Bioremediation of Petroleum Contamination. Augustine Ifelebuegu GE413

Transcription

1 Bioremediation of Petroleum Contamination Augustine Ifelebuegu GE413

2 Bioremediation Bioremediation is the use of living microorganisms to degrade environmental contaminants in the soil and groundwater into less toxic, or nontoxic materials. These microorganisms can be indigenous, commercial bacterial mixtures or may be genetically engineered.

3 Biodegradation Concept The breakdown of organic compounds by micro-organisms How might microorganisms attack hazardous organic wastes? Mineralize compound directly, compound converted to harmless inorganic molecules such as carbon dioxide and salts Of prime importance are microorganisms capable of producing enzymes that will degrade the hazardous chemical (target compound) as enzymes degrade compounds through exploitation of the organism s energy need. Converting compound to some other compound, which may also be toxic and recalcitrant to further degradation

4 Biodegradation Concept Heterotrophic microorganisms are the principal user of organic matter in the biosphere and are key in cycling carbon from the organic to the inorganic state. Provided that sufficient inorganic nutrients as an energy source and a terminal electron acceptor for metabolism are present, all naturally occurring organic material can be biodegraded eventually. Simple organic compounds such as acetate may persist under condition that do not favor microbial activity. These conditions include extremes in temperature or ph, the presence of toxicants or antimicrobial agents, the inhibition or exclusion of microbial enzymes, and the lack of water and an electron acceptor.

5 Environmental requirements

6 Operational Conditions Nutrients Delivery systems Electron acceptors for amendments (O 2, NO 3-, CO 2, etc.) Bioavailability and Temperature impact degradation rates of Toxicity control contaminants Organic contaminants Bioreactors Outputs Gases Biomass Liquid

7 Biodegradation Process Microbe Oil CO 2 +H 2 O CO 2 +H 2 O CO 2 +H 2 O Microorganisms eat oil and other organic contaminants. Microorganisms digest oil and convert it to CO 2 and H 2 0 Microorganisms release CO 2 and H 2 0

8 GMO s Superbugs have been constructed: A multi plasmid containing Pseudomonas strain can oxidize aliphatic, aromatic, terpenic and polyaromatic hydrocarbons A hydrocarbon degrading superbug has been licenced for use. It degrade s camphor, octane, xylene and napthalene Problems: Survival in nature? Release of GMO s into environment? 8

9 What Types of Compounds Can Be Treated Biologically? Petroleum Hydrocarbons Gasoline Diesel Fuel Gasoline Additives such as MTBE Polyaromatic Hydrocarbons Creosote Chlorinated Hydrocarbons Chlorinated Aliphatics: trichlorethylene Chlorinated Aromatics : PCB s, Pentachlorophenol Explosives RDX, TNT Inorganics via Reduction to a Lower Valence Causing Precipitation Uranium, Technicium Sulfur and Sulfuric Acid Ammonia or Nitrate/Nitrite

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11 TYPES OF BIOREMEDIATION The two main types of bioremediation are in situ bioremediation and ex situ bioremediation. In addition, another offshoot of bioremediation is phytoremediation.

12 Options Available for Bioremediation 12

13 In Situ Bioremediation In situ bioremediation is when the contaminated site is cleaned up exactly where it occurred. It is the most commonly used type of bioremediation because it is the cheapest and most efficient, so it s generally better to use. There are two main types of in situ bioremediation: intrinsic bioremediation and accelerated bioremediation.

14 Intrinsic Bioremediation Intrinsic bioremediation uses microorganisms already present in the environment to biodegrade harmful contaminant. There is no human intervention involved in this type of bioremediation, and since it is the cheapest means of bioremediation available, it is the most commonly used. When intrinsic bioremediation isn t feasible, scientists turn next to accelerated bioremediation.

15 Accelerated Bioremediation In accelerated bioremediation, either substrate or nutrients are added to the environment to help break down the toxic spill by making the microorganisms grow more rapidly. Usually the microorganisms are indigenous, but occasionally microorganisms that are very efficient at degrading a certain contaminant are additionally added.

16 In situ biodegradation involves supplying oxygen and nutrients by circulating aqueous solutions through contaminated soils to stimulate naturally occurring bacteria to degrade organic contaminants. Bioaugmentation Bioremediation frequently involves the addition of microorganisms indigenous or exogenous to the contaminated sites.

17 Bioventing In situ treatment which combines an increased O 2 supply with vapour extraction Apply vacuum at some depth in contaminated site to draw air into the site from holes drilled around the site This extracts volatile organic compounds Nutrient supplementation may help Only useful for volatile compounds and where soil is permeable 17

18 Bioventing process for removal of volatile contaminants

19 Biosparging Aims to increase biological activity of the soil by increasing the O 2 supply Air injection was used initially but now pure O 2 is injected Can be used together with biostimulation and bioaugmentation 19

20 Permeable reactive barriers to treat contaminated groundwater Active permeability barrier is a trench filled with stones and compost in the path of the contaminant flow biofilms develop on stones and compost provides nutrients 20

21 Ex Situ Bioremediation Another type of bioremediation is ex situ bioremediation, which is when contaminated land are taken out of the area to be cleaned up by the organisms. This type of bioremediation is generally used only when the site is threatened for some reason, usually by the spill that needs to be cleaned up Ex situ bioremediation is only used when necessary because it s expensive and damaging to the area, since the contaminated land is physically removed.

22 Ex Situ Bioremediation Landfarming is a simple technique in which contaminated soil is excavated and spread over a prepared bed and periodically tilled until pollutants are degraded. Composting is a technique that involves combining contaminated soil with non-hazardous organic compounds such as agricultural wastes. The presence of these organic materials supports the development of a rich microbial population and elevated temperature characteristic of composting.

23 Biopile process Contaminated soil is heaped into piles within a lined area to prevent leaching Covered with plastic and liquid nutrients are applied to surface Aeration is improved by applying suction to the base of the pile Leachate is collected by pipes at the base 23

24 Biopile process for treatment of contaminated land

25 Bioreactors-Slurry reactors or aqueous reactors are used for ex situ treatment of contaminated soil and water pumped up from a contaminated plume. Bioremediation in reactors involves the processing of contaminated solid material (soil, sediment, sludge) or water through an engineered containment system.

26 Phytoremediation is the use of plants to clean up potentially damaging spills. The plants work with soil organisms to transform contaminants, such as heavy metals and toxic organic compounds, into harmless or valuable forms. Phytoremediation

27 Rhizofiltration The removal of contaminants from flowing water by plant roots or organisms in the rhizosphere Compounds removed include organic compounds and metals Wetlands are constructed Reeds e.g. Phragmites are planted in reed beds and assist by pumping O 2 out of their roots This encourages growth of healthy biofilms in the rhizosphere

28 Simple artificial wetland 28

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30 Advantages of bioremediation Bioremediation is a natural process and is therefore perceived by the public as an acceptable waste treatment process Many compounds that are legally considered to be hazardous can be transformed to harmless products. Instead of transferring contaminants from one environmental medium to another, for example, from land to water or air, the complete destruction of target pollutants is possible. Bioremediation can often be carried out on site, often without causing a major disruption of normal activities. Bioremediation is less expensive

31 Disadvantages of bioremediation Bioremediation often takes longer than other treatment options Biological processes are often highly specific. Important site factors required for success include the presence of metabolically capable microbial populations, suitable environmental growth conditions, and appropriate levels of nutrients and contaminants.

32 Advanced Chemical oxidation Photochemical and Non Photochemical processes are available for generating OH radicals used for advance chemical oxidation: Ozonation at elevated ph (>8.5) Ozone + hydrogen peroxide (O 3 /H 2 O 2 ) Ozone + catalyst (O 3 /CAT) Fenton system (H 2 O 2 /Fe 2+ ) O 3 /UV H 2 O 2 /UV O 3 /H 2 O 2 /UV Photocatalytic oxidation (UV/TiO 2 )

33 ... finally