609-306-5250

fredp@biodeterioration-control.com

Author Archive

FUEL & FUEL SYSTEM MICROBIOLOGY PART 31 – MATCHING THE SAMPLING TOOL WITH THE SAMPLING OBJECTIVE

Dixon Pumps Fuel System Broadcast Emails

The folks at Dixon Pumps dixon@dixonpumps.com routinely send out broadcast emails about fuel system maintenance. Today’s article was inspired by their 31 October 2019 email: Water Removal Basics, by Patrick Eakins. After the fourth paragraph, Mr. Eakins has an action list. The first action he recommends is:

“1. Determine the volume of phase (e.g. free water, ethanol) at the bottom of the tank. This can be accomplished by using a fuel sampler. First take a sample on the very bottom of the tank, then at 1-inch increments until you determine where the phase ends and the fuel begins.”

The phrase: “using a fuel sampler” caught my attention and will be this article’s focus. Spoiler alert: In Fuel Microbiology Part 30, I wrote about fuel system sampling. In this article be covering some – but not all – of the same material.

What Sampler?

The Dixon Pump article advises folks to use a sample but makes no mention of what kind of sampler is best for determining the height of free-water (or phase-separated ethanol and water) in underground storage tanks. The problem with an open statement like this is that the samples obtained by different types of samplers tell different stories.

Bacon Bomb Samplers

The Bacon bomb is probably the best, currently available bottom sample. Part 30, figure 2a shows a photo of a chrome-plated Bacon Bomb sampler. Figure 1, is a photo of a Bacon Bomb with a clear, polymeric cylinder (the cylinder is the sampler’s primary container). To make it easier to clean, the cylinder is threaded at each end so that the cap and bottom can be removed. The cap and plunger each have a hole for inserting a ring clip. To facilitate lowering and retrieving the sampler into tanks, a sounding tape can be attached to the cap’s ring. A secondary line can be attached to the piston’s ring for sampling above the tank’s floor (when the sampler is at the desired depth, the secondary line is pulled for approximately 30 sec to allow the sampler to fill. It is then released so that the piston is sealed against the sampler’s inlet).

Fig 1. Bacon Bomb sampler.

Figure 2 illustrates what happens when a Bacon Bomb sampler is used to collect a bottom sampler. The piston rests against the sampler’s inlet as it is lowered through the fuel column (figure 2a1 and 2b1). When the piston contacts the tank bottom, it is pushed up to open the inlet (figure 2a2 and 2b2). Hydrostatic pressure from the fuel column forces fluid into the sampler. When the Bacon Bomb is lifted off of the tank bottom, the piston will drop back into place – sealing it closed with the sample retained inside the cylinder. If there is no water or sludge present, the sampler will fill with fuel (figure 2a3). However, if bottoms-water is present, it will be the first fluid to enter the sampler. Thus, if there was 500 mL or water, and the Bacon Bomb’s capacity was 500 mL, the sample would be all, or nearly all water (figure 2b3). This would not be an accurate means for estimating the tank’s water level.

Fig 2. Bottom sample collection using a Bacon Bomb sampler. a) No water on tank bottom: 1) as sampler is lowered through fuel, the piston’s seat rests against the sampler bottom’s inlet, preventing fluid from entering; 2) when the piston touches the tank bottom and sample continues to fall, the inlet is opened and fluid enters – driven by the force of the fuel column’s hydrostatic pressure; 3) as the sampler is lifted off the tank bottom, the piston once again falls to reseal the sampler’s inlet – retaining the sampled fluid. b) Bottoms-water present: 1) same as a1; 2) any bottoms-water and sediment are pushed into sampler before any overlying fuel can enter; 3) same as a3, but now sampler is filled with water instead of fuel.

What does this mean in practical terms? Take a look at figure 3. Three, 500 mL Boston round bottles were filled from Bacon bomb samples collected from a tank bottom. The first sample (figure 3a) captured 450 mL bottoms-water and 50 mL of diesel fuel. If this had been used to estimate the water level, one might have concluded that the tank bottom was covered with a 5 in (13 cm) high water-layer. All 490mL of 500 mL from the second Bacon bomb sample (figure 3b) was bottoms-water. Was there actually 6.7 in (17 cm) of bottoms-water? The third sample (figure 3c) was mostly fuel. Three successive Bacon bomb samples from the same spot were sufficient to pull most of the water out of the tank. Water paste had shown that at the fill-end, the tank had 0.5 in (1.2 cm) of water.

Fig 3. Three successive Bacon bomb samples form one sampling point. A, b, and c were the fist, second, and third samples, respectively.

Bailer Samplers

Bailer samples are normally used to collect fluids from monitoring wells. Figure 4a illustrates how monitoring wells are placed around underground storage tanks. Note that the bottom of the well is porous and at a depth below the water table. After sample collection, the contents of the bailer sampler are layered – reflecting the layering of fuel over ground water in the well (figure 4b – normally the sampler will contain only water). Figure 4c shows the primary components of a bailer sampler. There are numerous bailer designs. For sampling fuel tank bottoms, the sampler must be fabricated form fuel-compatible materials. Also, as shown in figure 4c, the bailer should have a flat bottom.

Fig 4. Monitoring wells and bailer samplers. a) schematic showing location of a monitoring well near a UST; b) bailer sampler retrieved from monitoring well – dark fluid next to ruler is leaked fuel that was captured in monitoring well; c) bailer sampler showing its key parts.

To collect bottom samples, the bailer is slowly lowered through the fuel column (figure 5a1 and 5b1) until it stands vertically on the tank floor (figure 5a2 and 5b2). Because it is not sealed as it descends through the fluid, it analogous to collecting a soil core sample (figure 6). Most bailer samplers have a ball that floats inside the cylinder as the sample is lowered, then settles to the base and seals the inlet as the sampler is raised (figure 5a3 and 5b3). As shown in figure 5c, just as with a soil core sample, the bailer sample reflects the profile of water, rag layer, and bottom fuel much as they are layered in the tank’s bottom. There is typically ∼0.25 in (∼1 cm) between the bailer’s bottom and the inlet. Consequently, bailer samplers are not good for collecting bottom sludge and sediment samples. However, they are useful for estimating bottoms-water height. The tank from which the figure 5c sample was taken had ∼3.5 in (∼9 cm) bottoms-water and 0.75 in (1.9 cm) thick rag layer. The water height in the sampler agreed well with that determined using water paste.

Fig 5. Bottom sample collection using a bailer sampler. a) No water on tank bottom: 1) as sampler is lowered through fuel, ball floats above sampler inlet; 2) when sampler comes to rest on tank bottom, the ball sinks to the inlet; 3) as the sampler is lifted off the tank bottom, the ball seals the sampler’s inlet – retaining the sampled fluid. b) Bottoms-water present: 1) same as a1; 2) water fills the sample to the level of bottoms-water in the tank; 3) same as a3, but now sampler has fuel over water; c) fuel tank bailer sample.
Fig 6. Soil core sampler. a) core sampler pressed into soil; b) soil core, showing three soil horizons: a – organic surface zone, b – surface soil, and c – subsoil.

Other Samplers

ASTM Practice D4057 describes other fuel samplers. However, none of these are useful for collecting true bottom samples.

Best Practice for Determining Height of Bottoms-Water Layer

As I explained in my previous fuel microbiology post, the best way to determine bottoms-water height is by coating either a sounding sick or bob with water paste and lowering it into the tank. The water will react with the paste to change its color. Because tanks are rarely level, best practice is to test for water at two – preferably three- points: fill end, ATG (automatic tank gauge well, and fill end).

The details

For more details about fuel tank bottom sampling and water accumulation determination, please contact me at either fredp@biodeterioration.control.com or 01 609.306.5250.

FUEL & FUEL SYSTEM MICROBIOLOGY PART 30 – looking for samples in all the right places

What samples are most useful for microbiological testing?

Earlier this week a colleague asked me to prepare a short piece about collecting samples from fuel systems when the intention was to perform microbiological tests. My initial response was to refer her to ASTM Practice D7463 Manual Sampling of Liquid Fuels, Associated Materials and Fuel System Components for Microbiological Testing and my recently published chapter on sampling in ASTM Manual 1, 9th Edition. My colleague responded that she was really looking for a two-page summary that she could share with her customer who wanted to monitor their fuel systems from microbial contamination. Today’s post provides that summary.

The right stuff…

I first addressed sampling in Fuel & Fuel System Microbiology Part 2 (December 2016) and discussed sample perishability in Fuel & Fuel System Microbiology Part 6 (January 2017), but have not previously addressed sampling directly in this posts. Two key principles lie at the heart of sampling for microbiological testing:

   1) 1. Fuel & Fuel System Microbiology Part 2Samples are diagnostic – not representative, and

   2) 2. Microbial communities develop at interfaces.

What’s a diagnostic sample?

Microbiological sampling is unique in that the objective is to capture a sample from a location that is most likely – within a fuel system – to harbor microbes. Our intent is to diagnose the risk of microbes causing damage (biodeterioration) to either the fuel or fuel system. This is in stark contrast to the more common objective of collecting a representative sample – one that we can use to determine whether the product is fit for its intended use. Consequently, I use the term diagnostic to differentiate microbiology samples from fuel samples.

What is an interface?

Interfaces are zones where two or more components of a system come into contact with one another. Figure 1 illustrates the interfaces found in fuel systems:

  • Fuel-vessel – the surface of tanks and other system components that are in contact with fuel.
  • Fuel-water – the surface at which fuel and fuel-associated water meet. The primary fuel-water interfaces are between fuel and bottoms-water, and between fuel and biofilms (slime layers) coating system surfaces.
  • Fuel-headspace – in fixed roof tanks, the fuel’s surface that is in contact with the tank’s air/vapor zone (ullage)
  • Water-vessel – areas of direct contact between fuel-associated water or biofilm and system surfaces.
  • Water-sediment (sludge/sediment) – the top surface of any sludge or sediment layer hat has accumulated on the tank bottom.
  • Sludge/sediment- vessel – the interface between sludge or sediment and tank bottom.
  • Vapor-vessel – exposed surfaces in a fuel tank’s ullage zone.

Fig 1. Fuel system interfaces.

The best fuel system microbial contamination diagnostic samples come from tank bottoms or interfaces. In practical terms, these are typically tank drain or bottom grab samples.

Sample collection – bottom drain

Supplies

  • Absorbent spill pads
  • Alcohol – methanol or ethanol liquid or wipes
  • Bottle, clear glass, Boston round, or HDPE, wide-mouthed, 500 mL.
    Note: Clear glass makes it easier to observe phase, particulates, etc. However, analytes, such as adenosine triphosphate (ATP) can adsorb onto glass – making HDPE the preferred container material for samples to be tested for ATP.
  • Bucket, 5 gal (20 L)
  • Funnel
  • Gloves, surgical
  • Rags, shop

Procedure

  •    1. Place absorbent spill pads on ground around drain to ensure that any spillage or splashing will be captured by pads.
  •    2. Don gloves to protect hands and to reduce risk of contaminating sample with microbes from your skin.
  •    3. Use alcohol to wipe down exposed surfaces of bottom-drain and funnel.
  •    4. If there is sufficient space between ground (floor) and drain, place sample bottle into bucket and place bucket under drain.
  •    5. Remove cap from sample bottle, place wide-end of funnel under drain and narrow-end into sample bottle.
  •    6. Open drain and fill sample bottle approximately 75 %.
  •    7. Close drain, remove funnel from sample bottle, replace cap, and label sample bottle with:
          a. Sample source identification
          b. Sample collection date and time
          c. Identity of sample collector
  •    8. If sample is not going to be tested immediately, place in ice of refrigerator.

Sample collection – bottom grab

  • Absorbent spill pads
  • Alcohol – methanol or ethanol liquid or wipes
  • Bottle, clear glass, Boston round, or HDPE, wide-mouthed, 500 mL.
    Note: Clear glass makes it easier to observe phase, particulates, etc. However, analytes, such as adenosine triphosphate (ATP) can adsorb onto glass – making HDPE the preferred container material for samples to be tested for ATP.
  • Bucket, 5 gal (20 L)
  • Funnel
  • Gloves, surgical
  • Sampler – Bacon bomb or bailer (figure 2)
  • Sounding tape

Fig 2. Bottom samplers – a) Bacon Bomb; b) bailer.

Procedure

  •    1. Place absorbent spill pads on ground around drain to ensure that any spillage or splashing will be captured by pads.
  •    2. Don gloves to protect hands and to reduce risk of contaminating sample with microbes from your skin.
  •    3. Use alcohol to wipe down the sampler and funnel.
    Note: If multiple samples are being collected, and the previous sample contained visible sludge, sediment, or both, use clean fuel to rinse out the sampler before disinfecting its internal surfaces.
  •    4. Place sample bottle into bucket.
    Note: This serves two purposes: 1) it reduces the risk of spillage onto ground around sampling bottle; and 2) it shields sample bottle from the view of those who are not directly involved in the sampling process – this is particularly important when sampling retail site underground storage tanks.
  •    5. Attach sampler to sounding tape and lower the sampler into the tank until it touches the tank’s bottom but remains vertical.
    Note: Follow standard fuel handling safety precautions to ensure that the sounding tape is properly grounded and that there is no risk of sparking.
    Note: Best practice is to first determine the height of any free-water in the tank (figure 3).


    Fig 3. Using water-detection paste to determine height of free-water in tank-bottoms – a) sounding plumb-bob; b) sounding stick. Both devices had been coated with white, water-detection paste that had turned purple on contact with water.
  •    6. Remove cap from sample bottle, place narrow-end of funnel into sample bottle.
  •    7. Recover sampler and place it over funnel.
  •    8. Drain contents of sampler into sample bottle (figure 4).

    Fig 4. Transferring bottom-samples to sample bottles – a) draining Bacon Bomb sample into glass bottle; b) draining bailer sample into HDPE bottle.
  •    9. Remove funnel from sample bottle, replace cap, and label sample bottle with:
          a. Sample source identification
          b. Sample collection date and time
          c. Identity of sample collector
  •    10. If sample is not going to be tested immediately, place in ice of refrigerator.

Sample handling

Best practice is to keep samples chilled (40  2 F; 5  1 C) and to begin microbiological testing within 4h after collection Fuel & Fuel System Microbiology Part 6 explains sample perishability. Samples that have been kept chilled can be tested reliably for up to 24h after collection. The total level of microbial contamination and types of microbes present in the sample are increasingly likely to change as sample age beyond 24h. This makes the test results less likely to reflect conditions inside the tanks from which the sample was originally collected. Consequently, the risk of either failing to detect heavy microbial contamination or incorrectly concluding that actually had negligible contamination when sample was heavily contaminated, increases with sample aging. Microbiological tests like ASTM Method D7687 for ATP are easy to run in the field, immediately after sample collection. Using this type of test eliminates the risks caused by sample aging.

The details

This brief explanation of sampling procedures will get you started on the right path. However, circling back my opening comments, I recommend using ASTM Practice D7464 for detailed, step-by-step sampling instructions, and referring to my sampling chapter in ASTM Manual 1 for a full discussion of the considerations that should be taken into account when deciding when and when to collect samples for microbiological testing. I also address sampling in considerable detail in BCA’s six-module fuel microbiology course. For more details about this course, please contact me at either fredp@biodeterioration.control.com or 01 609.306.5250.

FUEL & FUEL SYSTEM MICROBIOLOGY PART 29

What Does “Viable But Not Culturable” Mean and Why Should I Care?

In microbiology, the term used to describe microbes that appear to be healthy and active by test methods other than culturing is viable but not culturable – VNBC. Since the term first came into vogue in the 1980s, it has always reminded me of the Monty Python skit in which the customer – played by John Cleese – and the shop owner – played by Michael Palin – debate whether the parrot that Mr. Cleese had just bought was dead or simply resting, check it out at The Parrot Sketch.

Michael Palin (left) and John Cleese (right) in Monty Python’s “Pet Shop Sketch” (1969).

The viability versus culturability debate

The issue is relevant for two reasons. First, if a fuel or other industrial process fluid system (think heat exchange fluids, metalworking fluids, lubricating oils and hydraulic fluids) is home to a population of microbes that are biodeteriogenic (i.e., causing damage to the fluid, the system, or both) but are not detected by culture testing, the risk of experiencing a failure event can high.

Second, the term VNBC has numerous meanings – depending on researchers’ focus. The varied definitions creates confusion among both microbiologists and others who rely on microbiological test results to drive maintenance decisions.

What does viable mean?

The Online Biology Dictionary defines viable as an adjective meaning (“1) Alive; capable of living, developing, or reproducing, as in a viable cell.” ASTM is a bit more helpful offering several similar definitions. From F2739 Guide for Quantifying Cell Viability within Biomaterial Scaffolds we get: “viable cell, n – a cell capable of metabolic activity that is structurally intact with a functioning cell membrane.” D7463 and E2694 offer: “viable microbial biomass, n – metabolically active (living) microorganisms.” These slight variations all agree that viability relates to a microbe’s ability to:

  • function under favorable physical and chemical conditions (more on this in a bit), or
  • to survive in an inactive (dormant) state under unfavorable conditions, and
  • to become active again once conditions improve.

What does culturable mean?

ASTM defines culturable as an adjective: “microorganisms that proliferate as indicated by the formation of colonies on solid growth media or the development of turbidity in liquid growth media under specific growth conditions.” This definition is used in several ASTM standard test methods, guides, and practices.
When microbes reproduce – i.e., proliferate – go through repeated cycles of division – on a solid or semi-solid medium, after approximately 30 generations (doubling cycles, or generations) they accumulate enough mass to form a visible colony. Thirty generations (230) yields approximately a billion cells. Liquid growth media become visibly turbid once the population density (cells mL-1) reaches approximately one million (106) cells – 20 generations. The duration of a single generation varies among microbial species and growth conditions. At present, known generation times range from 15 min for the fastest proliferating bacteria to >30 days (recent discoveries of deep earth microbes suggest that these microbes might have generation times measured in years or decades – the generation time for humans is approximately 30 years). The key point is that culturable, microbes reproduce in or on growth media under specific environmental conditions.

Before leaving our discussion of culturable lets consider time. Microbes with 15 min generation times will turn broth media turbid in 5h to 6h and form visible colonies on solid media within 8h to 10h. For microbes with a 1h generation time, detection as turbidity or colonies lengthens to 20h and 30h respectively. Many culture-based test protocols state that final observations are to be made after 3-days – sometimes 5-days. Any microbe with a generation time longer than 4h is unlikely to produce a visible colony within 5-days. They will not be detected unless observations are continued for a week or longer. For example, the culture test for sulfate reducing bacterial is not scored negative until after 30-days observation. If you end a culture test at 3-days, are all of the slower growing microbes non-culturable?

What are growth media?

Since the mid-1850s, microbiologists have developed thousands of different recipes designed to support microbial growth and proliferation (recall from an early post that growth refers to the increase in mass, and as noted above, proliferation refers to an increase in numbers). Some growth media are undefined. They are simple recipes made up of extracts from yeasts, soy, and animals. These are the components of media used for the most common culture test: the standard plate count. Other media are prepared from individual chemicals. Their recipes can include more than a dozen ingredients. Solid and semi-solid media include a gelling agent such as agar (extracted from seaweed), gelatin, or silica gel. One of the most frequently referenced microbiological media cookbooks – the Difco Manual – lists more than a thousand recipes. Each of these recipes was developed to detect one or more types of microbes. In addition to the diversity of recipe ingredients, growth media vary in pH, total nutrient concentration (some microbes cannot tolerate more than trace concentrations of nutrients), and salts concentration (ranging from deionized water to brine). The microbes targeted for recovery dictate post-inoculation incubation conditions. Some microbes require an oxygen-free (anoxic) environment. Others require special gas mixtures. Microbes also vary widely on the temperatures at which they will grow. Some only grow at temperatures close to freezing. Others require temperatures closer to boiling.

The growth medium defines the chemical environment and the incubation conditions define the physical environment in which microbes are cultured. No single growth medium is likely to support the proliferation of more than a tiny fraction of the different types of microbes present in an environmental sample. Many microbiologists estimate that <0.1 % of the microbes in a sample will be culturable in a given medium. Similarly, we suspect that for every microbe that has been cultured, there are at least a billion that haven’t.

 

Is my microbe really dead or simply resting? When conditions are unfavorable to either growth, proliferation or both, many different types of microbes have coping mechanisms. For nearly 200 years, we have recognized that some types of microbes can form endospores – their cell wall chemistry changes and metabolic activity ceases. Only in the past 20 years, we have come to recognize that non-spore-forming microbes can enter into a dormant state that enables them to survive unfavorable conditions for centuries or millennia – becoming metabolically active once conditions once again become favorable. Moreover, in some environments, although the microbes are metabolically active, the rate of their activity is so slow as to be nearly undetectable.

Within some fields of microbiology, VNBC refers to microbes that have been injured due to exposure to a microbicide. Pre-incubation in so-called recovery media – improves their ability to reproduce in or on growth media. In my opinion, this is a very myopic view of VNBC.

Microbial ecologists define VNBC as microbes that are metabolically active or dormant in their home environments but will not growth on the culture media and incubation conditions used to detect them.

I first experienced this phenomenon in the 1970s when I was testing water from oilfield production wells. Using radioactive carbon labelled nutrients to measure metabolic activity, my team routinely found that samples that yielded <1 CFU mL-1 (CFU – colony forming unit: “a viable microorganism or aggregate of viable microorganisms, which proliferate(s) in a culture medium to produce a viable colony.” ASTM E2896) held very active populations. Poisoned controls demonstrated that conversion from radiolabeled acetic acid or glucose to radiolabeled carbon dioxide was from metabolic activity – not from a non-biological (abiotic) process.

This means that culture testing invariably underestimates the microbial population density in tested samples. Conversely, because microbes that were dormant in the environment from which they were sampled can become active once transferred into or onto nutrient media, culture testing can overestimate the presence of metabolically cells. For example, most microbes suspended in fuels or lubricants are dormant, but can become active and form colonies on growth media. These issues do not make culture testing good or bad. Culture testing is still the only practical tool for obtaining microbial isolates that can be used for further testing. Moreover, culture testing is a useful condition monitoring tool if you are tracking changes over time. The more important limitation of culture testing as a condition monitoring tool is the delay between test initiation and the availability of test results. In the days or weeks it takes for microbes to form colonies on growth media, they are also continuing to proliferate in the system from which the sample was collected. This is where real-time (10 min) tests such as ASTM D4012, D7687, and E2694 have a major advantage over culture testing.

For more information on the most strategic use of culture or non-culture microbiology test methods, I invite you to contact me at fredp@biodeterioration-control.com.

FUEL & FUEL SYSTEM MICROBIOLOGY PART 27 – RETAIL SITE OPPORTUNITY COSTS REVISITED

Opportunity Cost at the Forecourt

In my first Fuel & Fuel System Microbiology post in November 2016, I wrote about the cost of repairing and remediating sites at which underground storage tanks had leaked. At the time, I have not fully considered that most of this cost burden was borne by insurance underwriters – not site owners.

Today, I want to return to a theme I’ve been writing about since long before my November 2016 blog post: retail site opportunity cost. As I write this blog, regular unleaded gasoline (RUL) in my part of New Jersey is retailing for $2.30/gal. For dispensers delivering 8 gpm instead of 10 gpm, this translates to approximately $144,000 per year per dispenser opportunity cost at urban sites that experience four hours per day of rush hour traffic – periods during which customers must wait in line to purchase fuel.

In this blog post I’ll share some simple computations on the relationship between dispenser flow rates and opportunity cost.

What is Opportunity Cost?

Opportunity cost is the difference between the economic value of the theoretically optimal use of an assist and the value realized by its actual use. At fuel retail sites that experience rush hour peaks, where the dispenser flowrate is the primary factor controlling fuel sales revenues, the opportunity cost is the difference between sales generated while dispensing at 10 gpm (U.S. EPA’s maximum permissible flowrate at retail dispensers) and sales generated while dispensing at slower flowrates.

Fuel Retail Opportunity Cost Model

As with all economic models, opportunity cost models are based on assumptions. For fuel retail assume:

  • 1. At state-of-the-art forecourts, submerged turbine pump (STP) capacity is sufficient to ensure that having multiple dispensers operating simultaneously does not reduce flowrate measurably.

  • 2. Absent flowrate restrictions, all dispensers can deliver 10 gpm.

  • 3. Customers can refuel their vehicles for 30 min per hour – the remaining 30 min are spent moving vehicles, making fuel-purchase selections, completing fuel sales transactions

  • 4. Although rush hour periods at urban fuel retail sites vary, four hours per day is the median – two hours each during the morning and afternoon commuting peaks.

  • 5. Rush hour periods occur five days per week.

  • 6. Current sales price (P) is $2.30/gal.

From these assumptions we can compute the annual opportunity cost (CO) per dispenser.



Where CO is the opportunity cost, P is the sales price in $s, Gmax is the flow rate @ 10 gpm, and Gobs is the observed (actual) flow rate. Note that Gobs can be for each dispenser or the average flow rate measured for two or more dispensers.

Computing CO for 8 gpm flowrate:



Field studies have shown that it is not uncommon for dispensers to operate at 5 gpm to 7 gpm. I’ll leave it to readers to do the math, based on their own flowrate, peak hour, and fuel price data. Don’t forget to multiply the opportunity cost per by the number of dispensers in your forecourt. If you own multiple urban retail sites, don’t forget to multiple your cost per site by the number of sites.

Data and Cognitive Dissonance

The two images under this blog’s title illustrate how our brains interpret what we see. Most viewers will alternate between seeing a man’s portrait and a woman reading a book in the left image. Similarly, when looking at the right image, most will alternate between seeing a goblet and two profiles. Some readers will only be able to see each photo as a single image – subject to only one interpretation.

In psychology, cognitive dissonance is the term used to describe a number of ways humans respond to new information – including how we behave when new infromation contradicts our previously held beliefs. I mention cognitive dissonance here because of the frequency with which I have encountered it whenever I have suggested that a fuel retailer test my model. The few who have go so far as to test their average dispenser flowrates have declined to compute the impact of their test results.

There’s a psychology term for willfully choosing to either refrain from collecting data that you don’t want to see, choosing not to do calculations that will lead to results you don’t want to believe, or both, but you’ll have to look that term up on your own.

The Big Questions

The model I’ve provided in this post addresses only fuel sales. It does not include convenience store (C-store) opportunity costs. For example, ask yourself how many prospective C-store customers choose not to visit the store when they believe that have either waited too long to pull up to a dispenser, that it has taken too long to fill their tank, or both. These delays are major factors contributing to customer fuel quality concerns. The fuel quality might be fine, but customer perception is that a refueling experience that take too long reflects uncertain fuel quality. One major petroleum company determined that they were losing 15 % of their customers due to fuel quality perceptions. In response, they invested heavily in a refinery to C-store cleaning program, followed by an upgraded condition monitoring and predictive maintenance program. They realized a tremendous return on their investment.

If you are a petroleum retailer who relies on a service company to perform the monthly checks required by the current underground storage tank regulations, what would your incremental costs be to include the additional condition monitoring and predictive maintenance actions needed to reduce your opportunity costs by 10 %? What would your return on investment be?

As always, please share your thoughts with me by writing to fredp@biodeterioration-control.com.

FUEL & FUEL SYSTEM MICROBIOLOGY PART 25 – AND NOW FOR SOMETHING COMPLETELY DIFFERENT

In my October What’s New blog post, I highlighted several of my primary takeaways from PEI’s 2018 convention. In this post, I’ll focus on one new commercial offering. If it works as promoted, this system can be a game changer for contamination control in underground storage tanks (UST). At the convention Veeder-Root showed a model of their new CleanDiesel In-Sump Fuel Conditioning System (ISFC). I haven’t seen any field data from retail or commercial sites using this system, so I’m not able to endorse the system (I asked Veeder-Root for permission to discuss their system but have no financial interest in their company or this filtration system). Still, I think it is an exciting innovation with great potential.

The Issue

As I’ve discussed in previous articles – including my paraphrasing of Rebbeca Moore’s summary of contamination typically present in a 7,500-gal fuel delivery (i.e., 1 cup (∼0.25 L) of dirt + 1 to 2 gallons (3.8 L to 5.6 L) of water + up to 325 gallons of FAME (B5 ULSD is now included in ASTM Specification D975 Diesel Fuel Oils) + 1 gallon of glycerin + 5 to 40 gallons of additives). These concentrations of dirt and water are traces (<9 ppm by volume dirt and <200 ppm by volume water) on a per delivery basis, but they add up over time. For example, a UST receiving weekly ULSD deliveries will also received 52 gal to 104 gal (∼200 L to 400 L) of water per year. Even if only 10 % of the delivered water settles out, that’s plenty of water to provide an excellent niche in which microbes can facilitate microbiologically influenced corrosion – MIC (see
Fuel Microbiology Part 19 from April 2018). Amongst fuel industry folks who specialize in product quality control, the consensus is to minimize water accumulation in UST. As I discussed in Part 19, keeping tanks water-free is easier said than done.

Veeder-Root’s CleanDiesel In-Sump Fuel Conditioning System

I’ve copied figure 1 from Veeder-Root’s ISFC flier and added a few component labels. According to Veeder-Root, the ISFC uses recirculated fuel to create turbulence in fluid at the bottom of the UST. This turbulence causes water, sludge and sediment to be suspended into the product. These resuspended contaminants are then pulled through a perforated inlet component and subsequently flow through a particulate filter and water separator before the polished fuel is recirculated back into the tank. In theory, the turbulence and contaminant capture zones are both sufficient to prevent contaminants from accumulating anywhere along the UST’s bottom.

Potential Impact

When I saw the ISFC demonstration at Veeder-Root’s PEI Convention booth, I thought that the design was simple, elegant, and promising. Its design includes modes that trigger polishing when water is detected by the automatic tank gauge or by a timer (system activated for some number of minutes per scheduled interval). My principal concerns were about the dimensions of the turbulent zone and the polishing system’s contaminant capture efficiency. If only a fraction of the UST bottom is resuspended, water, sludge, and sediment will still accumulate elsewhere along the UST bottom. Any particulate or water contamination that’s resuspended will begin to settle immediately after the recirculation cycle ends. This could create a mechanism for redistributing – rather than removing – contaminants. Another concern is system maintenance. Veeder-Root has estimates of expected filter life. Additionally, they have sensors to measure pressure drops across the filtration unit and water levels in the water separator. Still I can’t help but wonder if sites using the ISFC will quickly grow tired of either having in-house staff or contractors keep up with system maintenance (i.e., changing filters and removing water). My concern here is based on my experience with several petroleum companies who had installed filtration systems between their terminal tanks and racks, only to later remove them because of the filter element replacement costs.

Bottom Line

I think that the ISFC has great potential – even if it’s less than 100 % effective. It directly addresses many of the current challenges related to keeping water and particulates from accumulating on the bottom of UST. I hope that within the next year or two, Veeder-Root will be able to publish a case study or two reporting the impact of ISFC installation and operation at retail and commercial sites. I encourage anyone interested in learning more about the ISFC to contact Diane Sinosky, Veeder-Root’s Global Product Manager, ATG. Diane can be reached at dsinosky@veeder.com. Of course, I always welcome your fuel & fuel system comments and questions at fredP@biodeterioration-control.com.

FUEL & FUEL SYSTEM MICROBIOLOGY PART 23 – PREVENTING MICROBIAL DAMAGE TO FUEL SYSTEMS PART 6; POST-TREATMENT CLEANUP

Biocide treatment releases biomass – now what?

Disinfection using microbicides is only one element of the fuel system decontamination process. This month’s post covers what needs to be done after a fuel system has been treated with a microbicide.

When a moderately to heavily contaminated fuel system is treated with an effective biocide, masses of biofilm material – flocs – get suspended into the fuel. As illustrated in figure 1, some of this biomass quickly settles to the tank bottom and the rest is carried with the fuel to the submerged turbine pump. Dispenser filters are designed to capture fuel particulates and biomass flocs. When the fuel is clean, a 10 m fuel filter, mounted in a retail dispenser, can process 500,000 gal (1,900 m3) to a million gal (3,800 m3) of fuel before it needs to be replaced (Note: there are no consensus criteria for filter life. Some retailers replace dispenser filters when the flow is less than 8 gpm – 30 L min-1. Others wait until flow is less than 2 gpm – 7.6 L min-1. In my November 2016 post, I detailed the economics of dispenser flow rates. The opportunity costs caused by slow flow can be startlingly expensive! After a fuel system has been treated, the next step is to get the flocs out of the fuel.

Floc removal – fuel polishing

There are three options for floc removal. Option 1 is to stop using the dispensers that draw product from the treated tank, give the flocs a day or two to settle to the bottom, and then to vacuum out the bottom sludge, sediment, and water. I can’t think of any retailers or fleet operators who would choose to put a tank out of commission for a couple of days.

Option 2 is to let the dispenser filters do all the work. This can translate into multiple filter changes per day for several days (fig 2). When the fuel reaching the dispenser is loaded with biomass flocs, filters can plug after 2,000 gal (7.6 m-3) to 10,000 gal (38 m-3) have flowed through them. This option might be feasible at rural sites that sell fewer than 10,000 gal (38 m-3) per week but is not particularly practical at high volume facilities. Long fuel turnover periods (i.e., more than two days) give biomass flocs time to settle to the tank’s bottom. As is the case for option 1, settled sludge and sediment needs to be removed from the tank as soon as possible after biocide treatment. Optimally, this is done one or two days after the treatment.

Option 3 is to use a fuel polishing rig (fig 3). Filtration rigs come in numerous configurations. Filtration rigs come in nearly as many configurations as there are companies who offer fuel filtration services. The number of filter housings on a rig typically ranges from one to three – although there are rigs with more than three housings. Diverse filter media are available – each with advantages and disadvantages relative to the others. Filter housing designs differ by the types and number of filter elements they contain, and by fluid flow patterns they use to optimize filtration efficiency. I’ll leave it to the mechanics and engineers to provide details on filtration technology and rig design. In this post, I’ll describe a generic rig.

Rigs with multiple housings use filters in series. Fuel first passes through a coarse filter (for example, designed to remove particles and masses that are >100 m), and then through a polishing filter (nominal pore size between 1m and 5m). Figure 4 shows a 16-element filter housing that’s mounted on a skid. Some filtration rigs include a fuel-water separator. Others rely on coalescer filters to strip water out of the recirculating fuel.

Filtration rigs have one or more pumps to drive fuel recirculation. Most commonly, a pump pushes fuel into the tank to create turbulent flow. This turbulence helps to keep particles and biomass flocs in suspension. The pump’s discharge creates pressure and its intake creates a vacuum. The vacuum draws product through the return riser and line to the rig. In fig 3, the pump drives fuel into the tank via a stinger that is inserted into the fill tube fitting and draws fuel through a stinger that is dropped through the turbine riser fitting. The fuel discharge stinger can be rigid or flexible. Some stinger designs include high pressure nozzle meant to source biofilm residual material from tank walls.

Depending on how heavily contaminated the fuel is, three to seven fuel-volumes might need to recirculate through the filtration rig to complete the polishing process. Depending on rig design, filtration flow rates range from 75 gpm (0.28 m3 min-1) to 350 gpm (0.9 m3 min-1). For a tank containing 5,000 gal (19 m3) of fuel, this means that post-treatment fuel polishing can take from less than 30 min [(5,000 gal 350 gal min-1) x 3 cycles  23 min] to 8h [(5,000 gal  75 gal min-1) x 7 cycles  470 min  8h]. As I mentioned above, greater flow rate also helps to keep particles in suspension.

My fuel is now clean – is my system also clean?

The answer depends what you mean by clean. Periodic microbicide treatment and subsequent fuel polishing can be enough to prevent tank deterioration problems. However, if biodeterioration damage began before the tank was treated and fuel polished, more thorough cleaning might be needed.

Even the best fuel polishing equipment can only direct pressure at surfaces that are in direct contact with the fuel. High pressure systems can be used to remotely clean the surfaces of empty tanks. It might be necessary for workers to enter the tank (personnel performing this work must be properly trained and certified to operate in confined spaces) and clean its surfaces manually (fig 5).

The only way to know for certain that a tank is clean is by visual inspection. Available remote camera technology can only be used to see exposed surfaces (for example, see: tanknology.com/petroscope. They cannot be used to see surfaces that are below the fuel level. Consequently, for visual inspection by remote camera, tanks must first be emptied (product can be drawn into either a tank truck or frac tank). Confined space entry and direct inspection remains the most reliable means of evaluating tanks for cleanliness, coating condition, and corrosion.

Why do routine condition monitoring if visual inspection is the gold standard?

If direct observation is truly the only way to know how heavily contaminated a tank is, why bother with the various types of tests I’ve described in previous Fuel Microbiology blog posts? The answer lies in return on investment (ROI). Data from routine sample testing (see my December 2016 Blog post provides important infromation about the fuel system’s condition. Most frequently, easy tests that require little or no equipment, act as the canaries in the mine. If results indicate that something is changing for the worse, more advanced tests help to determine what is going on. One can run routine tests and complete preventive maintenance actions for years for the cost of a single visual inspection. Consequently, internal inspections are reserved for when data (or regulatory ordinances) indicate they are needed.

For more information about detecting and controlling microbial contamination in fuel systems, please contact me at fredp@biodeterioration-control.com.

FUEL & FUEL SYSTEM MICROBIOLOGY PART 14 –TEST METHODS – STILL MORE ON MICROBIOLOGICAL TESTS

Let’s pick up with: “If no method provides a perfect measurement of microbial contamination, which one should I use?”

Currently, the primary microbiological test that I use for testing fuels, fuel-associated water and fuel system components is ASTM D7687 Test Method for Measurement of Cellular Adenosine Triphosphate in Fuel and Fuel-associated Water With Sample Concentration by Filtration. The ASTM method is based on a test kit manufactured by LuminUltra Technologies, Ltd.; with whom I collaborated to develop and validate the method.

Adenosine triphosphate (ATP) is the primary energy transfer molecule in all metabolically active, living cells. Living cells can be metabolically active or dormant. When a cell is metabolically active, it carries out all of the activities we use to define life: respiration, ingestion, excretion, response to stimuli, etc. Many (if not all) microbes can shut down – become dormant – when environmental conditions are unfavorable (for example, while they are suspended in fuel). Recently, researchers have discovered viable microbes that have remained dormant for 10’s of thousands of years. The key here, is that ATP is not detectable in dormant cells. Consequently, ATP testing does not detect dormant cells (more on this in a bit). ATP testing is based on the detection of light given off by a specific reaction, unique to fireflies and glow worms. This is the reaction that produces the characteristic yellow-green firefly light (Fig 1)

Fig 1. Firefly with its tail aglow.

In 1954, microbiologists first reported a method for using firefly tail extract to measure microbial population densities in water samples. By the late 1960’s it was known that bacteria had – on average – 1 x 10-15 grams (1 femtogram; 1 fg) of ATP per cell. Even though the actual amount of ATP per cell was quite variable, the 1fg/cell ratio soon proved to be quite reliable. In the mid-1970’s I ran thousands of ATP tests on ocean water samples.

However, when I attempted to use ATP to test oilfield produced water samples, I learned about interferences cause by salts and organic chemicals. High salt concentrations (brines) and some organic chemicals depressed test results – indicate that the ATP-biomass was less than it actually was. Other organic molecules emitted light (i.e. were chemiluminescent) that gave false positive test results in samples that had few metabolically active microbes. The bottom-line was that I could not use ATP for testing microbial contamination in complex organic fluids such as fuels, lubricants, or metalworking fluids. Between 1980 and 2008, a number of ATP test kit manufacturers made claims about the stability of their kits for testing fuels, but the QGO-M method – developed between 2008 and 2009 – remains the only one that is not affected by either the salts or organic chemicals that make other ATP tests unusable for fuel or fuel-associated water testing.

In most samples, ATP can be found in three states (Fig 2). ATP within whole cells is called cellular ATP (cATP). ATP attached to cell fragments and dissolved ATP are nominally detected as dissolved ATP (dATP; it would probably be less confusing to call dATP extracellular ATP). Most commercially available test methods start by breaking open cells. Consequently, the results they produce are total ATP (tATP):

[tATP] = [cATP] + [dATP]

Where [tATP], [cATP], and [dATP] are the concentrations of total, cellular, and dissolved ATP, respectively.

Fig 2. ATP in fuel and fuel-associated water samples: a) cellular ATP – ATP within whole (intact) cells; b) dissolved ATP – individual ATP molecules in solution; c) cell fragment ATP – ATP that is bound to pieces of cell wall from cells that have broken apart. Because there is no easy way to differentiate between (b) and (c), the term dissolve ATP generally refers to the sum of (b) and (c).

The QGO-M method washes away dATP before breaking open cells to release ATP for detection. This means that it measures what’s important: the [cATP] in whole cells. In contrast, test methods that give only [tATP] results cannot determine whether the detected ATP came from whole cells, cell fragments, dissolved ATP or some combination of the three.

The QGO-M method doesn’t provide all the answers about fuel and fuel system microbial contamination, but it’s my go to, first test. First, I can run the test out of the back of my car. Second, I can complete a test in less than five minutes. Third, I get results as actual ATP concentrations ([ATP]). The other commercially available test kits give results in instrument specific relative light units (RLU; more on this in a bit). Fourth, as explained above, the QGO-M method detects [cATP]. The other test [tATP]. Consequently, ASTM D7687 is the only ATP test method that provides reliable test results for fuel and fuel-associated water samples.

Coming back to RLU: as I mentioned above, the ATP test measures the intensity of light produced by a biochemical reaction. The device used to measure the light intensity is called a luminometer. Basically, it counts the number of photons (light emissions). The unit of measurement is RLU. The RLU is different for every luminometer. Unless RLU are converted to [ATP] data from different luminometers cannot be compared. The QGO-M method includes determination of the RLU produced by an [ATP] = 1 x 10-9 pg mL-1. It also provides an equation for converting test sample RLU to pg mL-1. Thus, numerous technicians each collecting data using their own luminometer can share data. Moreover, the ATP data can be pooled into large databases so that the relationships between [ATP] and biodeterioration can be better understood. I consider this to be a major advantage over other ATP tests.

I use QGO-M data for two purposes:

  1. As a primary microbial contamination screening tool; and
  2. As a first-tier test to tell me whether I should run additional microbiology tests (see Part 8).

Table 1 shows the criteria I use for screening fuel and fuel associated water samples. For routine condition monitoring and predictive maintenance (PdM), [cATP] data alone are sufficient to guide PdM actions. When results are in the negligible zone no additional PdM is needed. When they are in the moderate zone, it is time for preventive action, and when they are in the heavy zone, only corrective action will suffice (I’ll discuss preventive and corrective actions in a future blog post).

Table 1. QGO-M test method PdM criteria.

Part 15, I’ll discuss how to use ATP to detect and quantify biofilms (microbiological growth on surfaces). In Part 16, I’ll discuss using these data to determine what additional microbiological tests are needed. In the meantime, if you’d like to learn more about fuel and fuel system microbiology testing, please contact me at fredp@biodeterioration-control.com.

FUEL & FUEL SYSTEM MICROBIOLOGY PART 13 –TEST METHODS – MORE ON MICROBIOLOGICAL TESTS

In Part 13, I discussed culture testing. One of the points I made was that any given culture test (of which there are >5,000) is unlikely to detect >1 % of all of the microbes present. Before moving on to discuss methods that detect more of the microbes present – in terms of percent detection of each type of microbe and the fraction of the different microbes present that are detectable – I will invoke one of Donald Rumsfeld’s most famous quotes:

“There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don’t know. But there are also unknown unknowns. There are things we don’t know we don’t know.”

Although, in February 2002, when Secretary of Defense Rumsfeld offered this statement, he was discussing the possibility that Iraq had weapons of mass destruction; he could just as well been talking about microbial contamination condition monitoring. In Part 12’s fig 1, I indicated that genomic testing (you’ll have to wait until Blog Post 15 or 16 for more on genomics) detected a greater proportion of the total microbiome (all of the microbes present in a particular environment) than any other method currently available. However, I also noted that I doubted if current genomic testing detected more than 80% of a given microbiome. This begs the question: “If no method provides a perfect measurement of microbial contamination, which one should I use?”

The perhaps ungratifying answer is: “It depends on your intention.” Let’s start with an illustration. Fig 1 illustrates three ways to take a measurement. You can use a ruler or tape measure to determine an object’s dimensions. If It is a liquid, you can use a measuring cup or graduated cylinder to determine its volume. You can also use a scale to determine its weight. Each of these is a valid measurement, but each provides different information.

Fig 1. Three different ways to measure.

 

It’s the same thing with testing from microbial contamination. Each method that I illustrated in Blog Post 12, figure 1, provides useful information about the microbial population, but each provides different information. If you need to have pure cultures of microbes, on which to do research, culture testing is the most appropriate tool. If, however, you want to quickly determine how heavily contaminated your system is, then one of the chemical microbiology test methods is a better choice.

A chemical microbiology test method is a method that detects specific molecules that are either part of or are produced by microbes. The three chemical microbiology methods illustrated in Fuel Microbiology Part 12 are: catalase activity, adenosine triphosphate concentration, microbial antigen detection.

Today, I’ll write about the catalase test. In the interest of full disclosure, in the early 1980’s, after a University of Houston graduate student developed the HMB catalase test method (www.biotechintl.com), I did most of the method validation for a variety of industrial applications. I also developed ancillary HMB tests to verify that the test results were due to microbes. Starting in 1982, and for the next 27 years, the HMB was my primary field test for detecting and quantifying microbial contamination in industrial fluid systems.

The catalase test is based on the reaction between the enzyme catalase and hydrogen peroxide. Catalase is the enzyme that made life in an oxygen-rich atmosphere possible. Cells that grow in normal air (aerobes) produce hydrogen peroxide as part of their energy metabolism. Catalase converts that hydrogen peroxide into water and oxygen. What makes the HMB test quantitative are its two primary components: a patented, electronic pressure gauge (figure 2a) and a stoppered reaction tube (figure 2b).

Fig 2. HMB catalase test system. a) pressure measurement device; b) stoppered reaction tube

 

The HMB pressure gauge is unique because there’s very little volume between its probe and its sensor.

The stoppered reaction tube provides a fixed volume, so that headspace pressure increases as the concentration of oxygen gas increases within that space (the head space is the space between the top of the liquid and bottom of the stopper).

To run the test, add a standard sample volume (typically either 3 mL or 10 mL) to a reaction tube, and then add concentrated hydrogen peroxide (one drop – = 0.05 mL – per mL of sample). Quickly replace the tube’s stopper (it is a septum cap that re-seals itself after it has been pierced with a needle) and briefly vent the tube. This ensures that the headspace pressure is 0 psig when the reaction starts. If there are aerobic microbes in the sample, they will race to convert the hydrogen peroxide to water and oxygen gas, before the hydrogen peroxide kills them. In the meantime, as oxygen is produced, it accumulates in the reaction tube’s head space. The universal gas law teaches that if temperature and volume are constant, the pressure in an enclosed space is proportional to the concentration of gas in that space. Simply put: the more catalase enzyme in the sample, the more oxygen in the headspace; the more oxygen the greater the pressure increase (fig 3). The reaction runs its course in <15 min. At 15 min, stick the reaction tube with the needle that’s attached to the pressure gauge (fig 1a) and read the psig. The psig reading at 15 min is proportional to the microbial contamination load. Correlation between culture test data and HMB catalase test data is generally very strong.

Fig 3. Catalase reaction with hydrogen peroxide in reaction tube. a) negligible contamination = negligible oxygen accumulation = negligible pressure increase in headspace; b) heavy contamination = substantial oxygen accumulation = large pressure increase in headspace.

 

However, the HMB test has its limitations. First: it only detects organisms that have the catalase enzyme. This excludes all anaerobes (microbes that only grow in oxygen-free environments) and aerobes that don’t have a complete catalase enzyme. Second: dissolved iron reacts with hydrogen peroxide to release oxygen gas. Samples with dissolved oxygen will appear to have microbial contamination. Third: at ∼25 psig the pressure is sufficient to launch the reaction tube’s stopper. The noise can be disconcerting and flying stoppers can be eye hazards. Moreover, the foam pouring over the reaction tube’s wall creates a mess. When microbiological contamination is negligible, it generates <1.5 psig pressure. Heavily contaminated samples (many bottoms-water samples) will foam over before the reaction tube’s stopper can be put in place (have you ever seen the reaction when sulfuric acid is poured over a sugar cube; fig 4?). When this occurs, the sample must be diluted to get a quantitative test result. On the few occasions when curiosity has compelled me to get a quantitative answer, after observing a violent reaction in the original sample, I’ve found that the actual psig was 20,000 to 30,000 psig (yes, I had to dilute samples 10,000 to 50,000-fold in order to get a psig reading). Normally, either being unable to get the stopper onto the tube, or having the stopper launch before the end of the 15 min test period, provide the information I need to determine that the sample is heavily contaminated.

Fig 4. Column of sugar charcoal formed after adding sulfuric acid to sugar. The reaction is violent and exothermic (give off lots of heat).

 

Earlier, I mentioned that I had developed ancillary tests for the HMB catalase test. One is used to determine if dissolved iron is producing a false positive result. The other is used to inactivate any enzymes in the sample. When testing unknown samples (i.e.: I don’t know whether they sample is likely to have dissolved iron), I run four tests: hydrogen peroxide (H2O2) only, H2O2 + a chelating reagent (prevents the dissolve iron reaction), H2O2 + a poison (inhibits catalase activity), and H2O2 + chelating reagent + poison (serves as a background control). The H2O2 result tells me if there is a contamination issue. If the chelating reagent reduces the psig by >90 %, then the psig observed in the H2O2 only test is due to dissolve iron. Similarly, if the chelator has no effect but the poison reduces the psig by >90 %, then the psig observed in the H2O2 only test is due to microbes. If both the chelator and poison are needed to reduce the psig by >90 %, then the sample has substantial concentrations of dissolved iron and microbial contamination.

With all of these limitations, why use the HMB test? The truth is, for those 27 years during which I relied on it, the HMB test was the best test available for my specific objectives: to be able to obtain a sample and obtain reasonably reliable, quantitative microbiological data, quickly (15 min), near the point of sampling. These days, I compare the test method to early portable phones and so-called laptop computers (the former weighed in at > 10 lb., and the latter at > 20 lb.) At the time they were introduced, they did their respective jobs better than anything else available. I hope that you are now wondering: What test replaced the HMB test? That will be the topic of Part 14. Stay tuned…

In the meantime, if you’d like to learn more about fuel and fuel system microbiology testing, please contact me at fredp@biodeterioration-control.com.

VENDOR VIEW: FUEL SYSTEM BUGS DRAIN REVENUES

Twenty years ago I had a series of retail fuel system articles published in National Petroleum News. Ten years ago, I wrote a Looking Back preface for each of the original articles, and sent the updates to a selected distribution list. Quite a bit has changed since I wrote the original series and the 10-year updates. I’ve just launched a new series for publication in Fuel Marketing Reporter. This series will follow a series of themes similar to those I’m addressing in my Why is Microbial Damage to Fuel Systems so Hard to Detect blog series. You can find my new article: Vendor View: Fuel System Bugs Drain Revenues at Fuel Market News.

What’s New – June 2014

In January 2014, at TAE’s 19th Tribology Colloquium, I presented th preliminary results of field evaluations that were being performed on LuminUltra Technologies dQGO-M test method. The new ATP test method provides a simple and reliable means of differentiating between fungal and bacterial contamination in metalworking fluids (MWF).

Four international MWF compounders participated in the field evaluation. All of their data were subitted in time for my STLE 2014 Annual Meeting Presentation:

Recent advances in the differentiation between fungal and bacterial contamination in metalworking fluids using modifications of the ASTM E2694 Standard Test Method. Read more…

Search

Posts

Archives

Categories

Meta

MENU

OUR SERVICES

  • Consulting Services
  • Condition Monitoring
  • Microbial Audits
  • Training and Education
  • Biocide Market Opportunity Analysis
  • Antimicrobial Pesticide Selection

REQUEST INFORMATION




    captcha

    © 2025 Preferred Logistics Group, Inc.Website Design by Big Tuna