PlumeStop Liquid Activated Carbon represents a new patented technology innovation designed to address the challenges of excessive time and end-point uncertainty in groundwater bioremediation. Jeremy Birnstingl, Ph.D., Vice President of Environmental Technology at REGENESIS, presented this webinar as a guest speaker in partnership with the Midwestern States Environmental Consultants Association (MSECA).
Welcome, everybody. Thank you very much for tuning in to this webinar on the new PlumeStop technology. By way of framing this, I think the best way to provide context is that this was a technology that we were looking at in REGENESIS to really take bio to the next stage. It was originally coming from the bio perspective. Those of you who know us may recall or be aware that early technologies such as ORC and HRC, some of the very early injectable electron donors and acceptors, are about 20 years old now, 21 years old. PlumeStop was party conceived by looking at how we might take bio up further to the next level now there are so many donors and acceptors on the market.
Thinking through this, we realized that whilst bio has a lot of very good strengths and a lot of benefits – I’m a bio fan, my Ph.D. was in bio back in the ’80s – it has two arguable principle weak points, and those are this. Number one, it takes time. It takes a while to get to the target, and as a remediation technology, despite its benefits it can be slow. Number two, it’s not always certain to what endpoint it’s going to get to. It can generally get lower than most remediation technologies. But whether it’s actually going to get to the target in a timely manner or at all, still remains questionable. So PlumeStop was really conceived as a way of addressing these.
So against that background, the principle features of the technology are these. It will provide a very rapid reduction in groundwater concentrations. To give an idea of the scale of this, we’re talking about multiple orders of magnitude concentration reductions in days or weeks. That’s very quick. The technology will also provide an acceleration of the contaminant biodegradation rate. This can be a means of eliminating low-concentration performance tailing, but also an ability to get to very stringent clean-up targets.
The reagent can be dispersed widely in the subsurface. This is a benefit to the field work, because it means there are less injection points necessary for a site, for example, which keeps the cost down. It also helps by presenting an ability to address areas of restricted access, deep plumes, etc. If it’s 50 feet down to the plume, then each injection point is going to have 50 [feet of drilling activity before you actually get to the point of delivery. So the greater the number of wells that can be reduced, the better. Importantly, the technology has a long-term efficacy. The reagent is not consumed. It regenerates in situ.Click Here To Read Full Transcript
So what is the technology? Well, at its essence, it’s a highly dispersive, injectable sorbent and microbial growth matrix. Now, the sorbent here and the growth matrix are the same thing. These aren’t two components of a mixture. The sorbent and the growth matrix are the same things, and how this works is that the sorbent will provide a very rapid drop in dissolved-phase contaminant concentrations and an immediate risk-reduction. There’s no contaminant destruction going on at this stage. This is simply taking the contaminants out of the dissolved phase and out of the immediate risk pathway for a number of cases. The growth matrix is what provides the accelerated bio-destruction of sorbed mass and provides an ability to secure clean-up at very low targets.
So what do I mean by this? Accelerated bio-destruction, lower clean-up targets, well what are the processes by which this type of reagent can secure these things? Well, to get into that I’d like to really start with an In Situ Groundwater Microbiology 101, and go through a few of the basics of bio, so that perhaps it’ll be helpful to some of the non-microbiologists. The points I’d really like to bring out of these, number one, bacteria live on surfaces. They principally exist in the subsurface in biofilms. So conceptually, think of plug-hole slime or dental plaque, rather than free-living tadpoles swimming around and around in the groundwater finding things that they can eat. The image there, by the way for any of you who didn’t clean your teeth this morning is dental plaque.
Because they are sessile, because they don’t move, bacteria therefore have to wait for their growth substrate, the food, to come to them. They don’t go out hunting. This means that they either have to sit on or in their food source as they do with rotting vegetables, for example, or they have to wait for their food source to dissolve and come to them in solution, which is what typically happens in groundwater bioremediation.
Now, against this background, as bioremediation or clean-up proceeds and the plume gets progressively cleaner, well the contaminant concentration drops. That’s what clean-up is. But what this means is that the rate at which the substrate, the food source, comes to the bacteria reduces. As the contamination concentration drops, then the bacteria encounter less molecules of contaminant per unit time and so that the rate that they can degrade it reduces. This is the mathematical principle behind first order kinetics, this type of half-life curves that you see. It’s why the instantaneous rate of destruction declines overtime.
Beyond this, however, another step change can come into play. Below a certain concentration, the rate that bacteria break down a given contaminant can start to slow dramatically. It can effectively fall of a cliff. There are threshold concentrations, the minimum substrate concentration or Smin for microbial growth. This is the concentration of the contaminant, the food source, that’s at the minimum level that the bacteria will actually wake up their enzyme systems and degrade from. This is like the starvation boundary.
This threshold is variable. It’ll change from microbe to microbe, contaminant to contaminant. Typically, it’s in the low microgram per liter range. So it’s not relevant for every site, but every site has to clean up to the low microgram per liter range. But where we are below that range, it’s a very important consideration. This step change is in addition to the general rate diminishing returns described in the middle sections of this slide.
So to put some images to this, here’s a conceptual image of a contaminant, it doesn’t matter what it is. It’s hypothetical, with a half-life of seven days. For convenient math, I’ve started with a concentration of 12,000 micrograms per liter. So this is a first-order decay curve, a half-life decay curve, and what we can see from this is the following. After seven days, one half-life, the concentration drops by half. That’s a half-life. So in the first week, 6,000 micrograms per liter are removed. In the next week, the concentration drops by half, but now it’s only 3,000 micrograms per liter. In the third week, the concentration drops by half, but now it’s only 1,500 micrograms per liter. In the fourth week, again, it drops by half. Now it’s only 750.
So we’re looking at, after this four-week period, about 12.5% of the initial weekly mass removal rate. So the amount of contaminant that’s being removed overtime is dropping, dropping, dropping, dropping, simply because of these bioavailability issues of the contaminant having to find its way to the bacteria to be degraded. So the concept behind PlumeStop and its rate acceleration is really this. What would it be like if the linear rate that we can see at the top end of this graph towards the left could be continued at this lower concentration?
Well, what we’d be looking for would really be an extrapolation something like this. The idea is that if we could keep up that instantaneous destruction rate, we would reach our clean-up targets much, much quicker. Well, this is the basic concept. Although, in practice the top end is going to be slightly accelerated too. But this gives an idea of what we’re actually trying to do to overcome these rate limitations.
So I’ll come back to that slide a little later as we look at some of the bio data. But first, I want to get on to what the reagent is. Essentially, it’s made of colloidal activated carbon. So these are particle sizes of activated carbon, which are about one to two microns in size, much, much smaller than typical powdered activated carbons and naturally smaller than granular activated carbon. These are about the size of a bacterium or a blood cell. There’s no coincidence to that. The reason blood cells are about the size they are is arguably because mathematically this is the size that disperses best is a colloid. There’s a mathematical optimum, and it’s about the size of a bacterium or a blood cell. Nature is very clever.
The material therefore spends as a liquid and has a huge surface area, because the particles are smaller, and also because the shape and the nature of the particles [as] activated carbon. This leads to very fast sorption. This is not the point, however. What really turned this into a product with field practicality was the ability to prevent the carbon particles from clumping and clogging, and blocking formations. It’s the anticlumping or distribution-supporting surface treatment that is the core innovation that turns a material that would simply block pores and clog, like a photocopy toner would, into a material that can simply flow freely through the formation coating the surface and leaving a residue behind to provide the effects that we need.
The material also contains low-solubility, controlled availability matrix nutrients. [They’re] low-solubility, because there’s no point in having them soluble where they would be lost to the moving groundwater. They need to be trapped in the material itself to help [inaudible 00:10:50] microbial population establish and be used. They therefore do not impact the groundwater or lead to eutrophication or other concerns that may occur in different groundwater regulatory regimes.
The basic concept of how it works is it would be placed into the ground through a well or a direct push point. So that’s the spike on the right in this image. It would be injected under relatively low pressure, and it would be pushed out into the formation through general dispersive flow, rather than fracking or fingering. Let me just hide something on my screen there. That’s significant, because a fractured emplacement would have efficacy around the outside of the frack itself, but wouldn’t necessarily impact the wider body of the formation. So here in this image, where you can see it’s encountering a monitoring well, the monitoring well is actually picking up the full spectrum of the formation that’s actually [been] covered in this, and is therefore giving a representative reading of what would be happening.
If I zoom in on the space between the soil particles here, what we would see is something like this. We have the coating up here of the biomatrix, the actual PlumeStop material, and then between and on these particles grow the microorganisms that will be degrading the contaminant. These are what’s shown in yellow on this image. To give an idea of what this looks like, this is an electron micrograph of the dispersed material coating sand particles. We’re looking at a scale there, if you can see the scale bar in this of about 10 microns here. So you can really look at each of these particles and see that they’re about one to two micrometers in size. These rough surface edges are really the boulder field of PlumeStop particles that are coating sand in that particular image.
So the idea is this as a remediation concept. The material is injected. It will disperse widely, because it will pass freely through the formation coating it. This is rather like a bead of ink, if you’d like, rolling over a sheet of paper. The bead of ink will roll freely, but it’ll leave a trail over the paper, which is stuck hard like ink on a page. In the same way, the material will flow through the formation, but it will leave a coating. So the coating covers the particles in the formation. The contaminants can absorb. The biofilm will then grow within and around that, simply because the film is now replete with contaminants that the bacteria are eating.
Biological degradation accelerates. We talked about that in the previous slides. I’ll show you some data further on. What this then means is that the sorption sites on the material become regenerated, because the bacteria are breaking down the contaminants and therefore slowly freeing up the sorption sites for further contaminants. This is a similar principle to Bio-GAC in filter systems, for example.
The sorption sites then become regenerated and can capture a further influx or back diffusion of the contaminants. Biofilm growth on activated carbon is well-known in the wastewater industry, for example. It can typically support a microbial flock of something like 10 times that that natural sand would, for example.
To give an indication of how these principles would look in the field, here’s an example of the use of the technology and a mixed solvent plume. This is actually one of the early test sites in Indiana. So what we have here, mixed VOCs, we have TCE and TCA at moderate to low concentrations. This is a pretty good type of concentration for the PlumeStop technology. It’s not a technology that targets [an apple] any more than a carbon filter would be used as a technology for dealing with free product. The technology really focuses in at the lower end of the concentration range, and this would be a typical example of where we would be.
So we’ve got about 1,000 to 4,000 micrograms per liter of solvents. We’re in a sand to a silty-sand. Depth to groundwater is about 10 to 13 feet. Seepage velocity is about 12 feet per year, so we’re in the plume here away from the source area. We’re looking at a test site injection of PlumeStop with an electron donor to help support the colonization of the PlumeStop with an active microflora. No bacteria are added to this. It’s simply a combination of PlumeStop and an electron donor for biostimulation.
The results look something like this. Prior to the application of the reagents, there was some degradation. You can see the daughter products there down at the bottom of the screen. The concentrations of TCE and TCA were climbing if anything. There’s some PCE in there as well. Once we applied PlumeStop, the concentrations fell like a stone. To put this in perspective, we’ve got an order of magnitude reduction by the first sampling interval, two orders of magnitude reduction by the second sampling interval, three orders of magnitude reduction by the third sampling interval, and by six months we’re at non-detect.
Fine. That’s what we’d expect from sorption. What gets interesting is that when we look at the microbial [inaudible 00:16:43] data to get an understanding of how the microflora is responding to this, remember no bacteria being added to this, what we see is that the degrading microflora proliferates and increases significantly. So dehalococcoides through this period has gone up some 800% or so. But what’s notable is that this is while dissolved-phase VOCs are at or close to non-detect. So we’ve got a microflora which is growing. Dehalococcoides, for example, actually grows on the chlorinated solvents. So it’s growing on something, but nothing is showing in the groundwater. So this provides a reasonable line of evidence that the degradation is proceeding on and at the PlumeStop surface.
What gets interesting another stage beyond this is that around about this point, we would be at the point that the amount of material that we put in the ground would be saturated with the influx of solvents that is still migrating into the area. The actual hydraulic conductivity has not been changed significantly. We’ll see that further in this presentation. But yet, the groundwater concentrations still don’t increase. Presumably, this will be down to degradation if you line up the various factors that we can see there.
One year and counting, we’re still at non-detect, we’ve still got incoming flux, and we’re still not seeing the material becoming saturated. We’ve still got a microflora which is raging away, and we’ve still got nothing showing in the dissolved phase. At 450 days, it’s the same. Now, we’re about five months on from that and we’re still at non-detect. So this provides an indication of the capture and the ongoing biodegradation, and some of the bio-regeneration without the groundwater phase being impacted.
So through the rest of the slides, I’d like to drill into some of the points which are raised by this and look at them in more detail to get a more robust handle on what’s actually going on. The first of them that I’d like to deal with is the distribution through the soil itself, as this is one of the key attributes of the technology, the fact that it can be so easily emplaced dispersively through a formation. I’m going to start with a simple visual indication of what’s the distribution treatment prevised to the material.
Here we have two columns that are about two feet by two inches in length, and they’re packed with a sand. Into one of them we’re going to put powdered activated carbon. Into the other we’re going to put an equivalent, equal, mass of PlumeStop. The principle difference therefore being that one has the surface treatment that prevents the clumping and allows the distribution, and the other one doesn’t. See if you can spot the difference.
So that’s time-lapse of about a 10-minute flow. These are gravity feed. The volume going through each of them is exactly the same. Each of them was topped up with the same amount of water. The taps were simply opened at the bottom and the PlumeStop was allowed to permeate through the system. It took about 10 minutes, and it left a coating through the foundation, as we can see here. The powdered activated carbon, in contrast, remains a plug at the top of the system. When we actually look at the sand particles under an electron micrograph, this is what they look like prior to the PlumeStop being passed through, the scalebar that you can see at the bottom there. There’s about 50 microns. There we are.
When the PlumeStop is being passed through it, we see a coating something like this. The scalebar there is slightly smaller. The scalebar is about 20 microns. So again, you can see the PlumeStop particles clearly, about one to two microns in size. There’s another image of the same thing. It’s onto these that the bacteria will begin to grow simply because the particles in there are replete with the contaminant.
So which are the bacteria which are going to grow on them? Well, the ones that degrade the contaminants that they contain, naturally. The contaminants will then slowly grow their biofilm between the particles and between themselves, and we end up with a synergy between the microbe and the particles. The particles act as a reservoir of the contaminants and help create a local abundance of the contaminants, so the bacteria can grow. The bacteria grow on these, freeing up sorption sites so that more contaminants can then be captured.
What about field-practical distances? Two-foot columns are all very well, but two feet is not very far in the field. Well, here’s a long column. This is set up in the warehouse at our lab, about six feet long. We’ve got fine to medium silica sand in it. It’s got a porosity of about 20%, so it holds about half a gallon of fluid. This we’ve used to look at breakthrough dynamics and to get an idea of the amount of material that’s retained on the sand as it passes through. It’s an upflow column, as you can see from the cartoon on the right of the screen.
What we see looks something like this. Let’s see if this will run. There’s the first going through. You can see it’s hitting the top now. It should really ring a bell, but it doesn’t. We can see if we look at the container on the left how material is passing straight through the column and into the second container. So all of this material that’s shown here on the left has moved freely more than 16 feet. After a few we’ve switched to clean chase water. We push chase water through the column and we displace the material that’s in the pore space, and we flush it a few times, and then we move on to a very rigorous flushing, which I’ll come onto in a moment.
So in case the resolution wasn’t too good on that image, here’s an attempt to make it a little bit clearer. This is the four-foot mark on the column and we can see at zero minutes on the left, the sand only. In about 20 minutes, we can see the PlumeStop front moving through the column. Note that it’s moving through a fairly even dispersion here. It’s not fracking up the column. It’s not just squeezing around the side. It’s at a low pressure and is moving freely through the column like an ink might. 80 minutes, the column is full and after water flushing you may be able to pick up, depending on your screen resolution, that this is slightly darker than the column on the left. It’s not particularly clear, but there is a darkening in the color.
To get an idea there for what was actually retained, there’s the front progressively moving through by dispersive flow and there’s the post-flush coating apparent. To get an idea of the total mass that’s left, the breakthrough curves look something like this. So here on the Y-axis, we’re looking at the ratio of the influent concentration to the effluent. So one means that they’re broadly equivalent. What we can see is that for the time that the PlumeStop is being pushed through the column, we’re getting breakthrough of the PlumeStop out of the top of the column at about 1.2 pore volume. So it’s retarded about 20% behind the waterfront.
We can then see that through the majority of the study, the fact that the concentrations are broadly equal is an indication of the PlumeStop traveling more than the 16 feet, or 5 meters in metric units. When we switch to the clean chase water, then that quickly pushes through the column. It flushes out the PlumeStop that was still in the mobile phase, and a PlumeStop coating is left on the particles, which we’ll see in the next slides.
Also, significantly, if we look at the back pressure of pushing the water through the column, it’s static. There’s no permeability impact detectable before and after the material has been pushed through the formation. There was a slight change in back pressure as we pushed the PlumeStop through, but it wasn’t that significant. You could just tell something was happening.
What we did next then, was to gain an understanding of the wash-out. If this material moves so freely, why does it stop? Why does it not just keep moving and travel off the side, possibly carrying contaminants with it if it sold so well and moved so well? Well, this was a test to look at the degree to which it would wash out of a very low-sorption material of the coarse sand here. So after the application, we aggressively chased the PlumeStop with nine pore volumes of water.
Now, this is immediately post the application of the PlumeStop and this is significant, because the dispersive treatment on the PlumeStop will be active for about one to three months. So straight after application, a few hours after application, we’re well within that one to three-month time period. So the material is still in its mobile stage. This, by the way, would be a seepage velocity or a flow velocity equivalent of about 22 miles per year. So it’s not field-practical. This is a very aggressive test scenario.
After we’d flushed these nine pore volumes through at this rate, we broke the column into lengths and we analyzed the sand for elemental carbon corrected against the clean sand baseline that we had put in, and this is what we saw. I’ve shown again, on the right-hand side, a cartoon of the columns. So the blue bars that you can see are the mass of PlumeStop, or the concentration of PlumeStop on the sand in milligrams per kilogram at different heights up the column. So the bottom of the column is at the bottom. The top of the column is at the top. What we can see here is that there’s a reasonably even coating throughout the column.
But what we’re not seeing is either a major plug at the top or the bottom. The total mass retained within the column would be equivalent to about 0.1% of the pore volume. So it’s not surprising that the back pressure, and hence the hydraulic conductivity was not significantly changed by this. This is an important consideration if the materials are ever going to be used as a barrier. If it blocks the formation, it ain’t going to be a flow-through barrier. So yes, again, there’s another image to give an idea of the type of particle coating of one to two microns that we’ll be picking up through the column length.
So this is an extreme-case test. The sand of the column had a low surface charge and a very low surface area matrix. So the retention of the material on this will be relatively low compared to a natural aquifer where high concentration will be generally held on the formation. We had a high wash-out flux, significantly greater than field conditions and certainly within the time period that the dispersive treatment of the PlumeStop would be active. Yet, still we were able to retain the material on the column. In the field, we have much more latitude to how we can place PlumeStop where we need it. We can control flow. We can control the volume that we put in. We control the concentration and dilution of the material. We can change the degree or volume of chase water we might use, the injection spacings, and we can also disrupt the dispersion of treatments on the PlumeStop.
If necessary, if we wish the material to move this far and no further, then it’s possible to inject a [countering] agent, which will stop it dead in its tracks. Generally, we don’t do that, because seepage velocities under natural conditions are only a few tens of feet per year. So the migration distance of the material through evection in its dispersive window is relatively modest and actually how it’s increased the application evenness through the field, rather than as in anything else. If we’re right up against a surface water receptor or a site boundary, then we may look at other control opportunities. It’s for these reasons that at the present time we’re applying the material ourselves as a company through Remediation Services and REGENESIS.
Okay. That’s distribution. What about post-sorption bio? I’ve got a couple of sections on this. We’ll see if we’re going to do both of them or just one, depending on how time goes. So let’s look at post-sorption degradation and bio-regeneration. The principle that we’re looking to test here and this is in the lab, is this. The contaminants, when we put PlumeStop in the ground, with sorb to the sites available in the PlumeStop particle. The bacteria can then degrade the sorbed contaminants. The sorption sites then become available for additional contaminants to sorb, and around this merry circle we go. We’re not sponsored by Mercedes-Benz. The image is purely coincidental and does not constitute an endorsement on our part towards Mercedes or any other automobile manufacturer.
The test was done in microcosms. These are eight-ounce amber vials. You can see them pictured on the right. The test condition that we looked at is water, an electron donor, sodium lactate in this case, soil, PlumeStop, and an inoculum. There’s very little headspace, so the system has very quickly become anaerobic. The control system is exactly the same, other than it’s abiotic. So we have a biotic and an abiotic system. The same volumes of water, lactate, and soil are in each. However, the control condition contains no PlumeStop and is sterilized. Obviously, there’s no point in putting an inoculum in if you’re going to sterilize it too.
The systems are set up with equal volumes, no headspace, and we’ve got 27 replicates of each. What we do to these is load in 10 milligrams PCE net. In other words, enough PCE to push the concentration up by 10 milligrams per liter every 2 weeks. So this is to model influx of contamination coming into a treatment area. The study period is 10 weeks, and what we monitor thereafter is the dissolved-phase analysis, water only, but then the total system. We sacrifice the whole microcosm system and we look at the total mass in both the aqueous and the soil phases.
This is what we see in the aqueous concentrations. If you look at this, we can see that in the control system in blue, the PCE concentrations in water climb with each injection. They’re abiotic, so the degradation is absent or negligent. In the PlumeStop system, we can see that as the same volumes of PCE is added, it’s captured by the PlumeStop and very little shows in the groundwater. You can see it just showing on about the 28-day spike only. But pretty much, the line is flat.
Now, the total amount of PlumeStop in the test system and the amount of PCE that’s added, is designed to be sufficient to absorb about 95% of the PCE added. What that means is that as the subsequent spikes are added, we should be starting to see the concentration mount up in the PlumeStop system as the sorption capacity is overloaded. So theoretically, this would be the aqueous phase concentration if there was no sorption in any of the systems. We can see the dissolved-phase concentration going up by 10 milligrams per liter on every spike for the eight weeks of spiking.
What this shows us then is the difference between the theoretical and the actual. In the sterile system, it’s largely down to sorption onto the soil. With the PlumeStop system, we’ve got the sorption onto the soil, plus the PlumeStop. So this is showing some additional sorbs at capture. What’s interesting, though, is that because we’re pretty much at the saturation capacity of the PlumeStop at this stage, we would theoretically expect to see the concentration starting to mount up overtime, simply because the sorptive capacity is overloaded. These are numbers which are calculated from the sorption with PCE and PlumeStop.
The fact that this doesn’t show up is a suggestion that we are getting the bio-regeneration, because the principle difference between these systems is not just the fact that one’s got PlumeStop [in], but that’s it’s also biotic. So this is encouraging, but it’s still a little tentative, until we look at the soil phase. So this is now the total system extract. This is the soil and the water combined. This is all of the mass.
If you look at the scale on the right, we’re in milligrams here. It’s not milligrams per liter. This is just milligrams of PCE in the system. There’s nowhere here for the contaminant to hide, and what we can see is that in the abiotic system with no degradation, then unsurprisingly the PCE concentration climbs with the PCE mass, and that concentration climbs with every spike. This also provides an indication that abiotic losses or volatilization were negligible.
In contrast, if we look at the PlumeStop system, we can see that the total PCE mass, this is the total mass in both liquid and sorbed phases, drops back to baseline between each spike. This therefore provides us with a reasonable indication that we’ve got sorption and degradation going on, which will be consistent with bio-regeneration. We’re not seeing progressive sorption. We’re seeing the sorption drop back to zero.
So in summary, we’ve got same day capture of concentrations of PCE, as it’s [put it] in with the PlumeStop. This is effectively the clean-up of the groundwater/aqueous phase. We’ve seen close to complete PCE degradation post-sorption between each spike, because in the PlumeStop treatment, the PCE in the whole system declines back to zero. We’ve seen the aqueous phase being protected throughout this period. The aqueous phase protection is greater than would be predicted from the sorptive capacity of the carbon alone. So this provides some evidence of sorption site bio-regeneration.
Overall, therefore, this provides a suggestion of the functional longevity of the material, which can be extended for as long as the bio-regeneration can proceed, which would be indefinitely, and appropriate growth conditions. That’s another story of what appropriate conditions are. But that’s familiar to all of the bioremediation engineers among our numbers. This will provide significant opportunities for migrating plume capture, back-diffusion management, and all of the new opportunities that this technology brings.
Post-sorption biodegradation. I’ll go through these slides a little quickly, because I want to get on to some case studies and leave some time for questions. Does biodegradation proceed post-sorption? Yes, it does. We’ve seen that in the last case study. But one of the other early assertions was acceleration of the degradation rate. So what evidence is there that the net contaminant degradation rate can be enhanced by the PlumeStop? Is the net degradation rate enhanced, inhibited, or unaffected by sorption of the contaminants into the biomatrix?
So this time we’re going to look at Benzene. A lot of the other studies have been with solvents as a lot of [inaudible 00:37:31] have the technology to do with solvents. But the technology will work for really anything that’s biodegradable that’ll [solve] well or even just modestly to carbon. So this one is benzene, and we’re looking at four different treatments with and without PlumeStop, and sterilized and non-sterilized. We’re sampling these destructively every week for about a month. Again, we look at the aqueous concentrations and the total benzene masses we did before.
This is what we see in the aqueous phase. We see a very rapid sorption in both the PlumeStop treatments, regardless of whether they’re sterile. This is in about one day, and the sterile systems shown in green. Nothing changes after that. It’s saturated, and there’s the saturated capacity evident. What we can see in the system without the PlumeStop, soil only, is that there’s none of the same sorption with PlumeStop. We can see, however, that there’s an ongoing drop in benzene concentration in both the live systems compared to the sterile systems. The red one is without PlumeStop. The purple one is with the PlumeStop.
This would be suggestive of biodegradation. Now, significantly, what we’re looking at there is between about the day one and day seven, we’ve got about a 4% reduction through biodegradation and the system without PlumeStop. The PlumeStop system, disregarding the sorption simply from this point down to this point, we’ve got about a 96% reduction and concentration in the groundwater phase. This is at a lower dissolved-phase concentration, if you remember some of the earlier slides.
So it looks like the ongoing destruction is due to bio. Could it be a sorption artifact somehow? Well, again, this is where looking at the total system comes into play. So know this is the extracted total system in milligrams and what we can see is that there is no net loss in either of the sterile systems, the blue or the green line, with or without PlumeStop. This also provides a good indication of recoveries, whereas both of the nonsterile systems show a benzene reduction. Importantly, though, the degradation rate is significantly faster in the PlumeStop system. It’s a detection limit of I think about 300 micrograms I believe, by the end of the first week.
To put this in perspective, the degradation rate is shown without the PlumeStop. The biotic control, the red line, if you force a first-order approximation through that, you’ll be looking at a half-life of about 10 days, which is broadly the same as that that we see in some of the old published literature on this. So there is quite a significant increase that we’re seeing in the degradation rate in the presence of PlumeStop.
We talked about that in theory in some of the very early slides. It looked something like this. When the data came through in the lab, I was really quite amused at the visual similarity between the two of them, which is coincidental. I don’t know if your screen will refresh fast enough to see the toggling back and forth. But we’ve got pretty much the same type of image here, where theory meets the lab data.
Okay. What about the field? That’s enough of the lab. I’m going to show two quick case studies which actually give me a chance to close within the hour with some time for questions. So this one is significant. I’ve chosen this as one of the case studies, because it provides some lines of evidence for post-sorption degradation in the field. It’s a closed dry cleaner site, and this one is in California, for those who are interested.
Now, a bit of background to this. Groundwater bioremediation is typically monitored in the dissolved phase. We take samples out of wells, and we use lines of evidence approaches to multiple parameters to give us indications of how well biodegradation is proceeding. PlumeStop sorption proceeds the degradation. This means the contaminants are pulled out of the groundwater phase that we’re sampling, and therefore are not going to be there in the wells for us to test to get the same types of lines of evidence approach that we might without the PlumeStop. So what verification lines of evidence for degradation remain open?
So here’s a case study example of some of the geochemical and microbial diagnostic lines of evidence that can still be followed in parallel from this from groundwater samples alone. So we’re at a dry cleaner site. The sun is shining. It must be California. It’s a simple pilot test. It’s in a single well. It’s a former dry cleaner, and we’re looking at modest PCE residues. Here’s the well. We’re in a very forgiving Dune Sand formation. This was one of our only beta tests, which we were keeping simple. We’ve got about 33 feet per year in groundwater influx. Naturally, it’s a very high redox. It’s aerobic, and so there’s no attenuation of the PCE evident.
PCE concentrations are low, about half a milligram per liter. There are no daughter products. We wouldn’t expect them under aerobic conditions. We applied PlumeStop, and then we applied with that an electron donor and a microbial inoculant. PlumeStop does not take away the requirements for bio that we know from other spheres. We still need the right redox. We still need the right growth conditions. We still need the bacteria, even though they may be stimulated. We still need electron donors and electron acceptors. But again, we don’t always need to add them depending on what the attenuation rate would be under the baseline conditions.
Here’s a simple test arrangement. The test is what is shown in the middle. The white points show the application points of PlumeStop. So this is not a remediation example. This is a pilot test proof of concept example. Groundwater is flowing at about 33 feet per year in this direction, and we’ve applied PlumeStop with an electron donor and a microbial inoculant. Historic data looks something like this, going back for more than a decade. You can see that the PCE concentrations were slowly increasing if anything, and there were no daughter products at all, as we’d expect from aerobic conditions.
Graphed out, those same data, PCE concentrations look like this. To put this in perspective, here’s the PlumeStop application, and there’s the groundwater concentration after the PlumeStop application. This looks pretty good against the background trend that we’ve seen below. We’re below half a microgram per liter here. Fine. Sorption is wonderful. We’ve got sorption. How do we know there’s anything more going on?
Well, this is where the microbial diagnostics becomes interesting. Now, here I’ve got a double graph showing here. On the right-hand axis, I’ve got the geochemical parameters, the ORP, the dissolved oxygen, dissolved dinitrate, etc., etc. Zero is shown in the middle there, because this goes negative. On the left-hand axis, I’ve got the PCE concentration. What we can see is that with the PlumeStop application, the concentration of PCE drops down to zero. Here we go. This is kerchunk. It’s PCE concentration going down to the detection limit.
At the same time, we can see in this blue line the redox dropping down to about -150 millivolts, which is about optimum for dehalorespiration without getting into methanogenesis. We can also see throughout this period, not only are we at the redox sweet spot for sub-methanogenic chlorinated solvent degradation. But we’re seeing a nice steady decline in terminal electron acceptors that we can, so the nitrate, sulfate, dissolved oxygen, etc. start to drop down. So there’s one line of evidence that we get. We can at least see the PCE disappearing, although that could be sorption. But we’re seeing sweet spots for degradation occurring.
When we look at the microbial numbers, we get some further lines of evidence. So again, we’ve got the PCE concentration on the right-hand axis. We’ve got microbial numbers in terms of cells per mil shown on the Y-axis. So here’s the PCE dropping straight down as we’d seen before. What we can see is at the point of application, naturally the microbial numbers, especially for dehalococcoides shoot right up. No surprises there. We’ve bio-augmented. We’ve added bacteria. So of course, they shoot up.
But what gets interesting is that even though the PCE has gone down to non-detect, the microbe parameters increase post the initial spike, and then they decrease after about two months. So these are trends that might not necessarily be the strongest evidence for, but is certainly consistent with the microbial numbers growing and proliferating, even though we’re not seeing anything in groundwater. To give an indication of no solvents in groundwater, dehalococcoides for example increases by about 225% after the initial application. tceA reductase is increased by a potential 541% greater than the amount of the actual bacterial numbers increasing. So the activity is actually picking up nicely.
Vinyl chloride reductase, 676% post the initial inoculant spike. Dehalobacter, well it was initially non-detect. It wasn’t part of the inoculant, but its numbers have shot up very significantly. Similarly to dehalobacter, dehalogenimonas which was not part of the inoculant has increased 3,000-fold since the time of the application. So it looks like we’re getting some nice bio-stimulation in there, as well as the growth of the bacteria that we applied. Methanogens, by the way, are this purple line along the bottom, nothing showing. We’re not at a redox low enough for them to be kicking off. That -240 millivolts or so. Yet, we’re in a range which is entirely adequate for dehalorespiration.
So two orders of magnitude reduction in 14 days, stats in non-detect. Optimal conditions for dehalorespiration established. Redox dropped from +254 down to about -150. Competing electron acceptors are depleted, and we’re seeing post-inoculation microbial trends showing an increase, and then a decrease in both the dichlorination species and the active enzymes, which would be consistent with solid metabolism and depletion that we would see.
More specifically, the dehalococcoides enzyme activity provides a strong indicator of degradation and all of this is going on whilst TCE and vinyl chloride are remaining below detection limits in the groundwater. So the fact that these are proliferating and that these are bacteria which grow on the mixture of the dissolved hydrogen and the solvent, it’s reasonable to conclude that they’re growing on the solvent [inaudible 00:49:21] PlumeStop. Geochemical status, favorable for dehalorespiration, but not for competing methanogenesis.
Conclusions. Good lines of evidence, all data obtainable from groundwater samples alone. One short case study in Chicago now, and then I’ll close. So this is a larger site. The little pilot sites that I’ve shown are all very well for explaining data, but they’re not real-world remediation. What about the types of conditions that we typically face in the remediation industry? Well, this is a project in Downtown Chicago that’s underway at present. I’d like to show you some of the data from the first period of time on this side.
So we’re in reasonably Central Chicago. We’re in the neighborhood of McCormick Place. McCormick Place is not the site itself. It’s just to give an idea of where we are. We’re in a zone where a new sports stadium is being built, and a new hotel complex is being built. There are solvent residues in the area. The time window for remediation is very tight. There is therefore high cost implications of delay. If you imagine a hotel and a sports stadium, the hotel has to take bookings way ahead of sports events, and sports stadiums have to take bookings way ahead of the sports event. So these constructions have to be ready in time for the season. A delay is not an option. So the principle requirements on this is that the remediation is going to be fast.
So the solvent residues are up to about 7.5 milligrams per liter. We’re in a silty sand over clay. We’re looking at a treatment area of about 1,000 by 1,600 feet, treatment zones about 10 to 22 meters below ground level. Originally, the idea was to use chemical oxidation on the site, simply because it was going to be fast. However, the challenge of ISCO is that whilst it can be fast, it can be more prone to rebounds than bioremediation often is. I refer to the work of Travis McGuire different sites. But that bio rebound is generally not as bad as ISCO rebound.
But additionally, one of the reasons that the groundwater clean-up was taking place was to reduce solvent residues in abstracted water during construction activities, but also to protect workers. So one of the reasons that ISCO… One of the shortcomings of ISCO in this circumstance would’ve been that any ISCO residues that are pulled out of the ground and still active are not going to be too good for construction workers or for the water treatment in ongoing dewatering activities. Bio would be more forgiving in those circumstances, but bio is too slow, until you bring in PlumeStop.
So on this project, there was an enhanced bio activity with enough electron data and inoculant to address the contamination. But PlumeStop was added with it to provide the rapid risk reduction bio process acceleration. But to take the whole process out of the groundwater phase, so that any water that might be dewatered is not going to be impacted by this or with a contaminant. So this was done with about 17 days field work onsite through the Chicago winter. I think they took a day off for Christmas, and that’s about it, 138 direct push points, no resident equipment.
The results looked something like this. This would be a lovely shot of the Chicago skyline if it wasn’t for the skyscrapers in between. But we’re looking up in broadly that direction, as you can see from the shadows. Here’s the PlumeStop application. There weren’t many samplings, but by the first sampling event we’re at about 97% reduction in total VOCs. A second sampling event about a month ago, we’re about the same. But if you zoom into these and take a close look, what we see is this compositional change that’s consistent with biodegradation.
The PCE has gone right down. The TCE has gone right up. We’re a long way down from the original concentrations prior to the PlumeStop. What’s also important is that one of the clean-up targets on the site was to have TCE below 100 milligrams per liter, which we are on this particular point with bio still going on. This is now presently the highest concentration of TCE left on the site, and it itself is at compliance.
If we look across the site to the well, which now still has the highest remaining concentration in it, to provide a bit of perspective and balance, it’s this one. The actual total concentration is about the same as in the previous slide in these residues, but the starting concentration was a bit lower. So we’re into some 80%-plus degradation, and again with this one we can see that there’s a compositional change consistent with biodegradation. Through performance criteria on this project, for total VOCs, which we’re at compliance with on this well and all of the others… This is the dirtiest remaining well, and yet there’s evidence that we can see a degradation proceeding still from the contamination that’s still within the groundwater phase.
Interestingly, this slide also shows that there is some type of communication between the sorb phase and the aqueous phase, because this amount of cis would not be able to come from this amount of TCE, simply because it’s a lower molecular weight molecule. So we’re not at equivalence. There’s some dialog going on between compartments.
Status at present, 80% to 97% reduction in groundwater contaminations from the first sampling interval. Bio conditions established for good degradation, good redox, good microbial numbers. We’re seeing some of the expected parent-daughter compound ratio shifts consistent with bio. The targets have been met by the second sampling interval. The first sampling interval almost met them, but not quite. By the second sampling interval, we were there. So at present, the consultant for this project is evaluating the potential for closure, nicely in time.
Talking of nicely in time, I’m pretty much on my time now. So I’ll show just a few slides to close, and then we’ll have a moment for questions. PlumeStop, when do we use it? Typically, here are four of the principle indicators. One is when time is critical, such as the Chicago site. Two is when it’s important to get to very stringent clean-up targets in the low microgram per liter range, or microgram range. It can be used for passive control of migrating contamination. One of the projects at the moment is an alternative to what had been an ongoing active hydraulic containment system.
It can be used with the long-term means of addressing matrix back-diffusion. I’m short of time, so I want to focus on matrix back-diffusion rather than the others, which I think is self-evident. So the basic idea is that PlumeStop, when it’s in place, will maintain the concentration gradient out of the immobile porosity that would typically lead to back-diffusion, back-diffusion. The mobile porosity concentration therefore remains low due to capture of the contaminants in the PlumeStop, so the gradient is sustained.