Remediation of contaminated soil Flashcards
What is meant by “in situ”
- on site,either without excavation or excavation but not transported
What is meant by ex situ?
the soil is excavated and transported for treatment outsid of the site
name three remediation stratergies by contaminant fate
- destruction or degredation: chemical or biological
- extraction or separation/concentration: soil washing/flushing, solvent extraction
- immobilization: stabilization, containment
name remediation stratergies by treatment method
- biological treatment
- physical/chemical treatment
- thermal treatment
explain destruction or degredation as a remediation.
only works for organic contaminents
three types:
- thermal: combustion, in situ heating, hot air injection
- chemical: oxidation
- Biological: bioventing, enhanced bioremediation, phytoremediation
Explain what bioremediation is and the advanteges and draw backs
the use of microorganisms for degredation of hazardous chemicals. metabolize the chemical to produce carbon dioxide or methane
Advanteges:
- low cost (natur based)
- contaminents usually convert to milder products
- contaminents are actually destroyed
- relative easy to implement
draw backs:
- may be difficult to control
- amendments may cause other contamination problems
- may not reduce contaminent concentrations to required levels
- might take a long time
- might need extensive monitoring
- difficult to predict future effectiveness
What is biological reductive dechlorination?
=biostimulation
an in situ remediation technique relying on microorganismst that are stimulated by adding electron donors (hydrogen) and presence of electrone acceptors
ex. H can substitute for Cl in a stepwise exchange. the result is ethene if the process is completed.
also works for flurine (F), bromine (Br), iodine (I), astatine (At)
the reaction could be:
- biological: catalyzed by certain bacteria
- electrochemical: reduction by electrolysis (direct electric current)
- radiation: using gamma radiation
What are the restrictions of the reductive dechlorination process
it needs a high DOC and a low redox as well as a presence of microorganisms
what are some technics for extraction or separation/concentration?
physical separation of the polluted fraction
- sieving
soil washing (water)
- wet-sieving
- hydrocyclones
volatilization
- pyrometallurgical separation
extraction of the pollutant (also works in situ)
- leaching agent (water, EDTA)
- electrokinetic extraction (OBS NOT GOOD FOR METALS)
- soil flushing
Why can separation/concentration techniques be used?
- to pretreat to reduce volume of material to treat
- to recover metals in elemental form
- to recover metals as marketable compounds (in molecular form)
what is the three mechanisms of immobilization treatment?
- reducing infiltration of fluids into the contaminated media (using barriers)
- reducing infiltration of fluids by modifying the permability of the contaminated matrix
- reducing the solubility and hence mobility of the contaminant
what are some remediation methods that use immobilization?
encapsulation/containment
- isolation
- barriers
- covers
- landfilling
stabilization/solidification
- monolith (cementation)
- vitrification
- reduce water transport
stabilization/imobilization
- chemical amendments
- plants
- reduce pollutant mobility
what is the concept of PRB?
=permeable reactive barriers
the plume of contaminents must move through the barrier, workes as a passive treatment
OBS the permeability must be lower or equal to the surounding soil to make the flow go as you want
what is the most common reactive medium in a PRB, how does it work?
the most common: zerovalent iron (Fe0)
- can abiotically dissolve organic contaminants through ex. dechlorination
- oxidation of Fe0 results in iron (oxyhydro)oxides which resultst in sorption of inorganic contaminants ex, As Cu
What should the filling material in a PRB do?
- cause no adverse chemicla reaction or byproducts when reacting with the contaminats
- not be readily soluble or depleted in reactivity
- be readily available at low to moderate cost
- preferably have uniform granulometery
- be safe for workers
