A laboratory investigation was conducted to determine the effects of biologically produced surfactants (biosurfactants) on the solubility and biodegradation of petroleum hydrocarbons. Biosurfactants have been found to be produced by microorganisms during growth on insoluble organic substrates for the purpose of increasing substrate solubility so as to promote biological degradation. In this study, biosurfactants were produced by microorganisms during growth on two substrate groups, gasoline and a mixture of glucose with vegetable oil. Solubilization and biodegradation of selected gasoline compounds in the presence of biosurfactants were measured in both static batch and flow through column systems.Biosurfactants produced and used in this study acted similarly to commercial surfactants by increasing the solubility of gasoline compounds. Biosurfactants produced from growth on glucose and vegetable oil were effective at increasing the solubility of gasoline compounds but they inhibited biological degradation of these same compounds. Biosurfactants produced by microorganisms from growth on gasoline were also effective at increasing solubility but did not inhibit biodegradation.Laboratory column studies indicated that the effectiveness of biosurfactants for soil or groundwater remediation could be limited by the adsorption of the biosurfactant to soil.zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Water Environ. Res.,zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 64, 163 (1992).
trichloroethane (TCA) is more challenging than bioremediation of other chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE). TCA transformation often occurs under methanogenic and sulfate-reducing conditions and is mediated by Dehalobacter. The source area at the project site contains moderately permeable medium sand with a low hydraulic gradient and is approximately 0.5 acre. TCA contamination generally extended to 35 feet, with the highest concentrations at approximately 20 feet. The concentrations then decreased with depth; several wells contained 300 to 600 mg/L of TCA prior to bioremediation.The area of treatment also contained 2 to 30 mg/L of TCE from an upgradient source. Initial site groundwater conditions indicated minimal biotic dechlorination and the presence of up to 20 mg/L of nitrate and 90 mg/L of sulfate. Microcosm testing indicated that TCA dechlorination was inhibited by the site's relatively low pH (5 to 5.5) and high TCA concentration. After the pH was adjusted and TCA concentrations were reduced to less than 35 mg/L (by dilution with site water), dechlorination proceeded rapidly using whey (or slower with sodium lactate) as an electron donor. Throughout the remediation program, increased resistance to TCA inhibition (from 35 to 200 mg/L) was observed as the microbes adapted to the elevated TCA concentrations. The article presents the results of a full-scale enhanced anaerobic dechlorination recirculation system and the successful efforts to eliminate TCA-and pH-related inhibition. O
Enhanced anaerobic dechlorination is being conducted to remediate a 50-acre groundwater area impacted with chlorinated volatile organic compounds (CVOCs). The plume, which is over 3,000 feet (ft) long, initially contained tetrachloroethene and breakdown products at concentrations of 2 to 3 milligrams per liter. The site's high groundwater flow velocity (greater than 1,000 ft per year) was incorporated into the design to help with amendment distribution. Bioaugmentation was conducted using a mixed culture containing Dehalococcoides ethenogenes. There is evidence that it has migrated to distances exceeding 600 ft. The major benefit of the high groundwater flow velocity is greater areal coverage by the remediation system, but the downside is the difficulty in delivering sufficient donor to create the required anaerobic conditions. Overall performance has been excellent with total CVOC reductions and conversion to ethene of 98 percent within a 25-acre area downgradient of the treatment transect that has operated the longest. O
This article describes a design approach that has been developed for bioremediation of chlorinated volatile organic compound-impacted groundwater that is based upon experience gained during the past 17 years. The projects described in the article generally involve large-scale enhanced anaerobic dechlorination (EAD) and combined aerobic/anaerobic bioremediation techniques. Our design approach is based on three primary objectives: (1) selecting and distributing the proper additives (including bioaugmentation) within the targeted treatment zone; (2) maintaining a neutral pH (and adding alkalinity when needed); and (3) sustaining the desired conditions for a sufficient period of time for the bioremediation process to be fully completed. This design approach can be applied to both anaerobic and aerobic bioremediation systems. Site-specific conditions of hydraulic permeability, groundwater velocity, contaminant type and concentrations, and regulatory constraints will dictate the best remedial approach and design parameters for in situ bioremediation at each site.The biggest challenges to implementing anaerobic bioremediation processes are generally the selection and delivery of a suitable electron donor and the proper distribution of the donor throughout the targeted treatment zone. For aerobic bioremediation processes, complete distribution of adequate concentrations of a suitable electron acceptor, typically oxygen or oxygenyielding compounds such as hydrogen peroxide, is critical. These design approaches were developed based on understanding the biological processes involved and the mechanics of groundwater flow. They have evolved based on actual applications and results from numerous sites. An EAD treatment system, based on our current design approach, typically uses alcohol as a substrate, employs groundwater recirculation to distribute additives, and has an operational period of two to four years.An aerobic in situ treatment system based on our current design approach typically uses pure oxygen or hydrogen peroxide as an electron acceptor, may involve enhancements to groundwater flow for better distribution, and generally has an operational period of one to four years. These design concepts and specific project examples are presented for 17 sites. O
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