Chlorine has been a reliable disinfectant in the wastewater industry for quite some time. As we have become more conscious of protecting the environment, more stringent regulations, as well as the need for dechlorination, the processes and cost of disinfection have been evaluated more and more. A viable alternative has come to the forefront; so many systems are weighing out the advantages and disadvantages of changing to Peracetic acid disinfection.
Peracetic acid is a clear, odorless liquid combination of hydrogen peroxide, acidic acid and water, typically at a concentration of 5–15 percent. Peracetic acid reacts with organic matter in wastewater. The less the organic load is, the shorter reaction time that will be required. This is usually accomplished in less than 30 minutes, and any contact time after that is insignificant. Since peracetic acid is much safer for the environment as it reduces or eliminates disinfection by-products, sodium pollution and total dissolved salts in treated water. This also assures there are no toxic residuals, mutagenic or carcinogenic compounds after the disinfection process is completed. This is much safer for release into streams, lakes, rivers and other animal-inhabiting waterways. Peracetic acid is safer to store than conventional disinfectants, has a very low freezing point and is more stable than bleach or chlorine. Less than one percent activity is lost per year due to storage. Its great oxidizing capacity results in cell wall disintegration. There is very little retrofitting that has to take place to convert from chlorine to peracetic acid, and start-up costs are minimal. Some stainless steel piping may be required, which will be the most of the transition and expenses
Peracetic acid does have a few shortfalls. It is less effective than chlorine in the inactivation of spores, viruses and protozoa, which include Giardia and Cryptosporidium. When organic loads are high, higher initial doses of peracetic acid that satisfy the demand for proper treatment can allow the proper disinfection to occur and establish a residual. This has to be monitored closely in order to make sure that disinfection is complete and permit parameters are met. Also, regulatory agencies have been struggling with how to address permitting, due to the lack of an EPA-approved method to monitor peracetic acid.
For more information on conducting studies and implementing peracetic acid trials at your facility, please contact Terry Humphries or Greg Goode at the Division of Water 502-564-3410.