In situ chemical reduction (ISCR) advantages over emulsified oils



Adventus Americas, Inc., an international remediation biotechnology firm, recently outlined topical decision-making criteria for remediation engineers and environmental professionals. This summary compares and contrasts our EHC® ISCR technology with carbon-only substrates consisting of emulsified vegetable oils. While the latter can be effective, there exist a number of fundamental differences.

The Potential Significance of ISCR:

Many constituents of interest (COIs) such as chlorinated hydrocarbon compounds (CHCs) can be degraded via oxidative or reductive processes. Accordingly, various in situ chemical oxidation (ISCO) technologies using oxidizing agents such as Fenton's chemistry, permanganate and persulfate have been developed to remediate impacted environments. Each of these oxidants and their activators offer seemingly unique features and they can be very effective on a varying range of CHCs.

However, an equally or perhaps more effective remedial strategy, especially for plume treatment, entails in situ chemical reduction (ISCR) which combines carbon plus zero-valent iron. EHC is a patented combination of controlled-release, complex carbon plus zero valent iron (ZVI) that uniquely exhibits the recognized benefits of ISCR. Hence, EHC integrates chemical and microbiological degradation processes that conventional enhanced bioremediation technologies do not. When specifically compared to emulsified oils, EHC offers the following qualitative and implementation advantages:

Top Ten Reasons to Use EHC ISCR Technology vs. Emulsified Oils:

1. Better Contaminant Removal in Head-to-Head Test: Several independent comparisons of EHC and emulsified soybean oils have been conducted. The results consistently indicate that EHC provided greater removal efficiency for all contaminants tested, including TCE and metabolites, chlorinated ethanes, and TCFM. Several of these reports are archived online.

2. No 'Remediation' via Physical Sequestration and no Rebound: EHC contains a hydrophilic (water loving) complex carbon source that will lasts at least 5 years in most groundwater environments. Thus, EHC will not absorb chlorinated solvents or other hydrophobic COIs, nor will it migrate vertically once emplaced into the subsurface. Conversely, oils are inherently lypophilic and hydrophobic which will physical absorb contaminants which can yield temporary or apparent COI removal. Moreover, emulsified oil droplets will tend to attract one another and may float to the water table, or sink, thus moving out of the intended remediation zone, potentially carrying COIs with them.

3. Remediation without the Accumulation of Catabolites: EHC yields rapid COI removal without accumulation of potentially problematic catabolites. Various ISCR reactions unique to EHC promote rapid and complete dechlorination of target compounds (see 'Thermodynamics of Low Eh Reactions' for further scientific validation click here. Emulsified oils depend on the presence of specific microorganisms, and support degradation reactions that proceed along conventional sequential reductive dechlorination pathways. As such, potentially problematic / 'dead-end' intermediates such as DCE and VC from PCE or TCE, and DCM from CT or CF, will often accumulate. Emulsified oils may also reduce the bioavailability of COIs through their sorption to the oil matrix, whereas EHC does not.

4. No Mobilization of Contaminants: Optimal volume of EHC slurry is injected without the need for extensive water flushing, which avoids potential displacement and mobilization issues. EHC is often applied as aqueous slurry (15 to 40% solids/weight). The small amount of water used during the injection process therefore causes little displacement of groundwater. In contrast emulsified oil injections are performed at lower concentrations (3% to 12% oil in water) or with water chasers and can therefore cause substantial plume displacement. The Florida Department of Environmental Protection, for example, stated its concerns regarding contaminant migration through the injections of emulsified oils in its acceptance letter of an emulsified oil product.

5. Ease of Construction: EHC is available in solid and aqueous formulations and is manufactured regionally according to site-specific needs and conditions. It has been successfully applied to hundreds of sites with widely varying lithologies throughout the world. Given the high solids contents of injected slurries, field times are kept to a minimum. Oils are viscous liquids delivered as concentrated emulsions which typically require extensive dilution in the field to yield a viscosity between 1.3 and 2.1 times that of water and/or water flooding to facilitate in situ distribution. This can translate into significantly increased project costs due to the need for extended field time.

6. No Regulatory or Health & Safety Issues: Safe handling and easy application with no bulky or hazardous material disposal issues. No Genetically Modified Organism (GMO) issues. No surfactants. No secondary plume issues (TOC, heavy metal mobilization, etc).

7. pH Buffering: The alkalinity generated by the ZVI component of EHC offsets acidity generated by fermentation of the organic carbon portion. This results in a natural buffering of pH, which prevents acidification. There is no need for additional buffering agents which represent additional cost, field time and potential dilution / displacement affects. In contrast, fermentation of emulsified oils frequently leads to aquifer acidification, which can slow the rate of microbial dechlorination.

8. Superior Technology for Permeable Reactive Barriers (PRBs): EHC is ideal for placement as a PRB because it is solid, remains where placed, and will not migrate with groundwater.

9. Adaptable Formulations for Heavy Metals: EHC is uniquely effective for environments co-impacted with organic and inorganic contaminants (e.g., As, Hg, Ni, Pb, Zn). The presence of ZVI and other amendments unique to EHC-M™ formulations will yield rapid, irreversible, long-term immobilization of heavy metals - while simultaneously dechlorinating organic compounds. This is not an option with emulsified oils since they do not provide ZVI.

10. Full Patent Indemnification for You and Your Client: EHC ISCR technology is the subject of numerous Adventus patents. Adventus will provide full indemnification, backed by insurance coverage, to protect users and site owners from lawsuits purporting patent infringement.

1.; Florida Department of Environmental Protection, accessed 12 April, 2006

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