What are the most common treatment techniques for medical waste?

The selection of appropriate treatment technique is one of the important considerations for an efficient waste management system, and depends on a variety of parameters such as the waste type and quantity, required level of cleanup, duration of treatment, availability of financial, material and human resources, availability of land, electricity and means of transport, social factors, sufficient space around the hospital, etc.

Various technologies for medical waste treatment and disposal have been developed to meet the challenges of increasing medical waste generation, such as sanitary landfill, chemical disinfection, autoclaving, incineration, pyrolysis, plasma gasification, encapsulation, microwave radiation, etc. Below, we will briefly describe a few of these techniques.

Sanitary Landfills

Sanitary landfilling is the ultimate disposal method of medical waste. This method adopts measures such as anti-seepage layer, stratified landfill of garbage, and top layer covered with soil layer after compaction. If the sanitary landfill does not have anti- seepage measures, various harmful substances, pathogenic agents, radioactive substances, etc. will penetrate into the soil with rainwater, and then will enter the human body through the food chain. Moreover, landfilling of medical waste produces a large amount of harmful gases such as methane, ammonia, sulfides, nitrogen, carbon monoxide, etc., and also oxygen and hydrogen. Therefore, the disposal of medical waste in sanitary landfills must be carried out very cautiously according to relevant regulations.

Incineration

Incineration is considered as the typical method of medical waste treatment due to its ability to decompose different materials and destroy organisms and pathogens. However, this method cannot be applied to pressurized gas containers, reactive chemicals, silver salts, waste with high contents of heavy metals such as mercury or cadmium, halogenated plastics such as PVC. Three basic types of the incinerator are of interest for medical waste treatment: (a) Rotary kilns (>1200°C); (b) Double-chamber incinerators (800-900°C); and (c) Single-chamber incinerators (300-400°C). The incineration process converts the waste into ash and gases and is often suitable for all kinds of pathological and infectious wastes. One serious drawback of this process is the emission of dioxins, furans, and mercury. Dioxins and furans are classified as known human carcinogens, and are persistent footprints on the environment. These harmful gases emitted can also be treated using flue gas treatment. Nevertheless, this treatment is not implemented in many developing countries. So other methods are developed to supplement or replace traditional incineration method.

Chemical Disinfection

Chemical disinfection is used to kill microorganisms and fight off pathogens by using various chemicals such as phenolic compounds, hydrogen peroxide, sodium hypochlorite, peracetic acid, glutaraldehyde, formaldehyde, ozone, etc. In this method, the maximum contact between disinfectant and medical waste is essential to ensure the treatment effect. The chemical disinfection is suitable for the treatment of pathological garbage and liquid-based waste like blood, urine, or hospital sewage. But the chemotherapy waste, radioactive waste, volatile and semi-volatile organic compounds should not be treated with chemical disinfection. This treatment method directly affects those in charge of the treatment due to the inhalation of volatile chemicals or irritations to the skin and eyes. The residues of the chemical disinfection treatment are liquid and solid residues that are disposed of in the sewer system and landfill, respectively.

Autoclave

Autoclaving is an effective process of killing microbes through the application of moist heat under pressure. Autoclaves operate at a lower temperature than incineration but with pressure and steam influence to achieve disinfection. Because autoclave treatment merely heats the waste to a sufficient temperature to kill microorganisms, the appearance of the waste does not change, and the pathogens are not removed. As a result, autoclaved waste is often re-treated via incineration before final disposal in landfills. This double treatment of infectious medical waste increases the disposal costs and creates environmental impacts due to energy consumption in the autoclaving process. It should be noted that the autoclaving method is not suitable for chemotherapy treatment waste, volatile or semi-volatile organic compounds, mercury, radioactive waste, chemical and pharmaceutical wastes.

Pyrolysis

Pyrolysis is one of the thermochemical processes wherein the organic compounds present in medical waste are disintegrated at high temperatures in the absence of oxygen. Pyrolysis differs from incineration because the waste is thermally decomposed without oxygen into low molecular weight hydrocarbons, which can then be used as fuel to run the pyrolysis plant and produce renewable electricity. The main advantage of the pyrolysis process is the conversion of hazardous and dangerous medical waste into valuable products like oil and char. The absence of oxygen in the pyrolysis of chlorine-containing wastes leads to a remarkable decrease in the formation of dioxins in comparison with the incineration process, which indicates a significant advantage of pyrolysis over incineration in terms of ensuring the environmental safety of the disposal of medical waste containing chlorine.

Plasma

Plasma is a relatively new medical waste treatment technology that uses high electrical energy and high temperature created by an electrical arc gasifier. Due to the high operating temperatures of the plasma process, it can treat the highly cytotoxic and radioactive wastes. Although this method looks promising due to its lack of dangerous emissions, it is not now widely used in healthcare facilities due to its high energy consumption, huge capital investment and running costs, the need for refractory materials, and the limited lifetime of electrodes.

Conclusion

From the analysis of the above several treatment technologies, it can be seen that incineration technology is used as a treatment for a very wide range of wastes and can effectively destroy infectious and toxic medical waste. However, this process produces emissions such as dioxins and furans. Technologies such as plasma and rotary kiln are rarely used in healthcare facilities due to high operation costs. Relatively speaking, the pyrolysis treatment technology of medical waste offers a different approach to the diversification of waste treatment. This technology has the advantages of a high energy recovery rate, minimal secondary pollution, and sufficient economics.