CL Solutions provides a special consortium of microbes for oil-contaminated water treatment. Under various conditions, the oil removal rate was as much as 1,300 mg/L/day. In some situations the remediation goal is simply to remove the visible sheen or separate-phase oil. With aeration, CL Solutions microbes were able to remove the visible oil layer and reduce the TPH concentration from 29% to less than 1% in 30 days at a waste oil lagoon. For more information and other case studies click here.
The goal of bioaugmentation is to improve the rate of contaminant removal by adding a high population of beneficial microbes to the contaminated media. The additional microbes should provide short-term benefit as the microbes begin metabolizing the contaminants immediately upon injection. But what benefit does bioaugmentation provide in the long term? And how much benefit does bioaugmentation provide over biostimulation by adding nutrients to the native organisms?
A client of CL Solutions completed a bench-scale study to answer these questions. A bench-scale study was preferred to a field study because it removes the potential distribution and time-lag issues associated with the distances between injection and monitoring locations in the field.
Samples of petroleum-contaminated soils were obtained and separated into split samples for treatment with microbes and nutrients. Some were untreated for comparison. Samples were tested for petroleum concentrations, including C-fraction concentrations after 30, 40 and 60 days. Heterotrophic populations were measured at 40 and 60 days.
The tests showed the following results in the early stages:
- All of the treated samples showed more than 80% total petroleum reduction in the first 30 days.
- The sample treated with nutrients only had the same level of petroleum removal as the bioaugmented samples in the first 30 days.
- The heterotrophic population of the biostimulated sample was as high as in the bioaugmented samples at 40 days.
After 30 days the situation changed.
- The bioaugmented microbial population continued to increase after 40 days and may have increased by a factor of 100 times. Meanwhile, the biostimulated population appeared to stall.
- The petroleum removal continued in the bioaugmented samples and reached as high as 93% removal. In comparison the biostimulated sample stalled at 82% removal.
- The difference appears to be that the bioaugmented samples removed the C-21 to C-35 concentrations at a much higher rate than the biostimulated sample.
- Phenanthrene was target chemical for bioremediation. The biostimulated sample showed 39% removal while the bioaugmented samples showed complete removal to BDL.
Overall, the superior performance of the bioaugmented samples appears to be related to having a greater metabolic range that removed the heavier hydrocarbon fractions. Microbes with the extended metabolic range could continue to multiply as they grew on the heavy hydrocarbon fraction. The results are consistent with field results showing the recalcitrance of heavier hydrocarbon fractions and compounds like naphthalene and phenanthrene under natural attenuation.
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A history of spills and/or releases at two adjacent dry cleaning facilities near Houston, TX, resulted in significant soil and shallow groundwater contamination with PCE and daughter products. Soil was relatively permeable, with rapid groundwater flow beneath the site. A long, narrow, off-site plume extended beneath a residential neighborhood. Chemical oxidation was employed initially with only limited success in the areas of highest contamination. To take advantage of the soil permeability and other site conditions, the response action was amended to include enhanced aerobic bioremediation by cometabolism. Specialty microbes were introduced into the plume in several injections over a 15-month period. This approach achieved total contaminant level reductions in the source area from 1,600 to less than 40 µg/L, and at the front edge of the plume, levels decreased from 500 to 5 µg/L.
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Dry cleaning solvent spills in a storage area lead to the contamination of soil and ground water on the property of a 50-year-old dry cleaners in the middle of a hot brownfield redevelopment. After the contaminated soil was excavated for off site disposal to the most practical extent, residual perched ground water contamination impacted the redevelopment of the property.
The soil excavation was used as an infiltration gallery as part of a recirculating ground water recovery and treatment system. The flushing reduced contaminant concentrations, but the levels were still far above the levels required to achieve no further action status. CL-Out was added to the recirculating ground water and the cleanup goals were achieved in less than two years and were maintained through two years of post treatment monitoring.
Geology and Hydrogeology
The site is on a fluvial terrace adjacent to the Ohio River. The shallow soils are clayey silts to sit to eight feet deep. An interbedded sandy zone that formed the first water-bearing zone was encountered from 8 to 12 feet deep. Perched ground water occurred in the sandy zone at 12 feet below grade.
Ground Water Contamination
The size of ground water plume that resulted from the spills was estimated to be 3,500 square feet. The ground water contamination was mainly PCE with a maximum concentration of 11,000 ug/l prior to soil removal or ground water treatment. The daughter compounds TCE and DCE were detected up to 17 and 12 ug/l respectively. After three years of recirculation and flushing, the maximum PCE concentration was reduced to 2.3 ug/l and the daughter compounds were below detection limits.
CL-Out bioaugmentation was implemented to supplement the flushing system. By adding CL-Out on two occasions over two years, the contaminant concentrations were reduced to below drinking water standards. During two years of post treatment monitoring the DCE concentrations rebounded to above the MCLs. CL-Out bioaugmentation was implemented again and within three months the contaminant levels were below drinking water standards and remained below drinking water standards for nine months. After post closure monitoring verified the cleanup goals would be maintained, the KDEP issued a “No Further Action” letter for the site.
The following chart shows the PCE contaminant trend in one of the key monitoring wells during the remediation and post closure monitoring.
The CL-Out cost during this remediation project was less than $10,000.
Benzo(a)pyrene is a difficult remediation challenge. It is resistant to biological and chemical destruction and extraction from soil. CL Solutions Custom Blend microbes, however, have successfully remediated benzo(a)pyrene and other PAHs in soil during ex situ land farming treatment. By placing the contaminated material in windrows, controlling the temperature and moisture, the addition of Custom Blend microbes has reduced the benzo(a)pyrene concentration by as much as 330 ug/kg/day.
The same approach works on high as well as low concentrations. At a site in Oregon, the benzo(a)pyrene concentration was reduced from 140 ug/Kg to below detection limits in 7 days. At a site in Ohio, the benzo(a)pyrene concentration was reduced from 28,000 ug/kg to 3.8 ug/Kg in 60 days. At both sites, Custom Blend microbes effectively treated the full suite of PAHs along with the benzo(a)pyrene.