Pathological waste differs from most medical waste in that it has a higher moisture content. Human anatomical waste is 70 to 90 percent water. Most pathological waste is incinerated. Pathological waste tends to have a high moisure content and a heating value of about 400 to 2000 kcal/kg, or 720 to 3600 BTU/lb, so assist fuel is needed in the incinceration.
What is the difference between incineration and cremation? There isn’t one, really. It’s mostly a matter of how humans regard the process. Incineration is soulless and industrial. Cremation is done in the context of a ceremony, often with friends and family present. But both processes basically burn off the moisture and the combustible material, leaving remains that are often called ash. (Strictly speaking, this isn’t ash in an engineering sense, so the more correct term is "cremation remains".) The remains from cremation is often venerated or disposed of in a ceremony while the ash from incineration is packaged for disposal in a landfill.
Waste that is recognizable as a part of the body is called anatomical waste. Anatomical waste makes people “freak out” when they see it; the reaction is similar to that experienced in a horror movie. The emotional, visceral reaction is one of repulsion. Also, people are afraid the anatomical waste poses a hazard to their health. Bodies have a special place in most cultures, and we treat dead bodies with respect. Even parts of bodies are honored in many cultures; in Muslim countries body parts are expected to be given to the family of the diseased, and to be buried.
Anatomical waste includes organs, and amputated body parts as well as teeth and gums and jawbone. Hair and nails are included by some regulatory authorities. Pathological waste that is not anatomical waste includes body fluids and their containers including fluids that come out of the body during surgery.
Some cultures bury placentas, and burial reduces the odds of disease transmission in densely populated areas. Placenta pits are engineered systems, not just holes in the ground. About 5 liters is allowed for each placenta. It is also possible to put pieces of the body in a pit. When full, they are capped. Over time biological processes degrade the tissue and eliminate harmful pathogens.
Just as waste food can be composted, so can pathological waste, although some people may object to treating human tissue that way. Small backyard composters operate at ambient temperatures. Large compost piles that accept material from commercial sites and entire neighborhoods are generally more efficient and operate at higher temperatures (140 °F or so). Sometimes worms are put in the mix in a process called vermicomposting.
Pathological waste is not usually put in composters, with the exception of placentas. Human psychological considerations prevent human body parts from being composted.
Irradiation treatment exposes waste to electron beams, cobalt-60 or ultraviolet sources. The pathogen destruction efficacy depends on the radiation dose absorbed by the waste. Electron beams can penetrate waste bags, thereby eliminating the need for a mechanical shredding before treatment.
Ultraviolet radiation (wavelength 210 nm to 328 nm) can destroy airborne microorganisms. It is sometimes used as part of the overall treatment system, but it is rarely a main treatment unit. Unlike electron beams, UV radiation is not able to penetrate closed waste bags.
When waste management engineers incorporate irradiation into their process, they usually have to install personnel protective shielding.
Dissolved chlorine dioxide, bleach (sodium hypochlorite), peracetic acid, lime solution, and dry inorganic chemicals (e.g. calcium oxide) are employed in treatment of pathological waste.
In liquid systems, the waste may go through a dewatering section to remove and recycle the disinfectant. Besides harsh oxidants, acids, and bases, there are also encapsulating compounds that can solidify sharps, blood or other body fluids within a solid matrix before disposal. If done correctly, this process reduces the possibility of future leaching of hazardous materials into groundwater.
Some systems uses heated sodium hydroxide solution or calcium oxide/lime slurries to digest pathological waste in heated stainless-steel tanks. After the digestion/treatment, the waste is no longer recognizable as of human origin, and typically has little or no microbial activity. Further treatment (such as encapsulation or incineration) is required before final disposal.