PETROLEUM REMEDIATION AND PETROFIX
Frequently Asked Questions (FAQs)
Todd Herrington and Paul Erickson from REGENESIS presented a webinar on how to apply and evaluate the effectiveness of PetroFix™, a dual-action treatment approach consisting of micron-scale activated carbon for contaminant adsorption and electron acceptors to stimulate biodegradation. This activated carbon remediation technology is easily injected in-situ under low pressure, distributes in the subsurface without fracturing, and includes electron acceptors to stimulate biodegradation of petroleum contaminants in soil and groundwater. Along with design considerations, the presentation by Dr. Erickson and Mr. Herrington discussed a former bulk petroleum storage facility where PetroFix was injected in an area with over 50 ppm total petroleum hydrocarbons. Multiple lines of evidence were used to evaluate performance: contaminant concentrations to evaluate contaminant adsorption and removal from groundwater, geochemical parameters to document microbial utilization of added electron acceptors, and QuantArray®-Petro and mRNA analyses to evaluate biodegradation of BTEX and other hydrocarbons.
The following Q&A include questions from the audience, with answers from Dr. Erickson and Mr. Herrington of REGENESIS, as well as Dora Taggart, President of Microbial Insights, Inc.
There is no incompatibility using ORC Advanced with PetroFix. The only limitation to this approach would be the additional cost for ORC Advanced and the need to inject the material in separate injection points because they are incompatible to be injected together. However, once injected through separate grid injection points the combination of ORC Advanced plus PetroFix with provided nitrate and sulfate electron acceptors would be a very aggressive and effective remediation approach because the stimulation and growth of aerobic bacteria would happen quickly as well as subsequent aerobic oxidation of a broad range of fuel hydrocarbons. As oxygen is the preferred natural electron acceptor for hydrocarbon bioremediation based on the standard free energy available for oxidation it would be used preferentially and nitrate and sulfate use would be suppressed until oxygen was depleted. Following depletion of oxygen, nitrate and sulfate would be utilized. The combined use oxygen followed by nitrate and sulfate electron acceptors would be expected to improve syntrophic processes under anaerobic conditions because you have increased the total electron acceptor capacity and are bio-stimulating a more diverse range of bacteria capable of handling the more recalcitrant VOCs such as benzene. We do want to emphasize that while we would be highly confident on the combined use of ORC Advanced with nitrate and sulfate, we still believe that for most sites the provided nitrate and sulfate are sufficient for stimulating fuel biodegradation.
We agree with your question and statement in theory, but in practice we find that oxygen replenishment to aquifers from the atmosphere or surface water infiltration are insufficient to stimulate aerobic biodegradation in the time frames needed. If your aquifer already is anaerobic then we believe the use of the provided nitrate and sulfate a wise choice. However, if you evaluate the levels of dissolved oxygen and
oxidation/reduction potential (ORP) of your aquifer and find that it is indeed well oxygenated and aerobic then injecting PetroFix would still be beneficial by allowing the PetroFix to sorb and remove dissolved phase contamination while having the naturally high oxygen concentrations stimulate aerobic biodegradation of sorbed contaminants. The use of the additional electron acceptors provided in separate white buckets is optional.
But why is acetate inhibitory? I know it can be for nitrate-reducing organisms, but not for most others. Is it strictly a matter of an abundance of "simple" hydrocarbons that drive either a preference of the degradation of those compounds rather than the hydrocarbons, or because it stimulates methanogenesis and methanogenic conditions? Also, is there a ph-related component due to the buildup?
In short, it comes down to chemical equilibrium and when the overall syntrophic process is thermodynamically favorable. As fermentation end-products (acetate, H2) accumulate, the entire process yields less energy for the microbes. As long as these intermediates are being removed by sulfate reducers and/or methanogens and the pH doesn’t increase too much (which can slow things down) the process remains energetically favorable.
From lab studies we know hydrocarbons, and specifically benzene is biodegraded by doing full-bottle extractions on batch experiments. After incubating with benzene, activated carbon, soil and water, an entire bottle is extracted with another solvent and we see all benzene is gone. In control experiments like this (killed/sterile bottles) the benzene can be recovered from the activated carbon at very high recovery percentages, showing biodegradation is the removal process. REGENESIS PlumeStop technical bulletin 3.1 is available on regenesis.com showing a post-sorption contaminant biodegradation lab study with benzene
that documents benzene biodegradation on the activated carbon (PlumeStop and PetroFix use the same diameter carbon and this lab study is representative for PetroFix as well). In the field, we rely on multiple lines of evidence to show ongoing biodegradation after adsorption. The utilization of added nitrate and sulfate in the right pattern (nitrate first, sulfate second) is the first line.
Temperature will certainly affect the expected rate of biodegradation. At 4ºC biodegradation will beslower, but still occurring. Many deep lakes in cold climates have sediments at this temperature, yet still experience natural methane emissions from organic carbon being biodegraded. The effect is loosely comparable to how
quickly food would spoil inside vs. outside of a refrigerator. Despite this, PetroFix would still be a viable treatment option at low temperatures.
We have plenty of lab data confirming biodegradation is occurring, and did not see the need to use isotopic tests as a part of initial field product testing. With that said, when using PetroFix compound specific isotope analysis (CSIA) has limited field use because groundwater contaminant levels commonly drop to ND after treatment. Stable isotope probing (SIP) is a method offered by Microbial Insights where a labelled compound is placed on a bio trap (activated carbon beads) and its removal, as well as incorporation into microbial biomass, can be followed.
It is true that microbes must uptake TPH rather than rely on extracellular enzymes, but there are other potential ways for microbes to actively uptake TPH, including biofilm and/or biosurfactant production. While the exact mechanisms are not clear, we conclusively know (see answer 13) adsorbed compounds can be degraded.
The formulation of PlumeStop is proprietary, but the point is the polymer is a source of carbon for the microbes much the same as the hydrocarbons are. The added organic polymer must be biodegraded along with the PHCs and this process will consume electron acceptors.
Yes, the issue is bulk floating petroleum. We believe using a rule-of-thumb that the presence of continuously measured floating LNAPL is an indicator of high mass that usually results in an exceedance of the desired performance range of PetroFix. High amounts of LNAPL could both overwhelm sorption sites on the PetroFix carbon and the rates of anaerobic degradation. Our goal for PetroFix is to provide sustained multiple-order of magnitude reductions of BTEX and TPH and to let our customers know of site conditions where we think attaining this goal would be challenged. If uncertain, we advise that you order a single drum of PetroFix and pilot test at your site.
The particle size of PetroFix is 1 to 2 μm in diameters which is below the pore-throat size of fine sands and silts. However, PetroFix cannot be injected into tight clay without high-pressure fracturing which we try and avoid. We realize that sorbed LNAPL often is present as a source in clay and PetroFix is not designed to directly remediate LNAPL bound in clay. Instead, PetroFix is designed to infiltrate all permeable transport zones above, below, or interbedded in clays that lead from a source to downgradient receptors. By focusing on liquid delivery in these zones you will stop migration of contaminants, particularly by mitigating the impact of contaminant back diffusion into these zones, and reduce site risk which opens up possibilities for closing sites by this method alone or in conjunction with other source treatment approaches.
PetroFix is specifically formulated for hydrocarbon plumes and while it could sorb both solvents and petroleum, its formulation will not promote anaerobic destruction of chlorinated products. In fact, PetroFix injected with its electron acceptors in an area targeted for reductive dechlorination treatment of solvents would be expected to repress reductive dechlorination until they are depleted and this would negatively delay solvent treatment. What we advise is that if you are concerned about overlap that you contact Regenesis for design assistance to evaluate an optimal treatment scenario.
It is true water soluble electron acceptors can flush out of a system, while PetroFix will remain positionally stable. We see this as an issue for a minority, not majority of projects and keep in mind that there will be some co-migration of contaminants with electron acceptors, albeit at different rates. For nitrate, its utilization is so fast that we predict it will not migrate significantly before it is utilized in most aquifers.
Sulfate utilization is slower and generally dependent on nitrate being depleted first and may move out of the system in high velocity groundwater environments. If you are concerned about washout it may be possible to replenish the aquifer with additional soluble electron acceptors through further injections, drip system, etc. One option is to co-inject ORC Advanced within or upgradient of the PetroFix application to supply continuous oxygen (ORC Advanced material doesn’t migrate with groundwater).
We don’t see an issue with using soil once treated with PetroFix as long as treatment concentrations have achieved acceptable use concentrations. Aesthetically, treated soil will be black which might be a consideration on their use.
Yes, PetroFix will work well with treating dissolved phase contamination in those ranges. For readers who may not be familiar with Canadian F1 to F4 ranges they are: F1 (C6-C10); F2 (>C10-C16); F3 (>C16-C34), and F4 (>34). The Indiana case study we showed presented both TPH-GRO (C6-C10, or F1 fractions) and TPH-DRO (C10-C28; or F2 and partial F3 ranges) ranges each having reductions of +2 OOM and +1 OOM reductions, respectively. We don’t have direct experience stimulating the biodegradation of F4 fractions at this point, but know that both the susceptibility and biodegradation potential are related to respective solubility of hydrocarbons. Components for F3 or F4 that are water soluble and mobile would be expected to be sorbed and treated by PetroFix using our mixed electron acceptor approach.
When treating hydrocarbon sites we hope to achieve one or more order-of-magnitude (OOM) reductions of contaminants sustained, if not better, for BTEX and TPH ranges. Reductions will happen quickly upon contact with hydrocarbon followed by biodegradation. The Indiana case study we presented was a challenging site that performed well at high concentrations and we will continue to monitor for performance. We believe that upper limits depending on soil type is probably in the 30 to 50 mg/L range total hydrocarbons before you might need to consider future, supplemental electron acceptor injections. Keep in mind that we believe that a single injection of PetroFix is probably suitable for most sites and any additional rebound can be addressed with the injection of desired electron acceptor and/or nutrient blends. The caveat to this is if you suspect that aquifer distribution was not achieved and that might warrant supplemental PetroFix injections to fill in the gaps.
We believe that PetroFix is compatible with RegenOx and PersulfOx® chemistry and could be co-injected in the same areas as these products. However, these material should not be injected simultaneously in the same hole. Other constraints to consider would be the ability to get total volumes from both ISCO products and PetroFix in the ground simultaneously since both require high volumes and high effective pore space filled. We see PetroFix as a very strong option for post ISCO polishing as either a second subsequent injection or possibly simultaneous injection during a single mobilization. The practitioner would need to determine the optimal timing when PetroFix should be injected to coincide with the mass reduction goals of the ISCO injections and at which injection event PetroFix should be paired. Regenesis is happy to discuss such options and make recommendations.
Yes, this product can be applied in deep aquifers as long as injection wells were designed for that purpose. Achieving distribution would have to take into consideration the limited ROI and distribution potential for pressure injection of PetroFix or consider pump-and-pull well arrangements if the aquifer were highly permeable to enhanced distribution. Please also see question 21.
Under most circumstances there is no need to add anything besides what is delivered with PetroFix. If needed or desired, small amounts of other nutrients like diammonium phosphate can be added to PetroFix for injection as it is water soluble and doesn’t interfere with the chemistry.
We have had a project where PetroFix was distributed in a bedrock aquifer and distribution was better than expected because effective pore space is less than in soil. As long as fractures are interconnected and the aperture sizes of those fractures are large enough you would expect to be able to push PetroFix into the formation, potentially using larger ROI’s than what we normally estimate for direct push. In a fractured bedrock site with sufficient interconnectivity you also have the option to use a pump-pull arrangement using different wells to facilitate distribution in different directions. We would recommend a small pilot test using a drum of material to verify the deliverability of the product and validation of ROI.
Could PetroFix be used in a clay-rich environment that has been fractured to increase permeability? The thought is that the fractured zones could serve as a hydrocarbon sink to reduce BTEX concentrations in the impacted soils over time through diffusion from the soils into the groundwater within the fractures.
We advise caution and proper design in these situations since we are trying to avoid uncontrolled or partial placement of PetroFix in an aquifer. PetroFix as shipped and undiluted would possibly meet density/viscosity requirement as a frack fluid and possibly could be paired with a sand proppant. Hence, PetroFix fracturing could be performed and it’s also entirely feasible that PetroFix fractures could be replenished with additional electron acceptor blends if they were connected to re-injection wells. We also have evidence to believe that PetroFix may also diffuse into clays beyond the fracture. Furthermore, the amount of carbon and electron
acceptors in PetroFix would probably be insufficient for direct remediation of LNAPL in clay. The ideal application of PetroFix is in the high flux zones where the material can control future back diffusion from clays into permeable zones to control risk. It is worth considering that many sites, despite having tightly bound contamination in clay, may achieve closure simply by injecting PetroFix into conductive zones to reduce off-site flux to levels sufficient to protect human health and environment. We leave it up to the practitioner to determine the specific need for source treatment in clay and perspectives on answering such a question was covered recently by Dr. John Wilson in a webinar entitled “Defining Cleanup Success for Groundwater Remediation” which can be accessed at regenesis.com.