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Superfund Innovative Technology Evaluation (SITE)

 EPA/540/A5-91/003

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

 

BioTrol Soil Washing System for Treatment of a Wood Preserving Site
February 1992

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:

  1. 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.
  2. 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.
  3. 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 lower solubilities.
  4. 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.
  5. The BATS successfully degraded between 91 and 94% of the pentachlorophenol in the aqueous process liquor, the Combined Dewatering Effluent (CDE).
  6. 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 the cost.
  7. On an individual unit basis, costs for the process were:
    1. Soil Washer $185/metric ton or $154/short ton of soil or $197/yd3 (including incineration)
    2. SBR $9.22/1000 L or $34.39/1000 gal of 20% slurry
    3. 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:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.

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