Peracetic Acid: An Effective Wastewater Disinfectant
By Jacquelyn N. Wilson
Peracetic acid (PAA) is one of the most versatile and widely used disinfectants on the market. PAA has proven to be an excellent sanitizer and disinfectant in the food, beverage, cosmetic, pharmaceutical, and agriculture industries for industrial water treatment, as well as an excellent disinfectant for use in the wastewater treatment industry.
PAA exists in an equilibrium with hydrogen peroxide, acetic acid, and water, with a potent, non-discriminant, oxidizing chemistry that exhibits higher oxidization potential than common halogen chemistries such as sodium hypochlorite bleach, gaseous chlorine, and chlorine dioxide.
The most common PAA concentrations on the market for wastewater disinfection are 12 percent, 15 percent, and 22 percent active PAA.
PAA is a non-persistent chemistry. Upon addition to water, PAA will degrade naturally over time. In the presence of organic matter, the degradation rate of PAA is increased. PAA constituents eventually break down to their separate components: acetic acid and oxygen. This helps to reduce impacts to the receiving stream or body of water by releasing minimal residual chemicals.
Since PAA is not composed of halogens, such as chlorine, it does not produce harmful disinfection byproducts (DBPs) such as trihalomethanes (THMs). The environmentally friendly nature of PAA is one of the primary reasons for wastewater facility management to seek this alternative.
PAA can be used for the disinfection of all types of wastewater, including primary, secondary, tertiary, and bypass flows, as well as sanitary sewer overflows (SSOs) and combined sewer overflows (CSOs). Dosages of PAA can vary for each of these applications based on background levels of total suspended solids (TSS), color, algae, and reducing agents.
In secondary wastewater facilities, average feed dosages to achieve disinfection range from 1.0 ppm to 3.0 mg/L (ppm) active PAA. The PAA product is typically fed neat. Dilution prior to injection is not recommended because the product will begin to work as soon as it contacts the contaminated water.
PAA feed is best controlled with a flow-paced pump and residual monitoring. Concentration x Time (CT) curves have been developed for better control and efficient use of product. PAA can be fed using diaphragm or peristaltic chemical pumps. It is important to ensure that all equipment is comprised of PAA compatible material