United States
Environmental Protection
EPA/600/R-19/084 | March 2019 | www.epa.gov/research
Wastewater Disinfection with
Peracetic Acid (PAA) and UV
Combination: A Pilot Study at
Muddv Creek Plant

Office of Research and Development
Land and Materials Management Division

March 2019
Wastewater Disinfection with Per acetic Acid (PAA) and UV
Combination: A Pilot Study at Muddy Creek Plant
Achal Garg, Ph.D.: Principal Investigator (PI), Metropolitan Sewer District of
Greater Cincinnati MSD, Cincinnati, Ohio.
Vasudevan Namboodiri, Ph.D.: Co-PI, MMB, LMMD, National Risk
Management Laboratory (NRMRL), US Environmental Protection Agency,
Cincinnati, Ohio-45268.
Tylor Bowman, Brindha Murugesan and Abdulaziz Al-Anazi: Student Co-ops,
Metropolitan Sewer District of Greater Cincinnati MSD.

Any opinions expressed in this report are those of the author(s) and do not necessarily
reflect the views of the Agency or MSD; therefore, no official endorsement should be
inferred. Any mention of trade names or commercial products does not constitute
endorsement or recommendation for use. This report has not been subjected to EPA's
peer and administrative review and not been approved for external publication.

For the past several years, Metropolitan Sewer District of Greater Cincinnati (MSD) and the Office of
Research and Development (ORD) has been investigating the use of peracetic acid (PAA) as an
alternative to chlorination and several aspects of its implementation in the real world. We have studied
the treatment of secondary effluent with PAA alone and in combination with UV with an objective to
increase the efficiency and reduce the cost of disinfection treatment. This report on PAA-UV
disinfection summarizes the results from a full-scale plant-level pilot study that we conducted from
January to July 2018 at MSD's Muddy Creek Treatment Plant. In this study, we pre-treated secondary
effluent with PAA and investigated its impact on UV disinfection efficiency and the rate of microbial
inactivation. It was observed that pre-treating secondary effluent with low doses of PAA resulted in an
increased UV efficiency, which, in turn, resulted in significant increase in the rate of microbial
inactivation. The combined PAA-UV treatment achieved significantly greater log reduction in fecal
coliform, and E. coli number. The membrane method was employed to measure the microbial
inactivation. Results from this plant-level pilot study validates our lab and side-stream pilot studies
that a PAA-UV sequential treatment is more effective than the individual UV or PAA treatments.

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environmental regulations and strategies at the national, state, and community levels.
This report was submitted in fulfillment of the Safe and Sustainable Water Resources Research Program
under the (partial) sponsorship of the United States Environmental Protection Agency. This report on
Peracetic acid-Ultraviolet disinfection summarizes the results from a full-scale plant-level pilot study
that was conducted from January to July 2018 at City of Cincinnati-MSD's Muddy Creek Treatment

Executive Summary
Peracetic acid (PAA) and Ultraviolet (UV) combination was shown to provide effective bacterial
reduction during field pilot trialing at the Muddy Creek Wastewater Treatment Plant, located
in Cincinnati, OH. Reduction of both fecal coliform and E. coli to below the permitted
requirements was demonstrated even at low UV energy doses.
Key findings:
~	Pretreating secondary effluent with low PAA dose rate of <2.0 mg/L and a contact time of
20-23 minutes followed by UV treatment were enough to achieve the disinfection goal to
reduce the geometric mean of fecal coliform to below 200CFU/100 mL, which is the
current permit limit value for April to October. The same dose rate and contact time were
able to reduce the geometric mean of E. coli to below 126 CFU/100 mL.
~	Effectiveness of UV energy doses 41 and 89mJ/cm2 were evaluated to study the UV dose
effectiveness followed by PAA alone and PAA pretreatment-UV combination with same
UV doses revealed the advantages of PAA pretreatment.
~	At the effective doses of 2.0 mg/L and 0.75 mg/L, the residual PAA concentration at the
effluent discharge was always below 1.0 mg/L. As a result, it is anticipated that there will
be no requirement to quench residual PAA prior to discharge, although the Ohio
Environmental Protection Agency (OEPA) has not yet set a specific discharge limit.
~	Combining PAA with UV has the potential to increase disinfection treatment efficiency and
lower the energy cost. Further continuous full-scale plant studies are needed to collect
additional data and fully calculate the potential savings with the combined PAA-UV
disinfection treatment strategy.
~	The pilot study and lab studies recommend that dual disinfection using PAA and UV
provides better disinfection compared to individual disinfection at higher doses. The
mechanism of disinfection is different for PAA and UV. For example, UV less effective in

turbid water where PAA will be helpful to achieve the permit limit.
~ Economic savings can be achieved due to the reduction in UV capital expense, power usage,
operational expense, maintenance, easy installation of PAA (low capital need). In addition,
PAA can be used to support aging UV systems around nation without much capital expense.
This approach will also help to achieve new regulatory changes or needs without increasing
UV capital expense or energy footprint.

Muddy Creek plant treats about 15 million gallon wastewater per day. The plant is currently using a
UV-based disinfection system, one of the most commonly used for wastewater disinfection. There are
two major benefits of using UV for wastewater disinfection over chemical disinfectants. One, it does
not form any disinfection byproducts (DBPs) and, two, it does not produce/leave any chemical
residuals in the treated water. However, the higher cost is the biggest downside of the UV systems. UV
lamps consume large amount of electric power that can put significant financial burden on the utility.
Another disadvantage for UV disinfection is that it is not very effective in the waters with low UV
transmittance or high solid content.
MSD is exploring alternative methods to reduce the high-energy cost to run the UV disinfection system.
Combining UV with peracetic acid (PAA) is one of such possibilities. Peracetic acid (PAA) is a strong
oxidizing compound with a wide spectrum of antimicrobial/biocidal properties. It is a clear and
colorless liquid commercially available at a concentration of 12% to 15% in an equilibrium mixture of
acetic acid, hydrogen peroxide and water:
In the solution, PAA is considered to be the primary component responsible for solution's disinfection
PAA has been a known disinfectant outside the wastewater industry for decades. It has been widely
used in the food, beverage, medical, and pharmaceutical industries for over 20 years. Because of its
strong and wide-spectrum antimicrobial properties, now PAA is receiving a lot of attention as a
wastewater disinfectant as an alternative to chlorine and UV.
Combining UV with an oxidizing agent, such as PAA, H2O2, and ozone (O3), results into an Advanced
Oxidative Process (AOP). When oxidants are exposed to UV irradiation, a photolytic reaction takes
place, which leads to the formation of highly reactive hydroxyl (°OH) radicals. In the photolysis process,
the photons interrupt the 0-0 bond in the PAA molecule forming the hydroxyl radical (°OH) which
reacts vigorously with biological, organic and inorganic matters. Formation of hydroxyl radicals is
considered the key for the disinfection effect of PAA+UV combination treatment.
CH3COOH + H2O2 <->
Acetic Acid Hydrogen Peroxide
Peracetic Acid Water
+ °oh + ch3co2
CO2 + H2O + Inorganic ions

Commercial PAA contains significant amount of hydrogen peroxide (H2O2) in the mixture. The presence
of H2O2 maintains PAA in an equilibrium and also produces additional hydroxyl (°OH) radicals when
exposed to UV irradiation. The formation of additional °OH radicals by photolysis of H2O2 is a
contributing factor to the synergism of combined PAA+UV irradiation treatment.
PAA is usually produced at concentrations of 5-15%. Kitis (2004) reviewed the use of PAA as a
disinfectant for wastewater effluents since the 1980s and reported it to be an efficient bactericidal,
virucidal, fungicidal, and sporicidal chemical (Kitis, 2004). Typical PAA treatment concentrations for
secondary effluent are 0.50 - 2.0 mg/L, and enhanced primary effluent typically requires a PAA
concentration of 5 - 10 mg/L. PAA contact times are typically 10 - 30 minutes with the majority of the
PAA consumption is occurring within the first 10 minutes (Dancey, 2008). Peragreen Solutions and
Solvay Chemicals have treated between 5 and 8 million gallons per day of secondary effluent with PAA
dosages not exceeding 1.5 mg/l at the wastewater treatment plant in the City of Steubenville, Ohio
(Maziuk et a I, 2013). The disinfection action of PAA may occur through mechanisms such as the release
of active oxygen that could oxidize essential enzymes for cellular metabolism, disruption of cell
membrane and transport mechanisms, and denaturing proteins in spores (Kitis, 2004). A major
advantage of PAA as a disinfectant is that it is not known to produce any harmful disinfection
byproducts (Liberti and Notarnicola, 1999). Some limitations of using PAA as a disinfectant include
lower disinfection efficiency against some viruses and parasitic oocysts as well as potential for
regrowth of microbes since residual PAA contributes to organic carbon in the effluent (Kitis, 2004).
Ultraviolet (UV) irradiation is another alternative used for wastewater disinfection. UV disinfection is
achieved due to absorption of UV radiation at 254 nm wavelength by the bacterial DNA forming
pyrimidine dimers that inhibit its reproduction (Acher et al., 1997). The disinfection efficiency of UV
radiation in eliminating enteric bacteria, viruses, and bacterial spores has been well established
(Lazarova et al., 1998). One of the major advantages of UV irradiation treatment compared to chemical
assisted treatments is that it does not result in the formation of harmful byproducts. In addition, UV
radiation is very effective in disinfecting parasitic oocysts such as Giardia and Cryptosporidium that
pose challenges to conventional chlorination (Clancey et al., 1998; Hijnen et al., 2006). The efficacy of
UV radiation, however, is highly dependent on the wastewater quality as high solids concentration (>
30 mg/L) may lead to infective applications (USEPA, 1999).
Combined application of PAA and UV disinfection may be beneficial as it could destroy a broader range
of pathogens when compared to a single mode of disinfection. It has been proposed that pretreatment
of wastewater with PAA will reduce the required dose of UV light and reduce the operation costs of the
WWTP (Caretti and Lubello, 2003). The Metropolitan Sewer district of Greater Cincinnati (MSGDC) has
conducted bench scale tests demonstrating the reduction in UV dose with increasing PAA. Followed by
pilot scale PAA/UV disinfection studies were conducted at the U.S. EPA Test & Evaluation facility in
Cincinnati, OH. The current study describes about the field pilot study conducted at the MSD's Muddy
Creek plant. This field scale study examined parameters such as the effectiveness of using PAA, UV, and
PAA pretreatment for UV disinfection on the inactivation of enterococci, fecal coliforms, E. coli in
secondary wastewater effluent.

This full-scale plant-level pilot study had the following objectives:
1.	Validate the findings from our bench-scale and side-stream pilot studies
2.	Investigate if pre-treatment of secondary effluent with PAA before UV irradiation improves the UV
treatment efficiency or has any beneficial (i.e., additive or synergistic) effects on E. coli inactivation.
3.	Determine if the reduced UV footprint can result in financial savings to the plant
4.	Any other auxiliary benefits of PAA pretreatment such as reduction in algal growth, reduced TSS
levels and mineral deposit on the bulb surface to improve UV lamp life and reduce maintenance
Experimental Set-Up
For this pilot study, three sampling locations (LI - L3) were identified to collect secondary effluent
samples before and after the treatment (Fig. 1). All samples were grab samples. Location L-l was a
concrete chamber where the raw secondary effluent from two clarifiers was mixed. This location (LI)
provided untreated control samples of raw effluent to estimate the baseline of the water parameters
prior to PAA of UV treatments.
The samples treated with PAA-only were collected at location "L2". Various doses of PAA ranging from
0.75 to 2 mg/l was injected at the beginning of the mixing tank that provided approximately 17-20
minutes of contact time depending on the flow rate. Following PAA treatment, the effluent passed
over the UV lamps for final disinfection. The final sampling site, L3, was located at the end of the plant
and was used to collect samples to determine the effect of UV-only disinfection or PAA-UV combined
PAA and UV treatments: The UV treatment system at Muddy Creek treatment plant, Cincinnati, is
comprised of two banks. Each bank contains six rows (modules) of 8-UV lamps each. Thus, each bank
has 48 UV lamps. Both UV banks work independent of each other and can be controlled separately. As
described in Table-1, five combinations of PAA and UV treatment were tested to evaluate the
treatment efficiency individually or in combination. The treatment protocols were: PAA alone, 50% UV

alone (41 mJ/cm2 dose), 100% UV alone (89 mJ/cm2 dose), PAA+41 mJ/cm2 UV, and PAA+89 mJ/cm2
UV. Various concentrations of PAA, ranging between 0.75 and 2 mg/L were tested alone or in
combination with UV. For the treatment purpose, when all UV lamps of both banks were turned on, it
was considered 100% UV exposure. The 100% UV dose was equal to an average of 89 mJ/cm2.
However, the UV confluence varied depending on the flow rate and level of suspended solids at the
time. To achieve the 50% UV confluence/dose, one UV bank was turned off which on average yielded
about 41 mJ/cm2 UV dose. This experimental design allowed an understanding of the relative
contribution of each of the treatment components in the combined disinfection system. As described
in Table-1, the samples were collected at locations LI for control (no treatment), L2 for PAA alone and
at L3 for either UV only or combination of UV and PAA.
Fig. 1: Schematic of the wastewater effluent treatment with PAA and UV
Wastewater characterization:
The effluent samples were analyzed for E. coli, fecal coliform, total suspended solids (TSS), pH,
chemical oxygen demand (COD) and PAA residuals. For microbial analysis of E. coli and fecal coliform
the treated and untreated secondary effluent samples were collected in 100 ml sterile plastic bottles
containing 10 mg sodium thiosulfate (Thermo Fisher Scientific, Cat# 05-719-361) to neutralize residual
PAA and H2O2 instantaneously. The fecal coliform and E. coli were analyzed using a membrane filter
method. The plates were incubated for 24 ± 2 hours in a 44.5 ± 0.2°C for fecal coliform and in a 35 ±
0.59C water bath for E. coli. Chemical oxygen demand (COD), total suspended solids (TSS) and pH were
analyzed using the procedures as described in "Standard Methods for the Water and Wastewater, 23rd
Ed., 2017).

Table 1
Sampling location
Treatment conditions
Untreated raw effluent
PAA only
Various doses of PAA
UV only (41 mJ/cm2
No PAA pre-treatment; Only one
UV bank turned on
UV only (89 mJ/cm2
No PAA pre-treatment; Both UV
banks turned on
PAA+UV (41 mJ/cm2
Effluent pre-treated with PAA
followed by UV irradiation. Only
one UV bank turned on
PAA+UV (89 mJ/cm2
Effluent pre-treated with PAA
followed by UV irradiation. Both
UV banks turned on
PAA Residual Measurement.
The PAA residual was measured at the end of plant location (L3) using the Single Analyte Meter (SAM)
(ChemTrics, Midland, VA, USA, Cat. # 1-2020) and self-filling ampules (ChemTrics, Midland, VA, USA,
Cat. # K-7913) on grab samples. PAA residual levels were measured within 5 minutes of collecting the

Full Scale Plant-level Pilot Study:
Effect of Wastewater Characteristics on PAA Treatment: Attempts were made to assess the effect of
water parameters such as COD and TSS on PAA treatment efficiency. No significant correlation was
found between the levels of above water parameters and PAA disinfection efficiency to inactivate E.
coli and fecal coliform. Additionally, we did not notice any impact of PAA treatment (0.75 to 2.0 mg/L
doses) on either COD or TSS.
Wastewater Disinfection with PAA and UV Individual Treatments:
The disinfection efficiencies of PAA and UV were determined individually and in various combinations
by measuring inactivation of E. coli and fecal coliform after the treatment. As expected, the UV fluence
of 89 mJ/cm2 was sufficient to inactivate 99% (2-log reduction) fecal coliform and E. coli. At this dose,
there was an average 2.2-log reduction in fecal coliform and 2.4-log reduction in the E. coli
concentration. The average number of fecal coliform and E. coli in the final effluent treated with 89
mJ/cm2 was less than 50 CFU/100 ml. In comparison, when one UV bank was turned off, reducing the
UV dose by almost 50% to 41 mJ/cm2, the inactivation rate of E. coli dropped from 2.2 to 1.8-logs and
for fecal coliform from 2.4 to 1.7 log reduction (Fig. 3 and 5). A 50% reduction in the UV fluence or
41mJ/cm2 UV dose was insufficient to achieve the inactivation level needed to meet the plant's NPDES
permit requirement for fecal coliform and E. coli.
Table-2 (values are arithmetic mean; mg/L)

PAA only
Disinfection with PAA-only treatment was found to be highly dose-dependent. Four doses of PAA
ranging from 0.75 to 2.0 mg/l were tested independently or in combination with UV. With PAA-only
treatment, the inactivation ranged from 0.6 log (0.75 mg/l dose) to 1.5 log (2.0 mg/l dose) for E. coli
and 0.8 (0.75 mg/l dose) to 1.8 log (2.0 mg/l dose) in case of fecal coliform. Doses from 0.75 to 1.5
were found insufficient to meet the NPDES permit of the plant. However, at 2 mg/l PAA, the number of
fecal coliform was reduced below the permit requirement of 126 E. coli CFU/100 ml (Fig. 2 and 4).
Thus, 2 mg/l PAA dose or 89 mJ/cm2 dose of UV were able to provide sufficient disinfection individually
to meet the plant's permit microbial requirements.

The most interesting data came when PAA and UV treatments were combined. When the secondary
effluent was pre-treated with PAA followed by UV, an additive effect on disinfection efficiency was
observed. We did not observe synergism in the PAA-UV combined treatment in any treatment
combination. The efficiency of combined PAA and UV treatment depended on the doses of both PAA
and UV. However, every combination of PAA and UV that we tested during this study yielded better
disinfection or microbial inactivation than the individual treatments with either PAA or UV because of
additive effect of the treatment. For instance, 0.75 mg/l PAA and 41 mJ/cm2 of UV fluence individually
yielded about 0.8- and 1.6-log reduction in fecal coliform respectively. However, when 0.75 mg/l PAA
treatment was followed by 41 mJ/cm2 UV treatment, we achieved an average of 1.9 log reduction in
fecal coliform counts. Similarly, at 1.0 mg/l PAA and 41 mJ/cm2 dose, there was 2.5-log reduction in
both E. coli and fecal coliform, which was equal to the sum of 0.8-log reduction with PAA and 1.6-log
reduction with 41 mJ/cm2 UV separately. When both banks were turned on (100% UV efficiency; 89
mJ/cm2 dose), a 2.2 to 2.4 log reduction was observed in fecal coliform and E. coli with UV-only
treatment reducing the population of these microbes more than 99%. This level of disinfection virtually
eliminated all fecal coliform and E. coli bacteria in the final effluent. The additive effect of PAA on UV
treatment was more prominent at 1 mg/l or higher doses. When 1 mg/l dose of PAA was combined
with 89 mJ/cm2 UV fluence, the disinfection efficiency of the combined treatment was more than 3-
logs (i.e., 99. 9%) (Fig. 3 and 5).
—~—PAA only —PAA+89 mJ/cm2 UV —A— PAA + 41 mJ/cm2 UV
126 CFU/100 mL
0	0.75	1	1.5	2
Fig 2- Effect of PAA and UV combined treatment on E. coli inactivation

I0.75mg/I ¦ 1 mg/l ¦ 1.5 mg/l ¦ 2 mg/l ¦41mJ/cm2UV ¦89mJ/cm2UV
c 2
y 1.5
0.8 ¦
UV only	PAA only	PAA + 41 mJ/cm2 UV PAA + 89 mJ/cm2 UV
Fig 3. Log reduction of E.coli after UV, PAA and PAA+UV treatments
—~—PAA only —PAA + 89 mJ/cm2 UV —A—PAA + 41 mJ/cm2 UV
126 CFU/100 mL
Fig 4- Effect of PAA and UV combined treatment of fecal coliform inactivation

¦ 0.75 mg/l ¦ 1 mg/l ¦ 1.5 mg/l ¦ 2 mg/l ¦ 41 mJ/cm2 UV ¦ 89 mJ/cm2 UV
UV only	PAA only	PAA + 41 mJ/cm2 UV PAA + 89 mJ/cm2 UV
Fig 5- Log reduction of fecal coliform after UV, PAA or PAA+UV treatments
Residualperacetic acid: The PAA residual were measured at location L3, just prior to discharge. After
approximately 20 to 23 minutes of contact time, traces of PAA were detected in the final effluent. As
shown in Table-3, the residual level depended on the initial dosing. Up to 1 mg/L dosing, on an average
0.27 mg/L PAA residual was detected after about 20 minutes. At 1.5 mg/L and 2.0 dosing, the average
residual levels were 0.48 and 0.78 mg/L respectively (Table-3).
PAA Residual (Arithmetic mean; mg/L)

Conclusions: Both peracetic acid (PAA) UV are potent disinfectants against E. coli and fecal coliform.
When used individually, both PAA and UV require higher doses based on the water quality to achieve
full inactivation of fecal coliform and E. coli bacteria. However, by pretreating secondary effluent with a
low dose PAA prior to UV irradiation in the combined treatment, the treatment has been found to be
significantly more effective than the individual treatments. The disinfection effect in the combined
treatment was found to be additive on E. coli and fecal coliform.
Combining PAA with UV has the potential to increase disinfection treatment efficiency and lower the
energy cost. Further full-scale plant studies are needed to collect additional data and fully calculate the
potential savings with the combined PAA-UV disinfection treatment strategy.
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