Microwaves
Microwaves are electromagnetic waves with a frequency between radio waves and infrared waves on the electromagnetic spectrum[1].
When applied to the treatment of Healthcare Waste, the mechanism of microbialinactivation is thermal. It is important for the Waste to be wet, either as a result of moisture naturally occurring in the waste stream or by the addition of moisture in the form of steam. The combination of the two – microwaves and moisture – creates the thermal process[1]. Some treatment processes utilise Microwaves to heat water to form steam, which is then applied to the infectious Waste stream. “Dry” microwave systems are also available. These use direct microwave energy in a nitrogen atmosphere to treat the waste and produce higher treatment temperatures than those used by “wet” microwave technologies[1].
Microwave treatment units can be either on-site installations or mobile treatment vehicles. The processing usually includes front-end shredding of the waste, both to increase the efficacy of the microwave treatment and to reduce the volume of the end waste for disposal. If the waste is dry, water is introduced and the wet waste is introduced to the microwave chamber[2]. Typical operation is at 2450 Hz. Microwave power causes the temperature of the water to increase. If an autoclave provides heat from outside the waste, the microwave unit transmits energy as microwaves and that energy turns into heat inside the wet waste[2].
Microwave disinfection works only when there is water in the waste because the radiation directly works on the water, not the solid components of the waste[2]. For this reason, treatment units are often supplied with a humidifier. Processing time is in the region of 20 minutes per batch[2]. With enough power the water is converted to steam and makes all of the waste around 100°C. The entire process takes place within a single vessel[2].