6. Biodegradation and Water Pollution Flashcards
Sources of organic pollutants (8)
- domestic waste
- pulp and paper
- agriculture
- food processing
- mining
- textile industry
- chemical, pharmaceutical industries
- internal combustion engines
Types of organic pollution (11)
- proteins, fats
- carbohydrates
- lignin
- cellulosics
- chloro-organics
- dyes, solvents
- paints, resin, pigments
- fluorocarbons
- antibiotics
- hydrocarbons
- plastics
Contaminants associated with the chemical industry (7)
- acids
- alkalis
- metals
- solvents
- phenols
- organic compounds
- chlorophenols
Contaminants associated with the petrochemical industry (5)
- hydrocarbons
- phenols
- acids
- alkali
- asbestos
Contaminants associated with the metal industry (~1 → 7)
Metals like:
* Fe
* Cu
* Ni
* Cr
* Zn
* Cd
* Pb
Contaminants associated with the energy industry (4)
- phenols
- cyanides
- sulphur compounds
- coal and coke dust
Contaminants associated with the mineral extraction industry (3)
- metals: Cu, Zn, Pb
- gas
- lecheate
Contaminants associated with water supply and sewage (3)
- metals in sludge
- micro-organisms
- methane
How many deaths are caused by pollution (1 in how many)?
1 in 6 (~17%)
What are the fates of contaminants when they enter the environment (4)?
- water pollution
- groundwater pollution
- soil/sediment pollution
- air pollution
Characteristics that determine a compounds fate (2)
- volatile VS non volatile
- soluble VS non soluble
What is biomagnification?
- The increase in a pollutant in tissues or organisms at successive levels of a food chain
- Results in bioaccumulation at higher trophic levels
What is bioaccumulation?
The increase in concentration of a compound within an organism compared to the level found in the environment
What is biodegradation?
Degradation of a pollutant(s) by a living organisms, usually a microorganism
What is bioremediation?
Remediation of a contaminated site by using the biodegradative capacity of biology, usually microbiology
For biodegradation/bioremediation to occur, what are the three essential interactions that need to overlap?
- The contaminant must be biodegradable
- Environment physical/chemical parameters must allow biodegradation
- Biodegradive microorganisms must be present and active in the contaminated soil
What are xenobiotic compounds? (2)
- Xenobiotic compounds are compounds alien to existing enzyme systems
- They are not naturally occurying → man made
Examples of xenobiotic compounds (7)
- DDT
- 2,4-D
- Malathion
- Atrazine
- Monuron
- Chlorinated biphenyl (PCB)
- Trichloroethylene (TCE)
Are xenobiotics really foreign to life?
- No, some can actually be made naturally, albeit in minute quantities
- It more the concentration of these man made compounds that are foreign to life
Can microbes bioremediate xenobiotic compounds? (3 points)
- If these new xenobiotic compounds are similar to existing natural compounds, microbes might be able to easily switch to metabolism of these new compounds
- This is bc of the time-scale of microbial evolution that indicates that microbes can — or can evolve/adapt the ability to — degrade almost anything (eventuallt)
- Basically, we can expect to find microbes able to degrade practically any organic compound, it might just take a long time
What is recalcitrance?
A compound is recalcitrant if it is attacked poorly, or not at all, by microbial enzyme systems because of its molecular compelxity
What are some examples of recalcitrance? (6)
- Oligomerization (i.e. cellulose, polystyrene, plastics)
- Halogen substitution (H replaced by chlorine, fluorine, bromine)
- Other substitutions: H replaced by nitro-, sulfo-groups
- Branching (alkylation etc.)
- Molecules are too large to fit into enzyme pockets containing the catalytic sites
- Large molecular organic contaminants are more hydrophobic, less water soluble, therefore less bioavailable → i.e., plastics, large molecular weight PAHs
Which is biodegradable and which is recalcitrant?
2,4-D VS 2,4,5-T
- Biodegradable: 2,4-D
- Recalcitrant: 2,4,5-T
Which is biodegradable and which is recalcitrant?
Propachlor VS Propham
- Biodegradable: Propham
- Recalcitrant: Propachlor
Which is biodegradable and which is recalcitrant?
Carbaryl VS Aldrin
- Biodegradable: Carbaryl
- Recalcitrant: Aldrin
Which is biodegradable and which is recalcitrant?
Methoxychlor VS DDT
- Biodegradable: Methoxychlor
- Recalcitrant: DDT
Which is biodegradable and which is recalcitrant?
Alkanes VS PAHs
Alkanes easier to biodegrade than PAHs
What makes an alkane harder to biodegrade?
The bigger it is, the harder it is to biodegrade
Effect of the number of PAH rings on the difficulty to biodegrade them
The more rings there are, the harder the compound will be to biodegrade
Where can we look for microbes for biodegradation?
Look for biodegrading strains in soils where the previous contamination occured.
* Soil is one environment where we tend to spill pollutants
* In soil (compared to water) pollutants and microbes are easily located
* Once isolate, strains could perhaps be improved via genetic engineering
How much do microbes need to degrade before the environment is safe again?
Depends on the compound!
Is the contaminant bioavailable?
Available to biological systems for utilization as energy and C sources or to be biotransformed
What are the 6 important environmental parameters that bioremediation of contaminants depend on?
- Aeration
- pH
- Temperature
- Soil moisture
- Soil type
- Redox potential
Aeration: impact on bioremediation
- O2 is required as both a terminal electron acceptor and a substrate in oxygenase-catalyzed biodegradative reactions
- O2 is often limiting in soil and aqueous systems. O2 concentration is often the rate-limiting variable in petroleum degradation in soil and of gasoline in groundwater
How can we increase aeration? (3)
By tilling, adding bulking agents in polluted soils, venting in aquifers
Bioremediation under anaerobic conditions (4)
- Biodegradation of organic contaminants under anoxic conditions occurs under denitrifying, methanogenic, sulphate-reducing, and iron-reducing conditions
- Allows for reductive dechlorination (substitution of Cl with H) reactions
- Halogenated hydrocarbons act as an alternative electron acceptor
- Anaerobic degradation in subsoils and aqueous systems can be enhanced by supplying the appropriate electron acceptors
pH: impact on bioremediaton(2)
- pH can affect water solubility and sorption of contaminants to soil and sediments
- microbial activity dependent on pH
- e.g. bacteria: 6-9 ; yeast: 5-9 ; acidophiles: as low as 1
How can we increase pH?
Add lime to acid soils to bring up pH
Temperature: impact on bioremediation
- Q10 value: a change of 10 degrees Celsius will generally increase or decrease an enzyme’s activity by 2-fold
- Raising temperatures of contaminated soils (waters) can increase the rate of degradation by increasing microbial activity and solubility of contaminants
How can we manipulate temperature?
- Difficult to manipulate in the field except for biopiles, bioreactors
- Compost Materials - thermophilic biodegradation
Soil Moisture Content (%) or Water Content (WC)
- amount of water present in soil
- expressed as the ratio of dry weight / wet weight
Water activity (Aw)
Measures the water actually available for microbial use
(Microbes require available water for growth and metabolism)
Water Holding Capacity (WHC)
Amount of water a soil can holf before becoming saturated
Optimal soil moisture for aerobic microbial acitivty (in terms of WHC)
60-80%
Optimal soil moisture for hydrocarbon degradation (in terms of WHC)
30-90%
Low soil moisture content (dry soils): impact on bioremediation
Makes for a low Aw (water activity), so decreases microbial activity
Waterlogged soils (WHC > 100%): Impact on bioremediation
Anoxic conditions:(
How can we increase soil moisture content?
Adding water :D
How can we decrease soil moisture content?
By drying or amending the soil with agents that bind to free water such as gypsum, or bulking agents such as alfalfa
Nutrient supply: impact on bioremediation
Rate-limiting nutrients N and P
So if there isn’t enough bioremediation will be slowed/stopped
What is adding N and P to contaminated sites called?
biostimulation
What are the required C:N and C:P ratios?
- C:N = 20:1
- C:P = 50:1
Oleophilic fertilizers
- used in aqueous systems
- are hydrophobic compounds containing N, P
- remain associated with oil contaminants
