Tissue Digestion - Technical Information

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Formaldehyde Destruction

Aldehyde-Containing Fixatives and Embalming Fluids
The most common fixative used in preparing tissues for histology and histopathology is 10% formalin (4% formaldehyde); that most often used in preparing tissues for electron microscopy is 2% glutaraldehyde. Glutaraldehyde is also widely used in medicine and biomedical research as a disinfectant (under the name Cidexr) for instruments and surfaces. Both formalin and glutaraldehyde are classified by the U.S. Environmental Protection Agency as "characteristic hazardous wastes." It is well known that aldehyde groups react with amino groups to form Schiff bases, thus involving the reactive group(s) of the aldehydes in a stable chemical bond and rendering it harmless. This reaction has been the basis for several commercially available solutions for the disposal of waste aldehyde.

The WR2 Process produces a hydrolyzate solution that contains 5 to 6% amino acids and small peptides. Waste formaldehyde or glutaraldehyde may be added to Tissue Digestors at the beginning of the Process or, preferably, through an accessory port after the digestion cycle has been completed and the hydrolyzate has cooled to below boiling temperature.  After addition of the aldehyde, the solution may be heated, again, and circulated for 15 to 90 minutes (depending on the temperature at which the reaction is run) to allow the aldehyde and amino groups to react. The hydrolyzate produced from the digestion of 100 lbs of animal tissue will provide sufficient amino groups to dispose of up to 10 gallons of waste formalin. This method, too, has been in use regularly at the Albany Medical College since 1994, where it is used to dispose of the still bottoms from the redistillation of formaldehyde as part of their chemical recycling system. 

Conventional embalming fluids usually contain phenol, another characteristic hazardous waste, in addition to aldehydes. In a hot alkaline solution, formaldehyde and phenol react to form a plastic, Bakelite, which is completely insoluble, thus rendering both hazardous wastes harmless and leaving bakelite "crystals" of molecular dimensions suspended in the hydrolyzate.

Destruction of Formaldehyde in Solution Under the Conditions of the WR2 Process (at 1 atm. - 100°C) Measured With the Purpald Reaction