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Chapter: Microbiology and Immunology: Applied Microbiology: Biomedical Waste Management

Waste Treatment and Disposal of Biomedical Wastes

Waste treatment and disposal forms a very important compo-nent of the proper waste management program of the hospital.

Waste Treatment and Disposal

Waste treatment and disposal forms a very important compo-nent of the proper waste management program of the hospital. Segregation of infectious waste from noninfectious waste is the most important stage required before treatment and disposal of biomedical wastes. This is required to protect the health of medical personnel coming in contact with infectious biomedi-cal wastes (Table 78-2).

Infectious wastes include microbiology and biotechnology waste, waste sharps, animal wastes, solid wastes, and liquid wastes as mentioned above. These are segregated and collected in different colored plastic bags (Fig. 78-1, Color Photo 72):

Waste Treatment

There are various methods of treatment of biomedical wastes and are as follows:

Steam autoclaving: Steam autoclaving is an appropriatemethod for treating microbiology laboratory waste, human blood and body fluid waste (if applicable), waste sharps, and nonanatomical animal wastes. It must not be used for treating either human or animal anatomical waste.

Personnel who operate steam autoclaves need to be thoroughly trained in the use of the equipment. The effective-ness of decontamination of biomedical waste is dependent upon the temperature to which the waste is subjected as well as the length of time it is exposed to steam. Because the waste is heated by steam penetration and heat conduction, all air must be displaced and containers holding the waste must have good steam permeability. The penetration of steam into the waste is crucial to the effectiveness of the autoclaving process. For this reason, particular attention must be given to packaging to ensure effective steam penetration.

Special emphasis is given to the type of plastic bags used in the autoclave. Some bags impede steam penetration, while others may melt during the autoclave cycle. Plastic bags, therefore, are assessed under actual working conditions to ensure their effectiveness and integrity throughout the auto-clave cycle.


Organic wastes containing oxidizing agents like sodium hypochlorite or solvents are not autoclaved due to their poten-tial for explosion.

Chemical decontamination: Chemical decontamination isrecommended for treating microbiology laboratory waste, human blood, and body fluid waste. It is not used for treating anatomical waste. Waste sharps may be chemically decontami-nated; however, the sharps may not be completely sterilized unless mechanical shredding is involved. Shredding is only done where the shredder is integral to an incinerator, which is sealed to prevent any release.

Direct incineration is the preferred disposal method for waste sharps. If chemical decontamination is used, the following factors should be considered: type of microorganism, degree of contamination, type of disinfectant used, and con-centration and quantity of disinfectant. Other relevant factors include temperature, pH, degree of mixing, and the length of time the disinfectant is in contact with the contaminated waste.

Sodium hypochlorite (household bleach) is often used as an intermediate-level disinfectant, with the undiluted commercial product normally being a 5.25% solution of sodium hypochlorite (50,000 mg/L of free available chlo-rine). If a diluted hypochlorite solution is used, it should be made up daily in order to prevent loss of germicidal action.

Incineration: Incineration is a process in which combustiblematerials are converted into noncombustible residue or ash,  achieving a reduction of 90% by volume or 75% by weight when the incinerator is properly operated. Incineration has tradi-tionally been the principal method used by hospitals, medical colleges, and other healthcare facilities providers to process their anatomical and nonanatomical biomedical wastes. To date, incineration is the only disposal technology proven to be capable of handling all components of the biomedical waste stream.

Microwave treatment: Radiations produced by microwaveare increasingly used nowadays for treatment of infectious hospital wastes. The microwaves heat the biological wastes to a temperature of 97–100°C in a 40–45 minutes cycle. The advantage of the method is that it is not associated with any hazardous emissions, but it cannot be used to treat anatomical body parts and tissues.

Plasma torch: Waste treatment by plasma torch producesa very high temperature that is very useful for treatment of biological wastes. It is a very safe method, although it is highly expensive.

Disposal of Biomedical Wastes

Landfill, deep burial, and sewage are different methods used for safe disposal of biomedical wastes. Landfill or deep burial— although is a safe method  for disposal of sharps, and also for products of chemical disinfection—requires the presence of large areas of uninhabited land. Trenches are dug where the waste is buried and are covered with lime.

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