History, Synthesis and Storage Considerations
Peroxyacetic acid’s, also known as Peracetic acid “PAA”, process and production were issued a US and UK patent to FMC Corporation on March 11, 1969 (US Patent # 3,432,546). The process utilized a reactor tube vessel to blend Acetic anhydride, Hydrogen peroxide, and an Ammonia catalyst to carefully control and create an equilibrium mixture that had unique oxidative biocide properties. The Peroxyacetic acid molecule is the one that imparts the microbiocidal activity to the mixture, and its actual concentration is the one that is diluted down for a variety of sanitizer, disinfectant, and sterilant applications in various markets.
To this day, all commercial versions of liquid Peracetic acid concentrates are an equilibrium mixture of these 3 molecules, many times including a stabilizer (ex. Sulfuric acid). Peracetic acid mixtures can contain from roughly 5% PAA up to 35% PAA with each PAA concentration having a variety of Acetic acid and Peroxide concentrations.
For storage and stability along with application concerns, the Peroxide concentration in the PAA product is more critical than the Acetic acid. This is because due to the Peroxide moiety, the stored Peracetic Acid concentrate will generate Oxygen. That is why any manufacturer of PAA must utilize a vented container and prohibit any flame, smoking or electrical sparks that may ignite the flammable Oxygen generated by the PAA concentrate.
The Peroxyacetic acid molecule is the biocidal segment. In fact, 100-200 ppm of PAA is far more biocidal than 10,000 ppm of Hydrogen peroxide. Peracetic acid behaves like other true oxidant biocides like Ozone, Chlorine dioxide, and Hypochlorous acid in disrupting protein synthesis and other intracellular functions in bacteria and fungi including cell membrane and wall metabolic functions.
Peracetic acid, however, is sensitive to pH variances with alkaline conditions above pH 8, and especially at pH 9, which disrupts the equilibrium effect and the Peroxyacetic acid molecule itself, thus destroying its biocidal activity. Therefore, it’s a very important consideration in both liquid and foam applications of the PAA sanitizer/disinfectant to have an operational pH below 8, preferably below pH 7.
Applications and Exposure
Initially, Peracetic acid was utilized in bleaching applications for paper pulp. While it can still be utilized for this application, it is now currently utilized for ware wash bleaching applications. In fact, Peracetic acid can be generated in situ in some laundry detergents, in ware wash, and other generator applications without the above process originally patented by FMC Corp years ago.
In European pharmaceutical and food applications in the late 20th century, liquid Peracetic acid was utilized extensively in CIP applications because its disinfectant byproducts were deemed as safe to the environment (“GRAS”) while having broad microbiocidal activity. This same usage for Peracetic acid was established in CIP sanitation applications in North America as well.
However, because of its pungent odor, due to both the Peroxyacetic acid and the Acetic acid, limited its utilization as an open surface sanitizer. Only with the advent of foam additives, did the utilization for open sanitization and disinfection expand rapidly in janitorial, food and beverage, and other processing applications.
The foam additives were initially developed to expand the Peracetic acid use into open applications to control/suppress the odor. However, the actual benefits of the foam additive, based on my own microbiological application studies were a welcome surprise. These additional application benefits included targeted control usage, contact time, and most importantly, penetration of the Peracetic acid molecule into dried films, biofilms and bacterial/fungal spore coats. This has expanded application benefits to include environmental sanitization and disinfection applications in a variety of markets.
Another major avenue of application of liquid Peracetic acid has been in the realm of food product intervention strategies. There have emerged, in the past 20 years, a variety of Food Contact Notifications for Red Meats (beef, veal and pork), poultry, and seafood to reduce the bioburden in these raw products, particularly pathogen reductions of Listeria, Salmonella and STEC (ex. E. coli O157:H7) strains in both direct water rinse and ice applications.
Peracetic acid is also utilized to control biofouling in a variety of waste water treatment applications, and in cooling towers and swamp coolers. The CDC has identified it as an excellent chemo-sterilant for medical devices like endoscopes, etc. and many Peracetic acid manufacturers have EPA registered approvals for these applications.
Peracetic acid is the only approved sanitizer for USDA Organic under the NOP for organic processing surfaces. It is not only no rinse, but requires NO verification of a residual concentration threshold that are mandated for Chlorine dioxide and Chlorine.
Peracetic acid has always been heavily utilized in Brewery CIP applications because it can be safely and efficiently utilized under carbonation in Fermenters and Bright Beer tanks without removal of CO2. This is a huge benefit to the Brewery operations.
Since Peracetic acid is a strong oxidant, the inhalation concerns have been increasingly investigated the past several years. For many years, Peracetic acid inhalation exposure limits were monitored due to the acetic acid levels for both 15-minute exposure (STEL) and 8-hour occupational exposure (TWA).
The past decade has seen attempts to realistically quantitate the actual Peroxyacetic acid molecule in the air. This has proved more problematic than with Ozone or Chlorine dioxide, primarily because these 2 Biocides are actually gases, while Peroxyacetic acid is a liquid molecule. “Suggested” 15-minute and 8-hour exposure limits have been floated and studied. A range of 0.4 - 0.55 ppm in the air is suggested for a 15-minute inhalation exposure limit. Meanwhile, for an eight-hour exposure, a range of 0.15 - 0.17 ppm inhalation exposure limit for Peracetic acid has been put forth.
A variety of portable or mounted monitoring devices are currently being evaluated for accuracy and reliability in production environments and primarily employ electrochemical sensors to sniff out the actual Peracetic acid molecule in the working air environment. This segment of occupational exposure limits is actively evolving and ongoing with no set exposure regulatory limits established by either federal or state agencies.
There have been many ways developed to safely handle the concentrate products dispensed into diluting delivery systems. These include the excellent Safe-T-Feed systems for Peracetic acid concentrates which markedly reduce handling of the Peracetic acid products in their concentrate form.
The actual precise dilution systems include both wall mount water driven venturi systems (ex. Lafferty sanitizer wall mounts), sink delivery systems (ex. Hydro and Knight) for intervention and sanitizing, to more precise water driven dilution pumps (ex. Dosatron) to electric driven pumps (LMI, Etatron and ProMinent).
Verification of use-concentrations, and its regulation of dose, can be achieved via a variety of titration kit systems, bench top or in-line Ampero-metric probes specific for the Peracetic acid molecule.