Block 3 Flashcards
LNAPL vs DNAPL
LNAPL: accumulate at capillary fringe. Gasoline and BTEX.
DNAPL: more dense than water, migrate until they reach impermeable layer. PCE and PAH.
What factors control partitioning of a contaminant
- Pore space - Gas phase (VP/henry’s law)
- Solid phase - Kow (octanol), Koc (sorb/OM), Kd (sorb/solids)
- Liquid phase - Sw
- Free phase - NAPL
Three considerations for SVE
- Only for vadose zone
- Assumes volatile components
- Medium to coarse texture so air can flow
Most important property of soil to consider when applying rem technology
Intrinsic permeability
What properties of the contaminant should be considered?
- Boiling point - Low boiling point vs high vapor pressure
- Henry’s law - Partitioning between gas and liquid
When should multiphase extraction be used?
- When working in a wide range of permeability
- Vadose/capillary fringe/groundwater
- When contaminant is in multiple phases or have contaminants of different phases
Bioslurping
Uses bioremediation by pumping O2 in as a TEA and removes free phase product
Compare air sparging, vapor extraction, and bioventing
- Air sparging - GW and light end HC
- Vapor extraction - Vadose and light end
- Bioventing - Vadose zone and mid-weight
Two main points about PRB
- Can only be used in GW
- Mostly uses ZVI
Main points about reductive dechlorination in groundwater
- Microbes can’t oxidize Cl, so they use reductive chlorination
- ZVI transfers e- to Cl
- ZVI becomes Fe2+
Describe the process by which Cl is remediated in anaerobic conditions
Cl is the electron acceptor and carbon can be an electron donor. Can also inject H2S.
List four characteristics about sodium persulfate
- Can be used surface or subsurface
- Sodium persulfate is the oxidant
- Reacts with organic contaminants
Does dissolved carbon increase or decrease anaerobic conditions?
Increases.
Which option for permanganate should be used in phytorem?
Potassium permanganate - sodium version causes dispersion of water which is bad for plant growth.
Describe Fenton’s reaction
- Combines H2O2 (hydrogen peroxide) and Fe2+, creates a very strong oxidant
- Produces radicals which complete oxidation
- Hydroxyl radical is product of Fenton’s reaction
- Doesn’t travel so good for hot spots
List three characteristics about persulfate oxidation
- Compound is very persistent
- Generates radicals
- May require heat activation
Monooxygenase
Microorganisms use OXYGENASE enzymes to initiate or activate hydrocarbon degradation. Monooxygenases (incorporates one oxygen atom into the hydrocarbon).
What is the first step of remediation?
What is the redox state and can oxygen be added or how can oxygen be added.
List 3 things about phytoremediation and microbial enzymes
- Microbes transfer genes to plants via enzymes which promotes phytorem
- Microbes produce plant hormones and transfer them to plant via soil
- Bacterial cells may be attached to root and enzymes are taken up that way
Steps for offshore clean up
- Containment then skimming
- Removal from shorelines
- Sponges, surface washing, dispersants
- In-situ burning
- Biorem
- Natural attenuation
2 things about propane biosparging
- Inject propane and oxygen. Propane as co-metabolic substrate and oxygen as TEA.
- Microbes utilize propane and produce enzymes that incidentally co-metabolize other contaminants
During biosparging, what biogeochemical changes happen as oxygen is introduced?
Dissolved iron, manganese, and sulfides oxidize and precipitate as metal oxides which reduces their mobility.
What happens to the redox conditions as microbes respire?
They introduce CO2 which increases anaerobic conditions which can mobilize/immobilize contaminants depending on their redox sensitivity.
List important considerations for phytoremediation (2)
- Soil factors such as pH and OM content are important
- pH affects solubility of metals, want a lower pH to increase bioavailability
- Metals may bond with OM and reduce bioavailability
Oxygenase
During aerobic cometabolism, the contaminant is oxidized by an enzyme (Oxygenases) or cofactor produced during microbial metabolism of another compound with oxygen
Transformation of PCE (tetrachloroethylene)
PCE > TCE > DCE > VC > Ethene > Ethane
Reduction of Chromium with ZVI
Cr6 or Cr8 to Cr3
Reduction of Selenium with ZVI
Se4 or Se6 to Se0
Reduction of Uranium with ZVI
U6 to U4
Reduction of Cr, Se, U with ZVI - ZVI reaction
Fe0 to Fe2+ or Fe3+
What is partitioning?
Partitioning refers to how a contaminant distributes itself among the gas, liquid, and solid phases in soil and groundwater systems.
List 4 points about phytodegradation
- Contaminants are absorbed through roots into plant tissues
- They are degraded or transformed by oxidation, reduction, hydrolysis, or complexation
- Processes involve enzymes
- Less harmful products are then stored
Main points about aerobic alkane degradation
- Aldehydes
- Carboxylic acid
- B-oxidation and Krebs cycle
Main points about aerobic aromatic degradation
- Cleave ring
- Oxidize to catechol
- B-oxidation and Krebs cycle
Main points about anaerobic degradation
- Use NO3- and SO42- as TEA
- Fumarate addition
- Carboxylic acids enters Krebs cycle
Aerobic halogenated compounds
- Dehaloccoides
- Cleave CL-C bonds
- Hydroxyl group
- Oxygenase
Anaerobic halogenated compounds
- Reductive dechlorination
- Halo HC is TEA
- Organic carbon as donor
