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EPA/600/R-19/084 | March 2019 | www.epa.gov/research

Wastewater Disinfection with Peracetic Acid (PAA) and UV Combination: A Pilot Study at Muddy Creek Plant

Office of Research and Development Land and Materials Management Division

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EPA/600/R-19/084 March 2019

Wastewater Disinfection with Peracetic Acid (PAA) and UV Combination: A Pilot Study at Muddy Creek Plant

by

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.

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Disclaimer

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.

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Abstract 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.

Foreword The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the Nation's land, air, and water resources. Under a mandate of national environmental laws, the Agency strives to formulate and implement actions leading to a compatible balance between human activities and the ability of natural systems to support and nurture life. To meet this mandate, EPA's research program is providing data and technical support for solving environmental problems today and building a science knowledge base necessary to manage our ecological resources wisely, understand how pollutants affect our health, and prevent or reduce environmental risks in the future.

The National Risk Management Research Laboratory (NRMRL) within the Office of Research and Development (ORD) is the Agency's center for investigation of technological and management approaches for preventing and reducing risks from pollution that threaten human health and the environment. The focus of the Laboratory's research program is on methods and their cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface resources; protection of water quality in public water systems; remediation of contaminated sites, sediments and ground water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies that reduce the cost of compliance and to anticipate emerging problems. NRMRL's research provides solutions to environmental problems by: developing and promoting technologies that protect and improve the environment; advancing scientific and engineering information to support regulatory and policy decisions; and providing the technical support and information transfer to ensure implementation of 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 Plant.

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 C incinnati, 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.

Background 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:

CH3COOH + H2O2 ↔ CH3COOOH + H2O

Acetic Acid Hydrogen Peroxide Peracetic Acid Water

In the solution, PAA is considered to be the primary component responsible for solution’s disinfection activity.

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 O-O 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.

CH3COOOH + UV °OH + CH3CO2° CO2 + H2O + Inorganic ions

hv +Pollutants

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 al, 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.

Objectives:

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

Methodology Experimental Set-Up

For this pilot study, three sampling locations (L1 - L3) were identified to collect secondary effluent samples before and after the treatment (Fig. 1). All samples were grab samples. Location L-1 was a concrete chamber where the raw secondary effluent from two clarifiers was mixed. This location (L1) 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 treatment.

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 L1 for control (no treatment), L2 for PAA alone and at L3 for either UV only or combination of UV and PAA.

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 ± 0.5ºC 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).

Fig. 1: Schematic of the wastewater effluent treatment with PAA and UV combination

L1

L3

L2

PAA Injection

Final effluent for discharge

UV L

Clarifier-1

Clarifier-

Aeration tanks

PAA mixing t k

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. # I-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 sample.

Table 1

Treatment Sampling location Treatment conditions

Control L1 Untreated raw effluent

PAA only L2 Various doses of PAA

UV only (41 mJ/cm2 dose) L3 No PAA pre-treatment; Only one

UV bank turned on

UV only (89 mJ/cm2 dose) L3 No PAA pre-treatment; Both UV

banks turned on

PAA+UV ( 41 mJ/cm2 dose) L3

Effluent pre-treated with PAA followed by UV irradiation. Only

one UV bank turned on

PAA+UV ( 89 mJ/cm2 dose) L3

Effluent pre-treated with PAA followed by UV irradiation. Both

UV banks turned on

Results:

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.

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.

Table-2 (values are arithmetic mean; mg/L)

Control PAA only

COD 23 20

TSS 1.15 1.12

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).

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126 CFU/100 mL

Fig 2- Effect of PAA and UV combined treatment on E. coli inactivation

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Fig 3. Log reduction of E.coli after UV, PAA and PAA+UV treatments

0.75 mg/l 1 mg/l 1.5 mg/l 2 mg/l 41 mJ/cm2 UV 89 mJ/cm2 UV

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126 CFU/100 mL

Fig 4- Effect of PAA and UV combined treatment of fecal coliform inactivation

Residual peracetic 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).

Table-3

PAA Residual (Arithmetic mean; mg/L)

Dose Residual

0.75 0.27

1 0.27

1.5 0.48

2 0.78

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0.75 mg/l 1 mg/l 1.5 mg/l 2 mg/l 41 mJ/cm2 UV 89 mJ/cm2 UV

Fig 5- Log reduction of fecal coliform after UV, PAA or PAA+UV treatments

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.

References:

1. Achal Garg, Narasimman L.M., Jacob Hogg, Amy Nutter, and Galen Mahoney, WEFTEC 2016, Wastewater Disinfection with Peracetic Acid

2. Achal Garg, Pooja Chari, Youyi Shi, and Vasudevan Namboodiri, WEFTEC 2017, Wastewater Disinfection with peracetic Acid (PAA), UV Irradiation and Combined PAA-UV Treatments

3. Achal Garg, Vasudevan Namboodiri, Bruce Smith, Abdulaziz Anazi, Brindha Murugesan, and Tyler Bowman, Disinfection and Reuse Conference, 2018, Disinfection of Wastewater with Peracetic Acid (PAA) and UV Combined Treatment: A Pilot Study

4. Acher, A., Fischer, E., Turnheim, R., Manor, Y. 1997. Ecologically friendly wastewater disinfection techniques. Water Research 31 (6), 1398-1404.

5. American Public Health Association, 1998. Standard Methods for the Examination of Water and Wastewater, 20th Edition, Method 2540-D Total Suspended Solids Dried at 103º-105ºC.

6. Basu, O. D. and Gatchene, D., (2009). Evaluating Peracetic Acid for Wastewater Disinfection, Environmental Science & Engineering Magazine, September 2009.

7. Caretti, C., Lubello, C. 2003. Wastewater Disinfection with PAA and UV combined treatment: a Pilot Plant Study. Water Research 37, 2365-2371.

8. CB&I Federal Services LLB (2016). Quality Assurance Project Plan: comparative Evaluation of Sodium Hypochlorite and Peracetic Acid Disinfection of Muddy Creek Combined Sewer Overflow of Metropolitan Sewer District of Greater Cincinnati. NRMRL QA Tracking ID: G-STD-0019486-QP-1-4, May 17, 2016.

9. Clancy, J. L., Hargy, T. M., Marshall, M. M., Dyksen, J. E. 1998. UV light inactivation of Cryptosporidium oocysts. Journal of American Water Works Association 90 (9), 92-102.

10. Dancey, K. (2008). Peracetic Acid: A New Disinfection Approach. Presented at PNCWA 2009. 11. Hijnen, W. A. M., Beerendonk, E. F., Medema, G. J. 2006. Inactivation credit of UV radiation

for viruses, bacteria and protozoan (oo)cysts in water: A review. Water research 40 (1), 3-22. 12. Kitis, M. 2004. Disinfection of wastewater with Peracetic acid: a review. Environment

international 30 (1), 47-55. 13. Lazarova, V., Savoye, P., Janex, M. L., Blatchley, E. R., Pommepuy, M. 1999. Advanced

wastewater disinfection technologies: State of the art and perspectives. Water Science and Technology 40 (4), 203-213.

14. Lazarova, V., Janex, M. L., Fiksdal, L., Oberg, C., Barcina, I., Pommepuy, M. 1998. Advanced wastewater disinfection technologies: Short and long term efficiency. Water Science and Technology 38 (12), 109-117.

15. Liberti, L. and Notarnicola, M. 1999. Advanced treatment and disinfection for municipal wastewater reuse in agriculture. Water Science and Technology 40 (4), 235-245.

16. Maziuk, J., Freeborn, R., and Murphy, C. (2013). Peracetic Acid Proves Effective as Alternative Disinfectant Method. WaterWorld, v. 29, i. 9, p. 218, Sept. 2013.

17. USEPA. 1999. Wastewater technology fact sheet, Ultraviolet disinfection. 18. Vasudevan Namboodiri and Achal Garg, 2018, Evaluation of Combined Peracetic acid and UV

treatment for Disinfection of Secondary Wastewater Effluent, G-STD-0019486-RT-3-0.

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