A field study was conducted on a coastal salt marsh in Nova Scotia, Canada, during the summer of 2000. The objective of the study was to assess the effectiveness of biostimulation in restoring an oil-contaminated coastal marsh dominated by Spartina alterniflora under north-temperate conditions. Three remediation treatments were tested with two additional unoiled treatments, with and without added nutrients, serving as controls. This research determined the effectiveness of nitrogen and phosphorus addition for accelerating oil disappearance, the role of nutrients in enhancing restoration in the absence of wetland plants, and the rate at which the stressed salt marsh recovered. Petroleum hydrocarbons were analyzed by gas chromatography/mass spectrometry (GC/MS). Statistically significant treatment differences were observed for alkanes but not aromatics in sediment samples. No differences were evident in above-ground vegetation samples. GC/MS-resolved alkanes and aromatics degraded substantially (>90% and >80%, respectively) after 20 weeks with no loss of TPH. Biodegradation was determined to be the main oil removal mechanism rather than physical washout.
In this study, we investigated the treatability of co-mingled groundwater contaminated with polycyclic aromatic hydrocarbons (PAHs), gasoline hydrocarbons, and methyl tert-butyl ether (MtBE) using an ex-situ aerobic biotreatment system. The PAHs of interest were naphthalene, methyl-naphthalene, acenaphthene, acenaphthylene, and carbazole. The gasoline hydrocarbons included benzene, toluene, ethyl benzene, and p-xylene (BTEX). Two porous pot reactors were operated for a period of 10 months under the same influent contaminant concentrations. The contaminated groundwater was introduced into the reactors at a flow rate of 4 and 9 l/day, resulting in a hydraulic retention time (HRT) of 32 and 15 h, respectively. In both reactors, high removal efficiencies were achieved for the PAHs (>99%), BTEX and MtBE (>99.7%). All the PAHs of interest and the four BTEX compounds were detected at concentrations less than 1 lg/l throughout the study duration. Effluent MtBE from both reactors was observed at higher levels; nevertheless, its concentration was lower than the 5 lg/l Drinking Water Advisory for MtBE implemented in California.
The purpose of this field study was to evaluate bioremediation and phytoremediation in restoring an oil-contaminated freshwater shoreline. Weathered Mesa light crude oil was released intentionally onto small plots in the upper intertidal zone of a study site located along the St. Lawrence River. Treatments were established to examine the effect of nutrient addition and the role of plants (Scirpus pungens) on the removal of oil constituents from the contaminated plots. Fertilizers under evaluation included sodium nitrate, prilled ammonium nitrate, and triple super phosphate. Composite core samples were collected after 0, 1, 2, 4, 8, 12, 16, and 21 weeks for identification of remaining oil constituents by gas chromatography-mass spectrometry (GC-MS). To account for differences because of physical washout, all oil constituents were normalized to the conservative biomarker hopane. Although bioremediation and phytoremediation treatments achieved slightly better degradation of hydrocarbons than natural attenuation, no statistically significant evidence of stimulation through addition of nutrients or biodegradation enhancement by vegetation was observed. After 21 weeks, reduction of target parent and alkyl-substituted polycyclic aromatic hydrocarbons (PAHs) averaged 32% in all treatments. Reduction of target alkanes was of similar magnitude. The pattern of disappearance of hydrocarbons was characteristic of biodegradation: namely, the lower molecular weight alkanes declined to a greater extent than the higher carbon-number alkanes, as did the lower molecular weight PAHs compared to the higher molecular weight PAHs. Since there was little evidence supporting enhancement of biodegradation by nutrient addition with and without vegetation, it was concluded that oxygen limitation most likely dominated the persistence of oil hydrocarbons on the oil-contaminated plots.
Biostimulation has been shown to be an effective tool for the treatment of oil spills in medium to low-energy marine environments. Little information is available on the bioremediation of oil spills in low-energy coastal wetlands. Most of the previous laboratory studies have been carried out under total flooding conditions. In this study, a tidal salt marsh was simulated in laboratory microcosms. The study was carried out in glass columns filled to a depth of 10 cm with sediment. Each microcosm was operated on a 24 hours square tidal cycle with a 12-hour submergence period. The entire sediment was mixed with weathered fuel oil No 2 (F02) to a concentration of 20 g/kg of wet sediment. Two biomarkers, 5α-cholestane and heptamethylnonane were added to the oil for data normalization. Nutrients were premixed with the soil in an amount equivalent to 1 gram as nitrogen and 0.2 grams as phosphorus per column. The experiment was conducted with a no fertilizer control and three types of fertilizer: a slow-release, inorganic, granular fertilizer, prilled ammonium nitrate; sodium nitrate; and ammonium chloride. The source of phosphorus was sodium tripolyphosphate. Duplicate columns were sacrificed at 15, 30, 60 and 120 days after FO2 addition. Sediments were divided into two layers from the top and bottom of the columns, extracted with dichloro-methane (DCM) by Soxhlet extraction and analyzed for oil components by GC/MS. Nitrate, ammonia, and pH were monitored in the water samples on a weekly basis. Soil samples were also extracted for nutrients to perform a mass balance. Phospholipids analysis and Most Probable Number (MPN) were performed on the sediment samples to establish a measurement of biological growth. Results indicated that: (1) oil degradation was slightly higher for all treatments in the top 5 cm layer and it occurred mostly during the first 15 days of the experiment; (2) microbial growth of 2 orders of magnitude was detected in the top layer; (3) no significant differences were observed among treatments; (4) degradation was probably limited by oxygen availability.
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