Emerging Technology Bulletin

Institute of Gas Technology

Fluid Extraction-Biological Degradation Process

Technology Description: The fluid extraction-biological

degradation (FEBD) process is a three-step process that

remediates organic contaminants in soil. The system is shown in

figure 1. It combines three distinct technologies: (1) fluid extraction, which removes the organics from contaminated solids; (2)

separation, which transfers the pollutants from the extract to a

biologically-compatible solvent; and (3) biological treatment, which

degrades the pollutants to innocuous end-products.

In the fluid extraction step, excavated soils are placed in a

pressure vessel and extracted with a recirculated stream of

supercritical or near-supercritical carbon dioxide. An extraction

cosolvent increases removal of many contaminants.

Following extraction, organic contaminants are transferred to a

biologically-compatible separation solvent such as water or a

water/methanol mixture. The separation solvent is sent to the

final stage of the process, where bacteria degrade the waste to

carbon dioxide and water. Clean extraction solvent is recycled to

the extraction stage.

Biodegradation occurs in aboveground aerobic bioreactors, using

mixtures of bacterial cultures capable of degrading the contaminants. Selection of cultures is based on site characteristics. For

example, if a site is contaminated mainly with polycyclic aromatic

hydrocarbons (PAH), cultures able to metabolize or co-metabolize these hydrocarbons are used.

Project Description: The supercritical extraction stage of

the FEBD process was evaluated through a series of laboratory

scale tests with three PAH contaminated soils identified as soils

1, 2, and 3. The effectiveness of the extraction process was

determined by following the fate of sixteen compounds.

Soil 1 was collected from a wood treatment site in Texas and

soils 2 & 3 were from former town gas sites. Total contaminant

concentrations were similar for the soils at 1500 to 2000 mg/g,

but contaminant distributions are somewhat different.

Extraction tests were performed in a batch supercritical fluid

extraction (SCE) unit. Soil 1 tests varied temperature, pressure,

EPA/540/F-94/501

March 1994

United States

Environmental Protection

Agency

Contaminated

sediments

Stage 1

EXTRACTION

Decontaminated

sediments

Compressor

Extraction

solvent

Extraction solvent

with contaminants

Recycled or

cleaned

extraction

solvent

Make-up

extraction

solvent

Water, carbon

dioxide, and

biomass

Stage 3

BIOLOGICAL

DEGRADATION

Separation solvents

with contaminants

Stage 2

SEPARATION

Separation

solvent

Pressure

reducing

valve

Figure 1. Fluid extraction-biological degradation process.
CO2

 to contaminant ratio and the addition of 5% methanol cosolvent. Temperatures were not varied with soils 2 & 3 extraction

tests.

The extraction levels from the soils decreased from soil 3 to soil 1

to soil 2. Soils 2 and 3 were almost entirely sand while soil 1 was

sandy with a 14% clay content. Clay in soil 1 did not appear to

interfere with the extraction of the PAH contaminants.

Biological conversion of the measurable PAHs was obtained in

both batch-fed and continuously-fed constantly stirred tank reactors (CSTRs). The conversion rate and the removal efficiency was

significant in all systems examined. The PAHs were biologically

mineralized or transformed under short hydraulic retention times,

and all the PAHs, including the four to six ringed moieties were

susceptible to the biological action.

Demonstration Results: The results of this study show that

the FEBD process was able to:

1)Effectively extract 2-6 ring PAH contaminants at low

teperatures and moderate pressures.

2)Increase extraction levels with increasing pressure and increasing CO2

 to contaminant ratios.

4)Increase PAH extraction with a 5% methanol co-solvent

addition.

5)Effectively extract PAHs contaminants from soils with 14%

clay content.

6)Microbial consortium effectively metabolized or transformed

PAHs in batch- or continuously-fed reactors.

7)Growth or metabolic activities of the microbial consortium

were not inhibited by methanol extract.

For Further Information:

EPA PROJECT MANAGER:

Annette Gatchett

U.S. EPA

Risk Reduction Engineering Laboratory

26 West Martin Luther King Drive

Cincinnati, OH 45268

513-569-7697

Fax: 513-569-7620

TECHNOLOGY DEVELOPER CONTACT:

J. Robert Paterek

Institute of Gas Technology

3424 South State Street

Chicago, IL 60616

312-949-3947

Fax: 312-949-3700

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/540/F-94/501