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Wood
Treatment Site
Confidential Client
Project
Biotreatment of Sludge Impacted by Organic Wood
Preservatives
Summary
Adventus conducted laboratory and field-scale
pilot studies to demonstrate the effectiveness of
aerobic DARAMEND® bioremediation technology
to treat soil (lightly impacted) and sludge
(heavily impacted) by organic wood preservatives
(creosote [polycyclic aromatic hydrocarbons;
PAHs] and pentachlorophenol [PCP]). Laboratory
studies conducted to support field-scale designs
included a control (i.e., sludge only) and a
number of aerobic treatments, each consisting of
one or a combination of the following parameters;
(i) soil moisture content adjustment, (ii)
addition of DARAMEND® bioremediation
products, and (iii) addition of inorganic
nutrients (i.e., phosphorus and nitrogen). Soil
treatment consisted of biweekly monitoring of pH
and soil moisture content plus manual mixing of
the soil/sludge to promote oxic conditions.
The Challenge
Treat soil lightly impacted and sludge heavily
impacted by organic wood preservatives (PAHs and
PCPs).
The Solution
Substantial removal of CPs was achieved after 150
days of DARAMEND® treatment (Table 1). The
highest removal efficiency (>99%) occurred
with the 10% sludge/90% soil mixture. Here, total
CP concentrations were reduced from 392 mg/kg to
1.97 mg/kg (n=2). Effective removal of CPs was
also achieved in treatments with higher sludge
content. For example, a 91% reduction (from 1,126
mg/kg to 101 mg/kg total CPs) was achieved with a
40% sludge content. Substantial removal of PAHs
was also achieved after 150 days of DARAMEND®
treatment (Table 2). The highest removal
efficiency (>95%) also occurred with the 10%
sludge/90% soil mixture, which supported a
reduction in total PAHs from an initial
concentration of 219 mg/kg to 10.14 mg/kg (n=2)
following 150 days of treatment. Leachability
studies have shown these patterns of removal to
support the position of using alternative
end-points because the residual PAH constituents
are not bioavailable (i.e.,
biostabilization).
The Result
The biological processes required at least 60
days of acclimation (lag time) before
biodegradation of PCP commenced (Figure 1). The
treatment regimes with a higher percentage of
sludge required a slightly longer lead time.
Ultimately, the treatment regimes with the lower
proportion of the heavily impacted sludge (10 or
20%) mineralized 35 to 50% of the added
radiotracer; mixtures containing 40% sludge
mineralized approximately 30% of the 14C-PCP
within the first 150 days of treatment. Removal
of both CPs and PAHs continued with extended
incubation time, which suggests that treatment
beyond 150 days would result in even lower
residual concentrations of monitored organic
constituents.
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Depending on material end use,
the site-specific remedial objectives range from
3 to 20 mg/kg for PCP and from 10 to 100 mg/kg
for total PAHs. These data proved that the
various soil/sludge mixtures could be effectively
bioremediated using the aerobic DARAMEND®
technology. Field-scale pilot studie sare
scheduled to begin in early 2004 using
approximately 25 yd3 of three soil/sludge
mixtures (9:1, 4:6 and 2:8 ratios).
The Cost/Timeline
The estimated cost of treatment for the 4:6
materials ratio is approximately $100/yd3,
assuming a 12-month treatment time to reach the
industrial standards and 15-months of treatment
time to reach the lower residential
standards. |
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