Water Conditioning & Purification Magazine

Controlling Biological Contamination in Water Treatment Equipment

By Greg Reyneke, MWS

Introduction

Heterotrophic plate count (HPC) bacteria are a generally benign family of chlorine-resistant bacteria that inhabit most plumbing systems and can slowly colonize water treatment equipment. HPCs are evident as part of the slimy coating that can be found on drinking filters and inside water softeners, known as a biofilm. A biofilm is a collection or organic and inorganic material, as well as living and dead organisms, responsible for water quality and distribution problems, such as loss of residual disinfection levels, odors, color, microbial-induced corrosion, reduced material life and a reduction in dissolved oxygen content.

Pathogenic organisms can be introduced into a water quality management system in a variety of ways, including through the influent water supply, during regeneration or through outside action. For this reason, biological risk management (BRM) protocols are needed to prevent and eliminate the colonization of pathogenic and non-pathogenic entities within water treatment equipment. US EPA registers disinfecting agents as antimicrobial pesticides and they are used to control, prevent or destroy harmful microorganisms (fungus, bacteria or virus) present on objects and surfaces.

Before selecting a disinfectant to use, 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. The health and safety of workers are always the primary consideration.

Biocides and germicides are chemical agents that kill microorganisms. Actions may include oxidation, hydrolysis, denaturation or substitution. The word bacteriocide implies an actual destructive action, so biocides, bactericides, virucides, sporicides are killers. Words like biostatic, bacteriostatic, virostatic, sporostatic are used when the chemical compound inhibits growth or if it just prevents the organism from multiplying. Sanitizers don’t destroy or eliminate all bacteria or microorganisms. They are designed to reduce the concentration of microbial contamination on surfaces to levels that are generally considered safe from a public-health standpoint. Disinfectants are applied directly to inanimate objects and destroy or irreversibly inactivate most microorganisms and some viruses, but don’t have much activity against spores. Sterilization refers to a process, either physical or chemical, that destroys or eliminates biological contamination.

Detergents disperse and remove dirt (soil) and organic material from surfaces, allowing a disinfectant to penetrate and contact microbes inside or underneath the dirt. Detergents also reduce surface tension and increase the penetrating ability of water, thereby allowing more organic matter to be removed from surfaces. Detergents can be cationic, anionic and non-ionic. Cationic detergents are positively charged and with the exception of quaternary ammonium compounds, are not usually used for cleaning. Anionic detergents are negatively charged, usually consisting of an alkali metal salt or an ammonium salt of a strong acid, containing 12 to 24 carbon atoms together with an inorganic salt, sometimes a builder like sodium tripolyphosphate (STP). These are less desirable for our purposes because they can foam excessively and allow dirt and microorganisms to accumulate in that foam, inadvertently protecting them from disinfectant activity. Uncharged (non-ionic) detergents are excellent emulsifiers, have good dispersion and penetration capability, are effective at lowering surface tension and don’t foam very much.

US EPA-compliant product labels contain important information on the proper use and potential hazards of a disinfectant product. Careful attention must be given to the correct use of a product about its application, effectiveness and associated hazards to humans, animals and the environment.

Disinfectants may have a range of uses and label claims, such as cleaner, deodorizer, sanitizer, disinfectant or fungicide and even if it is only intended for hospital/institutional/industrial use. Label claims are usually determined by the product’s efficacy against the three most common test microorganisms: Staphylococcus aureus, Salmonella choleraesuis and Pseudomonas aeruginosa. Claims on the label will refer to whether the product is of limited efficacy (what it can kill) or if it can be used as a general purpose/broad spectrum disinfectant. Product testing is typically performed under hard-water conditions of up to 400 ppm hardness (CaCO3) in the presence of five-percent serum contamination to evaluate effectiveness under real-life conditions.

Ingredients will also be listed, specifically the active ingredients applicable to the US EPA registration, which are listed as a percentage by weight. Biologically inactive ingredients are often lumped into one disclosure (sometimes listed as proprietary formulation) and may include dyes, detergents, perfumes, pH adjusters and water or other carrying/dilution agents. Pay attention to the Precautionary Statements and First-Aid sections to understand how to safely store, handle and use the product, as well as how to deal with contact/ingestion by people and animals. There might also be further environmental warnings regarding discharge into bodies of water and safe disposal of empty containers.

Choosing the right tool for the job

Microorganisms vary in their ability to survive in the presence of various disinfectants and interfering factors. A perfect disinfectant is one that kills everything (broad spectrum), works in any environment, is non-toxic, non-irritating, non-corrosive and cheap. No such product exists yet, so we need to learn more about what is available in the marketplace. Here are some important factors to consider:

  • If you apply disinfectant at the incorrect concentration, you will not get the results you desire. Many disinfectants are more effective at higher concentrations but these levels may be limited by the amount of risk to workers, surfaces or equipment, as well as the cost of the chemical. Over-dilution of a product can also make the disinfectant ineffective.
  • Disinfectants can be applied manually into an open media tank, injected through an automatic, electronic disinfection injection apparatus or through a simple drip feeder. Some disinfectants might require that surface be completely dry before application and are unsuitable for a clean-in-place (CIP) application.
  • The minimum contact time needed to kill versus just inactivate microorganisms is important to understand. Some chemicals may have residual activity while others may dissipate and rinse away quickly.
  • Some disinfectants break down quickly after being prepared for use or when stored over extended periods, especially in the presence of heat or UV light. Make sure that you understand how long it can be stored before use and in what environment it can be stored.
  • Misuse of a disinfection product is not only illegal, but can also be dangerous. The label of a disinfectant may include limitations of the product and must be followed carefully. This will ensure maximum effectiveness, as well as properly protecting workers, equipment and the environment.
  • Most disinfectant products irritate skin, eyes and the respiratory tract, and can possibly cause injury or even death when improperly applied or handled.

Economic considerations are always important when selecting a disinfectant. Since disinfectants vary in cost, contact time and dilution, costs should always be calculated after dilution, rather than just the cost of concentrate/s. Always place health and safety requirements before the false benefit of cost-savings.

Working environment

Environmental factors can greatly impact the effectiveness of a disinfection protocol; organic loads, equipment design, water hardness, temperature, pH, heavy metals, oils and other contaminants are all important environmental factors to consider. The level of organic material within the equipment to be disinfected will impact the effectiveness of the disinfection protocol. Organic material protects microorganisms from contact with the disinfectant and can also neutralize many disinfectants, especially those containing chlorine or iodine compounds. Application of disinfectants where there is a heavy organic load (heavily fouled ion exchange media) is neither smart nor effective.

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, which may reduce their cleaning action. Many disinfection compounds include chelating agents, such as ethylenediaminetetraacetic acid (EDTA), to help bind these ions. Heavy metals and other metallic ions in water can inactivate certain disinfectants, while also potentially creating other complications due to precipitation of solids when using oxidative disinfectants and certain halides. Disinfectants should always be diluted with deionized water to ensure appropriate stochiometry.

Most disinfectants work best at temperatures above 68°F. Elevated temperatures, however, may cause damage to the equipment being treated and increase the potential occupational hazard to personnel applying the disinfection protocol. Colder temperatures can reduce the efficacy of some products. Oil and other contaminants in the system or in/on the filtration/softening media can also affect the efficacy of disinfectants. Always consult with the specifying engineer or manufacturer’s representative to ensure that deleterious chemical interactions are not overlooked.

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 the 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 quite difficult to disinfect. An ideal surface to be disinfected is smooth, clean and non-porous. Choose a disinfectant wisely and consult with industry experts and manufacturers to ensure that nothing is missed in the evaluation process.

The disinfection action plan

Disinfection protocols will vary depending on the need of the specific site and application. No single disinfectant or protocol is ideal for all situations.

Threat assessment
Assessing the level of bacterial contamination includes observing odor and appearance of contact surfaces, as well as plate culture to determine presence and species of pathogens.

Cleaning and surfactant wash
Experts agree that cleaning alone can usually remove over 90 percent of bacteria and other organisms from surfaces, significantly enhancing the disinfectant process and minimizing the chances of regrowth/colonization. This initial cleaning step involves wiping, scrubbing, brushing and scraping to physically remove as much dirt, biofilm, debris and organic material as possible from all surfaces wherever possible. Washing will further reduce the number of microorganisms. Add an anionic or non-ionic surfactant into the treatment equipment, allow sufficient contact time and then rinse vigorously to remove organics, oils, biofilm and other interfering factors. Adding phosphoric acid to the surfactant mixture can also be quite effective in reducing biofilm accumulation. Multiple bed volumes of fresh water must be rinsed through the system to ensure complete removal of surfactants and contaminants, since they can react with disinfectants.

Disinfection
Choosing the appropriate disinfectant will depend on the target microorganism/s, as well as environmental factors, cost and safety issues. Surfaces must be thoroughly clean, disinfectant should remain for the appropriate contact time and equipment should be completely cleaned and rinsed before returning the system to service.

Evaluation
Follow-up evaluation of the equipment should be conducted to be sure that biological colonies have been destroyed or reduced to acceptable levels. Where appropriate, bacteriological samples should also be obtained to determine the true effectiveness of the cleaning and disinfection protocol. Timing of sample collection is important. The best time to sample is two to three days after disinfection. Surface samples for small, smooth areas can be collected by wiping or swabbing a sterile swab across a non-porous surface. Commercially available testing methods include Replicate Organism Detection and Counting Plates and Petrifilm Plates. Other methods of environmental sampling include those collected from water by ultrafilter membranes.

Sample disinfection protocol
Every location is different, with varying water-usage patterns, waterborne contaminants and expectations of water quality. Cleaning and disinfection intervals should be based upon the aggregate amount of hardness and other inorganics processed by the system. Many industry experts agree that a system should be serviced and completely disinfected after processing approximately 1,000,000 grains of compensated hardness or at least every 12 months, whichever is sooner. Disinfection frequency should be increased if there is any suspicion that the influent water supply is not microbiologically safe.

Industry-standard employee safety precautions should always be taken before implementing this or any other disinfection protocol. While every possible effort has been made to ensure the efficacy of this protocol, you are still ultimately responsible for the microbiological safety of the equipment in your facility. You should completely familiarize yourself with the advantages, disadvantages and liabilities of this or any other protocol before applying it. Proceed with caution and at your own risk.

Disinfection of water treatment equipment

Determine the necessary quantities, types and concentrations as per manufacturer’s instructions. Chemicals required: anionic surfactant concentrate; detergent; EDTA; deionized water and concentrated biodegradable disinfectant. Tools required: appropriate protective equipment (eye protection, respirator, gloves); mechanical scrubbing apparatus and approved waste disposal materials.

Procedure

Surfactant injection

EDTA injection

Disinfectant injection

Testing and evaluation

  • Swab inside of regenerant tank and culture as per instructions.
  • Draw sample of effluent water and culture as per instructions.

Periodic disinfection procedure

Determine the necessary quantities, types and concentrations as per manufacturer’s instructions. Chemicals required: anionic surfactant concentrate; detergent; EDTA; deionized water and concentrated biodegradable disinfectant. Tools required: appropriate protective equipment, mixing apparatus.

Surfactant injection

EDTA injection

Disinfectant injection

Prophylactic application of disinfectant

Note: Surfactant, EDTA and disinfectant can be blended together to improve on-site efficiency, if performed within manufacturer’s specifications and industry best-practices.

Conclusion

Contamination is natural and almost inevitable unless preventative measures are taken. You should plan on having to deal with it on every system that you design and/or deploy. Properly implemented disinfection protocols can be a cost-effective means of reducing both benign and pathogenic organisms. Prevention of contamination is easier and more cost-effective than addressing an incident after colonization has occurred.

About the author

Greg Reyneke, Managing Director at Red Fox Advisors, has two decades of experience in the management and growth of water treatment dealerships. His expertise spans the full gamut of residential, commercial and industrial applications, including wastewater treatment. In addition, Reyneke also consults on water conservation and reuse methods, including rainwater harvesting, aquatic ecosystems, greywater reuse and water-efficient design. He is a member of the WC&P Technical Review Committee and currently serves on the PWQA Board of Directors, chairing the Technical and Education Committee. You can follow him on his blog at www.gregknowswater.com

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