Alternative Medical-waste-treatment Technologies

Various alternative technologies to incineration are available to hospitals to treat hazardous/infectious waste. Most alternative treatment systems rely on heat to decontaminate medical waste.

Steam Autoclaving
Steam autoclaving is the most widely used and most efficient alternative medical-waste-treatment technology.

Most available autoclaves are designed to handle both biohazard and normal hospital wastes simultaneously. However, they cannot treat pathological, animal wastes, chemotherapy wastes, and low-level radioactive wastes. These wastes have to be treated separately.

In autoclaves, the effects of heat from saturated steam and increased pressure decontaminate medical waste by inactivating and destroying microorganisms. The efficacy of autoclave on the treatment depends on sterilization duration and temperature. Medical-waste steam autoclaves usually jointly operate with a shredder, and a compactor (to minimize the waste volume). The volume reduction can be up to 85%, according to autoclave manufacturers.

There are two types of autoclaves, gravity displacement and pre-vacuum. Those designed for medical waste are mostly pre-vacuum and they are covered here.

After completion of the sterilization cycle, autoclaves usually vent down. Air is either evacuated through a high efficiency particulate air (HEPA) filter before exhausting to the atmosphere or mixed with jet steam, which is then re-condensed to water. This wastewater can be passed through a charcoal filter for odor removal. HEPA filters and mixing with steam ensures against potential pathogen release to the environment.

A "post-vacuum" usually is pulled inside the chamber after venting to remove residual condensate from water after sterilization. The air removed is again mixed with ejector steam, re-condensed, and filtered through charcoal.

EPA conducted a study on alternative medical-waste-treatment technologies, and obtained cost information on autoclaves. EPA estimated the average operational cost, including financing and disposal, for autoclaves with less than 200-lb/hr capacity to be approximately U.S.$0.25/lb of waste.

Chemical Treatment
In chemical treatment systems, an antimicrobial chemical—such as sodium hypochlorite, chlorine dioxide, or peracetic acid—decontaminates the medical waste. Factors affecting the efficacy of chemical treatment are a function of the active-ingredient, its concentration, and contact time between the contaminated surface and the treatment chemical. Most chemical-treatment systems currently in use operate at ambient temperature. However, antimicrobial activity may increase by raising the process temperature. The EPA estimated the operational cost, (including financing and disposal) for chemical treatment technologies at approximately $0.20/lb of waste, for systems with 200–500 lb/hr capacity.

Microwave Irradiation
In microwave technology, medical waste enters the system by batch or continuous mode where it is wetted with steam or water and heated by microwave irradiation to decontaminating temperatures. The efficacy of microwave treatment depends on treatment duration and temperature, the composition and moisture content of the waste material, and the frequency and wavelength of the radiation. The EPA's estimate of operating cost, including financing and disposal, for microwave technologies was approximately $0.29/lb of waste for systems of less than 200 lb/hr capacity

Other Thermal Systems
Some systems use a combination of infrared radiation and forced hot-air convection to treat the waste. The waste then is compacted, preparing it for landfill. Other systems use gamma radiation to heat the waste to disinfecting temperatures. A portion of the solid residue obtained is recycled while the remainder is disposed. Several other thermal systems currently under development use steam, oil, electricity, or some form of irradiation as their source of heat.

Efficacy of Alternative Technologies
The most widely used criteria for determining the efficacy of an alternative technology in decontaminating medical waste was developed by the State and Territorial Association of Alternate Treatment Technologies (STAATT). The STAATT criteria recommend Level III as a safe and satisfactory level of medical-waste treatment. This level corresponds to "disinfection" only, whereas level IV corresponds to "sterilization."

Levels III and IV produce the following levels of microbial inactivation:

• Level III: Inactivation of vegetative bacteria, fungi, lipophilic/hydrophilic viruses, parasites, and mycobacteria at a 6 log10 reduction or greater; and inactivation of B. subtilis spores or B. stearothermophilus spores at a 4 log10 reduction or greater.
• Level IV: Inactivation of vegetative bacteria, fungi, lipophilic/hydrophilic viruses, parasites, mycobacteria, and B. Stearothemophilus spores at 6 log 10 reduction or greater.

It appears that steam autoclaves with rotating sterilizing chambers are the most efficient to reach level IV. Efficacy test reports indicate that autoclave systems, chemical treatment systems, and microwave systems can all meet and exceed the STAATT efficacy criteria.

Environmental Impacts of Alternative Technologies
Air Pollution. The EPA has reported some air emissions from autoclaves of volatile organics, notably aldehydes. However, the emissions of heavy metals and particulate matter (PM) from autoclaves are insignificant compared with those from incinerators. (No EPA information on dioxin emissions is available.) The EPA also found that, on a pound of pollutant per pound of waste basis, treating medical waste in an autoclave rather burning it in a medical-waste incinerator produces far less total emissions.

The EPA did not find any data available on the air emissions from chemical treatment systems or microwave systems. Chemical treatment systems use steam in addition to a chemical to decontaminate the medical waste, thus, air emissions from chemical systems should be similar to autoclaves, with additional chlorine emissions. These chlorine emissions might require a state permit. Emissions from microwave systems are likely similar to autoclave emissions, since microwave systems only use water as their heat transfer media, and the temperatures used for disinfection are only slightly lower than those used in steam autoclaving.

Water Pollution. No water pollution is expected from these alternative technologies. The liquid discharged after autoclave or chemical treatment can be released into the sewer. The liquid effluent from chemical treatment usually is neutralized and filtered through activated carbon before released to the sewer.

Solid Waste. The alternative technologies might not reduce the waste volume as much as incinerators. However, the EPA has determined that treated waste from alternative treatment technologies for all hospitals surveyed was readily accepted at landfills, since there appears to be no problems with leachate from the treated-waste landfills.

Summary of Alternative Treatment Technologies
Alternative treatment technologies for hazardous/infectious medical waste appears to be a cost-effective alternative to incineration, which is subject to the new emission guidelines requiring costly add-on air pollution controls and costly source testing for at least three consecutive years. Alternative treatment technologies, however, might increase the cost of landfill disposal since the volume of the waste likely will be larger than for that from an incinerator.