Heat Treatment


A principle of medical waste treatment is that heat kills pathogens and under the right conditions high temperatures can break down hazardous chemicals. The engineer wants high temperature processes in his toolbox.

Let’s divide heat treatment into low-temperature processes and high-temperature processes. Low and high are relative, because all operate at temperatures above the boiling point of water.

Low-heat thermal technologies operate between 100 °C and 180 °C.

Low-heat processes can be either moist (saturated steam or high humidity) or dry-heat.

  • Microwave
  • Irradiation (sort of)
  • Autoclave (steam)
  • Hot Air Ovens
  • Encapsulation is not a heat treatment although sometimes heat evolves.

High temperature operations are

  • Pyrolysis
  • Incineration

Pyrolysis and incineration operate at over 200 degrees C or 400 degrees F and usually over 1000 degrees F.

Pyrolysis can be thought of as a "slow burn". It takes longer and is at a lower temperature, although it is usually paired with a secondary chamber to burn the gaseous exhaust from the primary pyrolysis hearth. In some starved-air pyrolysis units, the temperature is on the order of 1500 degrees. The secondary chamber is a true incinerator with an excess of air and a higher temperature (2000 F or more) to complete combustion of organic compounds like carbon monoxide. (Without this secondary chamber, pyrolysis units would be too polluting to be permitted.)

Incineration is a great technology for many wastes - it is a big, dumb operation that consumes so much. No pretreatment is typically needed. All types of incinerator destroy pathogens and effectively leave a sterile ash. In some sense this is overkill, as it is not necessary to destroy every pathogen (landfills where the ash ultimately goes are not sterile). However, there are other reasons to incinerate waste than just killing microbes. Incineration can destroy chemical toxins by oxidizing them. Some pharmaceuticals, in particular, pose environmental hazards at even low levels, so high efficiency is required in the treatment - this may require higher temperatures than what is needed to combust unobjectionable organic material and to sterilize.

As a rule of thumb, incineration units operate at 2000 degrees F, at least in the secondary chamber.