United States
Environmental Protection
Agency
EPA/540/MR-93/508
April 1993
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
i
Mobile Volume Reduction Unit
U.S. Environmental Protection Agency
Technology Description: The Volume Reduction Unit
(VRU), which was developed by EPA, is a mobile, pilot-scale soil
washing system for stand-alone field use in cleaning soil con-
taminated with hazardous substances. Removal efficiencies de-
pend on the contaminant as well as the type of soil.
Soil washing is a water-based ex situ process for mechanically
scrubbing soils to remove undesirable contaminants. The pro-
cess removes contaminants from soils by either dissolving or
suspending them in the wash solution (which is later treated by
conventional wastewater treatment methods) or concentrating
them into a smaller volume of soil through simple particle size
separation techniques. The concept of reducing soil contamina-
tion through the use of particle size separation is based on the
finding that most organic and inorganic contaminants tend to bind
to fine-sized clay and silt particles primarily by physical pro-
cesses. Washing processes that separate the particles from the
coarser soil particles effectively concentrate the contaminants
into a smaller volume. The clean larger fraction can be returned
to the site for continued use.
Figure 1 provides a diagram of the typical VRU operational setup.
(Thei VRU setup at the Demonstration site was modified slightly
from this typical setup.) The basic VRU system consists of the
following subsystems:
• Soil handling and conveying (feed soil)
• Soil washing and coarse screening (mini-washer and 100
mesh screen)
Makeup Water Tank
Slowdown Tank
Water Heater
Screw Conveyor
Carbon Drums
Trommel Screen
Mini-Washer
Steam Boiler
Air Compressor
Grizzly
Electric Generator
Screened Soil Fractions
Figure 1. Typical VRU operational setup.
Printed on Recycled Paper
-------
• Hnes/floatables gravity separation (Corrugated Plate
Interceptor tank)
• Fines flocculation/water clarification and solids disposal
(ffoc tank)
* Water treatment (10 micron fitter, liquid phase carbon
adsorbents, blowdown tank, and water storage tank)
* Utilities - electric generator, steam boiler, and compressed
air unit.
Two vibrating screens continuously segregate the soil into various
stea fractions. Mini-washer overflow, containing the coarser sol-
Jds, falls onto the first screen. Solids from the first screen overflow
are gravity-fed to a recovery drum. The first screen underflow is
pumped at a controlled rate to the second screen where it is
joined by the mini-washer underflow. The overflow from the sec-
ond screen Is gravity-fed to the same recovery drum containing
the other washed soils. The second screen underflow drains into
a tank with a mixer and is then pumped to a Corrugated Plate
Interceptor (CPI). Three streams exit the CPI: materials lighter
than water, solids and washwater. Materials lighter than water
(ffoatables such as oil) fbw over an internal weir, collect in a
compartment wHhin the CPI, and drain by gravity to a drum for
treatment and disposal. Solids are discharged by the bottom
auger to a recovery drum. Effluent from the CPI overflows into a
tank with a mixer to a static mixer located upstream of the floe
clarifier's mix tank.
Flocculating chemicals such as liquid alum and aqueous poly-
oloclrolyte solutions are metered into the static flash mixer tank.
The slurry overflows into the floe chamber, where bottom solids
are augured to a drum for disposal. Clarified water is pumped
from the floe overflow tank through 10-micron filters for fine
particle removal and through activated carbon drums for hydro-
carbon removal to permit recycle.
Waste Applicability: The VRU is a mobile research unit
that was developed for treatability studies on soils contaminated
With a wide variety of contaminants. It was designed to be ex-
tremely flexible in terms of equipment and washwater additives
usod. In general, soil washing is effective on soils with a large,
coarse sand and gravel fraction contaminated with a wide range
of organic, inorganic, and reactive contaminants.
Demonstration Results: The Demonstration took place at
the former Escambia Treating Company in Pensacola, FL be-
tween November 5 and 13, 1992. The 26-acre facility had used
pentachlorophenol (POP) and creosote (polynuclear aromatic
hydrocarbons or PAHs) to treat wood products from 1943 to
1982. The site is currently undergoing a Superfund cleanup that
is being managed by EPA Region IV.
During the Demonstration, the VRU operated at a feed rate of
approximately 100 Ib/hr and a washwater-to-feed ratio of about
6:1. The physical condition of the washwater was modified with
various combinations of surfactant, caustic, and temperature
change. Condition 1 (no surfactant and ambient pH and tempera-
ture), Condition 2 (surfactant addition and ambient pH and tem-
perature), and Condition 3 (surfactant addition, pH of 9-10 and
temperature of 150°F). A summary of the preliminary data is
shown in Table 1.
Table 1. Summary of Preliminary VRU Demonstration Data
Condition (%)
Average POP removal
Average PAH removal
Feed soil returned as washed soil
Mass balance of total mass
Mass balance of PCPs
Mass balance of PAHs
1
80
79
96
104
108
87
2
93
84
96
113
60
60
3
97
96
81
98
24
17
An Applications Analysis Report and a Technical Evaluation
Report describing the complete demonstration will be available in
the Fall of 1993.
For Further Information:
EPA Project Manager
Teri Richardson
U.S. Environmental Protection Agency
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7949
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/540/MR-93/508
------- |