In Situ Nitrate and Perchlorate Bioremediation Eliminated Pump and Treat and Ion-Exhange Treatment Cost
Site closure reached in less than half the projected time and cost
CL-Out® bioremediation was implemented at a confidential manufacturing site to remediate nitrate and perchlorate concentrations in soil and ground water. The consultant installed a pump and treatment system that was operated for several years in immediate response to the discovery of contamination. While perchlorate was the primary contaminant, the ion-exchange resin became quickly saturated with nitrate, which was present at much higher concentrations than the perchlorate. After reviewof various options andcompletion ofabench-scale test, the consultant implemented in situ CL-Out bioremediation to reduce the on-going cost of ground water extraction and treatment.
One of the key factors in CL-Out® cometabolism of perchlorate at this site was that CL-Out® organisms were able to reduce sequentially the oxygen and nitrate prior to perchlorate. The initial nitrate concentrations were much higher than the perchlorate concentrations and pre-maturely saturated the ion-exchange resin. The perchlorate concentration did not decrease until the nitrate concentration decreased to less than the perchlorate concentration. One of the benefits of the CL-Out® organisms was this ability to utilize these different electron acceptors.
The initial application of CL-Out to the soil reduced the perchlorate source concentration. After eight months of ground water bioremediation, the perchlorate concentration in the unconsolidated aquifer decreased from 128 mg/L to 3.4 mg/L immediately down gradient of the source area and from 220 mg/L to 39 mg/L farther down gradient.
Simultaneously, the CL-Out® microbes also removed the nitrate. Down gradient of the source area the nitrate concentration decreased from 105 mg/L to <1.0 mg/L. Farther down gradient the nitrate concentration decreased from 200 mg/L to 5 mg/L.
The in situ nitrate and perchlorate bioremediation provided immediate risk reduction and mitigated potential off-site migration. The bioremediation contaminant levels to the remediation target in 3 years. Bioremediation saved 5 years of projected treatment time and millions of dollars in OM & M costs. The owner sold the property without environmental impairment upon completion of bioremediation.
Project Consultant Received Green Leadership Award
The Massachusetts Department of Environmental Protection awarded Irwin Engineering of Natick, Massachusetts the 2016 Greener Cleanup Leadership Award for the innovative in situ bioremediation of perchorate contamination of soil and ground water at the Concord Road Site in Billerica, Massachusetts. The award honors LSPs and their clients for promoting greener cleanup principles and practices to reduce the overall net environmental footprint of hazardous waste site cleanup response actions under the Massachusetts Contingency Plan.
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.
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.
CL-Out aerobic PCE bioremediation in a keyhole treatmentreduced the mass of contamination near the source and down gradient concentrations in the plume. At a former manufacturing facility in Ohio the concentration of PCE near the source was over 100,000 ug/L. Down gradient of the source the PCE concentrations were less than 10% of the source concentration. Aggressive treatment in the source area reduced the source concentration and in the down gradient plume.
Source area concentrations decreased as follows after one treatment with CL-Out bioremediation:
- PCE decreased from 120,000 to 12 ug/L.
- TCE decreased from 2,000 to 12 ug/L
- Cis 1,2-DCE decreased from 9,500 to 8,100 ug/L.
- Vinyl chloride, however, increased from 1,200 to 22,000 ug/L.
The vinyl chloride increased as the aggressive cometabolic treatment stimulated incomplete reductive dechlorination by other naturally occuring organisms.
Down gradient from the source, the concentrations decreased with slight to no increase in daughter products. The down gradient plume had the following results:
- PCE decreased from 5,000 to 1,600 ug/L.
- TCE decreased from 43 ug/L to BDL.
- Cis 1,2-DCE decreased from 140 to 23 ug/L.
- Vinyl chloride was not detected before or after treatment.
Keyhole treatment was a cost effective approach to reducing the mass of contamination in a ground water plume by focusing aggressive treatment on the source area. Concentrations in the rest of the plume decreased as the microbes and treated water dispersed through the plume.
Aerobic PCE Bioremediation By Cometabolism
CL-Out is a consortium selected for aerobic PCE bioremediation. CL-Out cometabolizes PCE by growing on a simple sugar and producing a metabolic enzyme to degrade PCE. The microbes produce a dioxygenase enzyme that breaks the carbon bond in PCE. This reaction eliminates the biproducts of reductive dechlorination. Also, the synergistic effect of the CL-Out consortium cometabolizes the full suite of chloroethenes and chloroethanes.
In a pilot study to compare aerobic cometabolism with anaerobic reductive dechlorination to remediation TCE and 1,4-dioxane at a former industrial facility in New Jersey, aerobic cometabolism reduced the concentrations of both compounds while anaerobic reductive dechlorination was unsuccessful. For aerobic cometabolism, CL-Out microbes were injected into the aquifer to a depth of 60 to 90 feet below ground. The pilot treatment area was 500 square feet. Monitoring wells were placed upgradient, sidegradient and downgradient of the injection point. Ground water samples were taken on a monthly basis for 9 months.
The results showed that complete TCE mineralization, without the production of daughter products, was measured within the first month. CL-Out bioremediation removed 80% of the TCE at 40 feet downgradient in less than three months. CL-Out bioremediation reduced the 1,4-dioxane concentration to below detection limits at 20 and 40 feet downgradient in the first month.