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 (indirectly)
  • Pasteurization
  • Autoclave (steam)
  • Hot Air Ovens
  • Encapsulation is not a heat treatment although sometimes heat evolves.

High temperature operations are

Moist Heat Sterilization and Disinfection

Moist heat has been used to disinfect materials and equipment used in healthcare for decades. While this process started as a folk practice and evolved over the years, it has become accepted practice.

Pyrolysis and incineration operate at over 200°C or 400°F and usually over 1000°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°F. 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 does not discriminate on the basis of . 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 or around 2000 °F.


Water can be heated to destroy bacteria; pasteurization is a key part of food processing. The drug industry pasteurizes water at 65°C to 80°C before the water is used in production of medicine. A holding time of 30 minutes at this temperature is the industry standard.

Pasteurization per se finds limited use in medical waste treatment, although heat treatment of liquids at high temperatures could be considered pasteurization. These temperatures are not sufficient to disable bacterial spores, so the process is not a form of sterilization. Hospitals often pasteurize anesthesia equipment and respiratory devices after they are used.


Promession is a new technology that combines mechanical vibration and refrigeration to destroy pathological waste. Liquid nitrogen freeze dries the tissue and motion disintegrates the waste.

Coldness as a Way to Limit Infection Risk

We keep food in refrigerators because the low temperatures forestall the growth of bacteria that will cause food to spoil. Chilling biological materials can also lower the risk of infection from medical waste. Sometimes healthcare waste is refrigerated until it is transported off site. The World Health Organization suggests a rule of thumb that depends on the climate zone. For cold climates, maximum storage time should be 72 hours in the winter and 48 hours in the summer. For warm climates, the max storage time should be 48 hours in the cool season and 24 hours in the hot season. The WHO says infectious waste can be stored for a week in a refrigerated room or box (under 8 °C).