Soil 5483

Biodegradation and Soil Bioremediation

Overview

1. Definitions2. What are the components involved?3. Principles Role of microorganisms Role of plants Interactions

4. Bioremediation Technologies (CIVEN 5853, Bioremediation by Dr. William Clarkson)4.1. In Situ treatment 4.2. Composting4.3. Slurry reactors4.4. Solid-Phase bioremediation4.5. Vapor-Phase bioremediation4.6. Land farming

5. Applications

• Heavy metals• Hydrocarbons• Chlorinated organics• Nitroaromatics- explosives

Biodegradation—Biologically catalyzed reduction in complexity of chemical (Alexander, 1999).

Indeed, microorganisms are frequently the sole means of converting synthetic chemicals to inorganic products.

• In the case of organic compounds, biodegradation frequently leads to the conversion of much of the C, N, P, S, and other elements in the original compound to inorganic products. Such a process is known as mineralization.

Bioremediation—

• The use of biological processes for the remediation of contaminated environments. Or

• The use of living organisms to reduce or eliminate environmental hazards resulting from accumulations of toxic chemicals and other hazardous wastes (Francis, 1999).

Phytoremediation—

Inititally, the term has been closely associated with the potential use of hyperaccumulator species, plant being able to accumulate unusual levels of metals in their tissues.

Recently, the scope has been extended to include other plant-based processes that result either in containments or removal of pollutants, e.g., immobilization, degradation and volatilization (Wenzel et al., 1999).

Most of the hyperaccumulators are rather small herbaceous plants growing on naturally metalliferous sites or on old mining deposits.

Because of the low-biomass limitation of hyperaccumulator species, high-biomass vegetation, such as trees and grass are being evaluated as an alternative, even though the bioconcentration of metals is typically well below that found in the former.

Matrix

Soil—from farming operations, land spreading of industrial wastes, accidental spills, or sludge disposal, and the degradation of natural materials in soils.

Sediment Water Air

Contaminants (?)

Heavy metals (Hg, As, Cd, Pb,...) Hydrocarbon (Petroleum…) Chlorinated organics (TCE, PCE) Explosives (TNT, RDX) Radionuclides, such as plutonium Pesticides, such as atrazine, benlate,

and malathion

Contaminants

BTEX--benzen, toluene, ethylbenzene, xylene.

PAH--polycyclic aromatic hydrocarbons such as creosote mixtures,

PCB--polychlorinated biphenyl, such as acroclor mixtures.

Alexander, 1999

TCE

2,4-DAtrazine

• Each ring on the biphenyl structure can have up to 5 chlorine atoms

• So it is theoretically possible to make 209 different kinds (congeners) of PCBs.

Eweis et al., 1998

Sources of contamination

• leaking underground storage tanks

• landfills• waste-disposal ponds• agricultural runoff• Spills and improper

disposal of toxic materials.

Oklahoma Refining Company

Location: Cyril, Oklahoma in Caddo CountySize: 160 acresContaminants: organic, petroleum, and heavy

metal, including VOCs (benzene, toluene xylene..), PAHs, phenol, As, Cr and Pb.

Affected media: soil, sediment, surface water and groundwater

Estimated total cost: $31.7 million including an annual operation and maintenance cost of $425,000 every year for 30 yrs.

Http://www.epa.gov/superfund/sites/rodsites/0601172.htm

A NPL Site

Location: Northeast Oklahoma, the Tar Creek Watershed

Affected area: the entire Ottawa County by 1979 evaluation; 40 square miles by 1997 evaluation.

Cause: flooded undergraound lead-zinc mines of the picher field in Ottawa County

Estimated cost: $4 millionRemediation strategies used: diverting water,

plugging wells, and excavating soil

Tetrachlorodibenzo()dioxin (TCDD)

• Times Beach, Missour• A mixture of chemical wastes and used crankcase oil was

sprayed on roads and other unpaved areas as a dust-control measure.

• A number of animal deaths in 1971. Then, TCDD was found in the soil.

• Removal of the upper 6 in of soil proved unsatisfactory as a remediation measure, and eventually the community had to be evacuated.

What is Dioxin (2,3,7,8-TCDD)?

• The term Dioxin is commonly used to refer to a family of toxic chemicals that all share a similar chemical structure and a common mechanism of toxic action.

• This family includes seven of the polychlorinated dibenzo dioxins (PCDDs), ten of the polychlorinated dibenzo furans (PCDFs) and twelve of the polychlorinated biphenyls (PCBs).

Dioxin• PCDDs and PCDFs are not commercial chemical

products but are trace level unintentional byproducts of most forms of combustion and several industrial chemical processes.

• PCBs were produced commercially in large quantities until production was stopped in 1977.

• Dioxin levels in the environment have been declining since the early seventies and have been the subject of a number of federal and state regulations and clean-up actions; however, current exposures levels still remain a concern.

Backyard Burning of Trash was now the #1 Dioxin Source in 2002/4!

Why Are We Concerned?• Because dioxins are widely distributed throughout

the environment in low concentrations, are persistent and bioaccumulated.

• Most people have detectable levels of dioxins in their tissues. These levels, in the low parts per trillion, have accumulated over a lifetime and will persist for years, even if no additional exposure were to occur.

• This background exposure is likely to result in an increased risk of cancer and is uncomfortably close to levels that can cause subtle adverse non-cancer effects in animals and humans.

• Scientists in EPA's National Center for Environmental Assessment are currently working on a comprehensive reassessment of dioxin exposure and human health effects.

• The latest draft assessment, Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds posted in Dec 2003, is still undergoing revisions in light of the review by the National Academy of Sciences(NAS) in November 2004.

• A Workshop in Feb 2008 was held to discuss EPA's response to the NAS reports.

EPA Action

http://cfpub.epa.gov/ncea/CFM/nceaQFind.cfm?keyword=Dioxin

Lathrop, Califonia, where tank rinsate from manufacture of the soil fumigant dibromochloropropane (DBCP) was disposed of in a field behind the facility. Groundwater concentrations as high as 1,700 mg/L were found. DBCP was found to be male sterilant and a carcinogen.

Why are we concerned about groundwater (water

quality) most?

Example of Groundwater contamination with TCE: Density of pure TCE at 20oC: 1.46 kg/L.Maximum concentration limit in drinking water: 5 g/L

1 mL of TCE can contaminate 77,000 gal of water

Small leak in waste-disposal ponds and underground storage tanks can pollute very large quantities of water.

Contamination of soil and groundwater by leachate from a landfill.

Eweis et al., 1998

How much chemicals are produced in the U.S.?

How much are emitted?

Alexander, 1999

Alexander, 1999

In reality, what kinds of contaminants that we have nation wide?

How much does it cost to clean up the nation’s waste sites?

What are the technologies used in remediation and restoration of contaminated sites?

Remediators

Microorganisms Plants

Methodology (CIVEN 5853, Bioremediation by Dr. William Clarkson)

In situ treatment Ex situ treatments

Solid-Phase bioremediation Slurry-Phase bioremediation Vapor-Phase bioremediation

Some Common Strategies Used in Bioremediation

• Passive or intrinsic bioremediation• Biostimulation• Bioventing• Bioaugmentation• Landfarming• Composting• Phytoremedation

Criteria for Bioremediation (Alexander, 1999)

1. The organisms must have the necessary catabolic activity to degrade the contaminant at a reasonable rate to bring the concentration of the contaminant to a level that meets regulatory standards.

2. The target contaminant must be bioavailable.

Criteria for Bioremediation (Alexander, 1999)

3. The site must have soil conditions conducive to microbial or plant growth or enzymatic activity.

4. The cost of the bioremediation must be less than or, at worst, no more expensive than other technologies that can also remove the contaminant.