Gregory D. Sayles

STABILITY CONSTANTS FOR COMPLEXES OF THE SIDEROPHORE DESFERRIOXAMINE B WITH SELECTED HEAVY METAL CATIONS

Abstract Potentiometric titrations of desferrioxamine B were performed in the presence of Zn(II), Cu(II), Pb(II), Sn(II), Bi(III) and hg(II). Conditions were 0.1 ionic strength and 25 or 20 °C using KNO3, KCl or NaClO4 as supporting electrolyte. Stability constants for the metal complexes were estimated as follows; DFB-Zn(II): 9.55 in KNO3 at 25 °C, DFB-Pb(II): 10.00 in KNO3 at 25 °C, DFB-Sn(II): 21.14 in KCl at 25 °C, DFB-Cu(II): 13.73 in NaClO4 at 20 °C and 13.54 at 25 °C, DFB-Bi(III): > ∼ 23.5 in NaClO4 at 25 °C.

Methanogenesis and sulfate reduction in chemostats—I. Kinetic studies and experiments

Abstract Six anaerobic chemostats containing mixed microbial cultures were used to investigate the interactions between sulfate reduction and methanogenesis for three substrates: acetic acid, methanol and formic acid. Sulfate reducers outcompeted methanogens in acetate-fed chemostats while methanol was not utilized by sulfate reducers. In the formic acid-fed chemostats, competition was observed between methanogens and sulfate reducers with 62 and 24% of the substrate utilized through sulfate reduction and methanogenesis, respectively. Iron was added to the sulfate-reducing chemostats to precipitate the hydrogen sulfide produced, thus eliminating sulfide inhibition and ensuring stable chemostat operation. This study involved the measurement of the oxidation-reduction potential (ORP) of the chemostats using a novel technique. Batch spike tests were also conducted to evaluate kinetic parameters for the degradation of different substrates. Although both methanol-fed chemostats were exclusively methanogenic, scanning electron microscopy (SEM) analysis revealed the presence of two different strains of methanogens. This difference was also manifested by the ORP values and the kinetic parameters.

The application of siderophores for metal recovery and waste remediation: examination of correlations for prediction of metal affinities

The naturally occurring metal-chelating compounds known as siderophores may be useful in environmental applications, but limited metal specificity data is available for this class of compounds. Correlations that predict ligand–metal affinity vs metal ion charge density and hydrolysis behavior are applied to the case of the siderophore desferrioxamine B (DFB). DFB–metal complex formation constants are better correlated to the first hydrolysis constant of the respective metal cations than to the ratio of charge to metal–ligand interatomic separation. Test cases of PbII, SnII and BiIII confirm this conclusion.

Anaerobic DDT biotransformation: Enhancement by application of surfactants and low oxidation reduction potential

Enhancement of anaerobic DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane) biotransformation by mixed cultures was studied with application of surfactants and oxidation reduction potential reducing agents. Without amendments, DDT transformation resulted mainly in the production of DDD (1,1-dichloro-2,2-bis(p-chlorophenyl) ethane) upon removal of one aliphatic chlorine. The DDT transformation rate increased with the addition of the nonionic surfactants Triton X-114 or Brij 35. The addition of either surfactant or reducing agents did not significantly extend the DDT transformation. Addition of both surfactant and reducing agents extended DDT transformation by reducing the accumulation of DDD and increasing the accumulation of less chlorinated products. It is important to minimize the accumulation of DDD because it is a regulated pesticide and is recalcitrant to aerobic transformation. Controlled experiments revealed that the transformation of DDT requires microbial culture, but the culture need not be biologically active. Transformation results are presented for aqueous and soil phase contamination.

Biotransformation rates of chloroform under anaerobic conditions—I. Methanogenesis

Biotransformation of chloroform (CF) was studied in a methanogenic environment utilizing acetic acid as the primary substrate. CF removal efficiency of more than 99% was achieved in a chemostat, fed constant acetic acid concentration (2510 mg/l) and different CF concentrations, up to 16.74 μM. Biological methane potential tests were conducted in serum bottles using the culture from the chemostat with an average biomass concentration of 53 mg/l. The culture exhibited a maximum rate of CF transformation of 0.26 μM/h corresponding to an initial CF concentration of 1.25 μM. At initial CF concentrations higher than 2.76 μM, the rate of CF transformation became constant at 0.06 μM/h. CF present at any concentration inhibited the utilization of acetic acid, and at CF concentrations equal to or exceeding 2.7 μM, the culture was completely inhibited and no acetic acid was utilized by the culture even after the CF was completely degraded. The culture transformed CF without the addition of acetic acid, but the addition of acetic acid considerably increased the rate of biotransformation. However, increase in acetic acid concentration beyond 50 mg/l did not increase the rate. The culture exhibited higher rates of CF biotransformation when it was acclimated with higher influent concentration of CF in a chemostat. Reductive dehalogenation was one of the pathways for the transformation of CF leading to the formation of dichloromethane which was also transformed by the culture.

Biotransformation rates of chloroform under anaerobic conditions—II. Sulfate reduction

Abstract Biotransformation of chloroform (CF) was studied in a sulfate-reducing culture utilizing acetic acid as the primary substrate. In a chemostat, CF and its biotransformation product, dichloromethane (DCM) were transformed and CF removal efficiency of more than 96% was achieved, with influent CF concentrations up to 16.74 μM. Serum bottle reactor tests were conducted using the culture from the chemostat with an average VSS concentration of 259 mg/l. These tests showed that the culture exhibited a maximum rate of CF transformation of 16.3 μM/h corresponding to an initial CF concentration of 22.6 μM. The culture degraded CF primarily by reductive dehalogenation leading to the formation of DCM which degraded at a very slow rate compared to CF. No inhibition of acetic acid utilization was observed in the culture for CF concentrations as high as 29.3 μM. Compared to no acetic acid addition, acetic acid at 50 mg/l considerably increased the rate of CF transformation but further increase in acetic acid concentration to 200 mg/l did not affect the rate of CF biotransformation. Additional acclimation of the culture for 1 yr did not affect the rate of transformation of CF. The results indicate that the sulfate-reducing culture has much higher rates of CF transformation than a methanogenic culture, also grown on acetic acid at the same concentration.

Numerical modeling of oxygen exclusion experiments of anaerobic bioventing

A numerical and experimental study of transport phenomena underlying anaerobic bioventing (ABV) is presented. Understanding oxygen exclusion patterns in vadose zone environments is important in designing an ABV process for bioremediation of soil contaminated with chlorinated solvents. In particular, the establishment of an anaerobic zone of influence by nitrogen injection in the vadose zone is investigated. Oxygen exclusion experiments are performed in a pilot scale flow cell (2 x 1.1 x 0.1 m) using different venting flows and two different outflow boundary conditions (open and partially covered). Injection gas velocities are varied from 0.25 x 10(-3) to 1.0 x 10(-3) cm/s and are correlated with the ABV radius of influence. Numerical simulations are used to predict the collected experimental data. In general, reasonable agreement is found between observed and predicted oxygen concentrations. Use of impervious covers can significantly reduce the volume of forcing gas used, where an increase in oxygen exclusion efficiency is consistent with a decrease in the outflow area above the injection well.

Methanogenesis and sulfate reduction in chemostats—II. Model development and verification

Abstract A comprehensive dynamic model is presented that simulates methanogenesis and sulfate reduction in a continuously stirred tank reactor (CSTR). This model incorporates the complex chemistry of anaerobic systems. A salient feature of the model is its ability to predict the effluent concentrations of the various chemical species in the reactor directly from the feed conditions. Precipitation equilibria of the essential metals were also incorporated in the model. Model predictions were compared with results from steady-state and batch spike experiments. A detailed sensitivity analysis of the effect of key model parameters on model performance was conducted. The model was able to predict both the steady-state and the transient batch spike experimental data fairly well.

Comparing the solid phase and saline extract Microtox® assays for two polycyclic aromatic hydrocarbon‐contaminated soils

The performance of remedial treatments is typically evaluated by measuring the concentration of specific chemicals. By adding toxicity bioassays to treatment evaluations, a fuller understanding of treatment performance is obtained. The solid phase Microtox assay is a useful tool in characterizing the toxicity of contaminated soils and sediments. This study compares the performance of the solid phase and saline extract Microtox assays in two experiments using two soils contaminated with polycyclic aromatic hydrocarbons (PAHs). The first experiment, conducted to refine the solid phase assay procedures, evaluated sample holding times, sample replication, and reference toxicant controls. The effective concentration reducing light emission by 50% (EC50) of four samples was measured with eight replicates of each sample. Samples were stored for as long as two weeks without showing substantial changes in toxicity. For future studies, three replicates of each sample are recommended because that degree of replication yielded a statistical power of more than 95% in most samples. Phenol was a reliable reference toxicant with a mean EC50 of 21.76 and a 95% confidence interval of 15.6 to 27.9 mg/L. In a second experiment, the solid phase Microtox assay was compared to saline extract Microtox assays with mixing times ranging from 5 min to 16 h. The solid phase assay was more sensitive yielding EC50s 7 to 50 times lower than the extract EC50s. In addition, the saline extract assays displayed results that varied for mixing times of less than 2 h. Based on these two experiments, the solid phase Microtox test has proved to be a useful assay for measuring the toxicity of PAH-contaminated soils.

Field Test of Nonfuel Hydrocarbon Bioventing in Clayey-Sand Soil

Abstract A pilot-scale bioventing test was conducted at the Greenwood Chemical Superfund Site in Virginia. The characteristics of the site included clayey-sand soils and nonfuel organic contamination such as acetone, toluene, and naphthalene in the vadose zone. Based on the results of an earlier treatability study, an 80-ft by 80-ft (24-m by 24-m) treatment plot was established in a 35-ft (11-m) vadose zone. Air was injected at a low flowrate for 15 months. Performance monitoring included initial and final soil analysis and periodic soil gas analysis and in situ respiration tests. After beginning aeration, soil gas oxygen levels in the plot rose slowly, reaching 10% at virtually all measured locations in approximately 4 months. In situ respiration rates decreased with time indicating that the site was being cleaned. Soil concentrations of the target contaminants decreased significantly during the test, with > 98% confidence for acetone, naphthalene, benzene, chlorobenzene, and toluene, and > 90% confidenc...