Small-volume releases of gasoline in the vadose zone: impact of the additives MTBE and ethanol on groundwater quality

A controlled gasoline spill experiment was performed under outdoor conditions typical for winter in temperate regions to study the fate of methyl tert-butyl ether (MTBE), ethanol, benzene, and selected other petroleum hydrocarbons. Artificial gasoline containing MTBE and ethanol (5% w/w of each) was placed at a defined depth into a 2.3 m thick unsaturated zone of alluvial sand overlying a gravel aquifer in a lysimeter. During an initial period of 41 days without recharge, MTBE and hydrocarbon vapors migrated by vapor-phase diffusion to groundwater, while ethanol vapors were naturally attenuated. In a subsequent period of 30 days with 5-mm daily recharge, all soluble compounds including ethanol were transported to the groundwater. Ethanol disappeared concomitantly with benzene and all other petroleum hydrocarbons except isooctane from the aerobic groundwater due to biodegradation. MTBE persisted for longer than 6 months at concentrations larger than 125000 microg L(-1). No evidence for MTBE biodegradation was found, whereas > 99.6% of ethanol removal from the lysimeter was due to biodegradation. It is concluded that MTBE-free gasoline would be less harmful for groundwater resources and that ethanol is an acceptable substitute.     

Volatilization and biodegradation of naphthalene in the vadose zone impacted by phytoremediation

The combined remediation mechanisms of volatilization and biodegradation in the vadose zone were investigated for naphthalene remediation at a creosote-contaminated site where a poplar tree-based phytoremediation system has been installed. Concurrent field and laboratory experiments were conducted to study the transport and biodegradation of naphthalene in the vadose zone. Soil gas sampling showed that more than 90% of the naphthalene vapors were biodegraded aerobically within 5-10 cm above the water table during the summer months. Peak naphthalene soil gas concentrations were observed in the late summer, corresponding with peak naphthalene aqueous concentrations and the minimum saturated zone thickness. An analytical solution was developed for vapor transport where the diffusion coefficient and first-order biodegradation rate vary vertically in two discrete zones. First-order aerobic biodegradation rates in laboratory columns using unsaturated site soil ranged from 5 to 28 days(-1) with a mean rate of 11 days(-1). The observed naphthalene mass flux at the source (3.3-22 microg cm(-2) d(-1)) was enhanced by aerobic biodegradation and was greater than the mean observed flux in the abiotic control column and the maximum theoretical mass flux by factors of 7 and 28, respectively.     

Biofilters for stormwater harvesting: understanding the treatment performance of key metals that pose a risk for water use

A large-scale stormwater biofilter column study was conducted to evaluate the impact of design configurations and operating conditions on metal removal for stormwater harvesting and protection of aquatic ecosystems. The following factors were tested over 8 months of operation: vegetation selection (plant species), filter media type, filter media depth, inflow volume (loading rate), and inflow pollutant concentrations. Operational time was also integrated to evaluate treatment performance over time. Vegetation and filter type were found to be significant factors for treatment of metals. A larger filter media depth resulted in increased outflow concentrations of iron, aluminum, chromium, zinc, and lead, likely due to leaching and mobilization of metals within the media. Treatment of all metals except aluminum and iron was generally satisfactory with respect to drinking water quality standards, while all metals met standards for irrigation. However, it was shown that biofilters could be optimized for removal of iron to meet the required drinking water standards. Biofilters were generally shown to be resilient to variations in operating conditions and demonstrated satisfactory removal of metals for stormwater-harvesting purposes.     

Column extraction of heavy metals from soils using the biodegradable chelating agent EDDS

A possible remediation strategy for metal polluted soils is washing with chelants. Here, we compare the efficiency of batch and column extraction of Cu, Zn, and Pb from three soils using the biodegradable chelant EDDS. A total of 53-80% of Cu was extracted in batch and 18-26% in column extraction. For Zn, the extractability was 16-50% in batch and 20-64% in columns and for Pb 25-52 and 18-91%, respectively. Column leaching was therefore equally or better suited for Zn and Pb removal. The longer extraction time in the column resulted in more formations of Fe(III)EDDS by slow dissolution of iron oxides. Zn was uniformly washed from the column, while Cu and Pb were extracted in the top layers and deposited in the bottom layers, presumably by biodegradation of the metal-EDDS complexes and slow dissolution of iron oxides. Between 18 and 42% of the applied EDDS was lost through biodegradation after 7 weeks. In short time experiments, only 6% of EDDS was degraded. Using EDDS concentrations in excess of available heavy metals caused pronounced leaching of organic matter and clogging of the column. Our results prove that heap leaching using EDDS is a promising approach to reduce the heavy metal content of polluted soils.     

Laboratory and field verification of a method to estimate the extent of petroleum biodegradation in soil

We describe a new and rapid quantitative approach to assess the extent of aerobic biodegradation of volatile and semivolatile hydrocarbons in crude oil, using Shushufindi oil from Ecuador as an example. Volatile hydrocarbon biodegradation was both rapid and complete-100% of the benzene, toluene, xylenes (BTEX) and 98% of the gasoline-range organics (GRO) were biodegraded in less than 2 days. Severe biodegradation of the semivolatile hydrocarbons occurred in the inoculated samples with 67% and 87% loss of the diesel-range hydrocarbons (DRO) in 3 and 20 weeks, respectively. One-hundred percent of the naphthalene, fluorene, and phenanthrene, and 46% of the chrysene in the oil were biodegraded within 3 weeks. Percent depletion estimates based on C(30) 17α,21β(H)-hopane (hopane) underestimated the diesel-range organics (DRO) and USEPA 16 priority pollutant PAH losses in the most severely biodegraded samples. The C(28) 20S-triaromatic steroid (TAS) was found to yield more accurate depletion estimates, and a new hopane stability ratio (HSR = hopane/(hopane + TAS)) was developed to monitor hopane degradation in field samples. Oil degradation within field soil samples impacted with Shushufindi crude oil was 83% and 98% for DRO and PAH, respectively. The gas chromatograms and percent depletion estimates indicated that similar levels of petroleum degradation occurred in both the field and laboratory samples, but hopane degradation was substantially less in the field samples. We conclude that cometabolism of hopane may be a factor during rapid biodegradation of petroleum in the laboratory and may not occur to a great extent during biodegradation in the field. We recommend that the hopane stability ratio be monitored in future field studies. If hopane degradation is observed, then the TAS percent depletion estimate should be computed to correct for any bias that may result in petroleum depletion estimates based on hopane.     

Chemoeffectors decrease the deposition of chemotactic bacteria during transport in porous media

Bacterial chemotaxis enables motile cells to move along chemical gradients and to swim toward optimal places for biodegradation. However, its potentially positive effects on subsurface remediation rely on the efficiency of bacterial movement in porous media, which is often restricted by high deposition rates and adhesion to soil surfaces. In well-controlled column systems, we assessed the influence of the chemo-effectors naphthalene, salicylate, fumarate, and acetate on deposition of chemotactic, naphthalene-degrading Pseudomonas putida G7 in selected porous environments (sand, forest soil, and clay aggregates). Our data showed that the presence of naphthalene in the pore water decreased deposition of strain 67 (but not of a derivative strain, P. putida 67.C1 (pHG100), nonchemotactic to naphthalene) by 50% in sand-filled columns, as calculated by the relative adhesion efficiency (at). Similar effects were observed with P. putida G7 strain for the other chemoeffectors. Deposition, however, depended on the chemoeffector's chemical structure, its interaction with the column packing material, and concomitantly its pore-water concentration. As the presence of the chemoeffectors had no influence on the physicochemical surface properties of the bacteria, we suggest that chemotactic sensing, combined with changed swimming modes, is likely to influence the deposition of bacteria in the subsurface, provided that the chemoeffector is dissolved at sufficient concentration in the pore water.     

Dual biomarkers of anaerobic hydrocarbon degradation in historically contaminated groundwater

This study reports that ongoing in situ anaerobic hydrocarbon biodegradation at a manufactured gas plant impacted site is occurring, 9 years after the initial investigation. Groundwater samples from the site monitoring wells (MW) were analyzed for biomarkers by GC-MS, end-point PCR, and quantitative PCR (qPCR). Metabolic biomarkers included specific intermediates of anaerobic naphthalene and/or 2-methylnaphthalene degradation: 2-naphthoic acid (2-NA); 5,6,7,8-tetrahydro-2-NA (TH-2-NA); hexahydro-2-NA (HH-2-NA); and carboxylated-2-methylnaphthalene (MNA). The analogues of gene bssA, encoding alpha subunit of enzyme benzylsuccinate synthase, were used as a genetic biomarker. Results indicate 1-2 orders of magnitude higher abundance of total bacteria in the impacted wells than in the unimpacted wells. End-point PCR analysis of bssA gene, with degenerate primers, indicated the presence of hydrocarbon degrading bacteria within the plume. In qPCR analysis, using primers based on toluene-degrading denitrifying or sulfate-reducing/methanogenic bacteria, bssA genes were detected only in MW-24, located downstream from the source. Metabolic biomarkers were detected in multiple wells. The highest abundance of 2-NA (6.7 μg/L), TH-2-NA (2.6 μg/L), HH-2-NA, and MNA was also detected in MW-24. The distribution of two independent biomarkers indicates that the site is enriched for anaerobic hydrocarbon biodegradation and provides strong evidence in support of natural attenuation.     

Influence of petroleum deposit geometry on local gradient of electron acceptors and microbial catabolic potential

A field survey was conducted following the Deepwater Horizon blowout and it was noted that resulting coastal petroleum deposits possessed distinct geometries, ranging from small tar balls to expansive horizontal oil sheets. A subsequent laboratory study evaluated the effect of oil deposit geometry on localized gradients of electron acceptors and microbial community composition, factors that are critical to accurately estimating biodegradation rates. One-dimensional top-flow sand columns with 12-h simulated tidal cycles compared two contrasting geometries (isolated tar "balls" versus horizontal "sheets") relative to an oil-free control. Significant differences in the effluent dissolved oxygen and sulfate concentrations were noted among the columns, indicating presence of anaerobic zones in the oiled columns, particularly in the sheet condition. Furthermore, quantification of genetic markers of terminal electron acceptor and catabolic processes via quantitative polymerase chain reaction of dsrA (sulfate-reduction), mcrA (methanogenesis), and cat23 (oxygenation of aromatics) genes in column cores suggested more extensive anaerobic conditions induced by the sheet relative to the ball geometry. Denaturing gradient gel electrophoresis similarly revealed that distinct gradients of bacterial communities established in response to the different geometries. Thus, petroleum deposit geometry impacts local dominant electron acceptor conditions and may be a key factor for advancing attenuation models and prioritizing cleanup.     

Fate of surfactants in membrane bioreactors and conventional activated sludge plants

Two membrane bioreactors (MBRs) were operated at high sludge retention time (SRT) (between 30 and 75 d) in parallel to a conventional activated sludge plant (CASP) conducted at SRT = 10 d. The fate of linear alkylbenzene sulfonate (LAS), nonylphenol ethoxylates (NP(n)EO, n = 1-15), nonylphenoxy carboxylates (NP(n)EC, n = 1-2), and nonylphenol (NP) in these systems was investigated. All systems were very efficient in the removal of LAS (around 99%). The analysis of variance showed that the difference in the removal efficiency of LAS in the CASP and the MBR operated at SRT = 65-75 d (respectively 99.0 ± 0.43 and 99.8 ± 0.11) were significant (p < 0.05), confirming the importance of SRT in the removal of LAS. Comparison between the CASP and the MBRs in the removal efficiency of nonylphenolic compounds were conducted considering NP(3-15)EO, the sum of NP(1-15)EO, NP(1-2)EC, and nonylphenol (NP). In all cases MBRs were more efficient than the CASP. In the case of NP the removal was about 76 ± 7.5% for the CASP and 90% ± 12.1 and 82 ± 8.7% for the MBRs. Better performance of MBRs in the removal of nonylphenolic compounds can be attributed to a better degradation. For example, if the sum of NP(1-15)EO and NP(1-2)EC is considered, estimated biodegradation was about 48% for the CASP and 72% for MBRs.     

Capacity for biodegradation of CFCs and HCFCs in a methane oxidative counter-gradient laboratory system simulating landfill soil covers

The attenuation of methane and four chlorofluorocarbons was investigated in a dynamic methane and oxygen counter-gradient system simulating a landfill soil cover. Soil was sampled at Skellingsted Landfill, Denmark. The soil columns showed a high capacity of methane oxidation with oxidation rates of 210 g m(-2) d(-1) corresponding to a removal efficiency of 81%. CFC-11 and to a lesser extent also CFC-12 were degraded in the active soil columns. The average removal efficiency was 90% and 30% for CFC-11 and CFC-12, respectively. Soil gas concentration profiles indicated that the removal was due to anaerobic degradation, which was verified in anaerobic batch experiments where CFC-11 was rapidly degraded. HCFC-21 and HCFC-22 were also degraded in active soil columns (61% and 41%, respectively), but compared to the CFCs, the degradation was located in the upper oxic part of the column with overlapping gradients of methane and oxygen. High oxidation rates of methane and HCFCs were obtained in soil microcosms incubated with methane. When increasing the column inlet flow, the oxidation zone was moved upward in the column, and the removal efficiency of methane and HCFCs decreased. The removal of CFCs was, however, less affected since the anaerobic zone expanded with increasing inlet flow rates. This study demonstrates the complexity of landfill soil cover systems and shows that both anaerobic and aerobic bacteria may play a very important role in reducing the emission of not only methane but also trace components into the atmosphere.     

Disentangling oil weathering at a marine seep using GC x GC: broad metabolic specificity accompanies subsurface petroleum biodegradation

Natural seeps contribute nearly half of the oil entering the coastal ocean. However, environmental fate studies generally monitor fewer than 5% of these petroleum compounds. Hence, the rates and relevance of physical, chemical, and biological weathering processes are unknown for the large majority of hydrocarbons, both released from natural seeps and also from human activities. To investigate the specific compositional changes occurring in petroleum during subsurface degradation and submarine seepage, we studied the natural oil seeps offshore Santa Barbara, California with comprehensive, two-dimensional gas chromatography (GC x GC). With this technique, we quantified changes in the molecular diversity and abundance of hydrocarbons between subsurface reservoirs, a proximal sea floor seep, and the sea surface overlying the seep. We also developed methods to apportion hydrocarbon mass losses due to biodegradation, dissolution, and evaporation, for hundreds of tracked compounds that ascended from the subsurface to the sea floor to the sea surface. The results provide the first quantitative evidence of broad metabolic specificity for anaerobic hydrocarbon degradation in the subsurface and reveal new trends of rapid hydrocarbon evaporation at the sea surface. This study establishes GC x GC as a powerful technique for differentiating biological and physical weathering processes of complex mixtures at a molecular level.     

Competitive sorption between 17alpha-ethinyl estradiol and naphthalene/phenanthrene by sediments

Steroid hormones such as 17alpha-ethinyl estradiol (EE2) have been frequently detected at various levels in surface waters downstream of many municipal wastewater treatment facilities. Their fate, transport, and environmental risk are currently not well characterized. This study examined the competitive sorption between EE2 and two aromatic hydrocarbon compounds, phenanthrene and naphthalene, by three sediments. The sorption isotherms of phenanthrene and naphthalene were measured at 22 +/- 0.5 degrees C using a batch technique with initial aqueous concentrations (Co) of EE2 at 0, 100, 500, and 2000 microg/L. Competitive sorption varied between EE2 and phenanthrene or naphthalene on the sediments. The linearity of the naphthalene sorption isotherm was found to increase as a function of the cosorbate EE2 concentration from 0 to 2000 microg/L. The single-point naphthalene KD value at equilibrium aqueous-phase naphthalene concentration (Ce) of 25 microg/L was reduced by 19-26% and 27-48% at Co (EE2) = 100 and 500 microg/L, respectively. The sorption of phenanthrene at its low Ce range was similarly affected by EE2, but to a much less extent, possibly because phenanthrene is more hydrophobic than EE2. At high phenanthrene Ce, no measurable change was observed even at CO (EE2) = 2000 microg/L. While the effect of naphthalene on EE2 sorption was insignificant, the competitive effect on the sorption of EE2 by phenanthrene was very significant at low EE2 concentrations. The measured single-point EE2 KD values decreased as much as 35% as the phenanthrene Ce increases from below 10 microg/L to slightly above 100 microg/L. This study suggests that the fate and transport of emerging pollutants such as EE2 could be affected in the presence of more hydrophobic pollutants in aquatic systems.     

Fate of alkylphenolic compounds during activated sludge treatment: impact of loading and organic composition

The impact of loading and organic composition on the fate of alkylphenolic compounds in the activated sludge plant (ASP) has been studied. Three ASP designs comprising carbonaceous, carbonaceous/nitrification, and carbonaceous/nitrification/denitrification treatment were examined to demonstrate the impact of increasing levels of process complexity and to incorporate a spectrum of loading conditions. Based on mass balance, overall biodegradation efficiencies for nonylphenol ethoxylates (NPEOs), short chain carboxylates (NP(1-3)EC) and nonylphenol (NP) were 37%, 59%, and 27% for the carbonaceous, carbonaceous/nitrification, and carbonaceous/nitrification/denitrification ASP, respectively. The presence of a rich community of ammonia oxidizing bacteria does not necessarily facilitate effective alkylphenolic compound degradation. However, a clear correlation between alkylphenolic compound loading and long chain ethoxylate compound biodegradation was determined at the three ASPs, indicating that at higher initial alkylphenolic compound concentrations (or load), greater ethoxylate biotransformation can occur. In addition, the impact of settled sewage organic composition on alkylphenolic compound removal was evaluated. A correlation between the ratio of chemical oxygen demand (COD) to alkylphenolic compound concentration and biomass activity was determined, demonstrating the inhibiting effect of bulk organic matter on alkylphenol polyethoxylate transformation activity. At all three ASPs the biodegradation pathway proposed involves the preferential biodegradation of the amphiphilic ethoxylated compounds, after which the preferential attack of the lipophilic akylphenol moiety occurs. The extent of ethoxylate biodegradation is driven by the initial alkylphenolic compound concentration and the proportion of COD constituted by the alkylphenol polyethoxylates (APEOs) and their metabolites relative to the bulk organic concentration of the sewage composed of proteins, acids, fats, and polysaccharides. Secondary effluents from this study are characterized by low bulk organic concentrations and comparatively high micropollutant concentrations. Based on the biodegradation mechanism proposed in this study, application of high rate tertiary biological treatment processes to secondary effluents characterized by low bulk organic concentrations and comparatively high APEO concentrations is predicted to provide a sustainable solution to micropollutant removal.     

Fate, transport, and biodegradation of natural estrogens in the environment and engineered systems

Natural steroidal estrogen hormones, e.g., estrone (E1), 17beta-estradiol (E2), estriol (E3), and 17alpha-estradiol (17alpha), are released by humans and livestock in the environment and are the most potent endocrine disrupters even at nanogram per liter levels. Published studies broadly conclude that conventional wastewater treatment is efficient in the removal of 17beta-estradiol (85-99%), but estrone removal is relatively poor (25-80%). The removal occurs mainly through sorption by sludge and subsequent biodegradation. The long solids retention time in wastewater treatment systems enhances estrogen removal due to longer exposure and the presence of a diverse microbial community, particularly nitrifiers. In spite of the treatment, the effluent from conventional biological wastewater treatment systems still contains estrogenic compounds at a level that may cause disruption of endocrine systems in some species. Advanced wastewater treatment systems such as membrane processes remove the estrogen compounds mainly through physical straining of particle-bound estrogens. Another major source, which accounts for 90% of the estrogen load, is animal manure from concentrated animal-feeding operations (CAFOs). Manure is not required to be treated in the United States as long as it is not discharged directly into water bodies. Thus, there is an urgent need to study the fate of animal-borne estrogens from these facilities into the environment. A number of studies have reported the feminization of male aquatic species in water bodies receiving the effluents from wastewater treatment plants (WWTPs) or surface runoff from fields amended with livestock manure and municipal biosolids. Estrogenicity monitoring studies have been conducted in more than 30 countries, and abundant research articles are now available in refereed journals. This review paper focuses on estrogen contributions by wastewater and livestock manure, their removal rate and mechanisms in an engineered system, and their transport and ultimate fate in an engineered system and the environment. The review aims to advance our understanding of fate, transport, and biodegradation of estrogen compounds and outlines some directions for future research.     

Effects of gas flow rate, inlet concentration and temperature on biofiltration of volatile organic compounds in a peat-packed biofilter

The effects of incoming gas concentration, empty bed residence time (EBRT), and column temperature on the removal efficiency of volatile organic compounds (isoprene, dimethyl sulfide, chloroform, benzene, trichloroethylene, toluene, m-xylene, o-xylene and styrene) were studied for 101 d in a biofilter comprising two glass columns (I.D. 5.0 cm x height 62 cm) packed with peat. At an EBRT of 3 min the removal efficiency increased up to 90% 34 d after start up at both 25 degrees C and 45 degrees C when the incoming gas concentration was raised stepwise to 65 g.m(-3). When the incoming gas concentration increased to 83 g.m(-3), the removal efficiency was 93% at 25 degrees C, but dropped to 74% at 45 degrees C. At an incoming gas concentration of 92 g.m(-3) and an EBRT of 1.5 min, the removal efficiencies were 91% and 94% at 25 degrees C and 32 degrees C, respectively. However, at 1 min of EBRT, the removal efficiencies decreased to 68% and 81% at 25 degrees C and 32 degrees C, respectively. The removal rate per unit time and per unit volume of the biofilter was proportional to the incoming gas rate up to 3483 g VOC.m(-3).h(-1). Further increase of the incoming gas rate lowered the removal rate as compared to that predicted by the proportionality. The maximum removal rate was 3977 g.m(-3).h(-1) at 32 degrees C. At an EBRT of 1.5 min, the removal efficiency was highest for isoprene (93%), and lowest for chloroform (84%). Aromatic compounds (benzene, toluene, and xylene) were removed by 93-94%. The cell concentration increased 100-fold from the initial value, and reached 1.12 x 10(8) cells.(g of dry peat)(-1). At 32 degrees C, 67% of the incoming VOC was removed in the first quarter of the column.     

Performance evaluation using a three compartment mass balance for the removal of volatile organic compounds in pilot scale constructed wetlands

To perform a general assessment of treatment efficiency, a mass balance study was undertaken for two types of constructed wetlands (CWs), planted gravel filters and plant root mat systems, for treating VOC (benzene; MTBE) polluted groundwater under field conditions. Contaminant fate was investigated in the respective water, plant, and atmosphere compartments by determining water and atmospheric contaminant loads and calculating contaminant plant uptake, thereby allowing for an extended efficiency assessment of CWs. Highest total VOC removal was achieved during summer, being pronounced for benzene compared to MTBE. According to the experimental results and the calculations generated by the balancing model, degradation in the rhizosphere and plant uptake accounted for the main benzene removal processes, of 76% and 13% for the gravel bed CW and 83% and 11% for the root mat system. Volatilization flux of benzene and MTBE was low (<5%) for the gravel bed CW, while in the root mat system direct contact of aqueous and gaseous phases favored total MTBE volatilization (24%). With this applied approach, we present detailed contaminant mass balances that allow for conclusive quantitative estimation of contaminant elimination and distribution processes (e.g., total, surface, and phytovolatilization, plant uptake, rhizodegradation) in CWs under field conditions.     

Determination of steroidal hormone profiles along the Jalle d'Eysines River (near Bordeaux, France)

Steroidal estrogens have been shown to be the main contributors to the estrogenic activity observed in aquatic systems contaminated with sewage treatment work effluents. Although the occurrence of steroid hormones in the environment has received a great deal of attention, little is known about their fate in aquatic systems. In the presentwork, concentrations of conjugated and unconjugated hormonal steroids (estrone, 17beta-estradiol, estriol, 17alpha-ethynylestradiol, mestranol, progesterone, norethindrone, and D-norgestrel) were determined in the effluent of the Eysines sewage treatment plant (near Bordeaux, France), and along the receiving river, the Jalle d'Eysines River. Sampling was undertaken in summer and in winter conditions, to study both the temporal and the spatial distributions of steroids in this river. Only unconjugated natural estrogens were detected in the effluent. Estrone was the dominant compound (detected in all effluent samples, 17.1-71.0 ng x L(-1)), while estradiol and its metabolite estriol were detected only once, at much lower levels (4.4 and 2.9 ng x L(-1), respectively). Levels of estrogens were clearly raised above the detection limits downstream of the Eysines STP effluent discharge. Seasonal variations of estrone degradation rates were observed. In summer, the apparent decay rates of estrogen levels exceeded that of dilution, indicating high removal rates from the water column: 50% of the initial amount of this steroid was degraded within 1.7 km downstream of the effluent discharge. In winter, however, estrone levels did not significantly decrease over a 10 km reach downstream of the effluent discharge (1.9-1.8 ng x L(-1)). Steroids were determined in the particulate material of the river, but levels were below the detection limits (0.4-1.9 ng x g(-1)), indicating that sorption was not a major sink of estrogens. Therefore, it is likely that biodegradation plays a major role in the removal of steroids from the river and the different decay rates are probably related to differences in bacterial activity within the river.     

Laboratory study of treatment of trichloroethene by chemical oxidation followed by bioremediation

Studies were conducted with columns containing soil and emplaced trichloroethene (TCE) to investigate the potential for TCE source zone remediation with chemical oxidation followed by biologically mediated reductive dehalogenation. Following permanganate flushing of four columns, which resulted in rapid but incomplete removal of TCE DNAPL, no biological activity was observed following the addition of distilled water amended with ethanol and acetate, including two of the four columns that were bioaugmented with a TCE-dechlorinating microbial culture. Flushing with unsterilized site groundwater led to consumption of acetate and ethanol, accompanied by manganese reduction and methanogenesis. Reductive dechlorination of TCE to cis-1,2-dichloroethene (cis-DCE) followed the onset of ethanol and acetate biodegradation in bioaugmented columns only. Partial dechlorination of TCEto ethene was observed only in one of the bioaugmented columns after it was inoculated for a third time. At the end of the study (290 days), a trace amount of cis-DCE was observed in one of the two columns which was not bioaugmented. Reduced conditions created by biostimulation were also conducive to reduction of Mn(IV) from MnO2 in both bioaugmented and nonbioaugmented columns resulting in an increased dissolved manganese (Mn2+) concentration in groundwater.     

人工湿地系统处理化机浆废水小试研究

针对某化机浆厂 SBR 生化出水,采用小试规模的模拟人工湿地系统研究了不同基质和有无植物对废水中污染物的去除效果.选取了生物陶粒、无烟煤和页岩三种基质,并且对其进行两两组合,同时利用处理效果最好的基质生物陶粒构建了有无植物(风车草)的对照组湿地.研究表明:(1)三种不同基质对污水有不同的处理效果,其中生物陶粒对 COD...     

Carbon isotope fractionation during diffusion and biodegradation of petroleum hydrocarbons in the unsaturated zone: field experiment at Vaerløse Airbase, Denmark, and modeling

A field experiment was conducted in Denmark in order to evaluate the fate of 13 volatile organic compounds (VOCs) that were buried as an artificial fuel source in the unsaturated zone. Compound-specific isotope analysis showed distinct phases in the 13C/12C ratio evolution in VOC vapors within 3 m from the source over 114 days. At day 3 and to a lesser extent at day 6, the compounds were depleted in 13C by up to -5.7% per hundred with increasing distance from the source compared to the initial source values. This trend can be explained by faster outward diffusion of the molecules with 12C only compared to molecules with a 13C. Then, the isotope profile leveled out, and several compounds started to become enriched in 13C by up to 9.5% per hundred with increasing distance from the source, due to preferential removal of the molecules with 12C only, through biodegradation. Finally, as the amount of a compound diminished in the source, a 13C enrichment was also observed close to the source. The magnitude of isotope fractionation tended to be larger the smaller the mass of the molecule was. This study demonstrates that, in the unsaturated zone, carbon isotope ratios of hydrocarbons are affected by gas-phase diffusion in addition to biodegradation, which was confirmed using a numerical model. Gas-phase diffusion led to shifts in delta(13)C >1% per hundred during the initial days after the spill, and again during the final stages of source volatilization after >75% of a compound had been removed. In between, diffusion has less of an effect, and thus isotope data can be used as an indicator for hydrocarbon biodegradation.