Disinfection of Medical Waste Management Facilities

Disinfection, sanitation, and sterilization refer to degrees of cleaning and killing microorganisms. In general, disinfection attempts to eliminate bacterial and microorganism populations by killing all harmful species. Disinfection of a surface does not destroy the spores of some microorganisms, leading to eventual reappearance of those populations. Sterilization of a sample or a surface, on the other hand, kills all species; the spores are also destroyed. Both disinfection and sterilization can be accomplished by chemical or physical processes such as radiation and heat.

Chemicals can kill bacteria and fungi through one or more of these processes:

  • Starving the microorganisms by eliminating access to nutrients
  • Oxidizing the cellular membranes and viral envelopes
  • Creating a toxic environments towards the organisms

The efficacy of chemical disinfectants depends on operating conditions, including

  • the pH of the solution/ sample/ surface
  • temperature
  • presence of other materials such as organic compounds, inorganic salts, aggregates of pollutants, and nutrients

Most microorganisms exhibit tolerance towards some types of disinfectants. Broad spectrum disinfectants are effective against many bacteria and viruses. Narrow, or limited-spectrum disinfectants kill some pathogens but are not effective against others. Iodine and iodophors are narrow spectrum, which is one reason they are little used any more. Glutaraldehyde and Quats are broad spectrum.

Types of Industrial Disinfectants

Phenolic compounds, hydrogen peroxide liquid, quaternary ammonium compounds, formaldehyde and sodium hypochlorite are commonly used disinfectants. There is no ideal disinfectant, and the best choice depends on the needs of the facility and the situation. Waste managers often find themselves balancing the antimicrobial effectiveness with the toxicity of the disinfectant solution as stronger disinfectants are often dangerous to people and animals.

Relationship to Antiseptics

Medical facilities also use antiseptic preparations on patients. These are more or less disinfectants, but the word antiseptic is used when a body part is being cleaned. The familiar alcohol swab before a shot is an antiseptic. Unlike disinfectants used to clean floors and surfaces, antiseptic preparations should act quickly and have efficacy against bacterial flora normally found on the skin. Although the term might be used by lay people, waste management professionals should not refer to liquids used to clean buildings or equipment as antiseptics. Use the word disinfectant.

Quaternary Ammonium Compounds

Also called QACs or Quats, quaternary ammonium compounds have a Nitrogen atom located at the center of their molecular structures, bonded to four organic chains. The chains can be tailored in terms of length, crosslinking, and branching. Benzalkonium chloride is a well-known Quat. Quats work by disrupting the structures of proteins and lipid membranes. Preparations are typically 200 ppm to 400 ppm active ingredient.

Quats have surfactant properties like detergents. They are usually colourless and odorless. These function as both fungicides and bactericides but are less effective against gram-negative bacteria. Anti-bacterial soaps often contain quaternary ammonium compounds and concerns about human exposure to QACs is one reason public health authorities now discourage use of these soaps.

Oxidizing agents

This is the broadest category of disinfectants because so many different agents can induce oxidation of bacteria and fungi cell membranes. This category is based on functionality rather than chemical structure. Oxidizing agents include

  • sodium hypochlorite (NaClO) - ubiquitous janitorial chemical; bleach
  • formaldehyde (CH2O) -
  • hydrogen peroxide (H2O2) -
  • chlorine (Cl2) - gaseous elemental chlorine is rarely used because it is difficult to control, but it does destroy microorganisms.
  • chlorine dioxide ClO2
  • Iodine
  • electrolyzed water (a solution of hypochlorous acid and sodium hydroxide)
  • copper nanoparticles
  • potassium permanganate KMnO4
  • ozone (O3)
  • silver nanoparticles
  • peracetic acid (CH3CO3H)

Some industrial disinfectants combine conventional oxidation agents and novel materials.

Hydrogen peroxide is widely available and can be used as a disinfectant. It does not irritate the skin and few people are allergic to it, and it can be combined with nanoparticles of metals (like silver and copper) to enhance its efficiency. Chlorine dioxide is used mainly in water applications (industrial water treatment, sanitation, drinking water) due to its better performance for bacteria and microorganism killing and very low by product formation.

Silver nanoparticles are a disinfection agent that is also used in preservation of wood and in food packaging. Iodine is also a disinfectant that is widely used as an antiseptic as well; iodine is most commonly used in aqueous solutions as a wound treating agent or water additive. Electrolyzed water is an acidic solution (pH in the range 3.5-6.5) that contains hypochlorous acid and sodium hydroxide.

Ozone is a fast-acting disinfectant agent which when combined with light or heat can initiate free radical decomposition of organic compounds. Due to its high reactivity it should be applied close to the final use point of water, food, packaging or other application.

Peracetic acid is another important disinfectant especially for food applications as it combines the efficiency of strong oxidizing agents with a constant stability in chemical environments. Combines the efficiency of strong oxidizing agents with a constant stability in chemical environments.

Reducing agents

Work by chemical reduction (the opposite of oxidation). Includes citric acid and lactic acid.


Pure alcohols and concentrated aqueous solutions of alcohols are widely used as disinfectants in health care facilities. Alcohol solutions are employed as both disinfectants and antiseptics. Ethanol (ethyl alcohol) and isopropanol (isopropyl alcohol) are the most widely used alcohols at 60 to 90 percent concentration, although other types of alcohol sometimes find their way into disinfectants. Mixtures of alcohols and formaldehydes are also used. Pure alcohols sometimes have limited diffusivity, so they work on surfaces but do not penetrate materials like slightly diluted alcohol solutions do. Alcohols are effective against lipophilic viruses, less effective against non-lipid viruses, and ineffective against bacterial spores. Because of their quick evaporation rate, it may be difficult to achieve sufficient contact time.

Phenolic compounds

Phenolic compounds have been used more than any other category by the industrial manufacturers of disinfectants. Popular ones include Phenol (carbolic acid, C6H5OH), Thymol (2-isopropyl-5-methylphenol, C10H14O) and Chloroxylenol (para-chloro-meta-xylenol, C8H9ClO). Can leave a sticky residue on surfaces. Caution is advised when using these compounds (especially in pure forms) as some of them have shown toxicity towards humans and can be corrosive. PPE is often required when using phenolic compounds.

Novel materials

Carbon allotropes have been a field of active research for the development of novel disinfectant agents. Such allotropes include graphene, graphene oxides and functionalized forms of graphene. Research has shown that graphene oxides are extremely effective towards gram negative and sufficiently effective towards gram positive species [4, 5]. Advantages of these materials are their hardiness and resistance to degredation as well as their tailored porosity that can operate in dual fashion: starvation and killing of harmful species.

One way to establish if something is an effective disinfectant is if it passes the AOAC Use Dilution Test. This test dates back to the 1950s. It tests a disinfectant solution or liquid under certain conditions: a piece of stainless steel is exposed to bacteria and then immersed in the purported disinfectant. The EPA has more.

Physical disinfection

Techniques include heat application, sound treatment [6], and irradiation [7]. Physical approaches are effective against hardy microorganisms, and they often are used in combination with chemical treatment. Physical disinfection targets the mechanical, biological and chemical structure of microorganisms - not access to nutrients or the microenvironment around the pathogens. High frequency sound waves, for example, can break down the cell walls of microorganisms. Their greatest advantage over chemical methods is that they can function in all chemical environments.

Levels of Disinfection Power

Disinfectant types can be classified according to their effects which are described as follows:

  • Low-level disinfectants
  • Intermediate-level disinfectants
  • High-level disinfectant

Low-level disinfectants

These disinfectants destroy or kill vegetative bacteria along with medium-sized lipids containing viruses and few fungi excluding (M.tuberculosis) in less than 10 minutes. These disinfectants are not effective for small non-lipid viruses, mycobacteria and fungi. Low-level disinfectants include quaternary ammonium compounds, phenolics, and concentrated alcohol.

Intermediate-level disinfectants

These disinfectants have the potential to destroy or kill all microbial pathogens or vegetative microorganism (excluding bacterial endospores). Some may be classified as bactericidal, virucidal, fungicidal (do not kill sexual spores only asexual spores) and tuberculocidal. These formulations are usually used on building and facility surfaces.

Examples include a combination of quat and alcohol (effective on pathogens such as norovirus and mycobacteria), bleach, and mixtures of bleach and peroxide. Bleach disinfectant is frequently used in to clean clothing worn in a medical setting and it is effective against small viruses, bacterial spores (not all kinds)and mycobacteria. Bleach and hydrogen peroxide mixtures are more effective against complex bacterial spores than bleach alone.

The active ingredient in bleach is NaClO (sodium hypochlorite). The concentration of NaClO is important in formulation of liquid disinfectants. Sodium hypochlorite kills bacteria, viruses and fungi by denaturing the protein in disease-causing microorganisms.

Gaseous sterilization

There are advantages to using sterilizing agents that are gaseous. The agent can more readily penetrate to small niches that might escape contact with liquid if the object is immersed. The biggest downside is that gases pose hazards to workers if they are inadvertently released. Even if you do contain the sterilant, it has to be destroyed at some point and cannot be simply released to the atmosphere.

Agents used include ethylene oxide [LINK[, hydrogen peroxide, chlorine dioxide, ozone, and formaldehyde vapor. Hydrogen peroxide processes can be operated at low temperatures, thus making it acceptable for treating heat-sensitive medical equipment. OSHA's Permissible Exposure Limit (PEL) for hydrogen peroxide exposure is 1ppm over an 8-hour Time Weighted Average (TWA).

High-level disinfectants

Germicides are formulated to destroy or inactivate all microbial pathogens excluding plenty of bacterial endospores are high-level disinfactants. Active ingredients which are found commonly in high-level disinfectants are hypochlorite, glutaraldehyde, hypochlorous acid, hydrogen peroxide and ortho-phthalaldehyde. These are mostly used at terminal step during the cleaning/processing of critical devices and semi-critical devices in medical facilities, including dialysis units. These liquids are not used to clean floors or walls.

High-level disinfectants are effective within 20 minutes. They are often combinations of two disinfectant liquids. A combination of peracetic acid and hydrogen peroxide is often used. A blend of bleach and hydrogen peroxide is another formulation. Other commercially available disninfectants are a 0.8% peracetic acid + 1.0% hydrogen peroxide combination and 0.23% peracetic acid + 7.35% hydrogen peroxide.

Which Disinfectant Should I Use?

The waste manager or industrial hygienist gets paid to make these decisions. There is no answer from a textbook or website. The best disinfectant should be chosen from commercially available options. Don’t try to create your own disinfectant unless you have a thorough knowledge of chemistry. And you want the disinfectant to be available in the future. Selection factors include:

  • Antimicrobial activity against the range of pathogens of interest.
  • Impact to environment (important if disinfectant is used in large volume).
  • Toxicity to people, including risk of toxicity from trace disinfectants.

Never combine two disinfectants or two cleaning solutions. Use them sequentially if needed, with a rinse of the floor or equipment in between applications.

Staged cleaning

If you clean with detergent prior to disinfection, it is likely the disinfection will be more effective. Some preparations combine detergents with disinfectants, and there is nothing per se wrong with that. But cleaning in more than one stage is both theoretically superior and in real life shows better results than single-stage washing.

Switching Disinfectants

Although there is no firm industry practice here, managers should consider changing disinfectants used for a given application occasionally. This reduces the chances of resistant pathogens forming and it increases the overall spread of organisms being attacked. Commercial preparations tend to be unique - no two companies make the exact same formulation - but the active ingredients are often the same.

Validating disinfection


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