Treatment and Disposal of Regulated Medical Waste

Overview

Disposing of medical waste presents several unique problems:

• The risk of infection is the foremost among the challenges posed by medical waste disposal. Certain types of infectious waste pose additional risk factors:
  • Pathological wastes (infectious wastes that contain animal/human tissue) may harbor particularly dangerous or communicable infectious agents.
  • Laboratory cultures may contain high concentrations of infectious agents.
  • "Sharps" (objects sharp enough to pierce the skin) can deliver infectious agents directly into the bloodstream.
• Classification as a "hazardous waste". Some medical wastes contain certain highly toxic compounds, such as those used in chemotherapy, that can cause the waste to fall under the "hazardous waste" classification. These materials are subject to special regulation under the federal Resource Conservation and Recovery Act, as well as additional rules in many states. Wastes which are regulated both as medical wastes and as hazardous wastes can be particularly difficult to deal with, since most service providers that handle treatment and disposal of medical wastes are not willing to accept hazardous wastes, and vice versa.
• Other RMW waste types posing special problems include:
  • Fluids pose a potential containment problem during shipment.

Most states require that medical waste be treated before disposal to reduce the risk to acceptable levels. But different states have different requirements that apply to the various types of waste listed above.

This page reviews commonly available treatment technology options, outlines specific waste management challenges posed by the different types of medical waste, available waste treatment and disposal options, and indicates which options are particularly suitable for each waste type, from both a technical and a regulatory standpoint.

Treatment Technology Options for RMW

The main task of an RMW treatment system is to render the waste noninfectious. That in itself does not pose an especially difficult challenge. The technical means to render medical waste absolutely sterile has existed for a long time. For example, you can burn the whole load to a crisp, and the job will be unequivocally done. Incineration was indeed once the method of choice for dealing with medical waste, and many medical facilities burned their waste on site.

But it gradually became clear that, while protecting the public from infection, medical facilities using on site incinerators were exposing the public to an emission stream that included mercury, dioxins, and other highly toxic substances. Pressure from public interest groups, and new, more stringent EPA standards on emissions from medical waste incinerators (1997) brought about the closure of several thousand on-site medical waste incinerators at healthcare facilities. Fewer than 100 such installations nationwide are still operating. Currently, most facilities either ship their waste to large, centralized (and presumably more carefully monitored) incinerators, or use technologies other than incineration.

This section lists a range of available medical waste treatment and disposal options, and discusses some of the tradeoffs associated with each of them.

Treatment Options. Currently available treatment technologies rely on two basic approaches to sterilization. Infectious organisms can be killed by subjecting them to excessive heat, or by bringing them into contact with chemical agents.

The most popular options include:

• Heat:
  • Steam autoclaves
  • Microwave systems
  • Dry heat and hot air systems
  • Plasma arc
• chemical agents:
  • Chlorine compounds (including hypochlorite, chlorine dioxide)
  • Ozone
  • Alkali
  • Other disinfectants (peracetic acid, glutaraldehyde, etc.-- typically used for small batches)

Some systems use combinations of these treatments. Incinerators, for example, use both heat and a chemical reaction (oxidation by atmospheric oxygen). Another example is a system that operates at a relatively moderate temperature, which would otherwise leave the waste intact, but that uses alkali to liquefy the waste.

This does not exhaust the full range of theoretical possibilities. Radiation, for example, is an effective sterilization method that is used extensively on medical products, but is used only rarely for waste treatment. Systems using radiation for sterilization involve either radioactive sources (e.g. cobalt 60), with all the attendant risks and compliance obligations associated with handling them, or costly and energy-intensive equipment to generate the required intensity (e.g. for systems involving electron beams). The cost may be justifiable for high value-added products, but not for treating significant quantities of waste.

There is an additional important consideration relevant to the treatment of infectious waste. Whatever the lethal agent is, it can only be effective if it is applied in sufficient strength throughout the entire bulk of the waste. Either the treatment must be applied for a time sufficient to allow the agent to penetrate to the interior of the waste mass, or the waste must be shredded or ground up to bring the interior to the surface. The disadvantage of including a shredding or grinding system is the cost and the additional maintenance required. Breaking up the waste before it has been rendered non-infectious also involves the risk of disseminating the pathogens, so shredding or grinding operations must be carried out in equipment specifically designed for medical waste processing.

The following lists a few of the most significant points of comparison among the available treatment options. A more extensive discussion can be found in the publication Non-Incineration Medical Waste Treatment Technologies (August, 2001) from Health Care Without Harm.

Incineration

Incineration is unquestionably effective, but is associated with serious air quality concerns. Because atmospheric oxygen is used as the reagent, a large volume of air must constantly pass through the system. Unless the exhaust air passes through a control device, all substances that are volatile at the operating temperature of the system will be emitted with the exhaust stream. For example, hospital incinerators were once (and, though to a lesser extent in the U.S., continue to be) significant sources of environmental mercury contamination. In addition, the operating conditions inside incinerators can lead to the formation of organochlorine compounds such as dioxins.

Incinerators are also inherently inefficient from an energy standpoint, particularly when dealing with wastes with high water content. To maintain combustion temperatures, many pounds of fuel must be burned to destroy each pound of waste. Much of that energy is spent simply to boil off the water so that the organic portion of the waste will burn. This has historically been less of a consideration for medical waste, since processing costs are high in any case, but will undoubtedly become more of an issue as the cost of fuel (typically natural gas) increases. Moreover, the burning of large quantities of fuel entails the generation of excessive greenhouse gases (primarily carbon dioxide) relative to the amount of waste material destroyed. This is on the radar screen in the U.S. at present, and may also become a significant issue in the not-too-distant future.

Thermal Treatment

In contrast to incineration, some thermal treatment methods can use the high water content of medical waste to advantage. Water can provide an effective heat transfer medium, to help distribute heat throughout the mass of the waste.

One problem with water as a heat transfer medium is that the temperature at which water boils at normal atmospheric pressure is not sufficiently high enough to kill some of the hardier microorganisms (spore-forming species, for example). One common solution is to carry out the treatment in a pressure chamber. As the pressure is raised, the boiling point of water increases. At a pressure twice as high as normal atmospheric pressure, the boiling point of water increases by about 36°F, to 240°F (i.e. by about 20°C, to 120°C), which is sufficient to kill most organisms of concern. Systems using steam under pressure are called autoclaves, and are among the most common alternatives to incineration for medical waste treatment.

Another thermal treatment system that takes advantage of the properties of water uses microwaves as the energy source. In a microwave system, the waste is subjected to high intensity radio waves, tuned to a frequency that is readily absorbed by water molecules. It is an efficient way to deliver the energy where it is most needed for sterilization purposes. The other side of that coin is that microwave heating will be inefficient if the waste is too dry. Microwaves will penetrate bulk materials to some extent, but the heating will proceed more efficiently if the waste is shredded and mixed in the chamber during the process (for much the same reason that many kitchen microwave ovens use a rotating platform).

An advantage to both autoclaves and microwave systems is the fact that air does not have to move through the systems while they operate. Emission of volatiles only occurs during loading and unloading, and can be minimized with proper design and operation.

Autoclaves and microwave systems are effective, but the necessary equipment is somewhat expensive (pressure chambers and microwave generators, respectively). In contrast, dry heat systems use less demanding equipment, but typically require higher temperatures and longer exposure times to ensure that the heat supplied by the system penetrates to the center of the waste. Rather than directing the heat into the mass of the waste, evaporating water carries a substantial quantity of the heat away. On the other hand, the drying of the waste has some advantages, including substantial weight and volume reduction and easier handling of the residue.

Since dry heat systems do not involve combustion, unwanted reactions such as dioxin formation are not an issue. But if air moves through the system, it can carry volatiles and pathogens. The exhaust stream is typically filtered before release, but the potential for release always exists.

One disadvantage with all of these systems, stemming from the fact that they operate at substantially lower temperatures than incinerators, is that they require a certain minimum contact time to ensure that all pathogens have been destroyed. Higher temperatures are required to process large quantities of waste in a shorter time. To obtain a higher throughput while avoiding the problems associated with ordinary combustion, some large scale systems use advanced heating methods to create very high temperatures with a minimum of air passing through the system. One method to produce the desired temperature uses a plasma arc -- an electric discharge producing intense heat in the absence of combustion. Other types of heating, such as induction, may also be used. In any case, the heat is sufficiently high to cause the organic molecules in the waste to break down to simpler compounds, even though no combustion is occurring. (This kind of heat breakdown with minimal oxygen present is generally called "pyrolysis".) Unfortunately, those simpler compounds include a significant proportion of gases (including carbon monoxide), which are somewhat harder to handle than solid residue. Since they must flow out of the pyrolysis chamber as the reaction proceeds, the advantage of not having to flow combustion air through the system is somewhat nullified. The offgases are burned in an oxidation chamber. The volume of air that must be treated is somewhat less, but all the contaminants present in an incinerator exhaust stream are there as well, and must be filtered out or they will be emitted from the system.

Chemical Treatment

The obvious disadvantage of chemical treatment systems is that they consume chemicals. In addition, even if they are effective in rendering the waste noninfectious, the products of the chemical reactions they undergo are present in the waste, and may pose problems of their own. However, chemical treatment systems are convenient, and may be suitable in some situations, particularly when small quantities of waste are involved.

One of the most common constituents of chemical treatment systems is chlorine, either in the form of sodium hypochlorite solution (common bleach), or as the more powerful (and correspondingly more hazardous) gas, chlorine dioxide. These compounds are relatively cheap and effective. However, in the course of reacting with organic compounds, they tend to form objectionable byproducts such as chloroform and other persistent toxins.

The chlorine compounds work by "oxidizing" (stripping electrons from) organic compounds, including the constituents of pathogenic microorganisms. The original "oxidizer" is, of course, atmospheric oxygen. Although it is, in fact, a fairly powerful oxidizing agent, ordinary oxygen is not harmful to -- is in fact essential for the survival of -- many organisms, including most of the pathogens in medical waste. However, when oxygen (O₂) is converted to ozone (0₃), a much stronger oxidizer, it becomes toxic to most life forms. Ozone can readily be generated by passing an electric arc through ordinary oxygen gas. When used in a medical waste treatment system, ozone acts as an effective sterilizer, without the tendency to generate the types of by-products found with chlorine compounds. The major problem encountered with ozone systems is the need to avoid exposure to anyone in the vicinity of the treatment system, since ozone is highly injurious to lungs.

Alkaline agents are also used in medical waste treatment, either in highly corrosive form (sodium hydroxide, or lye), or in somewhat milder form (calcium oxide, or quicklime). Alkali tends to hydrolyze (decompose) proteins, among other effects. Apart from the cost of the reagents, the major disadvantage is the risk of contact, since alkaline solutions damage skin and lungs.

Disinfectants like glutaraldehyde and peracetic acid are also used for small-scale medical waste treatment. More information on these materials can be found on the VetCA Sterilants and Disinfectants page.

Disposal Options. After it has been rendered noninfectious, most medical waste can be disposed of as if it were ordinary solid waste. However, there are some important exceptions:

• Waste that must be managed as hazardous waste must be disposed of in compliance with RCRA regulations
• Some states require that recognizably anatomical waste must be rendered unrecognizble before being disposed of in a solid waste landfill.

Some states allow cremation or interment (burial) of certain kinds of untreated waste. "Interment" presumably refers to burial in a manner that follows standard mortuary practices, rather than disposal in a landfill.

Treatment Requirements for Special Types of RMW

Certain specific types of medical waste require special consideration when choosing a treatment technology. In this section, we will classify those types, indicate their special treatment requirements, and show instances where different states have singled those waste types out with specific rules that apply to them.

There is no one "standard" classification scheme for medical wastes. The categories chosen to classify medical wastes will differ, depending on the purpose for which the wastes are being classified. Moving and storing wastes involves a different set of concerns from treating and disposing of them, for example. Another source of variation is differences among the regulations adopted by different states.

The classification scheme below is based specifically on considerations involved in treatment and disposal, and on the most common regulatory distinctions found in state regulations. See the VetCA page on Types of Regulated Medical Waste for a more comprehensive overview of medical waste classification.

Types of RMW Associated with Elevated Infection Risk

The possibility of spreading infection is the primary concern associated with medical waste. Most microorganisms found in the environment are not particularly suited to colonizing animals, and most of the waste from healthcare facilities is no riskier than, say, typical household wastes. But three special categories of medical waste pose a particularly high risk of infectiousness:

• Pathological Waste
• Laboratory Cultures (microbiological waste)
• Sharps

Pathological Waste contains tissue, organs, and fluids. Microorganisms that have become established in animals tissues have already proved themselves capable of infecting animals, so it makes sense to apply extra precautions to handling this type of waste.

Some states, such as Connecticut, Delaware, Massachusetts, Maine, and Rhode Island, require either incineration or interment for pathological waste, apparently with no provision for exceptions. Other states allow alternative treatment methods, but spell out in detail which methods are allowed. For those state that do allow alternatives, steam sterilization (autoclaving) is the most common method indicated. A few states (e.g. Texas) also specifically provide for a broader range of thermal and chemical treatments for pathological waste. (See the table below for more specific links to paragraphs and sections in the state regulatory codes.)

Laboratory Cultures (also called Microbiological Waste): This designation refers specifically to waste products from microbiology laboratories. It can pose a special hazard because it typically contains colonies of microorganisms that have been intentionally encouraged to grow under conditions conducive to their growth (generally for diagnostic purposes). Thus a greater concentration of organisms can be assumed to be present in these wastes than in general medical wastes. In addition, the organisms that have been cultured are often precisely those with infectious potential (which is why they are of interest to healthcare laboratories in the first place).

Most of the states that make special provisions for pathological waste (see above) also make special provisions for laboratory cultures.

Sharps is a term applied to objects such as needles and scalpel blades. Their special hazard lies in the fact that, having been designed to pierce the skin, they are very efficient delivery mechanisms for putting infectious agents directly into the bloodstream. Wastes containing both infectious material and sharp objects create particular hazards for anyone handling them, or coming into contact with them.

There are basically two ways to address the risk of infection from sharps -- mitigate the infectivity, or mitigate the sharpness. The first approach typically involves specifying treatment methods for sharps, often of the same level of stringency as those applied to pathological wastes. The second approach can involve isolating the sharps, generally in special containers, mechanically processing them, or encapsulating them. Many states spell out detailed regulations for sharps containers, including conditions to ensure that they are resistant to punctures, and that they are clearly labeled. Some states require that sharps be mechanically rendered non-sharp (using terms like "blunted" or "shredded"). Others require that they be rendered unrecognizable.

Sharps are singled out for special regulatory provisions by more states than any of the other medical waste categories. Check the VetCA State-by-State Regulated Medical Waste Resource Locator for more information.

Hazardous Wastes

Certain materials have been singled out under federal law as being particularly dangerous to deal with and dispose of, and are included in a special regulatory category called "hazardous wastes". (See the VetCA Hazardous Materials Overview page under "Hazardous Wastes", and related pages, for more background on these regulations). One provision of the hazardous waste rules, known as the "mixture rule", specifies that if an otherwise non-hazardous waste is mixed with even a small amount of a "listed" hazardous waste, the mixture falls under all the restrictions that apply to hazardous wastes.

Mixtures of wastes which are simultaneously regulated medical wastes and hazardous wastes present special disposal challenges. Many hazardous waste haulers are not equipped to handle medical wastes. Few medical waste disposal facilities have permits to accept hazardous wastes.

The best course of action for a healthcare facility is to minimize the amount of this type of waste that it must deal with. (Of course, it may not be possible to eliminate mixed medical and hazardous waste entirely. For example, syringes and IV units that have been used to deliver certain chemotherapeutic agents may have to be treated as hazardous under some states' rules.)

Some states use a different definition for mixtures, according to which a waste material only falls into the "hazardous" classification if the hazardous components are present in concentrations above some minimal threshold. When chemotherapy wastes can qualify for a "trace" classification, a facility may provide special containers, often colored yellow, for such "trace" wastes, so they are not mixed in with the hazardous wastes. It is important to use these containers appropriately.  See the references under "Chemotherapy waste" in the More Resources section below, and consult the VetCA Hazardous Waste State Resource Locator for links to additional information for your state.

Other RMW Problem Types

Fluids pose a potential containment problem during shipment. There is an additional problem unique to fluids -- determining the regulations governing disposing of fluids in the facility's wastewater (i.e. pouring them down the drain). The rules vary from state to state. Facilities tied to a municipal sewer system might also be subject to local regulations.

Anatomical wastes, including recognizable body parts, can pose aesthetic issues. Several states require that such wastes be rendered unrecognizable before disposal.

More Resources

Health Care Without Harm:

• Non-Incineration Medical Waste Treatment Technologies, August, 2001 (118 pages)  Detailed descriptions of available technologies.

Centers for Disease Control (CDC):

• Healthcare-associated Infections (HAIs)