BIOREMEDIATION , BIOAUGMENTATION & PHYTOREMEDIATION
BIODEGRADATION AND BIOREMEDIAITON
Biodegradation is breaking down organic matter into nutrients that can be used by other organisms. The decay is carried out by a many bacteria, fungi, insects, worms, and other saprophytic organisms that eat dead material and recycle it into new forms.
By using some natural forces of biodegradation, we can reduce wastes and clean up environmental contaminants.
Through composting, we accelerate natural biodegradation and convert organic wastes to a valuable resource. Composting has been used as a biodegradation process for many different organic compounds. It is widely employed to recycle nutrients in garden and yard waste.
Through wastewater treatment we can accelerate natural forces of biodegradation. In this case the purpose is to break down organic matter so that it will not cause pollution problems when the water is released into the environment.
Through bioremediation, microorganisms are used to clean up oil spills and other types of organic pollution.
Bioremediation or bioaugmentation
Bioremediation or bioaugmentation is a waste management technique that involves the use of organisms to remove or degrade or neutralize pollutants from a contaminated site or to break down hazardous substances.
Bioremediation works by providing pollution-eating or "waste-eating" organisms with fertilizer, oxygen, and other conditions that encourage their rapid growth. These organisms would then be able to break down the organic pollutant at a correspondingly faster rate. In fact, bioremediation is often used to help clean up oil spills. A number of microorganisms can utilize oil as a source of food, and many of them produce potent surface-active compounds that can emulsify oil in water and facilitate the removal of the oil. Unlike chemical surfactants, the microbial emulsifier is non-toxic and biodegradable. Also, fertilizers have been utilized to increase the growth rate of the indigenous population of bacteria that are able to degrade oil.
in situ bioremediation: treating the contaminated material at the site.
ex situ bioremediation: removal of the contaminant material elsewhere.
Intrinsic bioremediation: bioremediation that may occur on its own. It is also known as natural attenuation.
Aerobic bioremediation: microbial reactions that require oxygen to go forward. The bacteria use a carbon substrate as the electron donor and oxygen as the electron acceptor.
Anaerobic bioremediation: A microbial reaction occurring in the absence of oxygen and involving many processes, including fermentation, methanogenesis, reductive dechlorination, and sulfate and nitrate reducing conditions. In anaerobic metabolism, nitrate, sulfate, carbon dioxide, oxidized materials, or organic compounds may replace oxygen as the electron acceptor.
Cometabolic bioremediation: microbes do not gain energy or carbon from degrading a contaminant. Instead, the contaminant is degraded through a side reaction.
Bioaugmentation: Microbes are made to eat and digest contaminants, changing them into small amounts of water and harmless gases like carbon dioxide and ethene. If soil and groundwater do not have enough of the right microbes, they can be added in a process called bioaugmentation. The microorganisms used are known as bioremediators. It may take a few months or even several years for microbes to clean up a site, depending on several factors like Contaminant concentrations are high, or contaminants trapped areas, or the contaminated site.
Biostimulation: Bioremediation that may only effectively occur through addition of fertilizers, oxygen etc. to help encourage the growth of pollution eating microorganism within the medium. For example, windrowing and aeration of petroleum contaminated soils enhanced bioremediation using technique of land farming.
Mycoremediaiton: A type of bioremediation in which fungi is used to decontaminate the area. Its mycelium secretes an extracellular enzyme and acids that break down lignin and cellulose.
Mycofiltration is a similar process, using fungal mycelia to filter toxic waste and microorganisms from water in soil.
Bioventing: Bioremediation requires good nutrient and environmental conditions for biodegradation. When oxygen is needed for oxidation of the organic contaminants, bioventing (pumping air into the soil) is often used. Sometimes, fertilizers are added to the soil. In certain places irrigation is necessary so that plants or microbes can grow.
Phytoremediation: Use of plants to stimulate the extraction, degradation, adsorption, stabilization or volatilization of contaminants is called as phytoremediation. Example: Using cloning technique with Agrobacterium, the mer A and mer B genes have been integrated into plant Arabidopsis thaliana, thus transforming extremely toxic organic mercury into elemental mercury.
Types of Phytoremediation
Phytoextraction: use of pollutants accumulating plants to remove metals or organics form soil by concentrating them in a harvestable plant parts.
Phytodegradation: use of plants and associated microorganisms to degrade organic pollutants.
Rhizofilteration: use of plant roots to absorb pollutants (metals from water and aquatic waste streams).
Phytostabilization: use of plants to reduce the bioavailability of pollutants in the environment.
Phytovolatilization: use of plants to volatilize pollutants.
Factors affecting bioremediation:
Contaminant concentrations: too high concentrations of the contaminants may have toxic effects on the present bacteria.
Contaminant bioavailability: Bioavailability for microbial reactions is lower for contaminants that are more strongly absorbed to solids.
Site environmental conditions: pH, temperature, water content, nutrient availability, and redox potential.
pH : optimal bacterial growth, pH should remain within the tolerance range for the target microorganism.
Redox Potential and oxygen content: influenced by the presence of electron acceptors such as nitrate, manganese oxides, iron oxides and sulfate.
Nutrients: for microbial cell growth and division, to stimulate bioremediation.
Temperature: increases with increasing temperature and decreases with decreasing temperature.
Advantages of bioremediation:
- As it employs natural processes to clean up sites, hence it may not require as much equipment, labor, or energy as some cleanup methods. Therefore, cost efficiency; less expensive than excavation followed by disposal elsewhere, incineration or other ex situ treatment strategies
- Bioremediation provides a good cleanup strategy for some types of pollution.
- Contaminated soil and groundwater are treated onsite without having to dig, pump, and transport them elsewhere for treatment. That is, Reduce or eliminates the need of ‘pump and treat’ practice (practice common at sites where hydrocarbons have contaminated clean groundwater).
- Microorganisms can be modified by Genetic engineering approach for making them more appropriate to be used as bioremediators: Bacteria Deinococcus radiodurans, the most radioresistant microorganism, has been modified to consume and digest toluene and ionic mercury from highly nuclear waste.
- Bacteria can be altered to produce certain enzymes that metabolize industrial waste components that are toxic to other life, and also new pathways can be designed for the biodegradation of various wastes.
- Use of microbes for bioremediation is not limited to detoxification of organic compounds. In many cases, selected microbes can also reduce the toxicity of heavy metals to the much less toxic and much less soluble elemental form.
- Can be employed in areas that are inaccessible without excavation.
Bioremediation has successfully cleaned up many polluted sites and has been selected at over 100 sites across the country.