การช วบ าบ ด (Bioremediation)

Transcription

1 Hazardous Organic Wastes การช วบ าบ ด (Bioremediation) Petroleum products Fungicides Insecticides Herbicides D Dalee Department of Biology Faculty of Science & Technology Yala Rajabhat University 2 Most Common Contaminants Commercial Hydrocarbons - gasoline - diesel and jet fuel - naptha: raw material used in industry - domestic heating oil Chemicals called BTEX compounds - Benzene, Toulene, Ethylene, Xylene Organo-halogenated compounds (solvents) - trichloroethylene, tetrachloroethane, etc Most Common Contaminants 2 Heavy hydrocarbons - crude oil: pipeline, tanker and rail spills - heavy fuels from electric plants -tars - creosotes used in wood treatments Heavy metals Explosives 3 4 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 ( bag of bugs or bug n a bag ) or may be genetically engineered. Bacteria feed on organic waste and derive nutrition for growth and reproduction. This is familiar to all as the decay of dead animals and vegetable matter. Bioremediation 2 Municipal wastewater treatment plants have been using this technology for decades. Bioremediation is an application of the same principles in a different setting. Over time, Mother Nature usually heals herself. Adding large amounts of certain enzymes and bacteria hastens the decay. Utilizing bioremediation speeds up the process by increasing the rate of bacterial metabolism and growth

2 Uses of Bioremediation Bioremediation can be used to decompose or degrade: Crude oil spills Sewage effluent Chlorinated and non-chlorinated solvents in the industrial areas Coal Products: phenols and cyanide BTEX compounds Uses of Bioremediation 2 Agricultural chemicals and pesticides in groundwater and rivers Gasoline and fuel oil contamination Creosote contaminants (wood preservatives) Ethylene glycol (antifreeze), methanol, methylethylketone (MEK), ethers 7 8 Reasons to use Bioremediation Bioremediation can be cost effective because: Contamination can often be treated in place, minimizing site disturbance. Natural microbial processes can be used at some sites. Chemicals Which are Difficult to Decompose Trichloroethylene (TCE) - threatens water supplies Perchloroethylene (PCE) - a dry-cleaning solvent PCBs and Dioxin Arsenic, chromium, and selenium (these have been stabilized by bacteria in the laboratory) DDT 9 10 Effectiveness Biodegradation is not very effective at sites with high concentrations of the following materials which are toxic to microorganisms. Metals - solidification/stabilization is the usual treatment process Highly chlorinated organics Inorganic salts Disposing of Heavy Metals Heavy metals are not biodegradable, but bacteria can be used to concentrate them into a more easily disposable form. Uranium: iron-eating bacteria can remove low levels of radioactive waste from water. Mercury: experiments with bacteria are on-going

3 Microorganism Types There are large numbers of microorganisms that can use many of the toxic chemicals as a source of nutrients and energy. Some examples include: Bacteria Yeast Fungi Beneficial Characteristics Beneficial characteristics of bacteria for bioremediation must include the following: Consume organic waste Grow and reproduce rapidly in selected environment Digest the waste quickly and completely Work without causing odors or poisonous compounds Non-pathogenic - (Does not cause disease in humans or animals) Classes of Bioremediation Aerobic (with oxygen) - Microorganisms use available atmospheric oxygen to function. Food sources are converted to energy by the transfer of electrons to oxygen, which is an electron acceptor. Anaerobic(without oxygen) - Microorganisms break down chemical compounds to release the energy required to function. As electron acceptors, they utilize: - nitrates - sulfates - carbon dioxide - ferrous metals (such as iron) How Bioremediation works... Many naturally occurring microorganisms can digest organic materials such as fuels or solvents and convert them to: carbon dioxide water smaller, less toxic organic compounds Classification of Bacteria Bacteria are characterized by their external sources of energy and carbon, as shown in accompanying table. Basic Metabolism Process of Bacteria ENERGY SOURCE CARBON SOURCE NUTRIENTS (Table 1 in your notes) CELL Growth and Reproduction NEW CELL MASS CO 2 Catalyzed by Enzymes H 2 O

4 Schematic Diagram of Biodegradation Microbe Oil CO 2 +H 2 O CO 2 +H 2 O Anaerobic Digestion of Organic Wastes Soluble Organics ACID FORMING BACTERIA Microorganisms eat oil and other organic contaminants. CO 2 +H 2 O Microorganisms digest oil and convert it to CO 2 and H 2 0 Microorganisms release CO 2 and H Bacterial Cells Volatile Acids CO 2 + H 2 CH 4 + CO 2 Bacterial Cells Other Products METHANE FORMING BACTERIA 20 Optimization To optimize and accelerate the bioremediation of contaminants found in water and soil, selectively adapted microbes are combined with: Food - organic waste containing water (moisture content between 30-80%) - added nutrients (nitrogen, phosphorous, sulfur) Optimization 2 Oxygen if required (aerobic types) 3-5 pounds of oxygen per pound of hydrocarbon to be converted Moderate ph - between 6-9, neither too acidic nor too alkaline Moderate Temperatures - 50 o to 100 o F Enzymes, chemical catalysts to break waste materials into smaller pieces Surfactants (detergents, for example) The Effect of ph on the Growth of Specific Microorganisms The following slide shows the optimum ph level for the growth of several types of microorganisms. Information on the high and low ranges of ph tolerance may be found in Table 2 in your notes

5 The Effect of ph on the Growth of Specific Microorganisms 2 Microorganism Optimum ph BACTERIA: Pseudomonas aeruginosa Bacillus alcolophilus 10.6 Nitrosomas spp Thiobacillus thiooxidans ALGAE: Cynidium caldarium 2.0 FUNGI: Physarum polycephalum 5.0 Some Microorganisms used in Bioremediation Microorganism Characteristics Significance Yeast aerobic/ micro-aerophilic Degrades complex compounds Cyanobacteria aerobic/ micro-aerophilic/ anaerobic Self-sustaining, light is primary energy source Oligotrophs aerobic Removes TRACE concentrations of organic substances Complete list can be found in Table 3 (Notes) Examples of Microbes used for Specific Chemicals Compound Name Microorganisms Conditions Aliphatics (non-halogenated) Ex. Acrylonitrile Mixed culture and activated sludge Aerobic Aliphatics (halogenated) Ex. Trichloroethane Aromatic compounds Ex. BTEX, creosol, phenol Marine bacteria, sewage sludge, soil bacteria, methanogens Pseudomonas spp., Bacillus spp., Rhodococcus spp., Mycobacterium spp. Aerobic + Anaerobic Aerobic + Anaerobic Complete list can be found in Table 2 (Notes) 27 Typical Bacteria Species include: (in descending order of occurrence) Pseudomas Arthobacter Alcaligenes Corynbacterium Flavobacterium Achrombacter Acinetobacter Micrococcus Nocardia Mycobacterium 28 Technology Selection Criteria The bioremediation technology for a site is determined by: Microorganisms present Site Condition Quantity and Toxicity of Contaminants 29 Oxygen Demand Values Oxygen demand values are used to measure biological treatment processes. Biological Oxygen Demand (BOD) - measures the amount of oxygen necessary for microbes to remove waste in wastewater in 5 days at 20 o C. Chemical Oxygen Demand (COD) - measures a chemical s ability to oxidize toxic chemicals in 3 hours. The difference between the two gives the operating efficiency of a biological process. 30 5

6 Categories of Bioremediation Typical in situ Bioremediation System Bioremediation treatment applications fall into 2 categories: in situ - soil or groundwater is treated in the location where found. This is usually the most cost effective method, but can also be slower and hard to manage. ex situ - requires the excavation of soil or pumping of groundwater before treatment. 31 Injection Well Old Water Table Nutrient/ Oxygen Addition New Water Table Water Treatment Contaminated Zone Recovery Well 32 Examples of in situ Bioremediation Bio-venting: air and nutrients are pumped into the soil through injection wells to flush out contaminants. Air Sparging: air or oxygen is pumped into the groundwater to flush out contaminants - the air increases the oxygen concentration and enhances biological degradation. Examples of in situ Bioremediation 2 Injection of Hydrogen Peroxide: sprinklers or a system of pipes deliver the chemical to the soil. Extraction Wells: remove the groundwater to an aboveground water treatment system where nutrients and oxygen are added. Injection wells return the conditioned water to the subsurface where microorganisms degrade the contaminants Air Sparging Bioreactor Contaminated soil Contaminated liquid Nutrient Vapor out Agitator Temperature control Liquid outlet Air inlet Soil to drying

7 Examples of ex situ Bioremediation Slurry Phase: a large tank, or bioreactor contains the soil, water, and added nutrients or oxygen to keep the microorganisms in the optimum environment to degrade contaminants. Examples of ex situ Bioremediation 2 Solid phase: soil remains on the site, but is placed in above-ground treatment areas where moisture, heat, and nutrients or oxygen are added. - Landfarming: contaminated soils are excavated and spread onto a pad. Moisture and nutrients are controlled. This is the most widely used bioremediation technique Examples of ex situ Bioremediation 3 Landfarming - Soil Biopile: the contaminated soil is piled in large heaps and air is pulled through with vacuum pumps. Composting: biodegradable waste is mixed with a bulking agent such as straw, hay, or corn cobs, which facilitates the delivery of water and nutrients. The three types of composting are: * Static pile * Mechanically agitated in-vessel * Windrow composting 39 Air Filter/Pump Gravel layer Contaminated soil Tank 40 Biopiles Nutrient/moisture Gravel layer Contaminated soil Impermeable layer Leachate collection Soil Treatment Processes Bioremediation: Stand-alone or combined with the other technologies described below Soil Vapor Extraction (SVE): vacuum is applied to a network of pipes or wells. Preferred for in situ bioremediation. It is the usual treatment for volatile organic compounds. Thermal treatments desorption: the soil is heated to volatize water and organic pollutants. Soil washing: consists of washing soil in situ or ex situ - analogous to washing a greasy spoon with only water; surfactants can be used and the resulting emulsion can be sprayed over soil where bacteria will degrade it

8 Soil Washing Injection Well Mixture Tank water & surfactants Water Table Mixture Separator/ Water Treatment Contaminated Zone Recovery Well 43 Ground Water Treatment Processes Contaminated ground water treatment usually involves pumping the water to the surface where it is then treated. Technologies to supplement the pump-and-treat method are being developed. These include: Biofiltration Thermal enhancements Surfactants/co-solvents Hydro-pneumatic fracturing Electrokinetics Permeable treatment walls to alter chemical condition 44 Diagram of Bioremediation Remediation Time Adding Oxygen -Bioventing -Biosparging Biostimulation Engineered Adding Oxygen and Nutrients in situ Bioremediation Intrinisic Bioaugmentation Adding Oxygen, Nutrients and Bacteria Landfarming ex situ Bioreactor in situ bioremediation time depends on the extent, depth, and concentration of the contamination. It varies from 1-6 years. ex situ remediation for easily biodegradable contaminants or when bioreactors are used can take as little as 1-7 months Soil vapor extraction for a typical site takes 6 months to 3 years Polluted Sites Accidental spills Service stations Old Air Force bases Storage tanks and pipelines Chemical plants and other industrial sites Unauthorized dump sites 47 8