11: Bioaugmentation and Biobarriers

Question 1

Define bioaugmentation.Discuss four factors that limit its effectiveness.

Answer 1

Bioaugmentation is an approach that inserts select bacteria to target specific contaminants. Select bacteria are typical genetically engineered.

Limiting factors:
§ Cultured organisms cannot compete with natural bacteria or resist predators. This “zoo” raised bacteria don’t have a wild nature.
§ Cultured organisms prefer to attach to a surface. Therefore, they do not treat soluable contamination well.
§ Bacteria are difficult to transport in aquifer.
§ Gaining regulatory approval of genetically modified organisms is difficult.

Question 2

Name the organism that has been successfully used for bioaugmentation. Describe its features.

Answer 2

Dehalococcoides ethenogenes (DHC) is an enriched, anaerobic bacteria that helps complete the dehalogenation of PCE and TCE to ethene and ethane once the progress stalls at the VC stage

Question 3

List four gimmicks that can make bioaugmentation effective.

Answer 3

1) Encapsulated bacteria to transport them through the aquifer
2) Expect death of bacteria and deliver as a chemical oxidant or reductant
3) Gene bioaugmentation: Attempt horizontal gene transfer to indigenous population
4) Inoculate plants or trees with bacteria in the roots

Question 4

Describe a common problem with biostimulation and how it can be avoided.

Answer 4

A common problem with biostimulation is delivering the stimulants in a uniform manner across a contamination plume. Impervious or semi-impervious subsurface lithology may limit the reach of the stimulants and negatively impact the effectiveness of bacterial activity.

Question 5

Define biobarriers and list the three most common types.

Answer 5

Biobarriers (BBs): A microbial consortium grown in porous media placed across the flow of a contaminated groundwater plume to promote biodegradation of the pollutant

Type 1) Continuous
Type 2) Funnel and Gate
Type 3) Layered

Question 6

Describe the choice in fill material in BB. List four types.

Answer 6

Fill material needs to ensure growth of bacteria while maintaining a high hydraulic conductivity

Fill material types:
	§ Sand
	§ Peat
	§ Pumice granules
        § Expanded perlite

Question 7

Describe three different ways oxygen can be delivered in BB.

Answer 7

Oxygen (common electron acceptor) can promote aerobic mineralization

Air sparging (common)

Pulsed pure O2

Diffuse delivery

Question 8

Describe how electron donors are typically delivered in BB.

Answer 8

Electron donors promote reductive dehalogenation

Best deliver thorough a fill material
§ Mulch
§ Compost
§ Sludge

Question 9

List advantages and disadvantages of BB.

Answer 9

BB Advantages
§ Cheaper treatment option. One time placement with possible regeneration.
§ Prevents spread if designed and installed properly

BB Disadvantages
§ Does not clean up contamination, only contains it
§ Excessive growth can cause clogging
§ Reactive fill must be replaced periodically