Archive for the ‘ATP Testing’ Category


In my August post (, I discussed using ASTM D7687 to quantify microbial loads (AKA bioburdens) in liquid samples – fuels and fuel associated water. This post will focus on surface samples.

Generally speaking, microbes tend to be most abundant on surfaces. By some estimates, in any given system, for every microbe floating in the bulk fluid, there are 1,000 to 1,000,000 growing on surfaces. These surface microbes are invariably part of biofilm communities. I’ll discuss biofilms in more detail in a future post. For now, it is sufficient to understand that biofilms are slime-encased microbial communities growing on surfaces (fig 1). It is much easier to grab a fluid sample than a surface sample. Consequently, most fuel system samples – even those intended for microbiology testing – are fluids. However, there are a few fuel system surfaces that can be sampled relatively easily.

Fig 1. Scanning electron micrograph of a mature biofilm. Note its structural complexity. Source

Fig 2. Automatic tank gauge, water float showing slime accumulation (right) and swabbed area (left).

Biofilms tend to develop on automatic tank gauge (ATG) water floats (fig 2). The left side of the water float shown in figure 2 has been swabbed. The right side shows the undisturbed deposit. This deposit includes microbes, their slime, and metal fins (i.e. rust). Most often, I use a swab to collect a sample from a premeasured surface area. If the deposit is > 2 mm (1/8 in) thick, I use a spatula to collect the sample.

The second location I routinely check for microbial contamination is the filter. Figure 3a shows a 76 cm (30 in) filter cartridge. It was one of 16 cartridges in a high-capacity filter housing. However, except for its length, the 76 cm cartridge does not look very different from the filter element inside a typical fuel dispenser filter (fig 3b). To test the filter element for microbial contamination, I first inspect the element visually; looking for slime accumulations or discolored zones. For larger filters, I use an alcohol-disinfected forceps and scissors to cut out a section ( 4 cm x 4 cm; fig 3c), and from that cut out a 1 cm x 2 cm piece of filter medium (fig 3d). For dispenser filters, I cut out a 1 cm x 2 cm piece directly. This is my specimen.

If a dispenser has a screen (fig 4), upstream of the filter I collect either a swab or spatula sample just as I would from the ATG water float.

Fig 3. Fuel filter sampling: a) 60 cm filter element from high-capacity housing; b) dispenser filter element; c) section of filter media taken from element shown in fig 3a; d) 1 cm x 2 cm specimen taken from section shown in fig 3c.

Fig 4. Fuel dispenser prefilter screen partially covered with slime.

Once I’ve collected my surface sample I run LuminUltra Technologies, Ltd, Deposit and Surface Analysis (DSA) test (for more information about the DSA method visit; for a video demonstration, visit The method provides me with a rapid, quantitative measure of the bioburden on these fuel system surfaces.

Total ATP concentration ([tATP]) <100 pg/cm2 indicates negligible surface contamination. [tATP] between 100 pg/cm2 and 1,000 pg/cm2 indicates moderate contamination (it’s time for maintenance action). [tATP] ≥ 1,000 pg/cm2 signals that prompt corrective action is needed! If you have weighed out samples, the [tATP] per g threshold levels are the same as those for [tATP] per cm2.

If you’d like to learn more about fuel system surface microbiology, please contact me at



How much of the total microbial load each type of test detects.


I’m starting this post with an illustration from one of my recent presentations (click on the image to enlarge it). The quote is from Daniel Kahneman’s book: Thinking, Fast and Slow. It reminds us of how often our perceptions are much more limited than we realize. Let’s turn to the circles to the right of the quote.



ASTM E2694, Method for Measurement of Adenosine Triphosphate in Water-Miscible Metalworking Fluids, was first approved in 2009. The 2016 revision of the method has just been published by ASTM ( This version includes a new Appendix X4 that provides a protocol for differentiating between bacterial and fungal contamination in metalworking fluids. I had first written about this protocol here in my 04 May 2015 blog. The original research on which the ASTM E2694 revision was based was published in 2014: Passman, F.J. and Küenzi, P., “A Differential Adenosine Triphosphate Test Method for Differentiating between Bacterial and Fungal Contamination in Water-Miscible Metalworking Fluids” International Biodeterioration & Biodegradation (2014), 0964-8305.
Appendix X4 is meant to be used only on samples that have high cATP concentrations as determined by the basic E2694 test. I generally consider ≥1,000 pg/mL to be high cATP, but others might choose to be more conservative. The differential method guides microbicide selection. If the ATP-biomass is all from bacteria, then a tankside addition of bactericide is generally the appropriate treatment. If it is from fungi, then a fungicide will be needed. A broad-spectrum microbicide or compatible bactericide and fungicide are needed to control an infection that is due to a combination of bacteria and fungi. For more information, contact me at 609.716.0200 or


I’ve recently had the privilege of co-authoring a paper with Dr. Griselle Montenaz, and others, on the use of LuminUltra Technology Ltd’s QGO-M test method to screen aqueous polymer emulsions (APE) for microbial contamination.  The paper describing the use of  QGO-M XL measuring cellular adenosine triphosphate (cATP) in aqueous polymer emulsions (APE) has just been published in the journal: International Biodeterioration and Biodegradation (IBB; 114 (2016) 216-221; doi:10.1016/j.ibiod.2016.06.007).  The procedure reported in the IBB paper reduces the time delay for microbiological contamination testing from the typical three to five days required for culture testing to less than 10 minutes.  Currently, the cost of holding APE in quarantine while waiting for a microbiological clean rating is estimated to be in the hundreds of thousand dollars per year range for a single manufacturing facility.  Additionally, the costs associated with spoiled APE batches can range from $50,000 to $250,000 per incident.  The QGO-M XL method described in this paper essentially eliminates quarantine inventory time and increases the reliability of microbiological contamination testing..

The multi-year investigation was a collaborative effort of researchers at the Advanced Polymer Technology team at The Dow Chemical Company, Biodeterioration Control Associates, Inc., and LuminUltra Technologies, Ltd.  Initial evaluations were run using a variety of APE that had been spiked with microbes that are known to be problematic to APE.  In these studies, cATP concentrations were compared with culture test results. Successful detection and quantification of microbial contamination in laboratory samples set the stage for the second phase of the research effort.  A total of 88 APE production run samples, including representative samples of 14 different types of APE, produced at 16 different production plants, were tested by QGO-M XL and standard plate count (SPC).

The traditional upper control limit for microbiological contamination in APE is ≤1,000 CFU mL-1.  The investigation demonstrated that QGO-M XL’s sensitivity was substantially greater than that of the SPC method.  The QGO-M LX test detected ≥100 cells mL-1 (»0.1 CFU mL-1), while the SPC protocol detected ≥10 CFU mL-1).  Consequently, QGO-M XL provided more data about actual bioburdens in samples with ≤10 CFU mL-1.  This additional information drives process improvement that reduces the risk of APE either being produced or shipped with unacceptably high microbial contamination.  Additionally, because QGO-M XL can be run in the lab or in the field, the test can be used to identify microbial contamination sources after APE has been shipped.  This improves APE product quality control for producers, transporters and users.  The improved quality control has already translated into substantial cost savings for stakeholders who have adopted QGO-M XL for APE microbial quality control testing.  For more information, contact me at


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