Thermal Combustion and Thermal Sterilization of Medical Waste
Thermal combustion treatment of medical waste uses the high water content of medical waste to provide a heat transfer medium that helps to distribute the heat throughout the waste. There are various types of thermal treatment for medical waste including microwave treatment and autoclaves.
The problem with thermal combustion is that when water is used as a heat transfer medium the water is not sufficient to kill many of the hardier microorganisms such as spore-forming species. Boiling water can effectively kill many biologicals but it does not neutralize all microorganisms and therefore it is necessary to add additional measures in order to make thermal treatment effective. One of the most common ways to increase the effectiveness of thermal combustion is to treat the waste in a pressure chamber that allows the boiling point of the water to increase as the pressure is raised within the chamber. This type of thermal combustion treatment is known as an autoclave and is a very commonly used form of medical waste treatment.
Another form of treatment that is widely used in medical units is the microwave. Microwave treatment of medical waste involves using the thermal combustion (water that is heated) as well as high intensity radio waves that deliver energy where it is needed for sterilization purposes. Unfortunately, if the medical waste is too dry then the microwave treatment will not be effective at sterilizing. Microwave treatment of medical waste is best performed when the waste is first shredded to allow the microwaves to penetrate evenly throughout the waste.
Autoclaves and microwaves do have some advantages including the lowered chance of volatiles being emitted during the treatment process. Since autoclaves and microwaves use thermal combustion and do not require air to be introduced during the treatment process the only time the emissions of volatiles will occur is during the loading or unloading process. This risk can be even further reduced with proper design and operation of the treatment unit.
Thermal combustion treatment methods are somewhat expensive in contrast to dry heat methods of treating medical waste such as incinerators. Additionally, dry heat methods can also reduce the weight and volume of the waste significantly more than a thermal combustion method such as autoclaving or microwaving. However, dry heat systems have additional concerns related to the emission of volatiles and pathogens into the air which is typically not a concern with thermal combustion methods.
Thermal combustion treatment of medical waste requires a minimum contact time to ensure that the heat reaches all of the waste to be treated and for the amount of time that is necessary to assure pathogen destruction. For large quantities of waste, higher temperatures are needed in order to process the waste in a shorter time. There are various other heating methods that are used to process medical waste including the use of plasma arcs that create an electric discharge to produce heat and pyrolysis which uses induction to break down organic molecules into simpler molecules. Unfortunately, with these types of waste treatment methods, it can become difficult to treat the resulting waste that is emitted into the air in the form of various gasses such as carbon monoxide.