การช วบ าบ ด (Bioremediation)

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การชีวบําบัด

(Bioremediation)

D Dalee

Department of Biology Faculty of Science & Technology Yala Rajabhat University

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Hazardous Organic Wastes

• Petroleum products • Fungicides

• Insecticides • Herbicides

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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…

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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

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.

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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

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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

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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.

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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

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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

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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

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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 14

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)

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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)

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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.

(Table 1 in your notes)

Basic Metabolism Process

of Bacteria

Growth and Reproduction Catalyzed by Enzymes CELL ENERGY SOURCE NUTRIENTS CARBON SOURCE NEW CELL MASS H₂O CO2

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Schematic Diagram of

Biodegradation

Oil Microbe CO2+H2O CO₂+H₂O CO₂+H₂O

Microorganisms eat oil and other organic contaminants.

Microorganisms digest oil and convert it to CO2and H20 Microorganisms release CO2and H20 1. 2. 3. 20

Anaerobic Digestion of Organic Wastes

Soluble Organics Bacterial Cells Volatile Acids CO₂+ H₂ Other Products CH4+ CO2 Bacterial Cells

ACID FORMING BACTERIA

METHANE FORMING BACTERIA

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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)

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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 - 50o_{to 100}o_F

• Enzymes, chemical catalysts to break waste materials into smaller pieces • Surfactants (detergents, for example)

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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

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The Effect of pH on the Growth of

Specific Microorganisms 2

Microorganism Optimum pH BACTERIA: Pseudomonas aeruginosa 6.6 – 7.0 Bacillus alcolophilus 10.6 Nitrosomas spp. 8.0 – 8.8 Thiobacillus thiooxidans 2.0 – 3.5 ALGAE: Cynidium caldarium 2.0 FUNGI: Physarum polycephalum 5.0 26

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)

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Examples of Microbes used for

Specific Chemicals

Complete list can be found in Table 2 (Notes) Compound Name Microorganisms Conditions

Aliphatics (non-halogenated)

Ex. Acrylonitrile

Mixed culture and activated sludge Aerobic Aliphatics (halogenated) Ex. Trichloroethane Marine bacteria, sewage sludge, soil bacteria, methanogens Aerobic + Anaerobic Aromatic compounds Ex. BTEX, creosol, phenol Pseudomonas spp., Bacillus spp., Rhodococcus spp., Mycobacterium spp. Aerobic + Anaerobic 28

Typical Bacteria Species include:

(in descending order of occurrence)

• Pseudomas • Arthobacter • Alcaligenes • Corynbacterium • Flavobacterium • Achrombacter • Acinetobacter • Micrococcus • Nocardia • Mycobacterium

Technology Selection Criteria

The bioremediation technology

for a site is determined by:

• Microorganisms present • Site Condition

• Quantity and Toxicity of Contaminants

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 20o_C.

• Chemical Oxygen Demand (COD) - measures a

chemical’s ability to oxidize toxic chemicals in 3 hours.

• The difference between the two gives the

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Categories of Bioremediation

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.

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Typical in situ Bioremediation System

Contaminated Zone Old Water Table New Water Table Water Treatment Nutrient/ Oxygen Addition Recovery Well Injection Well 33

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.

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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. 35

Air Sparging

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Bioreactor

Liquid outlet Soil to drying Temperature control Agitator Vapor out Air inlet Nutrient Contaminated soil Contaminated liquid

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Examples of ex situ Bioremediation

• Slurry Phase: a large tank, or

“bio-reactor” contains the soil, water, and added nutrients or oxygen to keep the microorganisms in the optimum environment to degrade

contaminants.

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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.

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Examples of ex situ Bioremediation 3

- 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 40

Landfarming

Tank Air Filter/Pump Gravel layer Contaminated soil

Biopiles

Nutrient/moisture Gravel layer Leachate collection Impermeable layer Contaminated soil

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.

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Soil Washing

Contaminated Zone Water Table Mixture Separator/ Water Treatment Recovery Well Injection Well Mixture Tank water & surfactants 44

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

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Diagram of Bioremediation

Adding Oxygen -Bioventing -Biosparging Adding Oxygen and Nutrients Biostimulation Adding Oxygen, Nutrients and Bacteria

Bioaugmentation Engineered Intrinisic in situ Landfarming Bioreactor ex situ Bioremediation 46

Remediation Time

• 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

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Polluted Sites

• Accidental spills • Service stations • Old Air Force bases

• Storage tanks and pipelines

• Chemical plants and other industrial sites