Industrial Microbial Control


Its not rocket science, but it can be complicated is my mantra for beginning discussions on microbial control challenges. Microorganisms play a significant and costly role in the stability, utility and safety of nearly any fluid material or product. In manufacturing and large-scale settings involving lubricants and metalworking fluids, microbial control can be particularly difficult and costly if done incorrectly.

The aim of this article is to outline the questions that users need to address to determine their systems microbial condition. It will also look at the most important issues in performing the assessments, and the tools needed for control, prevention and, if necessary, remediation of a contaminated system.

Factors Favoring Microorganisms

Does the manufacturing system have water, temperature and carbon? This first assessment, often simply stated as the Rule of Three, determines whether organisms can grow in your system. Biologically it is a bit more involved, but in most types of industrial settings, the rule of three is essentially fact.

Microorganisms readily acclimate to a range of conditions, from pH 1 to pH 11, from 0 to 250 degrees F, and to other environmental extremes. The take-home message here is: If your system has the three critical components, be assured that environmental conditions are permissive to the growth of microorganisms.

Confusion arises when a particular system is being evaluated, since the acceptable concentration of microorganisms for any particular process can differ. In a given system, acceptable concentrations can range from fewer than 10 colony forming units (CFU) per milliliter to as high as 104 CFU/ml. (Each colony forming unit is one viable bacterium or fungus, so a count of 105 CFU/ml, for example, represents 100,000 microorganisms per ml of liquid.)

So the assessment that needs to be made is: At what level is the concentration of microorganisms likely to cause either a quality control or safety problem? On average, a stable system with less than 103 CFU/ml is deemed in control, and 105 CFU/ml or higher is deemed out of control.

Its important to acknowledge that in most systems the aim of a microbial control strategy is not sterility. Rather, the aim is to balance microbial control acceptability with cost, safety and quality. At times, simply impeding the growth of microorganisms can be a better, more cost-effective strategy than outright elimination.

The Control Landscape

The factors that contribute to an otherwise acceptable level of contamination vary considerably. For oil and lubrication systems, common examples are stagnant volumes, excess nutrients, lack of biocides, aged formulation components, swarf, old and oxidized solutions, lack of chemical control such as pH buffers and antioxidants, and inappropriate waste addition. In all systems, these factors favor increased growth of microorganisms, which in turn results in faster deterioration of the fluid or product.

Much like artificial coral reefs, the metal swarf and agglomerated materials from metalworking operations provide a tremendous surface area and a safe reservoir of aging materials that will more readily support organism growth. Once established, these organisms form resilient biofilms which can only be removed by mechanical means such as scraping and scrubbing.

Some oil based fluid systems may appear safe from microorganisms due to their lack of water, but whether by condensation, fractionation from a supply or simply contamination, water can accumulate in oil systems and build into large stagnant pools. These pools may lack oxygen – but oxygen is not a requirement for growth of anaerobic (non-oxygen requiring) bacteria. In addition to degrading the solution, anaerobic bacteria can cause surface pitting, corrosion and weakening of long-lived metallic structures or materials. Therefore, the implemented control strategy needs to include assessment and management with these types of system issues in mind.

Tools for Assessment

There is no shortage of appropriate tools for assessing contamination of a system. The challenge is in knowing which tools are appropriate for a specific system. The process being monitored could be a metalworking fluid sump, fractionation fluid tank, oil or grease reservoir, the lid on a tank, or piping to and from a particular system. Key elements to know are where to pull samples, including where the void volumes are, and where biofilms are likely to be established.

Once we know where, we need to determine when and how often these samplings need to be taken. The measurements must be designed to monitor change over time to establish trends. Lacking trend data, a single data point does little to support controlled management of a system. Appropriate measurement times can range from twice daily to weekly. As a guideline, systems with higher temperatures (above 70 degrees F) and lower overall stability need more frequent measurements.

Ideally, the metric used for the samples will also identify the category and quantity of contaminating organisms present. Bacteria and fungi are the two most common categories of organisms, but algae can also play a role in systems that have a high proportion of water and are exposed to sunlight. Importantly, as organisms become established, they facilitate what is known as succession or increased acclimation of the system to other organisms, making deterioration faster and control of the system more difficult.

Common tools used in the assessment of organisms range from dip slides that provide results in as few as a couple of days, metabolic and antigen assays that can provide highly defined assessments in a few hours, and luminescent assays that are nearly instantaneous. However, familiarity with the measurements and what they actually mean for a given system can vary tremendously. Correct interpretation of the measurements is the most critical function in using any assessment tool. Fundamentally, there is no reason to select one measurement tool over another as long as the measurements and evaluation are done with a critical eye and they fit with the needs of the process.

Taking Preventive Action

Prevention is the best strategy for a microbial quality control process. There are essentially three steps that can be controlled.

First, keep material from entering the system, such as wash water or other waste products.

Second, filter or circulate the system to remove waste and aid in agitation.

Third, add preservatives or biocides targeted at inhibiting or neutralizing microorganisms.

The first and second of these steps can be implemented by modification of the manufacturing process or by mechanical filtering. The third step requires selection of an appropriate biocide. It is important that the quality control person has a good understanding of the process before implementing a biocide solution.

In one common scenario, preservatives are added to a system that shows high levels of organisms. Once added, the operators find that the biocide controls the fluid in the system temporarily – but then the system begins to grow high numbers of microorganisms relatively quickly. For a degraded system, this is commonly due to a buildup of organisms as biofilms in tanks, pipes, or swarf.

In addition, the responsible person also needs to have an understanding of the appropriateness of the biocide selected. For example, formaldehyde-containing or -releasing antimicrobials are good at controlling a broad spectrum of organisms, from bacteria to fungi and virus, but due to its chemical properties, formaldehyde is inappropriate for some applications.

Also, users must consider the local and federal regulatory approval of a particular biocide, so that issues are not created with potential discharge to the environment or worker safety. Finally, each particular biocide or combination of biocides should be evaluated as fit for use in terms of effectiveness and cost.

While combinations of biocides can provide great performance under ideal conditions, true performance can be significantly affected by the actual use environment. As the cost of using these chemicals can be significant, evaluation of the appropriate additive should be part of the baseline quality-control process. Cost per pound is the not the appropriate metric for selection. Rather, a cost:efficacy ratio is a better metric.

Start by benchmarking performance in the existing system. This may be a slow process, but the benchmark is the foundation for evaluating any change. Laboratory-scale work can be done to economize and speed up the process, but the best representation of the results will be in the in-use system. An appropriately formulated solution could result in significant cost saving – if implemented correctly.


In an ideal world, prevention would always work and material remediation would not be needed. However, controlling what comes into a system is not always possible and recovery of a soured system is sometimes necessary. Before initiating any large-scale remediation, it is important to determine if the recovered material will perform the intended purpose. Next, determine if a mechanical solution (such as filtration) and/or a chemical solution is most appropriate; if both, which sequence should be used? Typically, chemical recovery solutions are the most direct strategy, but mechanical means may be necessary as part of the process. Common chemical control measures include the addition of biocide, pH modifiers, antioxidants and other additives.

In recovery, the time frame becomes particularly important. Too slow, and no good will come of it. Too fast, and unintentional health and safety issues could arise. Be aware of these potential issues for your system. Once the fluid system is recovered, be sure to consider how to preserve the material against further contamination.

Long-term Implications

Safety considerations are an ever-growing component of the industrial microbial control equation. The chemical tools used to control microorganisms are highly regulated because of their inherent chemical properties. There are numerous potential health issues associated with a system that is contaminated with microorganisms. These factors affect not only the individuals in the immediate use environment, but also downstream handlers and local participants not directly connected to the process or product.

The U.S. Centers for Disease Control and federal Occupational Safety & Health Administration track the incidence of infection and illness associated with contaminated solutions in the work environment, including bacterial pneumonitis, MRSA infection (better known as methicillin-resistant staph), contact dermatitis and others.

While the incidents have decreased for some disorders, such as mycobacterium infections in metalworking fluids, through improved microbial management policy, certain disorders dont need living organisms to cause health issues. Currently, the highest rates of microbial-linked health issues are associated with toxic microorganism components – such as bacterial endotoxin and fungal mycotoxin – which can cause serious chronic allergic reactions and pneumonitis. As the buildup of these components is likely a long-term phenomenon, vigilance is key and appropriate management of system is the best way to control these and other microbiological issues.

If the system is well managed, safety, process costs, quality and hygiene are all improved. Start by creating the process for managing it. Then create a plan for controlling incidence and raising awareness of the indicators for a problem, and implement the plan as part of a standardized quality-control program.

Related Topics

Additive Components    Additives    Biocides