Formaldehyde reacts with ammonia to give hexamethylenetetramine, which is so less toxic compound as to be employed orally or intravenously in medicine. The treatment of waste formalin by use of the above reaction was studied. When ammonia, the molar ratio of which to formaldehyde in waste formalin was in the range from 2/3 to 2, was added to the waste formalin and adjusted to pH 8.5, the residual concentration of formaldehyde decreased from 92000 ppm to 30 ppm or less after 24 hours. No significant changes in pH before and after the treatment were observed.
