Download Wood-Preservs

Case study on bioremediation of
soils contaminated with wood
preservatives
Wood preservation is a two-stage
process:
1. Conditioning the wood to reduce
its natural moisture content and
to increase permeability,
2. Treating the wood with
preservative
Conditioning:
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seasoning in open yards
steam conditioning
vapor drying
kiln drying
controlled air seasoning
tunnel drying
• After conditioning, wood is
immersed in preservative
chemicals, sometimes under
pressure, at either ambient or
elevated temperatures.
Wood preservatives include
• creosote
• pentachlorophenol
• a combination of copper,
chromium, and acetate (CCA)
They are used to prevent decay and
to protect against fire and insects.
Creosote alone or in combination with coal
tar or petroleum is the major preservative
used in the wood pressure treating industry
• is made by high-temperature
carbonization of bituminous coal
• contains a complex mixture of organic
compounds consisting mainly of aromatic
hydrocarbons, tar acids (phenolic
derivative of the aromatic compounds),
and tar bases (heterocyclic compounds
containing N plus some neutral
oxygenated compounds)
The principle components are shown in
Table 25-1 and 25-2 in in your
handout
• The major PAHs are 2-, 3-, and 4-ring
compounds and their methyl derivatives.
• Commercial PCP contains
• 85 to 90% PCP
• 3-8% tetraphenols
• 2-6% other chlorinated phenols
• the remainder: other chlorinated compounds
and inert materials, including toxic
hexachlorodibenzo-p-dioxin (HCDD) and
heptachlorodibenzo-p-dioxin (HPCDD)
Tetrachlorodibenzo(r)dioxin (TCDD)
• Creosote contains many constituents
that are reported to be mutagenic,
carcinogenic, teratogenic, fetotoxic,
and/or toxic.
• The use of creosote has been
restricted by the USEPA to certified
applicators to protect applicators
and users of the treated wood from
unnecessary exposure.
• PCP toxicity and potential for uptake by
organisms are pH-dependent.
• The estimated acute sensitivities of 32
species at pH 6.5 range from 4.355 ppm
for larval common carp to greater than
44000 ppm for crayfish.
• Freshwater algae were affected by
concentration as low as 7.5 ppm, whereas
vascular plants were affected at 296 ppm
and above.
• Acute toxicity tested with 18 species of
saltwater animals range from 22.63 ppm
to 18,000 ppm.
• In general, fish are more sensitive than
invertebrates to PCP.
• Chlorinated dioxin and dibenzofuran
impurities in PCP also are of concern.
The USEPA has listed PCP
manufacturing wastes as acute
hazardous wastes because of the presence
of hexachlorodibenzo-p-dioxins.
• PCP, creosote with PAHs, and aqueous
solutions of CCA have been introduced
into soils and groundwater in the USA.
• In 1989, there were between 415 - 550
creosoting operations within the USA
using approximately 454,000 tons of
creosote annually.
• Leaking pipes, leaking tanks, drippings
from lumber, and leachate from unlined
ponds have caused contamination of soil
and/or groundwater at 1397 wood
preserving sites.
• In 1990, there were 58 wood preservative
sites on the USEPA National Priority
List, of which 51 were contaminated
with PCP and/or creosote (PAH), and
seven were contaminated with CCA.
Soil bioremediation technologies include:
• In-situ (not well evaluated) and ex-situ
(focus of most studies)
• Ex-situ include
• Prepared bed (share similarity with
land treatment. Treatments include
fertilization, tilling, soil pH adjustment,
moisture control, and others)
• Slurry bioreactor
• compost-biopile reactors
Case study
• Location: Champion International
Superfund Site in Libby, MT
• Major contaminants: PCP and
PAHs (residuals of creosote and
PCP wood preservatives)
• Bioremediations technology:
prepared bed technology for fullscale remediation
• Contaminated soils were excavated,
screened to remove rocks and placed in an
excavated waste pit area.
• Total carcinogenic PAHs: 88 mg/kg based
on a site specific risk assessment.
• The prepared bed system consisted of two
one-acre lined land treatment units (LTU
1 and LTU 2)
• Soil from the waste pit area was placed in
the prepared beds in approximately 15-cm
layers.
• Nutrients were added as
• C/N ratio = 12-30:1
• N/P ratio = 10:1
• Toxicity of water extracts of soil was
evaluated using the Microtox assay.
Pyrene concentration in soil (first-order
degradation model; Huling et al., 1995
Total carcinogenic PAHs (TCPAH) concentration in
soil (first-order degradation model; Huling et al., 1995
Conclusions
• Significant decreased PCP, pyrene, and
TCPAH concentrations to targeted
remediation levels.
• Mutagenicity testing indicated
detoxification to soil background levels in
three months.
• Biological processes represented the
primary mechanism for the decrease in
this system