For proper disposal of formaldehyde, a chemist or hazardous waste contractor adds chemicals, such as sodium hydroxide and hydrochloric acid, to the solution to bring the pH to a neutral level. Then, he discharges the neutralized solution to the sewer.
The hazardous waste contractor first places the formaldehyde in a neutralization container. After adding the neutralizing chemicals, he checks the pH of the solution with a pH meter or litmus paper. Then he tests for any residual aldehydes and discharges the solution only if all the tests provide normal results.
If the solution doesn’t have a pH value in the required range or presents high levels of residual aldehydes, the contractor tests the solution again in 15 minutes. If the results are still above the required limits, the contractor can’t sewer the solution and must dispose of it as hazardous chemical waste.