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First Annual Southeastern In Situ Soil & Groundwater Remediation Conference |
Oxygen
BioChem (OBC)™ Recent applications
of in situ chemical oxidation (ISCO) have shown that ISCO can be a
cost-effective remedial strategy for organic contaminants in groundwater and
soil. The application of ISCO to contaminated source areas usually results in an
immediate benefit to groundwater in the area. In addition, further contaminant
flux can be reduced or eliminated mitigating further contaminant plume issues.
Redox Tech has recently formulated a mixture of sodium persulfate and calcium
peroxide that can be employed for ISCO applications using FMC’s patent-pending
KlozurÔ
activation chemistry. The mixture in OBC
supports a two-fold mechanism for treating contaminants of concern. OBC delivers
one of the strongest chemical oxidants for short term ISCO, and also provides
electron acceptors (oxygen and sulfate) for longer-term biological oxidation. Sodium persulfate has
emerged recently as an important oxidant for in situ remediation of volatile and
semi-volatile organic compounds. Persulfate is the strongest oxidant within the
peroxygen family, with an electromotive force of 2.12 volts.
As illustrated below, the direct oxidation half-cell reaction for
persulfate involves a two-electron transfer: 2
S2O82- +
2 H+ + 2e- ®
2HSO4- However in most
cases, rapid destruction of the contaminant of concern requires that the
persulfate be activated in order to generate sulfate radicals.
Sulfate radicals are powerful oxidizing agents, with an oxidation
potential of 2.6 volts. Klozur activated persulfate is catalyzed with the
peroxide and base provide by the calcium peroxide S2O82-
+ calcium peroxide activator ®
2SO4● Activated persulfate can remain available in the subsurface for months providing an unrivaled combination of power and stability. The calcium peroxide
provides several benefits. First,
it imparts the alkalinity and peroxide needed to activate the persulfate using
FMC’s KlozurÔ
activation chemistry. Second, when
mixed with water it provides a long-term slow release source of hydrogen
peroxide and calcium hydroxide. CaO2 + 2 H2O à Ca(OH)2 + H2O2 The hydrogen peroxide that is slowly formed decomposes to oxygen and water, providing an extended oxygen source for subsequent bioremediation of petroleum hydrocarbons. The resultant calcium hydroxide (hydrated lime) that is produced serves several purposes. First of all, it increases the total dissolved ion concentration, which makes the solution less likely to leach metals from the soil into the groundwater. Secondly, the calcium from the hydrated lime will precipitate the sulfate that is produced during the consumption of the persulfate. The calcium sulfate (gypsum) precipitation helps to reduce sulfate groundwater concentrations, which may impact the secondary drinking water standard of 250 ppm. The mixture in OBCÒ
provides chemical oxidation as well as electron acceptors (oxygen and sulfate)
for longer term biological oxidation. The predominant short-term reaction is
chemical oxidation, while the longer-term remediation process is biological
oxidation. OBCÒ
has the advantages over more traditional oxygen compounds used for
bioremediation in that is works on a broader range of contaminants. Table
1. Contaminants Treated by Oxygen
BioChem (OBC)Ò
Table 2 summarizes
the advantages of OBCÒ
over other oxygenating compounds. OBCÒ
works on a wider range of contaminants than other oxygenates because provides
chemical oxidation and electron acceptors for bioremediation. The amount of
oxygen in OBCÒ
assumes that all of the oxygen in the sulfate is consumed through sulfate
reduction processes. Table 2. Advantages of Oxygen BioChem (OBC)Ò
CONTACT: John Haselow, PhD, PE Redox Tech, LLC 200 Quade Drive Cary, NC 27513 Phone: 919-678-0140 www.redox-tech.com | |||||||||||||||||||||
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