Distribution of Petroleum and Aromatic Hydrocarbons at a Former Crude Oil and Natural Gas Production Facility

Site characterization and remediation activities were performed at a former crude oil and natural gas production facility prior to redevelopment of the site. Field activities included delineation, excavation and segregation of approximately 1,250,000 m³ of soil impacted by total petroleum hydrocarbons (TPH) and the aromatic volatile organic compounds (VOCs) benzene, toluene, ethylbenzene, and xylenes (hereafter, collectively referred to as BTEX). Petroleum hydrocarbon chain length information was used to determine whether remediation was required in impacted areas, because the site-specific cleanup values for TPH compounds, established by the California State Regional Water Quality Control Board (RWQCB), were based on hydrocarbon chain length. Site-specific cleanup levels were also established by the RWQCB for BTEX. Subsurface investigation activities performed at the site indicated that the mean percentage of condensate and TPH compounds in the gasoline range was significantly greater at depths ranging from 4.6 to 18 m than in shallower samples. There was no significant difference in the mean concentration of BTEX compounds and mean percentage of diesel range and heavier hydrocarbons with depth. The occurrence of BTEX, diesel range, and heavier hydrocarbons at depth may result from preferential pathways for downward migration of contaminants, including blown out wells, abandoned wellbores, and the presence of faults. Vapor phase diffusion may also be a major transport mechanism controlling movement of BTEX compounds beneath the site.     

Prepared Bed Land Treatment of Soils Containing Diesel and Crude Oil Hydrocarbons

An ex situ, field-scale, prepared bed land treatment unit (LTU) was used to bio-remediate soils containing petroleum hydrocarbons. Two soils were treated in side-by-side units to compare performance: (1) a clayey silt containing crude oil hydrocarbons from releases 30 to 40 years ago and (2) a silty sand containing diesel fuel hydrocarbons from a leak about three years prior to the bioremediation. The effectiveness of the bioremediation in the LTU was evaluated over a period of 18 months. The results indicated that: (1) prepared bed bioremediation reduced the hydrocarbon concentration, mobility, and relative toxicity in the soil with the diesel fuel, and (2) chemical bioavailability appeared to limit bioremediation of the soil containing the crude oil hydrocarbons. Although the soils containing the crude oil hydrocarbons contained an average of 10,000?mg TPH/kg dry soil, these soils had limited hydrocarbon availability, nontoxic conditions, and low potential for chemical migration. For the soils containing the diesel fuel, active prepared bed bioremediation of about 15 weeks was adequate to reach an environmentally acceptable endpoint. At that time, there was little further TPH loss, no Microtox^TM toxicity, and limited hydrocarbon mobility.     

蒸发条件下潜水埋深对土壤-柽柳水盐分布的影响

盐水矿化度下模拟设置4个潜水埋深(0.9、1.2、1.5、1.8 m),分析不同土层的土壤相对含水量(RWC)、含盐量(S_C)和土壤溶液绝对浓度(C_S)等水盐参数,及柽柳叶片和新生枝条的含水量及Na~+含量,探讨盐水矿化度下土壤-柽柳水盐参数对潜水埋深的响应规律。结果表明:各土层RWC与潜水埋深呈负相关,0.9 m潜水埋深下各土层的RWC均最高,且各土层RWC随土层深度的增加呈先降低后增加的趋势,其它潜水埋深下各土层RWC均逐渐增加,1.2 m是地下水所能上升且保持柽柳柱体土壤表层湿润的最高高度。各土层S_C和C_S与潜水埋深呈抛物线型,均表现为先增加后降低,潜水埋深1.2 m时,各土层S_C均最高。随土层深度的增加,各潜水埋深下S_C先降低后增加,而C_S呈现减少趋势;潜水埋深越高,土层间C_S变化幅度越激烈。潜水埋深对柽柳叶片和新生枝条的含水量无显著影响(P0.05),而随潜水埋深的增加,柽柳叶片Na~+含量逐渐增加,新生枝条Na~+含量则先增加后降低。从整个柽柳土柱看,随潜水埋深的增加,整个土壤剖面的RWC均值逐渐降低,而S_C和C_S均值先增加后降低,潜水埋深1.2 m是盐分变化的分界点,建议栽植柽柳的潜水埋深大于1.2 m。     

Co-Composting of Residual Fuel Contamination in Soil

A remediation program was designed and implemented at a site in southeastern Australia that had become contaminated with nonvolatile, n-alkane total petroleum hydrocarbons (TPH). The remediation was conducted in two stages. The excavation, validation and reinstatement of two contaminated areas on the site was first conducted, followed by development of a composting treatment process. The total volume of contaminated soil (i. e., TPH concentration >1000?mg/kg C₁₀?C₃₆) was ～4300?m³ with a concentration of 3100±1270?mg/kg. The soil was stockpiled into four windrows, on a compacted, bunded clay base. Approximately 35% (v/v) of raw materials (green tree waste, cow manure, gypsum, and nutrients) were added to initiate composting. The piles were kept moist during the summer months, but no other maintenance was conducted. Once the composting process was initiated, the windrows were sampled at 2 and 6 months. After 6 months treatment, the average TPH concentration (C₁₀?C₃₆) was 730?mg/kg (with a 95% CI of 1020?mg/kg), which met the relevant clean fill criteria applicable to the site. There were no other contaminants of significance in the treated soil compost and it posed no unacceptable risk to human health or the environment, allowing it to be used as fill at the site.     

Bioremediation of volatile oil hydrocarbons by epiphytic bacteria associated with American grass (Cynodon sp.) and broad bean (Vicia faba) leaves

Fresh leaves of American grass and broad beans grown in pristine soil were naturally colonized with cultivable volatile oil hydrocarbon-utilizing bacteria, whose numbers increased significantly in plants grown in oily soil. According to their 16S rRNA gene sequences those bacteria were affiliated to various species of the genera Rhodococcus and Pseudomonas. Qualitative growth studies revealed that pure cultures of these phyllospheric bacteria could grow successfully on a solid mineral medium containing individual alkanes with chain lengths of C₉ through C₄₀ and the aromatics phenanthrene, naphthalene, and biphenyl as sole sources of carbon and energy. Quantitative measurements showed that the individual pure bacterial isolates degraded between about 20 and 30% of crude oil, n-hexadecane, or phenanthrene in batch culture after a one-week incubation. These results reflect the high hydrocarbon degradation potential of those bacteria. The isolates were diazotrophic (nitrogen fixers), meaning that they were self-dependent in covering their nitrogen requirements. Incubating fresh leaves in closed microcosms containing volatile oil hydrocarbons resulted in up to more than 80% attenuation of these compounds after two weeks. Experimental evidence was provided that the leaf tissues did not contribute to this attenuation, which was exclusively due to the bacterial activity.     

Microbial Degradation of Alkyl Carbazoles in Norman Wells Crude Oil

Norman Wells crude oil was fractionated by sequential alumina and silicic acid column chromatography methods. The resulting nitrogen-rich fraction was analyzed by gas chromatography-mass spectrometry and showed 26 alkyl (C₁ to C₅) carbazoles to be the predominant compounds. An oil-degrading mixed bacterial culture was enriched on carbazole to enhance its ability to degrade nitrogen heterocycles. This culture was used to inoculate a series of flasks of mineral medium and Norman Wells crude oil. Residual oil was recovered from these cultures after incubation at 25°C for various times. The nitrogen-rich fraction was analyzed by capillary gas chromatography, using a nitrogen-specific detector. Most of the C₁-, C₂-, and C₃- carbazoles and one of the C₄-isomers were degraded within 8 days. No further degradation occurred when incubation was extended to 28 days. The general order of susceptibility of the isomers to biodegradation was C₁ > C₂ > C₃ > C₄. The carbazole-enriched culture was still able to degrade n-alkanes, isoprenoids, aromatic hydrocarbons, and sulfur heterocycles in the crude soil.     

PlANT-ASSOCIATED BACTERIA AS TOOLS FOR THE PHYTOREMEDIATION OF OILY NITROGEN-POOR SOILS

The rhizospheres and phyllospheres of peas, beans, tomatoes, and squash raised in a desert sand soil mixed with 0.5% crude oil were rich in oil-utilizing bacteria and accommodated large numbers of free-living diazotrophic bacteria, with potential for hydrocarbon utilization. According to their 16S rRNA-sequences, the cultivable oil-utilizing bacteria were affiliated with the following genera, arranged in decreasing frequency: Bacillus, Ochrobactrum, Enterobacter, Rhodococcus, Arthrobacter, Pontola, Nocardia, and Pseudoxanthomonas. Diazotrophic isolates were affiliated with Rhizobium, Bacillus, Rhodococcus, Leifsonia, Cellulosimicrobium, Stenotrophomonas, Kocuria, Arthrobacter, and Brevibacillus. The crude oil–utilizing and diazotrophic isolates grew, with varying growth intensities, on individual aliphatic (C₈ to C₄₀) and aromatic hydrocarbons, as sole sources of carbon and energy. Quantitative gas liquid chromatographic measurements showed that representative bacterial isolates eliminated pure n-hexadecane, n-decosane, phenanthrene, and crude oil from the surrounding liquid media. Cultivation of oily sand–soil samples with any of the four tested crops led to enhanced oil degradation in that soil, as compared with the degradation in uncultivated oily sand–soil samples.     

Assessment of soil contamination caused by underground fuel leakage from selected gas stations in Riyadh,Saudi Arabia

ABSTRACT

Spills and leakage from underground fuel storage tanks (UFSTs) can potentially contaminate soil and groundwater and pose harmful effects to public health and the environment. This study evaluated the feasibility of using volatile organic compounds (VOCs), total petroleum hydrocarbons (TPHs), electrical conductivity (EC), and pH to examine the contamination caused by leaking UFSTs. Screening water assessments for VOCs and general water quality parameters were conducted on the premises of 53 gas stations in Riyadh, Saudi Arabia, to identify potentially contaminated sites, and 25 ground bores were drilled for the quantification of TPH concentrations, EC, and pH values in 407 soil samples. The experimental approach followed in this study included geochemical analyses based on borehole drilling at five targeted gas stations, analyses of water samples from underground storage reservoirs, and analyses of soil core samples obtained from different depths to determine the degree of TPH contamination. Thirty-five VOCs were identified in the water samples collected from gas stations. Methylene chloride, tribromomethane, toluene, chlorobenzene, dibromochloromethane, and benzene were frequently encountered in most of the water samples. Some of these samples exceeded the World Health Organization and Saudi Arabian guidelines for acceptable levels of pH, total dissolved solids, chloride, nitrate, sulfate, calcium, and total hardness. The measured TPH levels were clearly indicative of subsoil contamination and subsequent accumulation in soil over time, particularly at depths of 1–6 m; there was not a noticeable dependence or impact on pH.     

Bacterial Succession in a Petroleum Land Treatment Unit

Bacterial community dynamics were investigated in a land treatment unit (LTU) established at a site contaminated with highly weathered petroleum hydrocarbons in the C₁₀ to C₃₂ range. The treatment plot, 3,000 cubic yards of soil, was supplemented with nutrients and monitored weekly for total petroleum hydrocarbons (TPH), soil water content, nutrient levels, and aerobic heterotrophic bacterial counts. Weekly soil samples were analyzed with 16S rRNA gene terminal restriction fragment (TRF) analysis to monitor bacterial community structure and dynamics during bioremediation. TPH degradation was rapid during the first 3 weeks and slowed for the remainder of the 24-week project. A sharp increase in plate counts was reported during the first 3 weeks, indicating an increase in biomass associated with petroleum degradation. Principal components analysis of TRF patterns revealed a series of sample clusters describing bacterial succession during the study. The largest shifts in bacterial community structure began as the TPH degradation rate slowed and the bacterial cell counts decreased. For the purpose of analyzing bacterial dynamics, phylotypes were generated by associating TRFs from three enzyme digests with 16S rRNA gene clones. Two phylotypes associated with Flavobacterium and Pseudomonas were dominant in TRF patterns from samples during rapid TPH degradation. After the TPH degradation rate slowed, four other phylotypes gained dominance in the community while Flavobacterium and Pseudomonas phylotypes decreased in abundance. These data suggest that specific phylotypes of bacteria were associated with the different phases of petroleum degradation in the LTU.     

Authigenic mineralization and detrital clay binding by freshwater biofilms: The Brahmani river,India

This study sought to understand the origin and fate of one of the bitumen mounds found on the bottom of Lake Baikal. These mounds are located at a depth of 900 m beneath oil spots detected on the surface of Lake Baikal (53° 18′24^″, 108° 23′20^″). The two mounds were sampled with a manipulator from a “MIR” deep-water manned submersible. Mature mound No. 8 was subjected to chemical and microbiological studies. Mound No. 3 was subjected only to chemical studies; we failed to perform microbiological analyses of this mound for logistic reasons. Oil spots collected from the water surface, samples of mound No. 3 and No. 8, were subjected to GC/MS analysis. The water contained aliphatic hydrocarbons with chains between C₈ and C₂₃, with the most abundant chain length being C₁₈. Mound No. 3 with the most abundant chain length being C₁₈ actively released oil droplets into the water. It contained 770 mg/g of C₁₃-C₃₂ n-alkanes, with a maximum at C₂₃ (160 mg/g). Mound No. 8 was inactive and contained 148 mg/g of aliphatic C₂₂-C₃₄ n-alkanes, with a maximum at C₂₅. Mound No. 8 also consisted of 3% inorganic matter, 48% unresolved complex mixture (UCM) and less than 1% other compounds (polyaromatic hydrocarbons, isoprenoids, carotenoids, and hopanes). The core of this sample used as inoculate, yielded Rhodococci when cultivated on oil as the only source of carbon. Cultivation of the sample on agar-containing Raymond inorganic medium with crude West Siberian oil as the only source of carbon revealed colonies of these bacteria, which all appeared identical. PCR was performed with DNA isolated from 5 colonies, using primers for 16S rRNA genes. Comparison of the sequences of the 5 PCR products over a length of 714 bp revealed that they were almost identical. Phylogenetic analysis of these homologous sequences showed that they were similar to the corresponding sequences of the genus Rhodococcus. Substrate demands, the morphology of the colonies, and SEM and TEM data confirmed that the isolates obtained could indeed be Rhodococci. All of the isolates could grow in bulk cultures with inorganic medium supplemented with crude oil. Moreover, all of the isolates degraded aliphatic hydrocarbons with lengths between C₁₁ and C₂₉. C₂₃-C₂₉ hydrocarbons were degraded completely. The isolates could grow at 4–37°C. The most unexpected finding was that of the many microorganisms capable of consuming oil, only Rhodococci exhibited this ability in the inactive bitumen mound. The possible mechanisms of how crude oil is transformed into bitumen mounds and mature bitumen are discussed.     

Enhancing the Removal of Sorbed Crude Oil from Soil Through Multiple Oxidation Steps in Stepwise Fenton Processes

The stepwise Fenton oxidation process, in which hydrogen peroxide (H₂O₂) is added in a step-by-step manner instead of at the beginning, can achieve better sorbed crude oil removal effects. The results showed that if a high ratio of sorbed total petroleum hydrocarbon (TPH) was present in soil samples S1 (100%, initial TPH: 10,009 mg/kg) and S2 (94.2%, initial TPH: 4850 mg/kg), the TPH was oxidized in each step. In addition, the total TPH removal efficiency was 49.6% compared with the 27.9% achieved in conventional Fenton oxidation in which all H₂O₂ was added at the beginning. Nevertheless, when the ratio of sorbed TPH in the soil sample S3 was low (45.3%, initial TPH: 2850 mg/kg), the TPH removal efficiency was 18.9%, which was slightly higher than 18.2% achieved in the conventional Fenton process because if the sorbed TPH concentration was low, the sorbed TPH was mainly removed in the first step. The second and the third step resulted in long-chain alkanes entering the aqueous phase rather than removing them from the soil, which posed environmental risk. Therefore, it is clear that stepwise Fenton oxidation could improve sorbed TPH removal efficiency when the sorbed TPH concentration in the soil is high.     

Plant and fertiliser effects on rhizodegradation of crude oil in two soils with different nutrient status

Soils and sediments polluted with crude oil are of major environmental concern on various contaminated sites. Outdoors pot experiments were conducted to test the phytodegradation potential of common reed (Phragmites australis) and poplar (Populus nigra × maximowiczii) in fertilised and non-fertilised control treatments. Two topsoils (E, G) of different texture were mixed with crude oil. Soil analysis included hydrocarbon (HC) measurements, detection of labile phosphorus and mineralised nitrogen as well as dehydrogenase activity. Increased HC degradation by native soil biota was clearly related to higher P availability in soil G and to fertilisation in soil E. Except of the non-fertilised common reed treatment, plants did not enhance crude oil degradation. We found even inhibited degradation of high molecular weight HC in the presence of plants together with declining labile phosphorous concentrations due to planting on soil E. Native soil biota were able to use the whole range of crude oil compounds (C₁₀ to C₆₀) as a carbon source in the presence of sufficient nutrient concentrations in soil. This study is the first to show that reduced HC degradation in the higher molecular weight crude oil fraction (C₂₀ to C₄₀) is likely to be a consequence of decreased phosphorus availability for microorganisms in the plant rhizosphere.     

Hydrocarbon degradation by <Emphasis Type="Italic">Dietzia</Emphasis> sp. A14101 isolated from an oil reservoir model column

The hydrocarbon-degrading strain Dietzia sp. A14101 was isolated from an oil reservoir model column inoculated with oil-field bacteria. The column was continuously injected with nitrate (0.5 mM) from the start of water flooding, which lead to a gradual development of nitrate reduction in the column. Strain A14101 was able to utilize a range of aliphatic hydrocarbons as sole carbon and energy source during aerobic growth. Whole oil gas chromatography analysis of the crude oil phase from aerobic pure cultures showed that strain A14101 utilized the near complete range of aliphatic components and aromatic components toluene and xylene. Longer n-alkanes ≥C₁₇ were utilized simultaneously with the shorter C₁₀ and C₁₅. After 120 days aerobic incubation, the whole oil gas chromatography profile of the crude oil phase was similar to that of heavily biodegraded oils. Anaerobic degradation of hydrocarbons with nitrate was not observed. Nitrate reduction was, however, observed during anaerobic growth on propionate, which suggests that strain A14101 grows on fatty acids in the column rather than on hydrocarbons.     

High-temperature hydrocarbon degradation by Bacillus stearothermophilus from oil-polluted Kuwaiti desert

Kuwaiti desert samples contaminated with crude oil contained Bacillus stearothermophilus strains capable of growth on crude oil as a sole source of carbon and energy, obligately at high temperature. No thermophilic oil utilizers were present in water samples collected from the Arabian Gulf. Most of the desert strains had an optimum temperature of 60°C and grew best on pentadecane (C₁₅), hexadecane (C₁₆) and heptadecane (C₁₇). n-Alkanes with shorter and longer chains, n-alkenes, and aromatic hydrocarbons were less readily utilized. Correspondence to: N. A. Sorkhoh     

The Dynamic Change of Microbial Communities in Crude Oil-Contaminated Soils from Oil Fields in China

To study the biodegradability of microbial communities in crude oil contamination, crude oil-contaminated soil samples from different areas of China were collected. Using polyphasic approach, this study explored the dynamic change of the microbial communities during natural accumulation in oil field and how the constructed bioremediation systems reshape the composition of microbial communities. The abundance of oil-degrading microbes was highest when oil content was 3–8%. This oil content is potentially optimal for oil degrading bacteria proliferation. During a ～12 months natural accumulation, the quantity of oil-degrading microbes increased from 10⁵ to 10⁸ cells/g of soil. A typical sample of Liaohe (LH, oil-contaminated site near Liaohe River, Liaoning Province, China) was remediated for 50 days to investigate the dynamic change of microbial communities. The average FDA (a fluorescein diacetate approach) activities reached 0.25 abs/hr·g dry soil in the artificially enhanced repair system, 32% higher than the 0.19 abs/hr·g dry soil in natural circumstances. The abundance of oil-degrading microbes increased steadily from 0.001 to 0.068. During remediation treatment, oil content in the soil sample was reduced from 6.0% to 3.7%. GC–MS analysis indicated up to 67% utilization of C₁₀–C₂₀ normal paraffin hydrocarbons, the typical compounds that undergo microbial degradation.     

Assessment of crude oil degradation efficiency of newly isolated actinobacteria reveals untapped bioremediation potentials

Bioremediation is gaining favorable attention as a more economical and environmentally friendly technique for the remediation of crude oil hydrocarbons. This makes the search for crude oil–degrading microbes very crucial. In this study, the isolation and identification of actinobacteria in soil samples from a selected crude oil spill site were carried out. Eighteen isolates from different soil depths (20–120 cm) were screened for their ability to grow on crude oil–based medium (COBM). Actinomyces naeslundii, Actinomyces viscosus, Actinomyces israelii, Actinomyces meyeri, and Nocardia formicae from a 20 cm soil depth exhibited higher growth profiles on COBM than on glucose-based medium (GBM). A. viscosus and A. isrealii exhibited 5- and 3-fold increase in growth over GBM and were selected for biodegradation studies. Growth kinetics and residual crude oil were used to measure the degradation efficiency of A. viscosus and A. israeli over varying crude oil concentrations. Surprisingly, A. viscosus and A. isrealii achieved 98% degradation of 10 g/L crude oil in 12 days and 97% degradation of 30, 50, and 75 g/L in 16 and 18 days, respectively. Specific activity of total peroxidase was assayed over the biodegradation period. Peroxidase activity increased with degradation efficiency of A. viscosus and A. isrealii, suggesting that peroxidases play a key role in the crude oil biodegradation process. The unique tolerance exhibited by A. viscosus and A. israelii to crude oil and high crude oil degradation efficiencies indicate their promising potential for bioremediation applications.     

TECHNICAL NOTE: NITROGEN FERTILIZATION EFFECTS ON THE DEGRADATION OF AGED DIESEL OIL IN COMPOSTED DRILLING WASTES

Hydrocarbon-contaminated wastes generated from oil and gas drilling activities may be used as a soil amendment once composted and further decomposition of residual hydrocarbons can be accomplished after the composts are applied to soils. To test if N fertilization may enhance hydrocarbon decomposition, we investigated the effects of N application on hydrocarbon degradation in different-aged composts (1-, 2-, 3-, and 4-year-old composts, coded as 1Y, 2Y, 3Y, and 4Y composts, respectively) through a pot experiment planted with white spruce (Picea glauca [Moench] Voss) seedlings. The percentage degradation of total petroleum hydrocarbon (TPH, C11 to C40) in the composts without N fertilization was correlated to initial NH₄ ⁺ concentrations (R = 0.99, P < 0.001). The percentage degradation of TPH was highest in the 3Y compost (41.1%) that had an initial level of 325.3 mg NH₄ ⁺-N kg^?1 and the lowest in the 1Y compost (9.3%) that had an initial level of 8.3 mg NH₄ ⁺-N kg^?1. The degradation of TPH was enhanced by N fertilization in the 1Y (from 9.3 to 15.3%) and 4Y composts (from 14.3 to 22.6%) that had low initial NH₄ ⁺ concentrations. Our results show that application of NH₄ ⁺-based fertilizers may enhance the degradation of TPH when initial NH₄ ⁺ concentrations in the compost are low.     

Development of a method for the application of solid-phase microextraction to monitor biodegradation of volatile hydrocarbons during bacterial growth on crude oil

A quantitative solid-phase microextraction, gas chromatography, flame ionization detector (SPME-GC-FID) method for low-molecular-weight hydrocarbons from crude oil was developed and applied to live biodegradation samples. Repeated sampling was achieved through headspace extractions at 30°C for 45 min from flasks sealed with Teflon Mininert. Quantification without detailed knowledge of oil–water–air partition coefficients required the preparation of standard curves. An inverse relationship between retention time and mass accumulated on the SPME fibre was noted. Hydrocarbons from C₅ to C₁₆ were dated and those up to C₁₁ were quantified. Total volatiles were quantified using six calibration curves. Biodegradation of volatile hydrocarbons during growth on crude oil was faster and more complete with a mixed culture than pure isolates derived therefrom. The mixed culture degraded 55% of the compounds by weight in 4 days versus 30–35% by pure cultures of Pseudomonas aeruginosa, Rhodococcus globerulus or a co-culture of the two. The initial degradation rate was threefold higher for the mixed culture, reaching 45% degradation after 48 h. For the mixed culture, the degradation rate of individual alkanes was proportional to the initial concentration, decreasing from hexane to undecane. P. fluorescens was unable to degrade any of the low-molecular-weight hydrocarbons and methylcyclohexane was recalcitrant in all cases. Overall, the method was found to be reliable and cost-effective. Journal of Industrial Microbiology & Biotechnology (2000) 25, 155–162. Received 04 March 2000/ Accepted in revised form 25 June 2000     

Abatement of Sorbed Crude Oil by Heterogeneous Fenton Process Using A Contaminated Soil Pre-Impregnated with Dissolved Fe(II) and Humic Acid

Dissolved Fe(II) and humic acid (HA) were pre-impregnated into contaminated soil to catalyze hydrogen peroxide to remove crude oil (CO). The effects of parameters such as initial Fe(II), HA and H₂O₂ concentrations on the oxidation of total petroleum hydrocarbon (TPH) were investigated using response surface methodology based on Box–Behnken design. The rate of hydrogen peroxide decomposition is decreased by pre-impregnating with dissolved Fe(II) + HA compared with only pre-impregnated Fe(II) and modified Fenton (MF). Oxygen evolution is the predominant route of hydrogen peroxide decomposition at natural pH. Unlike O₂ evolution, the kinetics of hydroxyl radical (OH^?) production are clearly uncoupled from H₂O₂ decay in these systems. The steady-state hydroxyl radical production rate is higher in the systems with pre-impregnated dissolved Fe(II) and HA, and more significance is the decrease in detectable TPH (70.84% removal efficiency) when soil is pre-impregnated with dissolved 25 mM Fe(II) + 0.7 mg/mL HA, and with the application of 700 mM H₂O₂, possibly due to hydrogen peroxide catalyzed by the iron of this complex (CO-HA–Fe(II)) producing hydroxyl radical in close proximity to the CO. Meanwhile, the removal efficiency of C₂₁–C₃₀ is up to 65.69%, which is 2.6 times higher than that of the MF (25.52%).     

Bioremediation of Soils Contaminated with Nigerian Petroleum Products Using Composted Municipal Wastes

The efficiency of ready-to-use, source-separated, composted municipal organic wastes of Nigerian origin on degradation of soil total petroleum hydrocarbons (TPHs) in soils polluted with petroleum products (crude oil, diesel, and spent engine oil) was assessed in screen house experiments. The effect of compost:soil ratios and combined effect of compost-phytoremediation technique were also studied. TPH was determined spectrophotometrically, after extraction with 1:1 acetone-dichloromethane mixture at 425 nm. Soil pH, electrical conductivity, and phytotoxicity to seed germination and growth of maize (Zea mays L.) served as risk assessments on soil quality and evidence of recovery for the oil-impacted soil. Results showed that the treatments increased soil pH and electrical conductivity but reduced TPH. Reductions in TPH by compost technology ranged from 40% to 75.87%. Toxicity to seed germination reduced from 100% to 16.12%. Positive correlations were obtained for plant agronomical parameters and growth period, for all treatments, with coefficients in the range of .905 to .996, p < .05. This study revealed that ready-to-use composted waste has the potential for bioremediation of soils polluted with petroleum and petroleum products. This study is a contribution to the data bank of relatively simple bioremediation methods, suitable for workers in the developing countries, where there is no easy access to high-technology facilities. However, further development of this technique to achieve zero residual TPH is recommended.