Michelle Crimi

In Situ Chemical Oxidation of Contaminated Soil and Groundwater Using Persulfate: A review

Persulfate is the newest oxidant that is being used for in situ chemical oxidation (ISCO) in the remediation of soil and groundwater. In this review, the fundamental reactions and governing factors of persulfate relevant to ISCO are discussed. The latest experiences for ISCO with persulfate are presented, with a focus on the different activation methods, the amenable contaminants, and the reactions of persulfate with porous media, based primarily on a critical review of the peer-reviewed scientific literature and to a lesser extent on non-reviewed professional journals and conference proceedings. The last sections are devoted to identifying the best practices based on current experience and suggesting the direction of future research.

In situ chemical oxidation for groundwater remediation

Preface.- In Situ Chemical Oxidation: Technology Description and Status.- Fundamentals of ISCO using Hydrogen Peroxide.- Fundamentals of ISCO using Permanganate.- Fundamentals of ISCO using Persulfate.- Fundamentals of ISCO using Ozone.- Principles of ISCO Related Subsurface Transport and Modeling.- Principles of Combining ISCO with other In Situ Remedial Approaches.- Evaluation of ISCO Field Applications and Performance.- Systematic Approach for Site-Specific Engineering of ISCO.- Site Characterization and ISCO Treatment Goals.- Oxidant Delivery Approaches and Contingency Planning.- ISCO Performance Monitoring.- Project Cost and Sustainability Considerations.- ISCO Status and Future Directions.- Appendices.

Experimental Evaluation of Catalyzed Hydrogen Peroxide and Sodium Persulfate for Destruction of BTEX Contaminants

Due to the toxicity and prevalence of BTEX contaminants (benzene, toluene, ethylbenzene, and xylenes) at hazardous waste sites, approaches for their remediation are of interest, especially those that particularly address benzene, which is often the limiting factor for achieving regulatory cleanup at these contaminated sites. In situ chemical oxidation (ISCO) is a viable technology for BTEX destruction, and hydrogen peroxide and sodium persulfate are two oxidants of interest for BTEX treatment. Laboratory studies were conducted to compare BTEX contaminant destruction and oxidant persistence for these two oxidants and for varied methods of oxidant activation/propagation. Additionally, studies were performed to compare contaminant destruction and oxidant persistence in laboratory contaminant spike systems vs. field site contaminant systems. Finally, contaminant destruction and oxidant persistence in field porous media with varied characteristics were evaluated. Contaminant and oxidant concentrations were measured at multiple time points over a three-week reaction period in each oxidant and oxidant activation/propagation system. Under the comparable conditions evaluated here, sodium persulfate systems demonstrated greater BTEX contaminant destruction and greater oxidant persistence than hydrogen peroxide systems. FeSO4 and citric acid activation of sodium persulfate resulted in greater BTEX destruction and greater oxidant persistence than pH adjustment or hydrogen peroxide activation in both laboratory contaminant spike systems and field gas condensate systems. Additionally, results indicate that the response of the contaminant(s) and oxidant (extent and rate of depletion) are both contaminant-and porous media type-dependent.

Comparative study on oxidative treatments of NAPL containing chlorinated ethanes and ethenes using hydrogen peroxide and persulfate in soils

The goal of this study was to assess the oxidation of NAPL in soil, 30% of which were composed of chlorinated ethanes and ethenes, using catalyzed hydrogen peroxide (CHP), activated persulfate (AP), and H(2)O(2)-persulfate (HP) co-amendment systems. Citrate, a buffer and iron ligand, was amended to the treatment system to enhance oxidative treatment. Four activation/catalysis methods were employed: (1) oxidant only, (2) oxidant-citrate, (3) oxidant-iron(II), and (4) oxidant-citrate-iron(II). The NAPL treatment effectiveness was the greatest in the CHP reactions, the second in HP, and the third in AP. The effective activation and catalysis methods depended on the oxidant types; oxidant only for CHP and HP and oxidant-citrate-iron for AP. The treatability trend of chlorinated ethanes and ethenes in the soil mixture was as follows: trichloroethene > tetrachloroethene > dichloroethane > trichloroethane > tetrachloroethane. A significant fraction of persulfate remained in the oxidation systems after the 2-day reaction period, especially in the citrate-iron(II) AP. In general, oxidation systems that included citrate maintained a post-treatment pH in the range of 7-9. A final pH of AP oxidation systems was acidic (pH 2-3), where a molar ratio of citrate-iron(II) was less than 1.8 and where no citrate was amended.

Control of manganese dioxide particles resulting from in situ chemical oxidation using permanganate.

In situ chemical oxidation using permanganate is an approach to organic contaminant site remediation. Manganese dioxide particles are products of permanganate reactions. These particles have the potential to deposit in the subsurface and impact the flow-regime in/around permanganate injection, including the well screen, filter pack, and the surrounding subsurface formation. Control of these particles can allow for improved oxidant injection and transport and contact between the oxidant and contaminants of concern. The goals of this research were to determine if MnO(2) can be stabilized/controlled in an aqueous phase, and to determine the dependence of particle stabilization on groundwater characteristics. Bench-scale experiments were conducted to study the ability of four stabilization aids (sodium hexametaphosphate (HMP), Dowfax 8390, xanthan gum, and gum arabic) in maintaining particles suspended in solution under varied reaction conditions and time. Variations included particle and stabilization aid concentrations, ionic content, and pH. HMP demonstrated the most promising results, as compared to xanthan gum, gum arabic, and Dowfax 8390 based on results of spectrophotometric studies of particle behavior, particle filtration, and optical measurements of particle size and zeta potential. HMP inhibited particle settling, provided for greater particle stability, and resulted in particles of a smaller average size over the range of experimental conditions evaluated compared to results for systems that did not include HMP. Additionally, HMP did not react unfavorably with permanganate. These results indicate that the inclusion of HMP in a permanganate oxidation system improves conditions that may facilitate particle transport.

Enhanced permanganate in situ chemical oxidation through MnO2 particle stabilization: Evaluation in 1-D transport systems

In situ chemical oxidation using permanganate is an increasingly employed approach to organic contaminant remediation at hazardous waste sites. Manganese dioxide (MnO2) particles form as a by-product of the reaction of permanganate with contaminants and naturally-reduced subsurface materials. These particles are of interest because they have the potential to deposit in the subsurface and impact the flow regime in/around permanganate injection, including the well screen, filter pack, and the surrounding subsurface formation. Control of these particles can allow for improved oxidant injection and transport, and contact between the oxidant and contaminants of concern. Sodium hexametaphosphate (HMP) has previously been identified as a promising aid to stabilize MnO2 in solution when included in the oxidizing solution, increasing the potential to inhibit particle deposition and impact subsurface flow. The goal of the experimental studies described herein was to investigate the ability of HMP to prevent particle deposition in transport studies using four different types of porous media. Permanganate was delivered to a contaminant source zone (trichloroethylene) located within four different media types with variations in sand, clay, organic carbon, and iron oxides (as goethite) content. Deposition of MnO2 within the columns was quantified with distance from the source zone. Experiments were repeated in replicate columns with the inclusion of HMP directly with the oxidant delivery solution, and MnO2 deposition was again quantified. While total MnO2 deposition within the 60 cm columns did not change significantly with the addition of HMP, deposition within the contaminant source zone decreased by 25-85%, depending on the specific media type. The greatest differences in deposition were observed in the goethite-containing and clay-containing columns. Columns containing these two media types experienced completely plugged flow in the oxidant-only delivery systems; however, the addition of HMP prevented this plugging within the columns, increasing the oxidant throughput.

Release of chromium from soils with persulfate chemical oxidation.

An important part of the evaluation of the effectiveness of persulfate in situ chemical oxidation (ISCO) for treating organic contaminants is to identify and understand its potential impact on metal co-contaminants in the subsurface. Chromium is a redox-sensitive and toxic metal the release of which poses considerable risk to human health. The objective of this study was to investigate the impact of persulfate chemical oxidation on the release of chromium from three soils varying in physical-chemical properties. Soils were treated with unactivated and activated persulfate [activated with Fe(II), Fe(II)-EDTA, and alkaline pH] at two different concentrations (i.e., 41 mM and 2.1 mM persulfate) for 48 h and 6 months and were analyzed for release of chromium. Results show that release of chromium with persulfate chemical oxidation depends on the soil type and the activation method. Sandy soil with low oxidant demand released more chromium compared to soils with high oxidant demand. More chromium was released with alkaline pH activation. Alkaline pH and high Eh conditions favor oxidation of Cr(III) to Cr(VI), which is the main mechanism of release of chromium with persulfate chemical oxidation. Unactivated and Fe(II)-activated persulfate decreased pH and at low pH in absence of EDTA chromium release is not a concern. These results indicate that chromium release can be anticipated based on the given site and treatment conditions, and ISCO system can be designed to minimize potential chromium release when treating soils and groundwater contaminated with both organic and metal contaminants.

IN SITU Chemical Oxidation

This chapter presents a technology description of in situ chemical oxidation (ISCO) and discusses the key concepts associated with its use for remediation of chlorinated solvent dense nonaqueous phase liquid (DNAPL) source zones. A variety of oxidants are discussed including hydrogen peroxide, potassium permanganate, sodium persulfate and ozone. Current practices along with remedial design issues and approaches for application of ISCO to DNAPL source zones are described, including monitoring and optimization strategies. This chapter concludes with a discussion of emerging approaches and technologies, and a discussion of research needs and breakthrough areas.

Chemical Oxidation for Clean Up of Contaminated Ground Water

Contamination of soil and ground water by organic chemicals is a widespread problem across the U.S. and around the world. At sites where organic chemicals are present in the form of dense nonaqueous phase liquids (DNAPLs), clean up of contaminated ground water has been extremely difficult and costly; conventional ground water pumping and treatment approaches have commonly failed to achieve clean up goals. Major research and development efforts have been directed at finding alternative remedies that can clean up ground water and eliminate risks or reduce them to an acceptable level. Recent efforts have increasingly focused on source zone treatment of DNAPL contamination to reduce the volume and mass of DNAPLs available for dis- solution into ground water. A variety of in situ technologies have been developed and demonstrated, including in situ chemical oxidation (ISCO). ISCO involves the delivery of chemical oxidants into the subsurface to destroy organic chemicals (e.g., chlorinated organic solvents or fuels) and thereby remediate a site to a risk-based clean up goal. ISCO can feasibly be implemented alone to

Advances in Groundwater Remediation: Achieving Effective In Situ Delivery of Chemical Oxidants and Amendments

Contamination of soil and groundwater by organic chemicals represents a major environmental problem in urban areas throughout the United States and other industrialized nations. In situ chemical oxidation (ISCO) has emerged as one of several viable methods for remediation of organically contaminated sites. Many of the most prevalent organic contaminants of concern at sites in urban areas (e.g., chlorinated solvents, motor and heating fuels) can be destroyed using catalyzed hydrogen peroxide (H2O2), potassium permanganate (KMnO4), sodium persulfate (Na2S2O8), or ozone (O3) delivered into the subsurface using injection wells, probes, or other techniques. A continuing challenge for ISCO, as well as other in situ remediation technologies, is how to achieve in situ delivery and obtain simultaneous contact between treatment fluids, such as oxidants and amendments, and the target contaminants. During the past few years, advances have been made in several key areas including knowledge and know-how associated with: (1) use of amendments for enhanced delivery and distribution of treatment fluids in heterogeneous settings with zones of low permeability media, (2) use of direct push technology for targeted high resolution delivery of treatment fluids, and (3) use of monitoring and sensing methods for direct feedback for delivery control and evaluation of remediation effectiveness. This paper provides a summary of ISCO and highlights ongoing efforts to advance the effective in situ delivery of treatment fluids, with an emphasis on chemical oxidants and amendments, which can help achieve cleanup goals and protect groundwater and associated drinking water resources.