Barbara J. Butler

The effects of electron donor and granular iron on nitrate transformation rates in sediments from a municipal water supply aquifer

Abstract A municipal water supply well for the town of Baden, located about 10 km southwest of Waterloo, ON, Canada, was forced to close due to unacceptably high concentrations of nitrate in the groundwater. Stimulated in situ denitrification was considered a possible solution to the problem. In advance of a planned field test, the effectiveness of various electron donors (acetate, hydrogen gas, elemental sulphur, thiosulphate, aqueous ferrous iron and pyrite) at stimulating denitrification was compared in microcosm experiments involving sediment from the Baden aquifer. All electron donors tested, with the possible exception of pyrite, stimulated nitrate removal from solution. Acetate was found to be the substance that stimulated the quickest initial removal rates, and denitrification was confirmed as the mechanism using the acetylene block technique. Nitrite accumulation was minimal in most systems, although the local water quality guideline limit of 1.0 mg/l NO 2 − –N was briefly and temporarily exceeded (maximum value was 1.2 mg/l) in some of the acetate amended microcosms. Granular iron was also considered as an electron donor or abiotic reducing agent, but was found to reduce nitrate predominantly to ammonium, in a neutral pH solution buffered with pyrite. In mixed granular iron aquifer sediment systems, where several electron donors were present (hydrogen, ferrous iron and pyrite) that could have supported denitrification, the abiotic reaction with the granular iron appeared to dominate other transformation pathways, and ammonium was again the major product. Based on the testing completed as part of this project, the aquifer at Baden is considered a good candidate for acetate-stimulated in situ denitrification for the removal of nitrate from the groundwater near the municipal water supply well.

Migration and natural fate of a coal tar creosote plume. 2. Mass balance and biodegradation indicators

Abstract A source of coal tar creosote was emplaced below the water table at CFB Borden to investigate natural attenuation processes for complex biodegradable mixtures. A mass balance indicated that ongoing transformation occurred for seven study compounds. Phenol migrated as a discrete slug plume and almost completely disappeared after 2 years, after being completely leached from the source early in the study. The m -xylene plume migrated outward to a maximum distance at approximately 2 years, and then receded back towards the source as the rate of mass flux out of the source decreased to below the overall rate of plume transformation. Carbazole showed similar behaviour, although the reversal in plume development occurred more slowly. The dibenzofuran plume remained relatively constant in extent and mass over the last 2 years of monitoring, despite constant source input over this period, providing evidence that the dibenzofuran plume was at steady state. Meanwhile, the naphthalene and 1-methylnaphthalene plumes continued to advance and increase in mass over the observation period, although at a decreasing rate. The phenanthrene plume was also subject to transformation, although measurement of the rate was less conclusive due to the higher proportion of sorbed mass for this compound. Three lines of evidence are presented to evaluate whether the observed plume mass loss was due to microbial biodegradation. Measurement of redox-sensitive parameters in the vicinity of the plume showed the types of changes that would be expected to occur due to plume biodegradation: dissolved oxygen and SO 4 2− decreased in groundwater within the plume while significant increases were noted for Fe 2+ , Mn 2+ and methane. Further evidence that plume mass loss was microbially-mediated was provided by the accumulation of aromatic acids within the plume. Measurements of phospholipid fatty acids (PLFA) in aquifer material indicated that microbial biomass and turnover rate were greater within the plume than outside: also consistent with biodegradation. Study results highlight the potential for utilizing natural attenuation as a site cleanup approach for dissolved phase plumes from complex organic mixture like coal tar creosote.

Laboratory evidence of MTBE biodegradation in Borden aquifer material.

Mainly due to intrinsic biodegradation, monitored natural attenuation can be an effective and inexpensive remediation strategy at petroleum release sites. However, gasoline additives such as methyl tert-butyl ether (MTBE) can jeopardize this strategy because these compounds often degrade, if at all, at a slower rate than the collectively benzene, toluene, ethylbenzene and the xylene (BTEX) compounds. Investigation of whether a compound degrades under certain conditions, and at what rate, is therefore important to the assessment of the intrinsic remediation potential of aquifers. A natural gradient experiment with dissolved MTBE-containing gasoline in the shallow, aerobic sand aquifer at Canadian Forces Base (CFB) Borden (Ontario, Canada) from 1988 to 1996 suggested that biodegradation was the main cause of attenuation for MTBE within the aquifer. This laboratory study demonstrates biologically catalyzed MTBE degradation in Borden aquifer-like environments, and so supports the idea that attenuation due to biodegradation may have occurred in the natural gradient experiment. In an experiment with batch microcosms of aquifer material, three of the microcosms ultimately degraded MTBE to below detection, although this required more than 189 days (or >300 days in one case). Failure to detect the daughter product tert-butyl alcohol (TBA) in the field and the batch experiments could be because TBA was more readily degradable than MTBE under Borden conditions.

In situ sequential treatment of a mixed contaminant plume

Groundwater plumes often contain a mixture of contaminants that cannot easily be remediated in situ using a single technology. The purpose of this research was to evaluate an in situ treatment sequence for the control of a mixed organic plume chlorinated ethenes and petroleum hydrocar- . bons within a Funnel-and-Gate. A shallow plume located in the unconfined aquifer at Alameda .

A relative-least-squares technique to determine unique Monod kinetic parameters of BTEX compounds using batch experiments

An analysis of aerobic m-xylene biodegradation kinetics was performed on the results of laboratory batch microcosms. A modified version of the computer model BIO3D was used to determine the Monod kinetic parameters, kmax (maximum utilization rate) and KS (half-utilization constant), as well as the Haldane inhibition concentration, KI, for pristine Borden aquifer material. The proposed method allows for substrate degradation under microbial growth conditions. The problem of non-uniqueness of the calculated parameters was overcome by using several different initial substrate concentrations. With a relative-least-squares technique, unique kinetic degradation parameters were obtained. Calculation of the microbial yield, Y, based on microbial counts from the beginning and the end of the experiments was crucial for reducing the number of unknowns in the system and therefore for the accurate determination of the kinetic degradation parameters. The kinetic parameters obtained in the present study were found to agree well with values reported in the literature.

Substrate Interaction during Aerobic Biodegradation of Creosote-Related Compounds: A Factorial Batch Experiment.

The interactions among seven creosote-related compounds (phenanthrene, fluorene, p-cresol, pentachlorophenol, carbazole, dibenzothiophene, and dibenzofuran) during their aerobic biodegradation in groundwater were studied in factorial experiments. Three separate experiments were conducted in simple batch systems with phenanthrene, p-cresol, and carbazole as the response variable for the first, second, and third experiments, respectively, and other compounds as factors. In general, the more hydrophobic and recalcitrant compounds were more affected by substrate interaction. Mineralization of p-cresol was not affected by substrate interaction. In contrast, p-cresol inhibited mineralization of phenanthrene, but other compounds did not Mineralization of carbazole was severely affected by the presence of other compounds. p-Cresol was the main inhibitor. Phenanthrene inhibited biodegradation, butto a lesser extent, whereas fluorene enhanced mineralization of carbazole. Pentachlorophenol and dibenzofuran caused an increase in the lag time but did not affect mineralization of carbazole afterward.

Anaerobic Benzene Biodegradation: A Microcosm Survey

Benzene-amended microcosms prepared with saturated soil or sediment from five hydrocarbon-contaminated sites and one pristine site were monitored for a year and a half to determine the rate of benzene biodegradation under a variety of electron-accepting conditions. Sustainable benzene degradation was observed under specific conditions in microcosms from four of the six sites. Significant differences were observed between sites with respect to lag times before the onset of degradation, rates of degradation, sustainability of the activity, and environmental conditions supporting degradation. Benzene degradation was observed under sulfate-reducing, nitrate-reducing, and iron(III)-reducing conditions, but not under methanogenic conditions. The presence of competing substrates such as toluene, xylenes, and ethylbenzene was found to inhibit anaerobic benzene degradation in microcosms where sulfate or possibly nitrate was the electron acceptor for benzene degradation, but not in microcosms from where iron(III) w...

Evaluation of biodegradation and dispersion as natural attenuation processes of MTBE and benzene at the Borden field site

Abstract A natural gradient tracer test was performed in the shallow, aerobic sand aquifer at Canadian Forces Bases (CFB) Borden in 1988. A mixture of groundwater, spiked with dissolved oxygenate-containing gasoline, was injected below the water table along with chloride (Cl − ) as a conservative tracer. The mass of BTEX compounds in the plume diminished significantly over 16 months of monitoring due to intrinsic aerobic biodegradation; MTBE showed only a small decrease in mass over the same period. In 1995/1996, a comprehensive groundwater sampling program was undertaken to define the mass of MTBE still present in the aquifer. Only 3% of the original MTBE mass remained. Sorption, volatilization and abiotic degradation were ruled out as significant attenuation processes for the field conditions. As well, a study on the phytoremediation potential of the site showed that the plants in the study area were unlikely to contribute to the disappearance of the aqueous MTBE mass. These results indicate that biodegradation may have played a major role in the attenuation of MTBE within the Borden aquifer. In support of this hypothesis, significant MTBE mass losses were observed in aerobic batch experiments that used authentic Borden aquifer material and groundwater. Therefore, it appears that MTBE, like BTEX, can be remediated intrinsically due to biodegradation. Unlike BTEX, however, MTBE is biodegraded very slowly making biodegradation less likely to be sufficient in protecting aquifers and downgradient receptors once MTBE is spilled at a site.

Natural attenuation of a plume from an emplaced coal tar creosote source over 14 years

An emplaced source of coal tar creosote within the sandy Borden research aquifer has documented the long-term (5140 days) natural attenuation for this complex mixture. Plumes of dissolved chemicals were produced by the essentially horizontal groundwater flowing at about 9 cm/day. Eleven chemicals have been extensively sampled seven times using a monitoring network of approximately 280, 14-point multilevel samplers. A model of source dissolution using Raoults Law adequately predicted the dissolution of 9 of 11 compounds. Mass transformation has limited the extent of the plumes as groundwater has flowed more than 500 m, yet the plumes are no longer than 50 m. Phenol and xylenes have been removed and naphthalene has attenuated from its maximum extent on day 1357. Some compound plumes have reached an apparent steady state and the plumes of other compounds (dibenzofuran and phenanthrene) are expected to continue to expand due to an increasing mass flux and limited degradation potential. Biotransformation is the major process controlling natural attenuation at the site. The greatest organic mass lost is associated with the high solubility compounds. However, the majority of the mass loss for most compounds has occurred in the source zone. Oxygen is the main electron acceptor, yet the amount of organics lost cannot be accounted for by aerobic mineralization or partial mineralization alone. The complex evolution of these plumes has been well documented but understanding the controlling biotransformation processes is still elusive. This study has shown that anticipating bioattenuation patterns should only be considered at the broadest scale. Generally, the greatest mass loss is associated with those compounds that have a high solubility and low partitioning coefficients.

Substrate interaction during aerobic biodegradation of creosote-related compounds in columns of sandy aquifer material

Abstract A column study was initiated to study the effect of phenanthrene, fluorene, and p -cresol on the aerobic biodegradation of carbazole in columns of sandy aquifer material. Biodegradation of the contaminant mixture was sequential in space with p -cresol being preferentially degraded, followed by phenanthrene, then the other compounds. Both p -cresol and phenanthrene were completely biotransformed to non-detectable levels during passage through the 46 cm sand column but some carbazole and fluorene persisted throughout the approximately 3 month experiments. Influent p -cresol (10000ppb) was the only compound that affected adaptation of the microbial community to carbazole biodegradation, but its effect was of little practical importance, amounting to a 4.5 day difference in carbazole breakthrough. However, when influent p -cresol was at high levels (70 000 ppb), biotransformation of the other co-substrates in the mixture never ensued because p -cresol caused complete dissolved oxygen depletion. Conversely, influent p -cresol ultimately enhanced biotransformation of the other co-substrates in the mixture when present at a concentration (10000ppb) that did not deplete all available oxygen. The concentrations of the other, more recalcitrant compounds, ranging between 33 and 238 ppb, were probably too low to support bacterial growth so that slow, limited biotransformation resulted, although addition of an auxiliary substrate (i.e. the p -cresol) stimulated their biotransformation. Under quasi-steady-state conditions, the presence of phenanthrene in the influent inhibited fluorene biotransformation and possibly carbazole biotransformation. Results of the present study demonstrated also that interactions identified in static batch microcosms and in a hydrodynamic saturated column system can differ.