Aerobic Microcosms Research Articles

Mixed aerobic and anaerobic microbial communities in benzene-contaminated groundwater

To investigate the factors affecting benzene biodegradation and microbial community composition in a contaminated aquifer. We identified the microbial community in groundwater samples from a benzene-contaminated aquifer situated below a petrochemical plant. Eleven out of twelve groundwater samples with in situ dissolved oxygen concentrations between 0 and 2.57 mg l(-1) showed benzene degradation in aerobic microcosm experiments, whereas no degradation in anaerobic microcosms was observed. The lack of aerobic degradation in the remaining microcosm could be attributed to a pH of 12.1. Three groundwaters, examined by 16S rRNA gene clone libraries, with low in situ oxygen concentrations and high benzene levels, each had a different dominant aerobic (or denitrifying) population, either Pseudomonas, Polaromonas or Acidovorax species. These groundwaters also had syntrophic organisms, and aceticlastic methanogens were detected in two samples. The alkaline groundwater was dominated by organisms closely related to Hydrogenophaga. Results show that pH 12.1 is inimical to benzene biodegradation, and that oxygen concentrations below 0.03 mg l(-1) can support aerobic benzene-degrading communities. These findings will help to guide the treatment of contaminated groundwaters, and raise questions about the extent to which aerobes and anaerobes may interact to effect benzene degradation.

An Evaluation of Compound-Specific Isotope Analyses for Assessing the Biodegradation of MTBE at Port Hueneme, CA

The use of compound-specific isotope analysis (CSIA) as a diagnostic tool for MTBE biodegradation in aquifers was tested at the Port Hueneme, CA site. There, a 1500-m long dissolved MTBE plume and associated engineered aerobic flow-through biobarrier have been well-studied, leading to delineation of regions of known significant and limited bioattenuation. This allowed comparison of field-scale CSIA results with a priori knowledge of aerobic MTBE biodegradation, leading to conclusions concerning the utility of CSIA as a diagnostic tool for other aerobic biodegradation sites. Groundwater samples were collected and analyzed for both 13C and 2H (D) in MTBE through the bioactive treatment zone and within the larger MTBE plume. For reference, the 13C enrichment factor for MTBE biodegradation in laboratory-scale microcosms using site groundwater and sediments was also quantified. Aerobic microcosms showed a 13C enrichment of 5.5 to 6.4 +/- 0.2 per thousand over a two-order of magnitude concentration decrease, with an average isotope enrichment factor (epsilon(c)) of -1.4 per thousand, in agreement with other aerobic microcosm studies. Less 13C enrichment (about 25%) was observed for similar MTBE concentration reductions in groundwater samples collected within the aerobic biotreatment zone, and this enrichment was comparable to the scatter in delta13C values within the source zone. Increasing enrichment with decreasing MTBE concentration seen in microcosm data was not evident in either the 13C or D field data. The discrepancy between field and laboratory data may reflect small-scale (<1 m) spatial heterogeneity in MTBE biodegradation activity and the mixing of water from adjacent strata during groundwater sampling; for example, relatively nonattenuated MTBE-impacted water from one stratum could be mixed with highly attenuated/low-MTBE concentration from another, and this could produce a sample with both reduced MTBE concentration and low enrichment. Overall, the results suggest that 13C data alone may produce inconclusive results at sites where MTBE undergoes aerobic biodegradation, and that even with two-dimensional CSIA (13C and D), an increase in the confidence of data interpretation may only be possible with data sets larger than those typically collected in practice.

Treatment of chlorobenzene-contaminated groundwater in a pilot-scale constructed wetland

At industrial megasites worldwide, the natural seepage of contaminated groundwater from surface-near layers into rivers and river floodplains may give rise to serious environmental hazards. To prevent adverse effects on the environment, affordable and energy-efficient treatment methods for these sites are required. Large-scale constructed wetlands (CW) may represent a promising approach to protect river catchment areas. A pilot-scale horizontal subsurface flow CW planted with Phragmites australis and an unplanted reference plot were investigated for the removal of monochlorobenzene (MCB), 1,4-dichlorobenzene (1,4-DBC) and 1,2-dichlorobenzene (1,2-DCB) from polluted groundwater in Bitterfeld (Germany). At inflow concentrations of 20 mg L −1 MCB, 0.19 mg L −1 1,2-DCB and 0.25 mg L −1 1,4-DCB, the planted system showed high removals of MCB and 1,4-DCB already after 2 m of the flow path with averages of 48% MCB and 38% 1,4-DCB over all depths (71% MCB and 62% 1,4-DCB in the upper layer of the wetland). The unplanted wetland showed its highest mean removals only after 4 m of the flow path with 35% MCB and 32% 1,4-DCB. 1,2-DCB was not removed in either system. Oxygen limitation prevailed in both systems but concentrations were higher in the planted wetland with redox potentials of 65–90 mV (0–65 mV in the unplanted wetland). The presence and activity of aerobic MCB degraders in the wetland was shown via most probable number (MPN) determination and aerobic microcosm experiments. Since plants have a significant effect on chlorobenzene removal, constructed wetlands provide a high potential for the treatment of chlorobenzene-contaminated groundwater.

Evaluating Ozone as a Remedial Treatment for Removing RDX from Unsaturated Soils

Years of wastewater discharge at the Department of Energy’s Pantex Plant have contaminated the vadose zone and underlying perched aquifer with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Because the vadose zone is acting as a continual source of groundwater contamination, removing RDX from the unsaturated zone is paramount to prevent further contamination. We determined the efficacy of ozone to degrade and mineralize RDX. Solution experiments showed that ozone (27mgL−1; 150mLmin−1) was effective in mineralizing 80% of the RDX (30mgRDXL−1) provided that some Pantex soil was present to buffer the solution pH. Soil columns treated with ozone produced 50% RDX mineralization within 1 day and >80% within 7 day. Experiments designed to evaluate aerobic biodegradation following partial ozonation of a RDX solution showed that ozone-generated RDX products were much more biodegradable than untreated controls in aerobic microcosms (35 versus <0.3% cumulative mineralization). These results support the use of ozone as a remedial treatment for the contaminated vadose zone at the Pantex facility.

Phospholipid fatty acids of a marine sedimentary microbial community in a laboratory microcosm: Responses to petroleum hydrocarbon contamination

Laboratory microcosm experiments were performed to evaluate petroleum hydrocarbon biodegradation and phospholipid fatty acid (PLFA) composition in either non-contaminated (NC) or contaminated (C) sedimentary microcosms with a crude oil. An analytical procedure was developed to extract both hydrocarbons and PLFAs from the same culture. PLFAs were analyzed over time during an aerobic microcosm experiment (0–21 days) to obtain a better understanding of the structural changes in bacterial sedimentary communities. We observed an increase in both hydrocarbon degraders and heterotrophic bacteria as reflected in PLFA concentrations. Inferred total biomass ranged from 4 to 11.3 × 10 9 and 22.1 to 199.2 × 10 9 bacterial cells kg −1 dry sediment for NC and C sediments, respectively. Total biomass was greater in C than NC sediment, increasing by about twice, 3×, 13× and 50× for 0, 2, 7 and 21 days, respectively. These modifications coincided with removal of petroleum hydrocarbons that reached 35% of total hydrocarbon and 64% of total n-alkanes after 21 days. Microbial community structure changes over time in the C and NC microcosms were shown with principal components analysis and a study of some characteristic PLFAs as biomarkers. Some modifications occurred after several days of petroleum exposure, but crude oil addition did not produce an obvious increase in the biomass of petroleum degraders.

Litter quality effects on soil carbon and nitrogen dynamics in temperate alley cropping systems

Microcosm and litterbag experiments were conducted to determine the effects of litter quality, soil properties and microclimate differences on soil carbon (C) and nitrogen (N) mineralization in alley cropping systems. Bulk soils were collected from 0 to 20 cm depth at three sites: a 21-year old pecan ( Carya illinoinensis)/bluegrass ( Poa trivialis) intercrop (Pecan site) in north-central Missouri, a 12-year old silver maple ( Acer saccharinum)/soybean ( Glycine max)–maize ( Zea mays) rotation (Maple site) in northeastern Missouri and a restored prairie site (MDC site) in southwestern Missouri. Seven tree and crop litters with varying composition were collected, including pecan, silver maple, chestnut and walnut leaf litter (tree litter) and maize, soybean and bluegrass residues (crop litter). Aerobic microcosm incubations were maintained at 25 °C and a soil water potential of −47 kPa. Unamended MDC soil mineralized 24 and 18% more CO 2 than the Pecan and Maple soils, respectively. Soil amended with crop litter mineralized on average 32% more CO 2 than when amended with tree litter. Net N mineralization from soybean litter was 40 mg kg −1, while all other litter immobilized N for various durations. A double pool and a single pool model best described C and N mineralization from amended soils, respectively. Cumulative CO 2 mineralized, labile C fraction ( C 1) and potentially mineralizable C ( C 0) were correlated to litter total N and lignin contents and to (lignin + polyphenol):N ratio. In the field, bluegrass litter decomposed and released N twice as fast as pecan leaf litter. Soybean, maize and silver maple litter released 84, 75 and 63% of initial N, respectively, 308 days after field placement, while no differences in mass loss was observed among the three litter materials. At the Maple site, mass and N remaining, 308 days after field placement was lower at the middle of the alley, corresponding to higher soil temperature and water content. No differences in mass loss and N release patterns were observed at the Pecan site. Microclimate and litter quality effects can lead to differences in nutrient availability in alley cropping systems.

Effect of oxygen on survival of faecal pollution indicators in drinking water.

The aim of this study was to determine the effect of oxygen on the survival of faecal pollution indicators including Escherichia coli in nondisinfected drinking water. Aerobic and anaerobic drinking water microcosms were inoculated with E. coli ATCC 25922 or raw sewage. Survival of E. coli was monitored by membrane filtration combined with cultivation on standard media, and by in situ hybridization with 16S rRNA-targeted fluorescent oligonucleotide probes. Anaerobic conditions significantly increased the survival of E. coli in drinking water compared with aerobic conditions. Escherichia coli ATCC 25922 showed a biphasic decrease in survival under aerobic conditions with an initial first-order decay rate of -0.11 day(-1) followed by a more rapid rate of -0.35 day(-1). In contrast, the first-order decay rate under anaerobic conditions was only -0.02 day(-1). After 35 days, <0.01% of the initial E. coli ATCC 25922 population remained detectable in aerobic microcosms compared with 48% in anaerobic microcosms. A poor survival was observed under aerobic conditions regardless of whether E. coli ATCC 25922 or sewage-derived E. coli was examined, and regardless of the detection method used (CFU or fluorescent in situ hybridization). Aerobic conditions in drinking water also appeared to decrease the survival of faecal enterococci, somatic coliphages and coliforms other than E. coli. The results indicate that oxygen is a major regulator of the survival of E. coli in nondisinfected drinking water. The results also suggest that faecal pollution indicators other than E. coli may persist longer in drinking water under anaerobic conditions. The effect of oxygen should be considered when evaluating the survival potential of enteric pathogens in oligotrophic environments.

Potential for aerobic and anaerobic biodegradation of petroleum hydrocarbons in boreal subsurface.

We studied the role of aerobic and anaerobic petroleum hydrocarbon degradation at a boreal, light-weight fuel and lubrication oil contaminated site undergoing natural attenuation. At the site, anoxic conditions prevailed with high concentrations of CH4 (up to 25% v/v) and CO2 (up to 18% v/v) in the soil gas throughout the year. Subsurface samples were obtained mainly from the anoxic parts of the site and they represented both the unsaturated and saturated zone. The samples were incubated in microcosms at near in situ conditions (i.e. in situ temperature 8 degrees C, aerobic and anaerobic conditions, no nutrient amendments) resulting in the removal of mineral oil (as determined by gas chromatography) aerobically as well as anaerobically. In the aerobic microcosms on average 31% and 27% of the initial mineral oil was removed during a 3- and 4-month incubation, respectively. In the anaerobic microcosms, on average 44% and 15% of the initial mineral oil was removed during a 12- and 10-month anaerobic incubation, respectively, and e.g. n-alkanes from C11 to C15 were removed. A methane production rate of up to 2.5 microg CH4 h(-1) g(-1) dwt was recorded in these microcosms. In the aerobic as well as anaerobic microcosms, typically 90% of the mineral oil degraded belonged to the mineral oil fraction that eluted from the gas chromatograph after C10 and before C15, while 10% belonged to the fraction that eluted after C15 and before C40. Our results suggest that anaerobic petroleum hydrocarbon degradation, including n-alkane degradation, under methanogenic conditions plays a significant role in the natural attenuation in boreal conditions.

Bench-scale and field-scale evaluation of catechol 2,3-dioxygenase specific primers for monitoring BTX bioremediation

The objective of this work was to test a molecular genetic method for in situ monitoring of aerobic benzene, toluene, and xylene (BTX) biodegrading microorganisms. Catechol 2,3-dioxygenase (C23DO) genes occur in bacteria that biodegrade benzene, toluene, xylenes, phenol, biphenyl, and naphthalene. A competitive quantitative polymerase chain reaction (QC-PCR) technique using a single set of primers specific for an entire subfamily of C23DO genes was recently developed. To determine whether bacteria containing these C23DO genes actually exist in environments contaminated by BTX, aerobic microcosms containing previously uncontaminated soil were amended with different aromatic hydrocarbons and DNA extracts were analyzed by QC-PCR for C23DO genes. Anaerobic microcosms were established to confirm that oxygen was also necessary for the enrichment of C23DO genes. Field testing was done at two sites undergoing monitored natural attenuation. In microcosm experiments naphthalene, m-xylene, and p-xylene strongly enriched for C23DO genes while benzene, toluene, and o-xylene produced only transient, weakly detectable genes. In the field study, C23DO genes were detected in groundwater samples contaminated with either xylenes or naphthalene. The results of this study demonstrated that molecular genetic techniques can provide an accurate and rapid method to detect microorganisms capable of aromatic hydrocarbon biodegradation. Such a technique would be useful for monitoring the effectiveness of aeration technologies and for documenting microbial processes for monitored natural attenuation.

Field and Laboratory Evaluation of the Impact of Tall Fescue on Polyaromatic Hydrocarbon Degradation in an Aged Creosote-Contaminated Surface Soil

A field study was initiated in 1997 to assess the ability of tall fescue grass to remediate an aged creosote-contaminated surface soil. Field monitoring was combined with aerobic microcosm experiments, microbial enumerations, and plant tissue analysis to determine the impact of tall fescue on the degradation of six polycyclic aromatic hydrocarbons (PAHs), acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, and chrysene, and to elucidate the mechanisms of remediation. Fescue grass had a beneficial impact on the degradation of all PAHs except phenanthrene. Mean concentrations of the three-ring PAHs, acenaphthene and fluorene, were lower in fescue cells compared to unvegetated cells after 36 months. In microcosms with soil from fescue cells, acenaphthene had a significantly higher degradation rate and lower final concentration after 180 days than in microcosms prepared with soil from unvegetated cells. Mean concentrations of the four-ring PAHs, fluoranthene, pyrene, and chrysene, were statistically s...

Kinetic Study of Naphthalene Biodegradation in Aerobic Slurry Phase Microcosms for the Optimisation of the Process

The research was focused on the slurry-phase biodegradation of naphthalene. The biodegradation process was optimised with preliminary experiments in slurry aerobic microcosms. From soil samples collected on a contaminated site, a Pseudomonas putida strain, called M8, capable to degrade naphthalene was selected. Microcosms were prepared with M8 strain by mixing non-contaminated soil and mineral M9 medium. Different experimental conditions were tested varying naphthalene concentration, soil:water ratio and inoculum density. The disappearance of hydrocarbon, the production of carbon dioxide, and the ratio of total heterotrophic and naphthalene-degrading bacteria were monitored at different incubation times. The kinetic equation that best fitted the disappearance of contaminant with time was determined. The results showed that the isolated strain enhanced the biodegradation rate with respect to the natural biodegradation.

PCB BIODEGRADATION IN AGED CONTAMINATED SOIL: INTERACTIONS BETWEEN EXOGENOUS PHANEROCHAETE CHRYSOSPORIUM AND INDIGENOUS MICROORGANISMS

This work investigated whether the interaction between the white-rot fungus Phanerochaete chrysosporium and indigenous microorganisms could enhance polychlorinated biphenyl (PCB) removal from historically contaminated soil in aerobic microcosms. The PCB mixture was composed mainly of 14% tri-, 20% tetra-, 9% penta-, 17% hexa-, 26% hepta-, 11% octa-, and 3% nona-chlorobiphenyl (CB) congeners, determined by GC/MS. The fungus, which was grown on sugarcane bagasse and added via this solid substrate, successfully colonized the contaminated soil. The added fungi and the indigenous soil community biodegraded most PCB congeners, with removing efficiencies ranging from 13% to 100% for the 45-day incubation period. The interaction between the fungus and the microorganisms present in the added bagasse inhibited both heterotrophic activity (measured by CO2 evolution) and PCB degradation, suggesting a possible antagonism. In contrast, analysis of variance (ANOVA) inferred a synergistic effect between fungus and soil microorganisms, which resulted in a heterotrophic activity above 2.5 mg-CO2/g-initial dry matter/day. The statistical analyses also showed that the presence of fungus alone was particularly beneficial for the removal of penta- and hepta-CB.

Biodegradation of Trichloroethylene and Its Anaerobic Daughter Products in Freshwater Wetland Sediments

The wide range of redox conditions and diversity of microbial populations in organic-rich wetland sediments could enhance biodegradation of chlorinated solvents. To evaluate potential biodegradation rates of trichloroethylene (TCE) and its anaerobic daughter products (cis-1,2-dichloroethylene; trans-1,2-dichloroethylene; and vinyl chloride), laboratory microcosms were prepared under methanogenic, sulfate-reducing, and aerobic conditions using sediment and groundwater from a freshwater wetland that is a discharge area for a TCE contaminant plume. Under methanogenic conditions, biodegradation rates of TCE were extremely rapid at 0.30 to 0.37 d−1 (half-life of about 2 days). Although the TCE biodegradation rate was slower under sulfate-reducing conditions (0.032 d−1) than under methanogenic conditions, the rate was still two orders of magnitude higher than those reported in the literature for microcosms constructed with sandy aquifer sediments. In the aerobic microcosm experiments, biodegradation occurred only if methane consumption occurred, indicating that methanotrophs were involved. Comparison of laboratory-measured rates indicates that production of the 1,2-dichloroethylene isomers and vinyl chloride by anaerobic TCE biodegradation could be balanced by their consumption through aerobic degradation where methanotrophs are active in wetland sediment. TCE degradation rates estimated using field data (0.009 to 0.016 d−1) agree with the laboratory-measured rates within a factor of 3 to 22, supporting the feasibility of natural attenuation as a remediation method for contaminated groundwater discharging in this wetland and other similar environments.

Biodegradation of phenols in a sandstone aquifer under aerobic conditions and mixed nitrate and iron reducing conditions

Ammonia liquor with very high concentrations of phenol and alkylated phenols is known to have leaked into the subsurface at a former coal carbonization plant in the UK, giving high concentrations of ammonium in the groundwater. In spite of this, no significant concentrations of phenols were found in the groundwater. The potential for biodegradation of the phenols in the sandstone aquifer at the site has been investigated in laboratory microcosms under aerobic (oxygen amended) and mixed nitrate and iron reducing (nitrate enriched and unamended) anaerobic conditions, at a range of concentrations (low: ∼5 mg l −1, high: ∼60 mg l −1, and very high: ∼600 mg l −1) and in the presence of other organic coal–tar compounds (mono- and polyaromatic hydrocarbons (BTEXs and PAHs) and heterocyclic compounds (NSOs)) and ammonia liquor. Sandstone cores and groundwater for the microcosms were collected from within the anaerobic ammonium plume at the field site. Fast and complete degradation of phenol, o- and p-cresol, 2,5- and 3,4-xylenol with no or very short initial lag-phases was observed under aerobic conditions at low concentrations. 2,6- and 3,5-Xylenol were degraded more slowly and 3,5-xylenol degradation was only just complete after about 1 year. The maximum rates of total phenols degradation in duplicate aerobic microcosms were 1.06 and 1.76 mg l −1 day −1. The degradation of phenols in nitrate enriched and unamended anaerobic microcosms was similar. Fast and complete biodegradation of phenol, cresols, 3,4-xylenol and 3,5-xylenol was observed after short lag-phases in the anaerobic microcosms. 2,5-xylenol was partially degraded after a longer lag-phase and 2,6-xylenol persisted throughout the 3 month long experiments. The maximum rates of total phenols degradation in duplicate nitrate enriched and unamended anaerobic microcosms were 0.30–0.38 and 0.29–0.31 mg l −1 day −1, respectively. The highest phenols concentrations in the anaerobic microcosms apparently required very long adaptation periods or inhibited biodegradation of the phenols. For the intermediate concentration level, degradation occurred after comparable lag-phases and at comparable rates to those observed at low concentration. However, after a while degradation of phenols suddenly decreased drastically and then stopped. Dilution by addition of anaerobic groundwater resulted in continued but slow degradation of phenols in unamended microcosms. The effect of other organic coal–tar compounds (BTEXs, PAHs, NSOs) on the degradation of the phenols under unamended conditions was limited to slightly longer lag-phases for some of the phenols. Other constituents of the ammonia liquor did not appear to significantly affect the degradation of the phenols. Fast and complete degradation of 2,3- and 2,4-xylenol was indicated. These experiments were continued for a longer period of time and revealed complete degradation of 2,5-xylenol and, after an approximately 6-month-long lag-phase partial degradation of 2,6-xylenol. The potential for natural attenuation of phenols from process effluents from coal carbonization under aerobic conditions and mixed nitrate and iron reducing conditions appears promising.

Glucose-induced biodegradation of cis-dichloroethylene under aerobic conditions

The capability of the simple carbohydrate, glucose, to stimulate aerobic biodegradation of cis-dichloroethylene ( cis-DCE) was tested using a river sediment. Greater reductions in cis-DCE were observed in aerobic microcosms incubated with glucose than in either killed controls, bottles incubated with oxygen and no glucose, or bottles containing glucose and no oxygen. Two aquifer sediments from different geographic locations also showed similar trends in dichloroethylene reduction. A sediment-free transfer culture from the original river sediment was further tested for cis-DCE degradation. Results indicate that cis-DCE losses coincide with an increase in chloride-ion concentration. The increase was equivalent to the amount of chloride that would be expected from the measured reduction in dichloroethylene and the release of two chlorides per cis-DCE. The possibility that methanotrophic or ammonia-oxidizing bacteria mediated dichloroethylene destruction was eliminated, because the sediment-free suspension culture showed no evidence of either activity. Hence, it appears that a new type of activity mediated the observed dichloroethylene transformation. The implications of these results on in situ bioremediation of chloroethylenes are discussed.

Manganese oxide reduction in laboratory microcosms

Manganese biogeochemistry holds special interest for the characterization of passive treatment systems designed to treat acidic mine waters while meeting enforceable effluent discharge limits set for manganese. In the present study, an initial anoxic enrichment culture was developed for use as an inoculum in experimental systems. Standard anoxic microcosms capable of reducing manganese from Mn4+ to Mn2+ were established from the initial enrichment and altered to study the effects of electron acceptor availability and inhibitors on manganese reduction. Manganese reduction was not significantly inhibited in aerobic and nitrate amended microcosms; however, systems amended with metabolic inhibitors (sodium azide or sodium molybdate) exhibited significant inhibition of manganese reduction relative to standard microcosms. The presence of iron was found to influence the partitioning of reduced manganese with adsorption becoming more important with increasing iron to manganese ratios.

Biodegradation of NSO-compounds under different redox-conditions

Laboratory experiments were carried out to investigate the potential of groundwater microorganisms to degrade selected heterocyclic aromatic compounds containing nitrogen, sulphur, or oxygen (NSO-compounds) under four redox-conditions over a period of 846 days. Eight compounds (pyrrole, 1-methylpyrrole, quinoline, indole, carbazole, dibenzothiophene, benzofuran, and dibenzofuran) were degraded under aerobic conditions, whereas thiophene and benzothiophene were degraded only when other compounds were degraded concomitantly. Quinoline and indole were the only two NSO-compounds degraded under anaerobic conditions, even though the microorganisms present in the anaerobic microcosms were active throughout the incubation period. A high variability in the lag period among the NSO-compounds was observed under aerobic conditions. While quinoline, indole, and carbazole were degraded with a lag period of 3–25 days, the lag periods for pyrrole, dibenzothiophene, benzofuran, and dibenzofuran were significantly longer (29–278 days). Under anaerobic conditions, lag periods of 100–300 days were observed. Differences in the degradation rate among the compounds were also observed. Indole, quinoline, carbazole, and benzofuran were quickly degraded in the aerobic microcosms, whereas a slow degradation of dibenzothiophene and dibenzofuran was observed. Pyrrole and 1-methylpyrrole were slowly degraded and 1-methylpyrrole was not completely removed within the 846 days. The anaerobic degradation rate was significantly slower than the aerobic degradation rate. The degradation rate under sulphate-reducing conditions was higher than under denitrifying and methanogenic conditions, though after re-addition of a compound a quick removal was observed. The persistence of many NSO-compounds under anaerobic conditions together with the long lag periods and the low degradation rates under aerobic conditions suggest that NSO-compounds might persist in groundwater at creosote-contaminated sites.

Degradation of weathered diesel fuel by microorganisms from a contaminated aquifer in aerobic and anaerobic microcosms

AbstractA diesel fuel‐contaminated aquifer in Menziken, Canton of Aargau, Switzerland, was in situ bioremediated from 1989 to 1994 by adding O2, NO−3 PO3−4, and NH+4 through an infiltration well. After a remediation time of 3.5 years, aquifer material from the contaminated zone was excavated and found to contain &gt;106 hydrocarbon‐degrading microorganisms/g and 1.15 ± 0.15 mg/g weathered diesel fuel comprizing mainly isoprenoid alkanes and an unresolved complex mixture (UCM) of unknown components. Samples of this material were incubated for up to 470 days in aerobic and anaerobic microcosms. The microbial activity was determined by measuring the production of inorganic carbon and the consumption of O2 and NO−3. The degradation of the weathered diesel fuel was quantified by infrared spectroscopy and by capillary gas chromatography. In aerobic microcosms, all isoprenoid alkanes and most of the UCM were biodegraded as long as a nitrogen source was present. The O2 consumption could be stimulated by adding KH2PO4 and by elevating the temperature to 22° C. In anaerobic microcosms with KNO3, NO−3 was consumed, inorganic carbon was produced, and the isoprenoid alkanes and the UCM were partially metabolized. In some selected microcosms, the NO−3 consumption rate was stimulated by adding external substrates such as toluene, o‐xylene, m‐xylene, p‐xylene, n‐alkanes, or fatty acids. Mineralization of toluene, naphthalene, and hexadecane to CO2 under denitrifying conditions was confirmed by using [14C]‐labelled substrates.

Aerobic Biodegradation of Petroleum-Contaminated Soil: Simulations from Soil Microcosms

The capacity of natural bacteria to aerobically degrade hydrocarbon vapors was measured and modeled to assess the potential of bioventing to reduce exhaust vapor treatment requirements at a petroleum spill site. Five sets of aerobic soil microcosms from the vadose zone of a Massachusetts Highway Department contaminated right-of-way were dosed with different initial petroleum vapor standard concentrations, then monitored by gas chromatographic analysis over a 55-day period. The five sets yielded an average maximum reaction rate of 20 μg/m3 (soil gas)-sec, which compared favorably with studies of light hydrocarbon vapor degradation in sandy soils from other sites. The calibrated rate was incorporated into a steady-state bioventing model that simulated the evaporation of 34 000 L of petroleum over a 170-year natural release period and an 8-year accelerated release period for 10-day residence time. Aerobic degradation for a 10-day residence time reduced exhaust vapor concentrations by over 100 percent for natural release rates, with a 13 percent reduction under accelerated conditions.

Aerobic Biodegradation of Petroleum-Contaminated Soil: Simulations from Soil Microcosms

The capacity of natural bacteria to aerobically degrade hydrocarbon vapors was measured and modeled to assess the potential of bioventing to reduce exhaust vapor treatment requirements at a petroleum spill site. Five sets of aerobic soil microcosms from the vadose zone of a Massachusetts Highway Department contaminated right-of-way were dosed with different initial petroleum vapor standard concentrations, then monitored by gas chromatographic analysis over a 55-day period. The five sets yielded an average maximum reaction rate of 20 μg/m3 (soil gas)-sec, which compared favorably with studies of light hydrocarbon vapor degradation in sandy soils from other sites. The calibrated rate was incorporated into a steady-state bioventing model that simulated the evaporation of 34 000 L of petroleum over a 170-year natural release period and an 8-year accelerated release period for 10-day residence time. Aerobic degradation for a 10-day residence time reduced exhaust vapor concentrations by over 100 percent for nat...