Compiled by Mr. Nitin Swamy Asst. Prof. Department of Biotechnology

Transcription

1 BioREMEDIAtion Model Answers Compiled by Mr. Nitin Swamy Asst. Prof. Department of Biotechnology Page 1 of 11

2 What is Bioremediation? Bioremediation is a treatment technology that uses biodegradation of organic contaminants through stimulation of indigenous microbial populations by providing certain amendments, such as adding oxygen, limiting nutrients, or adding exotic microbial species. It uses naturally occurring or externally-applied microorganisms to degrade and transform hazardous organic constituents into compound of reduced toxicity and/or availability. At sites filled with waste organic material, bacteria, fungi, protists, and other microorganisms keep on breaking down organic matter to decompose the waste. If such environment is filled with oil spill, some organisms would die while some would survive. Bioremediation works by providing these organisms with different materials like fertilizer, oxygen and other conditions to survive. This would help to break the organic pollutant at a faster rate. In other words, bioremediation can help to clean up oil spills. A gross, but simple explanation of bioremediation is the use of maggots in wound care control. Wounds that have contamination can have maggots introduced to them. The maggots then eat the contamination, allowing the wound to heal correctly. That is a form of medical bioremediation but there are many other types that are used to control different waste contamination. According to the EPA, Bioremediation is a treatment that uses naturally occurring organisms to break down hazardous substances into less toxic or non toxic substances. Why Bioremediation is Important? Bioremediation is important for two reasons. 1. It uses no chemicals One of the issues with using man-made chemicals in the treatment and removal of contamination is that the chemicals eventually make it into the water supply. There were many chemicals used at the beginning of the waste management era that we now know were very harmful to plant, animal and human life once they reached the water supply. 2. It can allow waste to be recycled Another major reason that bioremediation is preferred is that once the waste is treated and the contamination neutralized or removed, the waste itself can then be recycled. When chemical remediation types are used, the waste is still contaminated just with a less toxic substance and in general, cannot then enter into the recycle process. Bioremediation allows for more waste to be recycled while chemical methods still create waste that cannot be used and has to be stored somewhere. Page 2 of 11

3 What are the 2 classes/types of Bioremediation used? There are two classes of bioremediation used. Don t confuse the class type with the actual types of bioremediation available, the classes describe the general application of the organisms. The two classes are: In-situ In situ refers to when contaminated waste is treated right at its point of origin. For example, there may be soil that is contaminated. Rather than remove the soil from its point of origin, it is treated right where it is. The benefit to in situ treatment is that it prevents the spread of contamination during the displacement and transport of the contaminated material. Advantages of in situ bioremediation: 1. Cost-effective, with minimal exposure to public or site personnel. 2. Sites of bioremediation remain minimally disrupted. Disadvantages of in situ bioremediation: 1. Very time consuming process. 2. Sites are directly exposed to environmental factors (temperature, O2 supply etc.). 3. Microbial degrading ability varies seasonally. Ex-situ Ex situ refers to treatment that occurs after the contaminated waste has been removed to a treatment area. To use soil as the example again, the soil may be removed and transported to an area where the bioremediation may be applied. The main advantage to this is it helps to contain and control the bioremediation products, as well as making the area that was contaminated available for use. Advantages of ex situ bioremediation: 1. Better controlled and more efficient process. 2. Process can be improved by enrichment with desired microorganisms. 3. Time required in short. Disadvantages of ex situ bioremediation: 1. Very costly process. 2. Sites of pollution are highly disturbed. 3. There may be disposal problem after the process is complete. Page 3 of 11

4 9 Types of Bioremediation There are far more than 9 types of bioremediation, but the following are the most common ways in which it is used. 1. Phytoremediation use of plants to remove contaminants. The plants are able to draw the contaminants into their structures and hold on to them, effectively removing them from soil or water. 2. Bioventing blowing air through soil to increase oxygen rates in the waste. This is an effective way to neutralize certain oxygen sensitive metals or chemicals. 3. Bioleaching removing metals from soil using living organisms. Certain types of organisms are draw to heavy metals and other contaminants and absorb them. One new approach was discovered when fish bones were found to attract and hold heavy metals such as lead and cadmium. Page 4 of 11

5 4. Landfarming turning contaminated soil for aeration and sifting to remove contaminants, or deliberately depleting a soil of nitrogen to remove nitrogen based organisms. 5. Bioreactor the use of specially designed containers to hold the waste while bioremediation occurs 6. Composting containing waste so a natural decay and remediation process occurs. 7. Bioaugmentation adding microbes and organisms to strengthen the same in waste to allow them to take over and decontaminate the area 8. Rhizofiltration the use of plants to remove metals in water. 9. Biostimulation the use of microbes designed to remove contamination applied in a medium to the waste. The Role of Microbes in Bioremediation The goal in bioremediation is to stimulate microorganisms with nutrients and other chemicals that will enable them to destroy the contaminants. The bioremediation systems in operation today rely on microorganisms native to the contaminated sites, encouraging them to work by supplying them with the optimum levels of nutrients and other chemicals essential for their metabolism. Thus, today's bioremediation systems are limited by the capabilities of the native microbes. However, researchers are currently investigating ways to augment contaminated sites with nonnative microbes including genetically engineered microorganisms especially suited to degrading the contaminants of concern at particular sites. It is possible that this process, known as bioaugmentation, could expand the range of possibilities for future bioremediation systems. Regardless of whether the microbes are native or newly introduced to the site, an understanding of how they destroy contaminants is critical to understanding bioremediation. The types of microbial processes that will be employed in the cleanup dictate what nutritional supplements the bioremediation system must supply. Furthermore, the byproducts of microbial processes can provide indicators that the bioremediation is successful. How Microbes Destroy Contaminants Page 5 of 11

6 Although bioremediation currently is used commercially to cleanup a limited range of contaminants mostly hydrocarbons found in gasoline microorganisms have the capability to biodegrade almost all organic contaminants and many inorganic contaminants. A tremendous variety of microbial processes potentially can be exploited, extending bioremediation's utility far beyond its use today. Whether the application is conventional or novel by today's standards, the same principles must be applied to stimulate the right type and amount of microbial activity. Basics of Microbial Metabolism Microbial transformation of organic contaminants normally occurs because the organisms can use the contaminants for their own growth and reproduction. Organic contaminants serve two purposes for the organisms: they provide a source of carbon, which is one of the basic building blocks of new cell constituents, and they provide electrons, which the organisms can extract to obtain energy. Figure: - Microbes degrade contaminants because in the process they gain energy that allows them to grow and reproduce. Microbes get energy from the contaminants by breaking chemical bonds and transferring electrons from the contaminants to an electron acceptor, such as oxygen. They "invest" the energy, along with some electrons and carbon from the contaminant, to produce more cells. Page 6 of 11

7 Pseudomonas The Predominant Microorganism For Bioremediation: Members of the genus Pseudomonas (a soil microorganism) are the most predominant microorganisms that degrade xenobiotic. Different strains of Pseudomonas, that are capable of detoxifying more than 100 organic compounds, have been identified. The examples of organic compounds are several hydrocarbons, phenols, organophosphates, polychlorinated biphenyls (PCBs) and polycylic aromatics and naphthalene. About microbial strains of micro-organisms, capable of degrading xenobiotics have been isolated. Besides Pseudomonas, other good examples are Mycobacterium, Alcaligenes, and Nocardia. Consortia of microorganisms for biodegradation: A particular strain of microorganism may degrade one or more compounds. Sometimes, for the degradation of a single compound, the synergetic action of a few microorganisms (i.e. a consortium or cocktail of microbes) may be more efficient. For instance, the insecticide parathion is more efficiently degraded by the combined action of Pseudomonas aeruginosa and Psudomonas stulzeri. Page 7 of 11

8 Phytoremediation Phytoremediation is a bioremediation process that uses various types of plants to remove, transfer, stabilize, and/or destroy contaminants in the soil and groundwater. There are several different types of phytoremediation mechanisms. These are: 1. Rhizosphere biodegradation: - In this process, the plant releases natural substances through its roots, supplying nutrients to microorganisms in the soil. The microorganisms enhance biological degradation. 2. Phyto-stabilization: - In this process, chemical compounds produced by the plant immobilize contaminants, rather than degrade them. 3. Phyto-accumulation (also called phyto-extraction):- In this process, plant roots sorb the contaminants along with other nutrients and water. The contaminant mass is not destroyed but ends up in the plant shoots and leaves. This method is used primarily for wastes containing metals. At one demonstration site, water-soluble metals are taken up by plant species selected for their ability to take up large quantities of lead (Pb). The metals are stored in the plant s aerial shoots, which are harvested and either smelted for potential metal recycling/recovery or are disposed of as a hazardous waste. As a general rule, readily bioavailable metals for plant uptake include cadmium, nickel, zinc, arsenic, selenium, and copper. Moderately bioavailable metals are cobalt, manganese, and iron. Lead, chromium, and uranium are not very bioavailable. Lead can be made much more bioavailable by the addition of chelating agents to soils. Similarly, the availability of uranium and radio-cesium 137 can be enhanced using citric acid and ammonium nitrate, respectively. 4. Hydroponic Systems for Treating Water Streams (Rhizofiltration):-Rhizofiltration is similar to phyto-accumulation, but the plants used for cleanup are raised in greenhouses with their roots in water. This system can be used for ex-situ groundwater treatment. That is, groundwater is pumped to the surface to irrigate these plants. Typically hydroponic systems utilize an artificial soil medium, such as sand mixed with perlite or vermiculite. As the roots become saturated with contaminants, they are harvested and disposed of. 5. Phyto-volatilization. In this process, plants take up water containing organic contaminants and release the contaminants into the air through their leaves. Page 8 of 11

9 6. Phyto-degradation. In this process, plants actually metabolize and destroy contaminants within plant tissues. 7. Hydraulic Control. In this process, trees indirectly remediate by controlling groundwater movement. Trees act as natural pumps when their roots reach down towards the water table and establish a dense root mass that takes up large quantities of water. A poplar tree, for example, pulls out of the ground 30 gallons of water per day, and a cottonwood can absorb up to 350 gallons per day. The plants most used and studied are poplar trees. The U.S. Air Force has used poplar trees to contain trichloroethylene (TCE) in groundwater. In Iowa, EPA demonstrated that poplar trees acted as natural pumps to keep toxic herbicides, pesticides, and fertilizers out of the streams and groundwater. The US Army Corps of Engineers has experimented with wetland plants to destroy explosive compounds in the soil and groundwater. Submersed and floating-leafed species (coontail and pondweed, and arrowhead, respectively) decreased trinitrotoluene (TNT) to 5% of original concentration. Submersed plants were able to decrease Royal Demolition Explosive (RDX) levels by 40%, and when microbial degradation was added, RDX decreased by 80%. Sunflowers, using rhizofiltration, were used successfully to remove radioactive contaminants from pond water in a test at Chernobyl, Ukraine. Page 9 of 11

10 Bioremediation of petroleum[edit] Oil degrading organisms have evolved to use the hydrocarbons and organic compounds in petroleum as energy, and utilize molecular transfer mechanisms to denature these toxins. The aerobic and anaerobic properties of these microbes allow them to respire and ferment compounds as well, and this tends to result in the transformation of toxins into innocuous compounds. These compounds have more stable ph levels, increased solubility in water, and are less aggressive molecularly. It is known that the composition of oil-degrading microorganisms in marine ecosystems is originally less than 1%. When these organisms are given the necessary substrate, they tend to thrive and grow to almost 10% of the complete microbiome. Dependent on physical and chemical properties, petroleum-degenerative microorganisms take longer to degrade high-molecular weighted compounds, such as polycyclic aromatic hydrocarbons (PAH's). These microbes require a wide array of enzymes for the breakdown of petroleum, and require very specific nutrient composition to work at an efficient rate. Microbes work in a step-wise fashion to breakdown and metabolize the components of petroleum. Linear Alkanes Branched Alkanes Small aromatic compounds Cyclic Alkanes Treatments that utilize these breakdown processes most commonly use heat and chemicals to extend the efficacy. Page 10 of 11

11 Pseudomonas putida is a Gram-negative, rod-shaped, saprotrophic soil bacterium. Based on 16S rrna analysis, P. putida was taxonomically confirmed to be a Pseudomonas species (sensu stricto) and placed, along with several other species, in the P. putida group, to which it lends its name. A variety of P. putida, called multiplasmid hydrocarbon-degrading Pseudomonas, is the first patented organism in the world. Because it is a living organism, the patent was disputed and brought before the United States Supreme Court in the historic court case Diamond v. Chakrabarty, which the inventor, Ananda Mohan Chakrabarty, won. It demonstrates a very diverse metabolism, including the ability to degrade organic solvents such as toluene. This ability has been put to use in bioremediation, or the use of microorganisms to biodegrade oil. Page 11 of 11