Plants‐associated microflora and the remediation of oil‐contaminated soil

The use of plants and their rhizospheric microorganisms is a promising emerging technology for remediating contaminated soils. The degradation of total petroleum hydrocarbon (TPH) in the rhizospheric and nonrhizospheric soil of three domestic plants, namely, alfalfa (Medicaga sativa) broad beans (Vicia faba) and ryegrass (Lolium perenne) was investigated. The experimental data from the studies of plantmicrobe‐soil interactions implicated the enhancement of TPH degradation by the rhizospheric microbial community. Although the three domestic plants exhibited normal growth in the presence of ～1.0% TPH, the degradation was more profound in the case of leguminous plants. The TPH degradation in the soil cultivated with broad beans and alfalfa was 36.6 and 35.8%, respectively, compared with 24% degradation in case of ryegrass. Such a high correlation between plant type and TPH degradation rates indicate that selection for enhanced rhizosphere degradation may be accomplished by selecting leguminous plants.     

Organic emissions from petroleum‐contaminated soil fixed in concrete

This study investigated a solidification treatment process for soils that are contaminated with hydrocarbons at levels of 0.5 and 3.0% by weight of benzene. The contaminated soils were bound in a concrete matrix and the migration of organics from the concrete to air was evaluated. If the hydrocarbon emissions are sufficiently attenuated, the concrete containing such contaminated soil can be used for exterior construction applications.

The experimental specimens consisted of concrete mixtures in which 40% of the sand was replaced with the contaminated soil. The mixtures’ ratio of cement, aggregate, sand, and water is 1:1.5:1.5:0.5 by weight. The study included specimens with and without class C fly ash replacing 10% of the cement. In addition, two unfixed control specimens were prepared for each contamination level. The concrete‐soil mixtures were placed in sealed jars and air was passed through the head space of the jars and then through carbon adsorption tubes for measurement of contaminant flux from the surface of the specimens. Measurements were made during and after concrete curing. The results were fitted to a Fickian diffusion model to estimate effective diffusivity in the concrete‐soil specimens.

The test results showed that the effective diffusivity of the contaminant within the concrete was reduced by three to five orders of magnitude over the molecular diffusivities in unfixed contaminated soil used as control. It was observed that the presence of fly ash in the concrete affects the hydrocarbon release and causes an additional decrease in effective diffusivity of about one order of magnitude. Contaminant emissions during the curing phase were found to exceed rates predicted by the Fickian model. This is apparently due to the water used in the concrete. Total emissions, however, never exceeded values emitted from the unfixed controls. This study indicates that fixation of low hydrocarbon levels within concrete is a technically viable and safe technology for recycling petroleum‐contaminated soil.     

Dose assessment considerations for remedial action on plutonium‐contaminated soil

This article describes some of the dose assessment issues that should be considered when planning and executing a soil remedial activity. What is the proper dose scenario/ model? What are the appropriate cleanup criteria? How is the data gathered and analyzed (both before and after) cleanup?

By describing the features and aspects of how these issues and others were considered or not considered in planning for the remedial action underway at Maralinga, Australia (former site of the Nuclear Weapons Testing Program of the United Kingdom) when compared with historical international experience of this type, the author attempts to illustrate that it is almost nonsensical to preselect a single soil value for Pu in soil (for national or international use), particulariy when expressed as a soil concentration (pCi/g or bq/g). This is especially so when the problem is Pu on the surface or near the surface of the soil. This is the situation common at nuclear test sites where “one point safe tests” were conducted. At these locations aspects of resuspension (i.e., area size, particle size, wind speed, etc.) become the dominant drivers for the development of cleanup criteria, sampling regimes, data gathering, and analysis regimes, etc. These particular elements and others are discussed and illustrated.     

Compositional changes during landfarming of weathered michigan crude oil‐contaminated soii

Laboratory landfarming experiments were conducted to study the bioremediation potential of weathered Michigan crude oil‐contaminated soils. It was found that landfarming was successful in removing up to 90% of the total petroleum hydrocarbons (TPH) in the soil within 22 weeks of treatment. Boiling point analyses of untreated and treated soils indicate a significant removal of TPH compounds independent of molecular weight or carbon number. Up to 85% of heavy petroleum hydrocarbons with carbon numbers above 44 were biode‐graded. In addition, approximately 93% of saturated and 79% of aromatic compounds of the TPH were biodegraded during the 22 week treatment period. The use of polyethylene sheeting as a landfarm cover does not appear to adversely affect biodegradation kinetics under laboratory conditions. Finally, equilibrium leachate concentrations for BTEX and regulated (in Michigan) polynuclear aromatics (PNAs) were below the respective detection limits for each compound. It can be concluded that landfarming of these weathered soils will be highly successful in removing petroleum hydrocarbons while not adversely impacting either ground‐water or surface water quality.     

Simplified methods for monitoring petroleum‐contaminated ground water and soil vapor

Portable meters and simplified gas Chromatographic (GC) techniques were investigated for monitoring volatile hydrocarbon (HC), CO₂, and O₂, concentrations in groundwater, exhaust gases, and soil vapor during in situ remediation using soil vapor extraction (SVE) and air sparging (AS). Results of groundwater samples analyzed in‐house using a headspace technique compared well to split samples analyzed by a certified analytical laboratory (r² = 0.94). SVE exhaust gas HC and CO₂ concentrations measured using a GT201 portable HC/O₂ meter and a RA‐411A meter (GasTech), respectively, were highly correlated with in‐house laboratory GC analyses (r² = 0.91). O₂ concentrations fell in a small range and meter analyses were not well correlated with laboratory analyses. Results of soil gas monitoring were not as well correlated as those for exhaust gases for HC, CO₂, or O₂, perhaps due to environmental conditions such as changes in relative humidity or the wider range of soil gas values. Overall, the meters were good indicators of vapor contamination, they greatly simplified estimates of total HC mass removal, and they allowed estimates of the biological contribution to contaminant removal during the remediation process.     

Bioremediation of a polycyclic aromatic hydrocarbon‐contaminated soil by using different aerobic batch bioreactor systems

The intrinsic depuration capability of a soil contaminated by polycyclic aromatic hydrocarbons (PAHs) originating from a contaminated industrial site was evaluated in this study by using different aerobic batch bioreactors: a slurry‐phase bioreactor, a blade‐agitated bioreactor, and a rotary vessel bioreactor. For each bioreactor, the disappearance of 14 target PAHs and of the total extractable organic matter was monitored. The three treatments exhibited rapid and extensive removal of the PAHs, which disappeared at different degradation rates according to their molecular weight and aromaticity degree. PAHs with two, three, and four aromatic rings were degraded in sequence, with average rates that generally decreased as the number of molecule rings increased. A slight increase in the bacterial biomass concentration and significant CO₂ production were also observed during the time course of the treatments. Among the three treatments, the slurry‐phase system provides the most effective and fastest removal of the PAHs and the organic extractable matter. However, the semisolid‐phase systems exhibited PAH depletion, capabilities higher than those reported in the literature for soils with similar particle size distribution in solid‐phase conditions.     

Comprehensive GC²/MS for the monitoring of aromatic tar oil constituents during biodegradation in a historically contaminated soil

The constituents of tar oil comprise a wide range of physico-chemically heterogeneous pollutants of environmental concern. Besides the sixteen polycyclic aromatic hydrocarbons defined as priority pollutants by the US-EPA (EPA-PAHs), a wide range of substituted (NSO-PAC) and alkylated (alkyl-PAC) aromatic tar oil compounds are gaining increased attention for their toxic, carcinogenic, mutagenic and/or teratogenic properties. Investigations on tar oil biodegradation in soil are in part hampered by the absence of an efficient analytical tool for the simultaneous analysis of this wide range of compounds with dissimilar analytical properties. Therefore, the present study sets out to explore the applicability of comprehensive two-dimensional gas chromatography (GC2/MS) for the simultaneous measurement of compounds with differing polarity or that are co-eluting in one-dimensional systems. Aerobic tar oil biodegradation in a historically contaminated soil was analyzed over 56 days in lab-scale bioslurry tests. Forty-three aromatic compounds were identified with GC2/MS in one single analysis. The number of alkyl chains on a molecule was found to prime over alkyl chain length in hampering compound biodegradation. In most cases, substitution of carbon with nitrogen and oxygen was related to increased compound degradation in comparison to unalkylated and sulphur- or unsubstituted PAH with a similar ring number.The obtained results indicate that GC2/MS can be employed for the rapid assessment of a large variety of structurally heterogeneous environmental contaminants. Its application can contribute to facilitate site assessment, development and control of microbial cleanup technologies for tar oil contaminated sites.     

Mercury translocation in and evaporation from soil. I. soil lysimeter experiments with 203Hg‐radiolabeled compounds

Due to a considerable increase of anthropogenic mercury emissions, the mercury load of many soils has risen significantly, for instance in northern Europe. Understanding the fate of mercury in soils is a prerequisite for assessing the effects of ecotoxicological concern. This paper presents a method for obtaining qualitative and quantitative information about mercury translocation in and evaporation from soil. Soil lysimeters were treated with ²⁰³Hg‐labeled HgCl₂ and CH₃HgCl and irrigated with artificial rain. It was demonstrated that the leaching of Hg can be detected by measuring the relative y‐activity throughout the soil profile by means of Na(TI)I detectors. Furthermore, the set‐up was designed to allow detection of Hg volatilization from soil by using traps of iodized charcoal, followed by a potassium peroxodisulfate solution and measuring the γ‐activity. The amount of radioactive Hg in soil leachate was measured by a Na(Tl)I well‐type detector after upconcentration. The determination of monomethyl ²⁰³Hg was been performed by extraction procedures that isolate the methyl mercury compounds. The amount of ²⁰³Hg retained in the soil profile and the real depth of leaching were determined by stratifying the soil profile at the end of the experiment and measuring the y‐activity. With control of all pathways of Hg, the experimental design allows performance of a mass balance analysis.     

Bioremediation of a petroleum‐contaminated cryic soil: Effects of phosphorus,nitrogen, and temperature

Bioremediation has been shown to be an effective means of treating petroleum‐contaminated soils in cold areas, although the conditions required to maximize bioremediation in cold region (cryic) soils are not well documented. A laboratory study was conducted to investigate the effects of nitrogen and phosphorus levels and temperature on petroleum bioremediation. A cryic entisol contaminated with diesel fuel was treated with nitrogen (0, 400, 800, or 1200 mg/kg of soil) and phosphorus (0, 60, 120, or 180 mg/kg of soil) and incubated at two temperatures (10 and 20°C). At 10°C, bioremediation rates were not affected by fertility treatments. At 20°C, reaction rates were increased by the addition of P, but unaffected by N. Regardless of fertility regime, the rate of diesel loss was much greater in soil incubated at 20°C than in soil incubated at 10°C.     

Prediction of leachate concentrations in petroleum‐contaminated soils

The efficacy of cleanup methods in reducing gasoline contamination at spill sites is typically determined by measuring benzene, toluene, xylene (BTX), and total petroleum hydrocarbon (TPH) concentrations in soil samples. Although these values may provide a direct measurement of soil contamination, they may not be indicative of what is transferred to percolating water. This study addresses this issue by measuring TPH, toluene, m‐ and p‐xylene, and naphthalene levels in gasoline‐contaminated soil columns before and after forced‐air venting and relating these values to the aqueous‐phase concentrations measured when water is percolated through the same columns.

Sandy soils with and without organic matter were packed into glass columns. The soils were brought to residual water and residual gasoline saturations by applying a vacuum to a ceramic pressure plate at the column bottom. Venting was performed by passing clean, moist air through the columns. The columns were subsequently leached under unsaturated conditions.

Soil samples were taken from the bottom of the columns upon completion of the venting or leaching phases of the experiments. Toluene, m‐ and p‐xylene, naphthalene, and TPH values were measured in soil samples extracted with either freon or methanol. Aqueous phase concentrations of these compounds were predicted using measured soil concentrations and either Raoult's law or organic matter‐water and fuel‐water partitioning theory (Boyd and Sun, 1990). The predicted results were compared with measured leachate concentrations from the same columns.

Mole fractions estimated from soil concentrations and TPH values used in Raoult's law gave good predictions of aqueous phase concentrations for compounds that had a high mole fraction in the residual nonaqueous phase liquid (NAPL). For compounds at low concentrations in the residual NAPL, an approach using a distribution coefficient that accounted for both the organic matter and residual NAPL in the soil provided better estimates than those based on Raoult's law.     

Bioremediation of multi-metal contaminated soil using biosurfactant — a novel approach

An unconventional nutrient medium, distillery spent wash (1:3) diluted) was used to produce di-rhamnolipid biosurfactant by Pseudomonas aeruginosa strain BS2. This research further assessed the potential of the biosurfactant as a washing agent for metal removal from multimetal contaminated soil (Cr-940 ppm; Pb-900 ppm; Cd-430 ppm; Ni-880 ppm; Cu-480 ppm). Out of the treatments of contaminated soil with tap water and rhamnolipid biosurfactant, the latter was found to be potent in mobilization of metal and decontamination of contaminated soil. Within 36 hours of leaching study, di-rhamnolipid as compared to tap water facilitated 13 folds higher removal of Cr from the heavy metal spiked soil whereas removal of Pb and Cu was 9–10 and 14 folds higher respectively. Leaching of Cd and Ni was 25 folds higher from the spiked soil. This shows that leaching behavior of biosurfactant was different for different metals. The use of wastewater for production of biosurfactant and its efficient use in metal removal make it a strong applicant for bioremediation.     

Laboratory studies of air stripping of VOC‐contaminated soils

Bench‐scale laboratory experiments were conducted to evaluate the effectiveness of air stripping for in situ remediation of benzene‐contaminated soils. Several parametric studies were performed to evaluate the effect of soil grain size, air injection flow rate, and air inlet temperature on the benzene recovery efficiency.

An increase in soil grain size produced a significant increase in benzene recovery efficiency especially during the early stages of air injection. After 2 h of treatment, an increase in soil grain size from D₅₀ = 0.31 mm to D₅₀ = 1.20 mm resulted in an increase in benzene recovery efficiency from 49 to 65%. When the air‐flow rate was increased from 5 l/min to 10 l/min, the benzene recovery efficiency increased from 56 to 70% after 4 h of venting operation. Maximum recovery of benzene was reached after approximately 37 h of soil venting at a flow rate of 5 l/min and after approximately 24 h at a flow rate of 10 l/min. Preheating the air to 45°C at the inlet resulted in an increase in recovery efficiency from 70 to 90% after 5 h of air stripping.     

Stabilization and solidification of hydrocarbon‐contaminated soils in concrete

This article describes an experimental program developed to investigate the potential for using hydrocarbon‐contaminated soils as a fine aggregate replacement in concrete. Five different contaminated soil types with a total petroleum hydrocarbon content of less than 1% were investigated. For each soil type, three concrete mixtures were obtained by replacing sand with contaminated soils (10, 20, and 40% replacement ratio). The resulting concrete was tested for setting times, compression strength, flexural strength, durability, and teachability of benzene to water.

The results indicate that the addition of hydrocarbon‐contaminated soil adversely affects the strength of concrete. The strength reduction at each soil replacement level depends on contamination concentration, contaminant type, and soil type. The durability of the tested concrete is comparable to normal concrete. For all five soils at a 40% replacement ratio, the leachability of benzene was nondetectable after 24 h and after 10 d. After testing the leachability of artificially contaminated soils (0.5 and 3% neat benzene contamination) for 24 h, it was found that the leaching of benzene increases with the percentage of contamination. However, the fraction of benzene that leached was about 95% lower than the values for loose soils.     

Laboratory studies of steam stripping of LNAPL‐contaminated soils

Bench‐scale laboratory experiments were conducted to evaluate the effectiveness of steam injection for in situ remediation of soils contaminated by light nonaqueous‐phase liquids (LNAPLs). Several parametric studies were performed with various combinations of soils, LNAPLs, and steam injection conditions.

An increase in steam injection pressure produced a significant increase in LNAPL recovery efficiency. An increase in steam injection pressure from 12.4 to 44.8 kPa resulted in increased LNAPL recovery efficiency from 86 to 95% after one pore volume of steam injection. Higher steam injection pressure yielded maximum LNAPL recovery efficiency in significantly less time and required a smaller amount of steam than at low pressure.

An increase in soil grain size or an increase in grain‐size‐distribution slope resulted in increased LNAPL recovery efficiency. The final LNAPL residual saturation was approximately 0.5% for coarse‐grained soils and 1.8% for soils with finer grain sizes. Soils with finer grains required more time for treatment than soils with coarser grains.

Steam injection experiments with No. 2 heating oil and with jet fuel showed no significant variation in steam front propagation, temperature profile, and maximum LNAPL recovery efficiency. The LNAPL residual saturation after steam injection was essentially independent of the starting LNAPL saturation.     

Characterisation of Arthrobacter sp. S1 that can degrade α and β-haloalkanoic acids isolated from contaminated soil

A bacterium identified as Arthrobacter sp. S1 by 16S rRNA was isolated from contaminated soil. This is the first reported study that Arthrobacter could utilize both α-halocarboxylix acid (αHA) [2,2-dichloropropionic acid (2,2-DCP) and D,L-2-chloropropionic acid (D,L-2-CP)] and β-halocarboxylix acid (βHA) [3-chloropropionic acid (3CP)] as sole source of carbon with cell doubling times of 5?±?0.2, 7?±?0.1, and 10?±?0.1 h, respectively. More than 85 % chloride ion released was detected in the growth medium suggesting the substrates used were utilized. To identify the presence of dehalogenase gene in the microorganism, a molecular tool that included the use of oligonucleotide primers specific to microorganisms that can grow in halogenated compounds was adapted. A partial putative dehalogenase gene was determined by direct sequencing of the PCR-amplified genomic DNA of the bacterium. A comparative analysis of the deduced amino acid sequence data revealed that the amino acid sequence has a low identity of less than 15 % to both group I and group II dehalogenases, suggesting that the current putative dehalogenase amino acid sequence was completely distinct from both α-haloacids and β-haloacids dehalogenases. This investigation is useful in studying the microbial populations in order to monitor the presence of specific dehalogenase genes and to provide a better understanding of the microbial populations that are present in soil or in water systems treating halogenated compounds.     

On‐site bioremediation treatment system design and on‐site analytical screening of hydrocarbon‐contaminated dredge sediments

In early 1991, a petroleum refining facility located on the Blair Waterway in Commencement Bay near Tacoma, Washington, wished to deepen its berthing facility. Sediments had accumulated in the berthing area adjacent to the facility's petroleum handling dock to the extent that tanker ships could go aground during low tides. A preliminary sediment characterization program had indicated that elevated polynuclear aromatic hydrocarbons such as anthracene and phenanthrene, and total petroleum hydrocarbons exceeded Puget Sound Dredge Disposal Analysis maximum level guidelines for unconfined, open‐water disposal. Enviros designated an on‐shore sediment treatment facility to receive the dredged sediments. Design criteria and construction details of a treatment area capable of accommodating 8000 yd³ of sediments are presented. Onsite, real‐time sediment analysis for total petroleum hydrocarbon (TPH) concentrations was conducted by an onsite mobile laboratory. Laboratory techniques to expedite sediment analysis for TPH using infrared spectrophotometry are described.     

A decision framework for selecting remediation technologies at hydrocarbon‐contaminated sites

A variety of remediation technologies are available to address hydrocarbon contamination, including free product recovery, soil venting, air sparging, groundwater recovery and treatment, and in situ bioremediation. These technologies address hydrocarbon contamination distributed between free, adsorbed, and dissolved phases in both the vadose and saturated zones. Selection of appropriate technologies is dependent on a number of factors, including contaminants, site‐specific characteristics, clean‐up goals, technology feasibility, cost, and regulatory and time requirements. This article describes a decision framework for selecting appropriate remediation technologies at hydrocarbon‐contaminated sites in a structured and tiered manner. Decision modules include (1) site characterization and product recovery; (2) vadosezone treatment: soil venting, bioremediation, and excavation; (3) saturated zone treatment: sparging, bioremediation, groundwater recovery, and excavation; and (4) groundwater treatment: carbon, air stripping, advanced oxidation, and bioreactors. Selection criteria for treatment technologies that address vadose‐ and saturated‐zone soils, as well as recovered groundwater, are described. The decision framework provides a systematic process to formulate solutions to complex problems and documents the rationale for selecting remediation systems designed to achieve closure at hydrocarbon‐contaminated sites.     

Selection of cold‐tolerant plants for growth in soils contaminated with organics

A mixture of organic chemicals (MOC) containing equal molar amounts of benzoic acid, hexadecane, 2,2‐dimethyl 4,n‐propyl‐benzene, phenanthrene, pyrene, and either cycloheptane or cis‐decahydronaphthalene (cis‐decalin) was applied to soil at rates of 0 to 8000 mg/kg. In a plant‐screening experiment, growth responses of four legume and five nonlegume species were determined at 10 and 25°C. The MOC applied at 2000 mg/kg reduced the growth of several species without resulting in significant seedling death. At 10°C, the growth of alpine bluegrass (Poa alpina L.) in the 1000 and 2000 mg/kg treatments of soil increased by more than 185%. In a plant growth response experiment, alpine bluegrass and alfalfa (Medicago sativa L.) were grown in soil that had been contaminated at rates of 0 and 2000 mg/kg. At 14 weeks, the shoot and root dry weights of alfalfa were 97% lower in the contaminated soil, while the shoot dry weight, root dry weight, and root length of alpine bluegrass were 135,235 and 268% higher, respectively. Except for pyrene, <23% of the compounds comprising the MOC remained in the soil after 4 weeks and <5% after 14 weeks. The disappearance of the MOC was not significantly influenced by the presence of alfalfa or alpine bluegrass.