Bioremediation

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. 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 What are environmental contaminants?

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 man-made 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 1980 • 1 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?

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____________________________________________

13. 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 What challenges exist for bioremediation of pollutants and xenobiotics?

14. Fundamentals of cleanup reactions • Aerobic metabolism • Microbes use O2 in their metabolism to degrade contaminants • Anaerobic metabolism • Microbes substitute another chemical for O2 to degrade contaminants • Nitrate, iron, sulfate, carbon dioxide, uranium, technicium, perchlorate

17. Metabolism of a Pollutant-degrading Bacterium Fe(III) ACETATE *U(VI) *Co(III) *Cr(VI) *Se(VI) *Pb(II) *Tc(VII) *Benzoate *Toluene *Phenol *p-Cresol *Benzene ATP CO2 Fe(II) *CCl4 *Cl-ethenes *Cl-aromatics *Nitro-aromatics

18. U6+sol U4+insol U6+sol U6+sol U4+insol Uranium reduction leads to uranium precipitation and immobilization

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

20. Cometabolism • Bacterium uses some other carbon and energy source to partially degrade contaminant (organic aromatic ring compound) degradation products contaminant bacterium corn starch CO2 + H2O

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

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. CO2 + H2O • Phenol-degrading dmp operon is regulated by DmpR, a NtrC-like positive regulator.

25. The layout of the genes involved in chlorocatechol-degradation on the plasmid is similar to the layout of the catechol-degrading genes on the chromosome

26. Genetic engineering of bacteria to remove toxic metals from the environment E. coli bacterium New gene/transport proteins Hg2+-metallothein Hg2+→Hgo Hg2+ New gene/enzyme Hgo (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

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