&EPA
United States
Environmental Protection
Laboratory
October 1978
Ptoaearefi and Development
An Assessment
Ozone and Chlorine
Dioxide Technologie
for Treatment of
Municipal Water
Supplies
Executive Summary
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RESEARCH REPORTING SERIES
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 "SPECIAL" REPORTS series. This series is
reserved for reports targeted to meet the technical information needs of specific
user groups. The series includes problem-oriented reports, research application
reports, and executive summary documents. Examples include state-of-the-art
analyses, technology assessments, design manuals, user manuals, and reports
on the results of major research and development efforts.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/8-78-018
October 1978
AN ASSESSMENT OF OZONE AND
CHLORINE DIOXIDE TECHNOLOGIES FOR
TREATMENT OF MUNICIPAL WATER SUPPLIES
Executive Summary
by
G. Wade Miller
R. G. Rice
C. Michael Robson
Ronald L. Scullin
Wolfgang Kiihn
Harold Wolf
Public Technology, Incorporated
Washington, D.C. 20036
Grant No. R804385-01
Project Officer
J. Keith Carswell
Water Supply Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
pFFICE 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 publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or comraercia'l products constitute endorsement or
recommendation for use.
ii
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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 solution
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, treatment, 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 publication is one of the products of
that research; a most vital communications link between the researcher and the
user community.
This report is an executive summary of a state-of-the-art survey of
municipal water treatment practices involving the use of ozone and chlorine
dioxide in Europe, Canada, and the United States. The study was sponsored by
the Water Supply Research Division of the EPA Municipal Environmental Research
Laboratory in an effort to assess the performance of advanced water treatment
techniques for use in the production of drinking water. It is hoped that this
report will be interesting and helpful to those active in water supply
treatment.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
iii
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SUMMARY
In 1974, the Safe Drinking Water Act (PL 93-523) was enacted by the U.S.
Congress. This act was necessary to update the U.S. Public Health Standards
of 1962 and to reflect results of research and development of sophisticated
monitored techniques which revealed that many communities water supplies were unsafe.
The Act directed the U.S. EPA to develop standards and promulgate regulations for
several classes of substances found in drinking water supplies. Also the EPA
was directed to support research on treatment technologies that would allow
public water systems to treat their waters to the quality mandated by the new
standards. As part of its overall mission, the EPA's Municipal Environmental
Research Laboratory, Drinking Water Research Division funded this study dealing
with the use of ozone and chlorine dioxide technologies in drinking water
treatment.
Many of the countries of Europe have long been faced with the necessity
of producing safe drinking water from chemically polluted raw water sources.
As a result, there has been extensive development of drinking water treatment
technologies in Europe, particularly related to the usage of ozone and chlorine
dioxide as oxidants, and use of granular activated carbon as a filtration/adsorption
process. The study summarized herein, and available in complete form from EPA,
involved a comprehensive review of European, Canadian, and U.S. practices
on the use of ozone and chlorine dioxide as process oxidants in the treatment of
municipal drinking water supplies. Some study of the use of granular activated
carbon with preozonation, or "biological activated carbon" (BAG), was carried
out. Further study of the BAG process now underway will result in additional
data on this process by late 1978.
This executive summary covers in abbreviated form each of the principal topics
of the full report. Emphasis in the summary, and in the full report, is given
to the fundamental uses and engineering design of ozone/chlorine dioxide systems.
A detailed treatise on the chemistry of the two oxidants and their reactions with
various classes of organic compounds is included in the full report. Data from
extensive questionnaires and on site surveys of several hundred drinking
water utilities are included in the full report and summarized herein.
The results of this study indicate that ozone, chlorine dioxide, and ozonation
followed by GAG are being employed successfully by a large number of European and
some Canadian water utilites to deal with the problems of trihalomethanes, synthetic
organic chemicals, bacterial disinfection, viral inactivation, and other substances,
in raw water supplies. Europeans in particular employ ozone for a wide variety
of applications which cannot be accomplished on a practical basis by other treatment
techniques. Ozone, in conjunction with granular activated carbon, was found to be
highly effective in removing organic chemical contaminants.
iv
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CONTENTS
Summary iv
Figures vii
Tables ix
Acknowledgments x
1. Introduction 1
Basis for the Ozone/Chlorine Dioxide Study 1
Scope of the Study and How it Was Conducted 2
Principal Results of The Study 4
Principal Recommendations of the Study 6
2. Water Treatment Philosophies 7
Introduction 7
European Water Treatment Philosophies 7
Canadian Water Treatment Philosophies 12
3. Ozone 13
Introduction and Background 13
Properties and Reactions of Ozone 15
Public Health Aspects of Ozonation 15
Operational Experiences With Ozone 16
Site Visits 21
Engineering Aspects of Ozonation Equipment and Processes. ... 25
Ozone Measurement and Control 35
Operation and Maintenance > 40
Costs/Benefits of Ozonation 41
Conclusions 41
4. Biological Activated Carbon 44
Introduction 44
Fundamental Principles 44
European BAG Practices 45
Conclusions 45
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CONTENTS (continued)
5. Chlorine Dioxide 47
Introduction 47
Preparation of Chlorine Dioxide 48
Oxidation Products of Chlorine Dioxide 48
Usage of Chlorine Dioxide in the United States 51
Usage of Chlorine Dioxide in Europe 55
Design of Chlorine Dioxide Systems 56
Costs for Producing Chlorine Dioxide 59
Conclusions 61
Appendix A 62
Condensed Bibliography 62
Appendix B 66
List of U.S. Ozone Manufacturers 66
VI
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FIGURES
Number
1 Typical Points of Application of Ozone in Drinking
Water Processes 11
2 Bank of Ozone Generators 14
2a Internal Arrangement of a Typical Horizontal
Tube Type Ozonator 14
3 Ozone System at Choisy-le-Roi, France 24
4 Sipplinger Berg, West Germany Water Treatment
Plant on Lake Constance 26
5 The Four Basic Components of the Ozonation Process 27
6 Low-Pressure Gas Preparation System 28
7 Air Feed Desiccation System, Annet-sur-Marne, France. ... 29
8 Modular Ozone Generator With Power Supply and Control
System 30
9 Interior of a Tubular Ozonator in Operation 32
10 Typical Details of Horizontal Tube-Type Ozone
Generator 34
11 Parallel Plate Ozonators at Konstanz Waterworks,
West Germany 36
12 Interior of Individual Plate Ozonator 36
13 Turbine Contactor at Zurich, Switzerland, Lengg Plant ... 37
14 Ozone Diffuser System Layout and Bubble Pattern 38
15 Chlorine Dioxide Generation From Acid and Sodium
Chlorite at Lengg Plant, Zurich, Switzerland 49
vii
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FIGURES (continued)
16 Preparation of Chlorine Dioxide From Gaseous Chlorine
and Sodium Chlorite at Tailfer, Belgium 50
17 Photographs of Typical U.S. Chlorine Dioxide
Generation Systems 53
18 Gaseous Chlorine-Sodium Chlorite Chlorine Dioxide
Generation System 57
19 The CIFEC System 58
viii
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TABLES
Number Page
1 Operational Plants Using Ozone 1977 9
2 Applications of Ozone in Water Treatment 10
3 European Plants Inspected by Site Visit Team 22
4 Canadian Ozone Plants Visited 23
5 Costs of Ozonation at European Drinking Water Plants ... 42
6 U.S. Chlorine Dioxide Plants Visited 52
ix
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ACKNOWLEDGMENTS
This project was conducted under EPA Grant No. R804385-01 to Public
Technology, Inc., of Washington, D.C., a non-profit, public interest corpora-
tion which conducts research on behalf of local governments.
Mr. G. Wade Miller, PTI Director of Environmental Programs, was the
Principal Investigator on the project. He was assisted by Dr. R. G. Rice of
Jacobs Engineering Group, Inc.; C. Michael Robson, P.E., of Purdue University
and the City of Indianapolis; Ronald L. Scullin, P.E., of Public Technology,
Inc.; Dr. Wolfgang Klihn of the Engler-Bunte Institute of the University of
Karlsruhe, Federal Republic of Germany; and Dr.Harold Wolf of the Department
of Environmental Engineering, Texas A & M University.
The project team was assisted greatly by Daniel Houck, P.E., who was
primarily responsible for condensing the large report into this Executive
Summary.
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SECTION 1
INTRODUCTION
BASIS FOR THE OZONE/CHLORINE DIOXIDE STUDY
In 1975, the results of the National Organics Reconnaissance Survey
(NORS) revealed the presence of potentially carcinogenic organic compounds
in the drinking water supplies of each of the 80 cities surveyed. The
compounds identified were all halogenated organics of the trihalomethane
group, including chloroform. The carcinogenicity of chloroform in rats and
mice was confirmed in a National Cancer Institute study published in 1976.
In 1977, another survey of drinking water supplies, this time in 113
communities, was conducted. This survey, the National Organics Monitoring
Survey (NOMS) included analyses for trihalomethanes for an entire year and
quantified a number of other synthetic organic compounds found in water.
The NOMS also demonstrated that trihalomethanes could form in finished water
on the way to the customer's tap, as a result of chlorine disinfection, and
that other potentially carcinogenic compounds could exceed the concentration
of chloroform.
The densely populated and heavily industrialized countries of Western
Europe have been faced with the problem of industrial effluents containing
potentially harmful synthetic organic compounds for some time. Consequently,
considerable effort has been expended in Europe, particularly in France, the
Netherlands, West Germany, Belgium, and Switzerland to develpp improved
drinking water processes for the production of chemically safe drinking water,
The fact that ozone and chlorine dioxide, and often activated carbon,
are widely used for treating drinking water in Europe and Canada, has been
known for years in the U.S. Europeans, in particular, favor ozone for a
wide variety of reasons, some iinked to aesthetic values and some related
to the need and desire to render highly polluted raw water sources safe.
Europeans judge their drinking water by the absence of taste and odor; by
contrast, Americans expect a slight taste of chlorine disinfectant and are
reassured by the presence of this taste that the water is safe. Europeans
have been faced with the necessity of using water which has already been
used for a variety of industrial and domestic purposes Americans are
finding themselves having to deal with this same problem more frequently.
Interest in these advanced treatment techniques used by other countries
has been stimulated by a heightened awareness of the presence of potentially
harmful substances in many U.S. drinking water supplies. The enactment of
the Safe Drinking Water Act of 1974, also has contributed greatly to this
increased interest. The Act reflects updated knowledge and technology which
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has allowed the water treatment community to learn more about the substances
contained in drinking water; this body of knowledge in turn has led to the
establishment of more stringent criteria for drinking water quality, intended
to protect the public health. The Safe Drinking Water Act specifically
mandates the establishment of maximum contaminant levels for a number of
microbiological, chemical and physical substances and mandates a program
of investigation of treatment technologies which will permit attainment
of new drinking water standards. Thus, as part of its responsibilities
under this Act, the U.S. EPA has funded the study of the two drinking water
treatment technologies summarized herein.
SCOPE OF THE STUDY AND HOW IT WAS CONDUCTED
In carrying out this study four approaches were used to collect a large
amount of data in a relatively short period of time:
A review of the international literature on ozone, chlorine
dioxide, and organic oxidation products resulting from
their use.
Development of working relationships with the manufacturers
of ozonation and chlorine dioxide equipment, the International
Ozone Institute, European water research institutes, and
drawing heavily on these sources for plant locations and
plant data.
Direct contact via detailed questionnaires with a large
fraction of those water treatment plants in the U.S., Canada
and Europe using either ozone or chlorine dioxide or both
in their process scheme.
Field visits to a substantial number of plants in the U.S.,
Canada and Europe by a multi disciplinary study team.
The literature review resulted in the identification of over 310 publi-
cations, reports and articles in the subject area. Where necessary, foreign
language publications were translated.
For marketing and research/development reasons, equipment manufacturers
normally keep good records on installed equipment. Thus, manufacturers often
are an excellent source of information on plant locations and on operational
data for the plants. Particularly in Europe and Canada, manufacturers and
large water companies* were a major source of information. They forwarded
detailed cost information, filled out questionnaires, helped to arrange for
site visits, often accompanied the site visit team, and answered many
*In France, there are large water companies that design, construct
and operate numerous water treatment plants through the use of
contractual arrangements with local governments.
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detailed questions posed by the study team. A list of the principal U.S.
manufacturers of ozonation equipment is included as an Appendix of this
report.
The International Ozone Institute (101) is the principal scientific
organization for ozonation manufacturers, researchers and users. The 101
has chapters in Canada and most European countries. Extensive data were
contributed by the 101 to this study.
After identifying a large number of plants to be contacted in the U.S.,
Canada and Europe, detailed questionnaires were prepared in English, French
and German and distributed. Often questionnaire distribution was aided by
manufacturers and water companies, consultants active in the field, profes-
sional associations, regulatory officials and consultants to the program.
The questionnaires requested data in the following categories:
General Plant Information
Plant location and contact person
Plant capacity
Basic process flow sheet
Purpose of ozonation
History of plant and history of ozonation use
Ozonation System
Feed gas source and gas preparation system
Design parameters of ozone generation system
Design parameters of ozone contacting system
Power consumption data
Analytical Procedures and Monitoring for Ozone Control
Ozone dosage data; how and where it is measured
Analytical procedures used to monitor the ozone process
Removal of specific compounds by the ozone process and
final products of the process
Use of residual disinfectant
Ozonation process controls and operating experience
Plant Water Quality
Source of raw water and analyses performed
Tests conducted on finished water
Chlorine Dioxide
Purpose of chlorine dioxide usage
Method of generation
Analytical methods for chlorine dioxide monitoring
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For plants which used chlorine dioxide and not ozone a separate questionnaire
was prepared. Similar to the ozone questionnaire, the chlorine dioxide
questionnaire asked detailed questions about the design, operation, monitoring
and costs associated with chlorine dioxide usage. When it was determined
that a plant using ozone also used chlorine dioxide, a follow-up mailing
of the chlorine dioxide questionnaire was carried out.
Aggregating all of the data from the questionnaires plus information
from the other sources discussed above, the plants of greatest interest
were selected for field visitation. In Europe and Canada, principal emphasis
was placed on plants which used ozonation, since many of these aso used
chlorine dioxide. Twenty plants in Europe, 6 plants in Canada, and 13 plants
in the U.S. were visited, the latter for the purpose of observing chlorine
dioxide usage. The results of the field tests are summarized in Sections 3
and 5 of this document.
PRINCIPAL RESULTS OF THE STUDY
The findings of this study are summarized below:
Ozone has many useful functions other than disinfection. It
is misleading to perceive ozone merely as a disinfectant. As
an oxidant, ozone is currently used to remove or break down
taste, odor, algae, organic compounds (phenol, detergents,
pesticides, etc.), cyanide, sulfides, iron, manganese, turbidity
and flocculate micropollutants (soluble organics), and to
inactivate viruses. Ozone also is used as a disinfectant
but rarely in the context of an "either-or" alternative
disinfectant to chlorine. It is normal to follow ozone as the
primary disinfectant with a small dosage (up to 0.6 mg/1) of
chlorine or chlorine dioxide. This practice assures a residual
of disinfectant to protect the distribution system against
bacterial regrowth.
The European approach to water treatment is based on a somewhat
different philosophy of treating water, which has led to the
use of different water treatment technologies. The cornerstone
of the European philosophy is the desire to produce waters
which are free from undesirable tastes, including chlorinous
tastes. The goal is to obtain water supplies which require
little or no treatment such as pure ground waters. Failing
this, the goal is to treat other water supplies to a quality
equivalent to that of a pure groundwater. Thus, emphasis is
placed on both chemical removal plus strict bacteriological
and virological standards, as opposed to the U.S. where the
main emphasis to date has been in producing bacteriologically
safe water.
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Ozone and chlorine dioxide are well established technologies
in Europe. Use of ozone for treating drinking water also is
well established in the Province of Quebec, Canada, the
Soviet Union, and to a lesser degree in Japan. Ozone is not
widely used or understood by water system practitioners in
the U.S. Chlorine dioxide is widely used in the U.S.,
but is generally not being used optimally. Little consistency
is evident in its application and the study team encountered
numerous U.S. plants where the generation and/or application
of chlorine dioxide is poorly understood.
Properly designed and operated ozonation system components
(electrical power supply, gas preparation, ozone generation,
ozone contacting) have an established history of reliable
performance and low maintenance service in Europe. Competent,
routine maintenance is a basic necessity, however, for
reasonably troublefree performance.
In the absence of halogenated organic compounds, granular
activated carbon can be operated in a steady state mode
with only infrequent regeneration using preozonation.
Aerobic bacterial growth in the activated carbon beds is
promoted by ozonating the processed water prior to the carbon
contactors. This results in the growth of a fixed biotnass
within the filter which works in conjunction with the activated
carbon to remove organics and ammonia. Activated carbon
systems with preozonation have been operated in Europe for
up to 2.5 years without need of regeneration. The study
includes a section on the process, popularly referred to
as Biological Activated Carbon. Further work to determine
the performance, engineering parameters and costs of BAG
are being studied by the EPA and will be available in the
future.
Pure chlorine dioxide, though more expensive than chlorine,
does not form trihalomethanes. As a final disinfectant,
it exhibits a longer lasting residual in distribution
systems and, because it is used in lower concentrations,
imparts little or no taste to the product water.
Chlorine dioxide is widely applied in Europe and the
U.S. The technology, especially in Europe, is well established.
The U.S. plants which responded to the questionnaire and/or were
visited by the study team largely displayed inadequate
monitoring control and understanding of the process with
the result that the chemical was often not being generated
or applied properly.
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PRINCIPAL RECOMMENDATIONS OF THE STUDY
An in-depth cost analysis of the use of ozone as a unit process
capable of performing a number of useful functions is needed.
Various combinations of air preparation, generation, contacting,
and off-gas use or destruction systems should be studied.
Epidemiological studies of populations using drinking water
treated with chlorine dioxide and ozone should be conducted.
Research directed at determining whether or not the chlorite
ion is toxic, and at what levels, would be a part of that study.
Toxicity of residual ozone in water is of little import because
of its short half life in water.
Technical assistance should be made available to those
municipalities currently using chlorine dioxide in order to
assure that it is being used properly and in safe concentrations.
This could be provided by EPA, supported by expert assistance <
by contractors as needed.
Granular activated carbon with preozonation appears to have
great potential for use in U.S. water treatment. Pilot projects
on this treatment combination should be initiated to determine
its effectiveness for organics and/or ammonia removal. Engineering
and cost details of currently operating BAG plants in Europe
should be developed.
A thorough investigation of the potential savings in activated
carbon regeneration costs resulting from extended life of the
biological activated carbon also should be investigated.
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SECTION 2
WATER TREATMENT PHILOSOPHIES
INTRODUCTION
Water treatment approaches in Europe, and to a lesser extent, Canada,
are markedly different than U.S. practices. In Europe, this is a result
of strongly held concepts of drinking water quality. Although variations
exist from country to country in actual practices, the philosophy of
approach is quite similar.
Summarized herein are philosophies and the results of questionnaire
surveys conducted in Europe and Canada.
EUROPEAN WATER TREATMENT PHILOSOPHIES
As one result of the study, several fundamental areas were found in
which European and American drinking water treatment differ significantly.
These areas include a different set of philosophies of treating drinking
water from which, in turn, have evolved the use of several drinking water
technologies.
The cornerstone of European water treatment philosophy is the desire
to produce drinking waters that are free from chlorinous or other undesirable
tastes, and which are chemically and bacteriologically safe. The philosophy
has been best summarized by Professor Dr. Heinrich Sonthimer, Director of
the Engler-Bunte Water Research Institute at the University of Karlsruhe,
Federal Republic of Germany, and a noted authority on the treatment of
polluted surface waters. Professor Sontheimer states simply that "in Germany
we prefer not to have to treat water, but if we do have to treat it, then we
treat it to a quality equivalent to that of a pure, unpolluted groundwater."
This sentiment is echoed by other European drinking water experts in France,
The Netherlands, Belgium and Switzerland.
The most striking difference between U.S. and European practices is the
concentration on bacteriological quality of water in the U.S. as an indicator
of safety. The Europeans, while concerned with bacteriological and virolog-
ical safety of water, are much more concerned with chemical contamination.
Europeans are brought up with the understanding that when there are any
unnatural tastes in water (especially chlorine tastes) the water is contami-
nated. Many urban dwelling Americans are brought up with the understanding
that when chlorine cannot be tasted, the water may be contaminated. Therein
lies one of the major reasons for the difference in approaches in treating
water supplies. Americans use relatively heavy dosages of chlorine in the
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water to assure bacteriological (but not necessarily chemical) safety;
Europeans reduce the chlorine demand of water (insuring chemical safety)
so that the residual chlorine used to maintain bacteriological safety in
the distribution systems will be so small as to be tasteless in the water.
Waters that do not need to be treated, such as pure groundwaters,
exhibit a number of chemical and biological parameters which have been
adopted as goals for treating German drinking waters. Two significant
parameters are Total Organic Carbon (TOG) and oxidant demand (chlorine
demand). If a German surface water supply is to be treated, then the product
water first must satisfy these two parameters, then other standards. The TOG
must be less than 2 mg/1 and oxidant demand (chlorine demand) less than
0.5 mg/1. In other words, if the water demands more than 0.5 mg/1 of chlorine
to produce a stable residual for German distribution systems, then the water
treatment process must be modified so that a higher quality drinking water
is produced.
Similarly, Switzerland, The Netherlands, France, Austria and other
western European countries are searching continually for groundwater supplies
or water from mountainous areas which is relatively pure and requires little
or no treatment prior to distribution. Several major European cities, do
not treat their water supplies at all; no chemicals are added. If the source
of raw water supply is polluted, however, as is the case of the Rhine in
northern Germany and the Seine downstream of Paris, Europeans are prepared
to utilize a range of technologies to produce a chemically and bacteriolgically
safe drinking water. Each water is analyzed for pollutants and subjected
to the treatment train that will remove them most effectively. Many of these
techniques are physical in nature (settling, adsorption, microstraining,
ozonation*) as opposed to the addition of chemicals.
At least 1039 municipal water plants in 29 countries worldwide use
ozone for some purpose (Table 1). Most of these plants are located in
Europe. France has 593 plants (Nice, France has employed ozonation
continuously since 1906), Switzerland has 150, Germany has 136, and Austria
has 42. By contrast, there are only four ozonation plants currently in
operation in the U.S. (Whiting, Indiana; Strasburg, Pennsylvania; Monroe,
Michigan; Bay City, Michigan) with one additional under construction
(Saratoga, Wyoming). Canada currently has 20, all but one located in the
Province of Quebec.
* Ozonation is viewed by Germans as being a natural product and not a
chemical since it reverts back to oxygen and thus does not remain in
the water.
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TABLE 1. OPERATIONAL PLANTS USING OZONE 1977
Country Number of Plants
France 593
Switzerland 150
Germany 136
Austria 42
Canada 23*
England 18
The Netherlands 12
Belgium 9
Poland 6
Spain 6
USA 5
Italy 5
Japan 4
Denmark 4
Russia 4
Norway 3
Sweden 3
Algeria 2
Syria 2
Bulgaria 2
Mexico 2
Finland 1
Hungary 1
Corsica 1
Ireland 1
Czechoslovakia 1
Singapore 1
Portugal 1
Morocco 1
Total 1,039
*Includes expansions. Actual number of operating plants in Canada
equals 20, with 3 more under construction
Ozone, as applied in Europe, is used for many purposes (Table 2), color
removal, taste and odor removal, turbidity reduction, organics removal,
microflocculation, iron and manganese oxidation, bacterial disinfection and
viral inactivation being the most prevalant. Most of these applications are
based upon ozone's high oxidizing power (it is the second most powerful
oxidant available on a commercial scale). Ozone is introduced at different
points in the water treatment process, depending on its intended applica-
tion^). When used for iron and manganese oxidation or to induce floccula-
tion, it usually is introduced at an initial point, and when used for taste
and odor removal it is introduced at an intermediate point. When used for
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viral inactivation or bacterial disinfection, it is introduced near the end
of the water treatment process, sometimes as the terminal step. In several
plants visited, multiple uses of ozone were observed, i.e., iron and manganese
oxidation and/or microflocculation in the initial treatment stages and
organics oxidation and/or disinfection near the end of the treatment processes,
Figure 1 shows a standard water treatment process with the points of
application of ozone for the purposes listed in Table 2.
TABLE 2. APPLICATIONS OF OZONE IN WATER TREATMENT
Bacterial Disinfection
Viral Inactivation
Oxidation of Soluble Iron and/or Manganese
Decomplexing Organically-Bound Manganese (Oxidation)
Color Removal (Oxidation)
Taste Removal (Oxidation)
Odor Removal (Oxidation)
Algae Removal (Oxidation)
Removal of Organics (Oxidation)
such as Pesticides
Detergents
Phenols
Removal of Cyanides (Oxidation)
Suspended Solids Removal (Oxidation)
Preparation of Granular Activated Carbon for Enhanced
Biodegradability of Ammonia and Dissolved Organics
In European water treatment practices, ozone is seldom considered simply
as an either-or "alternate disinfectant to chlorination", especially outside
of France. Instead it is recognized first for its ability to oxidize a
variety of materials and to inactivate viruses. In many plants the bacterial
disinfection capability of ozone is a secondary benefit which is provided
when ozone is installed for another primary purpose.
Ozonation is seldom used as a terminal step because of its short half-
life in water. It usually is followed by the addition of small dosages
(less than 0.6 mg/1) of chlorine or chlorine dioxide. Ozone causes chemical
transformations of dissolved organic compounds in the water, making them
more easily biodegradable and thus providing food for bacteria. This condition
can lead to bacterial regrowths in water distribution systems. Ozone can
be used as a terminal step if the dissolved organic carbon concentration
of water to be distributed is less than 0.2 mg/1. Also, ammonia
should not be present, otherwise regrowth of nitro-bacteria can occur.
10
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deconplexing organic-Mn
pretreatment for
biological processes
Fe & Mn oxidation
flocculation
algae removal
destruction of
off-gas ozone
pretreatment for
biological processes
organics oxidation
color removal
tastes & odors
- viral inactivation
- bacterial disinfection
1
Coagulation
V
Sedimen-
tation
/ ^
Sand or
Anthracite
Filtration
influent
water
To
Distribution
cia, cio2
or C1NH2
for residual
To
Distribution
Figure 1. Typical Points of Application of Ozone in Drinking Water Processes
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CANADIAN WATER TREATMENT PHILOSOPHIES
There appears to be no unified national water treatment philosophy as
such in Canada, but there are voluntary recommended national drinking
water standards. Each province decides whether to follow the Canadian
Drinking Water Standards, as developed in 1968 by a joint committee represent-
ing each of the country's provinces. These standards parallel in some
respects the U.S. standards and a revision of the current standards in
1978 is expected to reflect some of the provisions of the U.S. Safe Drinking
Water Act of 1974 (PL 93-523).
The two most populous Canadian provinces, Ontario and Quebec, are the
only two known to use ozone or chlorine dioxide to any appreciable extent.
There are currently 20 plants in Canada which use ozone, 19 of which are in
Quebec. Ten plants use chlorine dioxide and all are located in Ontario.
The philosophy of ozone usage in Canada evolved from a need to deal with
seasonal taste and odor problems, plus the disinfection needs of surface
water supplies. Ozone has been viewed in Canada as an alternate for both
chlorine disinfection and activated carbon treatment. For example, some
Canadian water treatment experts have pointed out that ozone costs are
comparable to those of chlorine plus activated carbon, and ozone provides
side benefits of decolorization, superior appearance and improved taste and
odor characteristics. Chlorine dioxide is used in Canada largely because of
its superior characteristics in destroying tastes and odors from phenolic
compounds.
12
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SECTION 3
OZONE
INTRODUCTION & BACKGROUND
Ozone was first discovered by Van Marun, a Dutch philosopher in 1785
when he noticed a characteristic odor in the air around his electrostatic
machine. In 1840, Schonbein reported the odor as a new substance and gave
it the name ozone, as derived from the Greek world "Ozein", meaning to smell.
Present day commercial ozonation equipment largely evolved from an
apparatus designed by Werner von Siemens in 1857 in Germany. The Siemens
ozonator has been developed into the present tube type ozone generators which
use glass tubes coated internally with a metal dielectric and individual
tube cooling with water, all housed in a cylindrical body. (Figures 2 and 3)
There are many variations in ozone generator design, including plate type
units which feature parallel plates rather than tubes, but all of the units
operate on the silent corona discharge principle by using the oxygen in air
(or pure oxygen feed) to form ozone. All ozone generators produce heat
which must be minimized in order to maximize ozone production.
The earliest use of ozone as a germicide occurred in 1886 in France,
when de Meritens demonstrated that diluted ozonized air could sterilize
polluted water. Pilot studies followed and in 1893 the first drinking water
treatment plant to employ ozone was erected at Oudshorrn, Holland. Other
plants quickly followed at Wiesbaden (1901) and Paderborn (1902) in Germany.
In 1906, the Nice, France plant was constructed using ozone for disinfection.
Nice has used ozone continuously to the present. Today there are more than
1000 drinking water treatment plants using ozone for one or more purposes.
In Canada, the first ozonation plant was built in Ste-Therese, Quebec
Province in 1956. There are now 20 ozonation plants in Canada, with three
more under construction including the largest drinking water treatment ozone
system in the world at Montreal, Canada.
In the U.S., the first ozonation plant was started at Whiting, Indiana
in 1941 for taste and odor control.
13
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Figure 2. Bank of Ozone Generators
Figure 2a. Internal Arrangement of a Typical Horizontal
Tube Type Ozonator
14
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PROPERTIES AND REACTIONS OF OZONE
Ozone is an unstable gas which boils at minus 112 degrees Celsius
(atmospheric pressure), is partly soluble in water (about 20 times the solu-
bility of oxygen), and has a characteristic penetrating odor, readily
detectable by humans at concentrations as low as 0.01 to 0.05 ppm. Ozone
is the most powerful oxidant currently in use for water treatment. Commercial
generation equipment produces ozone in concentrations of 1 to 3% in air
(2 to 6% in oxygen). Ozone is relatively unstable in a water solution but is
considerably more stable in air, particularly dry, cool air.
Because it is a powerful oxidant, ozone will react with a wide variety
of organic materials. Ozone oxidizes phenol to oxalic and acetic acids.
Ozone oxidizes trihalomethane (THM) compounds to a limited degree under
the proper pH conditions and also reduces their concentration by air stripping.
Trihalomethanes also are oxidized by ozone in the presence of ultraviolet light.
More significantly, oxidation with ozone does not lead to the formation of
THM's as does chlorination. A combination of ozone and ultraviolet radiation
destroys DDT, PCB's, malathion and other pesticides, but requires high dosages
and extended contact times not normally encountered in drinking water treatment
plants. Ozonized organic materials are generally more biodegradable and
adsorbable than the starting, unoxidized compounds. If ozonation is used as the
terminal treatment step in water containing significant amounts of dissolved
organics, bacterial regrowth in the distribution system can occur. Thus
ozonation generally is not used as the final treatment step but is followed
by granular activated carbon filtration and possibly the addition of a residual
disinfectant.
Oxidation of humic materials, the precursors of trihalomethanes, can be
accomplished by ozonation. Studies have shown that, given proper conditions,
there is significant reduction in THM formation when ozone is applied prior
to a chlorination step.
PUBLIC HEALTH ASPECTS OF OZONATION
Ozone has been shown to be effective against viruses. The French have
adopted a standard for the use of ozone to inactivate viruses. When an ozone
residual of 0.4 mg/1 can be measured four minutes after the initial ozone
demand has been satisfied, viral inactivation is assured. This characteristic,
along with its freedom from THM formation, is of major significance in
considering the public health aspects of ozonation. In addition, when ozone
is coupled with granular activated carbon filtration, a high degree of
removal of organic compounds, some of which may be potentially carcinogenic,
can be achieved.
There is a paucity of data for assessing the public health implications
of ozone usage. Only a limited amount of study has been carried out on the
toxicity of the oxidation products of ozone and the removal of specific
compounds by ozonation. During the study, some data were obtained regarding
ozone reactions on specific compounds, but the data are quite limited. Further
research efforts are planned for the study of ozonation end products. Data on
15
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the removal of specific organics by the BAG process is being developed
at the Rouen Plant in northwestern France. Preliminary results indicate
that the first ozonation step (applied dosage 1 mg/1, contact time 3 minutes)
results in a 63% quantitative decrease, and the sand filtration and carbon
adsorption yields an additional 13% decrease in the total mass of the
infrequent organics. The post treatment step (1 mg/1 dosage, contact time
12 minutes) accounts for a 9% decrease, for an aggregate decrease of 85%
through the process. Later data for the plant indicate even better results.
By way of summary, the evidence available does not indicate any untoward
health hazards associated with the use of ozone, either alone or in conjunc-
tion with granular activated carbon. Some questions regarding the possible
release of endotoxins by the BAG process should be answered with further
research, and there is a need for better research data on the products of
ozone oxidation of organic compounds.
OPERATIONAL EXPERIENCES WITH OZONE
Extensive information on current practices, engineering and costs was
obtained during the course of the study, primarily from three sources:
Questionnaire responses
Equipment manufacturers/Integrated Water Companies
Site visits
Questionnaire responses provided variable amounts of data on many plants, as
discussed below. Using other data supplied by ozonation equipment manufac-
turers and large integrated companies, together with questionnaire data,
literature search data, and assistance from other professionals and organiza-
tions, sites were selected for visitation. Questionnaire responses and
site visit results are summarized below.
Summary of Data From European Ozone Questionnaires
Eleven hundred niney-two (1192) questionnaires were mailed to municipal
water plants in western Europe in mid-1977. These questionnaires asked for
detailed information on various aspects of ozone usage. Questionnaires were
mailed to plants in France, The Federal Republic of Germany (FRG),
Switzerland, Austria, Belgium, the Netherlands, and Great Britain. Question-
naire mailings and responses by country are as follows:
Country Mailed
France 300
Germany 835
Great Britain 15
The Netherlands 10
Austria 11
Switzerland 20
Belgium 1
Total 1192
Estimated Total Municipal
Received Plants Using Ozone
63 593
31 136
9 18
7 12
5 42
9 150
1 9
122 900
16
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Great Britain
Fifteen questionnaires were mailed to British plants using ozone and
six responses were received. There are 18 water plants in Great Britain
known to be using ozone. Most have used ozone only a few years. The plants
responding averaged 105,000 cu m/day in size, and ranged in size from 5,000
cu m/day to 450,000 cu m/day. The primary application of ozone in Great
Britain is for color removal. Each of the six plants responding indicated
ozone use for this purpose. Other uses indicated include: bacterial disinfection
(2 plants); iron and manganese oxidation (2 plants); taste and odor removal
(1 plant);-and viral inactivation (1 plant).
Treatment processes vary. Ozone is used after a filtration step in each
of the six plants. In four of the plants microstraining is the filtration
method used. Chlorine is used as a final disinfectant in each of the six
plants. In 3 of 6 plants chlorination follows ozonation with no filtration
step in between.
Five of the six reporting plants use tube type water cooled ozone
generators. Ozone contacting methods include diffusers (3 plants), injectors
(2 plants) and turbine (1 plant). Off-gas treatment is practiced at five of
the six reporting plants.
Power consumption for ozone generation and application (including air
preparation, generation, contacting, and off-gas treatment) averaged 29.7
kwh/kg of ozone produced among the responding plants.
Ozone dosage averaged 2.37 mg/1 for the four plants that responded to
that portion of the questionnaire. It should be noted that chlorine dioxide
and ozone are not used jointly in any British plant. Chlorine dioxide is
often used as a distinct unit process, added stepwise to insure a better
oxidant residual.
The Netherlands
Questionnaires were mailed to 10 major plants in The Netherlands
using ozone. Seven were returned. Most of the Dutch plants which responded
have been using ozone for less than five years.
The prevalent water treatment approach is that physical and biological
treatment processes are preferred. Chemicals and disinfecting agents
are used only in cases where they are unavoidable. Chlorine dioxide currently
is not used. Chlorine is used as a terminal disinfecting agent although
many plants indicate plans to switch to chlorine dioxide in the future.
The plants responding to the questionnaire are relatively large,
averaging 49,500 cu m/day. The range in size is from 1000 cu m/day to 120,000
cu m/day. The primary application of ozone appears to be for color removal
(6 plants), taste removal (6 plants), and odor removal (4 plants). Other
applications are for bacterial disinfection (2 plants), viral inactivation
(2 plants), organics removal (3 plants) and as a filtration aid (1 plant).
Ozone dosages range from 0.23 mg/1 to 5 mg/1. Average dosage for seven plants
was 2.59 mg/1.
17
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Each of the seven reporting plants uses tube type water cooled ozonators.
Most of the plants use submerged turbines for contacting ozone. Five of
seven plants practice off-gas destruction.
Power consumption ranges from 17 to 20 kwh/kg of ozone produced at the
Houdsweg plant to 50 kwh/kg of ozone produced at the Engelse Werks plant.
Chlorine is used as a final disinfectant in 3 of the 7 plants; a fourth
applies 0.2 mg/1 sodium hypochlorite. Ozone is used as the terminal step in
the Engelse Werk plant. In the other two plants, sand filtration is the
terminal step and immediately follows the ozonation process.
Austria
There are 42 municipal water plants in Austria currently using ozone.
Questionnaires were mailed to 11 large water companies in Austria which
serve 50% of the Austrian people. Five questionnaires were returned from
water companies in Salzburg, St. Polten and Linz. Ozone has been used in
the five facilities an average of 6.6 years, with the oldest plant having
used ozone for 12 years. Plants range in size from 4,000 cu m/day to 48,000
cu m/day, average size being 21,000 cu m/day.
Bacterial disinfection is the main purpose of ozonation. Other
applications indicated are for viral inactivation (2 plants), color removal
(1 plant), and organics removal (1 plant).
Ozone dosages are relatively low, ranging from 0.06 mg/1 to 1.2 mg/1,
averaging 0.48 mg/1 for the five plants reporting data. The low dosage can
be attributed to the high raw water quality. The water source for each of
the plants is deep wells.
Ozone generators in three plants are tube type, water cooled units. In
the other two plants, plate type water cooled units are used. Contacting is
by injection in three plants, and by a surface aeration device at the other
two plants. Most of the plants reported that some type of off-gas destruc-
tion is practiced.
Power consumption for ozone production, contacting, and off-gas treat-
ment averages 34.4 kwh/kg of ozone produced. Consumption ranges from 16
kwh/kg at the two St. Polten plants to 55 kwh/kg at the Salzburg City Water-
works .
The only oxidant other than ozone used in the five Austrian plants is
chlorine (at one plant). In four of the five plants, ozonation is the
only treatment of the water. The fifth plant applies ozone and then adds
0.8 mg/1 of the sodium hypochlorite.
Switzerland
There are approximately 150 water plants in Switzerland which use ozone.
Many of these are very small plants. Questionnaires were not mailed to all
plants, but rather to 20 representative waterworks which serve more than one
18
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million people. Nine of 20 questionnaires were completed and returned.
Five of the nine plants have been using ozone for more than 10 years;
averaging period of usage is about 12 years.
The plants reporting data range in size from about 2,500 cu m/day
(Waterworks Alstatten) to the Lengg Plant in Zurich which has a capacity of
250,000 cu m/day. Average plant size for the nine plants is about 65,600
cu m/day.
Ozone is used for several purposes, among them bacterial disinfection
(7 plants), viral inactivation (7 plants), odor removal (7 plants), taste
removal (6 plants) and organics removal (4 plants). Ozone dosage reported
ranged from 0.3 to 1.5 mg/1.
Five of nine plants have tube type, water cooled ozone generators. The
other four have plate type, water cooled generators. Contacting is accom-
plished in a number of methods: submerged turbines (4 plants), injector
(3 plants), porous tubes (2 plants). Most of the plants did not treat
contactor off-gases.
Average power consumption for ozone generation and contacting for the
five plants reporting data is about 33.5 kwh/kg.
Six of nine plants use chlorine dioxide as a terminal step. It is
estimated that 80% of the Swiss plants which use ozone also use chlorine
dioxide as a final disinfectant. Chlorine dioxide is applied in very small
amounts. Chlorine is used as a disinfectant at two plants. Ozone is the
only treatment applied at the small (2500 cu m/day) Alstatten plant.
Four plants report the use of granular activated carbon directly
following ozonation.
Federal Republic of Germany
There are approximately 136 municipal waterworks in West Germany which
use ozone. Thirty-one of these waterworks responded to a questionnaire.
Ozone usage in West Germany is more varied than in any other country.
Purposes of ozonation, dosage, methods of contacting, and a number of
manufacturers supplying equipment do not fall into a consistent pattern
as is the case in other countries. Power consumption also varies greatly.
The average period that ozone has been installed in the German plants
responding is only 7.6 years, though ozone has been used in the Busseldorf
water plants since the mid 1950's. Plants using ozone in West Germany range
in size from 1000 cu m/day to 648,000 cu m/day.
Ozone is used for many purposes in West Germany. Twenty-four of the 31
plants indicate its use for organics removal, taste (13 plants), viral
inactivation (8 plants), iron oxidation (7 plants), manganese oxidation
(6 plants), odor removal (7 plants), turbidity reduction (6 plants), and
color removal (5 plants). Ozone dosages range from 0.15 mg/1 at the Diez/
Lahn plant to 5.7 mg/1 at the Osterode plant.
19
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Twenty-six facilities have tube type, water cooled generators while five
use plate type, water cooled generators. Contacting of ozone with the water
stream is accomplished mainly by means of injection (21 of 31 plants). Other
methods are submerged turbine (2 plants), packed column (3 plants), and
porous tubes (1 plant). Less than half of the reporting plants practice off
gas destruction.
Power consumption for ozone generation, air preparation, contacting and
off gas treatment appears to be higher at some West German plants than in
other countries surveyed. However, the lowest power consumption cited
(15 kwh/kg) is at Duisberg, the only known municipal water plant that
produces ozone from oxygen.
For final disinfection, 9 plants use chlorine dioxide, 8 use chlorine
and 2 use sodium hypochlorite. Nine plants apply ozone as their only
treatment step. In 3 other plants, ozone is the only oxidant used. Ten
of the 31 reporting plants use granular activated carbon (GAG) as an adsorbent,
In every case, GAG follows the ozonation step.
France
Ozone is used in approximately 600 French water plants. Questionnaires
were mailed to 300 of these plants and a total of 63 completed questionnaires
were received.
Ozone usage for water treatment began in France in 1906. While there
are 10 plants that have used ozone for more than 10 years (the oldest having
used ozone for 52 years), the average period of use among the responding
plants is about 8 years. The average size of plants responding to the
questionnaire is 29,100 cu m/day. Sizes ranged from 350 cu m/day to 240,000
cu m/day. Unlike West Germany, most of the plants use surface water as a raw
water source. Forty-three of 63 plants indicated use of surface water as a
raw water source.
The primary purposes cited for ozone use are bacterial disinfection
(59 plants), viral inactivation (35 plants), taste removal (31 plants), and
organics removal (24 plants). Other indicated uses include color removal
(18 plants), turbidity reduction (10 plants), iron removal (7 plants) and
manganese removal (5 plants). Ozone dosages range from 0.15 mg/1 to 10 mg/1.
Most of the plants use tube type, water cooled generators. Only nine
indicated usage of plate type, water cooled units. Contacting is accomplished
primarily by porous plate diffusers, this method being used in 44 plants.
Injectors are used in 10 plants, packed columns in 3 plants and spray towers
in 2 plants. Most of the plants reporting do not practice off-gas
destruction.
Power consumption is fairly consistent for the 33 plants that reported
power data. Average power consumption is 31.3 kwh/kg of ozone generated for
the total ozonation unit process.
20
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Chlorine is used as a final disinfecting agent in 26 plants. Chlorine
dioxide is used in 13 plants. In twenty-two of 63 plants, ozone is the only
oxidant used and often it is the terminal step.
The classic French water treatment process is remarkably similar to the
U.S. "conventional" process. The process used in many plants involves
prechlorination, coagulation, sedimentation, filtration, ozonation, and use
of chlorine or chlorine dioxide as a terminal treatment step. The only
marked difference is the ozonation step. This allows smaller quantities of
chlorine to be used as the residual disinfectant. Normally less than 1 mg/1
of chlorine is added, or less than 0.6 mg/1 of chlorine dioxide for purposes
providing a protective residual for the distribution system.
Summary of Data From Canadian Ozone Questionnaires
Eighteen questionnaires were distributed in Canada, and all were
completed and returned. These comprise all of the plants in Canada using
ozone with the exception of a plant at Frobisher Bay in the Northwest
Territories, and the Chomedey Plant at Laval, Quebec. Data for the latter
were obtained at the time of the plant visits. The study provides a
data summary for each of the responding Canadian plants.
Energy consumption for ozone treatment reported by the Canadian plants
falls mainly in the 20 to 30 kwh/kg range. One older plant, lie Perrot,
reported 45 kwh/kg whereas one of the newest Canadian plants, Pierrefonds,
reported 18 kwh/kg. Off-gas destruction is not normally practiced in
Canada.
Porous diffusers and injectors are the most widely used form of ozone
contacting. Only one plant, lie Perrot, uses a submerged turbine. Contact
times, where given, ranged from 5 to 20 minutes with most plants reporting
contact times of 2 to 10 minutes. The Roberval plant practices two stage
ozonation, utilizing ozone to enhance coagulation and then later for
disinfection.
SITE VISITS
A significant portion of the report is based on findings and observations
made during site visits to twenty municipal water treatment plants in
Europe and seven plants in Canada which use ozone. The 20 plants in four
European countries were visited in May 1977 by a team of scientists and
engineers. In August 1977, this team inspected seven plants in the Province
of Quebec, Canada. Tables 3 and 4 lists the plants visited in Europe and
Canada along with some of their pertinent characteristics.
Plants were selected on the basis of variability and uniqueness of ozone
application, size, and ozone treatment train variability. The site visit
team inspected plants in Europe ranging in size from Annet-sur-Marne (25,000
cu m/day) in France to one of the largest plants in West Germany, Sipplinger
Berg (648,000 cu m/day) (Figure 4).
21
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TABLE 3. EUROPEAN PLANTS INSPECTED BY SITE VISIT TEAM
Name
Choisy-le-Roi
Morsang-sur-Sei ne
Rouen-la-chapel le
Aubergenville
Neirilly-sur-Marne
Annet-sur-Marne
Clairfont
Super-Rimiez
Tailfer
Holthausen
Flehe
Am Staad
Dohne
Wuppertal
Wittlaer III
Lengg
Kreuzlingen
Konstanz
Sipplinger Berg
Langenau
Location
Paris suburbs
Paris suburbs
NW of Paris
NW of Paris
Paris suburbs
Paris suburbs
Toulouse
Nice
Brussels
DUsseldorf
Dusseldorf
DUsseldorf
MOlheim
Wuppertal
Duisburg
Zurich
Kreuzlingen
(Switzerland)
Konstanz
(Germany)
Sipplingen
(Germany)
near Ulm
(Germany)
Design
Capacity
(cu m/day)
800,000
150,000
30,000
100,000
600,000
25,000
110,000
90,000
260,000
192,000
88,000
144,000
48,000
168,000
48,000
250,000
34,560
50,000
648,000
198,700
Ozone Generator
Manufacturer
Trail igaz
Degremont
Trail igaz
Welsbach
Trail igaz
Trail igaz
Trail igaz
Trail igaz
Trail igaz
Herrmann
Herrmann
Herrmann
Trail igaz
Herrmann
Demag
Kerag
Sauter
CEO
(Trail igaz)
Herrmann
DegrSmont
Type
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Tube
Otto Plate
Otto Plate
Tube
Tube
22
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TABLE 4. CANADIAN OZONE PLANTS VISITED
Design Ozone Generator
Name Capacity Manufacturer Type
(cu m/day)
Quebec City 218,000 Trailigaz Otto
Sherbrooke 98,862 Degremont Tube
lie Perrot 6,800 Welsbach Tube
Pierrefonds 95,500 Trailigaz Tube
St. Denis sur
Richelieu 27,300 PCI Otto
Laval (Chomedey) 176,900 Welsbach Tube
Plants containing ozone equipment supplied by each of the major European
manufacturers were inspected. These included Trailigaz and Degremont
of France, Gebruder Herrmann and Demag of Germany, and KERAG and Sauter
.Corporation of Switzerland. Plants using U.S. manufactured and Canadian made
equipment also were observed in Europe (Welsbach) and Canada (Welsbach, PCI
Ozone, and Degremont Infilco Ltd). These manufacturers provided substantial
information on ozone installations and operational data.
The only operating municipal plant (Diiisburg, Germany) using oxygen as
the starting material for ozone production was visited. Five plants in the
Dusseldorf area which practice river sand bank filtration and which place
heavy emphasis on the use of ozone plus activated carbon were inspected. The
newest concepts in German drinking water practice were viewed at the Dohne
plant in Mulheim near Dusseldorf. In southern Germany, the Langenau plant,
which uses ozone primarily for microflocculation, followed by activated
carbon, was visited.
Rouen-la-Chapelie, located about 70 miles northwest of Paris, uses two
stage ozonation, and is the first French plant to use biological activated
carbon (BAG). This process began operating at Rouen in early 1976. Two
plants in southern France using ozone as the terminal step in the process,
Clairfont in Toulouse and Super Rimiez in Nice, were visited. Several
plants having highly sophisticated control systems were visited. The most
notable ones in this category were Neuilly-sur-Marne, (600,000 cu m/day)
in the Paris suburbs and Kreuzlingen on the Bodensee (Lake of Constance)
in northern Switzerland.
Ozone systems that had been in operation for a number of years were
also of interest. Choisy-le-Roi in Paris (Figure 3) has had its current
system in operation for more than 10 years. Holthausen (Dusseldorf) has been
operating ozonation and granular activated carbon systems for 20 years.
23
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NJ
-P-
Figure 3. Ozone System at Choisy-le-Roi, France
-------
Six of 19 operating plants in the province of Quebec, using ozone, were
visited. A seventh, the new Charles-J. des Baillets plant in Montreal,
scheduled to go on-line in 1980, also was visited. The largest ozone
plant in Canada, Quebec City (218,000 cu m/day), was inspected. The
other five visited were Sherbrooke, Pierrefonds, Laval-Chomedey, St. Denis,
and lie Perrot. Pierrefonds and Sherbrooke are the two newest ozone facili-
ties in Canada and thus represent the most recent efforts in North American
practices of the French technology. St. Denis is a very small plant (27,000 cu
m/day, 7.2 mgd) that has PCI ozone equipment. lie Perrot is an older small
system that has a Welsbach ozonator. The Chomedey plant, located in the
City of Laval, is rated at 39 million Imperial gallons per day (17/,990
cu m/day), but only 114,000 cu m/day is treated with ozone for taste and
odor control. The older part of the plant produces 63,890 cu m/day and
uses powdered activated carbon for taste and odor control. The newer side
uses ozone for the same purpose.
ENGINEERING ASPECTS OF OZONATION EQUIPMENT AND PROCESSES
INTRODUCTION
Extensive data were obtained during the course ot the study on engineering
design, operation and costs of ozonation systems. Engineering design practices
of ozonation systems vary widely by country and by equipment manufacturers, and
there can be considerable variation among similar water treatment plants with
regard to the efficiency of generation and contacting of ozone. Current U.S.
waterworks design standards and texts provide little guidance for engineering
design of ozonation systems. Manufacturers of ozonation equipment comprise
the principal source of design information in the U.S. at present. Hence,
one of the major goals of the study was to provide corroborating design
information to allow a range of understanding and appreciation of the
various design alternatives.
Ozonation systems consist of four major parts, plus ancilliary equip-
ment. The major parts of the system (Figure 5) are:
a. Gas preparation unit
b. Electrical power unit
c. Ozone generator
d. Contactor, include off-gas treatment
Ancilliary systems include instruments and controls, safety equipment and
equipment housing.
25
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NJ
Figure 4. Sipplinger Berg, West Germany Water Treatment Plant on
Lake Constance
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2
ELECTRICAL
POWER SUPPLY
1
GAS
PREPARATION
DRY GAS
3
OZONE
GENERATOR
UNOZONATED
WATER
OZONE-RICH,
GAT
4
CONTACTOR
OZONATED WATER
Figure 5. The Four Basic Components of the Ozonation Process
Ga.s Preparation
A high level of gas preparation, normally air, is required prior to
ozone generation. Air must be dried in order to prevent formation of nitric
acid and to increase the efficiency of ozone generation. The presence
of moisture greatly accelerates the breakdown of ozone. Nitric acid, which
will chemically attack the internal parts of the ozone generator, is formed
when nitrogen combines with moisture in the corona discharge; thus, the
introduction of moist air into the unit must be avoided. Selection of the
air preparation system depends to some extent on the contacting system chosen.
However, the gas preparation system normally will include refrigerant gas
cooling and desiccant drying to a minimum dew point of minus 40 degrees Celsius.
A dew point monitor or hygrometer appears to be an essential part of any air
preparation system. A schematic of a low pressure air preparation system
with turbine contacting is shown in Figure 6 and a gas drying system is shown
in Figure 7.
Oxygen can be used to generate ozone with much greater efficiencies
of conversion when the cost of producing the oxygen is not considered.
The plant at Duisburg, Federal Republic of Germany, is the only opera-
tional municipal water treatment plant known which utilizes high purity
27
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REFRIGERANT DRIER
AIR FILTER
DESICCANT TYPE DRIERS
LOW PRESSURE FAN
TURBINE CONTACTOR
Figure 6. Low-Pressure Gas Preparation System
oxygen instead of air as the ozone generator feed gas, although the
Tailfer plant of Brussels, Belgium, is installing this capability.
This is contrary to United States wastewater ozonation practice, where
it is frequently found that the use of high purity oxygen for both
oxygen activated sludge treatment and ozone generation for disinfection
is cost-effective.
Electrical Power Supply
Information available on the electrical power supply is limited. This
part of" the ozonation system was generally isolated and difficult to inspect t
in the plants visited, and the plant operators had little knowledge of power
supply design. Manufacturers indicated that the power supply normally is '
considered integral to the ozonation unit and designs are proprietary. Thus,
the information obtained in the study on electrical power supplies is of a
28
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Figure 7. Air Feed Desiccation System
Annet-sur-Marne, France
29
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Figure 8. Modular Ozone Generator With Power Supply and Control System (Courtesy, Degremont)
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general and theoretical nature rather than highly specific. Figure 8 shows
a power supply system normally provided as part of the ozonation equipment.
Empirically, power consumption and ozone generation capacity are
proportional to both voltage and frequency. Therefore, there are two ways to
control the output of an ozone generator: vary voltage or vary frequency. Three
common electrical power supply configurations are presently used in commerci-
ally available equipment:
low frequency (.bU hz; , variable voltage
medium frequency (600 hz), variable voltage
fixed voltage, variable frequency
Constant low frequency, variable voltage is the most common power supply
used. For larger systems, the 600 hz fixed frequency is often used because
it allows doubled ozone production with no increase in ozone generator
size, though at a higher power consumption tor unit weight of ozone produced.
Little information has been developed in this study regarding power
supply reliability. No general problems were identified, though there
have been some difficulties with air cooled transformers. It is recommended
that the ozone generator supplier be made responsible for providing the
electrical power supply.
Ozone Generation
The silent electrical (.corona; discharge method currently is considered
to be the only practical method of generating ozone in plant scale quantities,
and consequently was the only method covered in the study. Using this principle,
a simple ozone generator can be constructed from a pair of electrodes separated
by a gas space and a layer of glass insulator (Figure 9). An oxygen containing
gas is passed through the empty space and a high voltage alternating current
is applied. A corona discharge occurs across the gas space and ozone is
created when a portion of the oxygen is ionized and then become associated
with non ionized oxygen molecules.
0 + e ^ 2(0; + heat
2 electricity ionized
atmospheric oxygen
oxygen
2(0; + 20 > 2U
3
31
-------
Figure
Interior of a Tubular Ozonator in Operation
This reaction is an equilibrium reaction; hence, newly formed ozone is
simultaneously breaking down into molecular oxygen. Heat accelerates this
breakdown and since most of the energy fed to the ozonator is lost in
the form of heat, efficient cooling of the unit is a necessity. Most ozone
generators are water cooled with the exception of the Lowther plate design,
which uses air for cooling.
The various types ot ozone generators observed and their manufacturers
are as follows:
Horizontal tube type, water cooled (Figure 10):
Trailigaz, Degremont, Demag, Herrmann
Vertical tube, water cooled:
Kerag
32
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Vertical tube, double cooled (oil and water):
PCI Ozone
Plate, water cooled (Figure 11):
Cie des Eaux et de 1'Ozone (CEO), Sauter
Lowther plate, air cooled (Figure 12):
Union Carbide
There are other manufacturing firms in Europe, Japan and the U.S., but
installations with their equipment were not visited during this study. By
far the most common type of ozonator in use is the horizontal tube type
with water cooling (Figure 10). This unit is especially popular where
larger size units are required. The water cooled plate units are frequently
used in smaller plants but require considerably more floor space per unit
of output than the tube type units. The air cooled Lowther plate unit
is a relatively new design developed in the U.S. It appears to have the
potential for simplifying the use of ozone generating equipment, but to date
it has had little operating experience in water treatment plants.
Ozone Contacting
After generating the ozone, it must be mixed with the water stream
being treated. The objective is to maximize the dissolution of ozone into
the water at the lowest power costs and still accomplish the desired
objective. The wide range of ozone contactor designs in operation in
water treatment facilities includes the following:
Multi-stage porous diffuser contactors
- Single application of an ozone-rich gas stream
- Application of "fresh" ozone gas to second and
subsequent stages with off-gases being recycled
to the first stage
Eductor induced, ozone vacuum injector contactors
- Total plant flow through eductor
- Partial plant flow through eductor
Turbine contactor
- Positive pressure to turbine
- Negative pressure to turbine
33
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A. SINGLE-BAY
7 12
AIR
AIR
AIR
B. DOUBLE-BAY
AIR WATER
I
WATER
DIELECTRIC TUBES
I. DIELECTRIC TUBE
2. METALLIC COATING
3. H.V. TERMINAL
k. CONTACT
5- CENTERING PIECE
6. IONIZATION GAP
7. AIR INLET
8. FRONT CHAMBER
9. REAR CHAMBER
10. AIR OUTLET
I I. WATER INLET
12. WATER OUTLET
Figure 10. Typical Details of Horizontal Tube-Type
Ozone Generator
34
-------
Packed bed contactors
- Cocurrent water/ozone-rich gas flow
- Countercurrent water/ozone-rich gas flow
Two level diffuser contactor
- Application of ozone-rich gas to lower chamber
- Lower chamber off-gases applied to upper chamber
These contactors are described and illustrated in the large report.
Diffuser contacting (Figure 13) is the most commonly used design particularly
when ozone is used for disinfection. Turbine contacting (Figure 14) also is
quite popular in Europe, particularly for mass transfer controlled reactions
that do not require lengthy contact times.
Treatment of off-gas from the contactors is an important consideration.
Methods used for off-gas treatment include dilution, destruction with
granular activated carbon, thermal or catalytic destruction, and recycling.
OZONE MEASUREMENT AND CONTROL
Operational economics and good management practices require that high
levels of control of the ozonation system be maintained. Depending upon
specific process of applications of ozone, plant size, regulatory agency
policy, and design philosophy, the control system may be simple or complex.
The trend in France and Switzerland appears to be toward highly sophisticated
and centralized control, examples being the small (30,000 cu m/day) remotely
operated Kreuzlingen plant (Switzerland) and the large (600,000 cu m/day)
Neuilly-sur-Marne plant near Paris, France. On the other hand, water
treatment plants visited in the Federal Republic of Germany and in the
Province of Quebec, Canada, employ a higher degree of local control and
monitoring.
A number of parameters must be measured to provide a fully operable
ozonation system; these include the following:
There must be a means of providing a full temperature and
pressure profile of the ozone generator feed-gas from the
initial pressurization (by fan, blower, or compressor) to
the ozone generator inlet.
There must be a means of measuring the moisture content of
the feed-gas to the ozone generator. This procedure should
be conducted with a continuously monitoring dew point meter
or hygrometer.
35
-------
Figure 11. Parallel Plate Ozonators at Konstanz Waterworks, West Germany
Figure 12. Interior of Individual Plate Ozonator
36
-------
Figure 13. Turbine Contactor at Zurich, Switzerland, Lengg Plant
37
-------
Figure 14. Ozone Diffuser System Layout and Bubble Pattern
38
-------
There ijiust be a means of measuring the temperature, pressure,
flow rate, and ozone concentration of the ozone-containing
gas being discharged from all the ozone generators. This
is the only effective method by which ozone dosage and the
ozone production capacity of the ozone generator can be
determined.
There must be a means of measuring the power supplied to the
ozone generators. The parameters measured include amperage,
voltage, power, and, if a controllable variable, frequency.
There must be a means of measuring the flow rate and
temperature of the cooling water to all water cooled ozone
generators. Reliable cooling is important to maintain
constant ozone production, and to protect the dielectrics
in the generation equipment.
There must be a means to monitor the several cycles of the
desiccant drier, particularly the thermal-swing unit.
Three obvious analytical needs are measurement of ozone concentrations
in (1) the ozonized gas from the ozone generator, (2) the contactor off-gases,
and (3) the residual ozone level in the ozonized water. Methods of ozone
measurement observed during plant visitations include the following:
Simple "sniff" test
Draeger type detector tube
Wet chemistry potassium iodide method
Amperometric type instruments
Gas phase chemiluminescence
Ultraviolet radiation adsorption
Each of these methods is discussed in some detail in the study.
The use of control systems based on the measurements listed above vary
considerably in the water treatment plants that were visited. The French
plants using ozonation primarily for disinfection incorporate a closed-loop
control system by which the residual ozone level in the contactor is used
to control the amount of ozone supplied to maintain that ozone residual.
The key to successful operation of such a system is an accurate and reliable
residual ozone analyzer. On the other hand, the German ozonation systems
which are used primarily for iron, manganese and/or organics oxidation are
manually controlled through a periodic "sniff" test of off-gas from the
holding tanks after ozonation.
39
-------
At present, it appears that continuous residual ozone monitoring equip-
ment may be successfully applied to water that has already received a high
level of treatment. However, a more cautious approach must be taken with
the application of continuous residual ozone monitoring equipment for
water that has only received chemical clarification, because the ozone demand
has not yet been satisfied and the residual is not as stable. Instrumentation
for continuous monitoring of the ozone concentration in gas phases appears
to be reliable.
Ozone production must be closely controlled because excess ozone cannot
be stored, and changes in process demand must be responded to rapidly.
Ozone production is costly, under ozonation may produce undesired effects,
and over ozonation may require additional costs where off-gas destruction
is used. The study discusses the following ozone production control methods:
Manual Operation - Manual Sampling
Manual Operation - Automatic Sampling
Closed Loop Control - Automatic Sampling
Closed Loop Control of Voltage/Frequency and Gas Flow Automation
OPERATION AND MAINTENANCE
The site visits verified in most cases the relatively low maintenance
needs of ozonation equipment. The air preparation system requires frequent
attention for air filter cleaning/changing and for assuring that the
desiccant is drying the air properly. Both of these normally are simple
operations.
Two factors which impact ozone generator operation and maintenance
are the effectiveness of the air preparation system and the amount of
time that the generator is required to operate at maximum capacity. Mainte-
ance of the ozone generators commonly is scheduled once per year in the
plants visited. However, many plants perform this maintenance every six
months. Typically, one man-week is necessary to service an individual ozone
generation unit of the horizontal tube type. Dielectric replacement due to
failure as well as to breakage during maintenance may be as low as 1 to 2
percent. However, it appears reasonable to predict an average tube life of
ten years if a feed gas dew point of minus 60 degrees Celsius is maintained
and if the ozone generator is not required to operate for proloriged periods
at its rated capacity. Plate type ozone generators use window glass as
dielectrics. However, the same attention to air preparation is taken as
with the more expensive glass or ceramic tubes in order to avoid costly
down time.
Operation and maintenance of the ozone contactor also must be considered.
Turbines require electricity to power the drive motors, while porous diffusers
require regular inspection and maintenance to insure a uniform distribution
of ozone rich gas in the contact chamber. Experience with maintenance
of the ozone contact chambers in the Morsang-sur-Seine plant in France
40
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(diffuser chambers) indicates that even after purging of the
contact chambers with air, maintenance personnel entering the chambers should
be equipped with a self-contained breathing apparatus, since the density of
ozone is heavier than air and therefore is difficult to remove completely by
air purging.
COSTS/BENEFITS OF OZONATION
Based on the field cost data acquired, the capital costs of ozonation
systems can range from a low of $600/lb of ozone generation capacity/day
for large systems to a high of $4000/lb capacity/day for relatively small
systems. An added cost is housing for the system, which can range from
approximately 20% to 33% of equipment costs.
Total capital and operating costs depending on energy demand, period of
amortization, interest, subsystem components selected and cost of energy,
were found to range from 1.75 cents to about 4 cents/1000 gallons of water
treated based on the limited data available (see Table 5).
When one considers the versatility of ozone, its many applications, and
its effectiveness in breaking down potentially harmful synthetic organic
chemicals, these operating costs can be justified. Also, ozone combined with
granular activated carbon has been demonstrated in Europe to be one of the
most effective combinations known for the simultaneous removal of ammonia
and dissolved organic compounds. This combination at the Dohne plant of
Mulheim, Germany employs 3 mg/1 dosages of ozone which has replaced prechlor-
ination dosages of 30 to 50 mg/1. Prechlorination produced high concentrations
of chlorinated organics, which required frequent reactivation of the Dohne
GAG columns (every 6 to 8 weeks). Preozonation of granular activated carbon
also can result in much longer time periods between GAG regeneration. Precise
savings have not yet been investigated thoroughly.
CONCLUSIONS
Ozonation for drinking water treatment is a well established
and growing technology. Over 1000 operational plants throughout
the world (most are in Europe) use ozone for one or more of a
multiplicity of purposes, most of which are based upon its
strong oxidizing power.
As an oxidant, ozone currently is used to remove colors,
tastes, odors, algae, organics (phenols, detergents, pesticides,
etc.), cyanides, sulfides, iron, manganese, turbidity, to cause
flocculation of micropollutants (soluble organics) and to inactivate
viruses.
Ozone also is used as a disinfectant, but seldom in the context
of an either-or "alternative disinfectant to chlorine". It is
.normal to follow ozone as the primary disinfectant with a
small dosage (up to 0.6 mg/1) of chlorine or chlorine dioxide,
which provides a residual a residual for distribution systems.
41
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TABLE 5. COSTS OF OZONATION AT EUROPEAN DRINKING WATER PLANTS
Plant
Tailfer
Brussels
Belgium
Lengg
Zurich
Switzerland
Large
Automated
Paris Plant
Several
French
Plants
water
treatment
capacity
(mgd)
68.7
66
-
ozone
generation
capacity
(Ibs/day)
1267
1742
-
capital
cost of
ozonation*
$4,024,000
$1,120,000
""
capital
cost/lb
of ozone
generation
capacity
$2200
$ 643
~
amortization
period (yrs.)
20
20
20
10
av. dosage
of ozone
(mg/1)
1.7
1.5
2.5
1.5-3.0
ozonation
operating
costs
(c/1000 gal)**
2.52
1.75
2.76
3.95
electrical
cost (c/kwhr)
3.01
2.0
2.1
3.12
NJ
*includes air preparation equipment, ozone generation, ozone contacting, treatment of off-gas ozone,
instrumentation, installation and housing for ozonation system (including contact system)
**includes operation, maintenance and amortization
Table 5. Costs of Ozonation at European Drinking Water Plants
-------
Under specific circumstances, ozonation can be used as the
sole disinfectant. In addition to the obvious requirements
(e.g., ozonation is the terminal treatment step and the
distribution system must be free of contamination), the
distribution system should be short and the residence time
of treated water in the system also should be short. Ammonia
should be absent and dissolved organic carbon should be
less than 0.2 mg/1. It is also advantageous that the
temperature of treated water be low, so as to reduce the
potential for bacterial regrowth.
Ozonation system components (electrical power supply, gas
preparation, ozone generation, ozone contacting) operating
in Europe are reliable and do not exhibit unusual equipment
operation problems, provided that routine maintenance is
performed.
Costs of ozone treatment of drinking waters in Europe range
from 1.75 cents to 4 cents/1000 gallons of water treated
in operational plants visited. The range depends upon
the specific uses of ozone, the amounts of ozone required,
types of contacting employed, the type of equipment housing
and degree of control instrumentation selected. Ozonation equipment
normally is amortized over 20 years.
Chemical evidence obtained to date does not indicate any
untoward health hazard to be associated with the use of ozone.
Organic oxidation products formed upon ozonation are non-
halogenated, are more biodegradable than before oxidation,
and usually are less toxic. However, some pesticides pass
through intermediate stages of oxidation to produce more
toxic materials.
Formation of the same or similar non-halogenated, more
toxic intermediates also can occur, with the use of oxidants
other than ozone, for example chlorine and chlorine dioxide.
Therefore, it is important in using any oxidant for water
treatment to know the identity of dissolved organic matter
present, the chemistry'of intermediate oxidation stages,
and to design sufficient oxidant into the process to guarantee
that such intermediate stages are passed and potentially
toxic intermediates are destroyed through oxidation.
The sequential combination of ozonation, filtration, then
granular activated carbon filtration is being employed in newer
European water treatment plants to enhance removal of dissolved
organics and ammonia simultaneously by means of the biological
activity in the activated carbon. This process also is used
for extending the useful life of granular activated carbon.
Some European Biological Activated Carbon columns and/or
beds have operated 2.5 years without having to be regenerated.
43
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SECTION 4
BIOLOGICAL ACTIVATED CARBON
INTRODUCTION
Biological Activated Carbon (BAG) is a term used to describe processes
by which granular activated carbon contactors are made biologically active.
Dissolved oxygen (DO) is introduced before the carbon contactor in sufficient
quantity to maintain aerobic conditions within the carbon'. The availability
of surface area within the carbon, plus dissolved oxygen and organic matter
in the water stream, creates nearly ideal conditions for microbial growth.
The microbes, in turn, metabolize dissolved organics, thereby acting as an
organics removal process. The use of ozone before the carbon filters not
only creates the needed oxygen rich environment, but the ozone also oxidizes
the larger, less degradable organics into smaller molecules which are more
easily biologically degraded.
Many of the advantages of biological activated carbon were first
recognized by German water treatment scientists in the 1960's in drinking
water plants along the Rhine River in the Dusseldorf area. Subsequently,
BAG processes also have been installed in Swiss and French drinking water
treatment plants, and are subjects of active pilot studies in Holland and
Belgium. In the United States, the U. S. Environmental Protection Agency's
Water Supply Research Laboratory in Cincinnati, Ohio has been testing
a pilot BAG column since late 1976, although not continuously. EPA also
is planning to fund three pilot plant studies in Fiscal Year 1978.
FUNDAMENTAL PRINCIPLES
At the present level of understanding of the BAG process, two mechanisms
by which the process functions are proposed. It is thought that microbes are
present both on the surface of the carbon and in the pores of the carbon
surface. Organics passing through the process will be surface adsorbed and
pore adsorbed. The surface adsorbed organics do not have to be firmly
adsorbed, if they are biodegradable, in order to effect their removal
from the water stream, as the surface microbes will quickly metabolize
them. The less degradable organics are more slowly removed from the surface
or pores by the microbes, thereby "regenerating" the carbon. Preozonation
converts larger less biodegradable organics into smaller, more degradable
organics, and charges the water stream with dissolved oxygen.
Critical to the functioning of the process is the adsorptive capacity
of the granular activated carbon. Detention time in a carbon contactor is
short, usually on the order of 15-30 minutes empty bed contact time. Thus,
the surface area and pore volume of the carbon should be high.
44
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Many organic materials are readily adsorbed onto GAG, but many others
are not. For example, high molecular weight natural organic compounds,
such as the huraic acids, are poorly adsorbed by GAG. If, however, the
water is preozonized, the humic acids are broken down into more readily
adsorbable and biodegradable compounds. Other non polar and highly carbon
adsorbable organic compounds upon ozonation become more polar and more
biodegradable, but less adsorbable.
EUROPEAN BAG PRACTICES
Granular activated carbon was introduced into European drinking water
treatment practices after 1945, initially for dechlorination and taste/odor
control. Dechlorination was required whenever prechlorination was practiced,
such as with waters containing ammonia and treated by breakpoint chlorination.
Ammonia is effectively removed in this manner, but chlorinated organic
compounds are produced.
Combinations of ozone and GAG were installed in plants near Dusseldorf,
West Germany in the late 1950's, but the synergistic interaction of the two
processes was not fully recognized until nearly ten years later.
The BAG process has been studied extensively at the Bremen, West
Germany plant, on the River Weser. At Rouen, France, the process is being
applied to successfully treat polluted deep well waters drawn adjacent to
the Seine River. The Zurich, Switzerland system uses preozonation of
granular activated carbon at its Lengg plant, and there have been considerable
studies of the process in Holland. The U.S. EPA also has funded additional
investigation of European BAG practices. The project is currently underway
and hopefully will extend the data presented in this study.
At Mulheim, West Germany, a switch to BAG in mid 1977 resulted in signi-
ficant improvements of final water quality. The Dohne plant treats polluted
water from the Ruhr river, and had previously been removing ammonia by break-
point chlorination. This resulted in the formation of halogenated organic
compounds which were removed inadequately by the GAG systems, and also
created a need for frequent GAG regeneration. By switching to BAG, the
Dohne plant was able to attain equivalent nitrogen removals and improved
dissolved organic carbon removals while eliminating the breakpoint chlorination
process. At the time of this writing, over 13 months of running time had
been accumulating on the GAG columns without regeneration. Previously,
it was necessary to regenerate the carbon columns every 6 to 8 weeks.
CONCLUSIONS
For optimum pollutant removals, granular activated carbon
contactor depths should be 4 to 5 meters (13 to 16 feet) in
depth. Empty bed contact times in the carbon contactor should
be at least 15 minutes, and preferably 20 to 30 minutes, with
a safety factor for pollutant surges.
45
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Dissolved oxygen (DO) in the effluent from the GAG contactor
should be at least 2 mg/1 and preferably exceed 3.5 mg/1,
for optimal bacterial activity. Normally, sufficient DO is
provided by the breakdown of ozone added for organic compound
oxidation. If required, supplemental addition of DO is
made prior to carbon filtration.
BAG is an effective process for ammonia removal. In the absence
of chlorinated organics, regeneration frequencies of the GAG
reactors are low, possibly as high as 3 years between cycles.
Plants using breakpoint chlorination before carbon contactors
can expect to regenerate every 6 to 8 weeks under the worst
conditions.
BAG contactors generally require backwashing, due to buildup of
solids and adhesion between carbon particles, as a result of
bacterial action. A combination of air scouring and water
backwashing has been found to be effective.
46
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SECTION 5
CHLORINE DIOXIDE
INTRODUCTION
Chlorine dioxide was first discovered in 1811 by Sir Humphrey Davy,
who prepared the compound by reacting potassium chlorate with hydrochloric
acid. Other experimentation followed wherein it was determined that chlorine
dioxide exhibited strong oxidizing and bleaching properties. In the 1930's,
the Mathieson Alkali Works developed the first commercial process for
preparing chlorine dioxide from sodium chlorate. By 1939, sodium chlorite
was established as a commercial product for the generation of chlorine dioxide.
The use of chlorine dioxide expanded rapidly in the industrial sector.
In 1944, chlorine dioxide was first applied for taste and odor control at
a water treatment plant in Niagara Falls, New York. Other water plants
recognized the benefits of using chlorine dioxide and its use increased
rapidly. In 1958, a national survey determined that 56 U.S. water utilities
were using chlorine dioxide. The number of plants using chlorine dioxide
has grown more slowly since that time, to a total of 84 plants in 1977,
as determined by a survey carried out as part of this study.
Currently, chlorine dioxide is most commonly used for bleaching in the
pulp and paper industry. It is also used in large amounts by the textile
industry, as well as for the bleaching of flour, fats, oils and waxes. In
treating drinking water, chlorine dioxide is used in the United States for
taste and odor control, decolorization, iron and manganese oxidation,
oxidation of organics, disinfection and provision of residual disinfectant
in water distribution systems. Of the 84 plants in the U.S. currently
using chlorine dioxide, only one, Hamilton, Ohio, uses the chemical solely
as a disinfectant. The principal 'use of chlorine dioxide in the U.S.
is for taste and odor caused by phenolic compounds in the raw water supply.
Chlorine dioxide is a yellow green gas and is soluble in water at room
temperature to about 2.9 g/liter chlorine dioxide (at 30 mm mercury partial
pressure) or more than 10 g/1 in chilled water. The boiling point of
liquid chlorine dioxide is 11 degrees Celsius and the melting point is
minus 59 degrees Celsius. Chlorine dioxide has a density of 2.4 (air=l). The
oxidant is normally used in a water solution and is five times more soluble
in water than chlorine gas. Also, chlorine dioxide does not react with
water as does chlorine. Chlorine dioxide is quite volatile and therefore
can be stripped easily from a water solution by aeration.
47
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The compound has a disagreeable odor, similar to that of chlorine gas,
and is detectable by the human nose at 17 ppm. Chlorine dioxide is distinctly
irritating to the respiratory tract at a concentration of 45 ppm in air.
Concentrations of chlorine dioxide in air above 11% can be mildly explosive.
Chlorine dioxide as a gas or liquid may be readily decomposed upon exposure
to ultraviolet light. It also is sensitive to temperature and pressure which
are two reasons why chlorine dioxide is generally not shipped in bulk concen-
trated quantities.
Chlorine dioxide has a much greater oxidative capacity than chlorine and
therefore is a more effective oxidant in lower concentrations. Chlorine
dioxide also maintains an active residual longer in potable water than
does chlorine. Chlorine dioxide does not react with ammonia or with trihalo-
methane precursors when prepared with no free residual chlorine.
PREPARATION OF CHLORINE DIOXIDE
Chlorine dioxide is prepared from feedstock chemicals by a variety
of methods, depending on quantity needed and the safety limitations in
handling the various feedstock chemicals. The most common processes are:
From Sodium Chlorite (NaCIO ):
2
Acid and sodium chlorite
Gaseous chlorine and sodium chlorite
Sodium hypochlorite, acid and sodium chlorite
From Sodium Chlorate (NaCIO ):
3
The suphur dioxide process
The methanol process
The Hooker R-2 Process
The Hooker SVP (R) Process
The first group of processes are more adaptable to water utility operations
and therefore are more commonly used. The second group of processes are
frequently used by industry where the quantities produced are much greater
than in water utitilies. U.S. and European water utilities usually prepare
chlorine dioxide using sodium chlorite and gaseous chlorine (Figure 15)
rather than acid, although the acid based process is used extensively
in Switzerland (Figure 16).
OXIDATION PRODUCTS OF CHLORINE DIOXIDE
The study presents a detailed review of the literature and current
analysis of current knowledge on the oxidation products of chlorine dioxide.
Some of the reactions and conclusions regarding oxidation products and
chlorine dioxide are listed below.
Regardless of the oxidant employed, many (if not all) of the
same organic oxidation products will be present in the water
or wastewater at the same treatment point. More significantly
in the case of chlorine, these same (non-halogenated) oxidation
products have been present all along.
48
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Figure 15. Chlorine Dioxide Generation From Acid and Sodium
Chlorite at Lengg Plant, Zurich, Switzerland
49
-------
Figure 16. Preparation of Chlorine Dioxide From Gaseous Chlorine and Sodium Chlorite
-------
Oxidation of phenols with chlorine dioxide or chlorine produces
chlorinated aromatic intermediates before ring rupture.
Oxidation of phenols with ozone or chlorine dioxide produces
oxidized aromatic compounds as intermediates, which undergo
ring rupture upon treatment with more oxidant and/or longer
reaction times. In many cases, the same, non-chlorinated,
ring-ruptured aliphatic products are produced using ozone or
chlorine dioxide.
In oxidizing organic materials, chlorine dioxide can revert
back to chlorite ion. In the presence of excess chlorine
(or other strong oxidant) chlorite can be preoxidized to
chlorine dioxide.
Using large excesses of chlorine dioxide over the organic
materials appears to favor oxidation reactions (without
chlorination), but slight excesses appear to favor
chlorination.
When excess free chlorine is present with the chlorine
dioxide, chlorinated organics usually are produced, but
in lower yields, depending upon the concentration of
chlorine and its reactivity with the particular organic(s)
involved.
Treatment of organic compounds with pure chlorine dioxide
containing no excess free chlorine produces oxidation
products containing no chlorine in some cases, but products
containing chlorine in others.
Under drinking water plant treatment conditions, humic
materials and/or resorcinol do not produce trihalomethanes
with chlorine dioxide even when a slight excess of chlorine
(1-2%) is present.
Saturated aliphatic compounds are not reactive with chlorine
dioxide. Alcohols are oxidized to the corresponding acids.
USAGE OF CHLORINE DIOXIDE IN THE UNITED STATES
Summary of U.S. Questionnaire Results
Using data from chemical suppliers and other sources, 105 question-
naires were sent to plants which were thought to be using chlorine dioxide
or which had used it in the past. The water utilities provided information
on plant capacity, treatment processes, multiple uses of chlorine dioxide,
method of production, and methods of analyzing and monitoring chlorine
dioxide in the system. Most plants using chlorine dioxide have been in
service at least 15 years are less than 5 mgd in size, and generally are
located in the southeastern (EPA Region 4) and midwestern (EPA Region 5)
parts of the United States. The most frequent usage of chlorine dioxide
51
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reported was for the control of taste and odor in water supplies (47
responses), followed by disinfection and provision of an oxidant
residual in the water distribution system (22 responses), iron/manganese
control (18 responses), and oxidation of organic chemicals (12 responses).
Those plants using chlorine dioxide for taste and odor control cited
phenols and algae as the primary source of these problems.
The common method of chlorine dioxide generation in U.S. water plants
is by the gaseous chlorine/sodium chlorite method. One U.S. plant uses
the acid method and three use the hypochlorite method. All of the plants
reportedly using the gaseous chlorine method use single pass chlorination
equipment; none use the multiple pass chlorine enrichment system used by some
European plants.
Few plants offered any information on monitoring and analysis of
chlorine dioxide. Those that did reported that only the gross measurement
of total oxidants (chlorine and chlorine dioxide) is monitored in the
finished water. Few plants monitor the actual chlorine dioxide concentration
which is added to plant water, rather production rates are determined by
the weight of chemical reagents used for the generation process. Production
efficiencies are rarely monitored.
Summary of U.S. Plant Visits
During the months of September and October 1977, 13 water treatment
plants in the United States were visited. The purpose of these visits was
to learn first hand information about the engineering and operational aspects
of chlorine dioxide in water treatment operations. Of the thirteen plants
visited, five were located in Georgia, five in Ohio, and one each in West
Virginia, Kentucky and Michigan. These plants represent a cross section of
the use of chlorine dioxide in United States water treatment works. Data
collected were similar to that requested by the questionnaire, but in greater
detail, plus considerable information on engineering and operation of chlorine
dioxide systems. The plants visited are listed in Table 6:
TABLE 6. U.S. WATER TREATMENT PLANTS VISITED
WHICH USE CHLORINE DIOXIDE
Columbus, Ohio
Newark, Ohio
Bethesda, Ohio
Hamilton, Ohio
Toledo, Ohio
Atlanta, Georgia
Chattahoochee Plant
Hemphill Plant
Carrollton, Georgia
Fayetteville, Georgia
Marietta, Georgia
Wheeling, West Virgina
Covington, Kentucky
Ann Arbor, Michigan
52
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Most of the plants visited use chlorine dioxide to control taste and
odor problems or for manganese reduction in the raw water. Twelve of the
thirteen plants use the gaseous chlorine and sodium chlorite process for
chlorine dioxide generation. The reactor units for chlorine dioxide genera-
tion typically are made of PVC and have viewing ports where the color of the
chlorine dioxide formed can be viewed. (Figure 17)
There is little monitoring in U.S. plants of the production efficiency
or the chlorine dioxide concentration in the finished water. Hamilton, Ohio
is the only plant which analyzes for chlorine dioxide in the finished water.
Likewise, there is little routine monitoring and control of the processes.
As a result, the conversion efficiency and the chlorine dioxide actually
produced varies from plant to plant. There appears to be a lack of under-
standing of what can and does happen when chlorine and chlorine dioxide are
mixed in different ratios. Manufacturers of chlorine dioxide generation
systems recommend a 1:1 feed ratio by weight of chlorine and sodium chlorite.
A number of plants feed excess chlorine, however. Chlorine is needed to
depress the pH to a point where conversion efficiencies of 80-95% can be
obtained. If the chlorine is recycled, as is the case in one French manufac-
turer's system, the pH is depressed to 2.7 or less and conversion efficiencies
of 98-100% are said to be obtained. In a once pass through system, if excess
chlorine is added, the resulting free residual chlorine can 1) lead to the
formation of THM's and/or 2) negate the purpose of using chlorine dioxide.
If sodium chlorite is not converted to chlorine dioxide, the potentially
harmful chlorite ion remains in the water. If too much chlorine is added (or
not mixed properly), free residual chlorine will result.
Figure 17. Photographs of Typical U.S. Chlorine Dioxide Generation Systems.
53
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The Ann Arbor water treatment plant uses the acid-sodium chlorite method
for chlorine dioxide production. It is the only plant of 84 water treatment
plants using chlorine dioxide in the United States that uses this method. The
oxidant is added to control taste and odor problems at the 16 mgd facility.
These year-round problems are reportedly caused by actinomycetes in the Huron
River.
The chlorine dioxide is generated on-site by mixing sodium chlorite
(NaC102) and hydrochloric acid (HC1) in a dry weight ratio of 6.1:1, respectively.
The pH of the discharge of the chlorine dioxide reaction vessel is monitored
periodically to ensure proper acidity inside the vessel for efficient chlorine
dioxide generation. Otherwise the production of chlorine dioxide is monitored
visually by the richness of the dark-brown color which appears through the
transparent reaction vessel. The efficiency of chlorine dioxide addition is
gauged by the absence of tastes and odors in the finished water.
»
Ann Arbor uses the acid/sodium chlorite method because of the lower costs
for operating and maintaining the overall generating system. The pH of the
chlorine dioxide generation is better controlled with the acid-sodium chlorite
method. Liquid chlorine storage and feed facilities were removed in 1975 when
the plant switched to a liquid sodium hypochlorite (NaOCl) chemical feed system
for disinfection.
The cost of aqueous HC1, which is 31.45 HC1 by weight, is $8.95/100
pounds ($0.20/kg) and NaClC>2 which is 80% pure, costs $78.70/100 pounds
($1.75/kg). The chlorine dioxide is added ahead of the sand filters and costs
approximately 16C/1000 gallons (4.23$/cu.m) of water treated. (1977)
Hamilton, Ohio is the only known water treatment plant in the United
States using chlorine dioxide for final disinfection. This 15 mgd plant
switched from chlorine to chlorine dioxide as the final disinfectant when
customers complained about the taste of chlorine in the tap water. There also
were problems with iron bacteria in the distribution mains which were dis-
coloring the water. Since 1972, when chlorine dioxide addition began, the
complaints regarding the objectional tastes, odors and colors in the finished
water have reportedly ceased.
The chlorine dioxide is generated on-site by mixing sodium chlorite and
chlorine in the dry weight ratio of 1:1. The chlorine dioxide is added year
round and monitored three times daily in the plant water and once daily in
the distribution system. The chlorine dioxide concentration leaving the plant
is 0.15 mg/1 and 0.10 mg/1 at the extremities of the distribution system. The
chlorine dioxide in the water is measured spectrophotometrically. Production
of chlorine dioxide is monitored visually by the color of the chlorine dioxide
that appears inside the reaction vessel. The effectiveness of chlorine dioxide
is determined by bacteriological tests and the absence of taste and odor
problems in the finished water.
54
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USAGE OF CHLORINE DIOXIDE IN EUROPE
Summary of European Chlorine Dioxide Questionnaire Results
Substantial data were obtained on chlorine dioxide usage in Europe. It
is estimated that approximately 495 European water treatment plants currently
are using chlorine dioxide. Questionnaires were mailed to plants in West
Germany, France, Great Britain, Switzerland, and Austria. Forty-four responding
plants were in West Germany, 23 in France, 5 in Great Britain, and 2 plants
in Austria responded.
Unlike the U.S. practice, chlorine dioxide is used in Europe principally
for bacterial disinfection and provision of a long lasting, low oxidant
residual in the distribution system. This was particularly true in West
Germany, Austria, and Great Britain. French plants cited a variety of reasons
for using chlorine dioxide, principally bacterial disinfection, taste/odor
control and organics oxidation. The British cited taste/odor control as a
principal reason for chlorine dioxide usage.
As in the U.S., the principal method of chlorine dioxide preparation is
the gaseous chlorine/sodium chlorite process. Dosages at all of the plants
reporting were quite low, often about 0.3 mg/1 and seldom exceeding 0.6 mg/1.
Summary of European Chlorine Dioxide Plant Visits
During May 1977, the site visit team toured 15 European water treat-
ment plants which employ chlorine dioxide. Four of the plants were in
France, one in Belgium, eight in Germany, and two were in Switzerland. All
but two of the plants use ozonation in addition to chlorine dioxide.
In general Europeans use chlorine dioxide only when chlorine cannot
be used, mainly because of cost. In Europe, chlorine dioxide costs 3
to 3.5 times more than chlorine. The two primary processes for which
chlorine dioxide is utilized are in pretreatment and post-treatment. For
example, in pretreatment, chlorine dioxide is utilized at the Paris suburb
plants of Choisy-le-Roi (on the Seine River), Neuilly-sur-Marne (on the
Marne River), and at Annet-sur-Marne (upstream of Paris on the Marne River)
for breaking up organically bound manganese and iron and for presterilization
of water before filtration. At Toulouse, in southwestern France on the
Garonne River, chlorine dioxide is used in pretreatment for presterilization,
taste and odor control, and for color removal. Dosages of chlorine dioxide
employed in Europe for pretreatment generally range from 1 to 1.5 mg/1.
At the Tailfer plant in Brussels Belgium, both chlorine and chlorine
dioxide are used in pretreating Meuse River waters. Chlorine presterilizes
the raw water while chlorine dioxide decomposes the organic complexes of
iron and manganese and also presterilizes.
55
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In Germany and Switzerland, chlorine dioxide is used only for post-
treatment at the 10 water treatment plants visited in these countries.
Germans and Swiss use a maximum of 0.3 mg/1 of chlorine or chlorine dioxide
to provide a residual in the distribution systems. This dosage level
provides trace amounts of chlorine or chlorine dioxide in the distribution
systems. The tacit rule in these countries is that if finished water leaving
the plant requires greater than 0.3 mg/1 residual chlorine or chlorine
dioxide to provide stable residuals in the distribution system, then the
existing water treatment process must be modified to reduce oxidant demand
until this level of oxidant demand is attained. German water treatment
plants can add as much as 0.6 mg/1 of chlorine or chlorine dioxide to attain
residuals.
In post-treatment, chlorine dioxide is used only at Choisy-le-Roi
and Annet-sur-Marne of the plants visited in France and Belgium.
Four methods of generating chlorine dioxide on-site at European drinking
water treatment plants were observed:
1. Addition of chlorine gas to water, followed by addition of
excess chlorine solution to aqueous solution of sodium chlorite.
2. Addition of chlorine gas to water under pressure, then addition
of this solution under pressure to aqueous solution of sodium
chlorite under pressure.
3. Addition of chlorine gas to water and recirculation of this
aqeuous solution in a closed loop with continued addition of
chlorine until a pH below 2.7 has been attained. Then addition
of this pH 2.7 solution to aqueous solutions of sodium chlorite.
4. Addition of HC1 solution to aqueous solution of sodium chlorite.
DESIGN OF CHLORINE DIOXIDE SYSTEMS
The study included considerable review of the engineering details of
chlorine dioxide generation systems. The gaseous chlorine/sodium chlorite
and acid sodium/chlorite systems are the principal systems in use today.
The multiple pass enrichment technique, a recently developed variation
of the gaseous chlorine approach is rapidly being adopted in Europe
because of superior efficiency. The acid based process is less popular,
principally due to the difficulties and safety related problems of handling
concentrated acids. Both processes use a similar chlorine dioxide reactor,
usually a cylindrical vessel constructed from Pyrex glass of polyvinyl
chloride (PVC). Typically, the reactor is 36 to 42 inches high, 8 inches
in diameter and packed with Raschig rings. The feedstock chemicals are
usually added at the bottom of the vessel and flow upward, being mixed by
the packed column of rings.
56
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The Gaseous Chlorine-Sodium Chlorite System
This approach uses aqueous chlorine and aqueous sodium chlorite to
produce a mixture of chlorine dioxide and chlorine (commonly as HOC1).
Figure 18 is a schematic of such a system, which consists of a chlorine
dioxide generator, a gas chlorin ator, a storage reservoir for liquid
sodium chlorite, and a chemical metering pump. (Sodium chlorite solution can
be prepared from commercially available dry chemical by adding it to water.)
The recommended feed ratio of chlorine to sodium chlorite is 1:1 by weight.
Additional chlorine can be injected into the reactor vessel without changing
the overall production of chlorine dioxide.
rr
C102 SOLUTION TO
TREATMENT PROCESS
GENERATOR
CHLORINATOR
PUMP
H20
NaC102
Figure 18. Gaseous Chlorine-Sodium Chlorite Chlorine Dioxide Generation
System.
57
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A disadvantage of this process is the limitation of the "single pass" gas
chlorination. Unless increased pressure is used, this equipment is not able to
achieve higher concentrations of chlorine as an aid to a more complete and
controllable reaction with the chlorite ion. A French firm, CIFEC, has devel-
oped a variation of this process using a multiple pass enrichment loop on the
chlorinator to achieve a much higher concentration of chlorine and thereby
quickly attain the optimum pH for maximum conversion to chlorine dioxide.
(Figure 19)
VACUUM LINE
OF CHLORINE
CHLORINATOR
CHLORINE
FLOW METER
r
EJECTOR WITH CHECK
VALVE ASSEMBLY
C102 EXIT
ENRICHMENT
LOOP
CONTROL
EQUIPMENT
CHLORINE CYLINDER
RECIRCULATING PUMP-
FLOW METER
ELECTRIC VALVE
SODIUM
CHLORITE
TANK
SODIUM CHLORITE
METERING PUMP-
MAKE-UP WATER SUPPLY
Figure 19. The CIFEC System
The purpose of the multiple pass recirculation system is to allow enrich-
ment of the chlorine solution to a level of 5 to 6 g/1. At this concentration
the pH of the solution will drop to 3.0 and thereby provide the low pH level
necessary for efficient chlorine dioxide production. A "single pass''results
in a chlorine concentration in water of about 1 g/1, which produces a pH of
4 to 5. If sodium chlorite solution is added at this pH, only a 60% yield of
chlorine dioxide reportedly is obtained. The remainder is unreacted chlorine
(in solution) and chlorite ion. When upwards of 100% yield of chlorine
dioxide is achieved, there is virtually no free chlorite or free chlorine
carrying over into the product water.
58
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The CIFEC system can be designed for variable feed rates with automatic
control by an analytical monitor. This method has the advantages of eliminating
the chlorine dioxide storage reservoir. The production of the CIFEC system
can be varied by 20 equal increments of production. A 10 kg/hr (530 Ibs/day)
reactor can be varied in 0.5 kg/hr (26.5 Ibs/day) steps over the range of
0-10 kg/hr, and this can be accomplished by automatic control with the monitor
located in the main plant control panel.
Wallace and Tiernan offer a new single pass system which is pressurized
to produce a higher concentration of aqueous chlorine for chlorine dioxide
production. Gaseous chlorine is injected into feed water at about 7 bars
(102 psi). With a chlorine concentration of 5 g/1 produced, the pH of the
solution is reduced and chlorine dioxide is said to be produced quantitatively.
The chlorine dioxide solution is then diluted to 10 to 20 mg/1 (as chlorine
dioxide) for water treatment operations.
The Acid - Sodium Chlorite System
The combination of acid and sodium chlorite produces an aqueous solutions
of chlorine dioxide without production of significant amounts of free chlorine.
The acid based process avoids the difficulty of differentiating between chlorine
and chlorine dioxide for establishing an oxidant residual.
Figure 20 illustrates the chlorine dioxide production schematic for the
Lengg Waterworks of Zurich, Switzerland by the acid/sodium chlorite procedure.
This system uses liquid chemicals as the feed stock. Each tank has a level
sensor to avoid overfilling. The tanks are installed below ground in concrete
bunkers which are capable of withstanding an explosion. There are no floor
drains in these bunkers, and any spillage must be pumped with corrosion
resistant pumps. Primary and backup sensors with alarms warn of any spillage.
Because of the potential explosiveness, these chemicals are diluted
prior to the production of chlorine dioxide. The dilution is carried out on a
batch basis which is controlled by level monitors. Proportionate quantities of
softened dilution water along with the chemical reagents are pumped to mixing
vessels by means of calibrated double metering pumps. After the reactor is
properly filled, an agitator within the container mixes the solution for
15 minutes. Dilutions of 9% HC1 and 7.5% sodium chlorite are produced in
the chemical preparation process. The chlorine dioxide is subsequently
manufacturered on a batch basis. The final strength of the solution is
about 20%, 90-95% of this is chlorine dioxide, and 4-7% is chlorine.
COSTS FOR PRODUCING CHLORINE DIOXIDE
The cost for generating chlorine dioxide on-site is primarily dependent
on what method is used to generate the oxidant. There are other factors
that affect capital and 0/M costs for on-site chlorine dioxide production.
These include:
rate of chlorine dioxide production
59
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level of automation
back up equipment
availability of existing equipment to be incorporated into a
chlorine dioxide system
chemical storage facilities
type of chemical reagentliquid, powdered, drums, tank car,
rail car, etc.
size and frequency of chemical shipments
experience of plant operators
Although it is difficult to assign cost figures to chlorine dioxide produc-
tion because it is a site-specific assessment, chlorine dioxide production
generally follows an economy of scale. Larger plants that generate chlorine
dioxide on-site normally can produce it pound for pound less than smaller
water treatment plants. However, the larger plants will typically incur
higher capital costs for chlorine dioxide production because of higher levels
of system automation, chemical storage facilities, stand by equipment, etc.
The gaseous chlorine and sodium chlorite method is the most popular
chlorine dioxide generation technique in the U.S., Canada, and Europe.
Because few plants actually use the minimum practicable amount of chemicals
in this process, chemical costs have been estimated on the basis of
stoichiometric production. On this basis, chlorine dioxide produced from
gaseous chlorine and sodium chlorite costs approximately $1.35 to $2.00
per pound in chlorine dioxide in the United States. The cost for the acid
and sodium chlorite process is $1.80 to $2.60 per pound chlorine dioxide.
These estimates are based on 1977 dollars.
Capital costs for a chlorine dioxide system are largely dependent on
the type of chlorine dioxide process and the degree of sophistication desired.
Plants which have gaseous chlorine capability can install chlorine dioxide
generation equipment relatively inexpensively. At the other end of the scale,
the relatively efficient and sophisticated CIFEC system can be quite expensive,
The major equipment components needed for a relatively simple chlorine
dioxide system, along with their estimated 1977 costs, are tabulated below.
Capital Cost (U.S. dollars)
Chlorine Dioxide Reactor 650 - 1200
Chemical Feed Pumps (each) 400 - 800
Chemical Storage Tanks (up to 250 gallons)
Gas Chlorinator
(500 Ibs/day to 2000 Ibs/day) 1700 - 4000
Weighing Scale for Chlorine 350 - 500
60
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For a 10-15 mgd plant, a typical gaseous chlorine based chlorine dioxide
could cost $3000 to $4000 for materials and another $3000 to $5000 for
installation.
In Europe, the CIFEC system is becoming quite popular for generating
chlorine dioxide at water treatment plants. The manufacturer reports that
the capital cost for a 20 kg chlorine dioxide/hr (1058 pounds chlorine
dioxide/day) CIFEC system is about $100,000 (1977). Installation costs
are not included. A 200 g chlorine dioxide/hr (11 pounds/day) CIFEC system
costs about $24,000 (1977).
CONCLUSIONS
Chlorine dioxide, when free of chlorine, does not form
trihaloraethane compounds in drinking water processes. It is
less likely than chlorine to form chlorinated compounds with
most organic substances commonly found in raw water supplies.
Chlorine dioxide is effective in oxidizing organic complexes
of iron and manganese, imparts no taste and odor to the treated
water, and provides a very stable, long lasting oxidant residual.
The technology of chlorine dioxide generation is well established
and recent innovations have increased process efficiency.
There are no unduly hazardous aspects in the operation of
most chlorine dioxide systems when operated with care.
The European plants visited, and those responding to the
questionnaire, appeared for the most part to understand
and properly apply the chemical. By contrast, many of the
U.S. plants surveyed and/or visited demonstrated a limited
understanding of the process, often leading to incorrect and
inefficient operation of the chlorine dioxide system.
The cost of producing and using chlorine dioxide is considerably
higher than that of chlorine in both the U.S. and Europe.
Consequently, its use generally is limited to those locations
where chlorine cannot meet process needs.
61
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Appendix A
CONDENSED BIBLIOGRAPHY
Chedal, J., "Modes of Disinfecting Action of Ozone Stage Diffusion" Presented
at the International Symposium on Ozone and Water, Wasser Berlin,
May 1977, AMK-Berlin, International Ozone Inst., Cleveland, Ohio (1977).
Coin, L., Hannoun, C., & Cornelia, C., "Inactivation of Poliomyelitis Virus
by Ozone in the Presence of Water", le Presse Med. 72(37):2153-56
(1967).
Dellah, A., "Study of Ozone Reactions Involved in Water and the Present
Chlorination Controversy", Proc. Sec. Intl. Symp. on Ozone Technology,
R.G. Rice, P. Pichet & M.-A. Vincent, Editors, Intl. Ozone Inst.,
Cleveland, Ohio, (1975), pp. 161-168.
Diaper, E.W.J., "Practical Aspects of Water and Wastewater Treatment by
Ozone", Ozone in Water and Wastewater Treatment, edited by Francis
L. Evans III, Editor, Ann Arbor Science Publishers, Inc., Ann Arbor
Michigan, 1972.
Eberhardt, M., Madsen, S., & Sontheimer, H., 1974, "Untersuchungen zur
Verwendung Biologisch Arbeitender Aktivkohlefilter bei der Trinkwasser-
aufbereitung", Heft 7, Veroffentlichungen des Bereichs u. des Lehrstuhls
fur Wasserchemie Leitung: Prof. Dr. H. Sontheimer; Univ. of Karlsruhe,
Germany (1974); also Wasser/Abwasser 116 (6):245-247.
Eisenhauer, H.R., "The Ozonization of Phenolic Wastes", J. Water Poll.
Control Fed. 40(11):1887-1899.
Gall, R.J., "Chlorine Dioxide: An Overview of Its Preparation, Properties
and Uses", in Ozone/Chlorine Dioxide Oxidation Products of Organic
Materials, R.G. Rice & J.A. Cotruvo, Editors Intl. Ozone Inst., Cleveland,
Ohio (1978), pp. 356-382.
Gilbert, E., 1976, "Reactions of Ozone With Organic Compounds in Dilute
Aqueous Solution: Identification of Their Oxidation Products", Ozone/
Chlorine Dioxide Oxidation Products of Organic Materials, R.G. Rice
and J.A. Cotruvo, Editors, Intl. Ozone Inst., Cleveland, Ohio (1978).
62
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Cornelia, C., & Versanne, D., 1977, "Le Role de 1'Ozone dans la Nitrification
Bacterienne de I1 Azote Atnmoniacal Gas de 1'Usine de la Chapelle
Banlieue Sud de Rouen (Seine Maritime) France", Presented at 3rd
Intl. Symp. on Ozone Technology, Paris, France, May 1977, Intl. Ozone
Inst., Cleveland, Ohio.
Guirguis, W.A., Jain, J.S., Hanna, Y.A. & Srivastava, P.K., 1976, "Ozone
Application for Disinfection in the Westerly Advanced Wastewater
Treatment Facility", in Forum on Ozone Disinfection, E.G. Fochtman,
R.G. Rice & M.E. Browning, editors. Intl. Ozone Inst., Cleveland,
Ohio, pp. 363-381.
Guirguis, W.A., Melnyk, P.B. & Harris, J.P., 1976, "The Negative Impact
of Industrial Waste on Physical-Chemical Treatment", Presented
at 31st Purdue Indl. Waste Conf., Lafayette, Indiana, May, 1976.
Hoigne, J., "Comparison of the Chemical Effects of Ozone and Irradiation
on Organic Impurities in Water", Prov. Radiation for a Clean Environment,
Intl. Atomic Energy Agency, Vienna, Austria (1974), pp. 297-305.
Kuhn, W., Sontheimer, H. & Kurz, R., 1976, "Use of Ozone and Chlorine in
Water Works in the Federal Republic of Germany", Ozone/Chlorine
Dioxide Oxidation Products of Organic Materials, Intl. Ozone Inst.,
Cleveland, Ohio (1978).
Legeron, J.P., "Chemical Ozone Demand of a Water Sample by Laboratory
Evaluation, Presented at Symp. on Advanced Ozone Technology, Nov.
16-18, 1977, Toronto, Canada, Intl. Ozone Inst., Cleveland, Ohio.
Mallevialle, J., Laval, Y., LeFebvre, M. & Rousseau, Co., 1976, "The
Degradation of Humic Substances in Water by Various Oxidation Agents
(Ozone, Chlorine, Chlorine Dioxide)", in Ozone/Chlorine Dioxide Oxidation
Products of Organic Materials, etc.
Masschelin, W. Fransolet, G., Genot, J., 1975 & 1976 "Techniques For Dispersing
and Dissolving Ozone in Water/Part 1 and Part 2". Water and Sewage Works.
McCarthy, J.J., and Smith, C.H., "A Review of Ozone and its Application to
Domestic Wastewater Treatment", J. Am. Water Works Assoc., (1974), 66:718.
McCreary, J.J. & Snoeyink, V.L., "Granular Activated Carbon in Water
Treatment", J. Am. Water Works Assoc., (1977), 69(8):437-444.
Mignot, J. (1975), "Application of Ozone With or Without Activated Carbon
For Drinking Water Treatment", in Proceedings of First Intl. Symp. on
Ozone for Water and Wastewater Treatment, R.G. Rice, M.E. Browning,
editors, Intl. Ozone Inst., Cleveland, Ohio.
Mignot, Jean, 1976, "Practique de la Mise en Contact de 1'Ozone Avec le
Liquid a Traiter", Proceedings of Second Intl. Symp. on Ozone Technology,
R.G. Rice, P. Prichet & M.-A. Vincent, editors.
63
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Mills, J.F., "Competitive Oxidation and Halogenation Reactions
in the Disinfection of Wastewater", in Ozone/ Chlorine Dioxide Oxidation
Products of Organic Materials, Intl. Ozone Inst., Cleveland, Ohio (1978).
Nadeau, M. and Pigeon, J.C., "The Evolution of Ozonation in the Province
of Quebec", in Proceedings First Intl. Symp. on Ozone for Water and
Wastewater Treatment, R.G. Rice and M.E. Browning, Editors, Intl. Ozone
Inst., Cleveland, Ohio, (1975), pp. 167-185.
Pare, Maurice, "Operational Cost of Ozone and Energetic Balance", Paper
presented at Intl. Symp. on Ozone and Water, Wasser Berlin, May 1977,
AMK Berlin, Intl. Ozone Inst., Cleveland, Ohio.
Pare, Maurice, 1976, "Production de 1'Ozone en Moyenne Frequence", in
Proceedings Second Ozone Symp. on Ozone Tech.
Prengle, H.W., Jr., Hewes, C.G., III, & Mauk, C.E., 1976, "Oxidation
of Refractory Materials by Ozone with Ultraviolet Radiation", in
Proc. Second Intl. Symp. on Ozone Tech., R.G. Rice, P. Pichet, &
M.-A Vincent, editors, Intl. Ozone Inst., Cleveland, Ohio, p. 224-252.
Richard, Y., and Brener, 1978, "Organic Materials Produced Upon Ozonization
of Water", in Ozone/Chlorine Dioxide Oxidation Products of Organic
Materials.
Richard, Y., & Fiessinger, F., 1977, "Emploi Compleraentaire des Traitraets
Ozone et Charbon Actif", Presented at 3rd Intl. Symp. on Ozone Tech.,
Paris, France, May 1977, Intl. Ozone Inst., Cleveland, Ohio.
Rook, J.J., 1977, "Chlorination Reactions of Fulvic Acids in Natural Waters",
Env. Sci. & Tech. ll(5):478-482.
Rook, J.J., 1974, "Formation of Haloforms During Chlorination of Natural Waters,"
Water Treatment and Examination, 23 (2):234-243.
Rook, J.J., 1976, "Haloforms in Drinking Water", J. Am. Water Works Assoc.,
68(3):168-172.
Rosen, H.M., 1972, editor, Ozone in Water and Wastewater Treatment,
F.L. Evans III, Editor Ann Arbor Science Publishers, Ann Arbor, Michigan.
Rosenblatt, D.H., 1976, "Chlorine Dioxide: Chemical and Physical Properties",
in Ozone/ Chlorine Dioxide Oxidation Products of Organic Materials.
Schalekamp, M., "Experience in Switzerland with Ozone, Particularly
in Connection with the Neutralization of Hygienically Undesirable
Elements Present in Water", Presented at Intl. Symp. on Ozone & Water,
Wasser, Berlin, Germany, May 1977, AMK Berlin, Intl. Ozone Inst.,
Cleveland, Ohio (1977).
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Sontheimer, H., "Biological Treatment of Surface Waters in Activated
Carbon Filters", presented at Seminar on Current Status of Wastewater
Treatment & Disinfection with Ozone, Cleveland, Ohio, September 15,
1977, Intl. Ozone Inst., Cleveland, Ohio (1977).
Sontheimer, H., Heilker, E., Jekel, M., Nolte, H. & Vollmer, F.-H.,
"The Mulheim Process" J. Am. Water Works Assoc. (1978).
Sontheimer, H. & Maier, D., "Untersuchungen zur Verberserung der
Trinkwasseraufbereitungstechnologie am Niederrhein (1. Bericht)",
Wasser/Abwasser (1972) 113:187-193.
J. Valenta, W. Gahler, "Chlordioxidanlage", Gas-Wasser-Abwasser,
55(9):566-569 (1975).
White, G.C., 1972, Handbook of Chlorination, Van Nostrand Reinhold Co.,
New York, N.Y., pp. 592-624.
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Appendix B
LIST OF OZONE EQUIPMENT MANUFACTURERS
Accelerators, Inc.
212 Industrial Boulevard
Austin, Texas 78764
Alron Industries
4800 Dewey Avenue
Rochester, New York 14612
Benckiser Wassertechnik GmlH
6905 Schriesheim
Postfach 8, Germany
Brown, Boveri & Co., Ltd.
CH-5401
Zurich, Switzerland
Chemie und Filter GmbH
Verfahrenstechnik KG
D-6900
Heidelberg, Germany
Crane-Cochrane
P.O. Box 191
King of Prussia
Pennsylvania 19406
D-3 Company
4935 McConnell Avenue
Unit No. 7
Los Angeles, California 90066
Degremont
183 Aye. du 18 Juin 1940
92400 Rueil-Malmaison
Paris, France
Degremont Infilco, Ltd.
2015 Drummond Street
Montreal, Quebec H3G 1W7
Canada
DEMAG Metallgewinnung
Konigstrasse 57
4100 Duisburg 1, Germany
Erwin Sander Elektro-Apparatebau
3151 Eltze
Am Osterberg, Germany
Gebruder Herrmann
P.O. Box 300460
D5 Kohn-Ehrenfeld
Federal Republic of Germany
KERAG
CH-8805
Ritchterswil, Switzerland
Mather & Platt
Anti-Pollution Systems Ltd.
14 Buckingham Palace
London SW1 OQP England
Messer Griesheim
Homberger Strasse 12
Postfach 4709
400 Dusseldorf 1
OREC
Ozone Research & Equipment Corp.
3840 North 40th Avenue
Phoenix, Arizona 85019
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Ozomatic Water Purifier Co.
8343 Northeast Third Court
P.O. Box 381475
Miami, Florida 33138
Ozono Electronica Internazionale
Milano, Italy
PCI Ozone Corporation
One Fairfield Crescent
West Caldwell, New Jersey 07006
Pielkenroad Separation Co.
P.O. Box 53563
Houston, Texas 77052
Pure Air Products
949 White Bridge Road
Wilmington, New Jersey 07946
Pure-0-Zone
P.O. Box 82552
Atlanta, Georgia 30341
RHENO
CH-8952 Schlieren
Switzerland
Sauter AG
Geschaftsbereich Umwelttechnik
Lorracher Strasse 102
CH-4125 Richen
Switzerland
Scientific Industries of California
10632 Trask Avenue
Garden Grove, California 92643
Skandital Italiana
Via Valvassori Peroni 55
20133 Milano, Italy
Til Corporation
100 North Strong Avenue
Lindenhurst, New York 11757
Trailigaz
29-31 Bid. de la Muette
95140 Garges Des Gonesse
France
Union Carbide Corporation
P.O. Box 44
Tonowanda, New Yor 14150
U.S. Ozonair Corporation
1025 Grandview Drive
South San Francisco
California 94080
Welbach-Trailigaz Ozone Systems
Corporation
3340 Stokley Avenue
Philadelphia, Pennslyvania 19129
67
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
EPA-600/8-78-018
2.
3. RECIPIENT'S ACCESSIOt*NO.
4. TITLE AND SUBTITLE
AN ASSESSMENT OF OZONE AND CHLORINE DIOXIDE TECHNOL-
OGIES FOR TREATMENT OF MUNICIPAL WATER SUPPLIES
Executive Summary
5. REPORT DATE
October 1978 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
G. Wade Miller, R. G. Rice, C. Michael Robson,
Ronald L. Scullin, Wolfgang Klihn, and Harold Wolf
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Public Technology, Incorporated
1140 Connecticut Avenue, N.W.
Washington, D.C. 20036
10. PROGRAM ELEMENT NO.
1CC614
11. CONTRACT/GRANT NO.
R804385-01
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research LaboratoryCin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: J. Keith Carswell 513/684-7228.
See also full report EPA-600/2-78-147.
16. ABSTRACT
This executive summary covers in abbreviated form each of the principal topics of the
full report. Emphasis in the summary, and in the full report, is given to the funda-
mental uses and engineering design of ozone/chlorine dioxide systems. A limited
discussion of Biological Activated Carbon is included. Data from extensive question-
naires and from site surveys of several hundred drinking water utilities are included
in the full report and summarized herein.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Ozone, Water supply, Water treatment
devices, Engineering costs
Chlorine dioxide,
Oxidation products,
Drinking water treatment,
Engineering design, Bio-
logical activated carbon,
Canada, Western Europe,
United States
13B
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
78
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
68 #U.S. GOVERNMENT PRINTING OFFICE: 1978-657-060/1485 Region No. 5-11
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