United States Office of Water EPA 832-F-99-063

Environmental Protection Washington, D.C. September 1999 Agency

Wastewater
Technology Fact Sheet
Ozone Disinfection
DESCRIPTION bearing gas. Ozone is
generated onsite because it
Disinfection is considered is unstable and decomposes
to be the primary to elemental oxygen in a
mechanism for the short amount of time after
inactivation/destruction of generation.
pathogenic organisms to
prevent the spread of Ozone is a very strong
waterborne diseases to oxidant and virucide. The
downstream users and the mechanisms of disinfection
environment. It is using ozone include:
important that wastewater
be adequately treated prior • Direct
to disinfection in order for oxidation/destructio
any disinfectant to be n of the cell wall
effective. Table 1 lists with leakage of
some common cellular constituents
microorganisms found in outside of the cell.
domestic wastewater and
the diseases associated • Reactions with
with them. radical by-products
of ozone
Ozone is produced when decomposition.
oxygen (O2) molecules are
dissociated by an energy • Damage to the
source into oxygen atoms constituents of the
and subsequently collide nucleic acids
with an oxygen molecule to (purines and
form an unstable gas, pyrimidines).
ozone (O3), which is used
to disinfect wastewater. • Breakage of
Most wastewater treatment carbon-nitrogen
plants generate ozone by bonds leading to
imposing a high voltage depolymerization.
alternating current (6 to 20
kilovolts) across a TABLE 1 INFECTIOUS
dielectric discharge gap AGENTS
that contains an oxygen-
 POTENTIALLY PRESENT IN and the concentration of the ozone.
UNTREATED DOMESTIC A line diagram of the ozonation
WASTEWATER process is shown in Figure 1. The
components of an ozone
Organism Disease Caused
disinfection system include feed-
Bacteria gas preparation, ozone generation,
Escherichia coli ozone contacting, and ozone
(enterotoxigenic) Gastroenteritis
destruction.
Leptospira (spp.) Leptospirosis
Salmonella typhi Typhoid fever
Air or pure oxygen is used as the
Salmonella (=2,100 serotypes) feed-gas
Salmonellosis source and is passed to
Shigella (4 spp.) Shigellosisthe ozone generator at a set flow
(bacillary
dysentery) rate. The energy source for
Vibrio cholerae Cholera production is generated by
Protozoa electrical discharge in a gas that
Balantidium coli contains oxygen. Ozone generators
Balantidiasis
Cryptosporidium parvum are typically classified by:
Cryptosporidiosis
Entamoeba histolytica Amebiasis (amoebic
dysentery) • The control mechanism
Giardia lamblia Giardiasis (either a voltage or
Helminths frequency unit).
Ascaris lumbricoides Ascariasis
T. solium Taeniasis
• The cooling mechanism
(either water, air, or water
Trichuris trichiura Trichuriasis
plus oil).
Viruses
Enteroviruses (72 types, e.g., Gastroenteritis,
polio, echo, and coxsackie
•
heart anomalies,
The physical arrangement
viruses) meningitis of the dielectrics
Hepatitis A virus Infectious hepatitis (either vertical or
Norwalk agent Gastroenteritis horizontal).
Rotavirus Gastroenteritis
Source: Adapted from Crites and
• The name of the inventor.
Tchobanoglous, 1998.
However, generators
When ozone decomposes in water, manufactured by different
the free radicals hydrogen peroxy companies have unique
(HO2) and hydroxyl (OH) that are characteristics but also
formed have great oxidizing have some common
capacity and play an active role in configurations.
the disinfection process. It is
generally believed that the bacteria The electrical discharge
are destroyed because of method is the most
protoplasmic oxidation resulting in common energy source
cell wall disintegration (cell lysis). used to produce ozone.
Extremely dry air or pure
The effectiveness of disinfection oxygen is exposed to a
depends on the susceptibility of the controlled, uniform high-
target organisms, the contact time, voltage discharge at a high
or low frequency. The dew chamber can be recycled to
point of the feed gas must generate ozone or for reuse in the •
be -60EC (-76EF) or lower. aeration tank. The ozone off-gases
The gas stream generated that are not used are sent to the
from air will contain about ozone destruction unit or are
0.5 to 3.0% ozone by recycled.
weight, whereas pure •
oxygen will form The key process control
approximately two to four parameters are dose,
times that concentration. mixing, and contact time.
An ozone disinfection
After generation, ozone is system strives for the
fed into a down-flow maximum solubility of
contact chamber containing ozone in wastewater, as
the wastewater to be disinfection depends on the
disinfected. The main • transfer of ozone to the
purpose of the contactor is wastewater. The amount of
to transfer ozone from the ozone that will dissolve in
gas bubble into the bulk wastewater at a constant
liquid while providing temperature is a function of
sufficient contact time for the partial pressure of the
disinfection. The gaseous ozone above the
commonly used contactor water or in the gas feed
types diffused bubble (co- stream.
current and counter- There are no harmful residuals that
current) are positive need to be removed after ozonation
pressure injection, negative because ozone decomposes
pressure (Venturi), rapidly.
mechanically agitated, and
packed tower. Because After ozonation, there is no
ozone is consumed quickly, regrowth of microorganisms,
it must be contacted except for those protected by the
uniformly in a near plug particulates in the wastewater
flow contactor. stream.

The off-gases from the contact Ozone is generated onsite, and

chamber must be treated to destroy thus, there are fewer safety
any remaining ozone before problems associated with shipping
release into the atmosphere. and handling.
Therefore, it is • essential to
maintain an optimal ozone dosage Ozonation elevates the dissolved
oxygen (DO)
Disadvantage
s

for better efficiency. When pure concentration of the effluent. The

oxygen is used as the feed-gas, the increase in DO can eliminate the
off-gases from the contact need for reaeration and also raise
the level of DO in the receiving stream.

It is critical that all ozone C The ozonation

disinfection systems be pilot process
tested and calibrated prior to utilizes a short
installation to • ensure they contact time
meet discharge permit (approximatel
requirements for their y 10 to 30
particular sites. minutes).
•
APPLICABILITY Low dosage may not
effectively inactivate some
Ozone disinfection is generally viruses, spores, and cysts.
used at medium to large sized
plants after at least secondary Ozonation is a more complex
treatment. technology than is chlorine
In addition to disinfection, or UV disinfection, requiring
another common use for • complicated equipment and
ozone in wastewater treatment efficient contacting systems.
is odor control.
Ozone is very reactive and
Ozone disinfection is the least corrosive, thus requiring
used method in the U.S. corrosion-resistant material
although this technology has such as stainless steel.
been widely • accepted in
Europe for decades. Ozone Ozonation is not economical
treatment has the ability to for wastewater with high
achieve higher levels of levels of suspended solids
disinfection than either (SS), biochemical oxygen
chlorine or UV, however, the demand (BOD), chemical
capital costs as well as oxygen demand, or total
maintenance expenditures are organic carbon.
not competitive with available
alternatives. Ozone is Ozone is extremely irritating
therefore used only sparingly, and possibly toxic, so off-
primarily in special • cases gases from the contactor
where alternatives are not must be destroyed to prevent
effective. worker exposure.

ADVANTAGES AND The cost of treatment can be

DISADVANTAGES relatively high in capital and
• in power intensiveness.
Advantages
PERFORMANCE
C Ozone is more effective than
chlorine in destroying
viruses and bacteria.
Belmont and Southport Wastewater included the recent
Treatment Plants in Indianapolis, installation of a pilot-scale
Indiana ozone contactor to allow the
plant staff to measure ozone
In 1985, the City of Indianapolis, demand on a daily basis.
Indiana, operated two-125 million Also, tracer tests were
gallons per day (mgd) advanced conducted to measure
wastewater treatment plants at contactor short-circuiting
Belmont and Southport using ozone potential. Results
disinfection. The rated capacity of the demonstrated a noticeable
oxygen-fed ozone generators was benefit of adding additional
6,380 pounds per day, which was used baffles. Results also
to meet geometric mean weekly and indicated operating strategies
monthly disinfection permit limits for that could maximize fecal
fecal coliforms of 400 and 200 per coliform removal, such as
100 ml, respectively. reducing the number of
contactors in service at low
Disinfection was required at both and moderate flow
Indianapolis treatment plants from conditions.
April 1 through October 31, 1985.
Equipment performance OPERATION AND
characteristics were evaluated during MAINTENANCE
the 1985 disinfection season and
consequently, disinfection Ozone generation
performance was optimized during the uses a significant
1986 season. The capital cost of both amount of electrical
ozone systems represented about 8% power. Thus,
of the plants' total construction cost. constant attention
The ozone system’s must be given to the
Operation and Maintenance (O&M) system to ensure that
cost represented about 1.9% and 3.7% power is optimized
of the total plant O&M costs at the for controlled
Belmont and Southport plants, disinfection
respectively. performance.

In 1989, a disciplined process There must be no

monitoring and control program was leaking connections
initiated. Records indicated a in or surrounding the
significant effect on process ozone generator. The
performance due to changes in operator must on a
wastewater flow, contactor influent regular basis monitor
fecal coliform concentration, and the appropriate
ozone demand. subunits to ensure
that they are not
Previously, ozone demand information overheated.
was unknown. Several studies were Therefore, the
conducted to enable better control of operator must check
the ozone disinfection process. These for leaks routinely,
since a very small leak can problem occurs. All
cause unacceptable ambient safety equipment
ozone concentrations. The should be available
ozone monitoring equipment for operators to use in
must be tested and calibrated case of an
as recommended by the emergency. Key
equipment manufacturer. O&M parameters
include:
Like oxygen, ozone has limited
solubility and decomposes • Clean feed
more rapidly in water than in gas with a
air. This factor, along with dew point of
ozone reactivity, requires that -60EC (-
the ozone contactor be well 76EF), or
covered and that the ozone lower, must
diffuses into the wastewater as be delivered
effectively as possible. to the ozone
generator. If
Ozone in gaseous form is the supply gas
explosive once it reaches a is moist,
concentration of 240 g/m3.
Since most ozonation systems the reaction of
never exceed a gaseous ozone the ozone and
concentration of 50 to 200 the moisture
g/m3, this is generally not a will yield a
problem. However, ozone in very corrosive
gaseous form will remain condensate on
hazardous for a significant the inside of
amount of time thus, extreme the ozonator.
caution is needed when The output of
operating the ozone gas the generator
systems. could be
lowered by
It is important that the ozone the formation
generator, distribution, of nitrogen
contacting, off-gas, and ozone oxides (such
destructor inlet piping be as nitric acid).
purged before opening the
various systems or subsystems. • Maintain the
When entering the ozone required flow
contactor, personnel must of generator
recognize the potential for coolant (air,
oxygen deficiencies or trapped water, or
ozone gas in spite of best other liquid).
efforts to purge the system.
The operator should be aware • Lubricate the
of all emergency operating compressor or
procedures required if a
 blower in accordance wastewater. The
with the costs are based on the
manufacturer's wastewater having
specifications. Ensure passed through both
that all compressor primary and
sealing gaskets are in secondary treatment
good condition. processes of a
properly designed
• Operate the ozone system (the BOD
generator within its content does not
design parameters. exceed 30 milligrams
Regularly inspect and per liter [mg/L] and
clean the ozonator, air the SS content is less
supply, and dielectric than 30 mg/L). In
assemblies, and general, costs are
monitor the largely influenced by
temperature of the site-specific factors,
ozone generator. and thus, the
estimates that follow
• Monitor the ozone gas- are typical values and
feed and distribution can vary from site to
system to ensure that site.
the necessary volume
comes into sufficient Because the
contact with the concentration of ozone
wastewater. generated from either air
or oxygen is so low, the
• Maintain ambient transfer efficiency
levels of ozone below TABLE 2 TYPICAL
the limits of applicable COST ESTIMATE OF
AN OZONE
safety regulations.
DISINFECTION
COSTS Items Cos

The cost of ozone disinfection Capital Costs

systems is dependent on the Oxygen feed gas and compressor $245
manufacturer, the site, the
Contact vessel (500 gpm) $4,0
capacity of the plant, and the
characteristics of the Destruct unit:
wastewater to be disinfected. Small (around 30 cfm) $800
Ozonation costs are generally
Large (around 120) $1,0
high in comparison with other
disinfection techniques. Non-component costs $35,

Engineering $12,
Table 2 shows a typical cost
estimate (low to medium) for Contingencies 30%
ozone disinfection system used $12,
Annual O&M Costs
to disinfect one mgd of
 Labor acquired by John
Wiley & Sons, Inc.).
Power 90 kW
New York, New
Other (filter replacements, $6,500 York. pp. 209–213.
compressor oil, spare dielectric, etc.)
gpm = gallons
per minute cfm
3. Metcalf & Eddy, Inc.
= cubic feet per 1991. Wastewater
minute Engineering:
Source: Champion Technology, 1998. Treatment, Disposal,
and Reuse. 3d ed.
to the liquid phase is a critical The McGraw-Hill
economic consideration. For this Companies. New
reason, the contact chambers used are York, New York.
usually very deep and covered.
4. Rakness, K. L.; K. M.
The overall cost of an ozonation Corsaro; G. Hale; and
system is also largely determined by B. D. Blank.
the capital and O&M expenses. The 1993. "Wastewater
annual operating costs for ozone Disinfection with
disinfection include power Ozone: Process
consumption, and supplies, Control and
miscellaneous equipment repairs, and Operating Results."
staffing requirements. Ozone: Science and
Engineering. vol. 15.
Another consideration for the cost is no. 6. pp. 497–514.
that each ozonation system is site
specific, depending on the plant’s 5. Rakness, K. L.; R. C.
effluent limitations. Chemical Renner; D. B.
suppliers should be contacted for Vornehm; and J. R.
specific cost information. Thaxton. 1988.
"Start-Up and
REFERENCES Operation of the
Indianapolis Ozone
1. Crites, R. and G. Disinfection
Tchobanoglous. 1998. Small Wastewater
and Decentralized Systems." Ozone:
Wastewater Science and
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New York, New York.
6. Rudd, T. and L. M.
2. Martin, E. J. and E. T. Martin. Hopkinson.
1991. Technologies for December 1989.
Small Water and "Comparison
Wastewater Systems. of
Environmental Disinfection
Engineering Series. Van
Nostrand Reinhold (now
 Techniques for Sewage and 11. Rasmussen, Karen
Sewage (Frost & Sullivan).
Effluents." Journal of 1998. Pollution
International Water and Engineering Online.
Environmental Management. “Market Forecast:
vol. 3. pp. 612–618. Wastewater
Treatment Equipment
7. Task Force on Wastewater Markets.” WEFTEC,
Disinfection. 1986. Orlando, FL.
Wastewater Disinfection.
Manual of Practice No. FD-10. ADDITIONAL
Water Pollution Control INFORMATION
Federation. Alexandria,
Virginia. Mark Boner, P.E.
WWETCO
8. U.S. Environmental Protection 1825 2nd Avenue
Agency (EPA). 1986. Design Columbus, GA 31901
Manual: Municipal
Wastewater Disinfection. EPA Roy F. Weston Inc.
Office of Peter J. Lau
1515 Market
9. Research and Development. Street, Suite
Cincinnati,Ohio. EPA/625/1- 1515
86/021. Philadelphia,
PA 19102-1956
10. Water Environment Federation
(WEF). 1996. Operation of The mention of trade
Municipal Wastewater names or commercial
Treatment Plants. Manual of products does not
Practice No. 11. 5th ed. vol. 2. constitute endorsement
WEF. Alexandria, Virginia. or recommendation for
use by the U.S.
Environmental
Protection Agency.

The technical content of this fact sheet was provided by the National
Small Flows Clearinghouse and is gratefully acknowledged.