Peracetic acid (PAA, peroxyacetic acid; CAS 79-21-0) is an organic peroxyacid sold as an equilibrium mixture with hydrogen peroxide and acetic acid, dosed as an oxidizing disinfectant mainly for municipal wastewater effluent. Plants feed it as 12 to 22 % solutions and state every dose as PAA, not as product.
PAA replaces chlorine or UV at the end of a wastewater plant, and its first US commercial use came in 2005 at Frankfort, Kentucky, at 0.7 mg/L (ppm) with 26 minutes of contact. PAA is one of the oxidants in this reference of water treatment chemicals, documented with the same identity, dose and compliance fields as every other entry.
PAA carries no NSF/ANSI/CAN 60 listing (NSF listings, 2026-10-20), so this page covers wastewater, membrane and process water, not drinking water. The identity card below summarizes the attributes that define peracetic acid.
| Attribute | Value |
|---|---|
| Name | Peracetic acid |
| Abbreviation | PAA |
| Synonyms | Peroxyacetic acid, peroxyethanoic acid, ethaneperoxoic acid, acetyl hydroperoxide, peroxoacetic acid |
| CAS number | 79-21-0 |
| EC number | 201-186-8 |
| Formula | C2H4O3 (CH3C(O)OOH) |
| Molar mass | 76.05 g/mol |
| Class | Organic peroxyacid (peroxygen); equilibrium mixture with H2O2 and acetic acid |
| Function | Oxidizing disinfectant (municipal effluent), biocide (cooling and process water), sanitizer |
| Grades in water use | 12 %, 15 % and 22 % PAA equilibrium solutions |
| NSF/ANSI/CAN 60 | No listing under "Peracetic Acid" or "Peroxyacetic Acid" (NSF listings, 2026-10-20) |
| AWWA / EN product standard | None |
| GHS | Danger; harmonised CLP Annex VI classification, index 607-094-00-8 |
| Transport | UN3149, class 5.1, PG II for mixtures with not more than 5 % PAA |
Every value on this page is checked against primary sources (EPA, eCFR, EUR-Lex, NSF listings, PubChem); see our methodology and fact-checking process.
What Is Peracetic Acid (PAA)?#
Peracetic acid is the peroxyacid of acetic acid, formula C2H4O3 (CH3C(O)OOH) and molar mass 76.05 g/mol, used in water treatment as an oxidizing disinfectant and biocide. PubChem (CID 6585) lists it under CAS 79-21-0 and EC 201-186-8, with the synonyms peroxyacetic acid, peroxyethanoic acid, ethaneperoxoic acid, acetyl hydroperoxide and peroxoacetic acid.
PAA performs three water functions: municipal effluent disinfection, cooling and process water biocide treatment, and sanitizing. Commercial PAA is never pure. Every product is a stabilized equilibrium solution, and three strengths appear in the US wastewater record. The table below lists each grade and the document that names it.
| Grade (as PAA) | Named in | Source |
|---|---|---|
| 12 % | Frankfort, KY full-scale disinfection | US EPA PAA fact sheet (2012) |
| 15 % | Vendor pilot report | Supplier-authored pilot report |
| 22 % | MC Stiles WWTP pilot (2015) | Enviro Tech pilot study report |
All three grades are stabilized equilibrium solutions that also contain hydrogen peroxide and acetic acid.
How are peracetic acid and hydrogen peroxide related?#
Commercial PAA is an equilibrium of acetic acid and hydrogen peroxide, so every product also contains hydrogen peroxide and acetic acid. The reaction runs CH3COOH + H2O2 ⇌ CH3COOOH + H2O, and the US EPA 2012 fact sheet notes that commercial products contain a stabilizer to hold that balance.
The peroxide share explains why membrane sanitization dilutions are stated as peroxide rather than as PAA. Hydrogen peroxide itself (CAS 7722-84-1) is a separate chemical with its own EN 902:2016 standard. Peroxide used on its own for sulfide control and advanced oxidation is covered under hydrogen peroxide.
How Does Peracetic Acid Disinfect Water?#
Yes: PAA disinfects water by oxidizing microbial cell walls, which causes leakage of cellular constituents and breaks carbon-nitrogen (C-N) bonds. The US EPA 2012 fact sheet adds that radicals formed as PAA decomposes, the hydroperoxyl (HO2·) and hydroxyl (·OH) radicals, contribute to the kill.
PAA is halogen-free. It forms no chlorinated disinfection by-products such as trihalomethanes or haloacetic acids, because no chlorine enters the effluent. Disinfection by direct oxidation is the design intent here. Hydroxyl-radical treatment by design, with ozone, UV or peroxide, is a separate field covered under advanced oxidation processes.
Where Is Peracetic Acid Used in Water Treatment?#
PAA is used in 4 water applications: municipal effluent disinfection, combined sewer overflow (CSO) disinfection, cooling and process water biocide treatment, and RO/NF membrane sanitization. PAA is one of the wastewater treatment chemicals used at the end of the plant, and the table below compares the four uses.
| System | Dose (basis) | Feed point | Control | Target | Source |
|---|---|---|---|---|---|
| Municipal wastewater effluent | 0.7 mg/L as PAA (Frankfort); 2 to 7 mg/L secondary or tertiary, 5 to 15 mg/L primary (literature) | Secondary effluent ahead of the contact basin, static mixer | PAA residual, fecal coliform or E. coli, BOD, pH | Permit bacteria limits; residual < 1 ppm at discharge (Frankfort) | EPA 2012; Water Research 2005 |
| Combined sewer overflow | Not published here | Not published here | Not published here | Permit limits | EPA 2012 (use named) |
| Cooling and process water | Biocide use; no verified dose | Not published here | Not published here | Microbial control; see once-through cooling water treatment | EPA 2012 (use named) |
| RO/NF membrane sanitization | 0.1 % by weight as peroxide, ≤ 25 °C (77 °F) | CIP skid | Flush until H2O2 and PAA < 1 ppm | Clean element returned to service | DuPont FilmTec manual; NSF listings |
Municipal wastewater effluent disinfection#
Frankfort, Kentucky, disinfected its 9.9 MGD (37,500 m³/d) effluent in 2005 with 0.7 mg/L (ppm) as PAA from a 12 % product and 26 minutes of contact, the first US commercial PAA wastewater use. The plant switched to PAA temporarily while its ozone generator was replaced. Later full-scale data widen the dose range: Langley, British Columbia, dosed 1.5 mg/L (supplier-authored WEFTEC 2014 conference paper), and the East Bay Dischargers Authority (EBDA) trial reached fewer than 100 CFU/100 mL fecal coliform at 4 mg/L with 20 and 40 minutes of contact.
What range applies to other plants? A 2005 Water Research study reports 2 to 7 mg/L for secondary or tertiary effluent and 5 to 15 mg/L for primary effluent. PAA also serves CSO disinfection, where no dose is published here. The discharge permit sets the target: NPDES bacteria limits, plus residual PAA and acute toxicity where the permit names them. Chlorine, PAA and UV programs are compared under wastewater disinfection and dechlorination.
Does peracetic acid change effluent pH or BOD?#
Not measurably at Frankfort's 0.7 mg/L dose: the US EPA 2012 fact sheet reports no measurable pH or BOD effect there. The question arises because every PAA product carries acetic acid from its equilibrium. That finding is one plant at one low dose, and higher doses need their own pH and BOD monitoring.
Membrane sanitization and cooling water#
RO and NF membranes are sanitized with commercial H2O2/PAA concentrates diluted with permeate to 0.1 % by weight as peroxide at no more than 25 °C (77 °F), the same procedure as for hydrogen peroxide (DuPont FilmTec RO and NF manual, form 45-D01504). Hydranautics TSB110 caps peroxide at 0.2 %, at water no warmer than 25 °C, and rules it out where H2S, iron or manganese is present and for long-term storage. Sanitization follows the alkaline and acid steps described under RO membrane cleaning chemicals.
NSF-listed H2O2/PAA membrane cleaning products carry one condition: flush until H2O2 and PAA are below 1 ppm before the element returns to service. PAA also works as a cooling and process water biocide, but no verified cooling-tower dose, feed point or control range is published here. Oxidizing and non-oxidizing programs are compared under cooling tower biocides.
How Is the Peracetic Acid Dose Calculated and Fed?#
The PAA feed rate equals dose (mg/L as PAA) x flow (MGD) x 8.34 / product strength (decimal) in lb/day, or dose x flow (m³/d) / 1,000 / strength in kg/d (Florida DEP formula and conversion table). The strength divisor turns a dose as PAA into a feed rate as product. The worked example below uses the EBDA dose of 4 mg/L as PAA at 50 MGD (189,250 m³/d, from 1 MGD = 3,785 m³/d).
| Worked example: input or result | lb/day | kg/d |
|---|---|---|
| Inputs: 4 mg/L as PAA, 50 MGD (189,250 m³/d) | n/a | n/a |
| Feed as 100 % PAA | 1,668 | 757 |
| Feed as 12 % product | 13,900 | 6,308 |
| Feed as 15 % product | 11,120 | 5,047 |
| Feed as 22 % product | 7,582 | 3,441 |
Calculated with the Florida DEP pounds formula; results are mass of product. Volume (L/d or gal/d) needs the product density from the supplier SDS.
How do you convert a PAA dose between active and product bases?#
Divide the dose as PAA by the product's PAA fraction to get the dose as product. One mg/L as PAA equals about 8.3 mg/L of 12 % product, 6.7 mg/L of 15 % product and 4.5 mg/L of 22 % product (calculated).
Membrane sanitization breaks this rule: its 0.1 % dilution is stated as peroxide, not as PAA. For other flows and grades, the dosage and feed rate calculator converts the dose to kg/d and lb/day.
Which feed equipment does a PAA disinfection system use?#
A PAA disinfection system uses a supply tote, a flow-paced metering pump, an injection point with a static mixer and a contact basin, in that order. Most US systems receive PAA in one-way totes of up to 300 gallons (1.14 m³), and the pump follows a 4 to 20 mA effluent flow signal. The US EPA 2012 fact sheet put a tote-fed pump skid for 50 MGD at 4 ppm PAA below USD 50,000 in 2012. Pump types and wetted materials are compared under chemical dosing pumps.
How Is a Peracetic Acid Residual Measured and Controlled?#
Plants control PAA with 4 measurements, and Frankfort used all four in its 2005 program. The four measurements are listed below.
- PAA residual, read by test kit, held below 1 ppm at discharge at Frankfort without a quench step
- Fecal coliform or E. coli, the permit bacteria indicator that sets the dose
- BOD, a permit parameter tracked alongside the residual
- pH, checked at the outfall against the permit range
Flow pacing from the 4 to 20 mA effluent signal keeps the dose proportional between residual readings. Concentration times contact time is explained under CT values for disinfection; no PAA-specific CT value is published here.
How do plants test for peracetic acid: test kits or test strips?#
Frankfort tested its PAA residual with a CHEMetrics K-7905 test kit, and that kit result held below 1 ppm at discharge. No test-strip range for effluent residuals is published here, so the kit result is the reference reading.
What Is Peracetic Acid Incompatible With?#
PAA reacts explosively with acetic anhydride and violently with four other material groups (Hazardous Substances Data Bank, HSDB 1106). The five incompatibles are listed below.
- Acetic anhydride: explosive reaction
- Ether solvents: violent reaction
- Metal chloride solutions: violent reaction
- Olefins: violent reaction
- Organic materials: violent reaction
Membrane sanitization adds a process limit: Hydranautics TSB110 rules out peroxide sanitization where H2S, iron or manganese is present.
Which Standards Cover Peracetic Acid? NSF/ANSI/CAN 60, AWWA and EN#
No product standard covers PAA: it has no NSF/ANSI/CAN 60 listing, no AWWA B-standard and no CEN/TC 164 EN standard. The table below compares each standards route with its status for PAA.
| Document | Covers PAA? | Status |
|---|---|---|
| NSF/ANSI/CAN 60 | No | No listing under "Peracetic Acid" or "Peroxyacetic Acid" (NSF listings, 2026-10-20) |
| AWWA B-series | No | None among the 49 standards on the AWWA list (2026-10-20) |
| CEN/TC 164 EN standards | No | None for PAA; EN 902:2016 covers hydrogen peroxide |
| NSF-listed H2O2/PAA membrane cleaners | Product listings, not PAA itself | Flush until H2O2 and PAA are below 1 ppm before service |
Is peracetic acid NSF/ANSI/CAN 60 certified for drinking water?#
No: NSF lists no product under "Peracetic Acid" or "Peroxyacetic Acid" (NSF listings, 2026-10-20). The only NSF/ANSI/CAN 60 entries that involve PAA are H2O2/PAA membrane cleaning products, and they carry the condition that the element is flushed until H2O2 and PAA are below 1 ppm. How listings and maximum use levels work is covered under NSF/ANSI/CAN 60 certification.
What Is the Regulatory Status of Peracetic Acid in Water Treatment?#
PAA is a FIFRA-registered antimicrobial active ingredient, not listed in 21 CFR 173.310, and named on both US process-safety lists. Discharges answer to NPDES bacteria limits, plus residual PAA and acute toxicity where a permit sets them; Frankfort's PAA-disinfected effluent passed Ceriodaphnia dubia acute toxicity tests. The matrix below gives the status of PAA under each instrument as of 2026-10-20.
| Instrument | Status for PAA |
|---|---|
| US FIFRA | Registered antimicrobial active ingredient; see FIFRA registration of water treatment biocides |
| EU BPR | See EU Biocidal Products Regulation |
| 21 CFR 173.310 (boiler steam additives) | Not listed in 21 CFR 173.310 |
| NPDES | Bacteria limits; residual PAA and acute toxicity per permit; see NPDES permits and chemical discharges |
| EPA RMP (40 CFR 68.130) | Threshold quantity 10,000 lb (4,536 kg) |
| OSHA PSM (29 CFR 1910.119 App. A) | Threshold quantity 1,000 lb (454 kg) |
| OSHA PEL / NIOSH REL | None / none |
| NSF/ANSI/CAN 60 | No listing (NSF listings, 2026-10-20) |
Is peracetic acid covered by EPA RMP and OSHA PSM?#
Yes, under both, with different thresholds: EPA RMP sets 10,000 lb (4,536 kg) in 40 CFR 68.130, and OSHA PSM sets 1,000 lb (454 kg) in 29 CFR 1910.119 Appendix A. The PSM appendix lists the chemical as "Peracetic Acid (concentration >60% Acetic Acid; also called Peroxyacetic Acid)", so the product composition on the SDS decides whether a given grade meets that entry. The 2024 Safer Communities RMP rule is in force, and the proposal of 2026-02-24 (comments closed 2026-05-11) is not final. Program duties above the thresholds are set out under EPA RMP and OSHA PSM.
Is Peracetic Acid Dangerous? Hazards, Handling and Storage#
Yes: peracetic acid carries the signal word Danger under its harmonised CLP Annex VI classification (index 607-094-00-8), which comprises H242, H301, H310, H314, H330, H335 (STOT SE 3 at a concentration of 1 % or more), H400 and H410. The Annex VI entry also sets acute toxicity estimates of 0.2 mg/L by inhalation, 60 mg/kg bw dermal and 80 mg/kg bw oral, with M-factors of 10 and 100.
US workplace limits are thin. OSHA sets no PEL and NIOSH no REL, while the OSHA Occupational Chemical Database lists an IDLH of 0.64 ppm (1.7 mg/m³), marked as under NIOSH review. Most US plants store PAA in the one-way totes of up to 300 gallons (1.14 m³) in which it arrives; tank and piping materials, PPE and spill steps come from the supplier SDS. Containment by chemical is covered under chemical storage tanks. The table below summarizes the hazard and handling data.
| Item | Value |
|---|---|
| Signal word | Danger |
| Pictograms | GHS02, GHS05, GHS06, GHS09 |
| Harmonised H-statements (CLP Annex VI, 607-094-00-8) | H242, H301, H310, H314, H330, H335 (C ≥ 1 %), H400, H410 |
| Incompatibles | Acetic anhydride (explosive); ether solvents, metal chloride solutions, olefins, organic materials (violent) |
| Exposure limits | No OSHA PEL, no NIOSH REL; IDLH 0.64 ppm (1.7 mg/m³), OSHA database, under NIOSH review |
| Process safety | EPA RMP 10,000 lb (4,536 kg); OSHA PSM 1,000 lb (454 kg) |
| Package | One-way totes up to 300 gal (1.14 m³) |
| Tank material, PPE, spill response | Per supplier SDS |
What does a peracetic acid safety data sheet (SDS) cover?#
A peracetic acid SDS (formerly MSDS) gives the classification, composition, transport entry and handling data for one product at one strength. Product labels can show more than the harmonised line: ECHA C&L notifications (596 reports) add notified codes such as H226 (100 %) and H312 (99.8 %). Mixtures with not more than 5 % PAA ship as UN3149, class 5.1, packing group II; stronger grades take the entry in SDS section 14, and the customs code comes from the supplier or a broker. The SDS checks below apply to every delivery.
- Confirm the PAA and H2O2 strength on the certificate of analysis.
- Check the section 14 transport entry for that strength.
- Check section 10 against the five incompatibles listed above.
- Confirm tank and piping materials in section 7.
What Are the Alternatives to Peracetic Acid?#
The 4 main alternatives to PAA are sodium hypochlorite, ozone, chlorine dioxide and UV, and each trades PAA's process-safety listings for a different by-product or equipment burden. The table below compares them for wastewater disinfection.
| Chemical | CAS | Wastewater dose (basis) | By-product issue | NSF/ANSI/CAN 60 | Standard |
|---|---|---|---|---|---|
| Peracetic acid | 79-21-0 | 2 to 7 mg/L as PAA (literature, secondary/tertiary) | No chlorinated DBPs | No listing (2026-10-20) | None |
| Sodium hypochlorite | 7681-52-9 | 5 to 20 mg/L as Cl2 | Dechlorination needed for residual chlorine | 178 companies, 768 products, 1,551 product-function rows; most common MUL 84 mg/L as product (NSF listings, 2026-10-21) | ANSI/AWWA B300-24; EN 901:2024 |
| Ozone | 10028-15-6 | By pilot test, 10 to 30 min contact | Bromate MCL 0.010 mg/L in drinking water | No listing (2026-10-20) | EN 1278:2026 |
| Chlorine dioxide | 10049-04-4 | No wastewater dose published here | Chlorite MCL 1.0 mg/L in drinking water | Through precursors | EN 12671:2016 |
| UV (process) | n/a | Dose by design | None chemical | n/a | See UV disinfection in water treatment |
PAA vs sodium hypochlorite with dechlorination#
Sodium hypochlorite disinfects wastewater at 5 to 20 mg/L as Cl2 but needs dechlorination, which adds about 30 to 50 % to chlorination cost (US EPA, 832-F-99-062). PAA at Frankfort met its residual of below 1 ppm at discharge without any quench, and it forms no chlorinated by-products. Hypochlorite keeps the advantage of AWWA and EN product standards and NSF listings. Grades, maximum use levels and wastewater doses are covered under sodium hypochlorite.
PAA vs ozone#
Ozone is generated on site, while PAA arrives as a delivered liquid in totes. Ozone wastewater doses come from pilot tests with about 10 to 30 minutes of contact, and ozone is not economical at high suspended solids, BOD, COD or TOC; it raises effluent dissolved oxygen. Frankfort relied on PAA exactly while its ozone generator was replaced. Generation, CT and bromate are covered under ozone.
Peracetic Acid Grades, Suppliers and Sourcing#
PAA for wastewater is sold as 12 to 22 % equilibrium solutions by makers that include Enviro Tech and Evonik, and the trade name VigorOx WWT II is one Evonik wastewater product. Distributors by region are listed under water treatment chemical suppliers. The table below lists the makers named in the cited sources, alphabetically.
| Maker | Named for |
|---|---|
| Enviro Tech | 22 % PAA, MC Stiles WWTP pilot report (2015) |
| Evonik | VigorOx WWT II wastewater product (the source document also carries the PeroxyChem name) |
Listed alphabetically; no company is a partner of this site and none pays for inclusion. Proxitane appears as a PubChem synonym for peracetic acid; its owner is not stated here.
How is peracetic acid bought and quoted?#
Compare PAA offers per kg (lb) of PAA, not per tote, because a 22 % product carries about 1.8 times the PAA of a 12 % product per kg (calculated). Public procurement records show what buyers paid at a given date and place; they include delivery and local terms and are not a current price. The City of Snohomish, Washington, quoted USD 4,400 per 300-gallon (1.14 m³) tote of 15 % peracetic acid with a Safe-T-Feed system, one bid at its 2023/2024 contract pricing, in the Frequently Asked Questions of its 2025 WWTP Chemicals RFP. Quotes differ with strength and basis, annual volume, tote or bulk delivery, freight distance, contract term and the FIFRA-registered label the use requires. Send one specification and request quotes for water treatment chemicals on the same PAA basis.
Where Does Peracetic Acid Sit Among Oxidants for Water Treatment?#
PAA is the organic peroxygen among the water treatment oxidants, beside hydrogen peroxide. All 17 oxidant substances, peroxygens and halogens alike, are compared under oxidants and oxidizing biocides for water treatment. Oxidizing and non-oxidizing biocides are compared under biocides for water treatment.
Peracetic acid FAQs#
Does peracetic acid form chlorinated disinfection by-products?#
No: PAA is halogen-free and forms no chlorinated disinfection by-products. The US EPA 2012 fact sheet attributes this to PAA containing no chlorine.
Does a PAA-disinfected effluent always need quenching?#
No: Frankfort held its PAA residual below 1 ppm at discharge without any quench step.
Chlorinated effluents, by contrast, are quenched with dechlorination chemicals.
Is peracetic acid used in drinking water treatment?#
No NSF/ANSI/CAN 60 listing exists for PAA (NSF listings, 2026-10-20), so its water uses are wastewater, CSO, cooling, process water and membrane sanitization. Drinking water plants use listed disinfectants instead.
Is peracetic acid used outside water treatment?#
Yes: PAA is also a sanitizer outside water treatment. Its food-contact use falls under 21 CFR 173.370 (peroxyacids), a rule this reference does not cover.