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Before selecting a disinfectant, there are several factors that must be considered. Some disinfectants are
effective for routine disinfection protocols on water treatment equipment while others are necessary for contamination situations.
For an effective disinfection protocol, consideration should be given to the microorganism being targeted, the
characteristics of a specific disinfectant and operational environmental issues. Additionally, the health and safety of personnel are always the primary consideration.
Microorganism considerations
Microorganisms vary in their degree of susceptibility to disinfectants. In general, gram-positive bacteria are more susceptible to chemical disinfectants while mycobacteria or bacterial endospores are more resistant. The hydrophilic, non-enveloped viruses (adenoviruses, picornaviruses, reoviruses, rotaviruses) are more resistant to disinfection than lipophilic, enveloped viruses (coronaviruses, herpes viruses, orthomyxoviruses, paramyxoviruses, retroviruses). Pathogenic microorganisms also vary in their ability to survive or persist in the environment Additionally, some microorganisms are also effective at creating a biofilm that enhances their ability to persist in the environment and avoid the action of disinfectants. These also are important considerations when selecting a disinfectant and disinfection protocol. Whenever possible, identification of the target microorganism should be done; however, if the organism has not been identified, a broadspectrum
approach should be utilized until identification can be made.
Disinfectant considerations
An ideal disinfectant is one that is broad spectrum, works in any environment and is non-toxic, non-irritating, non-corrosive and inexpensive. Unfortunately, no known disinfectant is quite this ideal. Therefore, careful consideration of the characteristics of a disinfectant is essential to select the most useful, effective and
cost-efficient product.
Disinfectant concentration
Use of the proper concentration of a disinfectant is important to achieve the best results for each situation. Some products will have different dilutions depending on the desired use of the product (-static versus -cidal action). Although some disinfectants may be more efficacious at higher concentrations, these levels may be limited by the degree of risk to personnel, surfaces or equipment, as well as the cost of the chemical.
However, over-dilution of a product may render the disinfectant ineffective to the target microorganism. Product labels list the best concentration for use in each situation.
Application method
There are a variety of ways to apply disinfectants. They can be applied directly into an open media tank, injected through an automatic electronic disinfection injection apparatus, or through a regenerant feed tank.
Contact time
Appropriate contact times are essential. Disinfectants may vary in the contact time needed to kill versus inactivate microorganisms (i.e., 70 percent isopropyl alcohol can destroy M.tuberculosis in five minutes, whereas three percent phenol requires two to three hours). Minimum contact time needed is normally stated on product labels. Equipment being disinfected should be well soaked with the disinfectant selected to avoid dilution before the end of the optimum contact time. Some chemicals may have residual activity while others may dissipate and rinse away quickly.
Stability and storage
Some disinfectants lose stability quickly after being prepared for use or when stored over extended periods, especially in the presence of heat or ultraviolet light. Disinfectant product labels will list the shelf life of the concentrated product. To maximize stability and shelf life, products should be stored in a cool, dark place and preferably in standard concentrations. Use of an outdated or inactivated product will result in poor
performance.
Instructions for use
Misuse of disinfection products is in direct violation of USEPA regulations. Labels of disinfectants may include limitations of the product and must be followed carefully. This will ensure maximum effectiveness, as well as properly protecting workers, the equipment and the environment.
Safety precautions
Most disinfectants can cause irritation to eyes, skin and/or the respiratory tract; therefore, the safety of all personnel should be considered. Training on proper storage, mixing and application procedures is essential.
Personal protective equipment such as gloves, masks and eye protection should be worn during mixing or application of disinfectants. All disinfectants have a Material Safety Data Sheet (MSDS) listing the stability, hazards and personal protection needed, as well as first aid information. This information should be available to all personnel.
Expense
Economic considerations are always important when selecting a disinfectant. Since disinfectants vary in cost, contact time and dilution, costs should always be calculated on a per gallon (liter) of use/dilution equation rather than cost of concentrate. Always place health and safety requirements before the false security of cost-savings.
Environmental considerations
Operating environmental factors can greatly impact the effectiveness of a disinfection protocol. Organic loads, equipment design, water hardness, temperature, pH, heavy metals, oils and other chemicals are all important environmental factors to consider.
Organic load
Removal of all organic material prior to application of a disinfectant is essential. Levels of organic material within equipment to be disinfected can greatly impact the efficacy of a disinfection protocol. Organic matter provides a physical barrier that protects microorganisms from contact with the disinfectant. Debris and
organic material can also neutralize manydisinfectants, especially chlorine and iodine-containing compounds.
Certain disinfectants may have some efficacy or residual activity in the presence of organic material and should be considered in circumstances where complete removal of organic debris before disinfection is
difficult. Application of these products to a heavy organic load (heavily fouled ion exchange media), however, is neither smart nor effective.
Equipment design
The type of equipment to be disinfected can have a great impact on effectiveness of a disinfection plan. Equipment that includes electronic apparatus for the injection of a cleaning/disinfection fluid is much easier to
work with than equipment that was never designed to be properly disinfected. Components used in the manufacture of equipment also have an impact on the protocol, since most filtration media is extremely sensitive to oxidizing disinfectants. Porous, uneven, cracked or pitted surfaces can protect microorganisms and are quitedifficult to disinfect. An ideal surface to be disinfected is smooth, clean and nonporous.
Water hardness
The water source used when cleaning and diluting disinfectants is also important. Water hardness can inactivate or reduce the effectiveness of many disinfectants. Hard water contains calcium and magnesium ions at varying concentrations. These ions can react with certain cleaning/disinfection compounds, causing
chemical precipitation that may reduce their cleaning action. Many disinfection compounds include chelating agents, such as ethylenediaminetetraacetic acid (EDTA), to help bind these ions. Disinfectants should
always be diluted with deionized water to ensure appropriate stochiometry.
Temperature
Most disinfectants work best at temperatures above 68°F (20°C). Elevated temperatures, however, may cause damage to the equipment being treated and increase the potential occupational hazard to personnel applying disinfection protocols. Colder temperatures can reduce the efficacy of some products.
pH
Activity of some disinfectants is also affected by pH. For example, the efficacy of glutaraldehyde is entirely dependent on pH, working best at a pH greater than seven. Some quats have the greatest efficacy at pH of nine to 10 while others are still effective down to pH levels as low as six. Levels of pH can dramatically affect the activity of phenolics, hypochlorite and iodine compounds.
Heavy metals
Heavy metals and other metallic ions in water can inactivate certain disinfectants. They can also potentially create other complications due to precipitation of solids when using oxidative disinfectants and certain halides.
Oils
Oils in mineral or organic form can obstruct surface contact with disinfectants as well as creating undesirable byproducts. Equipment should be properly degreased before any disinfectant is applied to ensure consistent results.
Presence of other chemicals
Many other chemicals can affect the efficacy of disinfectants. For example, iodine agents are inactivated by quats, while phenols will achieve improved penetrability when applied with soaps or other surfactants. Always consult your specifying engineer or manufacturer’s representative to ensure that deleterious chemical
interactions are not overlooked.
Health, safety and the environment
The health and safety of humans and other animals should always be a primary consideration when selecting a disinfectant product. Most disinfectants have some level of hazard associated with their use. Some even pose a serious threat to human and animal health (aldehydes, phenols, sodium hydroxide). Personnel
training, personal protective measures and safety precautions should always be utilized. Environmental factors, such as septic tank discharge, sewer drainage and runoff into the environment must also
be considered when selecting a disinfectant. Many agents are known ecological hazards for plants and aquatic life (sodium carbonate, hypochlorites, phenolics); therefore, drainage, runoff and disinfectant biodegradability should be considered when developing a disinfection protocol.
Non-chemical disinfection
In addition to chemical disinfectants, heat, light and radiation can also be appropriately used to reduce or eliminate microorganisms in water treatment systems. The use of heat is one of the oldest methods of sterilization. Although both moist heat (steam or autoclave) and dry heat (direct flame or baking) can inactivate microorganisms, moist heat is much more effective and requires significantly less time than
dry heat. Ultraviolet (UV) light can have a detrimental effect on a number of microorganisms and may be a practical method for inactivating viruses, mycoplasma, bacteria and fungi. UV light sterilizing capabilities are limited on surfaces because of its lack of penetrating power. It also suffers from complicating factors such as ‘shadowing’ and fluctuations in delivered electrical energy to the lamp. Other forms of radiation are less frequently used but may include the use of microwaves or gamma radiation. Freezing is not a reliable method of sterilization and the risk of significant equipment damage makes this an entirely unsuitable option.
After development of a disinfection protocol, it is equally important to train personnel on the proper procedures to use and safety issues involved. Procedures should also be posted in prominent locations
throughout the facility to serve as a reminder of proper disinfecting techniques.
Next: Part 3, Classification of chemical disinfectants.