'Foundational Information' Topic 1:
Introduction to Bioremediation
This page has been created to help those of you who may have never even heard of Bioremediation until now. It explains the basic idea behind some of the key points regarding bioremediation: the need, history, application & a brief introduction into how it works. It is hoped to help you understand the main principles of bioremediation and to give an insight into the course.
Learning Objectives:
Learning Objectives:
- Conventional clean up methods & their drawbacks (within slide-show)
- Definition of bioremediation.
- How bioremediation works
- Why its safe.
- Glossary of terms used
What is Bioremediation?
Bioremediation is a treatment process that uses biological microorganisms (yeast, fungi, or bacteria) to naturally break down (digest/biodegrade) hazardous substances into less toxic/harmless products (inorganic salts, CO2 & H20).
*It is a cost effective and natural process, commonly used to treat organics, fuels or solvents.
Note: "organic" compounds are those containing carbon and hydrogen atoms.
*It is a cost effective and natural process, commonly used to treat organics, fuels or solvents.
Note: "organic" compounds are those containing carbon and hydrogen atoms.
Bioremediation requires apt levels of water, oxygen, heat and nutrients for healthy bacterial (microorganisms) growth.
It can be aerobic (with oxygen - more common) or anaerobic (without oxygen). Some nutrients come from the contaminating compounds being broken down, but additional nutrients are often required for healthy bacterial growth. These nutrients (e.g. Carbon, Nitrogen & Phosphate!) provide the cell building material for the microorganism population to grow (reproduce)! |
|
How Does it Work?
Note:
- Bioremediation can be used to clean up both soil and water, either in situ or ex situ.
- The microorganisms must be active and healthy for bioremediation to occur.
- Bioremediation technologies 'assist' microorganisms' growth and increase microbial populations by creating optimum environmental conditions (e.g. temperature, moisture content, pH, nutrients & electron acceptors).
- While contaminants are being broken down, intermediate products that are less/equally/more toxic than the original contaminants can be created.
- Strata must have med-high permeability (e.g. less effective in clays).
- The specific technology used is dependent on several factors (e.g. the type of microorganisms present, the site conditions, the quantity and the toxicity of contaminant chemicals).
Definitions:
- In situ: 'in place'- contaminated soil/groundwater is treated in the location in which it was found - no need to transport the hazardous materials.
- Ex situ: requires soil excavation/groundwater pumping & transportation to be treated 'out of place' (e.g. treatment plant).
- Indigenous microorganisms are those already living (native) in a given site. Their growth is stimulated by ensuring the apt soil temperature (heating), moisture content (water), oxygen, and nutrient content is provided (hence adding nutrients).
- Exogenous microorganisms are those needed (to digest certain contaminants) that are not present in the soil at the site. Here the microorganisms need to be carefully selected and added for bioremediation to occur. It is more complex because the soil conditions often need to be adjusted to ensure that these exogenous microorganisms will thrive.
Is Bio-remediation Safe?
- Bioremediation relies microorganisms that naturally occur in soil (hence no threat to the environment).
- No dangerous chemicals are used e.g. the nutrients added to enhance microbe growth are fertilisers (commonly used on lawns & gardens).
- Bioremediation destroys/changes the harmful chemicals into water and harmless gases.
- If in situ bioremediation - no need to excavate/pump up hazardous pollutants (no contact or release of harmful gases into the air).
- Often bioremediation require less equipment & labour compared to other treatment options.
How Long Does the Process Take?
The duration of bioremediation is site specific as it depends on multiple factors, e.g.:
• type, concentration, biodegradability & toxicity of contaminants
• size & depth of the polluted area
• soil characteristics
• in situ or ex situ, aerobic or anaerobic and natural or engineered bioremediation process?
It can vary from just a few days to even several years to have bioremediated enough of the harmful chemicals.
• type, concentration, biodegradability & toxicity of contaminants
• size & depth of the polluted area
• soil characteristics
• in situ or ex situ, aerobic or anaerobic and natural or engineered bioremediation process?
It can vary from just a few days to even several years to have bioremediated enough of the harmful chemicals.
WATCH THIS!!!
Common Terms/Abbreviations:
The video below has been provided to graphically explain some common terms referred to through the course, e.g. the water table, aquifer, ground strata, pumping wells and the cone of depression!
Absorption: the uptake of chemicals into plants or microorganisms.
These chemicals may be broken down or remain inside the plant or animal and be released back into the environment when the animal dies/plant decays.
Adsorption: the binding of compounds onto the surface of soil particles.
The amount adsorbed varies with the type of compound, soil, moisture levels, soil pH & soil texture.
G.W. : Groundwater
Leaching is the movement of contaminants into groundwater from the surrounding medium (e.g. soil/waste). It occurs downward, upward, or sideways (dependent on the soil, contaminant and GW flow).
Microbial breakdown is the breakdown of chemicals by microorganisms such as fungi and bacteria. Microbial breakdown tends to increase when:
- temperatures are warm
- soil pH is favourable (relatively neutral)
- soil moisture and oxygen levels are adequate
- soil fertility is good
MOs : Micro-organisms
Runoff is the movement water over a sloping surface. Contaminants are often mixed in the water & infiltrate the ground. These compounds may get dissolved into the ground water or become attached to soil particles.
Soil characteristics: very important to contaminant transport.
- Clay soils have a much smaller pores than sandy soils, thus a lower permeability which reduces the effectiveness of bioremediation. This limits the flow paths & flow rate through the soil, which adversely affects the delivery of oxygen, nutrients & water to the contaminated area.
- Clays have a much higher capacity to adsorb contaminants than sandy soils, hence further complicating their treatment!!
- Other site characteristics (e.g. depth to G.W., moisture content, fractured soil structures or highly variable stratas are also very important).
Volatilisation is the process of solids or liquids converting into a gas.
W.T. : Water Table
Catchment Area Scale
Agricultural pesticides can be transferred through the air (by wind), in ground and surface waters (runoff & infiltration) and through soil/in the ground.