L5 - In-situ microbial strategies

Question 1

Why are in situ stratefies preferable to ex situ?

Answer 1

Reduced disturbance
Can remediate underneath structures
Maintains soil structure
Reduced pollution (lorries etc)
No transport or excavation costs

Question 2

What is bioventing?

Answer 2

Induced air movement through unsaturated soils to maximise degradation and minimise release of volatiles

Question 3

How can oxygen be delivered by bioventing?

Answer 3

• Air injected directly in

- Creation of negative pressure in soil to draw in air from other soil

Question 4

What kind of hydrocarbon removal rates can bioventing achieve?

Answer 4

480-7300 mg per kg of soil per year

Question 5

Why are the downsides of bioventing?

Answer 5

• Not suitable for surface contamination or where water table is close to the surface
• Clay rich soil is unsuitable

Question 6

What is percolation / infiltration galleries?

Answer 6

Nutrients (N and P) sprayed onto surface to percolate into soil
- Leechate is collected and recirculated

Question 7

What are the downsides of percolation?

Answer 7

• Careful nutrient solution doesn’t enter aquifers
• Limited to highly permeable soils
• not suited to clay soils or where water table is close to the surface

Question 8

What is air sparging?

Answer 8

• Air introduced to saturated zone to transfer volatiles to unsaturated zone for biodegradation
• When pollutant reaches unsaturated zone limits set by poor solubility of oxygen in water are removed and remediation speeds
• Greater the depth of sparger, great area of influence

Question 9

What are the downsides of air sparging?

Answer 9

• High injection rates required to strip volatiles from aqueous phase
• Excessive air flow can lead to volatiles reaching surface

Question 10

What is the Raymond or Suntech technique?

Answer 10

Nutrients and oxygen injected into aquifer and groundwater removed via extraction wells, setting up a flow within saturated zone

Question 11

What is liquid delivery and why is it good?

Answer 11

• Oxygen is only sparingly soluble in water (approx. 8 mgl)
• Use hydrogen peroxide
• Conc of 0.05% produce greatest deg rates, above becomes toxic

Question 12

What is an alternative electron acceptor used to increase rate and why?

Answer 12

Nitrate

Readily soluble in water, avail, cheap, easy to transport

Question 13

Why introduce microbial inocula?

Answer 13

Natural pop of organisms may be reduced to such a low level that recovery not rapid enough

Question 14

What is introducing microbial inocula referred to as and how is it done?

Answer 14

Bioaugmentation - using saturated conditions as infiltration of organisms in unsaturated soils very slow

Question 15

What characteristics must inocula have?

Answer 15

High enzymatic activity
Genetic stability
Sustained viability in storage
Good growth and compete
Non-pathogenic
Don't produce toxic metabs

Question 16

What are the issues of GM bacteria?

Answer 16

Stability of genes within pop

Risk of transfer to other bacteria

Question 17

What hurdles can GM bacteria face when put in contaminated sites to make them fail?

Answer 17

Fail to adapt 
Insufficient substrate
Competition
Use other organic substrates instead of pollutant
Predation by protozoa

Question 18

What are problems with synthetic surfactants?

Answer 18

Issues with toxicity

Can be recalcitrant (form emulsions that are hard to move)

Question 19

Why are biosurfactants better than synthetic?

Answer 19

Generally less toxic and more biodegradable

10-40x better at forming micelles

Question 20

What is the process of landfarming?

Answer 20

Site ploughed and oil added
Fertiliser added if not good enough
- Site must not allow run off (impermeable membranes)
- Problems with volatile components into atmos