Introduction to bioremediation and its types (Lecture 21 & 22)
OVERVIEW:
*Introduction of Bioremediation
*Introduction of Phytoremediation
1.Applications
2.Various phytoremediation processes
Bioremediation:
- Bioremediation is the use of biological systems/organisms
for the reduction of pollution from air, aquatic or terrestrial systems.
- The process involves aerobic or anaerobic microorganisms
that results in degraded products.
- Bioremediation is used to reduce or remove hazardous waste
which has already polluted the environment.
- Cleanup of oil spills by the addition of nitrate and/or sulfate fertilizers to facilitate the decomposition of crude oil by indigenous or exogenous bacteria.
- To attack specific soil contaminants, such as degradation of chlorinated hydrocarbons by bacteria.
Overview and applications:
- Bioremediation technologies can be generally classified as in situ or ex situ.
- In situ bioremediation involves treating the contaminated material at the site.
- In-situ or on-site bioremediation is among the most attractive options for reducing or eliminating contaminants in soil and water.
- With benefits that include minimal site disturbance and lower cost compared to other remediation technologies.
- while ex situ involves the removal of the contaminated material to be treated elsewhere.
- Some examples of bioremediation technologies are bioventing, land farming, bioreactor, composting, bioaugmentation, rhizofiltration, and biostimulation.
Bioventing is a process of stimulating the natural in situ biodegradation of contaminants in soil by providing air or oxygen to existing soil microorganisms.
Bioventing uses low air flow rates to provide only enough oxygen to sustain microbial activity in the vadose zone.
The technology of choice for remediating many petroleum wastes, bioventing may eventually be used to treat a wider variety of more recalcitrant toxins (difficult to manage or operate, not responsive to treatment, resistant).
Limitations
- High soil moisture or low permeabilitysoils reduce bioventing performance.
- Low temperatures may slow remediation.
- Extremely low soil moisture content may limit biodegradation and the effectiveness of bioventing.
Land farming is a bioremediation treatment process that is performed in the upper soil zone or in biotreatment cells. Contaminated soils, waste, sediments, or sludges are incorporated into the soil surface and periodically turned over or tilled to aerate the mixture. Microbes that can metabolize the waste may be added, along with nutrients.
Limitations
Factors that may limit the applicability and effectiveness of the process include:
- large space requirements
- the conditions advantageous for biological degradation of contaminants are largely uncontrolled, which increases the required length of time until complete degradation, particularly for recalcitrant compounds
- inorganic contaminants are not biodegraded
- the potential of large amounts of particulate matter released by operations
- the presence of metal ions may be toxic to microbes and may leach from the contaminated soil into the ground.
- Hydrocarbon compounds that have been identified as being not readily degraded by land farming include creosote, pentachlorophenol(PCP),
Applications….
1.Waste water and Industrial effluents
2.Drinking and process water
3.Soil and land treatment
4.Solid waste
Contaminants Potentially Amenable to Bioremediation:
Biological solution:
PHYTOREMEDIATION:
Phytoremediation is the direct use of green plants to stabilize or reduce contamination in soils, sludges, sediments, surface water, or ground water.
Phytoremediation takes the advantage of the unique and selective uptake capabilities of plant root systems, together with the translocation, bioaccumulation, and contaminant degradation abilities of the entire plant body for the remediation process. This technology is environmental friendly and potentially cost effective.
Phytoremediation processes:
ØA range of processes mediated by plants are useful in treating environmental problems:
TRADITIONAL TREATMENTS FOR SOIL CONTAMINATION:
Traditional treatments for metal contamination in soils are expensive when large areas of soil are contaminated. Some treatments that are available include:
PHYTOREMEDIATION:
Phytoremediation is usually carried out to reduce the exposure of the polluted substrate to humans, wildlife, and the environment.
Phyto-remediation can be broadly categorized as::
The Use of Phytoremediation to Treat Metal Contaminants :
- Phytoextraction:
Ø Plant roots uptake metal contaminants from the soil and translocate them to their above soil tissues
Ø Once the plants have grown and absorbed the metal pollutants they are harvested and disposed off safely by drying, ashing or composting
Ø This process is repeated several times to reduce contamination to acceptable levels
Ø Hyper accumulator plant species are used on many sites due to their tolerance of relatively extreme levels of pollution
Ø Avena sp. , Brassica sp.
Contaminants removed:
Ø Metal compounds that have been successfully phytoextracted include zinc, copper, and nickel
Phytoextraction Advantages:
- The main advantage of phytoextraction is environmental friendliness.
- Traditional methods which are used for cleaning up
heavy metal contaminated soil, disrupt soil structure
and reduce soil productivity,
whereas phytoextraction can clean up the soil without
causing any kind of harm to soil quality.
- Another benefit of phytoextraction is that
it is less expensive than any other clean up process.
Disadvantages: As this process is controlled by plants, it takes more time than
traditional soil clean up methods.
Examples of phytoextraction from soils:
- Arsenic, using the Sunflower, or the Chinese Brake fern , a hype-raccumulator. Chinese Brake fern stores arsenicin its leaves.
- Cadmium, using Willow. As willow has some specific characteristics like high transport capacity of heavy metals from root to shoot.
- Cadmiumand zinc, using Alpine pennycress, a hyper-accumulator of these metals at levels that would be toxicto many plants.
- Lead, using Indian Mustard, Ragweed, Hemp, or Poplartrees, which accumulate lead in its biomass.
- Uranium, using sunflowers.
- Mercury, seleniumand organic pollutants such as polychlorinated biphenyls(PCBs) have been removed from soils by transgenic plants .