Story

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 EHC® 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.

For more information on EHC, please contact
Jim Meuller, Ph.D.
Adventus Americas Inc.
2871 W Forest Road, Suite 2
Freeport, Il 61032
(815) 235-3503