Description
Former Chemical Manufacturing Facility W.R. Grace Charleston,
South Carolina, USA
Project: Bioremediation of Soil Containing Toxaphene and DDT
Summary
The application of DARAMEND® served to reductively dechlorinate and
subsequently mineralize chlorinated herbicides and pesticides present in
soil. This project was the third in a series of three pilot-scale projects
aimed at validating DARAMEND bioremediation for use on various
chlorinated organic pesticides.
The Challenge
Treatment of about 250 tons of soil impacted with various chlorinated
pesticides including Toxaphene and DDT was conducted in a covered in situ
treatment cell. Toxaphene, the principle target contaminant, is known to
be extremely recalcitrant and is generally considered to resist
biodegradation. Due to the in situ nature of this application,
soil contaminant concentrations were highly variable and spatially
distributed.
For example, Toxaphene concentrations ranged from 1,600 mg/kg closest
to the former production facility, to 12 mg/kg at the furthest point. The
higher pesticide concentrations presented a particularly significant
challenge for effective remediation.
The Solution
The treatment process involved the application of DARAMEND to a 60 cm
thick layer of soil within a treatment area. To prevent unwanted
precipitation from impacting treatment, the treatment area was covered
with a polyethylene - clad greenhouse. Soil undergoing treatment was
subjected to several anaerobic / aerobic treatment cycles. Anaerobic
conditions were generated by the application of DARAMEND organic
amendments and zero valent powdered iron. Soil was then irrigated to
increase the soil moisture content to 90% of the soil water holding
capacity to minimize the diffusion of oxygen into the soil. Aerobic
conditions were generated through the repeated introduction of oxygen into
the soil via mechanical tillage. Eight separate treatment cycles were
required to achieve the remedial goal in some areas of the treatment cell
(total DARAMEND loading was <3.5% by weight).
The Result
The mean concentrations of the key target contaminants, Toxaphene and
DDT, were reduced from 239 mg/kg and 89.7 mg/kg to 5.1 mg/kg and 16.5
mg/kg, respectively. This corresponded to 98% and 82% reductions in
contaminant concentrations. In heavily impacted areas of the treatment
cell, the Toxaphene concentration was reduced from 1,600 mg/kg to 11 mg/kg
after eight treatment cycles. The application of four additional treatment
cycles in this area resulted in a further reduction of Toxaphene
concentration to 5.1 mg/kg, which corresponds to a 99.7% reduction.
The Cost
Estimates to apply this technology full scale at a similar site are
approximately at $95/ton, including the treatment cell cover, and about
$75/ton if the cover was not required.
The Timeline
Treatment of this material required application of eight treatment
cycles. Each treatment cycle required approximately one month, for a total
active treatment period of approximately eight months. Following a
thorough analysis of data from the site, an additional four treatment
cycles (for a total of 12 cycles) were applied to heavily impacted areas
of the treatment cell.
Companies On This Project
ADVENTUS GROUP
