2.4 Risk management of Land contamination

Question 1

Define what is meant by bioremediation and state two pollutants that can be treated using this technology.

Answer 1

Answer;

Bioremediation – the use of microorganisms in the treatment of environmental pollution / waste. {1}

Any two pollutants from; 
 Oil spills 
 Chlorinated pesticides 
 Heavy metals. 
 Diesel oil 
 PCBs.

Question 2

Question; Describe the process of bioremediation.

Answer 2

Answer;

Adding micro-organisms to soils {1} to remove contaminants {1}

Question 3

Bioremediation is defined as ‘a method of using micro-organisms to treat contaminated land’.

On a brownfield site which is to be remediated, each of the micro-organisms named in the below have been used.

Identify the possible pollutants that they can be used to treat.

Pseudomonas putida = ???
Pseudomonas aeruginosa = ???
Dehalococcoides ethenogenes = ???

Answer 3

Pseudomonas putida = Used to treat organic solvents
Pseudomonas aeruginosa = Use to treat oil contamination
Dehalococcoides ethenogenes = Used to treat Halogenated hydrocarbons

Question 4

Discuss the economic and environmental benefits of using bioremediation technology compared to traditional treatment methods. {6}

Answer 4

Answer;

Indicative content;

 Bioremediation can be carried out under atmospheric conditions.

 Bioremediation can be carried out in situ so soil is not removed from the site.

 The contaminants are reduced to (almost) zero.

 The by-products are non-toxic so water and air pollution is minimised.

 Bioremediation uses bacteria that occur naturally in the soil so the ecosystem is maintained.

 Bioremediation is economical because it does not require large energy inputs.

Traditional treatment;

 Traditional treatment is expensive because of the high energy costs (heating).

 Greenhouse gases such as carbon dioxide are produced.

 Soil may need to be treated ex situ / off site which required heavy machinery.

 Traditional treatment can produce toxic by-products which require further treatment.

 Soil may need to be disposed of after treatment which leads to increased landfill.

Question 5

There is significant research currently being undertaken into the use of genetic engineering to enhance the scope of bioremediation technology.

(I) Outline the role of genetic engineering in modifying micro-organisms for bioremediation. Your answer should focus on two points. {2}

(II) Identify two issues of concern from the use of genetic engineering of micro-organisms for bioremediation.

Answer 5

Answers;

(I) Any two points from below;

Micro-organisms can be genetically engineered to;

 Decontaminate a site more rapidly than unmodified micro-organisms.

 Tolerate harsher conditions.

 Remove toxic materials (such as heavy metals).

(II) Any two points from;

 Genetically engineered micro-organisms may wipe out existing bacteria.

 They may affect the existing soil ecology with unknown consequences.

 They may not behave the same way in the field as they do under laboratory conditions.

Question 6

Alpine Pennygrass is a wild flower found in many parts of Europe, the Middle East and North America. It has been shown to be very good at absorbing heavy metals such as Cadmium and Zinc from soil. It is therefore very suitable for use in phytoremediation.
Evaluate the use of Alpine Pennygrass in the decontamination of a suitable brown field site.

Answer 6

Indicative content;

Advantages;

 The cost of phytoremediation is lower than that of traditional processes both on and off site.

 This can prove to be cost effective as the initial cost of Alpine Pennygrass is low whilst the potential for recovery of sale of contaminant metals is high.

 The plants can accumulate and tolerate high levels of toxic metal ions.

Limitations;

 Phytoremediation is limited to the surface area and depth occupied by the roots.

 The use of Alpine Pennygrass has low environmental impact although plants cannot absorb all contaminants and will eventually be killed by toxicity of the soil.

 There is a potential threat to the food chain by contaminated Alpine Pennygrass.

Question 7

Identify and describe the process of Phyoextraction.

Answer 7

Answer;

Phytoextraction; Plants ‘uptake’ metals from contaminated soils {1} and concentrate them in above ground plant tissue / biomass {1}. This is then harvested for disposal and / or metal recovery {1}.

Question 8

Name one plant species used for Phytoextraction and the metal ore that it can extract.

Answer 8

Answer;

White mustard = Used to extract Copper
Sunflowers = Used to extract Gold

Question 9

Define Biohydrometallurgy (Biorefining).

Answer 9

Biohydrometallurgy: The use of bacteria (micro-organisms) to extract valuable metals from low grade ore {1}.

Question 10

Discuss two advantages and two disadvantages of biorefining in relation to traditional metal extraction methods.

Answer 10

Answer;

Any two from each of the two groups below;

Advantages;

 Bacteria can operate successfully in low ore concentration environments such as mine tailings that would not otherwise be economical {1}

 Simpler and cheaper to operate than traditional metal extraction methods – less necessity for expensive machinery / processes {1}.

 Much less environmental damage – bacteria grow naturally in mines and landscape is left untouched {1}.

 Bacteria can be harvested and recycled for use elsewhere {1}.

Disadvantages;

 Bacterial ‘leaching’ process can be very slow compared to traditional smelting. This can cause cash flow problems {1}.

 In certain circumstances the bacterial ‘leaching’ process can lead to the production of toxic chemicals. Therefore the process need to be carefully planned {1}.

 If something goes wrong it cannot be stopped as the bioleaching process will continue with rainwater and natural bacterial action {1}.

 If ore concentrations are reasonably high it is uneconomical and very slow compared to traditional methods {1}.

Question 11

Define In-situ and Ex-situ in relation to bioremediation

Answer 11

In-situ: Done without removing the contents from the soil. more cost effective as it lacks transportation costs and extraction costs.

Ex-situ: Done by removing contaminated soil from site and transporting it to a facility. it is the more costly option.

Question 12

Identify the two forms of phytoremediation

Answer 12

Answer:
Natural Hyperaccumulation: Where plants naturally take up contaminants in soil unassisted

Induced or assisted Hyperaccumulation: When a condition fluid containing a chelator or another agent is added to the soil to increase the metal solubility of the mobilisation so that the plants can absorbs them more easily.

Question 13

Discuss the benefits of using Alpine pennygrass and Indian mustard. identify the metals they are capable to extracting and their advantages.

Answer 13

Alpine Pennygrass;

1 - This plant naturally accumulates high levels of metals such as copper, cadmium and zinc from the environment in which they are grown.

2 – It is a hyper accumulator, which as we seen in the previous notes is a plant that can accumulate huge quantities of contaminants in the plants roots, stems and leaf systems. It can remain healthy with these high % values of contaminants, which would otherwise prove fatal for normal plants.

3 – It can also be used to extract traces of arsenic from soil.

4 – The alpine pennygrass takes the contaminants in through the roots of the plant, and stores them. When the plants have grown they are harvested and disposed of safely.

Indian mustard;

5 - This is used in the phytoremediation to remove heavy metals, such as lead from the soil in hazardous waste sites because it has a higher tolerance for these substances and stores the heavy metals in cells.

6 – Indian mustard can also be utilised in the extraction of gold and copper.

Question 14

Identify the bacteria that is capable of refining copper, Zinc, Lead and Uranium.

Answer 14

Thiobacillus

ferrooxidans