Bioremediation Flashcards
What is bioremediation?
The utilisation of microorganisms to transform contaminants into benign, harmless, and/or less mobile forms.
Aims: Remove, degrade and immobilise contaminant
What are 3 bioremediation strategies?
- Stimulate natural microbial communities
- aeration to increase oxygen
- adding nutrients and PEDs/TEAs - Add surfactants (soaps)
- Enchance microbial attachment to contaminant
- Disperse microbes over wide area - Add microorganisms
- Specifically bred/engineered/selected
- known as Bioaugmentation
What is in-situ bioremediation?
When the contaminant is treated in place.
What are two in-situ bioremediation techniques?
- Permeable reactive barrier
- Works with organic and inorganic contaminants
- Can be with or without microbes - Injection wells
- Air injected stimulates aerobic organisms
- Can idealise groundwater conditions for the microorganisms you want to be active
What is ex-situ bioremediation?
Pumping out/extracting contaminated materials and treating off-site.
e.g., Pump (extraction wells) and treat, Constructed wetlands, Slurry bioreactors
What are some types of organic contaminants?
- Petroleum hydrocarbons
- Chlorinated hydrocarbons
- Plasticisers
- Solvents
What is the main goal for bioremediating organic contaminants?
To degrade the organic contaminant.
Want to oxidise it (use as PED).
What is the main strategy used in organic contaminant bioremediation?
Aeration (to stimulate natural microbial communities):
- Use organic carbon as PED (contaminant)
- Want aerobic chemoheterotrophs
What does aeration involve in organic contaminant bioremediation?
Organic contaminants are degraded (oxidised) fastest via aerobic respiration.
Can either be done by pumping or in-situ.
Bioventing: Adds O2 to vadose zone (unsaturated)
Air Sparging: Adds O2 below water table (saturated)
What can be done to bioremediate organic contaminants if aeration is not feasible?
- Stimulate anaerobic chemoheterotrophs e.g., Shewanalla
- Acts as Fe(III)-reducer - Add nutrients and electron shuttles to stimulate anaerobic chemoheterotrophs
- will speed up reaction as not as thermodynamically favourable - Add surfactants
- help disperse microorganisms and attach to contaminants
What are natural sources of metals?
Rock and minerals
What are anthropogenic sources of metals?
Agriculture, mining, sewage, waste
How do terrestrial ecosystem relate to contaminants?
Soils are a major sink for metal contaminants.
Contaminants bound to OM and then transported by ground water.
How do aquatic ecosystem relate to contaminants?
Sediments are major sink for metal contaminants.
e.g., via runoff, leaching etc.
Mobility and metal toxicity depends on concentration and speciation.
Hard to clean up contaminated GW.
What are the 4 bioremediation strategies for metals?
- Bioreduction
- Biosorption
- Bioaccumulation
- Biomineralisation
What is the process of bioreduction?
bioremediation of metals
Enzymatic reduction of U(6+) to U(4+)
Type of biomineralisation process:
- stimulate by adding electron donors and increasing the organic carbon.
- want microbes to use U as TEA
What are the problems associated with bioreduction?
bioremediation of metals
- Competition from other TEAs more energetically favourable
- If stop adding PED, sulphate reduction takes over
- Too much U can inhibit growth
What is the process of biosorption?
bioremediation of metals
Uranyl UO22+ cation, U(6+), sorbed to cell (-ve).
- passive process where the biosorptant (dead or live cells) can be regenerated.
What are the problems associated with biosorption?
bioremediation of metals
- Can get fast U desorption from cell
- Other cations compete for surface sites
- Cell surfaces quickly saturated
- Not used for in-situ treatment
What is the process of bioaccumulation?
bioremediation of metals
UO22+, U(6+), cells uptake contaminant
- Organisms bioaccumulate U, Cs, Te etc. in low level nuclear waste
- Not well known how useful it is
What is the process of biomineralisation?
(bioremediation of metals) + Problems
U(6+) and PO43- compound.
No change in oxidation state (induced biomineralisation)
Problems:
Phosphate is highly reactive and can ppt. quickly with other cations
What is the goal at nuclear sites for bioremediating U?
Want to prevent uncontrolled dispersion and transport of U in ground water.
Don’t want U in oxidised U6+ form as very mobile.
