Surfactant-Enhanced In Situ Chemical Oxidation (S-ISCO®) 

VeruTEK® Technologies, Inc. is a US-based Green Chemistry company with an innovative approach for addressing source zone contamination and NAPL plumes: Surfactant-enhanced In Situ Chemical Oxidation (S-ISCO®). During the S-ISCO process surfactants and oxidant systems are injected simultaneously to destroy contamination on site and in place, providing timely and permanent solutions to soil and free-phase contamination. S-ISCO is field-proven and has been used in over 50 projects, including over 20 full-scale projects and three US Superfund sites.

S-ISCO has remediated LNAPLs, DNAPLs and sorbed residuals, such as hydraulic fluid oil, PAHs and chlorinated solvents, resulting in complete or near complete destruction of coal tar NAPLs and residues.   VeruTEK is a technology leader in remediation chemistry and continually expands its technologies and applications.   The company conducts ongoing research and development both in-house and through partnerships with academic institutions such as Yale University and the University of Connecticut, as well as with US EPA. Download Full S-ISCO Whitepaper >>

 

1- INTRODUCTION

At the foundation of Surfactant-Enhanced In Situ Chemical Oxidation (S-ISCO) is the subsurface transport of surfactants and free radical oxidant systems in combination to increase the solubility of contaminants which normally exhibit low solubility, such as NAPLs, and make them available for oxidative destruction. S-ISCO incorporates the following four key elements:

 

• Biodegradable surfactant and co-solvent mixtures that emulsify NAPL-phase contaminants and desorb source zone contaminants;
• Catalysts and oxidants that generate powerful free-radical oxidant systems;
• Free radical oxidant systems that destroy solubilized contaminants;
• Reduced oxidant consumption through increased contaminant availability

 
2 – S-ISCO TECHNOLOGY
2.1 – Surfactants

Because in situ chemical oxidation consists primarily of aqueous phase reactions, highly hydrophobic contaminants that are sorbed to soil particles or in a separate NAPL state are not available for reaction with the oxidant chemistry.  VeruTEK developed S-ISCO to address these sorbed or NAPL-phase contaminants. S-ISCO is highly differentiated from In Situ Chemical Oxidation (ISCO) through its incorporation of VeruSOL®, biodegradable, plant-based surfactant and co-solvent mixtures to address NAPL. VeruSOL creates a Windsor Type I oil-in-water micro-emulsion with NAPL allowing the NAPL to enter aqueous phase reactions, such as oxidation with hydrogen peroxide or sodium persulfate. 

2.2 – Free-Radical Oxidant Systems

S-ISCO oxidant systems often include sodium persulfate and/or hydrogen peroxide in conjunction with activators and/or catalysts, including alkaline (high pH), iron chelates, such as Fe-EDTA and Fe-EDDS, and VeruTEK’s innovative green-synthesized nanoscale iron activator (GnA). S-ISCO implementation consists of targeted simultaneous injections of the oxidant, its activator or catalyst and VeruSOL, in a formulation optimized for the contamination, hydrological and geological characteristics of a given site. Laboratory dosage studies that often precede a field implementation, along with groundwater monitoring of the progress and performance of the injected chemistry during treatment, are used to optimize the process. 

2.2.1 – Sodium Persuflate Systems

Persulfate treats more complex contaminants, often in silty clay or bedrock environments, and at deeper depths. A sulfate radical is one of strongest aqueous oxidizing species with a redox potential of approximately 2.6 V3. In addition to its oxidizing strength, sulfate radical systems are stable, lasting weeks to months in the soil and enhancing both the radius of influence of injections and also the contact time with recalcitrant compounds, such as chloroethenes. After a S-ISCO implementation at a New York MGP groundwater monitoring results showed that persulfate remained active for more than four months after the seven months of VeruSOL and Fe-EDTA-activated persulfate injections ceased.⁴ This treatment produced results which are typical of a S-ISCO treatment, destroying 91% of the 7,900 kg of PAH targeted, reducing visual staining by more than 80%, and improving soil vapor concentrations in nearby buildings. 

2.2.1 – Hydrogen Peroxide Systems

Hydrogen peroxide is an optimal oxidant for less complex hydrocarbon contaminants, such as petroleum hydrocarbons and lower concentrations of BTEX. Hydrogen peroxide can be used alone but is most often catalyzed to produce hydroxyl radicals. . In addition, peroxide can be used with persulfate as a first treatment stage. Peroxide quickly destroys the. shallower, more reactive contamination before persulfate provides a longer-lasting treatment for deeper, more recalcitrant impacts.

Figure 2 shows the effect surfactant has on the longevity of peroxide reactions, the orange line shows iron activated peroxide without surfactant – the peroxide decomposes within 6 hours, by contrast, the red, green, purple and light blue lines show the rate of iron activated peroxide decomposition with various doses of surfactant – the peroxide remains active after 25 hours.
 

3 – APPLICATIONS

S-ISCO is an effective and low impact approach for eliminating contamination that threatens the human and natural environmental. S-ISCO injections can target contamination beneath structures, without impact to the building or its users, and can be used at former MGPs; underground storage tanks; fueling stations; residences; and in industrial settings, such as manufacturing facilities.  In addition to its basis in Green Chemistry, S-ISCO is aligned with US EPA’s criteria for greener remediations⁵ —criteria including reduced energy and water use; air pollution and greenhouse gas (GHG) emissions; and waste material, and ecosystem improvement.   Because S-ISCO reactions are more efficient than ISCOa project’s length and energy use are reduced (energy). S-ISCO chemistry travels with groundwater and does not require re-circulating or extraction pumps (energy).  In situ remediation does not require heavy machinery used in excavations (energy), and treats material on site, reducing wastes hauled to landfills (waste, air pollution). S-ISCO improves water quality by destroying dissolved contaminants and their source, without disturbing the land (ecosystems). At the same time that VeruSOL is biodegradable and made from renewable plant material, waste products of S-ISCO reactions are non-hazardous (CO2, H2O and O2) (ecosystem, waste).