How to Identify and Maintain Ecoat Bacteria

Q. Our electrocoat supplier tested our system for bacteria and reported that we are positive for bacteria. What kind of bacteria are found in ecoat systems and where can they come from? How can this affect the operation of the system?

A. I would recommend that you discuss the positive bacteria report findings in more detail with your ecoat supplier to determine where samples were taken from, and to identify the types and quantities of bacteria colonies found.

Keep in mind that there are millions of naturally occurring micro-organisms and that some microbiological activity will always be present in and around surface treatment and ecoat systems. The positive presence of bacteria alone should not be a reason for alarm, at least not yet.

In the electrocoat world, certain types of bacteria thrive in the constant temperature, neutral or mildly acidic water-based solutions or moist conditions encountered around process tanks and associated equipment present in small, medium and large pretreatment and ecoat systems.

These bacteria are typically naturally occurring aerobic bacteria that are well distributed, openly transmitted and widespread throughout the environment. They thrive anywhere as long as they have water or a moist environment, oxygen, a habitat pH between 4 and 7 and temperatures between 20°C and 40°C (68°F to 104°F). There is no such thing as “ecoat bacteria” generic only to the industrial ecoat processes used.

Because they are naturally occurring, the colonies can originate in multiple point sources and live and multiply in different locations around pretreatment and ecoat systems. In well-operated ecoat systems, microbiological activity is characterized by low colony counts, low cumulative activity and therefore little or no impact on normal ecoat operations.

Regular bacteria monitoring protocols and some basic housekeeping and maintenance practices typically keep bacteria levels in pretreatment and ecoat systems well within acceptable ranges. However, if for any reason—of which there are many—the number and size of colonies are allowed to grow and reach biological infestation levels, then significant effects could impact ecoat operations.

Microbiological studies on several pretreatment and ecoat systems show that recirculated water-based systems are generally the epicenter of many bacterial point source originations. This is where these types of aerobic bacteria will most likely be found on pretreatment and ecoat systems. In other locations studied, RO and DI storage systems, raw parts, people and even air have been proven to be the origin point sources for the bacteria.

Predominant locations for infestations in pretreatment stages include recirculated water ecoat pre-rinses, wetting rinses and final rinse stages, often concentrated around filters, filter canisters or pots, scum or overflow lines, pump houses, micro or macro-screens. Concentration points also include housing walls and ceilings, gratings, spray nozzles, and piping and mountings.

All of the above predominant locations apply to the ecoat stages as well, as they relate to cream-coat, permeate or UF post-rinse stages, wetting or final DO/DI rinse stages, as well as UF membranes, piping and reservoirs. For bacteria colonies to form, low flow and semi-dark locations are preferred over high flow locations.

Ecoat systems generally show first signs of infestation by having difficulty maintaining pH because it wants to shift rapidly towards a more neutral pH around 7. Difficulty maintaining pH is one of the most widely known cause-effects in electrocoating.

Bacteria can also manifest as a decreasing UF production, too many bag filter changes, or dropping too many paint solids to the bottom of the ecoat tank, seeing material usage efficiencies decline or even foul odors in enclosed locations.

Bacteria can multiply into larger and larger colonies and form other cellular habitats known as slimes or biofilms.

Microbial slimes are typically young colonies that easily agglomerate into gelatinous masses and easily plug filters and piping. Biofilms are older and active agglomerations that have grown to form an outer and semi-porous physical protective barrier that can be visible to the human eye.

Monitoring of bacteria using identification and quantification procedures in pretreatment and ecoat systems is typically done using dipslides, bacterial sticks or petri dishes.

Those three techniques use cultivated media mixed with special mixtures of enhanced sugars and other selective materials specifically formulated to speed up the nucleation and multiplication of natural aerobic bacteria colonies. Many families and types of aerobic bacteria will grow on this type of dipslide or petri dish medium.

Some types of specific dipslides are designed to produce selective growth of bacteria on one side of the dipslide and fungi on the opposite side, called BF dipslides, representing bacteria and fungi detection by using chemical inhibitors. The bacteria side of the dipslide is impregnated with fungi inhibitors and the fungi side with bacteria inhibitors.

The bacterial identification and quantification occurs when the dipslides are dipped for 3 to 4 seconds in the specific liquid sample, capped in the container and then incubated as recommended by the dipslide manufacturer. Once the containers with the sample dipslides are allowed to incubate, the bacterial growth will be visually displayed on the exposed surface of the dipslide medium in the form of colored red or brown dots, also known as colonies. The unit of measurement used for comparison is the Colony Forming Units (CFUs) of bacteria detected per milliliter of sample. It is important to remember that it is the dot quantity that matters and not the size.

Bacterial contamination in an ecoat system is considered active when the CFUs/mL is 10⁴ or greater, depending on specific configuration and operation of the pretreatment and ecoat system. Maintaining a system at 10³ CFUs/mL or below is critical.

Again, the type of design and system, location, throughput, history and site-specific housekeeping, maintenance and prevention practices and procedures make each system unique.

Originally published in the June 2017 issue.