The reactive barriers permit the economic treatment, in situ, of chlorinated pollutants

Hervé SEGUIN
General Director and President of ATE

Background:

• The iron reactivity with chlorinated compounds was presented as early as 1925.

• The first patents date from 1972 (Sweeny).

• Encouraging trials have been made since 1984, called '' reactive barriers with Fe (0)" (ETI patents).

• The accomplishment of semi-permeable reactive walls (1992).

• New reagents and catalysts were identified in1995.

• The Solétanche Bachy patents of the drain panel (1997).

• The contract Solétanche Bachy / Rhodia for bringing reactive barriers into operation (1998).

• Rhodia patent application on the basis of new reagents (1998).

The concept of the abiotic process:

• The relative simplicity of the chemical reaction
• The reaction rapidity with an important spectrum of pollutants
• Efficiency of the process
• Wide spectrum of treated pollutants

The principles of reactive barriers

• A metal utilization (0) as a reduction base   metal(0) ® metal 2+ +2e -
• Electrons can enter into numerous reactions, especially with water

- 2H 2 O+2e - ® H 2 + 2OH - , pH ­

- metal(0) +H 2 O ® metal 2+ + 2OH - + H 2

The main pollutants targeted:

• chlorinated solvents, nitrates, certain metals (Cr, As; U).

The process application area

Pollution with organic chlorinated compounds:

• Polichlorides can be limited by an electron generated by the corrosion of a metal replacing a chlorine ion by a proton

- Metal + RCI + H+ ® metal(2+) + RH + CI-

- This dechlorination formula is known as hydrogenolysis (Vogel and of 1987)

Pollution with metals:

• reduction of hexavalent chrome or trivalent chrome
• precipitation under the form of hydroxides

- 2Cr 6+ + 6e - ® 2Cr 3+

- 3 metal ® 3 metal 2+ + 6e -

- 2Cr 3+ + 6OH - ® 2CrçOH) 3

Association of two innovating technologies

The technology of the "drain panel"

• No maintenance
• In situ, the operation of which cannot be seen by the public

"ATE/Rhodia" method

• Treating a large spectrum of organic halogenated pollutants
• Actual degradation of contaminants rather than transfer to another environment
• Sustainable performance at  low costs

Choosing a reagent for the reductive dechlorination

• The reaction general principle
• Study of the site
• Laboratory tests
• Application to the site
• Conclusion

Site characterization

• underground water characterization (geochemistry, water chemistry...)
• geology
• hydrogeology ( the phreatic aquifer substrate, flowing speed,.....)
• history

The flow and permeability estimation

Laboratory tests (Batch)

Objectives

• Testing the method feasibility
• Testing the efficiency of different reaction types

Laboratory tests (columns)

Objectives

• Confirming the ''batch'' trials
• Determining the kinetics of degradation of pollutants dissolved in water
• Determining the half-life of pollutants
• Choosing the reaction according to specific surface and permeability criteria

The analysis of water from the phreatic aquifer

Carbonates	mg/l	3
Hydrogenocarbonates	mg/l	283
Sulfates	mg/l	15,5
Nitrates	mg/l	0,5
Ammonium	mg/l	0,13
pH		7,46
Conductivity	m S/cm	329
Vinyl chloride	m g/l	329
Dichloromethane	m g/l	0,71
1,2 Dichloroethane	m g/l	1528
Trichloromethane	m g/l	64
1,1,1-trichloromethane	m g/l	400
Trichlorethylene	m g/l	19
Tetrachlorethylene	m g/l	13

Required parameters

• reagent permeability >10 -4 m/s
• flow estimated at 20 l/min
• reaction volume: 1 la 3 m 3
• vinyl chloride:      1 m g/l

The results of laboratory tests

		Input	Output Column 1	Output Column 2
Vinyl chloride	m g/l	77	5	0,5
Dichlormethane	m g/l	7,3	6,5	0,5
Trans-Dichloroethane	m g/l	0,5	0,5	0,5
Cis-Dichloroethane	m g/l	130	1,1	0,5
Trichloromethane	m g/l	2,2	2	0,5
1,1,1-trichloromethane	m g/l	43	0,5	0,5
Tetrachloromethane	m g/l	6,4	3	2,4
Trichlorethylene	m g/l	70	0,5	0,5
Tetrachlorethylene	m g/l	24	0,5	0,5

The results obtained on the site

		Input	Output	%
Vinyl chloride	m g/l	3	0,23	92,3
Cis-Dichloroethane	m g/l	199	2	99,0
Trichlorethylene	m g/l	94	0,46	99,5
Tetrachlorethylene	m g/l	25	0,16	99,4

• Vinyl chloride < 1 m g/l
• The parallel treating of many other molecules

The half-life of organic halogenated compounds

Organic halogenated comp.	Half-life/relatively
Trichloromethane	91.5
Tetrachloromethane	76.1
Monochloroethylene	210
1,1-Dichloroethylene	775
Cis-1,2-Dichloroethylene	521
Trans-1,2-Dichloroethylene	94.4
1,1,1-Trichloroethane	77.5
1,1,2-Trichloroethane	110
Trichlorethylene	100
1,1,2,2-Tetrachloroethane	143.7
1,1,1,2-Tetrachloroethane	73.2
Tetrachloroethylene	195.8
Hexachloroethane	85.9
Tetrabromoethylene	94.4

Conclusion

• New treatment method IN SITU
• Treatment of a large spectrum of organic halogenated pollutants
• Actual degradation of contaminants rather than a transfer to another environment
• No maintenance, low cost
• Operation away from the public eye
• Appropriate for remediation projects, especially large ones (treatment of chlorinated pollutants) or for metallic pollutants treatment around  waste dumps, large steel units or mining areas.