Oil Degradation Rate Research Articles

Experimental study on the treatment of oil-based drill cutting by pulsed dielectric barrier discharge plasma at atmospheric pressure

Oil-based drilling cuttings produced in the process of oil exploration and shale gas development are harmful to the ecological environment. The emerging low-temperature plasma technology has shown potential for environmental protection. In this paper, pulsed dielectric barrier discharge (DBD) plasma was used to treat contaminated drilling cuttings at atmospheric pressure. The effect of adding active aluminium oxide (Al2O3) balls to the oil-based cuttings on the degradation rate of mineral oil was evaluated. Results showed that when the oil-based drilling cuttings were mixed with active Al2O3 balls, the highest degradation rate of mineral oil (68.1%) was achieved when the treatment time was 30 min. This rate was 41.8% higher than that obtained by DBD treatment alone. The Fourier transform infrared spectroscopy showed that the content of alkanes in the treated samples decreased significantly. The gas chromatography-mass spectrometry and ion chromatography analysis showed that formic acid, acetic acid, and other by-products were formed. The contents of C and H in the samples treated by DBD decreased. Overall, this study provides much-needed insights into the reaction mechanism and pollutant degradation process of the synergistic treatment system of pulsed DBD and active Al2O3 balls in the field of oil-based drilling cuttings treatment.

Improvement of Oil Degradation and MEL Production in a Yeast Strain, Pseudozyma tsukubaensis, by Translation Elongation Factor 1 Promoter-driven Expression of a Lipase.

The basidiomycetous yeast Pseudozyma tsukubaensis produces a mannosylerythritol lipid (MEL) homologue, a diastereomer type of MEL-B, from olive oil. In a previous study, MEL-B production was increased by the overexpression of lipase PaLIPAp in P. tsukubaensis 1E5, through the enhancement of oil consumption. In the present study, RNA sequence analysis was used to identify a promoter able to induce high-level PaLIPA expression. The recombinant strain, expressing PaLIPA via the translation elongation factor 1 alpha/Tu promoter, showed higher lipase activity, rates of oil degradation, and MEL-B production than the strain which generated in our previous study.

Improvement of the electrokinetic fluxes by tall fescue: Alleviation of ion attenuation and maintainability of soil colloidal properties

In this study, we aimed to address the attenuation of electrokinetic fluxes that occur during plant (tall fescue)-based electrokinetic remediation of oil-contaminated soil. Following 60 days of treatment, the concentration of water-soluble cations and anions in the electrokinetics-assisted phytoremediation treatment (EK-P) were 20.03 mg/kg and 15.7 mg/kg higher than that in the electrokinetic (EK) treatment, respectively. At the electrode, plants were able to alleviate the ion aggregation effect caused by the electrokinetics, reduce the conversion of soluble ions to insoluble ones, and reduce the decay of water-soluble ions. In addition, the zeta potential of EK-P was 5.05 mV lower than that of EK. Plants maintained the stability of the soil colloid and reduced the movement of the peak of colloidal particle size from small to large particles, thereby reducing the amount of colloidal deposition. Finally, the EK-P current was 22.49% higher than that in EK while the electrokinetic effect was maintained. Meanwhile, electrokinetics increased plant biomass by 20.21%. Electrokinetics was found to create a synergy with the plants, an effect that eventually enhanced the rate of oil degradation.

Presence of Hydrocarbon Degrading Bacteria in Contaminated Soil Collected From Various Fuel Station in Bhilai, Chhattisgarh

Abstract: In this study, we isolated seven strains (termed BY1–7) from polluted soil at an oil station and evaluated their abilities to degrade total petroleum hydrocarbons (TPHs). Among 45 bacterial colonies one bacterial strain was identified based on the cultural, morphological and biochemical characteristics. The isolated bacterium was then subjected to a preliminary assessment of their crude oil after 48 hours of incubation on nutrient agar plates overlaid with 100 ML of petroleum crude oil, the zone of clearance was observed. The isolated bacteria showed 35% petrol degradation, whereas a relatively high oil degradation rate, almost 40% was observed when the bacterium was acclimatized. The selected bacterial strains crude oil resistance was analysed based on the growth ability on the crude oil containing mediums. This strain was identified as Brevibacterium brevis. After inoculation, growth ability was measured and the highest percentage of petrol degradation occurred at temperature 37 °C with the value 30.8%. Bacteria displaying such capabilities are often exploited for the bio-remediation of petroleum oil contaminated environments. Recently, microbial remediation technology has developed rapidly and achieved major gains. However, this technology is not omnipotent. It is affected by many environmental factors that hinder its practical application, limiting the large-scale application of the technology. Keywords: Petroleum hydrocarbon-degrading Bacteria, Petroleum oil, Bio-remediation, Bacterial consortia, Environmental factors, Enzymes.

Effects of Adding Laccase to Bacterial Consortia Degrading Heavy Oil

High-efficiency bioremediation technology for heavy oil pollution has been a popular research topic in recent years. Laccase is very promising for the remediation of heavy oil pollution because it can not only convert bio-refractory hydrocarbons into less toxic or completely harmless compounds, but also accelerate the biodegradation efficiency of heavy oil. However, there are few reports on the use of laccase to enhance the biodegradation of heavy oil. In this study, we investigated the effect of laccase on the bacterial consortia degradation of heavy oil. The degradation efficiencies of bacterial consortia and the laccase-bacterial consortia were 60.6 ± 0.1% and 68.2 ± 0.6%, respectively, and the corresponding heavy oil degradation rate constants were 0.112 day−1 and 0.198 day−1, respectively. The addition of laccase increased the heavy oil biodegradation efficiency (p < 0.05) and biodegradation rate of the bacterial consortia. Moreover, gas chromatography–mass spectrometry analysis showed that the biodegradation efficiencies of the laccase-bacterial consortia for saturated hydrocarbons and aromatic hydrocarbons were 82.5 ± 0.7% and 76.2 ± 0.9%, respectively, which were 16.0 ± 0.3% and 13.0 ± 1.8% higher than those of the bacterial consortia, respectively. In addition, the degradation rate constants of the laccase-bacterial consortia for saturated hydrocarbons and aromatic hydrocarbons were 0.267 day−1 and 0.226 day−1, respectively, which were 1.07 and 1.15 times higher than those of the bacterial consortia, respectively. The degradation of C15 to C35 n-alkanes and 2 to 5-ring polycyclic aromatic hydrocarbons by laccase-bacterial consortia was higher than individual bacterial consortia. It is further seen that the addition of laccase significantly improved the biodegradation of long-chain n-alkanes of C22–C35 (p < 0.05). Overall, this study shows that the combination of laccase and bacterial consortia is an effective remediation technology for heavy oil pollution. Adding laccase can significantly improve the heavy oil biodegradation efficiency and biodegradation rate of the bacterial consortia.

Testing an aerobic fluidized biofilm process to treat intermittent flows of oil polluted wastewater

An aerobic fluidized biofilm process of treating oil-polluted wastewater has been studied. A series of batch experiments were conducted using synthetic wastewater and the kinetic coefficients were evaluated. The maximum rate of substrate utilization per unit mass microorganisms (K) was 1.6 days-1, the substrate concentration at one-half the maximum growth rate (Ks) was 26 mg/L, the maximum specific growth rate (m) was 1.0 days-1, the ratio of the mass cells formed to the mass of substrate consumed (Y) was 0.61, and the endogenous decay coefficient (Kd ) was 0.044 days-1. The kinetic coefficients obtained were within the range of municipal wastewater. It was observed that up to 1500 mg/L oil (Motor oil SAE–40) could be degraded in a fluidized bed bioreactor (FBBR). The experiments, however, were limited to the oil concentration within a range of 1000-2600 mg/L. Average biofilm thickness () under specific conditions was found to be 22 m and average oil degradation rate of 0.053 mg oil/mg biomass/hour was measured in the FBBR. The results also support that the increase in the concentration of oil in the treatment process reduced significantly the degradation rate of non-oil carbon.

Microwave stabilization and process optimization of rice bran cultivar Jhelum

This study was optimizing microwave stabilization process of rice bran obtained from freshly milled paddy (Jhelum variety) using response surface methodology. This study was conducted at different moisture contents (12%–30%), sample weight (5–250 g), and heating time (1–5 min) which were examined to determine their influence on dependent variables––free fatty acids (FFAs) and color coordinates. Regression analysis showed effective influence of microwave heating on all response variables studied. Stabilization treatments resulted in reduction of FFAs, prime indicator of lipase activity, indicating that hydrolytic rancidity could be prevented thereby making it fit for human consumption and food applications. The optimum conditions obtained for microwave stabilization were found to be 16% sample moisture, 100 g sample weight, and 4 min microwave heating time. Proximate analysis showed that crude fat and crude fiber contents reduced while crude protein and ash contents increased after microwave heat treatment in rice bran. Practical applications Rice bran has the ability to be used as a food ingredient and oil source to satisfy the growing oil demands. However, the individual cells are disturbed and the inherent lipase enzyme comes into contact with fat during milling process while extracting bran layer from endosperm. This causes hydrolysis of fats to free fatty acids (FFAs) and glycerol leading to the development of hydrolytic rancidity which is responsible for off-flavor development during storage. The rate of oil degradation and FFA formation can be very high (about 5%–7% per day and 70% in a month) under favorable conditions. Bran oil with an excess of 10% FFA is unfit for human consumption. Now-a-days efforts are being made to stabilize the rice bran using stabilization techniques in order to improve its utilization in food. The microwave stabilization technique seems to be a wiser approach to widen the utilization of rice bran in food industry.

Effect of biostimulation and bioaugmentation on hydrocarbon degradation and detoxification of diesel-contaminated soil: a microcosm study.

Soil contamination with diesel oil is quite common during processes of transport and storage. Bioremediation is considered a safe, economical, and environmentally friendly approach for contaminated soil treatment. In this context, studies using hydrocarbon bioremediation have focused on total petroleum hydrocarbon (TPH) analysis to assess process effectiveness, while ecotoxicity has been neglected. Thus, this study aimed to select a microbial consortium capable of detoxifying diesel oil and apply this consortium to the bioremediation of soil contaminated with this environmental pollutant through different bioremediation approaches. Gas chromatography (GC-FID) was used to analyze diesel oil degradation, while ecotoxicological bioassays with the bioindicators Artemia sp., Aliivibrio fischeri (Microtox), and Cucumis sativus were used to assess detoxification. After 90 days of bioremediation, we found that the biostimulation and biostimulation/bioaugmentation approaches showed higher rates of diesel oil degradation in relation to natural attenuation (41.9 and 26.7%, respectively). Phytotoxicity increased in the biostimulation and biostimulation/bioaugmentation treatments during the degradation process, whereas in the Microtox test, the toxicity was the same in these treatments as that in the natural attenuation treatment. In both the phytotoxicity and Microtox tests, bioaugmentation treatment showed lower toxicity. However, compared with natural attenuation, this approach did not show satisfactory hydrocarbon degradation. Based on the microcosm experiments results, we conclude that a broader analysis of the success of bioremediation requires the performance of toxicity bioassays.

Investigation of microbial community changes in petroleum polluted sediments during hydrocarbons degradation

ABSTRACT Bioremediation is among the most basic and reliable way to eliminate pollutants by transforming the toxic petroleum components into less toxic metabolites. In order to compare the change of bacterial community during oil-biodegradation process, two oil-polluted sediments sampled from Tunisia were analyzed using 16S rDNA clone libraries. During the experimental period, measurements of microbial abundance along with qualitative and quantitative analysis of pollutants were carried out. Fingerprinting analysis of natural samples showed the presence of different classes of bacteria with the dominance of Gammaproteobacteria (>60%). The bacterial diversity decreased in enrichment cultures with crude oil with the appearance and predominance of Alcanivorax spp. Our data also showed that several Obligate Marine Hydrocarbonoclastic Bacteria (OMHB: Alcanivorax, Cycloclasticus and Marinobacter) were stimulated by the addition of petroleum. The shift of diversity and the dominance of OMHB were associated with high degradation rate of crude oil (the total degradation of petroleum TERHCs was estimated at 90% and 70% in TST1E and TST2E) and a decrease in sediment toxicity to Corophium orientale. Since several factors can influence the clean-up in-field, the effectiveness of biostimulation treatment and its optimization at lab scale under controlled conditions would facilitate and allow the application in-situ. Moreover, the study of the community diversity allows the detection and the identification of the dominant hydrocarbonoclastic species such as Alcanivorax which it would be beneficial in future experiments to facilitate the selection of the autochthonous strains (adapted to support the contamination) for the reconstruction of efficient consortia useful in the cleanup of hydrocarbon contaminated sites.

Enhanced biodegradation of light crude oil by immobilized Bacillus licheniformis in fabricated alginate beads through electrospray technique.

Petroleum contamination of marine environments due to exploitation and accidental spills causes serious harm to ecosystems. Bioremediation with immobilized microorganisms is an environmentally friendly and cost-effective emerging technology for treating oil-polluted environments. In this study, Bacillus licheniformis was entrapped in Ca alginate beads using the electrospray technique for light crude oil biodegradation. Three important process variables, including inoculum size (5-15% v/v), initial oil concentration (1500-3500ppm), and NaCl concentration (0-30g/L), were optimized to obtain the best response of crude oil removal using response surface methodology (RSM) and Box-Behnken design (BBD). The highest crude oil removal of 79.58% was obtained for 1500ppm of crude oil after 14days using immobilized cells, and it was lower for freely suspended cells (64.77%). Our result showed similar trends in the effect of variables on the oil biodegradation rate in both free cell (FC) and immobilized cell (IC) systems. However, according to the analysis of variance (ANOVA) results, the extent of the variables' effectiveness was different in FC and IC systems. In the immobilized cell system, all variables had a greater effect on the rate of light crude oil degradation. Moreover, to evaluate the effectiveness of free and immobilized B. licheniformis in bioremediation of an actual polluted site, the crude oil spill in natural seawater was investigated. The results suggested the stability of beads in the seawater, as well as high degradation of petroleum hydrocarbons by free and immobilized cells in the presence of indigenous microorganisms.

Optimization of Crude Oil Biodegradation by Brevibacterium sp. Isolated from the Native Sponges of the Persian Gulf.

Background: The native sponges of Persian Gulf are unique species facing difficult climate conditions and environmental contamination. It is necessary to investigate these native sponges because global warming most probably destroyed many of these creatures. Therefore, the study of the microorganisms associated with sponges will introduce new bacterial strains with various industrial and environmental applications and, in this way, a part of the Persian Gulf biodiversity will be preserved for posterity.Objective: The aim of this study was the isolation and molecular identification of bacteria associated with the ability of biodegrading crude oil from the native sponges of the Persian Gulf. Also, optimization of crude oil biodegradation was done for one of the most efficient bacterial strains.Materials and Methods: Isolated species were compared in terms of E24 index and growth rate in a culture medium containing at least 2% of oil as the sole carbon source. Molecular identification was done for five bacterial strains. Using the Taguchi experimental design, the effects of 4 factors, namely, carbon source auxiliary, organic and inorganic nitrogen sources, salinity and pH, were evaluated at 3 levels. GC-Mass analysis was performed on the remaining oil in the culture medium.Results: In the initial screening of two native species of sponges, 22 bacterial strains were isolated which were capable of decomposing oil. Five bacterial strains showed the best results and were recorded in NCBI with access numbers KY283126, KY283128, KY285290, KY285289, and KY285288. Brevibacterium sp. (KY283128) showed the highest level of oil degradation (about 97%) and growth rate. The results showed that the optimal oil degradation occurs in the absence of carbon source auxiliary, at 0.5% of salinity, with NH4Cl as the nitrogen source and at a pH of 6.5.Conclusions: This bacterial strain can be used for biodegradation in oil-contaminated areas and oil refineries. By isolating the oil degrading gene in this bacterial strain and cloning it in other bacterial strains, the efficiency of eliminating oil contamination can be increased.

Reduction of lag in crude oil degradation by Aspergillus when it is in synergy with Bacillus in biofilm mode

A major hindrance to the effective use of fungi in bioremediation is their inherent slow growth. Despite this, Aspergillus spp. may be used effectively. Our experiments demonstrate that bacteria, although inefficient in hydrocarbon degradation, may be effectively used in a consortium to overcome the lag in fungal utilization of petroleum hydrocarbons. Crude petroleum oil (160mg; at 8g/L) in minimal medium was inoculated with a previously isolated biofilm-forming consortium (Aspergillus sp. MM1 and Bacillus sp. MM1) as well as monocultures of each organism and incubated at 30 ℃ under static conditions. Residual oil was analyzed by GC-MS. Crude oil utilization of Aspergillus-Bacillus biofilm was 24 ± 1.4% in 3days, increased to 66 ± 7% by day 5 and reached 99 ± 0.2% in 7days. Aspergillus sp. MM1 monoculture degraded only 14 ± 6% in 5days. However, at the end of 7days, it was able to utilize 98 ± 2%. Bacillus sp. MM1 monoculture utilized 20 ± 4% in 7days. This study indicates that there is a reduction of the fungal lag in bioremediation when it is in association with the bacterium. Although in monoculture, Bacillus sp. MM1 is inefficient in crude oil degradation, it synergistically enhances the initial rate of crude petroleum oil degradation of the fungus in the consortium. The rapid initial removal of as much crude oil as possible from contaminated sites is vital to minimize detrimental impacts on biodiversity.

Long-term dynamics of plant communities after biological remediation of oil-contaminated soils in far north

We studied the long-term dynamics of plant communities after bio and phytoremediation of oil-polluted soils. Nine plots located in European Northeast and treated using various bioremediation methods were monitored from 2002 to 2014. Geobotanical descriptions (relevés) of each plot were performed in 2006 and 2014, and Grime’s theoretical CSR (competition–stress–ruderality) framework was used to assess the vegetation state and dynamics. We observed a clear shift of communities from pioneer (where ruderal species were prevalent) to stable (where competitor species were dominant) states. However, the remediation type did not significantly impact the vegetation recovery rate. After 12 years, all methods led to a 55–90% decrease in the oil content of the soil and a recovery of the vegetation cover. The plant communities contained mainly cereals and sedges which significantly differed from the original tundra communities before the oil spill. The control plot, treated only by mechanical cleaning, had minimum oil degradation rate (50%) and vegetation recovery rates, although, in CSR terms, its vegetation assemblage resembled the background community. Cereals (Agrostis gigantea, Deschampsia cespitosa, Phalaris arundinacea, and Poa pratensis), sedges (Carex canescens, Carex limosa, and Eriophorum vaginatum), and shrubs (Salix) were found to be the most effective species for phytoremediation, exhibiting high community productivity under the harsh northern conditions.

Aeromonas immobilized on chitosan for treating high-oil wastewater from kitchens

To effectively solve the serious impact of high oil in the kitchen wastewater on the downstream treatment process, an excellent oil-degrading strain Aeromonas allosaccarophila CY-01 was immobilized to prepare Chitosan-Aeromonas pellets (CH-CY01) by using chitosan as a carrier. Oil degradation condition and efficiency of CH-CY01 pellets were assessed. The growth of immobilized CH-CY01 was almost unaffected, and the maximum degradation rate of soybean oil was 89.7%. Especially at 0.5% NaCl concentration, oil degradation efficiency of CH-CY01 was increased by 20% compared with free cells. In the presence of a surfactant (sodium dodecylbenzene sulfonate) at 1 mg/L, the degradation efficiency of oil by CH-CY01 was increased by 40%. Moreover, using the high-oil catering wastewater as the substrate, more than 80% of the solid oil was degraded with 1% (V/V) CH-CY01 pellets treatment for 7 days, significantly higher than that of free cells. In summary, immobilized CH-CY01 significantly improved the efficiency of oil degradation.

Functional metagenomic and enrichment metatranscriptomic analysis of marine microbial activities within a marine oil spill area.

Microorganisms can degrade petroleum hydrocarbons, providing the advantages of low cost and few side effects towards ecosystems. Here, we evaluated the mechanisms of microbial degradation of marine petroleum hydrocarbon using metagenomics and metatranscriptomics approaches in order to provide new insight into microbial degradation of petroleum hydrocarbon. Seawater samples were collected at a depth of ∼8m from an area near a drilling platform in the Bohai Bay and metagenomic sequencing was used to evaluate the functional potential of these marine microbial communities. Metatranscriptomic sequencing, fluorescence in-situ hybridization experiments, and flow cytometry were also performed on the microbial communities of samples subjected to 12 different culture conditions. The data were also subjected to Weighted Gene Co-expression Network Analysis (WGCNA) and co-transcription data visualization to evaluate co-transcription of gene functions. Metagenomic sequencing indicated the presence of numerous genes that were related to petroleum hydrocarbon metabolism. Further, the high co-transcription of genes in multiple pathways, indicated that groups of genes were synergistically transcribed to metabolize petroleum hydrocarbons. Metatranscriptomics also showed that microbial metabolism was highly active in the enrichments and that the transcription of a large number of prokaryotic replication and repair genes were significantly up-regulated including those encoding for the type VI secretion system (T6SS) protein, DNA polymerase I, thymidine phosphorylase, mevalonate kinase, and two-component systems. Concomitantly, the transcription of ribosomal genes involved in translation and photosynthetic genes involved in energy metabolism were down-regulated. Overall, oil and oxygen presence can increase the oil-degradation rates and related genes' transcription. Lot different metabolisms are co-regulated to exploit nutrients derived from the metabolism of petroleum hydrocarbons. Our analysis of metagenomic, metatranscriptomic and degradation data in this study show that a widespread gene spectrum involved in oil-degradation and the cooperation among genes is of great importance.

Combined microbial degradation of crude oil under alkaline conditions by Acinetobacter baumannii and Talaromyces sp

The purpose of this work was to study the biodegradation of crude oil under alkaline condition by defined co-culture of Acinetobacter baumannii and Talaromyces sp. The n-alkanes in crude oil could be completely degraded by bacteria and fungi with the ratio of 1:1 at pH 9 in 14 d water simulation experiment. Meanwhile, the total degradation rate of crude oil could reach 80%. Fungi had stronger ability to degrade n-alkanes, while bacteria could better degrade other components such as aromatics and branched alkanes. The two strains were both capable of producing a small amount of biosurfactant. High cell viability was the main factor for strains to exert high degradation ability in alkaline environment. It was preliminarily verified that bacteria and fungi rely on the differences of enzyme systems to achieve synergy in the degradation process. These results indicated that the defined co-culture had great potential for bioremediation in alkaline soils.

Isolation and characterization of a high-efficiency marine diesel oil-degrading bacterium

In the recent 50 years, marine oil spills had resulted in severe environmental pollution problems worldwide. In this study, 12 petroleum-degrading strains named MJ1 to MJ12, which can use diesel oil as the sole carbon source for growth, were isolated from the seawater in Jiaozhou Bay, China. Strain MJ4 has the highest diesel-degrading rate which is up to 26.54% in 5 days with the diesel oil concentration of 10 g/L. According to the BLAST research, 16SrRNA sequence of MJ4 showed 99% similarity to Bacillus megaterium strain. Single-factor experiments and response surface methodology were carried out to optimize the environmental factors and their reciprocal action for affecting the diesel oil degradation process of Bacillus sp. MJ4. Results of single-factor experiments revealed that the highest degradation rate was obtained with temperature of 28 °C, pH of 8.8, diesel oil concentration of 25 g/L, P/N ratio of 0.56, nitrogen and phosphorus dosage quantity of 0.35 g/L and 0.18 g/L, respectively. A nonlinear regression equation of diesel oil degradation rate and pH, temperature, P/N ratio was obtained. The model predicted the maximum degradation rate of 72.21% with temperature of 28 °C, pH of 8.88, P/N ratio of 0.31, respectively.

Mid storage seed hardening: a mechanical method to maintain seed viability during long term jute seed preservation

Seed plays an important role in agricultural sector for both production and consumption purpose. Availability of vigour seed is one of the major constraints for maximizing crop production. However, healthy seed can also lose its viability during seed storage by changing different physio-chemical properties. Influence of environmental factors and seed containers during storage leading to seed deterioration. In this research, mid storage seed hardening treatment was applied in different aged seeds of jute species (C. Capsularis & C. olitorius) with two types of storage bags. Seed hardening treatment showed the less moisture content with better germination percentage compared to the untreated species of jute seeds. Seed packing in polythene bags during both short and long term seed storages had higher viable seeds compared to the cloth packing seeds. The effect of seed hardening treatment on seed oil content and pattern of oil degradation is distinct in early period of storage. The faster rate of oil degradation, soluble protein and free amino acids was found in seeds of un-treated stored seeds in cloth bag. Contrary, very slow rate of oil degradation was observed in harden seed and stored in polythene bag which indicated better storability of harden seeds.

Solid inoculants as a practice for bioaugmentation to enhance bioremediation of hydrocarbon contaminated areas

Vacuum freeze-drying is a scientifically advanced method to prepare solid inoculants from oil degrading bacterium. The introduction of oil-degrading microbes or bioaugmentation can be an efficient way to bioremediate oil spills in marine areas, where oil-degrading bacteria are deficient. The purpose of this study is to evaluate the potential use of solid inoculants of LZ-2 bacteria to enhance the degradation rate of crude oil. In this study, response surface methodology (RSM) was incorporated into the experimental design to optimize a response, which is influenced by different protectants. Our results showed that five factors have interactive and synergistic protective effects on the growth of LZ-2. Optimal growth of freeze-dried LZ-2 (63.8%) was observed with a 10.5% solution of skim milk supplemented with 14.3% sucrose, 14.4% of trehalose, 4.9% of glycerin and 14.7% of β-cyclodextrin. The culture grew in medium containing crude oil (3 g L−1) at 37 °C at 150 rpm for 30 d, GC and GC-MS analysis showed biodegradation of 44.2 and 21.6% for total saturate and aromatic hydrocarbons respectively. These results indicated that the solid inoculants of LZ-2 bacteria had the potential to be used for ex-situ bioremediation of hydrocarbon pollutants associated with crude oil.

Bioremediation of Crude Oil by Rhizosphere Fungal Isolates in the Presence of Silver Nanoparticles.

Background: This research work focuses on the utilization of indigenous fungi for in situ bioremediation of crude oil in the presence of silver nanoparticles. Methods: Two fungi belonging to two different genera showed promising crude oil-degrading abilities. Fungal isolates were identified based on internal transcribed spacer rDNA sequence analysis. Gas chromatography-mass spectrometry analysis of the crude oil remaining in the culture medium after seven days was performed. The response surface method (RSM) designed by Box-Behnken was used to establish a mathematical model. Inter-simple sequence repeat (ISSR) primers were used to examine the genetic variation of fungal isolates. Results: Gas chromatography-mass spectrometry (GC-MS) analysis after seven days showed that the optimum biodegradation of crude oil was 57.8%. The crude oil degradation rate was significantly affected by a temperature of 30 °C, pH value of 7, crude oil concentration of 4 g/L, a 1:1 ratio between A. flavus AF15 and T. harzianum TH07, and an silver nanoparticle (AgNP) concentration of 0.05 g. Molecular characterization in fungal isolates is extremely valuable when using ISSR markers. Conclusions: Two fungal isolates showed promising crude oil-degrading abilities with positive effect of low concentrations of AgNPs on biodegradation. RSM is an efficient mathematical method to optimize the microbial biodegradation of crude oil.