BioTrol Soil Washing System
for Treatment of a Wood Preserving Site
This project was an evaluation of theBioTro1, Inc.
soil Washing System (BSWS), consisting of a proprietary mechanical soil
washer and separation system, a Slurry Bio- Reactor (SBR) provided by
EIMCO Process Equipment Co., and BioTrol's proprietary Aqueous Treatment
System (BATS), a fixed-film, aerobic biological treatment process. In
this study, both biological processes use bacterial populations selected
to specifically degrade pentachlorophenol (penta).
This report summarizes and analyzes the results of the Superfund Innovative
Technology Evaluation (SITE) Program's demonstration at the MacGillis
and Gibbs Company wood preserving site in New Brighton, MN during the
Fall of 1989. Extensive sampling and analysis were carried out to establish
a data base against which the vendor's claims for the technology could
be evaluated reliably. Data from other investigations by BioTrol are included
to support the demonstration results. Conclusions were reached concerning
the technological effectiveness and economics of the process and its suitability
for use at other sites.
The primary conclusions from the demonstration study are:
- The Soil Washer effectively segregates the local soil into a coarse,
relatively uncontaminated fraction constituting the largest output portion,
smaller fractions of coarse and fine woody debris, and a contaminated
fine fraction accounting for about 10% of the input solids weight.
- Starting with soils containing either 130 mg/kg or 680 mg/kg of penta,
the removal efficiency for penta in the Soil Washer, defined as the change
in contaminant concentration (weighted average) between the feed soil
and the washed soil output stream, ranged between 89% and 87%. Removal
efficiencies for polynuclear aromatic hydrocarbons were slightly lower,
83% and 88%, in tests with two soils. Concern about the efficiency of
the extraction step during analysis of the feed soil, leading to low penta
and PAH values, suggests that these values may be biased low. The vendor
claims a 90% removal efficiency.
- Based on the demonstration study, 27.5% to 33.5% of the pentachlorophenol
mass is concentrated in the fine particle cake fraction (as-is weight
basis), between 18 and 28% is found in the coarse and fine oversize, and
34% to 39% is found in the processing water. The washed soil retains only
about 9%. Thus, while washing or extraction of pentachlorophenol takes
place, the predominant effect of the soil processing was segregation of
coarse and fine particles. Similar distribution occurs with PAHs except
that extraction into the aqueous fraction is much smaller due to the much
- While steady-state operation was not achieved in the anticipated acclimation
time (one week), the Slurry Bio-Reactor did achieve pentachlorophenol
removals as high as 93% and, based on extrapolation of the data, may well
be capable of even higher removal levels.
- The BATS successfully degraded between 91 and 94% of the pentachlorophenol
in the aqueous process liquor, the Combined Dewatering Effluent (CDE).
- Combined capital and operating costs for the integrated system are
estimated at $168/ton of feed soil, based on the MacGillis and Gibbs site.
The Soil Washer accounts for about 90% of the cost, followed by slurry
biodegradation of the fine particle slurry (about 2%) and treatment of
the aqueous stream (about 1%). Unassigned costs contribute about 5% to
the total cost. Incineration of the woody debris found in the soil is
a major component of the Soil Washer costs, contributing about 80% of
- On an individual unit basis, costs for the process were:
- Soil Washer $185/metric ton or $154/short ton of soil or $197/yd3 (including incineration)
- SBR $9.22/1000 L or $34.39/1000 gal of 20% slurry
- BATS $0.44/1000 L or $1.65/1000 gal of water treate
Secondary conclusions that have been reached on the basis of the demonstration
study and other data provided by the vendor include:
- The Soil Washer also separates highly contaminated coarse oversize
(wood chips) and fine oversize (sawdust) fractions, typical of wood preserving
facilities. These fractions may be incinerated.
- The nature of the soil has a significant effect on the efficiency
of soil washing and/or the segregation into coarse and fine fractions
that can be achieved. The soil character (e.g., particle size) must be
considered in evaluating the applicability of the Soil Washing System.
- Depending on the nature and concentration of contaminants of concern,
acclimation of the Slurry Bio-Reactor may take considerably longer than
the expected one week. Laboratory scale experiments would be needed in
each case to establish the acclimation period. This may be important in
scheduling and integrating units for a particular site.
- The system is not without mechanical problems and complexities that
still need to be resolved. For example, clogging in the soil feed system
forced a reduction in Soil Washer operating rates, and foaming in the
BATS, probably due to thickening agent added for dewatering of the fines,
created operational problems.
- The units evaluated in the demonstration study may not be appropriatelysized
for integrated operation. Similarly, for a full scale system, calculations have
indicated that a BATS capacity of about 300 gpm would be needed for the proposed
20 ton/hour soil processing rate. However, as discussed in the report, reuse of at least
a portion of the process water without treatment may be possible.