How to quench peracetic acid: Methods and safety

To quench peracetic acid, introduce a reducing agent such as sodium metabisulfite or sodium bisulfite into the solution. These agents react rapidly with the active peracetic acid, neutralizing its biocidal properties and converting it into non-harmful byproducts like acetate and sulfate. This process is critical when residual disinfectant could interfere with subsequent processes or pose a safety risk.

Choosing the right reducing agent

Sodium metabisulfite is a common choice because it is effective and readily available. Sodium bisulfite serves a similar function and is often preferred in aqueous environments due to its high solubility. Both substances work by donating electrons to the peracetic acid, effectively destroying the peroxide bond that gives the acid its oxidative power. The choice between the two often depends on local availability and specific equipment compatibility, but the chemical outcome remains the same: the loss of disinfectant activity.

Dosing and verification

The amount of quenching agent required depends directly on the concentration of peracetic acid present. Under-dosing leaves active oxidant in the system, which can cause corrosion or biological issues later. Over-dosing introduces excess sulfite into the stream, which may interfere with other chemical processes or increase the biological oxygen demand of the wastewater. Operators should calculate the dose based on the known concentration of the peracetic acid or conduct a small-scale test to find the endpoint. After adding the quenching agent, mix the solution thoroughly and allow time for the reaction to complete. Verify that the peracetic acid level has dropped to zero using appropriate test strips or a titration method before releasing the liquid or proceeding with the next step.