In Situ and Ex Situ Bioremediation
- Bioremediation techniques are destruction techniques to stimulate the growth of micro-organisms, using the contaminants as a food and energy source.
- These techniques have been successfully used to remediate soils/sludges & groundwater contaminated by petroleum hydrocarbons, solvents, pesticides, wood preservatives, and other organic chemicals.
- Oxygen, water & nutrients are added, and the temperature and pH are controlled.
- The rate microorganisms degrade the contaminants is influenced by: the specific contaminants present, their concentrations, the oxygen supply, moisture, temperature, pH, nutrient supply, bio-augmentation, and co-metabolism.
- Micro-organisms can be adapted to degrade specific contaminants or enhance the process.
ADVANTAGES OF BIOREMEDIATION (over physical/chemical treatment alternatives):
- typically lower cost to implement.
- often little to no residual treatment is required (.e. micro-organisms (in biological treatment) completely breakdown (biodegrade) the contaminant, whereas in physical/chemical treatment, the contaminants are often just separated (e.g. not actually remediating the contamination).
- Longer-term processes (than Chemical/Physical).
- Bioremediation does not treat inorganic contaminants nor every organic compound.
- Difficult to determine whether contaminants have been destroyed.
- Highly chlorinated compounds have very low biodegradability.
- Some compounds may be broken down into more toxic by-products (e.g., TCE to vinyl chloride) or PAHs to less degradable PAHs (carcinogens). These may be mobilized to ground water if not controlled.
- The biological technologies are sensitive to certain soil parameters e.g. the presence of clay or humic materials - these vary the effectiveness of the treatment. Must therefore evaluate the soil, aquifer, and contaminant before deciding which biological strategies may be applicable.
IN SITU BIOREMEDIATION:
Advantages of in situ bioremediation:
- No need to excavate & transport soils - typically less expensive
- Can treat a large volume of soil at once.
- Causes less contaminants to be released than ex situ techniques
- Creates less dust
- Most effective if permeable sandy soil (un-compacted)
- Least effective in clays/highly layered subsurface environments - oxygen cannot be evenly distributed throughout the treatment area.
- May be slower to reach cleanup goal (if less easily degradable contaminant, requires years).
- May be more difficult to manage (than ex situ techniques).
In-situ Bioremediation Technologies:
[The following in situ biological treatment processes are linked to the pages I have prepared for you (e.g. within this website). Additional links to relevant external websites and case studies are provided in the further learning tab - bioremediation links.
Biological Treatment: (Bioremediation)
- Air Sparging
- Enhanced Air Sparging
- Bio-venting (aerobic)
- Enhanced Bio-Degradation
- Natural Attenuation
EX SITU BIOREMEDIATION:
Advantages & Disadvantages of ex situ bioremediation:
- Ex situ techniques can be faster, easier to control, and used to treat a wider range of contaminants and soil types than in situ techniques.
- There is more certainty about the uniformity of treatment because of the ability to homogenize, screen, and continuously mix the soil.
- However, they require excavation of soils, leading to increased costs and engineering for equipment,
- More risk of material handling/worker exposure conditions.
- Usually requires treatment of the contaminated soil before and, sometimes, after the actual bioremediation step.
- Ex situ techniques include: slurry & solid phase bioremediation:
- Solid-phase soil treatment processes include landfarming, soil biopiles, and composting.
- Slurry-phase soil treatment processes include the slurry phase bio-reactor.
- Contaminated soil is combined with water and other additives in a large bio-reactor and mixed to keep the indigenous (native) micro-organisms in contact with the contaminants.
- Nutrients & oxygen are added & the conditions in the bio-reactor are controlled (to ensure optimum environment for the MOs to degrade the contaminants.
- Upon completion of the treatment, the water is removed from the solids - wastewater is disposed/further treated if still contaminated.
- - Slurry-phase is a relatively rapid process (compared to other biological treatment processes) - particularly for contaminated clays.
- Treats soils in above-ground treatment area
- Equipped with collection systems to prevent any contaminant from escaping the treatment.
- Moisture, heat, nutrients, or oxygen are controlled to enhance biodegradation rates
- Solid-phase systems are relatively simple to operate and maintain BUT require a large amount of space and require a longer time of treatment than or slurry-phase processes.
Pages I have prepared for you contain information about the applications, advantages & disadvantages of each process - just click to be taken directly to the page:
Bio-farming (solid phase)
Windrow Composting (solid phase)
Bio-piles (solid phase)
Bio-reactor (slurry phase)