Microbes could be growing in your cleaning process bath. Minimize unwanted microbes to achieve a more consistent, productive manufacturing process. Those of you not involved in producing pharmaceuticals or in final assembly of medical devices may think microbial contamination doesn’t apply. Think again! Let’s consider conditions that you and I enjoy, environmental conditions that help people thrive. Let’s see: there’s air, water, food, a neutral pH, moderately warm weather. Microbes are far more adaptable than people; they can grow under a very wide range of conditions. Microbes can grow in cleaning agents! Here’s how Ed Kanegsberg demonstrated microbial growth in aqueous cleaning baths at the 2021 Product Quality Cleaning Workshop.
For the demonstration, Ed used four beakers; each containing a dilute water-sugar solution (15 ml sugar plus 200 ml water). The beakers were heated to approx. 35 Deg C. To three of the beakers, he added a commercially-available cleaning agent: alkaline (pH 9), pH neutral, or acidic ( pH 4). The overall dilution of each cleaner was in the range recommended for industrial parts cleaning. The fourth beaker, the control, contained only the water and sugar. Finally: the microbes were added to each beaker, specifically, Baker’s yeast (5 ml) The beakers were set aside and allowed to coast down toward ambient temperature.
Within 40 minutes, both the control (sugar-water and yeast) and the near-neutral cleaning agent showed vigorous microbial growth as evidenced by bubbling and a thick layer of foam. The suspension with the acidic cleaner showed no visual change. The alkaline suspension showed some growth but significantly less than the neutral or control.
We chose Baker’s yeast to demonstrate microbial growth, even though it may not be a source of contamination in your cleaning process tank. Yeast is readily available, does not require specialized lab conductions and reproduces rapidly – in well under an hour, growth is obvious. You can see visual evidence of fermentation (CO2 bubbles).
Temperature
Yeast grows rapidly at a moderately elevated temperature, approximately 100 to 110 deg F ( 38 to 43 Deg C). High temperatures, above 130° F to 140° F (55° C–60° C), kills yeast. While some thermophiles have been reported to grow at temperatures as high as 140 Deg C, most organisms are not suited to survive exposure to very high temperature.
This is important because rather than clean at high temperatures, perhaps close to the boiling point of water, many manufacturers clean at reduced, albeit warm temperatures. In ultrasonic cleaning, temperatures near the boiling point do not promote effective cavitation. Lower temperatures are also favored to reduce cooldown time, to make handling the product more convenient, to reduce energy costs, and to reduce hazards to employees.
pH
Alkaline cleaning agents are effective for removing soils. However, extremely caustic cleaning agents (pH 12 or higher) are often not favored because they are difficult for employees to manage safely, not to mention the potential for materials compatibility problems. Some companies have policies requiring the use of near-neutral pH cleaners. While such cleaners can be safer for employees, there is the increased potential for microbial growth.
Nutrition
Cleaning agents are not recommended as a snack for people, but they can be a source of nutrition for microbes. “Biodegradable” implies the ability to be broken down by life forms. We added sugar to enhance rapid microbial development. Many industrial soils, including metalworking fluids and coolants, can be sources of nutrition for microbes. In fact, some metalworking fluids are formulated in a rather complex (and proprietary) manner to discourage the growth of microbes.
The solution – planning, awareness, ongoing observation
Life is persistent and adaptable. It is very difficult (i.e. impossible) to eliminate all life forms from manufacturing or to predict all instances of contamination. Microbes are not limited to cleaning baths. Bacteria are found in ultrapure water systems (1) Biofilms (a topic that deserves a separate discussion) can grow in transfer lines and block them.
There are occasions where microbes are helpful; one example is in some “sink-on-a-drum parts washers that use microbes to remove oils from the bath. in most instances, microbes are uncontrolled, inconsistent, and undesired contaminants that interfere with process performance. Controlling microbial contamination involves a well-designed, well-controlled cleaning process and an excellent maintenance program. It is also imperative to maintain ongoing observation of the process and of process equipment by assemblers, technicians, and facilities people.
Reference.
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- L.A. Kulakov et al, “Analysis of Bacteria Contaminating Ultrapure Water in Industrial Systems,” Appl Environ Microbiol. 2002 Apr; 68(4): 1548–1555. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC123900/
