Bioremediation. Chapter 8

Transcription

1 Bioremediation Chapter 8

2 What is bioremediation? The use of bacteria and fungi and plants to break down or degrade toxic chemical compounds that have accumulated in the environment

3 What are environmental contaminants? Pollutants naturally-occurring compounds in the environment that are present in unnaturally high concentrations. Examples: crude oil refined oil phosphates heavy metals Xenobiotics chemically synthesized compounds that have never occurred in nature. Examples: pesticides herbicides plastics

4 Early examples of bioremediation Outhouse Centralized engineered wastewater treatment systems Microorganisms oxidize organic waste molecules to carbon dioxide and water Why do we want to use engineered manmade for this?

5 More recent examples By 1970s it became apparent that we were polluting the environment faster than the natural microbial processes could degrade the pollutants Congress established the Environmental Protection Agency Identified Superfund Sites that had priority over other polluted systems for special funding and cleanup in in 5 Americans lives within 3-4 miles of a polluted site treated by the EPA Not much progress has been made even though $billions has been spent

6 Groundwater contamination Groundwater constitutes 96% of available freshwater in U.S. 95% of potable water in rural areas of U.S. comes from groundwater In 1988, EPA confirmed that 26 states had various amounts of 44 different pesticides in their groundwater Cost of cleanup is in the $ trillions Issues that are still hotly debated How clean is clean?

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8 Most recent National Institute of Environmental Health Sciences established the Environmental Genome Project Study impact of environmental chemicals on human disease Identify genes and their products that are sensitive to toxic chemicals in the environment Identify genes that encode for products that detoxify the chemicals

9 What types of treatment technologies are in use to remove contaminants from the environment? Soil vapor extraction air sparging bioremediation thermal desorption soil washing chemical dehalogenation soil extraction in situ soil flushing

10 What Makes Bioremediation a Promising Approach? permanence contaminant is degraded potentially low cost 60-90% less than other technologies

11 Economics of in-situ vs. ex-situ remediation of contaminated soils Cost of treating contaminated soil in place $80- $100 per ton Cost of excavating and trucking contaminated soil off for incineration is $400 per ton. Over 90% of the chemical substances classified as hazardous today can be biodegraded.

12 Contaminants Potentially Amenable to Bioremediation Readily degradable fuel oils, gasoline Somewhat degradable creosote, coal tars Difficult to degrade chlorinated solvents (TCE) Generally recalcitrant dioxins ketones and alcohols pentachlorophenol (PCP) some pesticides and herbicides polychlorinated biphenyls (PCB) monocyclic aromatics bicyclic aromatics (naphthalene)

13 What challenges exist for bioremediation of pollutants and xenobiotics? Pollutants may exist at high, toxic concentrations degradation may depend on another nutrient that is in limiting supply Xenobiotics microbes may not yet have evolved biochemical pathways to degrade compounds may require a consortium of microbial populations

14 Fundamentals of cleanup reactions Aerobic metabolism Microbes use O 2 in their metabolism to degrade contaminants Anaerobic metabolism Microbes substitute another chemical for O 2 to degrade contaminants Nitrate, iron, sulfate, carbon dioxide, uranium, technicium, perchlorate

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17 Metabolism of a Pollutant-degrading Bacterium ACETATE *Benzoate *Toluene *Phenol *p-cresol *Benzene ATP Fe(III) *U(VI) *Co(III) *Cr(VI) *Se(VI) *Pb(II) *Tc(VII) CO 2 *CCl 4 *Cl-ethenes *Cl-aromatics *Nitro-aromatics Fe(II)

18 Uranium reduction leads to uranium precipitation and immobilization U 6+ sol U 4+ insol U 6+ sol U 6+ sol U 4+ insol

19 Volatile organic compounds (VOC) These are major contributors to air pollution Paint industry Pharmaceutical industry bakeries printers dry cleaners auto body shops

20 This image cannot currently be displayed. Cometabolism Bacterium uses some other carbon and energy source to partially degrade contaminant (organic aromatic ring compound) contaminant bacterium degradation products corn starch CO 2 + H 2 O

21 Hard to degrade contaminants Chlorinated hydrocarbons solvents lubricants plasticizers insulators herbicides and pesticides.

22 Chemicals that exist as ring structures, which have chlorine atoms attached are referred to as halogenated aromatics and are often toxic. Examples: chlorobenzoates 2, -4-dichlorophenoxyacetate chlorobenzenes Removal of the Cl atom is the rate-limiting step in the degradation of the halogenated aromatic. A dioxygenase enzyme is used to replace the Cl atom with an OH group. The process requires the presence of oxygen.

23 Degradation of chlorinated hydrocarbons Degradation of organic toxins requires the participation of entire biochemical pathways involving many enzymes coded for by many genes. Some of the genes exist on the chromosome while other genes reside on plasmids.

24 phenol OH catechol cis, cis-muconate phea dmpx OH OH pheb dmpb COOH COOH succinate and acetyl CoA phenol hydrolase (monooxygenase) dioxygenase CO 2 + H 2 O Phenol-degrading dmp operon is regulated by DmpR, a NtrC-like positive regulator.

25 The layout of the genes involved in chlorocatecholdegradation on the plasmid is similar to the layout of the catechol-degrading genes on the chromosome 3-chlorobenzoate 3-chlorocatechol 2-chloro-cis,cismuconate COOH OH OH COOH A COOH Cl OH Cl B Cl C=O COOH o dieneiactone D succinate O COOH COOH O COOH COOH maleylacetate 3-ketoadipate A, pyrocatechase II B, muconate lactonizing enzyme II D, hydrolase II

26 Genetic engineering of bacteria to remove toxic metals from the environment New gene/transport proteins E. coli bacterium Hg 2+ Hg 2+ -metallothein Hg 2+ Hg o New gene/enzyme Hg o (less toxic form of metal)

27 Phytoremediation 350 plant species naturally take up toxic materials Sunflowers used to remove radioactive cesium and strontium from Chrenobyl site Water hyacinths used to remove arsenic from water supplies in Bangladesh, India

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29 Phytoremediation Drawbacks Only surface soil (root zone) can be treated Cleanup takes several years

30 Transgenic plants Royal Demolition explosive Gene from bacterium moved to plant genome Stimulates plant growth!

31 Careers in Bioremediation Outdoor inspection Lab testing Administration Government Employee Regulatory oversight Company employee

32 Summary Many factors control biodegradability of a contaminant in the environment Before attempting to employ bioremediation technology, one needs to conduct a thorough characterization of the environment where the contaminant exists, including the microbiology, geochemistry, mineralogy, geophysics, and hydrology of the system