How much Oxygen in Needed for Aerobic Cometabolism of PCE?

Aerobic Cometabolism of PCE

CL-Out bioremediation degrades PCE without the production of vinyl chloride under a wide aerobic range.  The degradation pathway is via organic acids. The following compilation of data from 14 locations shows PCE removal with ORP levels in ground water ranging from -150 to 250 standard units.  The concentration removed PCE concentrations ranging from 10 to nearly 1,000 ug/L.  The amount removed does not appear to be dependent on the ORP level.  The amount of PCE removed is probably a function of the initial concentration, with higher mass removal correlating with higher initial concentrations.

The relationship between the starting mass and amount of PCE removed appears to be unrelated to the ORP levels.  The following chart shows nearly 100% of the PCE concentration is removed at all ORP levels, even at less than -50.  The  PCE removal rate appears to decrease at ORP levels above +200, but sites with that level of ORP are rare.

The following chart shows the vinyl chloride concentrations at the same 14 sites.  As the PCE is degraded the vinyl chloride concentrations increased slightly at some locations.  The increase in vinyl chloride was 10 ug/L or less at most locations.  A high increase in vinyl chloride was observed at a location where the ORP was less than -50.  This result suggests that there may be a threshold relationship between a low ORP less than -50 and a significant increase in vinyl chloride.

As a percentage of the amount of PCE removed, the increase in vinyl chloride is much less than 10% except when the starting ORP was less than -50.

This compilation of data from different sites shows that with a starting ORP above -50, CL-Out bioremediation will be effective in PCE removal without the production of vinyl chloride.  These results should be significant in selecting a remediation option to prevent vinyl chloride vapor intrusion risk by source removal.

Contact us for more information and potential applicability to your situation.

Vinyl Chloride Bioremediation in Central Ohio

Aerobic Cometabolism of  Vinyl Chloride

CL-Out® bioremediation removed vinyl chloride and other chlorinated  solvents found in ground water at a former automobile repair shop.  The solvents were thought to have been released from an underground storage tank (UST).    After the UST and associated contaminated soil were removed, CL-Out bioremediation was implemented to reduce the levels of contamination to site-specific cleanup goals.

Geology

The site is set in the area of central Ohio where the ground moraine is relatively thin.  The underlying bedrock is limestone with a very porous and heavily fractures surface.   While the till of the ground moraine is relatively impermeable the bottom of the UST cavity was very close to the bedrock surface.

Hydrogeology

The affected ground water was in the weathered surface of the bedrock, which is a relatively prolific formation.    The depth to the top of water was approximately 9 feet and the monitoring wells were screened to a total depth of 15 feet.

Contamination

The size of ground water plume that resulted from leaching soil contaminants was estimated to be 4,000 square feet.  The original contaminant was suspected to be PCE, but the main contaminants at the time of the remediation were cis 1,2 DCE and vinyl chloride.  There may have been naturally occurring organisms that degraded the PCE to DCE and vinyl chloride.  CL-Out bioaugmentation was implemented to accelerate the natural process to achieve timely site closure.

Remediation Design

CL-Out bioremediation was implemented through temporary injection wells in the source area.  Two applications of CL-Out were made between February and August 2008.    Monitoring wells were sampled in the treatment area to assess the progress of the remediation.  The following table shows the contaminant concentration treads in the monitoring well with the highest pre-treatment contaminant concentrations.

  Contaminant Concentrations (µg/L)
PCE TCE DCE Vinyl Chloride
Pre-Treatment  11/13/07 BDL BDL 10.0 80.0
First Injection 2/29/08 – 1 Drum of CL-Out
Post-Treatment 6/16/08 BDL BDL 7.7 27.0
Second Injection 8/12/08 – 2 Drums of CL-Out
Post-Treatment 9/4/08 BDL BDL 1.6 4.6
Post-Treatment 12/9/08 BDL BDL 1.3 BDL

Maintaining Aerobic Conditions

CL-Out bioremediation is aerobic cometabolism that uses dextrose as the growth substrate.  Oxygen is required for the metabolism of the dextrose and to supply oxygen for the oxygenase enzyme that is responsible for the destruction of the DCE and vinyl chloride molecules.  During the project dissolved oxygen levels (DO) and redox conditions (ORP) were monitored.   Prior to CL-Out remediation the DO average was 1.4 mg/L and the ORP was -62.  With clearly anoxic site conditions, CL-Out bioremediation was selected, but the redox conditions were monitored to be sure the conditions did not fall out of the effective range for CL-Out bioremediation.

As the remediation progressed, the DO and ORP decreased to 0.42 and -225 respectively.  During the August 12, 2008 CL-Out application, ORP socks were installed in two monitoring wells to maintain aerobic conditions for the remainder of the project.

Microbial Population

CL-Out consists of naturally-occurring Pseudomonas sp. organisms.  The background population of Pseudomonas sp.  was tested prior to CL-Out bioaugmentation.  The background population was 19,000 cfu/ml.  The target population for effective remediation is 1,000,000 cfu/ml.  Thirty days after CL-Out bioaugmentation the population of Pseudomonas sp.  was 840,000 cfu/ml in a down gradient monitoring well.

 Results

After two small treatments, the contaminant concentrations in the source area were reduced to acceptable levels.  There was no rebound in the four months of post treatment monitoring.

 

CL-Out Bioremediation of Groundwater in Clay Soils

Successful In Situ Remediation in Low Permeability

CL-Out bioremediation of groundwater in clay soils reduced concentrations of PCE and TCE at a former dry cleaners in Illinois.  In just over 2 weeks after injection, CL-Out microbes cut the contaminant concentrations in half.

  • PCE from 62.2 to 25.6 mg/L
  • TCE from 11.2 to 6.0 mg/L
  • Cis 1,2-DCE from 3.8 to 1.2 mg/L
  • Vinyl chloride less than 0.001 mg/L before and after treatment

The remediation continues as the microbes grow and cometabolize the residual contamination.  Even in tight clay soils the aerobic cometabolism remediates dry cleaning solvents without producing vinyl chloride or other dangerous by products.

Contact us for a free assessment of your site for bioremediation.

Aerobic PCE Bioremediation

CL-Out Aerobic PCE Bioremediation Pilot Study Results

A CL-Out bioremediation pilot study confirmed that aerobic PCE cometabolism removed dry cleaning solvent contamination from ground water.  The pilot study was located at a former dry cleaners.  At the site, the PCE in ground water was 27 parts per billion (ppb).  Bioaugmentation introduced CL-Out microbes and dextrose as the metabolic substrate by injected into the ground water up gradient from the sentinal monitoring well.  After 30 days the PCE concentration decreased to 20 ppb.  After 6 months the PCE concentration decreased to 16 ppb.

As the PCE was decreasing, the site conditions stayed aerobic.  The dissolved oxygen level in ground water decreased from 1.07 to 0.71 mg/l.  Meanwhile,  the ORP decreased from 99 to 45 mv.  These aerobic aquifer conditions support the conclusion that the PCE removal was through aerobic bioremediation.

CL-Out cometabolism uses a dioxygenase enzyme that is produced constituatively as the metabolic substrate is consumed.  The dioxygenase enzyme destabilizes the carbon bond in the PCE to convert the molecule to an organic acid that leads to complete mineralization. Click here to view the PCE and TCE cometabolic degradation pathways.

CL-Out is a consortium of naturally-occurring microbes.  The microbes have the benefits of metabolic diversity and environmental stability.  They are non-pathogenic and safe for human health and the environment. Click here to find out more about CL-Out bioremediation.

 

 

Brownfield Plan Included CL-Out Bioremediation

A brownfield plan included Cl-Out bioremediation to reduce high concentrations of TCE and other contaminants in ground water at an industrial site near Newark, New Jersey. Using a dynamic remediation plan, three applications of CL-Out microbes followed remediation progress sampling during the site preparation for construction. After reducing the maximum CVOC concentrations from over 8,000 ug/L to less than 20 ug/L, the site met the remediation goals and received a No Further Action Letter from NJDEP. For more information and a detailed case study, click here.