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 microorganisms through one or more of these processes:

  • Starving the microorganisms by eliminating access to nutrients
  • Oxidizing the cellular membranes
  • Creating a toxic environments towards them
  • 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 groups of disinfectants so some disinfection jobs must take the types of microbes into account.

    Types of Industrial Disinfectants

    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. Quats work by keeping microorganisms and nutrients apart, thereby starving the microorganisms.

    Oxidizing agents

    This is the broadest category of disinfectants because so many different agents (and approaches) can induce oxidation of bacteria and fungi cell membranes. This category is based on functionality and not on chemical classification like the other categories. Oxidizing agents include

    • sodium hypochlorite (NaClO)
    • formaldehyde (CH2O)
    • hydrogen peroxide (H2O2)
    • chlorine (Cl2)
    • 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 can be used as an antiseptic as well. 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 agent 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 an efficient disinfectant agent which when combined with light or heat can initiate a free radical decomposition of organic compounds that affects bacteria and microorganisms in very short times. 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.

    Alcohols

    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 others 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.

    Phenolic compounds

    Phenolic compounds have been used more than any other category by the industrial manufacturers of disinfectants. Popular ones include Phenol, Thymol and Chloroxylenol. Caution is advised when using these compounds (especially in pure forms) as some of them have shown toxicity towards humans.

    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]. Significant advantages of these novel materials are their superb mechanical and electronic properties as well as their tailored porosity that can operate in dual fashion: starvation and killing of harmful species.

    Physical disinfection

    Techniques include heat application [LINK], sound treatment [6], and irradiation [7]. Physical approaches have proven effective towards 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; by-products can sometimes form when physical disinfection methods are employed, but the efficiency of the methods remains stable.

    References

    1 C.J. Volk, R. Hofmann, G. Ranger, R.C. Andrews, C. Chauret, G.A. Gagnon, Implementation of chlorine dioxide disinfection: effects of the treatment change on drinking water quality in a full-scale distribution system, J. Environ. Eng. Sci. 1 (2002) 323-330

    2 P. Xu, M.L. Janex, P. Savoye, A. Cockx, V. Lazarova, Wastewater disinfection by ozone: main parameters for process design, Water Res. 36 (2002) 1043-1055

    3 S.S. Birla, V.V. Tiwari, A.K. Gade, A.P. Ingle, A.P. Yadav, M.K. Rai, Fabrication of silver nanoparticles by Phoma glomerata and its combined effect against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, Lett. Appl. Microbiol. 48 (2009) 173-179

    4 S. Gurunathan, J.W. Han, A.A. Dayem, V. Eppakayala, J.H. Kim, Oxidative stress mediated antibacterial activity of graphene oxide and reduced graphene oxide in Pseudomonas aeruginosa, Int. J. Nanomed. 7 (2012) 5901-5914

    5 Biao Song, Chang Zhang, Guangming Zeng, Jilai Gong, Yingna Chang, Yan Jiang, Archives of Biochemistry and Biophysics 604 (2016) 167-176

    6 Huasheng Zou, Lifang Wang. Ultrasonics Sonochemistry, Volume 36, May 2017, Pages 246-252

    7 Ji Zheng, Chao Su, Jianwen Zhou, Like Xu, Yanyun Qian, Hong Chen. Chemical Engineering Journal, Volume 317, 1 June 2017, Pages 309-316