Learning the Language of Microbiological Control

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Water treatment specialists can forget that their clients may not understand the technical terms used in our industry. The language of microbiological control can be particularly confusing. To help establish a common working vocabulary, it’s important to define some key terms. Let’s get started!

Types of Microorganisms

Microorganisms are living organisms that require high magnification to see because they are so small.

Bacteria are single cell microorganisms that require water, but not light, for normal grow. They are so small (0.5 to 5.0 micron) that it would take 200,000 to two million bacteria placed end to end to measure a yard. Under ideal conditions, bacteria populations can double every 15 minutes. There are over 10,000 distinct species of bacteria, many of which can cause serious problems in water systems.

Aerobic bacteria require oxygen for growth. Many types of aerobic bacteria can form thick, sticky biofouling deposits that can block water flow, reduce heat transfer, increase pumping costs, cause corrosion, and increase the potential for disease. These deposits are generically called slime, and result from bacteria forming protective biofilms on system surfaces.

Anaerobic bacteria require an absence of oxygen for growth. They can often be found growing underneath biofilms and biofouling deposits.  Anaerobic bacteria including Sulfate Reducing Bacteria (SRB) are a major cause of microbiologically influenced corrosion (MIC) in water systems. Many anaerobic bacteria produce spores as a survival mechanism and can be cultivated from oxygenated water. 

Protozoa are single cell microorganisms that can move independently, and feed on biofilm associated bacteria and waste products.  Amoebae are a type of protozoa. Although microscopic, protozoa are typically 5 to 100 times larger than bacteria. The presence of protozoa in a water system indicates advanced microbiological growth associated with biofilms.

Legionella is a common waterborne bacteria that can cause a serious, sometimes fatal illness called Legionnaires’ disease in exposed individuals. It is caused by inhaling aerosolized droplets of water containing an infectious amount of Legionella bacteria. It is characterized by fever, chills, lung congestion, and severe pneumonia. The elderly, sick, immunocompromised, and smokers are most susceptible to develop Legionnaires disease upon exposure. Over 50 different species of Legionella have been identified. Only about half of the species have been associated with disease,

Colonization Characteristics

Microorganisms can be classified based on their colonization characteristics:

Planktonic bacteria are “free floating” in the bulk system water.  Whether performed in a laboratory or in the field using dip slides, bacteria culture tests on water samples only measure planktonic bacteria counts.

Sessile bacteria are “surface attached” associated with biofilm deposits. Sessile bacteria are not detected by bulk water bacteria counts.

Biofilms are complex communities of surface attached bacteria growing inside a protective microbial secretion often called slime. Although biofilms start out microscopic in size, they can grow into visible biofouling deposits in just a matter of days. A wide range of problem causing microorganisms can grow to high levels protected within biofilms and associated microorganisms, especially amoebae. Once established, biofilms are difficult to remove and kill.

Extracellular Polymeric Substances (EPS) are microbial secretions that establish the foundation for biofilms and biofouling deposits.  EPS secretions tightly bind biofilms to systems surfaces and protect growing microorganisms from environmental hazards including high level cleaner and biocide additions.

Biocides Types

Oxidizing biocides kill or inhibit bacteria growth by physically destroying cell structures. Chemical compounds that fall into this category are chlorine, bromine and peroxide.

Non-oxidizing biocides kill bacteria by interfering with essential metabolic processes, in effect poisoning the bacteria. Some common non-oxidizing biocides are glutaraldehyde and isothiazolin.

Sanitize, Disinfect, or Sterilize?

Although the exact definition will vary depending on the application, these terms refer to the relative effectiveness of processes for eradicating harmful microorganisms. The lowest level of cleaning and microbial control is sanitizing, followed by disinfection, and then sterilization.

• Sanitizing involves physical and chemical cleaning processes that reduce the number of microorganisms.
• Disinfection involves adding disinfection chemicals in low-level, intermediate level or high-level control strategies.
• Sterilization involves using chemicals, temperature, gas and/or pressure to kill or inactivate all disease-causing bacteria, spores, fungi and viruses

The First Step in Problem Solving

Understanding the terms used in the water treatment industry is always the first step in proper problem solving. Everyone working together on a problem must have the same basic knowledge of terms used in describing the conditions and the appropriate corrective tools. We will then be in a better position to achieve our common goal of maintaining clean cooling water systems that are free from uncontrolled microbiological growth.