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Oil spills interact with mineral particles to form oil-particle aggregates (OPAs), which promotes the oil's natural diffusion and biodegradation. We investigated the effect of bacteria on the formation and vertical migration of OPAs under different concentrations and types of particles and proposed and elucidated an oil-particle-bacteria coupling mechanism. The depth of particle penetration into oil droplets (13-17 μm) was more than twice that of the nonbacterial group. Oil that remained in the water column and deposited to the bottom decreased from 87% to 49% and increased from 14% to 15% at high/low concentration, respectively. Interestingly, the median droplet diameter showed a negative correlation ( R 2 = 0.83) and positive correlation ( R 2 = 0.60) at high/low concentration, respectively, with the relative penetration depth first proposed. We further demonstrated that bacteria increased the penetrating depth by a combination of reducing/increasing the interfacial tension, reducing the oil amount (C 17 -C 38 ) in the OPAs, and increasing the particle width. These effects reduced the droplet size and ultimately changed the vertical migration of OPAs. Finally, we provided a simple assessment of the vertical distribution of OPAs in nearshore environments based on experimental data and suggested that the role of bacteria in increasing the depth of particles penetrating into the oil droplets should not be ignored. These findings will broaden the research perspective of marine oil spill migration.

Hypothesis: Major oil spills highlight the need for environmentally responsible and cost-effective recovery technologies. However, challenges remain for heavy oil spill recovery because of its high viscosity and low fluidity. To achieve this goal, an ecofriendly bio-based aerogel with efficient photothermal conversion ability was developed as a novel absorbent to achieve the fast removal of heavy oil spill by reducing the oil viscosity., Experiments: From the renewable and abundant raw material sodium alginate (SA), hydrophobic and antibacterial SA/graphene oxide/ZIF-8 aerogel (SAGZM) was successfully fabricated via freezing-drying and chemical vapor deposition (CVD) technique. A series of characterization and tests, including aerogel structure, selective wettability, photothermal conversion ability, crude oil removal capability, and antibacterial ability, have been investigated in detail. SAGZM aerogels have rich pore structure, high porosity, excellent mechanical properties, and better photothermal conversion efficiency., Findings: Under sunlight illumination, the recovery ability of SAGZM for heavy crude oil was investigated through infrared thermal imaging, oil permeability behavior analysis, and the continuous absorption for crude oil. In addition, these results are well supported by the theoretical liquid absorption coefficient. This study indicates that SAGZM is highly efficient in in situ regulating oil viscosity through its remarkably photothermal conversion capability. Importantly, SAGZM possesses an excellent antibacterial ability that is often neglected in the design of environmentally friendly materials in extending its service life. The findings of this work not only provide an eco-friendly bio-based aerogel material but also demonstrate that the photo-responsive SAGZM is efficient in heavy crude oil absorption. The proposed solar-heated SA-based aerogel provides a sustainable approach and material to solve the recovery problem of viscous crude oil spills., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The migration of oil spills in marine environment is still not clear, especially the key processes of submerging and floating, which is an important concern for effective disposal of oil spills. In mesoscale wave tank (32 m × 0.8 m × 2 m), this study has evaluated the characteristics of oil submergence based on oil concentration and oil droplet size. The concept of effective submergence is put forward for the first time, utilized to analyze the effects of dispersant on submerging stability and associated mechanisms. The results indicate dispersants increase submerged oil concentration and promote homogeneous distribution and vertical penetration. Of concern is that dispersants increase the proportion of small oil droplets (2.5-70 µm), prolonging the residence time of oil droplets in water by delaying the floating process. Dispersants sharply reduce oil droplets size (VMD<44 µm) thus decreasing the coalescence probability. These contribute to better submerging stability. By contrast, the submerged oil, formed as oil patches, oil streamers, and large oil droplets (VMD>170 µm) when without dispersant, will float and reattach to oil slicks more quickly due to their large volume. These findings help to clarify spilled oil behaviors and provide a new idea for the research on oil submergence., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Hypothesis: High-efficiency dispersion and enhanced biodegradation play important roles in the treatment of oily wastewater. Due to the flaws of chemical surfactants, it is necessary to study the alternative dispersants that are eco-friendly and sustainable. Therefore, applying natural attapulgite (ATP) to coat Brevibacillus parabrevis for dispersion and biodegradation was studied., Experiments: To capture negatively charged bacteria in water, ATP was modified by positively charged Poly (allylamine hydrochloride) (PAH). The capturing capability of Poly (allylamine hydrochloride)-attapulgite (PAH-ATP) particles for bacterial cells, emulsification of PAH-ATP particles and bacteria on oil, toxicity of PAH-ATP to bacteria, biodegradation of oil, etc., were comprehensively investigated., Findings: PAH-ATP modified bacteria show a highly effective emulsification for oil due to the synergism of PAH-ATP and bacteria. The emulsion stabilized by (PAH-ATP)@bacteria presents small and stable oil droplets in one month, which is benefit for the following biodegradation. Compared with bare bacteria and PAH-ATP, PAH-ATP can capture bacteria to the surface of the oil droplets which can greatly improve the degradation of oil pollution. Importantly, the presence of PAH-ATP does not inhibit the reproduction and activity of bacteria. Treatment of oily wastewater by combining natural nanoparticles and oil-degrading bacteria has the advantages of economy, environmental protection, and sustainability., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The employment of dispersant was an effective method to treat marine oil spill pollution. However, conventional dispersants only showed a single oil dispersion. Here, by modifying TiO 2 nanoparticles with biosurfactant-Rhamnolipids (Rha), a highly efficient particulate dispersant with photocatalytic activity was developed. Rha-TiO 2 showed both excellent oil spill dispersion and facilitated photodegradation for oil simultaneously. The oil droplets dispersed by Rha-TiO 2 in seawater exhibited long time stability, which indicated the synergistic emulsification interactions between TiO 2 and Rha in artificial sea water (ASW). The dispersion mechanism of Rha-TiO 2 was analyzed, we found the TiO 2 nanoparticles alone weren't effectively emulsified oil in high salinity ASW, but the addition of a small amount of Rha could modify the surface wettability of TiO 2 nanoparticles to form the stable emulsion. In addition, the addition of a small amount of Rha could reduce the surface tension of the oil-water interface, which contribute to increasing the content of TiO 2 nanoparticles at the oil-water interface, form a steric rigid layer around the oil droplets to prevent droplet coalescence and facilitate the further photocatalytic degradation of oil. In short, the Rha-TiO 2 nanoparticles could effective disperse oil in ASW, meanwhile the TiO 2 also played the role of photocatalytic degradation of oil pollution. Hence, this study developed a novel photocatalytic particulate dispersant to remediate marine oil spill and delivered a new feasible solution for practical oil spill treatment in the future., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, the effect of particulate matter type, temperature, oil type and weathering degree on the interaction between dispersed crude oil droplets and particulate matter was investigated. The increase of total petroleum hydrocarbon (TPH) percentage in oil-particle aggregates (OPAs) could be attributed to the increase of oil polarity or viscosity. For small size particulate matter, there was a fine dependence relationship between the TPH percentage in OPAs and the oil viscosity and the content of polar components, respectively (R2 > 0.7502). And the total organic carbon content also played an important role in the formation of OPAs. The petroleum hydrocarbon extracts of OPAs showed a decrease in short-carbon-chain components and a relative increase in long-carbon-chain compounds. Petroleum hydrocarbon compounds trapped by three types of particulate matter exhibited a similar change tendency, but there was no apparent difference in the residual TPH percentage in water.

Eliminating the adverse environmental impact of chemical dispersants for oil spill has been a significant challenge since decades ago. Here, we prepared an effective and environmentally-friend dispersant with stable emulsifying capacity by the soybean lecithin and Tween 80. The mean droplet diameters of emulsions prepared by decane decreased from 11.3 to 4.1 μm, the emulsification index of emulsion climbed from 0 to 22.0% by 0.5 wt% dispersant. This dispersant exhibits favorable emulsifying capacity when the temperature ranges from 10 to 40 °C, pH within 5-7, and the concentration of inorganic cation is 30000 mg/L. Fluorescence microscopy analysis, FTIR, and the interfacial tension meter were employed to investigate the interaction between the soybean lecithin and Tween 80, a clear redshift of the hydroxyl group on the lecithin/Tween 80 dispersant and the detected surfactants over the oil-water interface confirm that there exists a synergy between the lecithin and Tween 80 due to the electrostatic attractions, which tremendously contribute to the reduction in the interfacial tension between water and oil. To further understand the influence of the dispersant on the oil hydrocarbon concentration in the water column, visualization simulation with the varying depths were performed. The results showed that the oil hydrocarbon concentration in the water column bottom was proportional to the addition of the dispersant, which facilitates spilled oil dispersing into smaller droplets, accelerates the biodegradation process. Hence, the lecithin/Tween 80 dispersant can be perceived as a promising alternative for oil spill remediation., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

In this study, a cloned almA gene was inserted into two plasmids PUC57 and pet-28a (+), and then transformed into Escherichia coli competent strains. The presence of almA was confirmed by PCR combined with restriction enzyme digestion. The results indicated two strains of PUC57/almA-E. coli and pet-28a (+)/almA-E. coli were all functioned on biodegradation long-chain alkanes, however, pet-28a (+)/almA-E. coli strain performed better and the speed of biodegradation was enhanced to about 12 mg L -1  h -1 when compared with PUC57/almA-E. coli strain. Furthermore, degradation degree of n-C32 was much higher than other long-chain alkanes for two engineered E. coli strains. Our results further suggested that exoenzyme was only detected in pet-28a (+)/almA-E. coli and followed a decreasing order of extracellular enzyme > intracellular enzyme > periplasmic enzyme. Besides, co-biodegradation of petroleum hydrocarbons by Pseudomonas sp. B-1, Bacillus subtilis PH-1 with exoenzyme or pet-28a (+)/almA-E. coli posed enormous potential that could reach 70%-80% in oil pollution bioremediation., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Microbes appear to play a key role in bioremediation of petroleum hydrocarbons pollution and little attention has been paid to the enzyme activity in the process of alkane bioremediation. Oil field bacterium identified as Pseudomonas synxantha LSH-7' was chosen as the tested strain. Periodically collected samples were analyzed by GC-FID (Gas Chromatography- Flame Ionization Detector) and RT-qPCR (Quantitative-Real-Time-PCR). GC-FID results showed this bacterial strain has great degradation ability on crude oil n-alkanes and RT-qPCR data indicated the differences between the three genes expression including AlkB-, Cytochromes P450-, and almA- related when grown on different-chain alkanes. Meanwhile, enzyme activity like alkane hydroxylase, alcohol dehydrogenase, dehydrogenase, protease, phosphatase, catalase and lipase were measured. Extracellular alkane hydroxylase was induced in a higher degree than intracellular in the early incubation time, alcohol dehydrogenase increased/decreased along with alkane hydroxylase, and the pH of the medium obviously decreased. Other enzymes were also described including dehydrogenase activity that reached a highest point that was slower than alcohol dehydrogenase, protease activity started multiplying after a period of culture while biomass was immediately increased, catalase activity dramatically enhanced in the presence of alkanes, phosphatase activity was closely linked to pH approximately but lipase activity was found to be moderate., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Simulated column was applied to research forming progress of single oil droplet in submerged process, floating progress, and study effects of environment factors and dispersants on the concentration of oil hydrocarbon in water as well as changing rules of oil droplet sizes. As expected, particular formation mechanism of single oil droplet was presented. When necking down length L is 0.5 time of oil droplet diameter (d) after expansion phase, necking down becomes long and thin; when L=2d, necking down begins to break. In floating progress, the shape changes oval and its motion trail becomes an auger-type. Fluctuation occurs at horizontal direction. Dispersants decrease oil droplet size by its dispersion effect, and cut down effect of Van Der Waals force among oil droplets. More broadly, these findings provide rare empirical evidence expounding formation mechanism of single oil droplet to increasing ability of oil spill response., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This study, adsorption behaviors of dispersed oil in seawaters by granular materials were explored in simulation environment. We quantitatively demonstrated the dispersed oil adsorbed by granular materials were both dissolved petroleum hydrocarbons (DPHs) and oil droplets. Furthermore, DPHs were accounted for 42.5%, 63.4%, and 85.2% (35.5% was emulsion adsorption) in the adsorption of dispersed oil by coastal rocks, sediments, and bacterial strain particles respectively. Effects of controlling parameters, such as temperature, particle size and concentration on adsorption of petroleum hydrocarbons were described in detail. Most strikingly, adsorption concentration was followed a decreasing order of bacterial strain (0.5-2μm)>sediments (0.005-0.625mm)>coastal rocks (0.2-1cm). With particle concentration or temperature increased, adsorption concentration increased for coastal rocks particle but decreased for sediments particle. Besides, particle adsorption rate of petroleum hydrocarbons (n-alkanes and PAHs) was different among granular materials during 60 days., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Rhodococcus erythropolis M-25, one of the representative biosurfactant producers, performed effectively during the biodegradation of four crude oil. The microbial degradation efficiency is positively relevant to the API of the crude oil. The chemical dispersant Corexit 9500A did not enhance the biodegradation of the petroleum hydrocarbons during the experimental period. 70.7% of the N-4 oil was degraded after 30days, while in the Corexit 9500A plus sample the biodegradation removal was 42.8%. The Corexit-derived compounds were metabolized by M-25 at the same time of the petroleum hydrocarbons biodegrading. Neither biodegradation nor chemical dispersion process has almost no effect on the biomarker (m/z=231). The saturated methyl-branched fatty acids increased from 37.3%, to 49.4%, when M-25 was exposed with the N-4 crude oil. Similarly, the saturated methyl-branched fatty acids in the membrane of N3-2P increased from 20.25% to 44.1%, when exposed it with the N-4 crude oil., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Oil plume is known to interact with density layer in spilled oil. Previous studies mainly focused on tracking oil plumes and predicting their impact on marine environment. Here, simulated experiments are presented that investigated the conditions inducing the formation of oil plume, focusing especially on the effects of oil/water volume ratio, oil/dispersant volume rate, ambient stratification and optimal conditions of oil plume on determining whether a plume will trap or escape. Scenario simulations showed that OWR influences the residence time most, dispersants dosage comes second and salinity least. The optimum residence time starts from 2387s, occurred at approximately condition (OWR, 0.1, DOR, 25.53% and salinity, 32.38). No change in the relative distribution under the more scale tank was observed, indicating these provide the time evolution of the oil plumes., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Custom-designed devices with 0.6 m (L) × 0.3 m (W) × 0.4 m (H) and a microbial consortium were applied to simulate bioremediation on the oil spill polluted marine intertidal zone. After the bioremediation, the removal efficiency of n-alkanes and polycyclic aromatic hydrocarbon homologues in crude oil evaluated by GC-MS were higher than 58% and 41% respectively. Besides, the acute toxicity effects of crude oil on three microalgae, i.e. Dicrateria sp., Skeletonema costatum and Phaeodactylum tricornutum, varied with concentration. The effects of microbe and surfactant treated water on the three microalgae followed a decreasing order: the microbial consortium plus Tween-80 > the microbial consortium > Tween-80. During 96 h, the cell densities of the three microalgae in treated seawater increased from 4.0 × 10(5), 1.0 × 10(5) and 2.5 × 10(5) cells per mL to 1.7 × 10(6), 8.5 × 10(5) and 2.5 × 10(6) cells per mL, respectively, which illustrated that the quality of seawater contaminated by crude oil was significantly improved by the bioremediation.

Biodegradation of marine surface floating crude oil with hydrocarbon degrading bacteria, rhamnolipid biosurfactants, and nutrients was carried out by a large-scale field simulated experiment in this paper. After a 103 day experiment, for n-alkanes, the maximum biodegradation rate reached 71% and the results showed hydrocarbon degrading bacteria, rhamnolipid biosurfactants, and nutrients have a comprehensive effect. It also showed that rhamnolipid biosurfactants could shorten the biodegradation time through an emulsifying function; the nutrients could greatly increase the biodegradation rate by promoting HDB production. For PAHs, the chrysene series had higher weathering resistance. For the same series, the weathering resistance ability is C1- < C2- < C3- < C4-. After 53 days, no comprehensive effect occurred and more biodegradation was found for different n-alkanes in two pools which only had added rhamnolipid biosurfactants or nutrients, respectively. Except for C14, C15 and C16 sesquiterpanes, most of the steranes and terpanes had high antibiodegradability.

This paper presents a simulated marine oil spill bioremediation experiment using a bacterial consortium amended with rhamnolipids. The role of rhamnolipids in enhancing hydrocarbon biodegradation was evaluated via GC-FID and GC-MS analysis. Rhamnolipids enhanced total oil biodegradation efficiency by 5.63%, with variation in normal alkanes, polyaromatic hydrocarbons (PAHs) and biomakers biodegradation. The hydrocarbons biodegradation by bacteria consortium overall follows a decreasing order of PAHs>n-alkanes>biomarkers, while in different order of PAHs>biomarkers>n-alkanes when rhamnolipids was used, and the improvement in the removal efficiency by rhamnolipids follows another order of biomarkers>n-alkanes>PAHs. Rhamnolipids played a negative role in degradation of those hydrocarbons with relatively volatile property, such as n-alkanes with short chains, PAHs and sesquiterpenes with simple structure. As to the long chain normal alkanes and PAHs and biomakers with complex structure, the biosurfactant played a positive role in these hydrocarbons biodegradation., (Copyright © 2013 Elsevier Ltd. All rights reserved.)