Since early 1900s chlorine is being used as water disinfectant. It was favorite to the industries
like water and wastewater for disinfection until several harmful disinfection by-products
(DBPs) in chlorinated water was discovered. Since then the water community started looking
for alternative disinfectant such as ozone, UV, PAA, and Hydrogen Peroxide (HP)etc.
Disinfection by-products (DBPs) form when organic and mineral materials in water react with
chemical treatment agents when disinfecting water. For example Trihalomethanes (THMs)
(haloforms), Haloacetic acids and and many others.
Trihalomethanes (THMs) are chemical compounds in which three of the four hydrogen atoms
of methane (CH4) are replaced by halogen atoms. THMs are also environmental pollutants,
and many are considered carcinogenic. Trihalomethanes with all the same halogen atoms are
Molecular Formula IUPAC name Common name
CHF3 trifluoromethane Fluoroform
CHCl3 trichloromethane Chloroform
CHBr3 tribromomethane Bromoform
CHI3 triiodomethane Iodoform
Currently chlorine is proven to be the main source for causing several harmful disinfection by
products (DBPs). Studies are being done to find and eliminate the DBPs precursors and look
for the alternative disinfectant. PAA, mostly known as a water & wastewater disinfectant in
European countries, because of its similar disinfection abilities to chlorine, without producing
any harmful DBPs.
The Peracetic Acid (PAA) is a chemical product belonging to the peroxide compounds as
Hydrogen Peroxide (HP). But unlike HP, it is a more potent antimicrobial agent, being rapidly
active at low concentrations against a wide spectrum of microrganism. It is sporicidal even at
low temperatures and it remains effective also in the presence of organic matter. Peracetic
Acid has high germicidal efficiency and sterilizant capability and his degradation residuals are
not dangerous for environment or toxic for human health. Until 1960 it has a little application;
though, from these years the Peracetic Acid has found special interests in the food processing
industry, and actually is considered the only agent able to replace the glutaraldehyde in the
surgical, medical and odontoiatric instruments sterilization. The core of actual medical
applications of Peracetic Acid is its potent antimicrobial action, also at low temperatures, and
the total absence of toxic residuals.
Physical and Chemical Properties
Peracetic acid (also known as peroxyacetic acid, or PAA), is a organic peroxide, explodes at
110 C. It should be is transported and stored in diluted solutions to prevent explosions.
Molar mass 76.05 g/mol
Appearance Colorless liquid
Odor Strong like vinegar
Density and phase 1.13 g/ml, liquid
Solubility in water 10 g/100 ml (19 °C)
Boiling point 105°C
There are several methods to produce peracetic acid.
1. PAA is produced by reacting acetic acid and hydrogen peroxide. The reaction is allowed to
continue for up to ten days in order to achieve high yields of product according to the
2. An additional method of preparation is the oxidation of acetaldehyde.
3. Alternatively, it is produced as an end product of the reaction of acetic anhydride, hydrogen
peroxide, and sulfuric acid.
4.Recently a solid powdered form of PAA involves the reaction of TAED in the presence of
an alkaline hydrogen peroxide solution.
Mechanism of the perhydrolysis
On dissolving the persalts (percarbonates) in water, Hydrogen peroxide is released, which
rapidly dissociates under the alkaline conditions of the washing liquor. The formation of
perhydroxyl anions necessary for the perhydrolysis stage is promoted by a high pH value.
Two molecules of peracetic acid are released by nucleophilic attack of the OOH– ions on the
instable imide bonds of the TAED molecule . Since the perhydrolysis takes place much more
quickly than a hydrolysis reaction, this side reaction can be largely excluded, providing the
pH value is below 11.
Mechanism of action
PAA kills microorganisms by oxidation and subsequent disruption of their cell membrane, via
the hydroxyl radical (OH·). As diffusion is slower than the half-life of the radical, it reacts
with any oxidizable compound in its vicinity. It damages virtually all types of
macromolecules associated with a microorganism: carbohydrates, nucleic acids (mutations),
lipids (lipid peroxydation) and amino acids.
The mechanism of oxidation is the transfer of electrons, therefore the strong oxidizer will
produce faster killings or inactivation of the microorganism.
The primary mode of action is oxidation. PAA disinfects by oxidizing of the outer cell
membrane of vegetative bacterial cells, endospores, yeast, and mold spores. The mechanism
of oxidation is the transfer of electrons, therefore the stronger the oxidizer, the faster electrons
are transferred to the microorganism and the faster the microorganism is inactiviated or killed.
It has also been reported to be virucidal.
Oxidation Capacity of Selected Sanitizers
Peracetic Acid 1.81
Chlorine Dioxide 1.57
Sodium Hypochlorite (chlorine bleach) 1.36
Therefore PAA has a higher oxidation potential than chlorine sanitizers but less than ozone.
EPA had registered PAA as an antimicrobial in 1985 for indoor use on hard surfaces. It is
being used in following industries as disinfectant:
• Meat, Poultry, Seafood, processing and packaging plants.
• Food processing industries.
• Hospitals and Healthcare facilities as sterilant.
• Paper and pulp Industries.
• Water and wastewater industries
• Plumbing disinfectant.
• Water reuse applications such as cooling tower water disinfectant where it prevents bio
film formation and effectively controls Legionella bacteria.
• No mutagenic DPBs. The absence of persistent toxic or mutagenic residuals or by-
products. The disinfection end products like carboxylic acids and water are harmless to
• Synergic effect of PAA and UV has greater effects (can save lot of cost caused by using
• No alteration in disinfection tank required.
• pH, hardness, and presence of organic matters has no or little effect on biocidal activity of
• Easy implementing treatment (without the need for expensive capital investment)
• Broad spectrum of activity even in the presence of heterogeneous organic matter
• No quenching requirement (i.e., no dechlorination)
• Short contact time
There are no doubts about PAAs bactericidal, virucidal, fungicidal abilities. Usages in food
processing and medical facilities itself is a kind of approval of harmless end products. The
cost factor (production, storage and transportation) can be reduce by local manufacturing and
a much stable percentage of quaternary solution of PAA (PAA, Acetic acid, H2O2 and Water).
Furthermore powdered non-active peracetic acid based disinfectants change the cost factor.
Storage and transportation is not problem anymore.