.
9
9
1
6
.2
0
0
.3
4
9.
0.
0.
1.
0,
0,
0,
0,
0,
.7
.9
.3
.4
.4
.2
.1
.6
.5
13
1.
0.
1.
1.
0.
0.
0.
0.
.1
7
4
6
1
4
2
9
7
19
1.
0.
1.
0.
0.
0.
1.
0.
.5
9
9
6
9
2
4
0
7
4.
0.
0.
0.
0.
0.
0.
0.
0.
9
2
0
1
0
0
0
05
08
dose, mg/£
9.
0.
0.
0.
0.
0,
0.
0.
0,
.7
.3
.2
.4
.2
.0
.0
, 2
,2
13
0.
0.
0.
0.
0.
0.
0.
0.
rag/H
.1
8
2
5
3
0
1
3
3
19.5
0.7
0.2
0.4
0.4
0.0
0.0
0.3
0.3
TABLE 27 ANOVA FOR OZONE RESIDUAL DATA
Source of
variation
Contactors (C )
i\
Doses (D.)
Reps (Ri)
CkD.
C, R.
k i
R.D.
R.D.C.
i ] k
Total
Degrees of
freedom
1
3
5
3
5
15
15
47
Sums of
squares
2
1
5
0
1.
0
0
12
.71
.69
.10
.37
.18
.75
.21
.02
Mean
squares F
2
0
1,
0
0
0
0
.71 7.80
.56 11.24
.02 20.32
.12 8.98
.24 16.99
.05
.01
F
(a=O.OS)
5.60
3.29
2.90
3.29
2.90
49
-------
The contactor-dosage (Cj,D.) interaction with respect to ozone residual
was also significant. This means that the difference in ozone residual be-
tween the contactors was not consistent with effluent quality.
The relationship between ozone residual and applied ozone dosage in each
contactor is depicted graphically in Figure 21. Each point is the mean of six
replicate experiments. It can be seen that ozone residual in the packed column
was higher than in the jet scrubber (significant contactor main effect) and
that ozone residual in both contactors was proportional to dosage (significant
dosage main effect). The fact that the two lines are not parallel illustrates
the significant contactor-dosage interaction (CD.). As dosage increased,
the increase in ozone residual in the packed column was greater than in the
jet scrubber. The significant replication main effect is illustrated in
Figure 22, where average ozone residual in each contactor at all dosage levels
is plotted against TCOD of the effluent. Each point is the mean ozone resi-
dual at the four dosage levels. It is evident that an increase in TCOD
corresponds to a decrease in ozone residual in both contactors. Moreover, the
significant contactor-replication interaction(C^R^) is evidenced by the fact
that the two lines intersect. Thus, the magnitude of the ozone residual in
the packed column appeared to be more sensitive to changes in applied ozone
dosage (Figure 21) and shift in ozone demand (Figure 22) than in the jet
scrubber. This is most likely because the packed column was a better overall
ozone contactor than the jet scrubber.
Ozone Consumption
Table 28 illustrates the split-split-plot layout and summarizes 'the data
for ozone consumption (i.e., the difference between actual ozone utilization
and ozone residual). Analysis of the data from Table 28 is given in Table 29.
Results indicate that all main effects were significant and both inter-
actions were significant. This is similar to the ozone residual data analysis
presented in Table 27. Thus, consumption in both contactors was significantly
different; dosage and wastewater quality significantly affected consumption in
both contactors; and the significant differences in consumption between the
contactors were not consistent over all levels of dosage and under different
conditions of wastewater quality.
The relationship between ozone consumption and applied ozone dose in each
contactor is depicted graphically in Figure 23''. Each point is the mean of
six replicate experiments. It can be seen that more ozone was consumed in the
packed column than in the jet scrubber (significant contactor main effect) and
that ozone consumption was proportional to dosage (significant dosage main
effect).. The fact that the two lines intersect illustrates the significant
contactor-dosage interaction (C,D.)- The replication main effect is illus-
trated in Figure 24, where the average ozone consumption in each contactor
at all dosage levels is plotted against total chemical oxygen demand in the
pilot plant effluent. Each point is the mean ozone consumption at the four
dosage levels. It is evident that an increase in TCOD corresponded to an
increase in ozone consumed in both contactor. However, the TCOD effect on
ozone consumption in both contactors, although statistically significant, was
for all practical purposes negligible, as a 60 mg/J, increase in TCOD
50
-------
PACKED COLUMN
-JET SCRUBBER
Figure 21
10 12 14
OZONE DOSAGE , mg/l
Ozone Residual as a Function of Ozone Dosage in the
Packed Column and Jet Scrubber
©-
A-
©
—PACKED COLUMN
-JET SCRUBBER
40 50 60 70 80 90 100
EFFLUENT TOTAL CHEMICAL OXYGEN DEMAND , mg/I
Figure 22. Ozone Residual as a Function of Effluent Total Chemical
Oxygen Demand in the Packed Column and Jet Scrubber
51
-------
TABLE 28. SPLIT-SPLIT-PLOT LAYOUT FOR
OZONE CONSUMPTION DATA
Packed column
ozone consumption,
Replicates
1
2
3
4
5
6
Mean
S.D.
4.
2.
2.
3.
3.
2.
3.
3.
0.
9
9
6
6
3
9
3
1
4
mg/£
Jet scrubber
ozone consumption
dose, mg/£
9.
4.
3.
4.
5.
5.
6.
4.
0.
7
6
,4
.7
1
4
.0
9
9
13
3.
4.
5.
4.
6.
6.
5.
1.
.1
8
8
5
6
1
7
3
1
19
4.
8.
6.
6.
8.
8.
7.
1.
.5
7
0
9
0
2
0
0
4
4.
2.
2.
2.
2,
2'.
3,
2,
0.
.9
.0
.6
.5
,5
9
.1
,6
4
, mg/1
dose, mg/i
9.
2.
3.
2,
3.
3.
4.
3.
0,
.7
.8
.1
.3
.1
.9
.2
.2
.7
13
2.
3.
3.
3.
4.
4.
3.
0.
.1
2
7
0
3
2
5
5
8
19
3.
6.
4.
3.
5.
5.
4.
1.
.5
2
8
6
8
3
3
8
3
TABLE 29. ANOVA FOR OZONE CONSUMPTION DATA
Source of
variation
Contactors (C, )
Doses (D.)
Reps (R.)
C, D.
k j
C, R.
k i
R.D.
i ]
R.D.C,
ilk
Total
Degrees of
freedom
1
3
5
3
5
15
il
47
Sums of
squares
27
56
17
4
2
13
1
123
.26
.44
.87
.56
.28
.52
.60
.53
Mean
squares F
27.
18
3.
1.
0.
0.
0.
.26 14.60
.81 20.87
.57 3.96
.52 14.20
.46 4.26
.90
.11
F
(a=0.05)
7.71
3.29
2.90
3:29
2.90
52
-------
PACKED COLUMN
A JET SCRUBBER
10 12 H IB
18 20
OZONE DOSAGE , mg/l
Figure 23. Ozone Consumption as a Function of Ozone Dosage in the
Packed Column and Jet Scrubber
70
60
50
40
^ 30
5
LU
S 20
10
©
0
A
"A
0-
A-
-PACKED COLUMN
-IET SCRUBBER
40 50 60 70 80 90 100
EFFLUENT TOTAL CHEMICAL OXYGEN DEMAND , mg/l
Figure 24. Ozone Consumption as a Function of Effluent Total Chemical
Oxygen Demand in the Packed Column and Jet Scrubber
53
-------
corresponded to less than 2 rag/5, increase in ozone consumption. The daily
variation of the difference in ozone comsumption between contactors
(contactor-replication interaction) was also satistically significant. Hence,
the two lines in Figure 24, although appearing parallel, have significantly
different slopes, but from a practical standpoint the difference is considered
negligible. Thus, it appears that ozone consumption in both contactors was
more dependent on applied ozone dosage (Figure 23) than on the demand of the
effluent being treated (Figure 24). More ozone was consumed in the packed
column than in the jet scrubber, and the increase in consumption as a
function of dosage was greater in the packed column.
Summary of the Factorial Experiment--
On the basis of total and fecal coliform log reduction, it is clear
that the packed column contactor was superior to the jet scrubber, at least
within the limits of effluent quality encountered and ozone dosages used
(5 - 20 rag/£). Effluent quality significantly affected microorgani'sm
reduction efficiency in both contactors.
On the basis of ozone utilization efficiency, several conclusions can
be made. First, the packed column was superior to the jet scrubber with
respect to percent ozone utilization, regardless of effluent quality and the
magnitude of applied dosage. This superiority was significant and consistent
at all dosage levels employed. Percent utilization in both contactors was
inversely proportional to dosage. Since dosage was increased by maintaining
the ozone concentration in the gas stream constant and varying the gas flow
rate, this result is not unexpected. Second, the packed column was superior
to the jet scrubber with respect to actual ozone utilization regardless of
effluent quality. The magnitude of this difference in performance actually
increased with increasing dosage (significant C,D. interaction). Ozone
utilization in both contactors increased with increasing dosage, as expected.
Third, both ozone residual and ozone consumption in each contactor increased
with increasing dosage. Effluent quality had a greater effect on the magni-
tude of ozone residual in both contactors than on the amount of ozone
consumed. Thus, since TCLR, FCLR, and ozone residual were significantly
affected by effluent quality while overall ozone utilization and ozone
consumption were less significantly affected, it follows that organism
reduction was not mass transfer limited, but overall ozone utilization and
consumption were. However, it should be emphasized that these were overall
effects and no account has yet been made of the effect of effluent quality
at each individual dosage level. This will be discussed in the following
section.
Linear Regression Analysis of Data from the Factorial Experiment
The foregoing analyses of variance (ANOVA) were useful in enabling
conclusions on the overall comparative disinfection and mass transfer
efficiencies of the packed column and jet scrubber contactors. However, the
ANOVA1s do not reveal which factors in the effluent contributed to the
variation in the data. Information of this kind would provide invaluable
54
-------
assistance in designing or upgrading ozone contactors.
The factorial arrangement used in this study facilitates performance of
other statistical tests to furnish the desired information, because both
contactors were treated in parallel under identical conditions at four sepa-
rate and distinct applied dosage levels. Thus, if it is desired to test the
effect of chemical oxygen demand, for example, on coliform reduction in each
contactor, there exists six data points at each dosage level to establish a
correlation. Tests performed were linear regression analysis.
Total Coliform Reduction Packed Column--
Table 30 summarizes the correlation between total coliform log reduction
(TCLR) in the packed column and each effluent quality variable at different
applied ozone dosage levels.
A correlation coefficient greater than 0.73 or less than -0.73 in
Table 30 is significantly different from zero at the 95 percent confidence
level.
It is clear from Table 30 that chemical oxygen demand (total and soluble)
and total organic carbon significantly interfered with TCLR in the packed
column at dosage levels ranging from 4.9 to 13.1 mg/£. At 19.5 mg/£ ozone
dosage, TKN and organic-N significantly interfered with TCLR, but not TCOD,
SCOD, or TOG. Thus, at all dosage levels TCLR appears to have been rate
limited since the magnitude of TC reduction was affected by the effluent
quality.
It appears that a strong negative correlation was associated with total
suspended solids and TCLR at 4.9 mg/£ ozone dosage but not at the higher
dosages. Although it is possible that TSS exerted an ozone demand at low
applied ozone levels, it is likely that this observation was an experimental
artifact, because the variation in TSS from day-to-day was not high enough
to warrant such a conclusion. Data on unfiltered effluent are needed to
better quantify this relationshiip.
It appears that a strong positive correlation existed between ammonium-N
and TCLR at 4.9, 9.7, and 13.1 mg/£ applied ozone but not at 19.5 mg/£. This
compares with the substantial negative correlation observed for TCOD, SCOD,
and TOC at the same dosage levels and the lack of correlation at 19.5 mg/fc
applied ozone. Since NH^-N was inversely related to TCOD, SCOD, and TOC in
this effluent (Table 17), it is likely that the above observation merely
reflects the effect of COD and TOC on TCLR.
Total Kjeldahl nitrogen and organic nitrogen did not appear to affect
disinfection efficiency until 19.5 mg/£ ozone was applied. This suggests that
the organic demand exerted by COD and TOC in this effluent significantly
affected TCLR in the packed column at lower ozone dosages but the demand
exerted by nitrogenous compounds became significant at higher dosages. This
conclusion would not be inconsistent with the observation that TKN and ORG-N
did not correlate with COD or TOC.
55
-------
TABLE 30. CORRELATION OF TOTAL COLIFORM LOG REDUCTION (TCLR)
IN THE PACKED COLUMN AT DIFFERENT APPLIED OZONE DOSAGE LEVELS
WITH EFFLUENT QUALITY PARAMETERS
Parameter
TCOD
SCOD
TOC
TSS
TKN
TURB
NH4-N
ORG-N
4.9
-0.96
-0.96
-0.90
-0.83
0.76
-0.10
0.87
0.38
TCLR Correlation
Dose mg/£
9.7
-0.84
-0.91
-0.68
0.10
0.44
0.03
0.72
0.13
Coefficient (r)*
13.1
-0.98
-0.97
-0.94
-0.29
0.16
-0.11
0.82
-0.08
19.5
0.22
0.14
0.18
0.64
-0.88
-0.71
-0.25
-0.88
6 data points used to derive each r-value
56
-------
Fecal Coliform Reduction - Packed Column--
Table 31 summarizes the correlation between fecal coliform log reduction
(FCLR) in the packed column and each effluent quality variable at different
applied ozone dosage levels.
Results from the FCLR data are similar to the TCLR data at 4.9 and 9.7
mg/£ applied ozone dosage. However, at 13.1 mg/£, COD and TOG no longer
affected FCLR, while TKN and ORG-N significantly interfered with FCLR. At
19.5 mg/£ ozone, the only variable adversely affecting FCLR was TCOD. No
explanation can be offered for the latter observation except to suggest the
observation may be artifactual. The demand exerted by nitrogenous material
with respect to FCLR in the packed column became significant between 9.7 and
13.1 mg/£ applied ozone, while the same demand with respect to TCLR became
significant at dosages greater than 13.1 mg/£.
Total Coliform Reduction - Jet Scrubber--
Table 32 summarizes the correlation between total coliform log reduction
(TCLR) in the jet scrubber and each effluent quality variable at different
applied ozone dosage levels.
Results from Table 32 indicate that TCLR in the jet scrubber was not
affected by any of the measured effluent parameters at 4.9 mg/£ applied ozone.
The reason for this is that little microorganism reduction occurred at this
dosage level (Table 18) to permit correlations to occur.
At 9.7 and 13.1 mg/£, the same trend in TCLR noted in the packed column
was observed in the jet scrubber. Thus, TCOD, SCOD, and TOC adversely
affected TCLR, while NHt-N showed a positive correlation. At 19.5 mg/£
ozone, the adverse affect of COD and TOC disappeared, but, in contrast to the
packed column, TKN and ORG-N did not correlate with TCLR. Hence, TCLR in the
jet scrubber was reaction rate limited at lower dosage levels but became mass
transfer limited at a dosage somewhere between 13.1 and 19.5 mg/£.
Fecal Coliform Reduction - Jet Scrubber--
Table 33 summarizes the correlation between fecal coliform log reduction
(FCLR) in the jet scrubber and each effluent quality variable at different
applied ozone dosage levels.
Results from Table 33 are similar to those in Table 32. The only
difference is the significant negative correlation of FCLR with TOC at 4.9
mg/£ ozone. Thus, in general, FCLR was affected by the same parameters as
TCLR in the jet scrubber.
Ozone Utilization - Packed Column--
Table 34 summarizes the correlation between ozone utilization in the
packed column and each effluent quality variable at different applied ozone
dosage levels.
57
-------
TABLE 31. CORRELATION-OF FECAL COLIFORM LOG REDUCTION (FCLR)
IN THE PACKED COLUMN AT DIFFERENT APPLIED OZONE DOSAGE
LEVELS WITH EFFLUENT QUALITY PARAMETERS
Parameter
TCOD
SCOD
TOC
TSS
TKN
TURB
NH4-N
ORG-N
4.
-0
-0
p
.9
.87
.82
-0.91
-0.
0.
-0.
0.
0.
,86
,44
,27
,66
,09
CLR Correlation Coefficient (r)*
Dose mg/J,
9,
-0,
-0,
-0.
-0.
0.
0.
0.
0.
.7
.84
.92
,72
07
61
03
80
28
13.1
-0
-0
0,
0
-0.
-0,
-0.
-0.
.25
.29
,08
.63
.82
,40
,28
84
19
-0.
-0.
-0.
-0.
0.
0.
0.
-0.
.5
77
41
64
72
21
07
56
02
6 data points used to derive each r-value
TABLE 32. CORRELATION OF TOTAL COLIFORM LOG REDUCTION (TCLR)
IN THE JET SCRUBBER AT DIFFERENT APPLIED OZONE DOSAGE LEVELS
WITH EFFLUENT QUALITY PARAMETERS
TCLR Correlation Coefficients (r)J
Parameter Dose mg/£
TCOD
SCOD
TOC
TSS
TKN
TURB
NH4-N
ORG-N
4
-0
-0
-0
-0,
0
0.
0.
0.
.9
.40
.36
.67
.74
.38
,57
,27
,32
9
-0.
-0,
-0.
0,
0.
-0.
0.
0.
.7
.94
.93
.86
.12
,41
46
88
02
13
-0.
-0.
-0.
-0.
0.
-0.
0.
-0.
.1
94
92
87
40
06
44
82
20
19
-0.
-0.
-0.
0.
-0.
-0.
0.
-0.
.5
39
51
55
19
40
70
39
64
6 data points used to derive each r-value
58
-------
TABLE 33. CORRELATION OF FECAL COLIFORM LOG REDUCTION (FCLR)
IN THE JET SCRUBBER AT DIFFERENT APPLIED OZONE DOSAGE LEVELS
WITH EFFLUENT QUALITY PARAMETERS
Parameter
TCOD
SCOD
TOC
TSS
TKN
TURB
NH4-N
ORG-N
4.9
-0.64
-0.60
-0.83
-0.78
0.24
0.07
0.38
0.04
FCLR Correlation
Dose
9.7
-0.83
-0.88
-0.78
-0.19
0.68
-0.25
0.90
0.32
Coefficient (r)*
mg/l
13.1
-0.99
-0.99
-0.90
-0.26
-0.01
-0.37
0.80
-0.26
19.5
-0.48
-0.51
-0.64
-0.02
-0.30
-0.69
-0.47
-0.57
6 data points used to derive each r-value
TABLE 34. CORRELATION OF OZONE UTILIZATION IN THE F-ACKED COLUMN
AT DIFFERENT APPLIED OZONE DOSAGE LEVELS WITH EFFLUENT QUALITY PARAMETERS
Parameter
TCOD
SCOD
TOC
TSS
TKN
TURB
NH4-N
ORG-N
Ozone Utilization Correlation Coefficients (r)*
Dose rag/?,
4.
-0.
-0,
-0.
-0.
0,
-0.
0.
0.
.9
.96
.96
.69
.69
,58
,32
96
05
9,
0
0
0
0
-0,
-0.
-0.
-0.
,7
.18
.23
.30
.78
.89
.59
,26
,90
13
0.
0.
0.
0.
-0.
0.
-0.
0.
.1
93
94
93
24
01
13
67
20
19
0.
0.
0.
0.
0.
0.
-0.
0.
.5
77
80
71
03
25
47
67
60
6 data points used to derive each value
59
-------
At an ozone dosage of 4.9 mg/£ there appears to be a significant negative
correlation between ozone utilization and COD (total and soluble), while at
9.7 mg/£ no correlation exists, and at higher levels there is a positive
correlation. This observation can be explained as follows. According to the
International Critical Tables (16), the magnitude of Henry's Constant (H)
increases as the temperature of the liquid increases. The mean temperature of
the effluent in the six replicate experiments was 14 °C. At that temperature
and an ozone concentration in the gas of 9.7 mg/£ the highest possible con-
centration of ozone which can exist in the liquid, regardless of the gas/liquid
flow ratio, is 4.8 mg/£. Thus, when the dosage is 4.9 mg/£, (gas/liquid ratio
= 0.5), it is theoretically possible for the liquid itself in the contactor to
absorb 4.8 mg/£ regardless of the organic demand of the liquid. The driving
force at any point in the column for mass transfer of ozone from the gas phase
to the liquid phase is determined primarily by the difference in concentration
of ozone in the gas stream and dissolved ozone. This difference in concentration
diminishes as the gas rises through the column. At low dosage levels, most of
the driving force occurs at the bottom of the column, and ozone will be absorbed
into the water with or without the presence of organic demand. Therefore, it
is reasonable to conclude that the significant negative correlation between
ozone utilization and COD observed at 4.9 mg/£ dosage was coincidental.
At 9.7 mg/£ dosage (gas/liquid ratio = 1), the exhaust gas concentration
was higher, and consequently a greater mass transfer driving force was available
at the top of the column. This means not only that ozone absorption occurred
more evenly through the length of the column but also that more ozone was
available to react with organic demand. An average of 5.4 mg/£ ozone was
utilized at that dosage, or 0.6 mg/£ more than the theoretical maximum
allowable concentration. Since only 0.6 mg/£ of the 5.4 mg/£ ozone utilized
can be attributed to the organic demand, no correlation was found between
TCOD or SCOD and ozone utilization at 9.7 mg/£ dosage.
At dosage levels greater than 9.7 mg/£, the dosage was sufficiently above
the ozone solubility at that temperature and the driving force at the top of
the column was sufficiently high relative to the TCOD and SCOD concentration
that a change in TCOD and SCOD caused a corresponding change in ozone utili-
zation. Hence, at 13.1 mg/£ applied ozone, an average of 6.2 mg/£ was utilized
(1.4 mg/£ greater than the theoretical maximum), while at 19.5 mg/£ applied
ozone, an average of 8.0 mg/£ was utilized (3.2 mg/£ greater than the theoretical
maximum). This explains the high positive correlation between ozone utilization
and TCOD, SCOD, and TOC at the high dosage levels.
The observations appear to contrast with the ANOVA for the ozone
utilization data (Table 25), which indicated no significant effect of effluent
quality on the amount of ozone utilized. However, the ANOVA averaged the data
for both contactors over all dosage levels, while the regression analyses
isolated and examined the effects of effluent quality at each individual dosage
level for each contactor. These individual effects cancelled each other when
averaged together in the ANOVA.
It is concluded that, at low doses (i.e., 4.9 and 9.7 mg/£), ozone
utilization was mass transfer limited, while at high dosages (i.e., >9.7 mg/£)
reaction kinetics influenced mass transfer. This contrasts with the
60
-------
conclusions made for TCLR and FCLR. It means that, as ozone absorption by
the effluent proceeded at low dosage levels, the ozone which had been trans-
ferred at those dosage levels was rapidly consumed in chemical reactions with
oxidizable materials, the concentrations of which far exceeded the concen-
trations of microorganisms. Thus, coliform reduction at dosages >9.7 mg/£
was essentially reaction rate limited while utilization was mass transfer
limited. At higher dosage levels, utilization exceeded that which would be
predicted by Henry's Law, due to the effect of COD and TOG. However, the
ozone which was transferred was immediately consumed by the organic demand
causing the excessive absorption. Hence, at the high dosage levels, coliform
reduction was again reaction rate limited, as was ozone utilization.
Ozone Utilization - Jet Scrubber--
Table 35 summarizes the correlation between ozone utilization in the jet
scrubber and each effluent quality variable at different applied ozone dosage
levels.
The correlation of ozone utilization with TCOD, SCOD, and TOC was
significant at 4.7 and 13.1 mg/£ applied ozone, but,not at 9.7 and 19.5 mg/&.
Perhaps more data points would have provided the necessary information to
establish the correlation, since the r-values were near the critical value
(i.e., 0.73) to be considered significant. The fact that the gas-liquid
contact time in the jet scrubber was so low (3 sec at 75 £/min liquid flow
rate) may have been a significant factor affecting absorption in this
contactor and/or reaction of ozone with organic matter.
Ozone Residual - Packed Column--
Table 36 summarizes the correlation between ozone residual in the
packed column and each effluent quality variable at different applied ozone
dosage levels.
It is clear from Table 36 that the magnitude of ozone residual in the
effluent from the packed column was significantly affected by the presence
of soluble organic material at all dosage levels studied. Thus, if the COD
(total and soluble) or TOC was high, the ozone residual was low and vice
versa. This would at least partially explain why coliform reduction in the
packed column was significantly affected by replication, i.e., effluent
quality (Tables 19 and 21).
Ozone Residual - Jet Scrubber--
Table 37 summarizes the correlation between ozone residual in the jet
scrubber and each effluent quality variable at different applied ozone dosage
levels.
It is evident from Table 37 that, as COD (total and soluble) and TOC
increased, ozone residual in the effluent from the jet scrubber decreased at
all dosage levels. Thus, the results from the jet scrubber are comparable to
those from the' packed column and the same conclusions apply.
61
-------
TABLE 35. CORRELATION OF OZONE UTILIZATION IN THE JET SCRUBBER
AT DIFFERENT APPLIED OZONE DOSAGE LEVELS WITH EFFLUENT QUALITY PARAMETERS
Ozone Utilization
Parameter
4.9
TCOD 0.91
SCOD 0.91
TOC 0.81
TSS 0.60
TKN -0.48
TURB 0,05
NH4-N -0.69
ORG-N -0.12
9.7
0.63
0.71
0.62
0.48
-0.87
-0.12
-0.74
-0.62
Correlation Coefficients
Dose mg/X,
13.1
0.96
0.95
0.95
0.38
-0.06
0.31
-0.79
0.19
(r)*
19.5
0.62
0.70
0.61
-0.08
0.38
0.66
-0.58
0.71
* 6 data points used to derive each r-value
TABLE 36. CORRELATION OF OZONE RESIDUAL IN THE PACKED COLUMN
AT DIFFERENT APPLIED OZONE DOSAGE LEVELS WITH EFFLUENT QUALITY PARAMETERS
Ozone
Parameter
4.9
TCOD -0.96
SCOD -0.93
TOC -0.90
TSS -0.77
TKN 0.48
TURB -0.35
ORG-N 0.08
Residual Correlation Coefficients
9.7
-0.74
-0.77
-0.71
-0.21
0.64
-0.37
0.29
Dose mg/i
13.1
-0.97
-0.97
-0.91
-0.31
0.04
-0.38
-0.22
(r)*
19.5
-0.90
-0.86
-0.96
-0.78
0.58
-0.09
0.22
* 6 data points used to derive each r-value
62
-------
TABLE 37. CORRELATION OF OZONE RESIDUAL IN THE JET SCRUBBER
AT DIFFERENT APPLIED OZONE DOSAGE LEVELS WITH EFFLUENT QUALITY PARAMETERS
Ozone Residual
Parameter
TCOD
SCOD
TOC
TSS
TKN
TURR
NH4-N
ORG--N
4.9
-0.88
-0.83
-0.88
-0.77
0.34
-0.40
0.61
-0.01
9
-0
-0
-0
-0
0
-0
0
0
Correlation Coefficients (r)*
Dose rag/Jl
.7
.80
.85
.76
.30
.78
.04
.84
.46
13
-0.
-0.
-0.
-0.
0.
-0.
0.
-0.
.1
96
92
88
41
14
24
79
10
19
-0.
-0.
-0.
-0.
0.
-0.
0.
-0.
.5
98
90
94
56
35
02
87
01
* 6 data points used to derive each r-value
Ozone Consumption - Packed Column--
Table 38 summarizes the correlation between ozone consumption in the
packed column and each effluent quality variable at different applied ozone
dosage levels.
Data from Table 38 parallel the trends noted in the ozone utilization
data (Table 34), namely, that at higher dosage levels, ozone consumption
TABLE 38. CORRELATION OF OZONE CONSUMPTION IN THE PACKED COLUMN
AT DIFFERENT APPLIED OZONE DOSAGE LEVELS WITH EFFLUENT QUALITY PARAMETERS
Parameter
TCOD
SCOD
TOC
TSS
TKN
TURB
NH4-N
ORG-N
Ozone Consumption Correlation Coeff icie'nts (r)*
Dose mg/5.
4.9
-0.
-0.
0.
0.
0.
-0.
0.
-0.
.34
.37
.06
.07
.27
.68
52
04
9
0
0
0.
0
-0.
-0.
-0.
-0.
.7
.23
.21
.40
.61
.71
.78
.03
.82
13
0.
0.
0.
0.
-0.
-0.
-0.
-0.
.1
76
73
85
39
24
29
50
10
19
0.
0.
0.
0.
-0.
0.
-0.
0.
.5
98
87
86
38
07
16
81
30
* 6 data points used to derive each r-value
63
-------
increased as carbonaceous demand increased. Thus, at dosage levels greater
than 9.7 mg/£, the dosage was sufficiently high relative to COD and TOG that
a change in COD or TOC caused a concomitant change in ozone consumption. At
lower dosage levels, mass transfer was determined primarily by the concen-
tration of ozone in the inlet gas and secondarily by organic demand.
Ozone Consumption - Jet Scrubber--
Table 39 summarizes the correlation between ozone consumption in the jet
scrubber and each effluent quality variable at different applied ozone dosage
levels.
A significant positive correlation is noted in Table 39 between ozone
consumption and TCOD, SCOD, and TOC at all dosage levels. This contrasts
with the data observed in the packed column in which positive correlations
were observed only at dosage levels greater than 9.7 mg/£.
Summary of Regression Analyses--
This section attempted to explain the variation observed in the micro-
organism reduction and ozone utilization data from the factorial experiments
by quantitatively examining the effect of each effluent constituent on
TABLE 39. CORRELATION OF OZONE CONSUMPTION IN THE JET SCRUBBER
AT DIFFERENT APPLIED OZONE DOSAGE LEVELS UTTH EFFLUENT QUALITY PARAMETERS
Parameter
TCOD
SCOD
TOC
TSS
TKN
TURB
NH4-N
ORG-N
0:
4.
0.
0.
0.
0.
-0
0,
-0
-0
:one Consumption Correlation Coefficients (r)*
Dose mg/S,
9
90
89
.86
.69
.45
.02
.66
.11
9.
0.
0.
0.
0.
-0,
-0.
-0
-0
7
74
SO
71
.35
.SO
.04
.79
.52
13
0.
0.
0.
0.
-0.
0.
-0.
0.
.1
96
94
97
43
16
12
77
06
19
0.
0.
0.
0.
0.
0.
-0.
0.
.5
76
78
71
05
27
53
67
63
* 6 data points used to derive each r-value
coliform reduction and ozone utilization, consumption, and residual at
each dosage level studied. Results indicated that TCLR in the packed column
was significantly and adversely affected by COD and TOC at ozone dosages less
than 13.1 mg/£, while at higher dosages demand exerted by nitrogenous mate-
rials became significant. In the jet scrubber, the same trends were noted
64
-------
except that no correlations were found at 4.9 mg/X, ozone dose, where very
little coliform reduction occurred anyway. Variations in the levels of
nitrogenous materials did not significantly affect coliform reduction in
the jet scrubber at any dosage level, presumably because of the exceedingly
short reaction time available.
Ozone utilization and consumption in the packed column were significantly
affected by COD and TOC at dosage levels greater than 9.7 mg/£. At lower
dosage levels absorption was governed primarily by Henry's Law. In the jet
scrubber, ozone consumption and utilization were significantly affected by
COD and TOC at essentially all dosage levels studied.
Ozone residual in both contactors was significantly affected by COD and
TOC at all dosage levels.
PHASE 3 - CONTINUOUS OPERATION - PILOT PLANT EFFLUENT
During this phase of the investigation, an attempt was made to evaluate
the reliability of each contactor in achieving a consistent 3-log reduction
in coliform numbers, and to determine if the ozonation system (generator,
drier, contactors, and analyzer equipment) could be operated for 100 contin-
uous hours without major breakdowns. Ozone gas concentrations and flow rates
were varied to maintain the highest possible ozone residuals in both con-
tactors. This necessitated the use of high gas/liquid flow ratios in the
jet scrubber, which in turn caused a reduction in percent ozone utilization.
Ozone gas concentrations were monitored continuously by a Fisher and Porter
Residual Ozone Analyzer. Grab samples of inlet and exhaust gas and ozonated
effluent from each contactor were also taken manually for measurement. All
bacteriological and physical-chemical analyses were performed on grab
samples collected at 10-hour intervals. The experiment commenced at 7:00 AM
on February 28, 1977, and terminated at 1:00 AM on March 3, 1977. The
wastewater effluent was filtered prior to ozonation.
All systems operated satisfactorily for the entire 100 hours. Results
are presented in Table 40. A 3-log reduction in total coliforms was
achieved in 5 out of 10 samples in the packed column and only 1 out of 10
in the jet scrubber. A 3-log reduction in fecal coliforms was achieved in
4 out of 10 samples in the packed column and only 2 out of 10 in the jet
scrubber. Thus, neither contactor gave reliable results in this particular
wastewater. Short contact times (20 seconds in the packed column and 3
seconds in the jet scrubber) may partially explain the low microorganism
reduction efficiencies observed. Wastewater quality may have played a key
role in affecting the reliability of ozone disinfection in both contactors
during these tests. The ranges of TCOD and TSS were 51 to 91 mg/Jl (mean of
66 mg/£) and 4 to 30 mg/£ (mean of 20 rag/A), respectively. The TSS levels
were considerably higher than in the prior testing period. Thus, it appears
that additional wastewater treatment beyond secondary may be needed to
achieve a reliable, and consistent microorganism reduction by ozone, generated
from air and applied in a packed column or a jet scrubber.
65
-------
TABLE 40. CONTINUOUS OPERATION OF PACKED COLUMN AND JET SCRUBBER
FOR THE 100-HOUR PERIOD OF FEBRUARY 28, 1977 TO MARCH 3, 1977
Date
Time
Contactor
G/L
Inlet
ozone,
nig/ft gas
Exhaust
ozone,
Ozone
residual
mg/8. liq.
TCLR
FCLR
2/28/77
2/28/77
3/01/77
3/01/77
3.01/77
3/02/77
5/02/77
3/03/77
3/03/77
3/04/77
0700
1700
0300
1300
2300
0900
1900
0500
1500
0100
Packed column
Jet scrubber
Packed column
Jet scrubber
Packed column
Jet scrubber
Packed column
Jet scrubber
Packed column
Jet scrubber
Packed column
Jet scrubber
Packed column
Jet scrubber
Packed column
Jet scrubber
Packed column
Jet scrubber
Packed column
Jet scrubber
1.2
2.0
1.3
2.0
1.0
2.0
0.6
2.0
0.6
2.0
1.2
2.0
1.1
2.0
1.8
2.0
13.4
13.4
13.2
13.2
14.
14.
14.5
14.5
17.0
17.0
14.2
14.2
14.3
14.3
11.9
11.9
11.5
11.5
10.9
10.9
5.7
10.0
6.1
10.0
3.9
5.9
6.3
11.2
5.5
13.4
3.5
12.7
6.4
10.8
2.4
6.1
4.8
9.2
6.4
0.7
0.3
0.6
0.3
0.5
0.7
1.1
1.0
0.4
0.3
0.5
0.4
1.0
0.9
3.22
2.22
1.92
1.08
1.42
<1.00
2.66
2.52
3.00
2.54
2.86
2.28
2.85
3.04
1.48
3.48
1.18
3.38
3.33
2.69
2.38
1.76
1.62
1.46
<0.31
3.00
3.17
2.23
2.75
3.15
3.00
2.71
1.50
3.42
1.69
3.38
1.50
2.50
2.65
66
-------
REFERENCES
1. American Public Health Association. 1975. Standard Methods for the
Examination of Water and Wastewater, 14th ed. American Public Health
Association, Inc., New York.
2. American Standards for Testing and Materials. 1974. Interfacial
Tension of Oil Against Water by Ring Method. ASTM D-071, p. 576.
3. American Standards for Testing and Materials. 1974. Kinematic
Viscosity of Transparent and Opaque Liquids. ASTM D-445, p. 355.
4. Anderson, Virgil L., and Robert A. McLean. 1974. Design of Experiments
A Realistic Approach. Marcel Dekker, Inc., New York, N. Y., 418 pp.
5. Dixon, W. J. (Ed.). 1973. Biomedical Computer Programs. University of
California Press, Berkeley; California, 773 pp.
6. Birdsall, C. M., A. C. Jenkins, and Edward Spadinger. 1952. lodometric
Determination of Ozone. Anal. Chem. 24:662.
7. Farooq, S., R. S. Engelbrecht, and E. S. K. Chian. 1977. The Effect of
Ozone Bubbles on Disinfection. Progress in Water Technology, 7_:233.
8. Chan, H. B., C. L. Chen, R. P. Miele, and I. J. Kugelman. 1975.
Wastewater Disinfection With Ozone. California Water Pollution Control
Association Bulletin 12(2):47.
9. Hicks, Charles R. 1964. Fundamental Concepts in the Design of
Experiments. Holt, Rinehart, and Winston, Inc., New York, N. Y.,
293 pp.
10. Kamphake, L. J., S. A. Hannah, and J. M. Cohen. 1967. Automated
Analysis for Nitrate by Hydrazine Reduction. Water Research 1_:205.
11. Kenner, Bernard A., and Harold P. Clark. 1974. Detection and
Enumeration of Salmonella and Pseudomonas aeruginosa. J. Water Poll.
Con. Fed. 46_:2163^
12. Marks, Henry C., and G. L. Banister. 1974. Amperometric Methods in
the Control of Water Chlorination. Anal. Chem. 19:200.
67
-------
13. Masschelein, W., G. Fransolet, and J. Genot. 1975. Techniques for
Dispersing and Dissolving Ozone in Water. Part 1. Water and Sewage
Works, L22_(12) :57.
14. Masschelein, W., G. Fransolet, and J. Genot. 1976. Techniques for
Dispersing and Dissolving Ozone in Water. Part 2. Water and Sewage
Works, 125(1):34.
15. Methods Development and Quality Assurance Research Laboratory. 1975.
Methods for Chemical Analysis of Water and Wastes. EPA-625/6-74-003,
U. S. Environmental Protection Agency, Cincinnati, Ohio, 298 pp.
16. National Research Council. 1928. International Critical Tables of
Numerical Data, Physics, Chemistry, and Technology. McGraw-Hill Book
Co., Inc., New York, N. Y., _3, p. 255.
17. Natrella, M. G.. 1966. Experimental Statistics. U. S. Government
Printing Office, Washington, D. C., 485 pp.
18. Nebel, C., P. C. Unangst, and R. D. Gottschling. 1973. An Evaluation
of Various Mixing Devices for Dispersing Ozone in Water. Water and
Sewage Works, 120:R6.
19. Rosen, H. M., F. E. Lowther, and R. G. Clark. 1974. Get Ready For
Ozone. Water and Wastes Eng. 11(7):25.
68
-------
APPENDIX A
THE MODIFIED KENNER-CLARK PROCEDURE
FOR ENUMERATING SALMONELLA SPP.
The following describes the quantitative method used for enumerating
Salmonella spp. from ozonated and unozonated activated sludge effluents. It
is based on the original technique developed by Kenner and Clark (11) but with
certain modifications.
SAMPLE TREATMENT
Concentration of organisms is attained by filtration through either
membrane filters (0.45 ym) or glass fiber filters (Reeve Angel 984H ultra
glass fiber filter). To obtain MPN results in the per 10 liter range, three
1000 ml samples are filtered through three membranes or glass fiber filters
and the filters placed into enrichment tubes containing single strength
enrichment broth (first row). Three 100 ml samples are filtered through three
membrane or glass fiber filters and the filters placed into enrichment tubes
containing single strength enrichment broth (second row). Three 10 ml samples
are pipetted into three tubes with double strength enrichment broth (third row),
row). Finally, three 1.0 ml samples are delivered into three tubes containing
9 ml of single strength enrichment broth (fourth row).
CONFIRMATION OF SALMONELLA SPP.
Primary enrichment medium is Dulcitol Selenite Enrichment (DSE) broth
(Difco) and incubation is for 24 to 48 hours at 40 °C + 0.2 °C.
After incubation for 24 hours a loopful is removed from each culture tube,
streaked onto Xylose Lysine Desoxycholate (SLD) agar (Difco) plates, and
incubated at 35 °C for 24 hours. The DSE tubes are placed back into the 40 °C
incubator, incubated for an additional 24 hours, and the isolation procedure
on XLD plates is repeated as above. This allows an additional 24 hours of
enrichment for any salmonellas which may have been originally present but had
not yet grown to sufficient numbers to be detectable.
After the XLD plates have incubated 24 hours, they are examined for
appearance of Salmonella-type colonies. Typical Salmonella colonies appear
clear and pink-edges with black centers. The presumptive Salmonella colonies
(at least 2 per plate and well isolated) are picked to Triple Sugar Iron Agar
(TSIA) or Kligler's Iron Agar (KIA) slants (Difco) and Lysine Iron Agar (LIA)
slants (Difco) for biochemical identification. Slants are incubated 24 hours
69
-------
at 35 °C. If the black -centered colonies on the XLD plates are not well-
isolated, another XLD plate must be streaked from the poorly isolated colony
to purify the culture for subsequent biochemical identification. The typical
reactions of Salmonella spp. on TSIA are alkaline slant, acid stab, and I^S
production. The reactions on LIA are alkaline slant and stab (i.e., positive
for lysine decarboxylase) and F^S production.
Confirmation is achieved in a very short time. The agglutination
reaction, performed on the culture from the TSIA slant, using Salmonella
0 Antiserum Poly A-l, will confirm the presence of Salmonella spp. in a
few minutes. Thus, the serological agglutination reaction will confirm or
deny the presence of Salmonella.
If the TSIA and LIA reactions are not typical for Salmonella, repurifi-
cation from the TSIA on XLD followed by picking subsequent black colonies (if
any) back to TSIA and LIA is necessary before concluding that Salmonella are
not present. This adds an additional two days of work to the test. Thus
the time span for the entire method will produce results in as little as
three to four days and as many as six days.
The method described is one of several methods in existence capable of
quantifying Salmonella in natural samples. The limitations are indeed
recognized. The precision of the 3-tube MPN is certainly inferior to the
5-tube procedure, but the trade-off in effort required in performing the
5-tube procedure for Salmonella enumeration does not justify its use at this
time. It should be cautioned, however, that only an experienced micro-
biologist or microbiological technician should attempt the above procedure
for routine analysis, as the number of tubes, plates, slants, etc., could
overwhelm the investigator who has not been properly trained.
70
-------
PACKED COLUMN MASS TRANSFER CALCULATIONS FOR PHASE 1
DATE
G
i/min
1
rag/1
2
mg/1
mg/min
Temp.
°C
1
mg/1 ww
H@T
1
mg/1
mg/1
KgVa
iair/rain
37
9-13
9-13
9-14
9-14
9-20
9-20
9-21
9-21
10-4
10-4
10-5
10-5
10-12
11-1
37
37
37
37
37
37
37
37
37
37
37
37
37
37
7.5
5.0
7.7
5.0
12.2
7.6
12.2
7.5
17.6
16.3
16.1
16.0
5.0
5.9
1.4
0.9
1.5
1.4
2.3
1.3
2.0
1.4
3.4
3.1
4.1
4.2
0.5
0.3
226
152
229
133
366
233
377
226
525
488
444
437
167
207
23
23
23.5
23.5
23
23
22
22
21
21
21
21
19
14.5
1.2
0.6
1.3
0.7
1.8
0.8
2.3
1.4
1.8
1.4
1.4
1.6
0.3
0.4
2.85
2.85
2.90
2.90
2.85
2.85
2.74
2.74
2.63
2.63
2.63
2.63
3.4
1.7
3.8
2.0
5.1
2.3
6.3
3.8
4.7
3.7
3.7
4.2
2.43
2.07
0.7
0.8
1.08
1.30
0.96
0.76
1.13
1.41
1.08
0.97
1.33
1.40
1.11
1.03
2.15
2.83
2.50
1.85
2.50
2.11
4.25
2.84
3.61
2.37
7.14
6.79
7.48
7.38
1.77
1.70
90
82
92
63
86
82
104
95
74
72
59
59
94
122
G « 73.6
7-26
7-27
8-2
8-2
8-2
8-3
8^9
8-9
8-10
8-10
73.6
73.6
73.6
73.6
73.6
73.6
73.6
73.6
73.6
73.6
11.5
7.6
3.7
7.4
11.9
11.9
3.8
7.7
3.7
7.6
3.4
1.7
0.7
2.1
3.8
3.9
0.8
2.3
0.8
2.5
596
434
221
390
596
589
221
397
213
375
24
24
23
23
23
23
23
21
23
2.2
1.2
0.7
1.9
2.1
2.4
0.5
1.7
0.8
2.0
97
97
85
85
85
85
85
2.85
2.85
2.85
6.5
3.6
2.0
5.4
6.0
6.8
1.4
4.8
2.3
5.7
0.39
0.85
0.89
0.05
0.44
0.27
1.10
0.23
0.56
0.28
4.10
2.71
1.12
2.00
4.77
4.44
1.45
2.61
1.07
2.14
145
160
197
195
125
133
152
152
199
175
13
T)
Z
o
1— 1
X
GO
110
8-16
8-»7
8-Z3
8-24
8-30
110
110
110
110
110
9.7
9.6
9.6
5.1
8.4
5.0
5.4
4.5
2.2
4.0
147
8-16
8-23
8-24
8-30
147
147
147
147
7.5
7.5
4.1
7.0
4.6
4.0
2.1
4.0
517
462
561
319
484
426
514
294
441
23
23
23
24
23
2.9
2.6
3.0
0.8
2.4
2.85
2.85
2. 85
2.97
2.85
8.3
7.4
8.6
2.4
6.8
23
23
24
23
2.3
2.0
0.8
2.1
2.85
2.85
2.97
2.85
6.6
5.7
2.4
6.0
1.27
0.90
1.50
0.21
0.92
1.63
0.80
0.21
1.39
2.83
3.56
2.33
2.38
2.61
2.27
2.75
1.90
2.16
183
130
241
134
185
188
187
155
204
G = 55
10-18
10-18
11-1
55
55
57
13.8
9.5
5.9
4.4
2.8
1.3
517
368
262
17
17
14.5
2.1
2.1
0.9
2.25
2.25
2.06
4.7
4.7
1.9
0.73
0.54
1.12
6.47
3.71
2.40
80
99
109
-------
PACKED COLUMN MASS TRANSFER CALCULATIONS FOR PHASE 2
DATE G Yj Y2 ^VV TeI"P' H9T Xl Yl* *" Y1~Y1* AYLM KgVa
G = 37
H/min mg/1 mg/1 mg/min °C J,ww/£air mg/1 ww mg/1 Y mg/i J.air/min
1-27-77 37 9.7 3.2 240 14 2.04 0.1 0.2 1.09 5.78 42
1-31-77 37 9.6 2.1 278 14 2.04 0.6 1.2 1.39 4.53 61
2-7-77 37 9.6 2.6 259 13 2.00 0.2 0.4 1.26 5.24 49
2-8-77 37 9.6 3.7 218 14 2.04 <0.1 0.2 0.93 6.13 36
2-8-77 37 9.5 3.0 240 14 2.04 <0.1 0.2 1.13 5.58 43
1-24-77 37 9.9 2.2 285 13 2.00 0.9 1.8 1.30 4.54 63
G = 76
1-27-77 76 9.7 4.9 365 14 2.04 0.3 0.6 0.62 6.78 54
1-31-77 76 9.7 4.7 380 14 2.04 1.4 2.9 0.37 5.69 67
2-7-77 76 9.8 4.3 418 13 2.00 0.4 0.8 0.74 6.36 66
2-8-77 76 9.6 4.0 426 14 2.04 0.2 0.4 0.83 6.24 68
2-8-77 76 9.7 3.6 464 14 2.04 0.1 0.2 0.97 6.08 76
1-24-77 76 9.6 4.1 418 13 2.00 0.9 1.8 0.64 5.75 73
G = 101
1-27-77 101 9.8 5.0 485 14 2.04 0.4 0.8 0.59 6.81 71
1-31-77 101 9.7 5.2 455 14 2.04 1.6 3.3 0.21 5.78 79
2-7-77 101 9.9 5.6 434 13 2.00 1.1 2.2 0.32 6.52 67
2-8-77 101 9.9 5.0 495 14 2.04 0.4 0.8 0.60 6.85 72
2-8-77 101 9.8 4.6 525 14 2.04 0.2 0.4 0.71 6.72 78
1-24-77 101 9.9 5.7 424 13 2.00 1.7 3.4 0.13 6.10 70
G = 151
1-27-77 151 9.8 5.8 604 14 2.04 0.9 1.8 0.32 6.84 88
1-31-77 151 9.7 5.8 589 14 2.04 1.6 3.3 0.10 6.10 97
2-7-77 151 9.9 6.4 528 13 2.00 0.9 1.8 0.23 7.22 73
2-8-77 151 9.8 5.6 634 14 2.04 0.2 0.4 0.52 7.34 86
2-8-77 151 9.8 5.6 634 14 2.04 0.4 0.8 0.47 7.17 88
1-24-77 151 9.7 6.4 498 13 2.00 1.9 3.8 0.08 6.17 81
-------
JET SCRUBBER MASS TRANSFER CALCULATIONS FOR PHASE 1
DATE
G = 37
G
H/min
mg/1
2
mg/1
mg/min
9-13
9-13
9-14
9-14
9-20
9-20
9-21
9-21
10-4
10-4
10-5
11-1
11-2
37
37
37
37
37
37
37
37
37
37
37
37
32
7.6
5.3
7.7
5.3
12.0
7.4
12.0
7.7
17.4
16.1
16.2
5.9
9.2
3.9
2.1
3.8
2.4
4.5
4.0
5.0
4.5
8.1
8.3
8.6
2.9
4.5
137
118
144
107
278
126
259
118
344
289
281
111
150
G = 55
10-18
10-18
H-l
73.6
55
55
57
13.8
9.5
5.9
7.1
6.8
3.5
369
149
137
7-26
7-27
8-2
8-2
8-2
8-3
8-9
8-10
73.6
73.6
73.6
73.6
73.6
73.6
73.6
73.6
11.5
7.5
3.7
7.3
12.0
12.0
3.7
7.9
7.2
3.9
1.7
3.3
6.5
6.6
1.8
4.7
316
265
147
294
405
397
140
236
Temp.
°C
23
23
23.5
23.5
23
23
22
22
21
21
21
14.5
16
17
17
14.5
24
24
23
23
23
23
23
23
A2
rag/1
0.5
0.2
0.4
<0.1
0.5
0.2
0.6
0.3
1.2
0.6
1.0
0.3
0.5
2.7
1.3
0.3
0.9
0.5
0.0
0.3
0.7
0.7
0.2
0.7
H@T
fcww/fcair
2.85
2.85
2.90
2.90
2.85
2.85
2.74
In Y-,-V
74
62
62
62
06
2.18
2.25
2.25
2.06
2.97
2.85
mg/1
1.4
0.6
1.2
0.3
1.4
0.6
1.6
0.8
3.1
1.6
2.6
0.6
1.1
6.1
2.9
0.6
2.7
1.5
0.0
0.9
2.0
2.0
0.6
2.0
r'2
1.11
1.26
1.09
0.96
1.35
0.78
1.26
0.73
1.25
0.88
0.99
0.94
1.00
2.62
0.89
0.71
0.94
1.14
0.78
1.11
0.98
0.96
0.90
1.07
AY
LM
rag/1
4.59
3.02
4.68
3.33
6.59
5.13
6.83
5.48
9.92
10.68
10.30
3.82
5.83
4.89
6.29
4.22
7.46
4.48
2.57
4.40
7.65
7.71
2.81
4.84
KgVa
iair/min
30
39
31
32
42
25
38
22
35
27
27
29
26
75
24
32
42
59
57
67
53
51
50
49
G = 110
8-16
8-17
8-23
8-24
8-30
110
110
110
110
110
9.6
9.8
9.8
5.3
8.5
7.5
6.2
6.8
3.4
7.0
231
396
330
209
165
23
23
23
24
23
1.6
0.9
1.5
0.7
1.1
2.85
2.85
2.85
2.97
2.85
4.6
2.6
4.3
2.1
3.1
1.20
1.00
1.37
1.41
0.78
5.60
6.19
5.34
2.85
5.90
41
64
62
73
28
G = 147
8-16
8-17
8-23
8-24
8-30
147
147
147
147
147
7.4
7.4
7.7
4.0
6.9
5.7
5.8
5.6
2.6
5.4
250
235
309
206
220
23
23
23
24
23
1.2
0.7
0.6
0.4
0.7
2.85
2.85
2.85
2.97
2.85
3.4
2.0
1.7
1.2
2.0
1.17
0.67
0.68
1.05
0.71
4.36
5.40
5.59
2.48
4.95
57
44
55
83
44
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JET SCRUBBER MASS TRANSFER CALCULATIONS FOR PHASE 2
DATE G Y Y2 G(Y1-Y2) Temp. X2 H8T Y2* Hn Y2 -Y2* AY^ KgVa
£/min mg/1 mg/1 mg/min °C mg/1 ww 5,ww/J.air mg/1 Y^ mg/1 t-air/min
G = 37
1-27-77 37 9.7 4.2 204 14 -?0.1 2.04 0.2 0.85 6.67 31
1-31-77 37 9.6 4.6 185 14 0.1 2.04 0.2 0.78 6.67 28
2-7-77 37 9.6 4.5 189 13 <0.1 2.00 0.2 0.80 6.60 29
2-8-77 37 9.6 3.7 218 14 <0.1 2.04 0.2 1.01 6.05 36
2-8-77 37 9.5 3.3 229 14 <0.1 2.04 0.2 1.12 5.71 40
1-24-77 37 9.9 5.4 166 13 0.2 2.00 0.4 .68 7.17 23
G = 76
1-27-77 76 9.7 6.6 236 14 0.2 2.04 0.4 0.45 7.82 30
1-31-77 76 9.7 7.2 190 14 0.4 2.04 0.8 0.42 7.94 24
2-7-77 76 9.8 6.5 251 13 0.2 2.00 0.4 0.47 7.80 32
2-8-77 76 9.6 5.7 296 14 <0.1 2.04 0.2 0.56 7.36 40
2-8-77 76 9.7 5.5 319 14 <0.1 2.04 0.2 0.60 7.28 44
1-24-77 76 9.6 6.5 236 13 0.3 2.00 0.6 0.49 7.60 31
G = 101
1-27-77 101 9.8 6.7 313 14 0.2 2.04 0.4 0.44 7.92 40
1-31-77 101 9.7 7.3 242 14 0.5 2.04 1.0 0.43 7.88 31
2-7-77 101 9.9 7.2 273 13 0.3 2.00 0.6 0.41 8.14 34
2-8-77 101 9.9 6.7 323 14 <0.1 2.04 0.2 0.42 8.08 40
2-8-77 101 9.8 6.4 343 14 0.1 2.04 0.2 0.46 7.86 44
1-24-77 101 9.9 7.6 232 13 0.8 2.00 1.6 0.50 7.80 30
G = 151
1-27-77 151 9.8 6.2 544 14 0.2 2.04 0.4 0.52 7.63 71
1-31-77 151 9.7 7.3 362 14 0.4 2.04 0.8 0.40 7.99 45
2-7-77 151 9.9 7.8 317 13 0.4 2.00 0.8 0.35 8.37 38
2-8-77 151 9.8 7.2 393 14 <0.1 2.04 0.2 0.34 8.32 47
2-8-77 151 9.8 7.2 393 14 <0.1 2.04 0.2 0.34 8.32 47
1-24-77 151 9.7 7.8 287 13 0.7 2.00 1.4 0.42 7.93 36
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APPENDIX C
SAFETY PRECAUTIONS USED IN THE OZONE TEST FACILITY
A safety program was instituted for this research project based on the
draft report of "Technical Standards for Ozone" by the Occupational Safety
and Health Administration (OSHA). The major thrust of the program was to
provide containment and destruction of residual ozone in and near the working
environment.
The maximum permissable exposure concentration of ozone in air is less
than 0.1 part per million (ppm) on a volumetric basis. The action level is
0.05 ppm ozone. This low level of exposure was never exceeded during the
evaluation of the contactors.
Four major areas of control in the research facility were established to
guard against the accidental release of ozone into the work area.
POTENTIALLY HIGH OZONE CONCENTRATION AREA
The area between the generator and contactors was the most vulnerable
area to accidental ozone release because of the location of transmission
lines containing the highest levels of ozone in the facility (approximately
2,000 to 15,000 ppm). The transmission lines were fabricated from aluminum
tubing and located underneath or alongside support beams to protect the lines
from accidental falling objects.
If an accidental ozone release had occurred, the operators were
instructed to immediately vacate the area. An electrical cut-off switch
was located in an adjacent room for de-energizing the ozonator. A self-
contained breathing apparatus with a full facepiece and operated in a
pressure demand mode was located at an exit door from the building. During
an emergency, re-entry would be permissable with this apparatus into an area
containing toxic levels of ozone.
POTENTIALLY MODERATE OZONE CONCENTRATION AREA
The exhaust gases from the contactors contained ozone at concentrations
between 300 and 5000 ppm. In this area, PVC pipe was used to convey the
ozone from the contactors to a thermal decomposer. The decomposer was
controlled to maintain a temperature of 290 °C to insure complete decom-
position of the ozone before discharge to the outside atmosphere. A test was
conducted on the effect of temperature on ozone decomposition. Results
showed that temperatures above 260 °C were required to achieve a 90+% destruc-
tion of ozone. The data from this test are shown in Table C-l.
75
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TABLE C-l. EFFECT OF TEMPERATURE ON OZONE GAS DECOMPOSITION
Temp.
°C
90
150
200
260
Ozone
In
7.0
7.0
7.0
5.2
cone. , mg/£
Out
6.8
2.3
0.8
0.1
Ozone decomposed
2
67
86
98
A sample outlet was located in the line from the decomposer to the out-
side vent. During normal operation gas samples from the decomposer were
checked by a Dasibi analyzer. No evidence of ozone in the gas released to
the outside atmosphere was even indicated.
POTENTIALLY LOW OZONE CONCENTRATION AREA
After ozone treatment, the secondary effluent was discharged into an
open trench. Residual ozone flashed (vaporized) from solution and ozone
could be detected in the work area. To remedy the situation, a hood and
exhaust system were installed at the trench to collect the ozone gas and
vent it outside the building. Following completion of the jet scrubber
evaluation, the scrubber was modified by installing a recirculating sodium
thiosulfate solution through the jet scrubber to neutralize the ozone
escaping from the discharging effluent. Ozone from the effluent was col-
lected by a fan and duct system and vented to the jet scrubber.
SAMPLING STATION
A central gas sampling station containing gas outlets from all gas
transmission lines was located on a laboratory bench adjacent to the ozone
contactors. During wet gas analyses, the gas outlets required purging to
insure collection of a representative sample. These ozone enriched gases
were decomposed by bubbling the purge gas through a concentrated solution of
potassium iodide. This technique was effective for maintaining an ozone
free work area.
A Dasibi analyzer was located at the central sampling station for
continuous monitoring of various ozone gas streams. The exit gas from the
Dasibi analyzer was vented into a line leading to the exhaust system located
at the effluent discharge trench.
In addition to the above preventive measures, all systems were tested
with air for leakage. Joints were bubble checked with soap solution before
ozone was introduced into the system.
76
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TECHNICAL REPORT DATA
(Please rerd Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-79-098
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
COMPARISON OF OZONE CONTACTORS FOR MUNICIPAL
WASTEWATER EFFLUENT DISINFECTION
Packed Column Versus Jet Scrubber
5. REPORT DATE
August 1979 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Albert D. Venosa, Edward J. Opatken and Mark C. Meckes
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Municipal Environmental Research Laboratory--Cin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
10. PROGRAM ELEMENT NO.
1BC611, TOS #3, Task A/02
11. CONTRACT/GRANT NO.
In-house Report
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
Interim Report 8/19/76-6/19/77
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Contact: Albert D. Venosa (513) 684-7668
16. ABSTRACT pjQot scaie investigations were made comparing two ozone contactors, a jet
scrubber and a packed column, for ozone utilization and effluent coliform reduction
efficiency. The contactors were operated in three phases: (1) Batch operational phase
contactors were operated separately under identical conditions on a batch sample of
activated sludge effluent. (2) Parallel operational phase; both contactors were
operated in parallel on the same activated sludge effluent. (3) Continuous operational
phase; both contactors were operated on the same activated sludge effluent to achieve
a specified coliform reduction.
Results showed that the packed column significantly outperformed the jet scrubber
with respect to microorganisms reduction. Effluent quality interfered with disin-
fection in both contactors, the most important variables being chemical oxygen demand
(total and soluble) and organic carbon. Initial bacterial density and ozoen residual
were also important factors affecting log reduction of coliforms and fecal streptococci
in both contactors.
The packed column significantly outperformed the jet scrubber with respect to
ozone utilization. Organic demand measured as TCOD, SCOD, and TOC significantly
affected ozone utilization at high but not low ozone dosages.
These results indicate that the use of a single stage jet scrubber type ozone
contactor is not suitable for wastewater disinfection with ozone.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COS AT I Field/Group
Wastewater, Disinfection, Comparison, Ozone
Contactors, Statistical Analysis, Micro-
organism Control, Coliform Bacteria,
Bactericides, Ozonization, Utilization,
Waste Treatment, Analysis of Variance
Parallel Streams
Packed Column
Jet Scrubber
Cincinnati, Ohio
43F
68D
91A
57K
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
93
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Rev. 4-77)
77
iUS GOVERNMENT POINTING OFFICE 1979 -657-146/5464
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