v>EPA
                       United States
                       Environmental Protection
                       Agency
                       Off ice of Water
                       Washington, D.C.
EPA 832-F-99-033
September 1999
Combined Sewer Overflow
Technology  Fact  Sheet
Alternative Disinfection  Methods
DESCRIPTION

Combined sewer overflows (CSOs) occur when
flows exceed the hydraulic capacity of either the
wastewater treatment plant  (WWTP)  or  the
collection system that transports the combined
flow of storm water and sanitary sewage to the
WWTP.  When an overflow occurs, the excess
flows tend to be discharged into a receiving body
of water.  CSOs typically discharge a  variable
mixture of raw sewage,  industrial/commercial
wastewater, polluted runoff, and scoured materials
that build up in the collection system during dry
weather periods.  These  discharges contain a
variety of pollutants that may adversely impact the
receiving  water body,  including pathogenic
microorganisms, viruses, cysts, and chemical and
floatable materials. Health risks associated with
bacteria-laden water may  result through dermal
contact with the discharge, or through ingestion of
contaminated water or shellfish.

Preliminary reduction of microorganisms  and
bacteria may be accomplished through  physical
reduction of solids in the  wastewater, primarily
through sedimentation,  flotation, and filtration.
Following solids reduction, most systems further
reduce  bacterial  concentrations   through
disinfection.    Disinfection  occurs  as  the
wastewater is brought into contact with oxidizing
chemicals (such as chlorine, bromine, ozone,
hydrogen peroxide, and related compounds).

Chlorine has long been the disinfectant of choice
for most disinfection systems.  It offers reliable
reduction of  pathogenic  microorganisms at
reasonable  operating costs.   (See  EPA's CSO
Technology   Fact   Sheet  832-F-99-021,
Disinfect!on-Chlorination, for more information).
                      While chlorine disinfection is the most common
                      method used to kill pathogenic microorganisms at
                      wastewater treatment plants, this methodology
                      may not be  feasible at  all  CSOs for several
                      reasons, including:

                            CSOs occur intermittently and their flow
                            rate is highly variable, thus  making it
                            difficult  to  regulate  the  addition  of
                            disinfectant.

                      •     CSOs  have  high   suspended  solids
                            concentrations.

                            CSOs vary widely in temperature  and
                            bacterial composition.

                      •     Residual  disinfectants  from  chlorine
                            disinfection  may be  prohibited from
                            receiving waters.

                      •     CSO outfalls are often located in remote
                            areas  and thus may require automated
                            disinfection systems.

                      In addition to these problems, the increased health
                      and safety concerns regarding the use of chlorine
                      to disinfect CSOs has prompted the development
                      of alternative disinfectants,  which often pose
                      fewer problems  and hazards.  Alternatives to
                      chlorine have been developed and evaluated for
                      continuous disinfection of wastewater discharges
                      to small streams or sensitive water bodies, and are
                      now being considered for treatment of CSOs and
                      other episodic discharges.

                      This fact sheet  addresses the use of chlorine
                      dioxide, ozonation, ultraviolet radiation, peracetic

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acid and Electron Beam Irradiation (E-Beam) to
treat CSOs.

Chlorine Dioxide

Studies have shown that chlorine dioxide is an
effective wastewater disinfectant, although its use
in the United States is limited.  Chlorine dioxide
is applied to wastewater as a gas that is generated
on-site using excess  chlorine.  Although  it is
relatively  easy  and  economical   to  produce
chlorine dioxide is unstable and reactive and any
transport is hazardous.

Chlorine dioxide is effective at oxidizing phenols,
but does not react with aquatic humus to produce
trihalomethanes (THMs).  However, any excess
chlorine  remaining  from the  generation  of
chlorine   dioxide   would  react  with  THM
precursors and form THMs. Therefore, operators
must be careful to use the correct amounts  of
chlorine when generating chlorine dioxide.  And
while  chlorine  dioxide will  not react   with
wastewater to form chloramines, it can produce
potentially toxic byproducts such as chlorite and
chlorate.

Ozonation

Ozone is  a strong oxidizer and  is applied  to
wastewater  as a gas.  Its use  in CSO treatment
facilities for wastewater disinfection is relatively
new in the United States, and there are few
facilities currently using ozone for disinfection.
This can be potentially attributed to high initial
capital costs associated with ozone generation
equipment. Ozone is equal or superior to chlorine
in "killing"  power, but  it does not cause the
formation  of halogentated organics  as   does
chlorination.

Ultraviolet (UV) Radiation

UV radiation is one example of electromagnetic
radiation used for disinfection.  UV disinfection
incorporates the spectrum of light between 40
nanometers  and 400  nanometers.   Germicidal
properties   range  between   200  and   300
nanometers, with 260 nanometers being the most
lethal.  The primary  method  for utilizing UV
disinfection is to expose wastewater  to a UV
lamp. Historically, most UV disinfection facilities
have been designed to utilize Low Pressure Low
Intensity UV lamps for disinfection. For example,
low-pressure   mercury   arc   lamps   emit
approximately 90 percent of their light energy
around 254 nanometers.

UV disinfection works by penetrating the cell
walls of pathogenic  organisms and structurally
altering  their   DNA,  thus  preventing  cell
replication and function. No hazardous chemicals
are produced or released while treating CSOs with
UV.

Because UV  is not  a chemical  disinfection
method, it disinfects without altering the physical
or chemical properties of water. However, UV
efficiency is affected by suspended solids in the
wastewater, which can scatter and absorb light.
Thus,  UV  disinfection  is  not  effective  in
wastewaters with a high TSS level.

Peracetic Acid

Peracetic acid (CH3COOOH) (PAA), also known
as ethaneperoxoic acid, peroxyacetic acid, or actyl
hydroxide, is a very  strong oxidant.  Based on
limited  demonstration data for disinfection  of
secondary treatment plant effluent, peracetic acid
appears to be an effective disinfectant and should
be evaluated further for treating  CSOs.   The
equilibrium mixture  of hydrogen peroxide and
acetic acid that produces PAA is too unstable and
explosive  to transport, and  so PAA must be
produced  on site.  The decomposition of PAA
results in acetic acid, hydrogen peroxide and
oxygen.

Electron Beam Irradiation

Electron Beam Irradiation (E-Beam) uses a stream
of high  energy electrons that are directed into a
thin film of water or sludge. The electrons break
apart water molecules and produce a large number
of highly reactive chemical species.  There are a
few reactive species  formed during this process
and include oxidizing hydroxyl radicals, reducing
aqueous electrons and hydrogen atoms.

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APPLICABILITY

A  brief  summary  illustrating  the   general
applicability of chlorine dioxide, peracetic acid
and UV radiation as alternative CSO disinfectants
is provided in Table 1. While ozonation and the
E-Beam process are discussed in this fact sheet as
potential alternative disinfectants for CSOs, they
are not currently considered  practical for CSO
disinfection and thus they are not included in
Table 1. Because ozone must be generated on-site
and the amount  generated is dependent on the
demand,  ozone   is  not  currently  considered
practical for intermittent use in situations where
the system would be frequently turned on and off
or where there are wide fluctuations in flow rate
and  disinfection  demand,  such  as in  CSO
treatment applications. The E-Beam system was
initially  developed   for  the  disinfection  of
municipal wastewater treatment plant sludge and
the destruction of hazardous organic compounds,
and  it has  not  been   evaluated for  CSO
disinfection. EPA will continue to evaluate the E-
Beam   system   as  a  promising  innovative
technology for wastewater technology.

ADVANTAGES AND DISADVANTAGES

As discussed above, one of the primary reasons
for seeking alternatives to chlorine disinfection of
CSOs  is the growing concern  over safety  in
handling gaseous chlorine and the possible toxic
side effects of treatment with chlorine. Studies on
alternative disinfectants such as peracetic acid,
ozone, E-Beam, and UV, have shown that these
alternatives serve as good substitutes for chlorine
because  they  produce no  toxic  byproducts.
Although   chlorine  dioxide   does  produce
byproducts and  residuals, the  limited use  of
chlorine  dioxide  in this  country  has  made it
difficult to assess these byproducts for toxicity.

The alternatives to chlorine for CSO disinfection
are  not  problem-free,   however,  and   their
effectiveness depends  on  the  physical  and
chemical characteristics of the wastewater (e.g.,
the presence  of  large  particles  may hinder
disinfection). They require certain storage and use
precautions,  and  disinfection  residuals  and
byproducts may be a concern in receiving waters.
As discussed above, Table 1 provides comparative
data for chlorine dioxide, peracetic acid, and UV
radiation to help in determining which compounds
may  be  most   advantageous  for  specific
applications.  The following sections  summarize
the advantages  and disadvantages  of using
ozonation and  E-Beam  as  alternative  CSO
disinfectants.

Ozonation: Advantages

•  More powerful disinfectant than most chlorine
   compounds.

•  Inactivates most strains of bacteria  and viruses
   and is noted for destroying chlorine-resistant
   strains  of   both.   Highly  effective   for
   Cryptospiridium eradication.

•  Will  oxidize  phenols   with  no negative
   residuals such as trihalomethane production.

•  Does not produce a disinfection residual that
   would prevent bacterial growth.

•  Degenerates into  oxygen, which can elevate
   oxygen levels in treated water. It does not alter
   pH of water.

•  Increases coagulation.

•  Helps remove iron and manganese.

•  Has taste and odor control properties.

•  Requires short contact time

Ozonation:  Disadvantages

•  More  costly  than  traditional   chlorinated
   disinfection techniques.

•  Forms nitric oxides and nitric acid which can
   lead to corrosion.

•  Ozone is chemically unstable  as  a gas, and
   hazardous to transport. It must be generated on
   site and used immediately.

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                     TABLE 1 SUMMARY OF GENERAL ATTRIBUTES OF
                        CHLORINE DIOXIDE, PAA AND UV RADIATION
                                          CIO,
           PAA
UV RADIATION
Stability
Persistent Residual
Potential Byproduct Formation
Reacts with Ammonia
pH Dependent
Ease of Operation
Temperature Dependent
Contact Time
Safety Concerns
Effectiveness as Bactericide
Effectiveness as Viricide
Likelihood of Regrowth
Moderate
Moderate
Yes
No
Moderate
Moderate
Moderate
Moderate
High
High
High
None
Low
None
No
No
No
Complex
Complex
Low
High
High
High
None
High
None
No
No
No
Simple to Complex
Simple to Complex
Low
Low
High
High
High
Source: Compiled from various sources.

E-Beam: Advantages

Currently, there is insufficient information on the
E-Beam process to make a full determination of
its usefulness for CSO disinfection, but a pilot
study  performed  for  the  New  York  City
Department  of   Environmental   Protection
(NYCDEP) determined several advantages of the
E-Beam system:

•  No disinfectant chemicals required.

•  No toxic byproducts are known to be produced.

•  Short contact time required.

•  Potential  to  deactivate a wide  range   of
   pathogens.

•  Potential to penetrate waste streams with high
   solids concentrations.

E-Beam:  Disadvantages

•  Increased safety considerations due to use of
   high- voltage technology and the generation of
   X-ray radiation.
•  No full scale application experience for CSOs.

•  High capital costs.

•  High O&M costs.

•  Thin process flow stream.

•  Abundant pretreatment straining of influent is
   required for this delivery system.

DESIGN CRITERIA

Design criteria for different disinfection systems
will differ based on site-specific needs. However,
the following general factors  should  always be
considered  when  evaluating  disinfection
alternatives.

•  Safety (transport and storage in inhabited areas,
   potential for release)

•  Effectiveness  (ability  to  reduce  indicator
   organisms  to  target   levels,   reliability,
   conditions of use)

•  Cost (capital cost, operation and maintenance,
   amortization cost)

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•  Complexity   of  use  (on-site  generation,
   application and control, flexibility)

•  Environmental/adverse   effects   (aquatic
   toxicity, persistent residuals, formation of toxic
   or bio-accumulating byproducts)

•  Flow and wastewater characteristics (range of
   flows, duration of event, TSS  concentration,
   downstream  channel conditions, monitoring
   and control points)

Generally, the efficacy of a disinfectant depends
on factors such as the flow rate, volume, pH, TSS
concentration, and temperature of the wastewater.
For CSOs, these factors vary from location to
location, and even  from discharge  event  to
discharge event, and thus a typical concentration,
contact time, and mixing intensity for a particular
disinfectant is difficult to characterize.   CSO
facilities will need to conduct preliminary baseline
studies to characterize the range of conditions that
exist for a particular area and the design criteria to
be considered.

Chlorine Dioxide

Chlorine dioxide is an effective bactericide and
viricide that works over a wide range of pH values
but is unstable and explosive as a gas.   On-site
generation  of C1O2  may  be accomplished by
combining sodium chlorite with either aqueous or
gaseous chlorine (Reaction 1). C1O2 can also be
produced by combining  sodium chlorite with
hydrochloric acid (Reaction 2).

Reaction 1:

2NaClO2 + C12 -> 2C1O2 + 2NaCl (chlorine)

Reaction 2:

5NaClO2 + 4HC1 -» 4C1O2  + SNaCl  + 2H2O
(hydrochloric acid)

Reaction 1 requires 1.34 grams of sodium chlorite
to react with 0.526 grams of chlorine to produce
1 gram of C1O2  (pH of chlorine water  1.7-2.4).
Reaction 2 requires  1.67 grams of   sodium
chlorite to react with hydrochloric acid to produce
1 gram of C1O2.  Excess chlorine is typically
required  in both of these reactions, potentially
resulting in chlorinated byproducts.

A new method of C1O2 generation that does not
involve chlorine is to radiate sodium chlorite with
UV radiation as follows:
Reaction 3:
       NaClO2 + hv (254 nanometers)-
       C1O,
                         Na+ +
       Na+
H9O -»  NaOH
Chlorine dioxide produced via UV radiation does
not use aqueous or gaseous chlorine, involves a
single chemical reactant, and is cheaper while not
producing any toxic by-products.

A chlorine dioxide  disinfection system requires
chlorine dioxide generation on site by one of the
three generation methods above.  An adequate
reactor vessel with metering pumps and ancillary
piping is required.  Chlorine dioxide is directed
from the generator into an ejector, with the rate of
flow controlled by a chlorinator. The ejector is a
hydraulic chamber designed to  carry  a fraction of
wastewater flow through  it, thereby creating a
vacuum or negative pressure.  The chlorinator,
which uses a negative pressure diaphragm valve,
is triggered by the vacuum and releases gas into
the ejector as wastewater flows through. Once in
the ejector, chlorine dioxide enters into solution
and is  sent to  a diffuser where it  is mixed with
wastewater. Mixing can be accomplished  using
one of four available methods:

•  A diffuser can be placed in the center of a pipe
   or channel with flow running at full turbulence.

•  A hydraulic structure may be placed in the flow
   stream to induce turbulence (e.g., submerged
   weir, hydraulic jump).

•  A mechanical mixer (propeller, turbine) can be
   used in conjunction with a small residence time
   mixing chamber and the ejector.

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•  A jet mixer can discharge disinfectant solution
   at high pressure into the wastewater.

The degree of mixing at the point of disinfectant
application affects the initial rate of inactivation.
After mixing, wastewater enters into a contact
basin to be held for sufficient time until desired
microbial inactivation  has been attained.   The
discharge pipe or channel may be used for contact
if sufficiently long distance is available.   If a
contact chamber is to be built,  baffles should be
used to provide the longest possible pathway for
flow to minimize dispersion and approach plug
flow conditions.   The design  of the contact
chamber is dependent on the disinfectant dose, the
nature of the wastewater, and the required level of
disinfection.

Designs for an ejector should be based on the
maximum capacity of the chlorinator, the inlet
water pressure, the back pressure of the ejector
outlet,  and the distance between the ejector and
the diffuser.  The ejector should be located as
close to the mixing point as possible to minimize
both the lag in the  solution line and the back
pressure at the ejector.  The vacuum line carrying
gas between the chlorinator and ejector should
have a pressure drop of less than 0.7 pounds per
square inch. The temperature of the supply lines
and impurities in the gas are chief concerns in the
design of such a system.

Ozonation

Ozone disinfection is similar in most respects to
chlorine disinfection. The major difference is that
ozone is unstable, so it must be  generated on site.
For water treatment, ozone is  produced by an
electrical   corona   discharge   or  ultraviolet
irradiation of dry air or oxygen.  Ozone can be
injected or diffused into the water supply stream.

Ozone can be generated from any gas containing
oxygen molecules. The most common sources for
ozone generation are oxygen gas or atmospheric
air. Although the use  of pure oxygen gas will
result in a higher efficiency of ozone generation,
it will also  increase the initial cost of the gas
source.  On the other hand, using atmospheric air
requires preparation of the  gas source.   Most
ozone  generators  require  clean,  dry gas  for
optimal conditions.  Therefore, atmospheric air
must   first   be  compressed,   cleansed  and
dehumidified. Compression of the air serves to
increase the concentration of ozone in the supply.
The removal  of foreign particulates  such as dirt
and dust is often accomplished through filtration.
Air humidity is usually decreased by lowering the
dew point through refrigeration.

The solubility of ozone in water is a function of
temperature and pH.  The amount of ozone in the
system can  be regulated in the generator by
adjusting the voltage of the current or the flowrate
of the gas. The maximum ozone concentration
produced  by  a generator is 50  g/m3 and  the
maximum solubility concentration of ozone in
water is 40 mg/L.

Ozone has an average half-life of 20 minutes if it
is not oxidized by particulates. Depending on the
water quality  at a  given time, a  portion of the
dissolved  ozone may pass through the system
unoxidized.   Regulations require the resulting
concentration of ozone to be reduced to less than
0.002 mg/L before the water is released from the
plant.  Ozone degradation can be  accelerated by
the addition of hydrogen peroxide or by  passing
the system through a UVc system.  Contact time
can also be lengthened to allow for further ozone
destruction.

Ultraviolet Radiation

The following factors must be monitored for the
successful operation of a UV system:  flow rate,
suspended solids concentration, UV absorbency
coefficient, initial  and  final coliform density,
number of lamps  in operation,  average  lamp
output,  and   average  transmissibility  of  the
transmitting surface.

Two generic designs are available for disinfection
with UV. The non-contact design suspends lamps
away  from contact with the wastewater.   The
contact reactor-type design uses lamps encased in
a quartz sleeve submerged in wastewater at all
times.  The two primary types of submerged UV
systems are:

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•  Open channel (horizontal and vertical); and

•  Closed channel.

An open  channel  system submerges lamps in
either a horizontal  or vertical arrangement in an
open channel from a self-supporting stainless steel
enclosure. Lamps in both positions are arranged
perpendicular to the horizontal flow.  A closed
channel system is a sealed disinfection chamber
which can be used in  pressurized systems.  UV
lamps are installed in a stainless  steel chamber
with removable ends for interior access.  All
lamps are housed on racks (ballasts) that require
ventilation or cooling to reduce heat build up.
Excessive heat causes  failure of ballasts.

The water level in the channels must be kept fairly
constant.  Fluctuations in the water level may
result in several problems. In horizontal systems,
the top row of lamps can become exposed, or the
depth of water above this row can become so great
that adequate exposure of wastewater to UV does
not occur. Automated control valves downstream
from the UV lamps can control water level, but
these systems require electrically-operated valves
and electronic controllers.  Self-adjusting level
control gates can control upstream water levels
over a wide range of flows.  Although these gates
are inexpensive and require little maintenance,
they require proper installation and  use  more
hydraulic head than an appropriately sized control
valve or weir. Weirs may also be used to control
water level in UV tanks.  Weirs are inexpensive,
reliable, predictable, and have no moving parts.

UV dosage is dependent upon the frequency and
the intensity of UV radiation, the number of lamps
and their configuration, the  distance between the
wastewater  and the lamp surface, the chamber
turbulence, the exposure time, and the absorption
coefficient  of the   wastewater.     Design
considerations should  account for the number of
lamps required for disinfection and the number of
channels required to minimize headloss. UV dose
is  usually expressed  as  milliwatt-seconds per
square centimeter (mW-s/cm2).  Lamps emitting
wavelengths in the  range  of  250 to  265
nanometers are  usually adequate for disinfection.
Preliminary sizing and design for a system should
be based on 1.0 million gallons per day per UV
kilowatt.

UV disinfection of CSO wastewater requires that
proper UV intensity be applied to wastewater for
sufficient time to render pathogens inactive.  A
spectrophotometer can be used in a UV system to
ensure that  proper  light intensity  is delivered.
Unfortunately,  many  factors  may  limit  the
intensity of the light  delivered for treatment.
Suspended solids absorb and scatter UV light
while shielding microorganisms in the particles
from exposure to UV light.  Studies have shown
that reduced TSS concentrations are necessary to
obtain adequate disinfection with UV  systems;
therefore, sedimentation or filtration prior to UV
is usually required.   Proper disinfection is also
dependent upon the light  transmitting surface
remaining clear.

Peracetic Acid

Peracetic acid has been used as a disinfectant in
demonstration projects for  the  treatment  of
primary effluent such  as that  found in CSOs.
PAA is a very strong oxidizer, and is produced by
combining glacial acetic acid, hydrogen peroxide,
and water.   Sulfuric acid is typically used as a
catalyst for the reaction. A stabilizer chemical is
also added to solution to  slow biodegradation.
Equilibrium concentrations are:

 Peracetic Acid         15.0%

 Glacial acetic acid      14.0%

 Hydrogen peroxide    28.0%

 Water                 42.2%

 Sulfuric Acid          0.8%
A  15  percent solution  would be made with the
following proportions:

 Glacial acetic acid      39.4%

 Water                 38.8%

 Hydrogen peroxide    21.0%

 Sulfuric Acid          0.8%

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Because of the high reactivity of the final product,
liquid reactants must be delivered to the site in
separate tanks, and mixed on an as-needed basis.
PAA residuals  appear to be non-toxic and are
readily biodegradable in receiving waters.

Electron Beam Irradiation

A limited amount of  information exists  on the
applicability, performance and optimum  design
features for E-Beam systems. To limit the size of
particles  to the E-Beam  delivery system  and
prevent clogging  of the delivery  unit, the pilot
study for NYCDEP allowed the  wastewater to
flow through a basket strainer  equipped with
either a 1/32-inch or a 1/64-inch screen basket
before  reaching the E-Beam.  Water was then
pumped through  the  E-Beam system using  a
progressive-cavity, positive displacement pump.
The  pump  provided  positive  control  of the
wastewater  flowrate  discharge.    The  pump
discharge was then fed to the E-Beam delivery
system where the wastewater film was scanned by
the electron beam. Thermocouples attached to the
delivery system influent and effluent monitored
the temperature change of the wastewater and
were  used  to  calculate  the  absorbed dose.
According to the study, the absorbed E-Beam dose
was  determined  as a function  of wastewater
temperature changes  in the contact  tank.   A
temperature increase  of  1°C  equates  to  an
absorbed dose of 418.6 krads.

The E-Beam disinfection pilot was operated at a
flow rate of 20 gpm. The pilot flow rate was held
relatively constant during each of the test runs.

PERFORMANCE

Disinfectants for  treating CSO  events  require
"high rate" disinfection practices. Ideally, high
bacterial kills should be accomplished with low
contact times, a high mixing intensity,  and an
increased disinfectant dosage. Since most of the
alternative  disinfectants evaluated in this  fact
sheet are new and innovative, performance data is
limited. In cases where actual CSO data were not
available,  primary  and/or secondary effluent
treatment   data  were  used  to  evaluate  the
effectiveness of the disinfectant.
Comparisons of performance data from different
applications may be further complicated by the
fact  that it  is often difficult to determine the
appropriate disinfectant concentration to apply to
achieve  the  desired   bacterial   reduction.
Concentrations of fecal and total coliform bacteria
in the  CSO  are commonly used to assess the
performance of  the  disinfection  process  in
wastewater applications. However, the coliform
count for storm flow is often uncorrelated to the
pathogenic organism concentrations in the flow.
Therefore,   other   methods   may  be  more
appropriate for determining  the concentrations of
disinfectants to add to the  flow to achieve the
desired results.

Chlorine Dioxide

The  effectiveness of chlorine dioxide in treating
CSO discharges is measured in terms of reduction
in bacterial concentrations.  According to a pilot
scale study  in  New York,  a  dosage of  12
milligrams/liter C1O2 applied for a two minute
contact time achieved the following:

•  Total coliform (TC) bacteria reduction to target
   levels of 1,000 colonies/100 milliliters.

•  Fecal coliform (FC) and fecal streptococci (FS)
   bacteria   reduction   to   200   colonies/100
   milliliters.

Ozonation

Venosa (1983) compiled data on several studies
on ozonation as a CSO disinfectant. Venosa cites
a 1977 study by Scaccia and Rosen showing that
the disinfection efficiency of ozone is related to
the amount of ozone transferred into the process
water,  regardless of the  contactor type. Venosa
also  cites his own 1978 study demonstrating that
the amount  of ozone transferred to a municipal
effluent is directly related to the reduction in the
number of  coliforms  entering the  disinfection
system. In this study, Venosa also developed a
model  to predict the effluent coliform number
based on the amount of ozone being transferred
and the total chemical oxygen demand (TCOD).
This and other research demonstrates that  ozone
disinfection is a function of the absorbed dose and

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the effluent's ozone-demanding  properties.  In
addition, monitoring off-gas ozone levels can help
to control disinfection efficiency.

Ultraviolet Radiation

A dose-response relationship exists between UV
dose and reduction of TC and FC. The quality of
wastewater will dictate what dose should be used.
A 30 megaWatt-second/square centimeter (mW-
s/cm2) dose is recommended for a 4 log reduction
in fecal coliform for wastewater with a 65 percent
transmittance   and  a  suspended   solids
concentration of 30 milligrams/liter.  Results of
several studies on UV disinfection are presented
below.  In  several  of  these  studies, bacterial
concentrations  are given in terms  of the  most
probable number, or MPN:

•  A  simulated CSO study carried  out at  the
   Brampton WPCP  in 1991 used a 60/40 blend
   of raw wastewater and final effluent. A UV
   dosage of 75  mW-s/cm2 was needed to achieve
   a  target  bacterial   concentration  of  100
   colonies/100 milliliters.   Results from  the
   Central Contra Costa Sanitary District facility
   (CCCSD) indicated  that  UV doses of 55
   mW- second/square centimeter were required to
   achieve 240 MPN/100 milliliters TC bacterial
   densities  in  unfiltered  secondary  effluent
   (WERF,   1995).     Doses   less  than  50
   mW- second/square centimeter were required to
   achieve 2.2 MPN/100 milliliters total coliform
   bacterial densities in filtered effluent.

•  A study using a UV dose of 40 mW-m/cm2 on
   tertiary effluent with flows ranging from 9 to
   30 liters/second was able to achieve a 3 log kill
   up to a 4.8 log kill (99.8 percent removal) of
   fecal coliforms, total coliforms, Pseudomonas
   aeruginosa,   salmonellae,   Staphylococcus
   aureus, F+ bactedophage, and enterovirus.

•  A  study performed on   wastewater  being
   discharged into shellfish waters around  St.
   Michael's, MD  found that  total coliform
   densities could be reduced to 70 MPN/100 ml
   or less with UV at 25,000 uW-second/square
   centimeter and UV transmittance at an average
   65 percent (as cited in U.S. EPA, 1986).
•  Under  laboratory  conditions,  a  study  in
   Syracuse, NY, suggested that a dose of 500
   mW-s/cm2 would be  required to achieve a
   residual coliform level of 2500 MPN/100
   milliliters (as cited in U.S. EPA, 1986).

•  A similar pilot scale study at CCCSD designed
   to examine UV and chlorine inactivation of the
   MS2 bacteriophage indicated that UV doses of
   20 to 100 mW-s/cm2 were sufficient to cause a
   1 to 4.7-log  reduction in these organisms. In
   comparison,  chlorination using a dose of 30 to
   300 milligrams/liter per minute achieved little
   or no inactivation of the MS2 bacteriophage.

Electron Beam Irradiation

According to  the  pilot  study  done for  the
NYCDEP, E-Beam is not  appropriate for the
disinfection of CSOs.   The study showed  no
increased   disinfection  with  an  increase  in
disinfection  dose  for   total  coliform, fecal
coliform, andEscherichiacoli. A weak trend was
observed  for  increased  disinfection  of  the
Enterococcous group with increased disinfection
dose.

OPERATION  AND MAINTENANCE

In  order  to   assure  proper   operation  and
maintenance for CSO disinfection, operators and
facility managers  should  have access to, and be
aware of, all Material Safety Data Sheets on any
chemicals being used.  These data sheets provide
information on  several  aspects of the chemical,
including  handling and  storage,  regulations,
disposal   considerations,  and   toxicological
information.

Chlorine Dioxide

Proper operation and maintenance of a chlorine
dioxide facility should  include the  following
procedures.

•  All  tubing  should  be inspected every  six
   months and faulty or corroded tubing should be
   replaced.

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•  Any gas filters should be inspected every six
   months.

•  Chlorine  dioxide pressure reducing valves
   should be cleaned with isopropyl alcohol or
   tri chl oroethy 1 ene.

•  The valve spring should be replaced every two
   to five years.

•  Ejectors should be disassembled and cleaned
   every  six months.

•  Chlorine  dioxide analyzers (if used) should be
   inspected regularly.   All  lines  should be
   inspected daily. Results  from the analyzer
   should be compared with results from a manual
   analysis.

•  Granular  sodium chlorite should be stored in
   its own building equipped with sloped floors
   and equipment to hose down spills.

•  Increases in temperature,  exposure to light,
   changes in pressure, and exposure to organic
   contaminants  should  be  avoided  as  they
   increase the chance of C1O2 explosions.

Ozonation

Maintenance of an ozone  residual at  a given
concentration for  a specific period (detention
time) is  necessary  for  proper  disinfection.
Because  ozone has a  tendency to decompose
naturally and is consumed rapidly, it must be
contacted uniformly  in a    near plug  flow
contactor.

The ozone dosage must be calculated based on the
gas flow  and the  concentration applied to  the
contactor versus   the  gas  flow  and   the
concentration out of the contactor and the aqueous
ozone residual and flow. The calculation requires
consideration of gas volume and concentration
versus  aqueous  volume  and  concentration.
Maintenance activities that  should be addressed
include:
•  Prevent leaking connections or other leaks in
   or around the ozonator because this presents an
   electrical shock hazard.

•  Schedule cleanings of ozonator and its parts.

•  Lubricate compressor or blower as scheduled.

•  Monitor   ozone    generator   operating
   temperature.

•  Clean the ozone generation cells periodically to
   maintain maximum efficiency.

Ultraviolet Radiation

Maintenance for a UV disinfection facility would
include  area  maintenance  and  component
cleaning/repair. As with most surfaces exposed to
wastewater, bacterial growth occurs in spite of the
disinfecting ability of the UV  radiation  (the
associated warmth facilitates growth). Bacterial
growth on the quartz tubes surrounding the UV
lamps  gradually  reduces the amount of  UV
radiation   reaching,   and  disinfecting,   the
wastewater.  UV systems have  transmittance
meters that measure the  amount of UV  light
coming from  the bulbs and passing  through the
wastewater.  When the transmittance reading
reaches a predetermined low level, the bulb covers
must be cleaned,  chemically  and/or physically.
Several methods are available for cleaning lamps
including:

•  In-place recirculation;

•  Mechanical wipers;

•  Dip tanks;  and

•  Removing   modules   (rinse,   clean   with
   chemical, rinse and return)

Several cleaning  agents  available for cleaning
lamps include:

•  Citric acid;
                                                      Dilute HC1;

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•  Phosphoric acid;

•  Tile/bowl cleaner;

•  Lime away;

•  Detergent; and

•  Sulfuric acid.

Chemical cleaning may not restore the lamp
covers to their original transmittance level.  The
amount of restoration is likely to be less with each
subsequent cleaning. Ultimately, covers must be
manually cleaned or replaced.

The   period   of  time  between  cleaning  is
determined by the rate at which the quartz sleeves
become coated and reduce the ultraviolet output.
The coating composition and the rate at which it
accumulates are site-specific and depend on the
chemical properties of the water. Pilot studies are
recommended to produce data that correspond to
actual operating conditions.

The lamps themselves will ultimately burn out or
lose their intensity. The normal life span of a UV
lamp  is  approximately  14,000  hours.   Strict
inventory should be  made  of all lamp  usage,
relative  output,   and   estimated   cumulative
operating life. Inventories should also be made on
quartz sheaths, Teflon tubes, and ballasts.  The
ballast cages used to  house  the lamps  will also
need to be replaced approximately every 10 years.
Reactors taken out of service should be rinsed
with clean water, drained, and held in a drained,
dry condition.  A bypass should be constructed
around the entire UV disinfection system for use
during maintenance tasks.

Limited  safety  data  is   available  on  UV
disinfection systems. Moderate skin exposure to
UV can cause erythema, or reddening of the skin.
Excessive  exposure may cause bleeding and
blistering.   UV  exposure  to eyes  can cause
kerato-conjunctivitis or inflammation of the eye,
retinal lesions, chronic yellowing of the lens, and
cataract formation.
The following precautions are suggested to help
reduce UV exposure:

•  Open-channel  lamps should be  arranged in
   metal frames.

•  Interlocks should  be incorporated  into the
   channel lamp design to allow for the shutdown
   of entire lamp  blocks. Interlocks should also
   prevent lights from illuminating when they are
   not completely submerged.

•  Protective goggles and a face shield should be
   worn at all times around UV lamps even when
   the lamps appear to be emitting little light.

•  Protective electrical devices should be included
   in electrical designs for the facility.

•  Precautions should be taken to avoid electrical
   shocks. Facility plans should provide limited
   access   and  traffic  through  electrical and
   equipment areas.

•  Access to those areas should be limited only to
   necessary personnel.

•  Hazard  placards   should  be  placed  in
   appropriate areas of the facility describing the
   risks associated with the UV equipment.

Peracetic Acid

Maintenance for  a PAA facility should include
periodic inspections of feed lines, storage  areas,
leakage  detection  equipment,  and  chemical
injectors.  Blocked or silted  sewer lines should be
flushed and cleaned on a regular basis.   Spent
chemical  containers  should  be  discarded  in
approved  receptacles.  Spilled chemicals should
be cleaned up immediately. The chemical housing
facility   should  be   cleaned and  inspected
periodically to  ensure structural integrity.  The
explosive nature of the chemical agents stored at
the facility requires that the sprinkler system be
inspected regularly.

The following basic safety precautions should be
observed while handling PAA.  More detailed

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safety precautions are available from the manufacturer.

•  Chemicals   for  use  in  PAA  disinfection
   processes should be  stored in a  cool, dry,
   well-ventilated area and should be kept in their
   original,  DOT-approved  shipping containers
   with hazard labels intact.  PAA is thermally
   unstable  and decomposes explosively at high
   temperatures. The storage building should be
   constructed  of   materials  with   maximum
   resistance to fire and explosive potential, and
   should include  deflagration venting.   The
   facilities  must be designed with interior walls
   capable of withstanding 125 pounds per square
   foot internal overpressurization and ceilings
   must be  insulated.  Storage buildings should
   have an automatic sprinkler system  designed
   for 0.40 gallons per minute per square foot.

•  The storage room should be kept separate from
   all other processes  and should be separated
   from acids,  alkalies,  organic  materials,  and
   heavy metals.

•  A  backup  power supply  is  necessary  for
   housing structures at all times.

•  No  more than 4,800  gallons of the product
   should be allowed inside the facility at any one
   time; a greater  quantity requires  storage in
   separate buildings.
•  PAA may only be stored in 30 gallon closed
   drums and cannot be stacked.

•  Personnel  must   wear  special  protective
   clothing and positive pressure self-contained
   breathing apparatus.

•  Release detecting equipment must be located
   near chemicals, and near valves and equipment
   that pose a potential threat. Releases in excess
   of 1 pound should be reported.

•  Chemical spills must be contained and diluted
   with water.

COSTS

Costs  for chlorine  dioxide,  ozonation,  UV
radiation,  peracetic acid, and E-Beam processes
cannot be easily  compared due to the different
variables and the varying application methods for
the various disinfectants. Each alternative should
be evaluated based on the  characteristics of a
particular site.  Tradeoffs should be weighed to
determine any overriding factors to be ultimately
incorporated into the system. In a report prepared
for the NYCDEP, a cost projection was created
for chlorine dioxide  and ozone.   This data is
presented in Table 2.  Due to  limited information
on E-Beam processes there is no cost information
currently available.
               TABLE 2 CSO DISINFECTION PILOT STUDY COST PROJECTIONS
                                Conceptual Level Disinfection Costs
Technology
Peak Design Flow (cfs)
Capital Costs
Annualized Capital Costs
Annual O&M Costs
Total Annualized Costs
Chlorine Dioxide
1,250
$651,000
$66,000
$275,000
$341,000
2,500
$1,085,000
$111,000
$275,000
$386,000
5,000
$1,808,000
$184,000
$275,000
$459,000
Ozone
1,250
$18,000,000
$1,833,000
$500,000
$2,333,000
2,500
$23,000,000
$2,343,000
$550,000
$2,893,000
5,000
$28,600,000
$2,913,000
$615,000
$3,528,000
Source: NYCDEP, 1997.

Notes:
1. Costs are present worth in 1997 dollars.
2. Capital costs are based upon sizing to meet peak design flow and a 4-log reduction in fecal coliform.
3. Capital costs are for installation at Spring Creek and are for process equipment only. Costs do not include additional contact
tankage (if required) or support facilities.

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Chlorine Dioxide
                           REFERENCES
Costs will vary for a chlorine dioxide generation
system based  on design specifications.  The
estimated cost for a  chlorine dioxide  system
(wired and installed) capable of producing a feed
rate  of  over   100   pounds   ClO2/day  is
approximately $21,000.

The system would convert chlorine dioxide from
sodium chlorite or chlorine.  Production of gas
would be dependent upon demand and would not
be affected by variations in flow rate.

Ultraviolet Radiation

A detailed cost analysis was obtained from a pilot
demonstration   project  performed  at  the
Downingtown WPCP in Downingtown, PA. This
system was not  used for treatment of CSOs;
however, the equipment and O&M costs provide
baseline estimates for similar treatment flows.
Costs and equipment designs were based on the
following data:
 Peak Flow (GPM)

 Avg. Flow (GPM)

 Influent BOD mg/1

 Influent SS mg/1

 UV Transmission
7297.5 (10.5 mgd)

2919(4.2mgd)

30

30

65
Based  on this data,  an open channel vertical
system with the specifications shown in Table 3
would  be required to produce  effluent which
meets the minimum fecal coliform count of less
than 200 colonies per 100 milliliters for any 30-
day geometric mean of daily samples at peak flow.
The present  worth  analysis based  on a  life
expectancy of 20 years and an 8  percent interest
rate for  both  capital  cost  and  operation  and
maintenance is approximately $446,897 for a
vertical system and $492,517 for a horizontal
system.
Arnett, C.J., and M. Boner, 1998.  Wet
Weather  Demonstration  Programs.
Presented at WEFTEC '98 Workshop.

Dunham, R., H. He, and K. Woodard, no
date.  "Water Disinfection with Ozone."
Internet    site    at
http://www.ce.vt.edU/enviro2/wtprimer/o
zone/ozone.html, accessed July 1999.

Goldstein, S.,  1997.   CSO  Disinfection
Pilot  Study-Spring  Creek  AWPCP
Upgrade - Final Report. Prepared for the
New  York  City   Department  of
Environmental  Protection  by   Camp
Dresser & McKee..

Hall, Jr., L.W., D. T. Burton,  and L. B.
Richardson, 1981. "Comparison of Ozone
and Chlorine Toxicity to the Development
Stages of Striped Bass, Morone Saxatilis."
Canadian Journal of Fish and Aquatic
Science, Volume 38.

Hass, C.N., K. Longley, and T.  Selfridge,
1990. "High-Rate Coliform  Disinfection
of Storm Water Overflow."  Research
Journal  of the Water  Pollution Control
Federation,   Volume  62,  No.  3,
pp.282-287.

Kramer, S. and S. Leung, undated.  "Dis-
infection with Ozone." Internet site at
http://www.ce.vt.edU/enviro2/wtprimer/o
zone/ozone.html, accessed July 1999.

Maher, M. B.,  1974. Microstrainingand
Disinfection  of Combined  Sewer
Overflows-Phase III.

Metcalf  and  Eddy, 1995.    Combined
Sewer   Overflow   Disinfection
Effectiveness.

Rein, D.A., G.A.  Jamesson,  and R.A.
Monteith, 1992.  "Toxicity Effects of
Alternate Disinfection Processes."  Water

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   TABLE 3 ULTRAVIOLET RADIATION COST FACTORS FOR AN OPEN CHANNEL VERTICAL
   SYSTEM CAPABLE OF PRODUCING AN EFFLUENT WITH A MAXIMUM FECAL COLIFORM
                 COUNT OF LESS THAN 200 COLONIES PER 100 MILLILITERS
 SPECIFICATION
 Number of Channels

 Number of Modules/Channel

 Total Number of Modules

 Number of Lamps/Module

 Total Number of Lamps

 Dose Level (megawatts per second
 per square centimeter)

 Retention Time (seconds)

 Headless (inches)

 Power Requirement

 Capital Cost: $278,400

 OPERATION AND MAINTENANCE

 Electrical Consumption

 Consumption/Lamp


 Lamp Replacement Cost

 Cleaning Frequency

 Labor rate


 Number of Lamps "On"

 Electrical

 Replacement

 Cleaning


 Replacement Labor


 Total Replacement Costs	
2; Water Depth will be a maximum of 62", Minimum of 57.5"

6

12

40

480

36


12-38

<3"

(2)208v, 3 ph, 60 Hz, 60 amp
$.055/kWh

$0.075/kW (Vertical)
$0.085/kW (Horizontal)

$55.00 every 8760 operating hours

Once/month (may vary depending on site-specific conditions)

$15.00/hour

Vertical                         Horizontal

160                            176

$5,782                          $7,208

$8,800                          $9,680
$180 (30 minutes per channel per
month)

$2,400 (30 seconds per lamp per
year)

$17,162	
$990 (15 minutes per module per
month)

$4,224 (8 minutes per lamp per year)

$22,102
      Environment  Federation, 65th  Annual
      Conference and Exposition.                   11.

10.    lift, E.G., P.E. Moffa, S.L.  Richardson,
      and R.I. Field, 1977.  "Enhancement of
      High-Rate Disinfection  by  Sequential
      Addition   of   Chlorine  and   Chlorine
      Dioxide."  Journal of the Water Pollution       12.
      Control Federation. July, 1977.
                         Ward, R.W., and G.M. DeGraeve, 1978.
                         "Residual   Toxicity   of   Several
                         Disinfectants  in Domestic Wastewater."
                         Journal of the Water Pollution Control
                         Federation.

                         U.S. EPA, 1975.  Bench-Scale High Rate
                         Disinfection   of  Combined  Sewer

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             Overflows  With  Chlorine and
             Chlorine Dioxide. EPA 670/2-75-
             021.

13.    U.S.  EPA,  1984.   Combined  Sewer
      Overflow Control Manual.  EPA 625-R-
      93-007.

14.    U.S.  EPA,  1986.   Design Manual:
      Municipal WastewaterDisinfection. EPA
      625-1-86/021.

15.    U.S. EPA,  1994.  Stormwater Pollution
      Abatement  Technologies.  EPA/600-R-
      94/129.

16.    Venosa,   A.D.,   1983.     "Current
      State-of-the-Art   of   Wastewater
      Disinfection."    Journal  of  the  Water
      Pollution Control Federation, Volume 55,
      No. 5., pp 457-466.

17.    Water Environment  Federation,  1996.
      Wastewater  Disinfection.  Manual  of
      Practice FD-10.
The  City  of  New  York  Department  of
Environmental Protection
Barry Zuckerman
96-05 Horace Harding Expressway, 5th Floor
Corona, NY  11368

Wet Weather Engineering and Technology
Mark Boner
1825 2nd Avenue
Columbus, GA 31901

The  mention  of trade  names  or  commercial
products  does not constitute  endorsement  or
recommendation  for the  use by  the  U.S.
Environmental Protection Agency.
18.    Water Pollution Control Federation, 1989.
      Combined  Sewer  Overflow  Pollution
      Abatement.

ADDITIONAL INFORMATION
The City of Columbus, Georgia
Cliff Arnett
Columbus Water Works
1501 13th Avenue
Columbus, GA 31902

HydroQual, Inc.
Karl Scheible, Principle Engineer
1 Lethbridge Plaza
Mahwah, NJ 07430

Moffa and Associates
Peter Moffa
5710 Commons Park
P.O. Box 26
Syracuse, NY 13214
        For more information contact:

        Municipal Technology Branch
        U.S. EPA
        Mail Code 4204
        401 M St., S.W.
        Washington, D.C., 20460
         IMTB
                                                         Excellence fn compliance through optimal technical solutions
                                                         MUNICIPAL TECHNOLOGY

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