Ultrasound and Electrokinetic Treatment

Introduction to Ultrasonic Testing

2006-10-26T04:15:00.000-07:00

Introduction
Basic Principles
History
Present State
Future Direction

Physics of Ultrasound
Wave Propagation
Modes of Sound Waves
Properties of Plane Waves
Wavelength/Flaw Detection
Elastic Properties of Solids
Attenuation
Acoustic Impedance
Reflection/Transmission
Refraction & Snell's Law
Mode Conversion
Signal-to-noise Ratio
Wave Interference

Equipment & Transducers
Piezoelectric Transducers
Characteristics of PT
Radiated Fields
Transducer Beam Spread
Transducer Types
Transducer Testing I
Transducer Testing II
Transducer Modeling
Couplant
EMATs
- Lamb Wave Generation with EMATs
- Shear Wave Generation with EMATs
- Velocity Measurements with EMATs
- Texture Measurement I with EMATs
- Texture Measurement II with EMATs
- Stress Measurement with EMATs
- Composite inspection with EMATs
Pulser-Receivers
Tone Burst Generators
Function Generators
Impedance Matching
Data Presentation
Error Analysis
-

Measurement Techniques
Normal Beam Inspection
Angle Beams I
Angle Beams II
Crack Tip Diffraction
Automated Scanning
Velocity Measurements
Measuring Attenuation
Spread Spectrum
Signal Processing
Flaw Reconstruction

Calibration Methods
Calibration Methods
DAC Curves
Curvature Correction
Thompson-Gray Model
UTSIM
Grain Noise Modeling
References/Standards

Selected Applications
Rail Inspection
Weldments

Formulae and Tables
UT Material Properties
References

Quizzes
20 Question Quiz
35 Question Quiz
50 Question Quiz

Note: These quizzes draw from the same database of questions. Each time a quiz is opened, a new set of questions will be produced. The Collaboration for NDE Education does not record the names of individuals taking a quiz or the results of a quiz.

Online folders and links

2006-10-11T13:10:00.000-07:00

References of Literature Reviews

2006-10-11T00:55:00.000-07:00

References

1. Acar, Y. B. et al. Electrokinetic remediation: Basics and technology status. Journal of Hazardous Materials. 1995; 40:117-137.

2. Adewuyi YG. Sonochemistry: Environmental sciencce and engineering applications. Ind Eng Chem Res. 2001; 40:4681-4715.

3. Alshawabkeh AN. Basics and Applications of Electrokinetic Remediation. Federal University of Rio de Janeiro: 2001.

4. Aydin ME, Tor A, Özcan S. Ultrasonic solvent extraction of organochloride pesticides from soil. Analytica Chimica Acta. 2006; 559:173-180.

5. Blume T, Neis U. Improved wastewater disinfection by ultrasonic pre-treatment. Ultrasonics Sonochemistry. 2004; 11:333-336.

6. Cauwenberghe LV. Electrokinetics – Technology Overview Report. 1997.

7. Chemat S, Lagha A, Amar HA, Chemat F. Ultrasound assisted microwave digestion. Ultrasonis sonochemistry. 2004; 11:5-8.

8. Chung HI, Kamon M. Ultrasonically enhanced electrokinetic remediation for removal of Pb and phenanthrene in contaminated soils. Engineering Geology. 2005; 77:233-242.

9. Collings AF, Farmer AD, Gwan PB, Sosa Pintos AP, Leo CJ. Processing contaminated soils and sediments by high power ultrasound. Mineral Engineering. 2006; 19:450-453.

10. Concurrent Technologies Corporation, University of Pittsburgh. The Ground-Water Remediation Technologies Analysis Center (GWRTAC) <http://www.gwrtac.org/html/techs.html>. Accessed March 2006.

11. Dewulf J, langenhove HV, Visscher AD, Sabbe S. Ultrasonic degradation of trichloroethylene and chlorobenzene at micromolar concentration: Kinetics and modeling. Ultrasonics Sonochemistry. 2001; 8:143-150.

12. Emery RJ, Papadaki M, Mantzavinor D. Sonochemical degradation of phenolic pollutants in aqueous solutions. Environmental Technology. 2003; 24:1491-1500.

13. Entezari MH, Petrier C, Devidal P. Sonochemical degradation of phenol in water: A comparison of classical equipment with a new cylindrical reactor. Ultrasonics Snochemistry. 2003; 10:103-108.

14. Federal Remediation Technologies Roundtable (FRTR). Remediation Technologies and Screening Matrix <http://www.frtr.gov/matrix2/top_page.html>. Accessed March 2006.

15. Gedanken A. Sonochemistry and its application to nanochemistry. Current Science. 2003; 85(12)

16. Hanna Kyllönen H, Pirkonen P, Hintikka V, Parvinen P, Grönroos A, Sekki H. Ultrasonically aided mineral processing technique for remediation of soil contaminated by heavy metals. Ultrasonics Sonochemistry. 2004; 11:211-216.

17. Heerwani P. Envirotools.org Fact sheet <http://www.envirotools.org/factsheets/contaminatedsediments.shtml>. Accessed March 2006. State University - TOSC Program,

18. Ho, S. V. et al. Scale-up aspects of the lasagna™ process for in situ soil decontamination. Journal of Hazardous Materials. 1997; 55:39-60.

19. Hogan F, Mormede S, Clark P, Crane M. Ultrasonic sludge treatment for enhanced anaerobic digestion. Water Science and Technology. 2004; 50(9):25-32.

20. Hua I, Ulrike Pfalzer-Thompson. Ultrasonic irradiation of carbofuran: Decomposition kinetics reactor characterization. Wat Res. 2001; 35(6):1445-1452.

21. Ince NH, Tezcanli G, Belen RK, Apikyan G. Ultrasound as a catalyzer of aqueous reaction systems: The state of the art and environmental applications. Applied Catalysis B: Environmental. 2001; 29(3):167-176.

22. Jiang Y, Petrier C, Waite TD. Effect of pH on the ultrasonic degradation of ionic aromatic compounds in aqueous solution. Ultrasonic Sonochemistry. 2002; 9:163-168.

23. Jiradecha C, Urgun-Demirtas, M. Pagilla K. Enhanced electrokinetic dissolution of naphthalene and 2,4-DNT from contaminated soils. Journal of Hazardous Materials. 2005;

24. Joseph JM, Destaillats H, Hung H, Hoffmann MR. The sonochemical degradation of azobenzene and related azo dyes: Rate enhancement via Fenton’s reactions. Journal of Physical Chemistry Analysis. 2000; 104:301-307.

25. Joyce E, Mason TJ, Phull SS, Lorimer JP. The development and evaluation of electrolysi in conjunction with power ultrasound for the disinfection of bacterial suspension. Ultrasonics Sonochemistry. 2003; 10:231-234.

26. Khan FI, Husain T, Hejazi R. An overview and analysis of site remediation technologies. Journal of Environmental Management. 2004; 71:95-122.

27. Khay Chuan Teo, Yanrong Xu, Chun Yang. Sonochemical degradation for toxic halogenated organic compounds. Ultrsonics Sonochemistry. 2001; 8:241-246.

28. Kim SS, Kim JH, Hana SJ. Application of the electrokinetic-fenton process for the remediation of kaolinite contaminated with phenanthrene. Journal of Hazardous Materials. 2005; B118:121-131.

29. Kolosov, A.Y. et al. Electrokinetic removal of hydrophobic organic compounds from soil. Russian Journal of Applied Chemistry. 2001; 74:631-635.

30. Kyllönen H. Electrically or ultrasonically enhanced membrane filtration of wastewater.[dissertation]. Lappeenranta: Lappeenranta University of Technology, 2005.

31. Lens P, Grotenhuis T, Malina G, Tabak H. Soil and Sediment Remediation - Mechanisms, Technologies and Applications. IWA Publishing, 2005.

32. Manahan SE. Fundamentals of Environmental Chemistry. 2nd ed. CRC Press LLC, 2001.

33. Mao T, Hong SY, Show KY, Tay JH, Lee DJ. A comparison of ultrasound treatment on primary and secondary sludges. Water Science and Technology. 2004; 50(9):91-97.

34. Mason TJ. An Introduction to Sonochemistry <http://www.sonochemistry.info/research.html>. Accessed March 2006. 2005.

35. Mason TJ. Sonochemistry and sonoprocessing: The link, the trends and (probably) the future. Ultrasonics Sonochemistry. 2003; 10:175-179.

36. Mason TJ, Collings A, Sumel A. Sonic and ultrasonic removal of chemical contaminants from soil in the laboratory and on a large scale. Ultrasonic Sonochemistry. 2004; 11:205-210.

37. Mason TJ, Joyce E, Phull SS, Lorimer JP. Potential uses of ultrasound in the biological decontamination of water. Ultrasonics Sonochemistry. 2003; 10:319-323.

38. Maturi K, Reddy KR. Simultaneous removal of organic compounds an heavy metals from soils by electrokinetic remediation with a modified cyclodextrin. Chemosphere. 2005;

39. Mecozzi M, Amici M, Pietrantonio E, Romanelli G. An ultrasound assisted extraction of the available humic substance from marine sediments. Ultrasonics Sonochemistry. 2002; 9:11-18.

40. Meegoda JN, Perera R. Ultrasound to decontaminate heavy metals in dredged sediments. Journal of Hazardous Materials. 2001; 85:73-89.

41. Oh CH (ed). Hazardous and Radioactive Waste Treatment Technologies Handbook. CRC Press LLC, 2001.

42. Pamukcu S, Huang CP. In-situ Remediation of Contaminated Soils by Electrokinetic Processes. In: Hazardous and Radioactive Waste Treatment Technologies Handbook. CRC Press LLC, 2001:

43. Suslick KS. Summary of Sonochemistry and Sonoluminescence <http://www.scs.uiuc.edu/suslick/execsummsono.html>. Accessed March 2006. Suslick Research Group University of Illinois, 2005.

44. Suslick KS. Sonoluminescence and Sonochemistry. In: Meyers RA (ed). Encyclopedia of Physical Science and Technology. 3rd ed. San Diego: Academic Press, Inc, 2001:

45. Suslick KS. The chemical effects of ultrasound. Scientific American. 1989;

46. Terran Corporation. A Case for Electroosmosis Remediation <http://www.terrancorp.com/electrokinetic/acase/acase.htm>. 2004.

47. Tezcanli-Guyer G., Ince NH. Degradation and toxicity reduction of textile dyestuff by ultrasound. Ultrasonics Sonochemistry. 2003; 10:235-240.

48. TOTAL group. Report on soil contamination and remediation <http://www.total.com/en/group/corporate_social_responsibility/special_reports/soil/focus_on_soil/remediation_technologies_soil_7763.htm>. Accessed March 2006.

49. U.S E.P.A. In situ Remediation Technology – Electrokinetics. 1995.

50. U.S. Department of Energy. Innovative Technology Summary Reports. 1996.

51. Virkutyte J, Sillanpää M, Latostenmaa P. Electrokinetic soil remediation – critical overview. The Science of Total Environment. 2002; 289:97-121.

52. Wikipedia. The free encyclopedia <http://en.wikipedia.org/wiki/Main_Page>. .

53. Xuan Yin, Pingfang Han, Xiao Ping Lu, Yanru Wang. A review on the dewaterability of bio-sludge and ultrasound pretreatment. Ultrasonics Sonochemistry. 2004; 11:337-348.

54. Yang GC, Liu CY. Remediation of TCE contaminated soils by in situ EK-fenton process. Journal of Hazardous Materials. 2001; B85:317–331.

55. Yang J. Electrokinetic Remediation - Research Status & Case Study. EREL Environmental Remediation Engineering Laboratory, KAIST Korea Advanced Institute of Science and Technology,

56. Yasman Y, Bulatov V, Gridin VV, et al. A new sono-electrochemical method for enhanced etoxification of hydrophilic chloroorganic pollutants in water. Ultrasonics Sonochemistry. 2004;

57. Young FR. Cavitation. New York: McGraw-Hill, 1989.

Lasagna (tm)

2006-03-20T04:03:00.000-08:00

1. Summary

2. Technology Description

3. Performance

4. Technology Applicability & Alternatives

5. Cost

6. Regulatory/Policy Issues

7. Lessons Learned

Appendix A: References

Innovative Technology Summary
Lasagna (tm)

GNET makes these documents available in the Adobe Portable Data Format (.PDF) which can be read using the Adobe Acrobat Reader.

Summary:

Technology Description

Lasagna is an integrated, in situ remediation technology being developed by an industrial consortium consisting of Monsanto, E. 1. DuPont de Nemours & Co., Inc. (DuPont), and General Electric, with participation from the Department of Energy (DOE) Office of Environmental Management, Office of Science and Technology (EM-50), and the Environmental Protection Agency (EPA) Office of Research and Development (Figure 1).

Lasagna tm remediates soils and soil pore water contaminated with soluble organic compounds. Lasagna TM is especially suited to sites with low permeability soils where electroosmosis can move water faster and more uniformly than hydraulic methods, with very low power consumption. The process uses electrokinetics to move contaminants in soil pore water into treatment zones where the contaminants can be captured or decomposed. Initial focus is on trichloroethylene (TCE), a major contaminant at many DOE and industrial sites. Both vertical and horizontal configurations have been conceptualized, but fieldwork to date is more advanced for the vertical configuration. Major features of the technology are

electrodes energized by direct current, which causes water and soluble contaminants to move into or through the treatment layers and also heats the soil;
treatment zones containing reagents that decompose the soluble organic contaminants or adsorb contaminants for immobilization or subsequent removal and disposal; and
a water management system (not shown), which recycles the water that accumulates at the cathode (high pH) back to the anode (low pH) for acid-base neutralization. Alternatively, electrode polarity can be reversed periodically to reverse electro-osmotic flow and neutralize pH.

Technology Status

A proof-of-concept field demonstration was conducted at the Paducah Gaseous Diffusion Plant in Paducah, Kentucky.

U. S. Department of Energy
Paducah Gaseous Diffusion Plant (PGDP) Cylinder Drop Test Area (SWMU 91 )
Paducah, Kentucky
January 1995 through May 1995

The demonstration was sponsored by the DOE EM-50 Industrial Program through the Morgantown Energy Technology Center.

The PGDP site consists of a 4-ft layer of gravel and clay overlaying a 40-ft layer of sandy clay loam with interbedded sand layers. The clay soil had been contaminated with TCE at concentrations ranging from 1 ppb to 1760 ppm. Because of its very low organic content, the soil adsorbed very little TCE. The zone to be remediated measured 15-ft wide by 10-ft across and 15-ft deep, with average contamination of 83.2 ppm. The highest TCE concentrations (200-300 ppm) were found 12-16 ft below the surface. Steel panels were used as electrodes and the treatment zones consisted of wick drains containing granular activated carbon to adsorb the TCE. A plastic-wrapped shed was built above the test area, and a vent fan directed soil off-gas to an in-line filter for TCE capture.

Two patents covering the technology have been granted to Monsanto, and the term Lasagnatm has also been trademarked by Monsanto. Developing the technology so that it can be used with assurance for site remediation is the overall objective of the sponsoring consortium.

Key Results

Soil samples taken throughout the test site before and after the test indicated an average removal efficiency of 98% for TCE, with some samples showing greater than 99% removal. TCE soil levels were reduced to an average concentration of 1.2 ppm.
Flow rate by electroosmosis was 4 L/h, and three pore volumes of water (between adjacent treatment zones) were transported during the 4-month operating period.
Dense, non-aqueous-phase liquid (DNAPL) locations were cleaned to 1 -ppm levels except for a 15-ft deep sample that was reduced to 17.4 ppm (Note that because treatment zones were only 15-ft deep, diffusion from untreated deep zones may have contributed to the 17.4-ppm result.)
A TCE mass balance at test conclusion accounted for about 50% of TCE. Differences may be a result of passive diffusion (5%), evaporation (5%), in situ degradation of TCE during the test, or incomplete extraction of TCE from the activated carbon prior to analysis. About 20% (12 of 64) of the wicks were sampled. Given the highly nonuniform TCE concentrations in the soil and the limited sampling, a mass balance of 50% is an excellent result.
Based on the initial field tests, treatment costs for a typical 1-2-acre site with contamination to a depth of 40-50 ft were estimated to be about $50-$90/yd 3 of treated soil.

Phase II

A commercial-scale development demonstration (Phase Ila) is planned for the Paducah site in 1996, using iron filings in the treatment zones to dechlorinate the TCE in situ. The goal is to reduce soil contamination to 5.6 ppm or less in the 20 ft x 30 ft x 45-ft deep treatment zone. If successful, this will be followed by a full-scale first application demonstration (Phase II) encompassing the entire contaminated region (105 ft x 60 ft x 45-ft deep), with treatment accomplished in 12 to 24 months.

Contacts

Technical

Sa V. Ho, Principal Investigator, Monsanto, (314) 694-5179
Steven C. Meyer, Project Manager, Phase 11A, Monsanto Enviro-Chem, (314) 275-5946
Joseph J. Salvo, General Electric, (518) 387-6123
Stephen H. Shoemaker, DuPont, (713) 586-2513

Management

Skip Chamberlain, DOE EM-50 Program Manager, (301 ) 903-7248
Jim Wright, DOE Plume Focus Area Manager, (803) 725-5608
Kelly Pearce, DOE Contract Representative, (304) 285-5424

Paducah Site Support

Myrna Redfield, DOE EM-40 Program Manager, (502) 441-6815
Fraser Johnstone, Lockheed Martin Energy Systems Project Manager, (502) 441-5077
Jay Clausen, Lockheed Martin Energy Systems Technical Manager, (502) 441-5070

ELECTROOSMOTIC SOIL REMEDIATION

2006-03-20T03:34:00.000-08:00

ELECTROOSMOTIC SOIL REMEDIATION

Terran Corporation can solve your hard to treat soil contamination problems. Terran employs electroosmosis to mobilize volatile organic contaminants including DNAPLs from clay or mixed soil types. Our systems use inexpensive materials with expert design and conventional or novel treatment systems to remove tough organic contamination. Treatment systems can be ex-situ or in-situ and include the patented Lasagna^TM system.

Lasagna is a Registered Trademark of Monsanto Company, St. Louis, MO

We have prepared a short paper about electroosmosis.
A Case for Electroosmotic Remediation (PDF version of this paper)

We have also prepared two short presentations about electroosmosis.

Principles of Electrokinetics
The Latest on Lasagna

As each slide is displayed you can read notes that provide a brief description of the slide.

Terran’s current electroosmosis experience includes the design and implementation of the first Lasagna^TM site at DOE’s Paducah Gaseous Diffusion Plant for the in-situ treatment of TCE in clay using electroosmosis and zero valent iron treatment. Electroosmosis-induced pore water flow and elevated temperatures have been proven effective in the treatment of TCE in clay soils in a most cost efficient manner. At Paducah, the process reduced the soil concentrations from an average of 84 mg/kg (with a high of 1,500) to an average of 0.38 mg/kg (with a high of 4.5) in two years of operation. The project was highlighted in a recent "Technology News and Trends" newsletter (EPA, TIO). The Final RA Report for Paducah show the details of the installation and verification soil sampling.

Let Terran Corporation help you. If you have volatile organic contamination in a mostly clay soil, contact Chris Athmer or Brent Huntsman at 937-320-3601.

Additional References

Record of Decision (ROD) for Paducah Site Specifying Lasagna

GWRTAC Technology Overview Report - Electrokinetics

Rapid Commercialization Initiative Verification Statement for Lasagna^TM, March 2, 1998. This statement shows the agencies that recognize Lasagna as an acceptable remediation technology.

The Lasagna Technology for In Situ Soil Remediation. 1. Small Field Test, Sa V. Ho , Christopher Athmer, P. Wayne Sheridan, B. Mason Hughes, Robert Orth, David Mckenzie, Philip H. Brodsky, Andrew Shapiro, Roy Thornton, Josepy Salvo, Dale Schultz, Richard Landis, Ron Griffith and Steve Shoemaker, Environmental Science & Technology, 33, 7, 1086-1091, 1999.

Lasagna^TM Soil Remediation, U. S. Department of Energy, Innovative Technology Summary Report (Green Book).

Cooking Up Solutions, Cleaning Up With Lasagna^TM, United States Environmental Protection Agency, Solid Waste and Emergency Response, EPA505-F-99-004, April 1999.

Lasagna^TM/RTDF Technical Documents, Lasagna Remediation Technology, The Remediation Technologies Development Forum (RTDF).

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Contents

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Send mail to webmaster@terrancorp.com with questions or comments about this web site.

Innovative Technology Inventory (ITI)
Terran Corporation
Lasagna™

Company Address:
4080 Executive Drive
Beavercreek, Ohio 45430

Contact: Christopher Athmer
Phone #: 937-320-3601
Fax #: 937-320-3620
E-mail: cjathmer@terrancorp.com
Website: www.terrancorp.com

Technology Type:
Remediation

Technology Description:
Click here to enlarge the image
LasagnaTM is the integration of electroosmosis with in-situ treatment designed to provide uniform treatment of non-homogenous soils or clay and silt-laden soils. Electroosmosis is used to move soil pore water and contaminants to treatment zones placed in the contaminated area. A set of steel electrodes and a series of treatment zones are emplaced around and in the contaminated soil with little or no waste soil. A DC voltage is applied to the electrodes causing pore water and contaminants to move towards the negative electrode in a very uniform manner. Intercepting treatment zones are designed to destroy or capture contaminants in-situ. Soil Heating is an additional benefit to using electroosmosis when treating volatile organics. Soil temperatures can easily reach 80oC in moderately conductive soils causing increased mobilization of volatile species. The entire soil mass between the electrodes is affected. According to Terran Corporation, uniform pore water movement and elevated soil temperatures make electroosmosis the most effective way to remediate contamination in silts and clays.

Application:
Lasagna is best suited for fine-grained soils like clay and silt or heterogeneous soils. Electroosmosis, unlike hydraulic or diffusion processes, is not sensitive to pore size. Lasagna is a proven technology for trichloroethylene (TCE) at DNAPL or pure phase levels of contamination in clay using zero valent iron treatment zones. The technology can be easily adapted to other contaminants using similar treatment schemes.

Environmental Benefits: The primary environmental benefit is the cleanup of contaminated soil with a minimum of disruption to the soil and the surrounding area. Minimal waste is produced and no contamination is brought above ground. Exposure to site personnel and site neighbors is kept to a minimum.

Performance:
At a Department of Energy (DOE) site in Paducah, KY, TCE contaminated soil was treated effectively using the Lasagna process. The levels of contamination before treatment were as high as 1500 mg/kg and post treatment levels were around 1 mg/kg. According to Terran Corporation, lower levels can be achieved. The DOE site is approximately 10,000 cubic yards and the depth treated was 45 feet. Larger and deeper applications are definitely possible.

Limitations:
Lasagna does not work well in sandy soils where there is not enough hydraulic resistance to create significant electroosmotic gradients. That is, forward movement generated by electroosmosis is countered by the prevailing hydraulic flow. Highly electrically conductive soils such as coastal or saline soils are also not practical due to the high current draw and excessive soil heating.

Cost:
Cost for Lasagna is about $50 - $100 per yard depending on the scale of application. A large portion of the cost is the installation of the materials (capital). The operational costs are low. The primary operational cost is electricity. Once installed, there is minimal site inspection required. System monitoring can be done remotely.

Electrokinetics for Environmental Restorations

2006-03-20T03:31:00.000-08:00

http://www.terrancorp.com/electrokinetic/present/NewPrinciples/New%20EK%20Presentation_files/v3_document.htm

Electrokinetics for Environmental Restorations

Electrokinetic
Effects

Main EK Processes

Principles of Electrokinetics

Slide 5

Electrokinetic vs. Hydraulic
Conductivity

Comparison of Electroosmotic Permeability and Hydraulic Conductivity for Various Soils

Temperature Plays a Big Part !!

Effects of Elevated Temperatures

Decrease in Viscosity off-sets Increasing Electrical Conductivity

Problems to Overcome

Problems to Overcome
(especially with electromigration)

Ion Concentration Gradients

Slide 14

Some Solutions

Electromigration

Electroosmosis

The 1-2 Punch of Electroosmosis

Comparison of Some Remediation Technologies

Innovations Made

Key Soil Properties

Electrokinetic Remediation

2006-03-16T05:13:00.000-08:00

http://www.gec.jp/SGC_DATA/EN/html/sgce-032.html

Soil and Groundwater Contamination Survey and Countermeasure Technologies

Electrokinetic Remediation

Category of Tchnology	Treatment	In Situ Extraction Technology
Media	Soil, Groundwater
Contaminants	Heavy Metal (Cd, Pb, As, Hg, Se, etc) Inorganic Compounds (total CN, etc) Reducible Inorganic Compounds (Cr⁶⁺, etc) Volatile Chlorinated Organic Compounds (TCE, PCE, etc)
	Applied (Demonstrated) Substances	Hexavalent Chromium Cr (VI)
Scope	Concentration Range
	Hydrogeological Conditions	Saturated Unsaturated	Permeable Layer
	Chemical Soil Properties	The care must be taken in dealing with the soil containing a large quantity of chloride (halogen) ion.
	Other Remarks
Technology Description	Classification
	Status	Under Demonstration Soil and Groundwater Countermeasure Test Study (Performed 1995)
	Outline of Technology	The contaminated ground is saturated with water, and a direct current is passed through the ground. Chromium in the form of Cr (VI) are attracted to the anode by electric charge, and so could be removed by draining the water around the anode. This treatment derives its supply of water from ground water pumped up.
	Required Pre- and Post-treatment	It is necessary to treat draining water containing contaminants.
	Enhance Effectiveness through Combination
	Case History	The 10m³ tank was filled with Chromium contaminated soil (Cr content is 8,590-10,100mg/kg), and 40-60V DC was passed through this soil for 88 days. It was shown that water-soluble chromium content decreased from the initial value of 32-36 mg/l to 11mg/l.
	Application Examples	None
	Limitations	When this technology apply to partially saturated soil, the soil must be saturated with water by setting up a cut-off wall.
	Properties of Treated Soil	Properties are Generally Retained
Schematic Flow Process	(Example in case of Cr (VI) contaminated soil)
Applicability	In Situ Applicability	Possible
	Ground Structures	Not Applicable
	Required Excavation	There are some cases where the establishment of cut-off wall needs excavation of soil.
	Groundwater Extraction
	Required Space
	Operational Time	This remedial speed is not so fast, so it takes a lot of time occasionally.
	Installation Time
	Maintenance and Control Requirements	water supply, drainage, disposal of sludge
	Additional Remarks
Secondary Impacts to Environment	Secondary Treatment Required?	Effluent Water Treatment
	Effects on Living Environment	Others (stray current)
	Additives	Water
	Possibility of Contaminant Spreading	None
	Secondary By-products	It can be considered theoretically that Cl2 gas occur by electrolysis in the case of this treatment applying to the soil containing a large quantity of Cl ion.

(July 2002)

Understanding the Contamination Survey and Countermeasure Technology Description Sheet

Where to make contact

Soil Environment Management Division, Water Environment Department, Environmental Management Bureau, Ministry of Environment
Tel: +81-3-5521-8319
E-mail: MOE@env.go.jp

Electrochemistry Encyclopedia

2006-03-16T05:11:00.000-08:00

(http://electrochem.cwru.edu/ed/encycl/)

ENVIRONMENTAL ELECTROCHEMISTRY

Jorge G. Ibanez
Department of Chemistry and Chemical Engineering
Mexican Microscale Chemistry Center
Iberoamericana University
Prol. Reforma 880
01210, Mexico D.F., Mexico
E-mail: jorge.ibanez@uia.mx
(March, 2004)

The search for alternatives to better our environment is imperative. The voluntary or involuntary contributions to its degradation have grown to the point that the health of many people and of ecosystems is seriously threatened. A bird's eye view of the substances involved in the pollution arena allows one to note that most of them can normally be subject to either an oxidation or a reduction. For example, compounds containing highly oxidized chromium are quite toxic whereas their reduced counterparts are much less dangerous (in fact, chromium compounds in reduced form are essential nutrients). In other words, simple electron transfer can change a compounds toxicity, probably as a result of the concomitant geometry and standard potential changes. Likewise, many organic compounds lose their toxicity upon oxidation (often all the way to carbon dioxide). Such an electron transfer can frequently be achieved on an electrified surface (electrode); this opens a wide door for the electrochemical treatment or destruction of pollutants.

In the same vein, the application of an electric signal and the monitoring of the resulting current or voltage can detect most of these substances. A series of electroanalytical techniques offers the possibility of performing a plethora of qualitative or quantitative determinations of pollutants in a variety of matrices. Some examples include: polarography, voltammetry, chronopotentiometry, chronoamperometry, etc. In addition, many substances are analyzed by other techniques that make use of electrochemical detectors. Electrochemical techniques offer increasing degrees of accuracy and detection limits, often involving dramatically lower costs than other techniques.

In addition, electrochemistry offers a series of advantages that in many cases can be used to make "green" processes. Some include the minimization of waste emissions by improved process design involving the minimization of by-product formation, raw material usage, and energy consumption.

In this way, electrochemistry offers important degrees of:

Environmental compatibility. Electrons are clean reagents per se.
Energetic efficiency. Electrochemical processes are not subject to some limitations inherent to other processes.
Cost. Among the reducing agents commonly employed, electrons have the lowest cost per unit of charge. In addition, electrochemical reactors normally do not require moving parts, and thus are mechanically simple and of relatively low maintenance.
Versatility. The same electrochemical reactor can often be used for a more than one purpose.
Ease of automation. The main variables in electrochemical reactors are current and voltage that are ideally suited for process automation, optimization, monitoring, and control.
Friendly requirements. Contrary to other techniques or processes like incineration, supercritical oxidation, wet oxidation, etc., electrochemical techniques normally do not require high temperature or pressure.
Selectivity. An adequate combination of experimental conditions (electrolyte composition, temperature, degree of convection, applied potential, current) and reactor characteristics (shape, size, construction materials, electrode materials, membranes) can be judiciously selected as to prevent or minimize energy waste and by-product generation. Such by-products not only mean a waste of materials, but also introduce additional difficulties for their separation and/or disposal.

In spite of these advantages, there are also some challenges to be faced:

Electrode materials may be prone to erosion, complexation, oxidation, wearing, or inactivation.
Since most of the electrochemical processes are performed in aqueous solutions, solvent decomposition (that is, water oxidation/reduction) is often hard to avoid and thus there is a concomitant energy waste.
The production of gases from the above decomposition (hydrogen and oxygen) may form explosive mixtures.
The best electrode materials in terms of durability and inertness frequently involve precious metals, and this increases costs.
The cost of electricity in many areas is prohibitive.
Initial capital investment may be large.
The lack of knowledge or understanding of electrochemistry is perhaps the greatest hindrance for its utilization.

The commercial availability of many electrochemical reactors and systems for the applications discussed below attests to their maturity as competitive technologies in the environmental arena.

The literature on these processes is quite abundant, and this article is not intended as a detailed review. Interested readers are encouraged to seek other general or specific sources according to their needs (see the Bibliography). Instead, a summary of the main concepts as applied to these processes is given below. Note that physical states of reactants or products are only given when they are not aqueous.

Direct and indirect processes

Fig. 1. Electron-transfer schemes for direct (left) and indirect (right) processes.

It is often possible to transfer electrons directly from an electrode to an electroactive species or vice versa. These are called "direct" processes. In other instances this is not possible since the target species may not be electroactive (that is, capable of receiving or donating electrons at an electrode), or else the rate of the reaction may be extremely slow.

To circumvent these impediments one can generate active species (called "mediators") at the electrodes, which are capable of moving into the solution and react there with the target pollutant. Such processes are called "indirect" processes. An advantage here is that the reaction takes place in a homogeneous fashion, and thus the diffusion of the pollutant towards the electrode is not the rate-determining step of the overall process, and thus the effect of low concentrations does not impair the whole reaction pathway. Depending on whether the mediator can be regenerated or not, the process is called "reversible" or "irreversible", respectively. (See Figure 1.)

Direct processes

Direct oxidations

Many organic pollutants (and some inorganics as well) are treated by direct oxidation at anodes of different materials. The materials selection must take into account issues such as cost, accessibility, stability at the required potentials, selectivity, the composition and pH of the reaction medium, the nature of the intermediates and products, and the environmental compatibility. Likewise, the main secondary reaction in aqueous media is water oxidation, which may greatly decrease yields and increase costs (equations of the chemical reactions occurring in this and other processes are shown in the Appendix). In order to avoid the oxidation of water, researchers have developed electrodes that make this reaction to become very slow and thus require an overpotential. A modern example is the boron-doped diamond electrode that is quite durable, resists oxidation, and has a large overpotential for oxygen production; this last property makes possible the oxidation of other substances with standard potentials higher than that for the oxidation of water. Substances that have been treated by this technique include:

Organic compounds. Phenols, aromatic amines, halogenated compounds, nitrated derivatives, fecal wastes, dyes, aldehydes, carboxylic acid anions, etc.

Inorganic compounds. Perhaps the inorganic substance that has been most commonly treated by the electrochemical route is cyanide. The main product is the much less toxic cyanate ion.

Direct reductions

In parallel with the above discussion concerning oxidations, the main secondary reaction here is water reduction. The hydrogen thus produced (high purity, electrolytic grade) can sometimes be sold. There are efforts to utilize it in devices such as fuel cells that work with higher efficiencies than the combustion engines.

The electrochemical reduction processes that have reached the highest degree of maturity are undoubtedly those for metal ion recovery from their dissolved ions, as discussed below. Other noxious compounds amenable for direct reduction include:

Organic compounds. The cathodic dehalogenation of chlorinated hydrocarbons (many of which have been classified as toxic and/or carcinogenic) has a triple advantage:

electrons are selectively used for the removal of the halide and produce a skeleton amenable for further treatment by cheaper methods (for example, biodegradation),
chloride ions are produced as by-product, and are not environmentally dangerous, and
the treatment does not require additional substances to be completed.

Organic acids have also been reduced in this way to the corresponding alcohols or phenols.

Inorganic compounds. These include chromates, oxychlorinated species (for example, chlorites and chlorates), oxynitrogenated ions (nitrates and nitrites), etc. Metallic ions are treated next.

Metallic ions. Among the most penalized metals in environmental legislation are: cadmium, copper, chromium, mercury, nickel, silver, lead, and aluminum. Fortunately for our environment, their concentrations are typically small. However this introduces an additional complication for their treatment in electrochemical reactors since mass transport becomes severely limited. To counter this, electrochemists have designed reactors that promote more turbulence and higher contact areas. Three-dimensional and moving electrodes offer promising alternatives, many of which have already been implemented in commercial processes.

Indirect processes

Indirect oxidations

Among the main problems with direct oxidations is the large amount of electrons required for the complete oxidation (that is, all the way to carbon dioxide) as well as the large variety of intermediates. Sometimes the intermediate is even worse than the parent pollutant. Other times, intermediates polymerize and block the electron transfer surface. An alternative to circumvent these problems is to use indirect processes capable of the in situ production of oxidizing or reducing agents at the anode or cathode, respectively. These agents produce oxidation or reduction of pollutants.

Among the most popular oxidants are:

Hydrogen peroxide, which can be formed by the reduction of dissolved oxygen at basic pH.

Metallic ions in higher than normal oxidation states. For example, doubly charged silver cation is an excellent oxidizer for organophosphorous, organosulfur, and chlorinated compounds, both aliphatic and aromatic. Triply charged iron cation is also an oxidizer – albeit much weaker – that can also be used in successful cases of degradation of grease, cellulose derivatives, urea, meat packing wastes, sewage water, carbonaceous fuels, etc. Cerium ions are well known oxidants used in organic synthesis reactions; they are now used in an environmental application to destroy organic pollutants and munitions residues, converting them into innocuous carbon dioxide. When doubly charged manganese cation is electrochemically oxidized to triply charged cation, these ions can also oxidize pollutants on their own. Insoluble metallic oxides such as bismuth oxide and cobalt oxide have also been proposed for this application.

The production of basic hydroxide ions at the cathode can facilitate removal of water hardness-causing species, for example calcium.

On the other hand it is now common to find wastewaters containing emulsions, formed with water and a dispersed immiscible liquid (for example, in gasoline stations and oil extraction sites). To counter this type of pollution, an electrical field may be used to break up the emulsion since another electrical field can destabilize dispersions formed by charge stabilization. This phenomenon can be coupled to the electrochemical production of flocculating-coagulating agents (like aluminum and iron hydroxides) and the production of a gas (typically hydrogen). As a result of this flocculation-coagulation, pollutants are removed. The resulting solid is a low-density waste due to the flotation action by the gas, which facilitates its separation from the aqueous phase. This is also applied to the removal of dyes that impair the passage of light to the lower parts of aquifers, thus interfering with natural cycles. (Flotation is a process also used in the separation of metal ores.)

Indirect reductions

An example of indirect reductions is that of nitrates and nitrites at electrodes covered with metallophthalocyanines, which act as catalysts. Depending on process conditions, the products may be as innocuous as nitrogen.

Hybrid processes for the treatment of aqueous wastes

Fig. 2. Coupled electrochemical-biological treatments. (From: "Environmental Electrochemistry" K. Rajeshwar and J. G. Ibanez, Academic Press, 1997.)

In view of the complexity of the different wastes to be treated by biological processes (some of which are refractory, highly toxic, etc.), some hybrid alternatives offer the possibility for partial electrochemical degradation (for example, the transformation of a non-biodegradable material into biodegradable). This involves large electricity savings, since in order to completely oxidize for example a molecule of benzene, thirty electrons need to be removed! However, partial oxidation of this same molecule can be done to produce the biodegradable organic acids (such as: fumaric, maleic, oxalic, etc.). This process requires much less electrons per molecule. Such products are then amenable for biological treatment. (See Figure 2.) Other alternatives consist of hybridizing electrochemical processes with catalytical, photochemical, sonochemical, or microwave-induced processes.

Processes based on ion exchange

Aqueous industrial wastes can be difficult to treat due in part to their high salinity, high metal content, or pH values that fall outside the limits set by environmental regulations. Then a double incentive becomes attractive since one can prevent pollution, and at the same time also recover valuable materials by recycling, reusing, or recovering metals. An electrochemical method that has been used for quite some time is electrodialysis that is based on the application of an electric field to guide ion migration and – through the use of ion-selective membranes – concentrate solutions of waste ions and dilute the waste streams. A high degree of selectivity can thus be achieved. Such processes have been successful and their applications extend well beyond the environmental arena. Typical examples include: nitrate removal, boron elimination, desalination of brackish water, nitric acid concentration, glycerin recovery, etc.

Some of the processes involving anion or cation selective membranes are called electrohydrolysis due to the fact that hydrogen ions from water electrolysis hydrolyze the target salt. Some others are called electro-electrodialysis since there is an electrolytic component besides simple electrodialysis. Some examples include:

Fig. 3. Membrane cell electrolysis; top: two-compartment cell, bottom: three-compartment cell. (From: "Environmental Electrochemistry" K. Rajeshwar and J. G. Ibanez, Academic Press, 1997.)

Two-compartment cells. Here, sodium cations migrate towards the cathode where they encounter the hydroxyl anions produced by water reduction (or else by oxygen reduction). This produces sodium hydroxide. In the same way, hydrogen cations produced at the anode react with the sulfate ions in solution to yield sulfuric acid. In summary, using a waste salt as starting material, the corresponding generating acid ("father" acid) and the generating base ("mother" base) can be recovered. (See Figure 3.)

Three-compartment cells.Much like the above process, sodium ions migrate towards the cathode and form sodium hydroxide with the hydroxyl ions produced there, while the sulfate ions migrate towards the anode and produce sulfuric acid. The effluent from the central compartment is a dilute solution of the original feed.

Recent developments in the field include the design and production of bipolar membranes, consisting of two membranes "glued" together (one cationic, one anionic); the result is that water is broken at the interface into its component ions: hydrogen and hydroxyl ions that migrate towards the cathode and anode, respectively. During their migration they react with the target salt to yield its "father" acid and its "mother" base. An advantage in using bipolar membranes is the low energy used (since water "dissociates" rather than being "electrolyzed", and the voltage is used for driving the ion migration rather than for electrolysis). The membranes used in these electrochemical processes are typically organic in nature, with ionizable groups bonded to a highly stable (both mechanically and chemically) organic skeleton.

Membrane-based separation technologies are now an important component in many chemical industries and further applications are on sight. In electrochemical applications alone, membrane sales have soared up to 500% in one year. A clever spin-off technology involves usage of an ion exchange medium (typically resins) bonded onto an electrode surface. The resin adsorbs the target pollutants from an aqueous solution that are later eluted by a polarity change into a separate chamber. This method is called "electrochemical ion exchange (EIX)".

Water disinfection

Fig. 4. Electrolytic generation of microorganism deactivators.

The practice of eliminating unhealthy microorganisms in water dates back to ancient times. There are innumerable treatises on the disinfection of water, including brackish water, sewage water, cooling water, etc. The purpose of this section is to give a brief review of the application of electrochemical methods for the production of disinfection agents.

It is necessary to distinguish here between disinfection and sterilization. The first refers to the deactivation of "pathogen" (disease causing) microorganisms, whereas the second refers to the deactivation of all microorganisms present in the target medium. Mechanisms for such a deactivation include modification of, or attack to:

The cell wall (rupture, property modification).
The cell internal components (protoplasm or nucleic acid modification, alteration of protein synthesis, fatal induction of abnormal redox processes).
The enzymatic activity.

The disinfecting agents most commonly used have properties as oxidants. This makes them useful for the deactivation of most microorganisms, but also brings about undesirable effects such as the discoloration of dyes and the attack of some organic substances. This has an additional drawback in the sense that such effects involve the consumption of extra amounts of the disinfecting agent, thus elevating the corresponding costs. Furthermore, some of these disinfecting agents can produce "disinfection by-products" (DBP) upon their addition or reaction with organic substrates. Such DBP's are frequently toxic, as is the case of most chlorinated hydrocarbons.

The main disinfectants produced by the electrochemical route can be classified according to the oxidizing element as (Figure 4):

Chlorine-based: chlorine gas, hypochlorite, hypochlorous acid, and chlorine dioxide.
Oxygen-based: ozone, hydrogen peroxide, and hydroxyl radicals.
Others: permanganate, ferrate, ions of other transition metal ions (for example copper and silver), percarbonate, persulfate, other halogens and derivatives (for example, bromine, iodine), and the electrochemical production of high levels of acidity or basicity.

Gases

The conventional processes for the remediation of gases are not always flexible enough as to face flow discontinuities, large concentration variations, or the presence of dust particles. On the other hand, wet processes normally consume large amounts of chemicals, and the final products have low commercial value. In addition, sludge generation can be quite large. For these reasons, the electrochemical route has found a market niche for the treatment of various gases, as discussed below. (See the Appendix for some schematic reactions.)

Carbon dioxide

Carbon dioxide reduction is – in principle – attractive from several stand points. On one hand it is a very abundant substance in the atmosphere, and is a large contributor to the "green house effect". If a synthetic route based on carbon dioxide could be found, not only humanity would have an almost inexhaustible source of raw material, but also the danger of global warming could be greatly reduced. Carbon dioxide is relatively easy to handle, and has very low toxicity. Its reduction products are quite varied according to the reaction conditions, ranging from saturated hydrocarbons (with four or less carbon atoms) and ethylene, to small linear alcohols (with three or less carbon atoms), carbon monoxide, formic acid, and oxalic acid. However, it is not clear at present whether these reactions can ever be made energetically and economically viable.

Nitrogen oxides

Nitric oxide is the most problematic oxide of this family due to its low solubility in water that impedes its removal from a gas stream by absorption in aqueous solutions. This is the main component of chimney gases. Reactive dissolution can do the trick by oxidizing it, or by forming a soluble nitric oxide complex (for example with iron aminopolycarboxylic chelates). It can then be reduced at a later stage.

Nitrogen dioxide is soluble and can be electrochemically reduced by direct or indirect processes. For example, direct reduction in an acid solution can yield nitrogen gas; an indirect method with thiosulfate (that can then be regenerated) also produces nitrogen.

Nitrous oxide is also much more soluble than nitric oxide and can be captured by solutions of amines; it can also be electrocatalytically reduced to nitrogen in basic or acidic media.

Sulfur-containing gases

The sulfur geochemical cycle is among those that has been most altered by human activity, mainly fossil fuel and biomass combustion. Most sulfur in the gas phase is in the form of sulfur dioxide (and a smaller portion as hydrogen sulfide).

Hydrogen sulfide. Once removed by absorption, this gas can be recovered by the thermal regeneration of the absorbing liquid and sent to the Claus process for the recovery of elemental sulfur (See the Appendix). Unfortunately this process has several limitations, as the hydrogen from hydrogen sulfide is essentially wasted (since it forms water); also, the required conditions are not flexible enough as to withstand sensible variations in hydrogen sulfide composition, and post-treatments are required. Some modern methods involve the use of oxidants such as hydrogen peroxide, and highly oxidized iron species that can often be regenerated in an external cell process and returned to the absorber unit.

Sulfur dioxide. "Flue Gas Desulfurization" processes (FGD) remove sulfur dioxide by its irreversible reactive absorption with lime or limestone, or by its reversible absorption in sodium citrate solutions. There are many electrochemical methods that have been studied for this purpose. Most of these involve the direct or indirect oxidation of sulfur dioxide to sulfate ion, although some involve its reduction to elemental sulfur.

Sulfur trioxide. A technically and economically viable process for the selective removal of sulfur trioxide from thermoelectrical plants uses high temperature, 500^oC (932^oF), for its selective removal by a molten electrolyte.

Other gases

Hydrocarbons. Solid electrolyte cells provide heterogeneous catalysis for their treatment by oxidation.

Chlorine. Waste and impure chlorine can be treated by its dissolution in a metal ion solution, whereby chlorine oxidizes metallic ions and becomes reduced to chloride ions. These are then sent to the anodic compartment of a divided cell to be re-oxidized and produce pure gaseous chlorine.

Electrokinetic treatment of soils

Fig. 5. Electrokinetic remediation of soil. (From: "Environmental Electrochemistry" K. Rajeshwar and J. G. Ibanez, Academic Press, 1997.)

The pollution of soils, sediments and wetlands is a very serious problem. The application of electric fields has gained considerable ground for the treatment of a wide variety of polluted soils. It is based upon the passage of electrical current through electrodes strategically buried underground. This originates the movement of charged (and some uncharged) species due to three main phenomena: electrophoresis, electroosmosis, and electromigration. (Figure 5.)

Electrophoresis involves the movement of charged particles (typically colloids) under the influence of an electric field.

Electroosmosis involves the movement of the solvent (typically water) within the soil pores, due to the formation of an electric double layer between charged surface particles and dissolved ions or solvent dipoles. The external field then attracts the solvent, which in turn drags dissolved species. This phenomenon is known since the middle of the past century by civil engineers, who use it for the removal of humidity from soils, walls, and roofs. Waste wet solids or sludge can also be dewatered in this way.

Electromigration consists of the movement of ionic species in the liquid phase towards the oppositely charged electrode.

Electrokinetic remediation (also called electroreclamation, electrorestoration, electroremediation, electrokinetic processing, or electropotential ion transport) has been used for a variety of applications. Among the species in soils that have been treated with this technique are organic substances (benzene, toluene, ethyl benzene, xylenes, gasoline, warfare agents, acetates, phenols, trichloroethylene, etc.), inorganic species (metallic ions of zinc, mercury, cadmium, nickel, lead, chromium, copper, iron, and silver, in addition to anionic forms of arsenic, chloride, nitrate, sulfate, and cyanide anions, complexes, etc.) as well as radioactive substances. This technique is also in use for the clean up of sludge and groundwater.

Electrokinetic remediation is also used in combination with biological remediation in cases where the organic pollutant is very insoluble or else has a large mass/charge ratio. The problem with soil bioremediation alone is the difficulty for the transportation of oxygen and nutrients to microorganisms, and the requirement of temperatures somewhat higher than ambient. Fortunately, electrokinetic remediation is capable of transporting the necessary oxygen and nutrients in the remediation fluid; also, the passage of electrical current generates some heat that helps to reach the necessary temperature for bioremediation, and facilitates the movement of microorganisms in a directed way (after all, they have a certain surface charge). Thus, the combination of both techniques is a promising route. Numerical simulations of electrokinetic phenomena are an important aid in the calculation of the required parameters for an efficient use of the current.

Electrochemical recycling

The recycling of pollutants is one of the main ways in which an industry can balance its productive activity with environmental care. If a process consumes recyclable materials it is advantageous from at least two standpoints, since it does not add to pollution and it recovers useful materials. In this way, electrochemical processes can be used for the recycling of toxic materials used as reagents or catalysts in chemical processes. For example, a highly oxidized chromium species is used as an oxidizer in the synthesis of anthraquinone. The resulting reduced chromium species can then be electrochemically reoxidized, and reused in the main process. A field in which this approach is quite promising – and that has not been fully exploited – is that of battery and catalyst recycling.

Interestingly, oxidized electronic components that cannot be soldered due to the presence of oxide layers on their surfaces can be chemically reduced to restore their solderability, and the spent reducer can be electrochemically regenerated.

Commercial applications

Many of the techniques discussed in this review have reached the commercial stage. This means that they are competitive with other alternative techniques. In this brief review they cannot be summarized. For example, effluents from the following industries or activities are electrochemically treated: pharmaceutical, textile, veterinary, food processing, polymers, chemicals, pulp and paper, agricultural, etc. As discussed above, many soils, gases, and hazardous, toxic, or radioactive wastes are now treated electrochemically. The book written by Rajeshwar and Ibanez gives an account of companies devoted to these endeavors (see the Bibliography).

Concluding remarks

Electrochemical techniques and processes offer important alternatives for the monitoring, prevention, and remediation of the environment. This overview focused on the remediation aspect, emphasizing direct and indirect processes, with discussions of applications for the treatment of gases, liquids, and soils as well as for water disinfection. The battle to preserve our environment is a fierce one; hopefully this account gives an overview of many of the ways in which electrochemistry contributes with its best munitions.

Appendix

Some reactions occurring in the above described processes

[1]	2H₂O_(l) ==> O_2(g) + 4H⁺ + 4e^-	(water oxidation)
[2]	2H₂O_(l) + 2e^- ==> H_2(g) + 2OH^-	(water reduction)
[3]	R–Cl + 2H⁺ + 2e^- ==> R–H + HCl	(dehalogenation of hydrocarbons)
[4]	HCO₃^- + OH^- ==> CO₃^2- + H₂O_(l)	(hardness removal – 1)
[5]	Ca²⁺ + CO₃^2- ==> CaCO_3(s)	(hardness removal – 2)

[6]	H₂S_(g) + 3/2O_2(g) ==> SO_2(g) + H₂O_(g)	(Claus process – 1)
[7]	H₂S_(g) + SO_2(g) ==> 2S_(g,l) + H₂O_(g,l) + 1/2 O_2(g)	(Claus process – 2)

Electrochemical treatment of gaseous pollutants

The only products shown are those that contain the main atom. Reactions are not balanced, and physical states are omitted for clarity.

CO₂ + (ne^- + nH⁺) ==> (HCOO)₂, HCOOH, CO, C, HCHO, CH₃OH, CH₄

H₂ ==> S, S₂, SO₄^2-, H₂S_(conc) + (ne^- + H₂)

SO₂ ==> SO₃, H₂SO₄ + (ne^-)

SO₂ + (ne^-) ==> S

NO + (ne^- + nH⁺) ==> N₂, N₂O, NH₂OH, NH₃

NO₂ + (ne^- + nH⁺) ==> NH₃

N₂O + (ne^-) ==> N₂

Bibliography

Environmental Electrochemistry, K. Rajeshwar and J. G. Ibanez, Academic Press, San Diego, CA, 1997.
Electrochemical Membrane Flue-Gas Desulfurization: K₂SO₄/V₂O₅ Electrolyte, D. S. Schmidt and J. Winnick, "American Institute of Chemical Engineers Journal" Vol. 44, pp 323-331, 1998.
Steady State and Limiting Current in Electroremediation of Soil, J. M. Dzenitis, "Journal of The Electrochemical Society" Vol. 144, pp 1317-1322, 1997.
Ferrate(VI) Oxidation of Hydrogen Sulfide, V. K. Sharma, J. O. Smith, and F. J. Millero, "Environmental Science and Technology" Vol. 31, pp 2486-2491, 1997.
Environmental Oriented Electrochemistry, C. A. C. Sequeira (editor), Elsevier, Amsterdam, 1994.
Electrochemistry for a Cleaner Environment, D. Genders and N. Weinberg (editors), The Electrosynthesis Company Inc., East Amherst, NY, 1992.
Industrial Electrochemistry (2^nd edition), D. Pletcher and F. Walsh, Chapman and Hall, London, 1990.

Listings of electrochemistry books, review chapters, and proceedings volumes are also available in the Electrochemistry Science and Technology Information Resource (ESTIR). (http://electrochem.cwru.edu/estir/)

The Encyclopedia is hosted by the Ernest B. Yeager Center for Electrochemical Sciences (YCES) and the Chemical Engineering Department, Case Western Reserve University , Cleveland, Ohio.
Copyright Notice.
Edited by Zoltan Nagy (nagy@anl.gov) The Center for Electrochemical Science and Engineering and Department of Chemical and Environmental Engineering, Illinois Institute of Technology, Chicago, Illinois.

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Combined ultrasound and electrokinetic treatment of organic contaminants: chemical and analytical approach

2006-02-28T22:50:00.000-08:00

Introduction

Decontamination of soils through the removal of the organic contaminants becomes more and more urgent problem in present world. Various kinds of chemical pollutants have recently been detected in the environment, and this has created large social problems. Sediment contamination in estuarine and coastal regions is widespread in the whole world. Hydrophobic organic compounds such as polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) are of particular concern because of their long life span and toxicity. Sediment serves as a contaminant reservoir for aquatic organisms that can accumulate toxic compounds like PCBs that are then passed up the food chain.

Contamination can be solved by the use of different techniques, like thermal or biological treatment of soils, pumping of solutions containing agents capable of extracting the toxic contaminants from the soil. However, usually those conventional techniques require high costs and remediation time. In addition, those remedial options may cause habitat alteration, and require large-scale material handling and long-term management. Therefore, in-situ stabilization methods that do not involve sediment relocation or capping are attractive.

Electrokinetic remediation technique has attracted an increased interest among the scientific community all around the world. This technique is based on the application of low-level direct current, which is used to solubilise and mobilize contaminants via electro-migration, electro-osmotic and electrophoresis phenomena. In addition it is economically feasible and the time scale of remediation can be reduced applying different enhancement methods. Sonochemistry is one of the novel approaches to enhance the reactions and processes by increasing a speed and output of reactions, more efficient use of energy, performance improvement of phase transfer catalysis, activation of metals and solids as well as increase in reactivity of reagents or catalysts.

The electrokinetic treatment process efficiency highly depends on the electro-osmotic phenomenon, which is mainly controlled by electrokinetic potential so called zeta-potential. It is well documented in the literature that usually soil or sediments surface is negatively charged having low zeta potential. In order to raise the efficiency of the contaminants removal there it is necessary to raise the zeta potential.

Aim of the research

To apply electrokinetic method to remove organic contaminants from low permeability clayey soils.

Materials and Methods

Laboratory scale experiments will be conducted in specially designed electrokinetic cells with the possibility to conduct batch scale experiments and in situ trials.

Set up of the experiments

Laboratory scale electrokinetic experiments will be conducted in cylindrical glass cell. The distance between electrodes will be 70 cm, diameter of the glass cell 30 cm, the length of sludge chamber 50 cm, the length of cathodic and anodic (with modification for electromigration experiments) will be 10 cm each. The contaminated medium will be separated from cathodic or anodic chambers by either fiber glass filter paper (0.45mm, Advantec GS25 Japan) or cation as well as anion membrane (Ionics Inc, the USA). The electrodes used for the experiments will be platinized titanium or titanium bars 7 cm length and 1 cm width. The pH, amount of heavy metals in the effluent and the amount of water, electric current, different potential gradient and other important parameters will be constantly monitored throughout the tests.

Work plan

2006-02-27T21:38:00.000-08:00

2006 January – 2006 June

This period will involve literature reviews and analysis of existing data on removal activities.

2006 July – 2006 December

During this period, the research will use the criteria and information generated initially to determine the effectiveness of ultrasound enhanced electrokinetic removal activities. Most trace organic contaminants undergo significant degradation in the biologically and chemically active zone known as the “schmutzdecke”, and removal rates decrease with increasing depth. The fate of organic contaminants in the subsurface depends on geochemical and nutrient conditions, with low dissolved oxygen/low nutrient conditions favoring long-term persistence.

2007 January – 2007 July

The interactions of contaminants with soils, sediments, and some aquifer sands will be deeply investigated with the help of computer MINTEQ modeling and other additional speciation and interaction software available. There is a necessity to be able to predict the extent to which contaminants will distribute within a subsurface environment, and how that distribution should impact the selection of optimal contaminant removal techniques.

2007 August – 2007 December

Different contaminant speciation experiments will be carried out to evaluate the forms and availability of the mobile species under the applied electric current. Ultrasounds will be applied to the contaminated system to enhance the possible migration and solubilization of the contaminants and the effect of other enhancement methods how to increase zeta potential will be applied.

2008 January – 2008 June

Possibilities of in situ tests will be developed and evaluated. It is anticipated that the results of this research will be useful to hydrogeologists, engineers, and other specialists who must understand how contaminants retained by soil, sediments and/or sludge move or can be removed.

2008 July – 2008 December

The final report of the project will be written.