10 bioremediation

10 bioremediation - CEE 266 ENVIRONMENTAL BIOTECHNOLOGY...

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Unformatted text preview: CEE 266 ENVIRONMENTAL BIOTECHNOLOGY Lecture 10 (Biodegradation and Bioremediation) Definitions   Xenobiotic: synthetic chemicals that are not naturally occurring, e.g., pesticides, PCBs, munitions, dyes, chlorinated solvents, etc.   Biotransformation: Alteration of the chemical structure by microbiological (enzymatic) activity.   Biodegradation: subset of biotransformation that causes decrease in molecular weight or simplification of an organic's structure   Biocatalysis: Use of catalysts, such as enzymes, to produce commercially-important compunds. More Definitions   Mineralization: conversion of an organic molecule into its inorganic constituents or mineral salts.   Bioaccumulation: concentration of compound in tissue (e.g. PCBs)   Biomagnification: concentration in food chain (not excreted, toxic to species near top of chain)   Recalcitrant: resists biodegradation   Cometabolism: fortuitous transformation of molecule by an enzyme that routinely acts on another (primary substrate)” molecule. Metabolic vs. Co-metabolic Processes Organic Growth Substrate Products Growth-supporting Organic Compound Same enzyme Products Non-growth-supporting Still More Definitions   Primary Substrate: used as growth substrate   Cometabolic/Secondary substrate: unable to support growth   present in insufficient concentrations to support growth   does not provide energy or nutrients for cell growth   causes substrate or product toxicity   Detoxification: change of compound to less toxic form   e.g., toluene to benzoate; chloroform to methane   Activation: increase in toxicity of compound   e.g., TCE to VC, benzene to phenol) Important Classes of Pollutants   Petroleum hydrocarbons and associated compounds   Aliphatics, e.g., butane, octane (linear or branched)   Aromatics, e.g., BTEX, PAHs   Oxygenates, e.g., ethanol, MtBE   Chlorinated compounds   Methanes/Ethanes, e.g., CH3Br, 1,1,1-TCA   Ethenes, e.g., PCE, TCE, cDCE, VC   Aromatics, e.g., chlorobenzene, PCBs, dioxins More pollutants   Pesticides: e.g., 2,4,5-T, DDT   Explosives: e.g., TNT, RDX, HMX   Metals and radionuclides: e.g., As, Cr, Cu, Hg, Pb, U, Pu,   Emerging contaminants   1,4-dioxane, pharmaceuticals, disinfection by-products, flame retardants, antibiotics, fluorinated surfactants, nanomaterials Examples of Xenobiotic Compounds Figure 24.23 Petroleum Biodegradation   Diverse bacteria, fungi, and some cyanobacteria and green algae can oxidize petroleum products aerobically   Oil-oxidizing activity is best if temperature and inorganic nutrient concentrations are optimal   Hydrocarbon-degrading bacteria attach to oil droplets and decompose the oil and dispense the slick Figure 24.20 Petroleum Biodegradation   Gasoline and crude oil storage tanks are potential habitats for hydrocarbon-oxidizing microbes   If sufficient sulfate is present, sulfate-reducing bacteria can grow and consume hydrocarbons (anaerobic)   Some microbes can produce petroleum, e.g., green algae Anaerobic Biodegradation of PCE Aerobic Biodegradation of TCE Class Exercise: Who dun it? BTEX Biodegradation University of Minnesota Biocatalysis and Biodegradation Database (http://umbbd.msi.umn.edu/) In-situ Processes for Contaminant Fate and Transport Bioremediation Options   Natural Attenuation: combination of natural biological, chemical and physical processes that act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of the contaminants (e.g., biodegradation, dispersion, dilution, sorption, or volatilization).   Engineered Bioremediation: managed process in which biological catalysis acts on pollutants, thereby remedying or eliminating contamination present in water, wastewater, sludge" soil, aquifer material, or gas streams. Advantages of Bioremediation   Generally cheaper than removal and incineration, or pump and treat Minimum land and environmental disturbance   Does not dewater the aquifer   Completed on site, eliminates transportation cost & liability   Can attack hard-to-withdraw hydrophobic pollutants   Environmentally sound and public acceptance Disadvantages of Bioremediation   Potential for partial degradation to metabolites that are still toxic and/ or potentially more highly mobile in the environment   Highly sensitive to environmental conditions (O2, pH, temperature, permeability, dissolved ions, organic content, co-contaminants, etc.   Extensive monitoring required to determine biodegradation rates   Generally takes longer treatment time than other remediation technologies Requirements for Bioremediation 1.  Existence of organism(s) with required catabolic potential 2.  Presence of organisms in the contaminated environment 3.  Accessability of pollutant to biodegrading organism 4.  Induction of enzymes, e.g., by primary substrates 5.  Environmental factors, e.g., temperature, pH, soil moisture, 6.  Availability of electron acceptors, e.g., O2, or e- donors, e.g., H2 7.  Time… Steps in Feasibility/Design of in-situ Bioremediation 1. Site Investigation (Diagnose problem prior to selecting cure) 2. Physical Measures to Contain Plume (Free Product Recovery and Prevent off-site migration with interdiction wells) 3. Evaluation of Bioremediation Potential (Extrapolate experience, lab studies) 4. System Selection and Design (Aerobic vs anaerobic, nutrient delivery system) 5. Operation 6. Monitoring Bioremediation Process Selection Reduced compounds (e.g. hydrocarbons)   Oxidation is thermodynamically feasible   Degrade faster aerobically   Halogenated compounds (e.g. PCE) or metals   Already oxidized (by chlorine), so aerobic degradation is not as thermodynamically favorable   Contaminant often serves as electron   They degrade faster anaerobically donor and carbon source to support microbial growth.   Add oxygen (and/or nitrate?) to contaminated zone (reductive dechlorination)   Contaminant serves as e- acceptor for microbial respiration   Add e- donor to induce anaerobic conditions Biostimulation and Bioaugmentation   Natural Attenuation aka Intrinsic Bioremediation: do nothing!   Biostimulation: provide electron donors/acceptors, nutrients, etc.   Bioventing   Biosparging   Water circulation   Biobarriers   Bioaugmentation: introduce non-indigenous biodegrading organisms into the contaminated site   Enrichment cultures   Pure isolates   Genetically-modified cultures Biostimulation Systems O2 Bioventing Biosparging Water Circulation System Permeable Reactive Barriers Clean groundwater Biobarrier (microbes + nutrients) Contaminated groundwater Biostimulation Systems: Bioventing   Used to bioremediate volatile contaminants trapped in unsaturated zone above the water table   Vacuum pumps pull air through unsaturated soil   Need to infiltrate water (with nutrients) to prevent desiccation, but not too much so that soil permeability (to gas flow) is not adversely affected. Biostimulation Systems: Biosparging   Injection of compressed air directly into saturated contaminated zone through a series of injection wells   Stimulates aerobic degradation, strips volatile organic compounds (VOCs)'into unsaturated zone to be removed by vapor-capture systems   Not effective when low-permeability soil traps or diverts airflow Biostimulation Systems: Water Circulation   Used to bioremediate non-volatile contaminants in saturated zone   Contaminated water is extracted, treated ex-situ (air-stripping, activated carbon, or chemical treatment, or biodegradation), amended with nutrients, and reinjected   Clogging near injection well screens and infiltration galleries may be a problem (bacterial growth, mineral precipitation)   Pulsing reduces clogging (may need occasional Cl2, H202) Biostimulation Systems: Biobarriers   Biologically active zone is created in the path of the plume by injecting nutrients and electron acceptors (could use oxygen releasing compounds, nitrate-releasing briquettes, or inject compressed air and form an air curtain)   Microorganisms may also be injected. Thick biofilms can also plug up pore spaces, creating a vertical "biobarrier"   Hydraulic or physical controls on groundwater movement (e.g., funnel and gate) may be required to ensure that contaminants pass through the barrier ...
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