Presentation on theme: "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."— Presentation transcript:
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
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
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?
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
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?
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
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
What Makes Bioremediation a Promising Approach? permanence –contaminant is degraded potentially low cost –60-90% less than other technologies
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.
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
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
ATP ACETATE CO 2 Fe(III) Fe(II) Metabolism of a Pollutant-degrading Bacterium*Benzoate*Toluene*Phenol *p-Cresol *Benzene *U(VI)*Co(III)*Cr(VI)*Se(VI)*Pb(II)*Tc(VII) *CCl 4 *Cl-ethenes*Cl-aromatics*Nitro-aromatics
Uranium reduction leads to uranium precipitation and immobilization U 6+ sol U 4+ insol U 6+ sol U 4+ insol
Volatile organic compounds (VOC) These are major contributors to air pollution –Paint industry –Pharmaceutical industry –bakeries –printers –dry cleaners –auto body shops
Cometabolism Bacterium uses some other carbon and energy source to partially degrade contaminant (organic aromatic ring compound) bacterium corn starch CO 2 + H 2 O contaminant degradation products
Hard to degrade contaminants Chlorinated hydrocarbons –solvents –lubricants –plasticizers –insulators –herbicides and pesticides.
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.
Phenol-degrading dmp operon is regulated by DmpR, a NtrC-like positive regulator. CO 2 + H 2 O
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
Genetic engineering of bacteria to remove toxic metals from the environment Hg 2+ -metallothein Hg 2+ → Hg o Hg 2+ New gene/enzyme New gene/transport proteins E. coli bacterium Hg o (less toxic form of metal)
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
Phytoremediation Drawbacks –Only surface soil (root zone) can be treated –Cleanup takes several years
Transgenic plants Royal Demolition eXplosive Stimulates plant growth! Gene from bacterium moved to plant genome
Careers in Bioremediation Outdoor inspection Lab testing Administration Company employee Government Employee Regulatory oversight
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