Definition and Classification of Medical Waste
Medical waste refers to waste generated by medical and health institutions during medical, preventive, health care, and other related activities that is directly or indirectly infectious, toxic, or otherwise hazardous.
Medical waste is divided into five categories: infectious waste, pathological waste, sharps waste, pharmaceutical waste, and chemical waste. All of these are currently included in the National Hazardous Waste List.
Because medical waste has special hazardous properties, it also requires specific treatment methods to eliminate its dangerous characteristics. Currently, the following medical waste treatment methods are commonly used domestically and internationally.
1. Sanitary Landfill
The sanitary landfill method involves burying waste in the ground, where it decomposes into harmless substances over time through the action of microorganisms.
If the landfill system for medical waste is not properly impermeable, various toxic substances, pathogens, and radioactive materials will seep into the soil with rainwater, and harmful substances will enter the human body through the food chain, endangering human health.
Therefore, sanitary landfill sites must be scientifically selected and lined with clay, high-density polyethylene (HDPE), and other impermeable materials. Landfill gas collection and extraction pipelines must also be installed.
Thus, the landfill treatment method must be used very carefully, and medical waste must undergo strict pretreatment in accordance with relevant regulations.
2. High-Temperature Incineration
Incineration treatment is a deep oxidation chemical process. Under the action of a high-temperature flame, medical waste inside incineration equipment undergoes three stages: drying, ignition, and incineration, transforming into residue and gas.
Infectious and harmful substances in medical waste can be effectively destroyed during the incineration process. Incineration technology is suitable for various types of infectious medical waste.
Incineration requires high and stable furnace temperature, good oxygen mixing conditions, sufficient gas residence time, and other conditions. At the same time, the final discharged flue gas and residue require environmentally sound disposal.
3. Autoclave Sterilization
The pressure steam sterilization treatment method processes medical waste under high-temperature, high-pressure conditions for more than 20 minutes. The pressure steam penetrates the interior of the objects, causing microbial proteins to coagulate, denature, and be killed.
It should be noted that when using this treatment method, medical waste must be shredded. Shredding can be performed before or after cooking.
However, according to the “Medical Waste High-Temperature Steam Sterilization Treatment Technology Control Specifications” announced by the State Environmental Protection Administration, pathological waste such as human tissue and animal carcasses are not suitable for treatment by this method, and it is not efficient for treating pharmaceutical and chemical waste.
4. Pyrolysis Method
Pyrolysis is a process that extracts fuel oil, grease, and gas by utilizing the thermal instability of organic matter in waste. It involves heating and distilling under anaerobic or oxygen-deprived conditions, causing the organic matter to undergo thermal cracking and form various gases, liquids, and solids after condensation.
5. Chemical Disinfection Method
The essence of the chemical disinfection method is to mix shredded medical waste with a certain concentration of disinfectant (sodium hypochlorite, peroxyacetic acid, glutaraldehyde, ozone, etc.) and ensure sufficient contact area and contact time with the disinfectant.
Organic matter is decomposed and microorganisms are killed during the disinfection process. Maximum contact between disinfectant and medical waste is a prerequisite for treatment effectiveness. Shear-type crushing equipment is used to increase the degree of fragmentation and ensure disinfectant penetration.
The chemical disinfection method is suitable for treating liquid medical waste and pathological waste, but recently it has also been gradually used for medical waste that cannot be sterilized by heating or wetting.
6. Microwave Sterilization Treatment Method
Microwave disinfection technology is a newer medical waste treatment technology, but it is still limited to small-batch, intermittent treatment of medical waste and cannot meet the requirements of high-volume, continuous treatment.
Other methods such as dry thermal shredding technology, irradiation technology, plasma method, and electric arc furnace technology are very rare in practical applications and are not described in detail in this article.
Comparison of Six Medical Waste Treatment Methods
Sanitary landfill is generally used as a supporting means for the final treatment of other technologies and is rarely used alone.
High-temperature incineration is suitable for all types of medical waste. The volume and weight of incinerated waste are significantly reduced. Disinfection, sterilization, and pollutant removal effects are good, and the technology is mature. However, construction and operating costs are very high, and it produces dioxins and other highly toxic substances and harmful gases.
Autoclave sterilization has low investment, low operating costs, and low residue hazard. However, it is prone to malodor and possible air pollution emissions. Medical waste must be crushed to a size less than 50 mm.
Chemical disinfection is divided into dry and wet types. Its process equipment and operation are simple and convenient, with good deodorization effect and a rapid disinfection process. The dry type needs to be used together with crushing treatment, while the wet type produces waste liquid and exhaust gas.
Current Status in China
Currently, 261 large and medium-sized cities in China have established their own medical waste disposal facilities, achieving centralized disposal of medical waste in their regions.
Among them, more than 140 disposal centers use the high-temperature incineration method, more than 120 disposal centers use the autoclave sterilization method, and several use microwave sterilization, dry chemical, and pyrolysis methods. It is worth noting that the market share of the autoclave sterilization method is still growing.
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