Bioremediation Flashcards
Bioremediation: definition, method, why
Use of biotechnology to remove or reduce pollution (in water, soil, food, ecosystems, etc) to acceptable levels
Microbes have evolved to use pollutants as energy source and nutrition source so we can utilise to reduce pollution via converting to something else
Why:
Industrial activities had low levels of regulation of dangerous compounds and accidents (chemical spills, etc)
Increased demand for development of new properties so now Brownfield sites (previously used for industry) want to be used for building houses on, but doesn’t meet regulation
Additionally, digging through soils from unsaturated zone (gaps in soil are air) to saturated zone (gaps in soil are water) then the soluble pollutants will move in water underground to sea, or a public well of water supply, or into field growing crops
Soil and water samples are tested to identify level of pollution
Pollution: definition, classes, examples, persistence,
Pollution is the introduction by man into the environment of substances liable to cause hazards to human health, harm to living resources and ecological damage
Pollution can be point source (factory smoke) requiring in-situ bioremediation or a non-point source (fumes from cars, pesticides on farm) requiring ex-situ bioremediation
Natural: compounds that occur naturally somewhere in the environment but human activity (mining industrial sites, metal smelting) leads to unnaturally high concentrations.
Ex. crude oil, heavy metals (lead, mercury, etc), carbon dioxide, phosphates
Xenobiotics: chemically synthesised compounds that have never occurred in nature
Ex. pesticides, herbicides, plastics
Persistance:
Pollutants can be classified as:
Degradable: Not stable in the environment
Degraded by biological and non-biological processes
Ex. simple hydrocarbons and petroleum fuels (degradability decrease as MW and degree of branching increase)
Persistent: Stable in the environment (at least in some conditions) for long periods of time.
Ex. typically fat soluble molecules, chlorinated hydrocarbons
Recalcitrant: Intrinsically resistant to any degradation
When may using microbes be inefficient/difficult in bioremediation
Xenobiotics are likely to be more persistent/recalcitrant because microbes have not had time to evolve pathways to degrade them. e.g. halogenated hydrocarbons
Insoluble compounds such as nylon, polyethylene and other plastics are recalcitrant because of low biological availability (not in a form that can be taken up by microbe, too large). Microbes can’t access them to degrade them since insoluble in water
Heavy metals can’t be enzymatically degraded by microbes so instead are made less harmful via oxidation, precipitated (therefore less bioavailable), purified and reused, or concentrated and stored safely
Case study of bioremediation project; reason, process, how pollutants were cleared
London Olympics 2012
* Clean-up of a 350-hectare area of Brownfield site for London 2012 Olympic Park.
* Started with >3,500 sampling locations, creating more than 5 million chemical test results to check which pollutants were there
* 2.2 million square metres of soil was excavated, of which 764,000 square metres was treated on- or off- site by soil washing,
chemical stabilisation, bioremediation or sorting. Or was removed
* 2,500 litres of free product (hydrocarbon) was removed and 235,000 square metres of contaminated groundwater pumped and treated.
Free products being the pollutant in it’s original form (not diluted in water, etc)
Pool of original pollutant sitting underground
DDT: structure, what it is, use, downside
DDT is a very effective insecticide (Paul Muller won the Nobel Prize in 1948 for developing)
Benefits
Sprayed over crops, in houses, etc
Controlled spread of vector borne diseases (malaria) which provided crop protection
Downside
DDT is stable and slow to degrade (half-life in soil up to 30 years) so remains in ecosystem
Accumulates in insect eating crops, and when bird eats insect has higher concentration. Process repeats up the food chain (biomagnification)
Accumulates and persists in fatty tissue
DDT accumulated in bird eggs (ex. eagle and falcons), thinned eggs so more fragile and breeding success declined
In humans over time it has carcinogenic potential
DDT ban increased breeding success
[See structure]
Mercury case study: how it occurred, effect, solution
Chisso factory producing acetaldehyde using a
Mercury Sulphate catalyst
* 1951 changed catalytic cycle leading to bi-product methyl mercury
* 1956 first patient identified with central nervous system disease
* Local cats going crazy: “dancing cat” disease
* Families in coastal villages eating local fish and shellfish were affected
* 1958/1959 cause identified as organic mercury compounds. Bacteria convert inorganic mercury to methyl mercury (mercury poisoning).
* Up to 2kg mercury per ton sediment at mouth of plant outflow
* Company change waste-water route to pollute
river instead of harbour and installed “water treatment plant” that did not work
* Continued to pollute until 1968 when production of acetaldehyde with mercury stopped and another catalyst was used
* Over 2000 certified victims and 10,000 other
claimants have been paid $100s millions in
compensation
Instead oxidised metal into reduced metal that can be collected or released in air. However, danger of microbes turning it into more toxic compounds
Pollution cycle
Pollutants introduced via chemical spills, vehicle emissions, toxic chemical (pesticides), etc
Enters air, water (drinking water, groundwater), rain, soil
Transports long distances via air currents, water flow, and soil erosion
Acid rain dissolving monuments, bioaccumulation in our bodies from eating in food, etc
Underground:
Top layer soil
Unsaturated zone; soil is full of air
Saturated zone; soil is full of water (wells for drinking water)
Petrol from leak at petrol station goes through gaps of air in soil and puddles on top of water table as a free liquid.
Some is soluble and goes into water table, carrying pollutants, which can end up in water for public or agriculture
Oil pollution: source, localisation, bioremediation strategy
Oil has been in environment for millions of years
Cracks in sediment allows oil to seep out naturally and microbes have evolved to use as carbon and energy source
Humans drill underwater to access deposits of oil underground
Around 2/3rds of oil in sea is from industrial waste
10% from natural sources
Localisation depends on weight:
Oil seeps out of reservoir underground
Some deposit as heavy oil seep on seabed
The rest as oil droplets migrate up through water column to become oil slick on water surface
Light petroleum hydrocarbons evaporate into atmosphere
Over time some deposits back down to seabed as fallout plume of heavy petroleum hydrocarbons
Methane from reservoir bubbles up and releases into atmosphere or dissolves in water column
Bioremediation:
Microbes degrade as all this happens
Speed process up by spraying detergent onto oil spill to disperse and make more accessible to microbes
Could cause oil spill to become more toxic and sink down into water
Bag oil
Spread fertiliser onto beach
Microbes need nitrogen, phosphates, etc so providing as fertiliser, allows them to uptake with more carbon (from spill) to increase growth
Dispersant (to make oil more accessible) injected into well head
Oil formed clouds of small droplets that didn’t rise
Oxygen and phosphate levels decreased around clouds suggesting microbial activity
To identify which microbe, do PCR to amplify 16s (in all bacteria), sequence, and identify which bacteria (different in all)
Microarray showed genes involved in oil degradation increased
Oil contamination case study, prevention example
Exon valdez - oil spill
Ship with oil tanker ran into rocks and spilt a fifth of oil
Wind wasn’t high so oil wasn’t broken up and dispersed, instead blew ashore onto beaches killing wildlife
Took ~10 years for bird and mammal populations to recover
MTBE added to petrol to make petrol burn better by delivering O2 in too in car engine (used to be lead until realised it was toxic)
Reduces harmful emissions
Components of crude oil, petrol, extraction
Crude oil:
Aliphatics - pentane, etc
Aromatics - benzene, etc (a little more water soluble than straight chain)
Cyclic hydrocarbons -
Non-hydrocarbons
Sulphurs
Nitrogens
Oxygens
Metallics
Petrol:
~20% is the BTEXs: benzene, toluene, ethylbenzyne and xylene
Very dangerous, benzene is a carcinogen
Aromatic so resistant to degradation
Slightly water soluble
~80% is other hydrocarbons (cyclic, branched, straight chain)
Heat crude oil and filter based on temperature it heats at. Take 3-10 C in length
Light non-aqueous phase liquids: definition, effect, removal
Non-aqueous phase liquid - Most hydrocarbons don’t mix well with water so crude oil and petrol float to top after a while
Underground petrol storage tank leakage into soil below then onto top of ground water of light non aqueous phase liquid
Moves down to unsaturated zone then settles on impermeable rock or travels to saturated zone
Lighter than water so floats on top of water table and is carried downstream
Slightly soluble bits (ex. BTEX) dissolve into water and carried with water flow in pollution plume and can end up in water used for wells
Residual phase binds soil particles
Removal:
Drill well into ground and pump up oil (groundwater comes up too)
Separate water and oil to recover
Energy intensive
Pump air below LNAPL in saturated zone to make hydrocarbons volatile and encourage aerobic degradation
Use microbes to degrade
Add fertiliser to boost activity
Introduce microbes
Microbes to degrade hydrocarbons: how to improve, requirements for bioremediation
Degraded by specific enzymatic pathways, and different microbes degrade different pollutants
Complete degradation - mineralisation into CO2, water and salts
Since degradative enzymes are encoded on genomic DNA or plasmids, can engineer to degrade new pollutants or move plasmid from one to another
Requirements:
Microorganisms capable of producing enzymes to degrade or immobilise target (bioaugmentation; add microbes that will reduce pollution)
Biostimulation: For growth, require energy source (hydrocarbon oxidation) and electron acceptor (O, N, etc reduction) is required for growth (redox reactions gives us energy)
Biostimulation: Appropriate conditions for cell growth (pH, moisture, nutrients (N, P, K), temperature)
Absence of toxicity (pollutant doesn’t kill microbes)
Removal of metabolites (complete conversion of pollutant, not into another toxic compound)
Absence of competitive organisms
Redox reaction: importance, use in bioremediation,
Microbes can use hydrocarbon pollutants as an energy source (electron donor/acceptor) and nutrition source (carbon and nitrogen source)
In aerobic conditions, hydrocarbons are used as electron donors and O2 as electron acceptor, breaking down the pollutant to generate ATP
Very important:
Macronutrients - C, H, N, O, P (comprises most of microbe)
Micronutrients - S, K, Na, Mg, Fe, etc
Humans oxidise carbohydrates/acetyl coA to get energy
Microbes can use multiple as electron acceptors:
Reduce O2 into water
Reduce sulphur, nitrogen (and sometimes) carbon.
Each has different oxidation state
Carbon in CO2 = +4
Carbon in methane = -4
Carbon in sugar = 0
Means it takes different number of
1 O2 can be reduced into 2 water
Can couple oxidation of O2 to one carbon in a carbohydrate to turn into CO2
Nitrate can be used a acceptor into nitrogen and carbohydrate as donor
Sulphate to hydrogen sulphate (smells)
Most efficient is O2 but used up early on so microbes that utilise nitrate (2nd most energy releasing) dominates, then the next when that runs out
Methanogenesis (reduction of methane) is slow to degrade pollutant
Pump oxygen into water
Can use pollutant (ex. chloroform) as electron acceptor so sugar added as electron donor
In bioremediation, pump malate into ground
