Rate Of Oil Biodegradation Research Articles

Immiscible Rayleigh–Taylor turbulence: Implications for bacterial degradation in oil spills

An unstable density stratification between two fluids mixes spontaneously under the effect of gravity, a phenomenon known as Rayleigh-Taylor (RT) turbulence. If the two fluids are immiscible, for example, oil and water, surface tension prevents intermixing at the molecular level. However, turbulence fragments one fluid into the other, generating an emulsion in which the typical droplet size decreases over time as a result of the competition between the rising kinetic energy and the surface energy density. Even though the first phenomenological theory describing this emulsification process was derived many years ago, it has remained elusive to experimental verification, hampering our ability to predict the fate of oil in applications such as deep-water spills. Here, we provide the first experimental and numerical verification of the immiscible RT turbulence theory, unveiling a unique turbulent state that originates at the oil-water interface due to the interaction of multiple capillary waves. We show that a single, non-dimensional, and time-independent parameter controls the range of validity of the theory. Our findings have wide-ranging implications for the understanding of the mixing of immiscible fluids. This includes in particular oil spills, where our work enables the prediction of the oil-water interface dynamics that ultimately determine the rate of oil biodegradation by marine bacteria.

Integrated approach for efficient crude oil bioremediation: Bacterial consortium development, mathematical modelling and scalable bioprocess design

Crude oil pollution has a significant impact on the surrounding ecosystem, making its remediation an urgent necessity due to the waste discharge and seepage from petroleum industries. To address this issue, we developed an efficient bacterial consortium from strains isolated from petroleum refinery waste. These strains were identified as genera Pseudomonas, Ochrobactrum, Alcaligenes, and Bacillus, specifically chosen for their ability to biodegrade crude oil. Through the optimization of process parameters, we enhanced the biodegradation efficiency of the bacterial consortium. Furthermore, the scalability of the biodegradation process was established in 6L batch bioreactor, which featured a total TPH removal of 80.10 %. The independently obtained substrate inhibition data and bioreactor batch kinetics data were utilized to develop a batch mathematical-model. The mathematical model accurately simulated batch bioreactor kinetics and was further extrapolated to design a fed-batch nutrient feeding strategy. Implementing this strategy, based on the model, led to a higher TPH removal rate of 86.86 % in a constant feed batch-fed-batch approach, as validated through experimental implementation. Validation of the biodegradation process was confirmed through Gas Chromatography-Mass Spectrometry (GC–MS) analysis of degraded samples, which confirmed the biodegradation of petroleum hydrocarbons. The increased rates of oil biodegradation achieved through our developed consortium and advanced bioprocess offer a promising solution for the effective clean-up of oily pollutants present in petroleum wastewater and oil spillage scenarios.

Investigating the crude oil biodegradation performance in bioreactor by using a consortium of symbiotic bacteria

Crude oil pollution is one of the most serious environmental issues today, and the clean-up procedure is perhaps the most difficult. Within one to three weeks, the vast majority of oil bacteria may degrade approximately 60% of the crude oil, leaving approximately 40% intact. The by-product metabolites produced during the breakdown of oil are essentially organic molecules in nature. These metabolites inhibit its enzymes, preventing the oil bacteria from further degrading the oil. By combining a variety of different oils with heterotrophic bacteria in a bioreactor, the rate of crude oil biodegradation was accelerated. In this study, two strains of oil-resistant, heterotrophic bacteria (OG1 and OG2-Erythrobacter citreus) and a bacterium that uses hydrocarbons (AR3-Pseudomonas pseudoalcaligenes) were used. Gas chromatography-mass spectroscopy was used to investigate the effectiveness of this consortium of symbiotic bacteria in the biodegradation of crude oil. According to gravimetric and gas chromatography analyses, the consortium bacteria digested 69.6% of the crude oil in the bioreactor, while the AR3 single strain was only able to destroy 61.9% of it. Under the same experimental conditions, consortium bacteria degraded approximately 84550.851 ppb (96.3%) of 16 aliphatic hydrocarbons and 9333.178 ppb (70.5%) of 16 aromatic hydrocarbons in the bioreactor. It may be inferred that the novel consortium of symbiotic bacteria accelerated the biodegradation process and had great potential for use in increasing the bioremediation of hydrocarbon-contaminated locations.

Burial and Denudation Alter Microbial Life at the Bottom of the Hypo‐Critical Zone

AbstractHow subsurface microbial life changed at the bottom of the kilometers‐deep (hypo) Critical Zone in response to evolving surface conditions over geologic time is an open question. This study investigates the burial and exhumation, biodegradation, and fluid circulation history of hydrocarbon reservoirs across the Colorado Plateau as a window into the hypo‐Critical Zone. Hydrocarbon reservoirs, in the Paradox and Uinta basins, were deeply buried starting ca. 100 to 60 Ma, reaching temperatures >80–140°C, likely sterilizing microbial communities present since the deposition of sediments. High salinities associated with evaporites may have further limited microbial activity. Upward migration of hydrocarbons from shale source rocks into shallower reservoirs during maximum burial set the stage for microbial re‐introduction by creating organic‐rich “hot spots.” Denudation related to the incision of the Colorado River over the past few million years brought reservoirs closer to the surface under cooler temperatures, enhanced deep meteoric water circulation and flushing of saline fluids, and likely re‐inoculated more permeable sediments up to several km depth. Modern‐ to paleo‐hydrocarbon reservoirs show molecular and isotopic evidence of anaerobic oxidation of hydrocarbons coupled to bacterial sulfate reduction in areas with relatively high SO4‐fluxes. Anaerobic oil biodegradation rates are high enough to explain the removal of at least some portion of postulated “supergiant oil fields” across the Colorado Plateau by microbial activity over the past several million years. Results from this study help constrain the lower limits of the hypo‐Critical Zone and how it evolved over geologic time, in response to changing geologic, hydrologic, and biologic forcings.

Long-term patterns of hydrocarbon biodegradation and bacterial community composition in epipelagic and mesopelagic zones of an Arctic fjord

Oil spill attenuation in Arctic marine environments depends on oil-degrading bacteria. However, the seasonally harsh conditions in the Arctic such as nutrient limitations and sub-zero temperatures limit the activity even for bacteria capable of hydrocarbon metabolism at low temperatures. Here, we investigated whether the variance between epipelagic (seasonal temperature and inorganic nutrient variations) and mesopelagic zone (stable environmental conditions) could limit the growth of oil-degrading bacteria and lead to lower oil biodegradation rates in the epipelagic than in the mesopelagic zone. Therefore, we deployed absorbents coated with three oil types in a SW-Greenland fjord system at 10–20 m (epipelagic) and 615–650 m (mesopelagic) water depth for one year. During this period we monitored the development and succession of the bacterial biofilms colonizing the oil films by 16S rRNA gene amplicon quantification and sequencing, and the progression of oil biodegradation by gas chromatography – mass spectrometry oil fingerprinting analysis. The removal of hydrocarbons was significantly different, with several polycyclic aromatic hydrocarbons showing longer half-life times in the epipelagic than in the mesopelagic zone. Bacterial community composition and density (16S rRNA genes/ cm2) significantly differed between the two zones, with total bacteria reaching to log-fold higher densities (16S rRNA genes/cm2) in the mesopelagic than epipelagic oil-coated absorbents. Consequently, the environmental conditions in the epipelagic zone limited oil biodegradation performance by limiting bacterial growth.

Oil biodegradation in permeable marine sediments: Effects of benthic pore-water advection and solute exchange

Oil spills have been recognized as among the worst kinds of environmental disasters, causing severe coastal ecological and economic damages. Although benthic flow and solute fluxes are known to have strong impacts on fate and transport of oil deposited within marine sediments, their endogenous mechanisms still remain to be uncovered. In this paper, simulations of flow and solute transport processes along with hydrocarbon biodegradation were conducted in a cylindrical benthic chamber system to investigate influences of benthic hydrodynamics on oil biodegradation in permeable marine sediments. Results show that ripple-flow interactions create subsurface recirculation cells whereby seawater infiltrates into the benthic sediments at ripple troughs while groundwater discharges near the crests. It results in a spatially varied oil biodegradation rate in marine sediments. Significant oil biodegradation occurs near sediment ripple troughs due to direct oxygen recharge, while biodegradation of oil deposited uphill becomes slow due to limited oxygen replenishment. Oil biodegradation decreases subsurface oxygen content, and consequently impedes discharge of oxygen from benthic sediments. Our results reveal a dynamic interaction between oil biodegradation and benthic flow and solute transport processes, which has strong implications for predicting oil persistence and biodegradation within marine sediments and its associated impacts on benthic biogeochemical processes.

Oil Absorbent Polypropylene Particles Stimulate Biodegradation of Crude Oil by Microbial Consortia.

Oil absorbent particles made from surface-modified polypropylene can be used to facilitate the removal of oil from the environment. In this study, we investigated to what extent absorbed oil was biodegraded and how this compared to the biodegradation of oil in water. To do so, we incubated two bacterial communities originating from the Niger Delta, an area subject to frequent oil spills, in the presence and absence of polypropylene particles. One community evolved from untreated soil whereas the second evolved from soil pre-exposed to oil. We observed that the polypropylene particles stimulated the growth of biofilms and enriched species from genera Mycobacterium, Sphingomonas and Parvibaculum. Cultures with polypropylene particles degraded more crude oil than those where the oil was present in suspension regardless of whether they were pre-exposed or not. Moreover, the community pre-exposed to crude oil had a different community structure and degraded more oil than the one from untreated soil. We conclude that the biodegradation rate of crude oil was enhanced by the pre-exposure of the bacterial communities to crude oil and by the use of oil-absorbing polypropylene materials. The data show that bacterial communities in the biofilms growing on the particles have an enhanced degradation capacity for oil.

Microplastic and oil pollution in oceans: Interactions and environmental impacts

Microplastics (MPs) have been found in oil-polluted oceans, but studies on MPs and oil were still focused on their respective transport, biodegradation, and bioaccumulation. The interactions between MPs and oil in the marine environment remain unknown. MPs would incorporate with oil to form MP-oil agglomerate (MOA), the behaviors of MOA were thus discussed in this study. It was found that the MOA formation resulted in the decreased oil dispersion efficacy and affect marine oil spill response operations. Moreover, oil biodegradation rate would be changed when oil existed as the form of MOA. The slow vertical transport of MOA might lead to wider ocean contamination. MOA would cause much worse impacts on phytoplankton, zooplankton, and high trophic species in the marine environment than MPs or oil individually. MOA assembling with phytoplankton in oceans may reduce carbon dioxide (CO2) transport to deep seas. Exploring the interactions between MPs and oil in the marine environment opened a door for understanding MPs and oil as co-contaminants.

Temporal variation of crude and refined oil biodegradation rates and microbial community composition in freshwater systems

Freshwater systems are vulnerable to contamination by oil extraction and transportation. Thus, it is critical to understand how large freshwater ecosystems such as the Great Lakes will respond to released oil. In this study, we investigated differences in the microbial response to oil in the Straits of Mackinac at different times throughout the year and if crude (Bakken) and refined (non-highway diesel) oil exposure differentially altered the microbial community composition and hydrocarbon biodegradation rates. We also investigated the impact of temperature on the microbial response to oil by incubating samples collected in October of 2018 at 23 °C and at 4 °C. Ambient microbial communities differed between sample collection times, with significantly enriched microbial groups present between most sample types. We found significantly different microbial communities between control and oil-amended samples, but no significant differences between either oil type. We found that the bacterial family Solimonadaceae were significantly enriched in all oil-amended microcosms compared to the control microcosms across sampling times. We assessed oil biodegradation using CO2 production as a proxy for hydrocarbon metabolism. We observed a general trend of increased respiration rates with oil amendment compared to the control. No statistically significant differences in daily CO2 production rates existed between the two oil types. These findings suggest that microbial community in the Straits of Mackinac shifts over time even without oil amendment, and that the microbial communities in the Straits of Mackinac are compositionally and metabolically responsive to the presence of varying oil types throughout the year.

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.

Influence of biodegradable lubricant on the ecology, lubrication, and machining process in minimum quantity lubrication

In minimum quantity lubrication (MQL) processing, lubricating oil is passed through the air flow field in the form of oil droplets. The oil droplets penetrate the field and are adsorbed by it to form a film in the capillary tube at the workpiece–tool interface. Therefore, the type, atomization, penetration, and adsorption of the lubricating oil have crucial influences on the lubrication quality. Three types of lubricant—trimethylolpropane trioleate, vegetable oil, and polyethylene glycol—were used in this research. To protect the environment and meet application requirements, the biodegradability, oxidation stability, and placement stability of the aforementioned three oils were tested in accordance with the relevant national standard. The biodegradation rate and storage stability of vegetable oil 6000 were high; however, its oxidation stability was poor. A three-dimensional particle dynamic analyzer was used to measure the atomization of oil droplets, and the amount of oil penetrating the tool–workpiece contact area was quantitatively evaluated using a specially designed penetration sampling device. The contact angles of the droplets on AISI 1045 carbon steel and TiN coating were measured, and experiments were performed on the MQL machining of AISI 1045 carbon steel. According to the experimental results, the main cutting force, coefficient of friction, surface morphology, and roughness obtained using vegetable oil 6000 were superior to those obtained using polyethylene glycol 400 and trimethylolpropane trioleate, because a more focused oil drop distribution, higher amount of penetrated oil, and higher wettability were obtained with vegetable oil 6000.

Bio-electrokinetic remediation of crude oil contaminated soil enhanced by bacterial biosurfactant

The present study evaluating the coupling between bioremediation (BIO) and electrokinetic (EK) remediation of crude oil hydrocarbon by using bio-electrokinetic (BIO-EK) technique. The application of bacterial biosurfactant (BS) may increase the remediation efficiency by increasing the solubility of organic materials. In this work, the potential biosurfactant producing marine bacteria were isolated and identified by 16S rDNA analysis namely Bacillus subtilis AS2, Bacillus licheniformis AS3 and Bacillus velezensis AS4. Biodegradation efficiency of crude oil was found as 88%, 92% and 97% for strain AS2, AS3 and AS4 respectively, with the optimum temperature of 37 °C and pH 7. FTIR confirm the BS belongs to lipopeptide in nature. GCMS reveals that three isolates degraded the lower to higher molecular weight of the crude oil (C8 to C28) effectively. Results showed that use of BS in electokinetic remediation enhance the biodegradation rate of crude oil contaminated soil about 92% than EK (60%) in 2 days operation. BS enhances the solubilization of hydrocarbon and it leads to the faster electromigration of hydrocarbon to the anodic compartment, which was confirmed by the presence of higher total organic content than the EK. This study proven that the BIO-EK combined with BS can be used to enhance in situ bioremediation of petroleum contaminated soils.

Bioremediation of Crude Oil-Contaminated Water and Sediments from the Shatt Al-Arab River (SAR)

In the SAR, the oil-degrading bacteria (O-DB) are widespread, forming 8 % to 14 % of heterotrophic bacteria(HB). The O-DB numbers and biodegradability of petroleum hydrocarbons (PHY) are important in summer(SU) and sediments (SE) compared to winter (WI) and water (WA). The common O-DB retrieved from theSAR are Pseudomonas sp. (PS), Pseudomonas putida (PP), Pseudomonas fluorescens (PF), Pseudomonasaeruginosa (PA), Pseudomonas cepacia (PC), Corynebactrium sp. (CO), Bacillus sp. (BA), Bacillus cereus(BC), Bacillus subtilis (BS), Flavobacterium sp. (FL), Aeromonas sp. (AE), Arthrobacter sp. (AR), Vibriosp. (VI), Nocardia sp. (NO), Acintobacter sp. (AC), Micrococcus sp. (MI), and Staphylococcus sp (ST). Themost effective O-DB utilized more than 52 % of oil in 21-days. A mixed culture made of mutant PP+ARutilized 93 % of oil during the same period. The oil biodegradation rates in the SAR have been restrictedby biotic and abiotic factors. By providing these factors to the oil-contaminated sites would improve thedegradation rates. The biodegradation of n-alkanes was much faster than polycyclic aromatic compounds(PAC).

Effects of suspended particulate matter, surface oil layer thickness and surfactants on the formation and transport of oil-sediment aggregates (OSA)

This study illustrated the significant effects of oil surface layer thickness, the presence of suspended particulate matter (i.e. sediment resuspension) and surfactants (chemical oil dispersants and a bio-surfactant) on the formation and transport of oil-sediment aggregates (OSA). Oil spill thickness on surface waters influenced the weathering rates of residual oil. Thin oil slicks on the water surface were more readily dispersed by physical processes. This study provided evidence for the dispersion of thin oil slicks by the bursting of air bubbles. The OSA formation within the water column by interaction of oil with suspended particulate materials promoted the sedimentation of oil. The addition of a chemical dispersant (i.e., GM-2) and biosurfactant (i.e., rhamnolipid) to a surface oil slick increased the dissolved and aggregated oil concentrations in the aqueous phase and subsequent oil biodegradation rates. These findings provide a deeper understanding on the processes influencing vertical distribution and environmental persistence of a crude oil spilled on the ocean surface both in the presence and absence of surfactant additions.

TOUGHREACT-CO2Bio – A new module to simulate geological carbon storage under biotic conditions (Part 2): The bio-geochemical reactive transport of CO2-CH4-H2-H2S gas mixtures

The capabilities of TOUGHREACT-CO2Bio to simulate the multiphase flow of CO2-CH4-H2-H2S gas mixtures and brine in deep geological formations were presented in Shabani and Vilcáez (2019) [Journal of Natural Gas Science and Engineering. 63, 85-94]. Here we present the capabilities of CO2Bio to simulate bio-geochemical reactive transport of CO2-CH4-H2-H2S gas mixtures and brine in depleted oil reservoirs under biotic conditions where CO2 and/or crude oil can be converted to CH4. In CO2Bio, the microbial production/consumption of gases (CO2, CH4, H2, and H2S) is coupled with the multiphase flow of CO2-CH4-H2-H2S gas mixtures and brine through a sequential iterative method. The kinetic model used to represent rates of crude oil biodegradation and microbial production/consumption of gases accounts for the different response of microbial species to changes in pH derived from the dissolution of CO2 into the aqueous phase and water-rock reactions. To verify the microbial capabilities of CO2Bio, we simulate batch experiments conducted to analyze the stimulation effect of CO2 and a nutrient package on the microbial conversion of CO2 and crude oil to CH4. To confirm the capabilities of CO2Bio to simulate the multiphase bio-geochemical reactive transport of CO2-CH4-H2-H2S gas mixtures and brine in deep geological formations under biotic conditions, we conducted a 3D field-scale simulation of alternate injection of CO2 and produced water into a section of the Cushing oilfield of Oklahoma. Overall, simulation results show that CO2Bio can simulate the complex multiphase-multicomponent reactive transport of CO2-CH4-H2S-H2 gas mixtures and brine under biotic conditions.

Kurstakin molecules facilitate diesel oil assimilation by Acinetobacter haemolyticus strain 2SA through overexpression of alkane hydroxylase genes

ABSTRACT Biodegradation is a cost-effective process commonly used to eliminate many xenobiotic hydrocarbons such as diesel oils. However, their hydrophobic character reduces the biodegradation efficiency. In order to overcome this hurdle, kurstakins isolated from Bacillus thuringiensis strain 7SA were used as emulsifying agents. The influence of kurstakin molecules on diesel oil degradation by Acinetobacter haemolyticus strain 2SA was evaluated in the presence and absence of the aforementioned lipopeptide. The degradation rates and gene expressions of alkane hydroxylases were evaluated at days 4, 10, 14 and 21. Results showed that kurstakin molecules increased the hydrophobicity of 2SA. Moreover, diesel oil degradation activities were higher in the presence of kurstakin with 29%, 35%, 29% and 23% improvement at 4th, 10th, 14th and 21st day respectively. Statistical analysis indicated that the difference between the degradation rates in the presence and absence of kurstakin was significant with p = 0.03. The detection of three different hydroxylase genes namely alkB, almA and cyp153 in 2SA genome, might have allowed more efficient degradability of alkanes. According to the real-time PCR results, cyp153 was the most induced gene during diesel oil degradation in the presence and absence of kurstakin. Yet, the three genes demonstrated higher levels of expression in the presence of kurstakin when compared to its absence. This study showed that kurstakins enhance the diesel oil biodegradation rate by increasing the hydrophobicity of 2SA. In addition to their anti-fungal activities, kurstakins can be used as biosurfactant to increase biodegradation of diesel oil.

Assessment of crude oil bioremediation potential of seawater and sediments from the shore of Lebanon in laboratory microcosms

With the planned oil and gas exploration activities off the coast of Lebanon, the risk of shoreline contamination with crude oil spills has become a major concern. This study aimed at assessing the crude oil bioremediation potential of the chronically polluted Lebanese shores in light of the continuous discharge of nutrient-rich sewage into the Mediterranean Sea and the long-lasting absence of proper sewage treatment systems. It was anticipated that, with the high pollution levels of the coastline, background concentrations of nutrients would be sufficient to sustain high intrinsic biodegradation rates without human intervention. Biodegradation experiments were conducted using crude oil-spiked beach sediments and seawater under natural attenuation and biostimulation conditions. The experiments were conducted at 18 and 28 °C to account for seasonal variation in temperature, background nutrient levels, and microbial communities. The biodegradability of oil constituents – namely alkanes and polycyclic aromatic hydrocarbons (PAHs), was monitored over a 42-day period using gas chromatography–mass spectrometry (GC–MS). Under biostimulation conditions, significant enhancement in the overall biodegradation rates of alkanes and PAHs was observed in seawater at 18 and 28 °C, while little to no improvement was measured at both temperatures in sediments where background nutrient levels were sufficient to induce near maximum intrinsic biodegradation rates. Under both natural attenuation and biostimulation treatments, the increase in temperature increased the oil biodegradation rates in sediment and seawater microcosms. In both instances, the overall trend in the biodegradation of individual alkanes and PAHs suggested a typical decrease in biodegradation rates with the increase in carbon number/rings and alkyl groups.

Post Remediation Assessment of Residual Hydrocarbons in Contaminated Soil in Ogoni Using Gas Chromatographic Fingerprinting Technique and Phytotoxicity Bioassay

Post-remediation assessment of residual total petroleum hydrocarbon (TPH) in an aged crude oil-contaminated soil (ACOCS) in Ogoni after seventy-day enhanced remediation by bio stimulation was investigated using gas chromatographic fingerprinting technique and phytotoxicity bioassay. Seven treatments were designed and composted water hyacinth (EC), Mexican sunflower (TD) and Bermuda grass (CD) was applied as bio stimulants. EC, TD and CD (2,500g each) were used to bio stimulate 4,000 g of ACOCS in situ in TPA (treatment plot A) through TPG. The treatments were monitored for a period of seventy days and the rate of crude oil biodegradation analyzed. Gas chromatographic fingerprints of crude oil in the soil showed the absence of n-C1 to n-C8 carbon length and could be attributed to weathering processes. Carbon lengths between n-C9 to n-C34 were significantly (ρ >0.05) attenuated in plots with 2 nutrients, thus indicating microbial utilization of crude. Crude oil attenuation as depicted by the trend in the disappearance of low-molecular-weight hydrocarbons could be due to their preferential utilization by microbes. TPG with all 3 supplements had TPH reduced significantly (ρ >0.05) from 93,867 ppm to 1,002 ppm, (99% loss), meeting the Department of Petroleum Resources intervention value of 5000 mg/kg. The decreasing peak counts show that the crude were from petrogenic source. The germination index of L. sativum ranged from 65 and 100% thus, could be considered non-phytotoxic and ecologically save.

The enhanced stability and biodegradation of dispersed crude oil droplets by Xanthan Gum as an additive of chemical dispersant

It is necessary for chemical dispersant to disperse oil effectively and maintain the stability of oil droplets. In this work, Xanthan Gum (XG) was used as an environmentally friendly additive in oil dispersant formulation to enhance the stability and biodegradation of dispersed crude oil droplets. When XG was used together with chemical dispersant 9500A, the dispersion effectiveness of crude oil in artificial sea water (ASW) and the oil droplet stability were both greatly enhanced. In the presence of XG, lower concentration of 9500A was needed to achieve the effective dispersion and stabilization. In addition to the enhancement of dispersion and stabilization, it was found that the biodegradation rate of crude oil by bacteria was dramatically enhanced when a mixture of 9500A and XG was used as a dispersant. Because of the low environmental impact of XG, this would be a potential way to formulate the dispersant with lower toxicity.

The Rate of Crude Oil Biodegradation in the Sea

Various groups have studied the rate of oil biodegradation in the sea over many years, but with no consensus on results. This can be attributed to many factors, but we show here that the principal confounding influence is the concentration of oil used in different experiments. Because of dilution, measured concentrations of dispersed oil in the sea are sub-parts-per-million within a day of dispersal, and at such concentrations the rate of biodegradation of detectable oil hydrocarbons has an apparent half-life of 7-14 days. This can be contrasted with the rate of degradation at the higher concentrations found in oil slicks or when stranded on a shoreline; there the apparent half-life varies from many months to many years.