Irradiation
Irradiation disinfects waste by exposing it to gamma rays that are fatal to bacteria using the radioactive isotope of Cobalt75[1]. In irradiation for sterilization of equipment or treatment of waste, the radiation is intended to kill pathogens[1]. When UV is used for disinfection, the radiation in the UV-C spectrum, which is more germicidal is employed[1]. Some irradiation treatment systems use electron beams. Both gamma rays and electron beams can penetrate plastic bags used for waste collection, so the waste does not need to be removed from the bag before treatment[1].
Irradiation does not change the appearance of the waste so process designers often install mechanical grinding or shredding upstream. This also makes the waste pieces smaller, which tends to enhance the efficacy of the treatment.
Unlike some other treatment methods, irradiation requires a dedicated place, there are no mobile treatment modules that use radiation[1]. It is fairly expensive to build an irradiation facility and operating precautions must be taken to protect workers from radiation. These are among the reasons this method is not widely used, especially when heat treatment methods are typically just as effective[1]. The efficiency of irradiation as a sterilization process depends to a large extent on the total energy delivered, but even then, waste surfaces facing the radiation source get more sterile than the waste on the shaded side. Odd-shaped waste pieces may not get adequate exposure to the radiation, if contaminated surfaces face away from the cobalt source. Heat treatment, by contrast, brings every piece of waste to an adequate temperature for sterilization if done correctly[1].