Oxygenates in Gasoline - American Chemical Society

Chapter 13

Downloaded by STANFORD UNIV GREEN LIBR on September 15, 2012 | http://pubs.acs.org Publication Date: November 6, 2001 | doi: 10.1021/bk-2002-0799.ch013

Fenton's Reagent for Destruction of Methyl tert-Butyl Ether and Other Petroleum Hydrocarbons in Water 1

Cindy G. Schreier and Lara Pučik

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PRIMA Environmental, 10265 Old Placerville Road, Suite 15, Sacramento, CA 95827-3042 Walker and Associates, Inc., 2618 J Street, Suite 1, Sacramento, CA 95816

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Fenton's reagent is a potentially effective method of destroying MTBE and other petroleum hydrocarbons in water. Treatment of groundwater with 1% H O and 5 mM Fe(II) at pH 3 destroyed >99.8% MTBE, >93.2% TPH, and >98.5% BTEX within 24 hours. Less than 0.01% of the MTBE, 5.1% of the TPH and OH" + Fe(III) H0 * + Fe(III) -> 0 + H + Fe(II) H 0 + HO" -» H 0 + H0 " R" + Fe(III) -> Fe(II) + products 2HO" -> H 0 2

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Eqn. Eqn. Eqn. Eqn. Eqn. Eqn.

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3 4 5 6 7 8

Other factors to consider when evaluating Fenton's reagent as a remediation option are the formation of oxygen gas (0 ), heat and iron floe. In addition to reacting with Fe(II) and Fe(III) [Eqns. 1, 3], H 0 decomposes according to Eqn. 9. Based on this stoichiometry, 1 L of 1% H 0 (v/v) will generate 4.5 L of 0 at standard temperature and pressure (25°C, 1 atmopshere). The Fenton reaction is exothermic and thus can increase the temperature of the surrounding material. In the presence of H 0 , Fe(II) is rapidly oxidized to Fe(III) [Eqn. 1], which will precipitate as an iron hydroxidefloewhen the pH rises above about pH 5. 2

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2 H 0 -> 0 + H 0 2

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Eqn. 9

Treatability testing conducted by the authors has shown that Fenton's reagent can successfully destroy many types of organic compounds in water, including MTBE, BTEX, petroleum hydrocarbons, and chlorinated solvents. Most tests were conducted using site water and mild conditions (1-5% H 0 , 2.550 mM Fe(II)). This paper describes some of these tests and uses the data to 2

In Oxygenates in Gasoline; Diaz, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2001.

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179 illustrate important issues associated with the full-scale in situ or ex situ implementation of Fenton oxidation technology.

Materials and Methods Reagent grade ferrous sulfate heptahydrate (FeS0 -7H 0) was obtained from J.T.Baker. Fe(II) solution was prepared by dissolving FeS0 -7H 0 in deionized water acidified to pH 2-3 with sulfuric acid such that the concentration of Fe was 360mM. H 0 (30%, A.C.S. reagent) was obtained from Fisher Scientific. Contaminated groundwater was obtained from various sites in California. Contaminanted soils were from Indiana. Although the soils were impacted with chlorinated hydrocarbons rather than petroleum hydrocarbons, the conclusions drawn from the data are unaffected. Sample locations and COCs are summarized in Table I. 4

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Table I. Summary of Samples Tested. Site Location Central California Northern California Indiana

Matrix Groundwater Groundwater Groundwater, soil

COCs MTBE, TPH, BTEX TPH, BTEX Chlorinated hydrocarbons

Disappearance of Contaminants Batch tests were performed in closed systems in order to determine whether losses were due to contaminant destruction or volatilization. Typically, contaminated water was acidifed to pH 3 with sulfuric acid and FeS0 -7H 0 added such that the initial Fe(II) concentration was 5-500 mM. This water was then transferred to a Tedlar bag and 30% H 0 added to obtain an initial concentration of 1-5% H 0 . In some cases, both H 0 and Fe(II) were added to the Tedlar bag. During the transfer step, a sample was collected and analyzed for the COCs in order determine the initial concentration. Immediately after addition of H 0 , the Tedlar bag was connected to a second Tedlar bag in order to collect off-gases. The bags were placed on shaker table and gently mixed. After approximately 24 hours, the volume of gas was determined by measuring the volume of water the filled bag displaced. An aqueous sample was collected and in some cases the pH was adjusted to pH ~7 to quench the Fenton reaction. Aqueous and gas phases were analyzed via EPA Method 8015, 8020, or 8260. 4

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180 Rate of 0 Formation/H 0 Decomposition 2

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The gases formed during Fenton oxidation are primarily 0 , though carbon dioxide and other compounds may also be present. The rate of gas formation is assumed to be equal to the minimum rate of H 0 decomposition. (Because H 0 also reacts with iron, the actually rate of H 0 may be faster than the rate of 0 formation. See Introdcution.) The rate of 0 formation was measured by conducting the experiment as described above, except that the reaction vessel was an Erlenmeyer flask connected to an inverted graduated cylinder filled with water. The amount of water displaced by the gases was recorded periodically. The initial conditions were pH 3, 2.5 mM Fe(II), and 3-9% H 0 . In some cases, soil was added such that the liquid to soil ratio was 1.3:1. 2

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Change in Temperature An experiment was conducted in an Erlenmyer flask using a liquid to soil ratio of 1.3:1 and the following initial conditions: pH 3; 2.5 mM Fe , and 3% H 0 . A thermometer was placed in the aqueous phase and the temperature monitored over time. The flask was not mixed in order to simulate the expected method of field appplication. 2+

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RESULTS Disappearance of Contaminants Central California Groundwater A series of tests was conducted on groundwater from a site in Central California to determine the amount of Fe(II) and H 0 that would be needed to remove MTBE and other contaminants in an ex situ reactor. The initial concentrations of H 0 and Fe(II) used are shown in Table II. The results are given in Tables III and IV. Complete removal of all contaminants from the aqueous phase was accomplished for Tests 2, 3, 6 and 7 (Table III). Gas collected during these tests contained only TPH-g and MTBE. A mass balance (Table IV) showed that the maximum amount of contaminant volatilized was 5.1% TPH, < 1.1%) MTBE, and 1.0% BTEX, indicating that the primary mechanism of removal was destruction, not volatilization. (Note that the values in Table IV are conservative. When performing the mass balance calculations, contaminants not detected were assumed to be present at the detection limit. Because this assumption may 2

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181 overestimate the contaminant concentrations, the percent volatilized or remaining in solution may be lower than reported, while the percent destroyed may be greater.)

Table II. Reaction Conditions for Determination of Dose Requirements in Groundwater from Central California.


Test 1 2 3 4 5 6 7

Total Volume, mL Initial H 0 , % 450 1.1 450 1.1 450 1.1 450 1.1 450 3 450 3 450 3 2

Initial Fe(II), mM 0 4.8 48 480 0 4.5 45

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Table III. Concentration of Contaminants in Aqueous and Gaseous Phases after Treatment of Groundwater from Centeral California". Test Time 1 Initial Final 2 Initial Final 3 Initial Final 4 Initial Final 5 Initial Final 6 Initial Final 7 Initial Final a

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Aqueous, μg/L MTBE TPH BTEX 7,100 2,200 95.7 210* 220*

Oxygenates in Gasoline - American Chemical Society

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