Formaldehyde Treatment

treating formaldehyde (11K)


Formaldehyde, or formalin, is commonly used at concentrations near 3.7% in water to preserve specimens and samples. It also qualifies as hazardous waste when it is no longer needed. However, King County Wastewater Treatment Division allows us to discharge toxic formaldehyde to the sewer at concentrations of less than 0.1%. Therefore, formaldehyde must be treated to reduce its concentration before it is poured down the drain.

Treatment of formaldehyde in your laboratory is simple and easy. We currently recommend Neutralex or a similar product to destroy the formaldehyde. Use of Neutralex according to instructions will reduce formaldehyde concentrations to well below 0.1%. The concentration of formaldehyde after treatment can be determined with an indicator that looks much like pH paper.

Finally, please let us know that you are doing formaldehyde treatment by calling us at 206.616.5835 or emailing us at; by law we are required to keep track of all hazardous waste treatment on campus.

Formaldehyde treatment protocol

Below are instructions for using a packet of Neutralex to destroy 5 gallons of formaldehyde at concentrations of roughly 4% or less in water.

  1. First, put on nitrile gloves, an apron or lab coat, and goggles.
  2. Work in a fume hood or an appropriately ventilated workstation.
  3. Fill the waste container (formaldehyde neutralization container) up to the fill line (5 gallons).
  4. Add one packet of Neutralex powder.
  5. Mix the solution. This can be accomplished by stirring or by sealing the container and tipping or swirling the container from side to side. Then let the waste container sit for 15 minutes. Swirl once again right before testing.
  6. Check the pH.
    • Using a pipette, extract 5 ml of the treated waste solution and transfer it to the plastic cuvette.
    • Compare the color of the solution with the color chart provided.
    • The solution must be between 6 and 9 to be suitable for discharge.
  7. Test for residual aldehydes.
    • Add 20 drops from the brown squeeze bottle labeled "Aldehyde Test Reagent."
    • Mix the solution thoroughly.
    • Remove test strip from vial and immerse reaction zone into solution for a minimum on one second.
    • Shake off excess liquid from the strip and wait sixty seconds.
    • Compare the reaction zone color of the strip to the color scale on the side of the vial. The matching color will designate a number. This is the residual aldehyde content in parts per million (ppm) of the treated waste solution. The reading must be below 100ppm.
  8. If the results are below 100 ppm, use the siphon and discharge neutralized formaldehyde solution to the sewer. Record the quantity, pH, and formaldehyde concentration on the Chemical Treatment Log.
  9. If the reading is above 100 ppm, stir or swirl the solution and let sit for another 15 minutes. Test again. If the residual aldehyde content remains at or above 100 ppm, the waste solution cannot be sewered and must be disposed of as hazardous chemical waste.


The above procedure should neutralize formaldehyde without any trouble. The only times in our experience that it has not worked is when other chemicals, such as formic acid, were accidentally added, or if the formaldehyde concentrations much greater than 4%. To ensure that the treatment protocol works every time, keep your formaldehyde waste stream separate from other wastes and make sure that you only treat working solutions (ie, 3.7% solutions) of formaldehyde. Any waste solution that does not pass both the pH and the formaldehyde tests cannot be sewered and must be disposed of as hazardous chemical waste.

Contact us

If you have any questions or would like help with setting up this protocol for the first time, please call us at 206.616.5835 or email