Biomedical subjects

Angela R Bielefeldt

Publications and source records attributed to Angela R Bielefeldt.

9 recordsLinked to original sources

PubMed2005

Partitioning of dissolved chlorinated ethenes into vegetable oil.

Food-grade soybean oil (SoyOil) has been used to enhance in situ anaerobic bioremediation at sites contaminated with chlorinated ethenes (CEs). The abiotic interactions of SoyOil with the CEs may be significant and need to be better understood. The oil: water partition coefficients (Kp) of dissolved CEs into SoyOil were measured in batch tests and ranged from 22 to 1200 with increasing chlorination. CE mixtures significantly reduced the Kp for tetrachloroethene (PCE), but not the other CEs. Simple flow tests were used to quantify the mass transfer coefficients (kL) of dissolved CEs into SoyOil. Higher kL values corresponded to the CEs with higher diffusivity in water. CE mixtures reduced the kL for all of the CEs. The results can be used to predict abiotic interactions and distribution of contaminant mass expected after SoyOil injection, and thus provide a more accurate estimate of the mass of CEs removed due to enhanced biodegradation.

Absorption↗

PubMed2005

Dual substrate biodegradation of a nonionic surfactant and pentachlorophenol by Sphingomonas chlorophenolica RA2.

The simultaneous biodegradation of the nonionic surfactant Tween 20 (Tw20) and pentachlorophenol (PCP) by Sphingomonas chlorophenolica sp. Strain RA2 (RA2) was measured. As a sole substrate, Tw20 biodegradation was best described by the Contois kinetic model. During concurrent biodegradation of Tw20 and PCP, the biodegradation rates of Tw20 were not significantly affected by 50 or 100 mg/L PCP, but were significantly inhibited by 500 mg/L PCP. Decreases in cell yield in the presence of PCP suggest that PCP was acting as an uncoupler. Cultures were pre-grown on PCP or Tw20 before degradation of PCP to evaluate enzyme induction effects, and long lags before PCP biodegradation after growth on Tw20 occurred. Although biokinetic models could accurately describe some of the data sets of RA2 growth and Tw20 and PCP degradation, finding a single set of kinetic parameters that predicted all dual substrate tests was not achieved. The complicating factors to modeling PCP and Tw20 interactions are described and may be more widely applicable to the biodegradation of toxic organic compounds in the presence of a biodegradable surfactant.

Biodegradation, Environmental↗

PubMed2005

Non-ionic surfactant flushing of pentachlorophenol from NAPL-contaminated soil.

Column studies were conducted to assess the suitability of a non-ionic surfactant Tergitol NP-10 (TNP10) for washing pentachlorophenol (PCP) from soil and non-aqueous phase liquids (NAPLs). Flushing of 50 and 200 pore volumes of 5 g/L TNP10 was required to exhaust the surfactant sorption capacity of the soil and soil plus NAPL, respectively. The sorption of surfactant to the soil in the columns was four times greater than the quantity previously observed in batch tests. Flushing with 5 g/L TNP10 removed 71-79% of the 200mg/kg soil-sorbed PCP after 160 pore volumes compared to 0.7-2% PCP removal without surfactant. In columns additionally containing 0.2% and 0.4% PCP-contaminated heavy oil NAPL, the PCP removal efficiency after flushing 200 pore volumes of 5g/L TNP10 was nearly 100%. Therefore, removal of the PCP was more efficient in the NAPL-containing columns, potentially due to competition of the NAPL for PCP sorption sites. Rate-limited desorption of PCP and TNP10 likely occurred.

Adsorption↗

PubMed2003

Aqueous chemistry and interactive effects on non-ionic surfactant and pentachlorophenol sorption to soil.

Non-ionic surfactant addition was investigated as a method to remediate pentachlorophenol (PCP) contaminated soil. The goal was to quantify surfactant (Tergitol NP-10 (TNP10)) and PCP sorption to soil and their interactive effects under varying pH, ionic strength, and soil conditions. Up to 16,700 mg/kg of TNP10 partitioned to soil, with increasing sorption far above the critical micelle concentration (CMC) and with greater amounts of PCP present. Approximately 40-45 times more TNP10 and 20-30 times more PCP sorbed to the finer soil with higher organic matter content. Aqueous TNP10 concentrations well above the CMC (>/=5500 mg/L) were required to enhance PCP desorption from the soil. As pH increased by 0.5-0.85 units, TNP10 sorption decreased by 14-25% and PCP sorption as measured by the log of the equilibrium partition coefficient decreased by 1-1.5. A lower ionic strength of 0.03 versus 0.112 M increased PCP desorption from contaminated soil by 5-17% in the presence of TNP10. This work is relevant to designing ex situ soil washing or surfactant-aided PCP remediation.

Adsorption↗

PubMed2003

Equilibrium partitioning of a non-ionic surfactant and pentachlorophenol between water and a non-aqueous phase liquid.

The partitioning of the non-ionic surfactant Tergitol NP-10 (TNP10) and pentachlorophenol (PCP) into a mineral oil light non-aqueous phase liquid (NAPL) were quantified in batch tests. Due to the ionizable nature of PCP, the effects of pH and ionic strength (micro) on the equilibrium partitioning were evaluated. NAPL:water partition coefficients (K(n:w)) of TNP10 ranged from 3 to 7 l(water)/l(NAPL). Enhanced PCP dissolution into water from the NAPL was achieved at aqueous TNP10 concentrations > or =200mg/l. Surfactant addition of 1200 mg/l TNP10 increased the aqueous PCP concentrations by 14-fold at pH 5 versus 2 to 3-fold at pH 7 as compared to PCP aqueous solubility. The more significant response at the lower pH is likely due to the greater hydrophobicity of PCP at the lower pH, which is approaching PCP's pK(a) of 4.7. Higher ionic strength (micro 0.11 versus 0.001 M) increased K(n:w) of PCP by 10-33% without surfactant, compared to a more than 150% increase with a dose of 4000 mg/l TNP10. This work contributes information relevant to the application of surfactants to remediate sites contaminated with NAPLs.

Environmental Pollution↗

PubMed2002

A kinetic model for surfactant inhibition of pentachlorophenol biodegradation.

A kinetic model is used to describe the effect of the nonionic surfactant Tergitol NP-10 (TNP10) on pentachlorophenol (PCP) biodegradation by Sphingomonas chlorophenolica sp. strain RA2. Different initial biomass to initial substrate ratios ranging from 13 to 418 were tested with 23 TNP10 concentrations ranging from 0 to 1500 mg/L. Tests were also conducted at 10 degrees C and 20 degrees C. No PCP biodegradation inhibition was observed at concentrations below the critical micelle concentration (CMC) of 50 mg/L. TNP10 concentrations above 100 to 200 mg/L were increasingly inhibitory to PCP biodegradation rates. This inhibition was best described by the Monod kinetic equation wherein the effect of TNP10 inhibition is reflected in the half-saturation constant (Ks). The value of the Ks increased from between 1.5 and 13.5 mg/L with no surfactant present to 44 to 131 mg/L at 1000 mg/L TNP10. Using a standard competitive inhibition approach, the inhibition constant for TNP10 was approximately 100 mg/L at both 10 degrees C and 20 degrees C.

Biodegradation, Environmental↗

PubMed2002

Nonionic surfactant effects on pentachlorophenol biodegradation.

Several potential mechanisms of surfactant-induced inhibition of pentachlorophenol (PCP) biodegradation were tested using a pure bacterial culture of Sphingomonas chlorophenolicum sp. Strain RA2. PCP degradation, glucose degradation, and oxygen uptake during endogenous conditions and during glucose degradation were measured for batch systems in the presence of the nonionic surfactant Tergitol NP-10 (TNP10). TNP10 did not exert toxicity on RA2 as measured by dissolved oxygen uptake rates under endogenous conditions and glucose biodegradation rates. TNPIO reduced the substrate inhibition effect of PCP at high PCP concentrations, resulting in faster PCP degradation rates at higher concentrations of TNP10. Calculations of a micelle partition coefficient (Kmic) show that PCP degradation rates in the presence of surfactant can be explained by accounting for the amount of PCP available to the cell in the aqueous solution. A model is discussed based on these results where PCP is sequestered into micelles at high TNP10 concentrations to become less available to the bacterial cell and resulting in observed inhibition. Under substrate toxicity conditions, the same mechanism serves to increase the rate of PCP biodegradation by reducing aqueous PCP concentrations to less toxic levels.

Biodegradation, Environmental↗

PubMed2002

Biodegradation of propylene glycol and associated hydrodynamic effects in sand.

At airports around the world, propylene glycol (PG) based fluids are used to de-ice aircraft for safe operation. PG removal was investigated in 15-cm deep saturated sand columns. Greater than 99% PG biodegradation was achieved for all flow rates and loading conditions tested, which decreased the hydraulic conductivity of the sand by 1-3 orders of magnitude until a steady-state minimum was reached. Under constant loading at 120 mg PG/d for 15-30 d, the hydraulic conductivity (K) decreased by 2-2.5 orders of magnitude when the average linear velocity of the water was 4.9-1.4 cm/h. Variable PG loading in recirculation tests resulted in slower conductivity declines and lower final steady-state conductivity than constant PG feeding. After significant sand plugging, endogenous periods of time without PG resulted in significant but partial recovery of the original conductivity. Biomass growth also increased the dispersivity of the sand.

Adsorption↗

PubMedDate not supplied

Low-temperature chromium(VI) biotransformation in soil with varying electron acceptors.

Effective and low-cost strategies for remediating chromium (Cr)-contaminated soil are needed. Chromium(VI) leaching from contaminated soil into ground water and surface water threatens water supplies and the environment. This study tested indigenous Cr(VI) microbial transformation in batch systems at 10 degrees C in the presence of various electron acceptors. The effects of carbon addition, spiked Cr(VI), and mixing highly contaminated soil with less contaminated soil were investigated. The results indicated that Cr(VI) can be biotransformed in the presence of different electron acceptors including oxygen, nitrate, sulfate, and iron. Sugar addition had the greatest effect on enhancing Cr(VI) removal. Less dissolved organic carbon (DOC) was consumed per amount of Cr(VI) transformed under anaerobic conditions [0.8-93 mg DOC/mg Cr(VI)] compared with aerobic conditions [1.4-265 mg DOC/mg Cr(VI)]. Toxicity of high concentrations (< 160 mg/L) of spiked Cr(VI) were not evident. At Cr(VI) concentrations > 40 mg/L, aerobic conditions promoted faster Cr(VI) reduction than anaerobic conditions with nitrate or sulfate present. Biotransformation of Cr(VI) in highly contaminated soil (22,000 mg Cr/kg) was facilitated by mixing with less-contaminated soil. The study results provide a framework for evaluating indigenous Cr(VI) microbial transformation and enhance the ability to develop strategies for soil treatment.

Bacteria, Aerobic↗