12: Chemical Oxidation, Reduction, and NAPL Flushing Flashcards
Define ISCO and list advantages and disadvantages of the technology.
In Situ Chemical Oxidation (ISCO) is the delivery of oxidation chemicals into a contaminated subsurface.
Advantages: Best for addressing sources of contamination (DNAPLs). Method is very aggressive.
Disadvantages: Oxidation chemicals will kill bacteria and sanitize the subsurface leading to problems with bioredmediation. This method is expensive and disruptive as well.
Name the four most common additions for ISCO and what forms they come in.
1) Potassium Manganate (KMnO4): Solid, hazardous, must be made onsite
2) Sodium Manganate (NaMn04): Liquid
3) Hydrogen peroxide (H2O2): Liquid
4) Ozone (O3): Gas
5) Persulfate (S2O8): Powder or solution (NaS2O8)
Explain why with H2O2addition you often get accelerated oxidation rates and sometimes reduction reactions.
H202 breaks down into a hydroxyl radical, a very reactive oxidizing compound. This radical will accelerate oxidation rates.
The highly reactive nature of the hydroxyl radical can create reduction reactions when then hydroxyl radical looses it’s unpaired electron, and become a hydroxide ion in solution.
Describe the hydroxyl radical and explain why it is so reactive.
The hydroxyl radical is an unstable compound produced when ozone or hydrogen peroxide are used as oxidants.
The hydroxyl radical is so reactive because it has an unpaired electron. This makes the presence of a hydroxyl radical very brief because it bonds so quickly.
Explain conditions that would make chemical oxidation a poor choice for in situ remediation.
If a NAPL (non-aqueous phase liquid, almost pure chemical) is not present, chemical oxidation will kill microorganisms in the subsurface thereby harming any bioredmediation effectiveness.
Some chemical oxidation compounds will concentrate minerals listed on the EPA secondary maximum contaminant list. If high levels of SMCL minerals are naturally present, chemical oxidation may elevate levels above the SMCL.
Explain why SVE would be needed in addition to a hydrogen peroxide or ozone treatment system.
Soil vapor extraction (SVE) is required during hydrogen peroxide or ozone treatment because oxygen gas is produced. Excess oxygen is explosive and is not desired in the subsurface.
Describe four possible treatment systems that could be used in conjunction with chemical oxidation.
○Excavation
○ Soil vapor extraction (SVE)
○ Bioremediation
○ Groundwater recirculation
List which two chemical oxidants could be best paired with bioremediation and explain why.
H2O2 and KMn04: H202 will raise the temperature of the subsurface and increase bioactivity. KMnO4 has been identified as not sterilizing aquifers other oxidants do.
Describe the chemistry of dithionite and how it should be used for reduction zones.
Dithionite is a reductant compound that reduces Fe(III) to Fe(II). Fe(II) can be used to breakdown certain contaminants.
Define a surfactant, micelle, and the critical micelle concentration.
○ Surfactant: Molecule with a hydrophobic and hydrophilic end that bonds to non-soluble compounds and makes them soluble
○ Micelle: A non-soluble compound surrounded by surfactant molecules that is soluble
○ Critical micelle concentration: The concentration of a surfactant that will make a non-soluble compound soluble.
List advantages and disadvantages for surfactant flushing.
Advantage: Increase mobility of NAPLs
Disadvantage: Difficult to design; NAPLs may migrate to uncontaminated areas if mobile portions are not captured.
List mechanisms of NAPL removal for alcohol flushing.
Alcohol flushing can make NAPL soluble thereby increasing the mobility of the NAPL
List advantages and disadvantages for alcohol flushing.
Advantage: Increase mobility of NAPLs
Disadvantage: NAPLs may migrate to uncontaminated areas if mobile portions are not captured.
