Description
Introduction
Adventus' groundwater bioremediation technology, EHC® is a patented
combination of controlled-release solid carbon and zero valent iron (ZVI)
or other reduced metal particles. This unique combination stimulates
reductive dechlorination of otherwise persistent organic solvents in
groundwater and source zones. EHC is particularly effective for in
situ treatment of subsurface environments impacted by chlorinated solvents
such as 1,2 dichloroethane (1,2-DCA). Adventus has performed
extensive testing of EHC for treatment of 1,2-DCA and offers the
technology for full-scale site remediation.
Overview of EHC
Technology
EHC technology causes destruction of
contaminants through two primary mechanisms: (i) chemical reduction and
(ii) enhanced biological degradation. EHC consists of solid-phase
controlled-release carbon integrated with micro-scale ZVI or other metals
(e.g., zinc). Together these two components provide powerful reducing
conditions (e.g., < -550 mV), which result in complete destruction of
many contaminants. In addition, natural attenuation processes in
groundwater are enhanced through the release of dissolved organic carbon,
as well as major, minor and micro-nutrients. As these compounds
migrate through the treatment zone, they provide ideal conditions for
growth of indigenous microorganisms. Because the rate of carbon release is
controlled, the extent of biological colonization can also be managed, and
flow rates can be maintained. This combined chemical and biological
approach allows for more reliable and effective in situ treatment of
targeted contaminants.
EHC Treatment Performance on
1,2-DCA
Adventus completed a bench-scale treatability
investigation to demonstrate the capability of EHC to treat a site
groundwater impacted with about 400 mg/L of 1,2-DCA. A set of eight
flow-through systems was set up, which included two control systems and
systems to test EHC applied in a PRB mode (EHC mixed with sand at ratios
of 7.5%, 15% and 30%) and dispersed mode (EHC mixed with site soil at
ratios of 0.5%, 1% and 2%) (Figure 1). The
effectiveness of these EHC systems was assessed in three sampling events
over a period of 98 days of operation.
Figure 2 shows the results of the 1,2-DCA measurements
in the effluent of the 1% and 2% EHC dispersed columns and the 7.5%
EHC/sand column (selected because it showed best removal rates among the
three EHC/sand columns used). The influent concentrations of 1,2-DCA
were degraded completely within the 1% column in the first two sampling
events (36 and 57 days), whereas the 1,2-DCA removal effectiveness in this
column declined to 75% in the last sampling event at 98 days (Figure
2). In contrast, in the 2% EHC column, 1,2-DCA was not completely
removed in the first sampling event (a removal rate of 90%), and then
complete degradation was observed in the following two sampling
events. Incomplete removal was observed in the 7.5% EHC/sand column
in all sampling events, with the highest removal observed in the second
sampling event (85%).
Figure 3 shows the 1,2-DCA concentration trends in the
last sampling event in the three systems including the downgradient
microcosm vessels. This trend shows that the remnant 1,2-DCA in the
effluent of the 1% EHC column degraded completely in the first
downgradient microcosm.
Chloroethane was not detected in any
samples and chloride mass balances of close to 100% were obtained in both
dispersed systems, confirming complete degradation of the 1,2-DCA without
formation of chlorinated byproducts.
Benefits of Using
EHC
The EHC materials can be applied using various construction
techniques. Because EHC releases a zone of dissolved organic carbon and
low redox conditions, the targeted contaminants do not need to come into
direct contact with EHC to be treated. Thus, EHC may be injected into the
subsurface at an in situ application rate that is sufficiently low to be
very cost effective (typical range from 0.1 to 1% by dry soil mass). EHC
is provided as a dry powder that can also make a good slurry for
injection. Therefore, methods such as hydraulic fracturing, pneumatic
fracturing and direct injection can be used, depending on site
hydrogeology. The material may also be placed in a trench using
conventional or modified PRB techniques.
Another benefit
of EHC is found in its adaptability to site conditions, including
contaminant concentrations and groundwater flow rates. A range of EHC
products is available, and each product has its own carbon and nutrient
release and buffering characteristics. This allows product characteristics
to be tailored to meet site-specific needs. Through appropriate selection
of EHC products, the longevity, redox conditions and pH can be controlled.
This protects the downgradient treatment area from large shifts in pH that
can hinder enhanced natural attenuation.
Cost / Benefits of
EHCR Biotechnology
Data indicate that EHC will remain
active for a period of at least 12 to 60 months in the subsurface,
depending on the product used and hydrogeological conditions. This is
longer than many other organic carbon based treatment materials. The price
of EHC, depending on the product used, starts from US$2.25 per pound, with
volume discounts available.
EHC has become the industry-leading
bioremediation treatment technology, both in terms of site economics and
scientifically validated field performance.
Companies On This Project
ADVENTUS GROUP
