The back cover picture shows a photocatalytic remediation of polycyclic aromatic hydrocarbons (PAHs) from wastewater with graphene oxide (GO) enwrapped silver phosphate as visible light-driven photocatalysts. PAHs are a class of highly mutagenic and carcinogenic organic pollutants that pose serious threats to human health and the ecosystem. GO/Ag3PO4 was synthesized by a simple precipitation method. The photocatalysts exhibited superior photocatalytic activity and stability. The degradation efficiency of naphthalene, phenanthrene and pyrene could reach 49.7%, 100.0% and 77.9%, respectively within 5 min irradiation. Meanwhile, the efficiencies of 44.6%, 95.2% and 83.8% were achieved for naphthalene, phenanthrene and pyrene degradation even after 5 times of recycling in the GO/Ag3PO4-PAHs photocatalysis system. More details are discussed in the article by Bao et al. on page 1549–1558.

Effective removal of polycyclic aromatic hydrocarbons (PAHs) from wastewater before their discharge into the environment is an ever pressing requirement. In this study, for the first time, simulated PAHs contaminated wastewater was photocatalytically remediated with graphene oxide (GO) enwrapped silver phosphate as visible light-driven photocatalysts. The GO/Ag3PO4 photocatalysts exhibited superior photocatalytic activity and stability compared with pure Ag3PO4, g-C3N4 and TiO2 (P25). The degradation efficiency of naphthalene, phenanthrene and pyrene could reach 49.7%, 100.0% and 77.9%, rspectively within 5 min irradiation. The apparent rate constants of photocatalytic degradation of 3 wt% GO/Ag3PO4 composite photocatalyst were 0.14, 1.21 and 2.46 min−1 for naphthalene, phenanthrene and pyrene, respectively. They were about 1.8, 1.5 and 2.0 times higher than that of pure Ag3PO4, and much higher than that of g-C3N4 and TiO2. Meanwhile, the efficiencies of 44.6%, 95.2% and 83.8% were achieved for naphthalene, phenanthrene and pyrene degradation even after 5 times of recycling in the GO/Ag3PO4-PAHs photocatalysis system. Reactive species of ∙O2− and h+ were considered as the main participants for oxidizing naphthalene, phenanthrene and pyrene.

•A novel NF membrane using SiO2 thin film as rejection layer was achieved.•The membrane exhibited high rejection towards negatively charged organic dyes.•The membrane showed a great stability during a long-term NF test.In the past decades, application of nanomaterials in fabrication of organic-inorganic composite nanofiltration (NF) membrane for membrane performance improvement has been intensively studied. Herein, novel SiO2 organic-inorganic NF membrane was achieved using an ultrathin and ordered stacking SiO2 thin film as rejection layer assisted with layer-by-layer method. The resultant membrane showed a great enhancement in hydrophilicity with a membrane surface charge of −44 mV. It exhibited typical characteristics of negatively charged NF membranes because of the rejection against negatively charged methyl blue and methyl orange was 99.5% and 97.6%, while the rejection for positively charged methylene blue decreased to 90.1%. Correspondingly, the water flux declined from 20 L/m2·h to 9.1 L/m2·h using 20 ppm dye solutions as feed solution at 4 bar. In addition, the salt rejection of the produced membrane followed the sequence of MgSO4 (88.7%) > Na2SO4 (82.1%) > MgCl2 (64.5%) > NaCl (43.1%), which was in accordance with the size exclusion and Donnan effect. The SiO2 organic-inorganic membrane presented a remarkable stability under high operating pressure as well as long-term NF test. To conclude, this work paves a new avenue to fabricate highly permeable and selective NF membrane by using inorganic thin film as rejection layer.Download high-res image (88KB)Download full-size image

•W10O324− polyanion was well integrated with g-C3N4 photocatalyst.•Graphene modified (C16H33(CH3)3N)4W10O32/g-C3N4 composites were synthesized.•8.0 wt% (C16H33(CH3)3N)4W10O32/g-C3N4/rGO showed excellent photocatalytic activity and reusability toward methyl orange and phenol photodegradation.•A photocatalytic mechanism of the (C16H33(CH3)3N)4W10O32/g-C3N4/rGO was well proposed.The photocatalytic performance of the g-C3N4 photocatalyst was restricted by the low efficiency because of the fast charge recombination. The present work constructed a “killing two birds with one stone” composite (C16H33(CH3)3N)4W10O32/g-C3N4 heterostructured photocatalysts with the aim to greatly promote the charge separation and recycle decatungstate in aqueous solution. Decatungstate was immobilized on g-C3N4 in the form of modified decatungstate (C16H33(CH3)3N)4W10O32 via surface bonding method for the first time. Furthermore, a novel ternary (C16H33(CH3)3N)4W10O32/g-C3N4/rGO photocatalyst was successfully constructed by integrating graphene into the binary (C16H33(CH3)3N)4W10O32/g-C3N4 composite as the electron mediator. The photocatalysts were characterized by XRD, FTIR, FESEM, TEM, UV-vis DRS, PL and EIS measurement. The photocatalytic properties were evaluated in photodecomposition of aqueous methyl orange and phenol under visible-light irradiations. It has been shown that the obtained (C16H33(CH3)3N)4W10O32/g-C3N4 photocatalyst exhibited improved photocatalytic activity and enhanced reduced charge recombination as compared with those of g-C3N4 and (C16H33(CH3)3N)4W10O32. It has been found that the introduction of graphene revealed a synergistic effect between the (C16H33(CH3)3N)4W10O32 species, g-C3N4 and graphene existed in the ternary photocatalyst. Consequently, the photocatalytic activity of the ternary (C16H33(CH3)3N)4W10O32/g-C3N4/rGO photocatalyst was superior to that of the binary one, originating from its stronger visible-light absorption and more reduced charge combination. Finally, recycling experiments revealed that the ternary composite photocatalyst was not only highly efficient but also robust, because it can be used six times without loss of activity, which efficiently solved the problem of recycling decatungstate in reaction system. This work demonstrated that rational design and construction of g-C3N4-decatungstate composites could open up a new avenue for the development of new efficient visible-light photocatalysts for water disinfection.Download high-res image (235KB)Download full-size image

The behaviour end-result of dissolved petroleum hydrocarbons (DPHs) is known to interact with sediments in marine environments. The simulated experiments presented here investigated the progress of behaviour end-results, including the adsorption isotherm, adsorption kinetics, and thermodynamics parameters, and focuses specifically on the effects of factors in the presence of sophorolipids. The results show that there is good agreement between the experimental data and the Lagergren pseudo-second-order model (R2 = 0.968). A Freundlich isotherm model (R2 = 0.924) was derived to describe the adsorption process, where ΔHθ and ΔSθ were 39.1 kJ mol−1 and 104.0 J (K mol)−1, respectively. Such calculations indicated that this process is part of a complex physical and chemical reaction and is an endothermic reaction. It is worth noting that randomness at the solid-solution interface increased during the adsorption process. The adsorption sites met the need of petroleum hydrocarbon molecules when the sediment concentration reached 3 g L−1. The dominant sediment grain size fractions were <150 μm, and the total adsorption quantity of the fraction accounted for 0.27. The DPHs adsorbed hydrocarbons more easily when a chemical dispersant, GM-2, was applied, but at the same depth, the hydrocarbon content adsorbed by the sediment under biosurfactant application was relatively low. It is significant that sediment samples had a lower adsorption capacity when using a sophorolipid as a biosurfactant, rather than a rhamnolipid. Understanding the adsorption of DPHs onto sediment under sophorolipid application will broaden the understanding of heavy oil transport mechanisms and will provide a theoretical basis for remediation of areas with serious oil pollution.

In the present study, hydrophilic Al2O3 nanoparticles were used as additives in both substrate and polyamide active (PA) layer to improve forward osmosis (FO) membrane properties. Via incorporation of 0.5 wt% Al2O3 into the substrate and 0.05 wt% Al2O3 into the PA layer (PS0.5-TFN0.05 membrane), the water flux reached 27.6 L m−2 h−1 with a relatively low solute reverse flux of 7.1 g m−2 h−1 using DI water as a feed solution and 1 M NaCl as a draw solution. Simultaneously, we found that the incorporation of Al2O3 nanoparticles into both the substrate and PA layer resulted in a better enhancement of FO performance and a higher increase in water flux than the simple incorporation of nanoparticles in substrate. Moreover, the PS0.5-TFN0.05 membrane remained stable during long-term FO tests and under serious water environment. To the best of our knowledge, this is the first study to report the effect of Al2O3 nanoparticles on FO performance, and the results verify the potential use of these nanoparticles in the fabrication of highly permeable FO membranes.

•We quantitatively demonstrated both DPHs and oil droplets were absorbed by granular materials.•We confirmed the adsorption ratios of DPHs and oil droplets about three particles.•Maximum adsorption was bacterial strain particle when compared with another two particles.•Particle concentrations and temperature could affect adsorption of three particles.•Particle adsorption rate of petroleum hydrocarbons were different from three particles.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 (0.5–2 μm) > sediments (0.005–0.625 mm) > coastal rocks (0.2–1 cm). 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.Download high-res image (259KB)Download full-size image

•Individually immobilized and surface-modified oil-degrading bacteria were prepared.•The treated bacteria demonstrated dual effects in oil spill bioremediation.•Effective oil emulsification in seawater was realized by the treated bacteria.•The biodegradation of oil was dramatically enhanced by the treated bacteria.Effective emulsification plays an important role in the treatment of marine oil spills. The negative effects of chemical surfactants have necessitated a search for alternative dispersant that are sustainable and environmentally-friendly. To identify alternate dispersants, oil-in-seawater emulsions stabilized by hydrocarbon-degrading bacteria were investigated. After individual immobilization and surface-modification, the hydrocarbon-degrading bacteria, Bacillus cereus S-1, was found to produce a stable oil-in-seawater Pickering emulsion, which was similar to particle emulsifiers. The individual immobilization and surface-modification process improved the surface hydrophobicity and wettability of the bacterial cells, which was responsible for their effective adsorption at the oil–water interface. Through effective emulsification, the biodegradation of oil was remarkably facilitated by these treated bacteria, because of the increased interfacial area. By combining the emulsification and biodegradation, the results of this reported work demonstrated a novel approach for developing environmentally-friendly bioremediation technology in the field of oil treatment.Download high-res image (124KB)Download full-size image

•The particular formation mechanism of single oil droplet was presented.•The oil particle formation depends on necking down length and droplet diameter.•The shape changes oval and its motion trail becomes an auger-type.•Dispersants can cut down effect of Van Der Waals force among oil droplets.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 = 2 d, 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.Download high-res image (204KB)Download full-size image

The adsorption and desorption behaviors of dissolved petroleum hydrocarbons (DPHs) in a seawater–sediment system were investigated. Tidal flat sediment was used as the adsorbent, and crude oil was used as the adsorbate. The processes of adsorption and desorption at low concentration (<14.3 mg L−1) were described by the first-order kinetics model. The rate of desorption was slower than that of adsorption, and about 49% of the DPHs remained on the sediment. Therefore the potential risk of pollution would exist for a long time. The adsorption isotherms could be better fitted to the linear isotherm model than the Freundlich and Langmuir models. The adsorption process is a physical adsorption, because |ΔH| was 39.0 kJ mol−1 which is less than 42.0 kJ mol−1. The change in n-alkanes in the process was more obvious than the aromatics; the weathering loss rate was 25.56%, the emulsification loss rate of the dispersant was 0.65% and the microbial degradation rate was 15.46%. The results showed the degradation processes of petroleum hydrocarbons in tidal flats.

In total, 164 oil samples, including 56 crude oils (OILs), 12 light fuel oils (LFOs), 66 heavy fuel oils (HFOs), 12 weathered fuel oils (WHFOs), and 18 weathered crude oil (WOILs) samples, were used to screen the sensitivity and identification indexes using principal component analysis (PCA) biplots. Also, 31 oil samples, including 1 LFO, 15 HFOs and 15 OILs, were used for validation by PCA biplots. The sensitivity indexes were determined from PCA biplots based on 143 components; light n-alkanes exhibited good positive correlation with LFOs, aromatic hydrocarbons displayed positive correlations with HFOs, and terpanes and steranes were indicative of OIL characteristics. Among 43 diagnostic ratios, the sensitive diagnostic ratios were screened for LFOs, HFOs, and OILs, using PCA biplots. Thirty-eight (38) diagnostic ratios that could discriminate three types of oils were chosen: 21 diagnostic ratios were chosen for the classification of OILs and HFOs, 19 diagnostic ratios could identify OILs and fuel oils (FOs) (including LFOs and HFOs), and 6 diagnostic ratios could discriminate between LFOs and the other two types of oils (OILs and HFOs). In addition, all of the ratios could resist weathering, which means that all of the results included weathered oil samples. All of the identification indexes, including 143 hydrocarbon components, and 43, 38, 21, 19, and 6 diagnostic ratios, were validated by PCA biplots based on 31 oil samples.

In oil fingerprinting studies, hundreds of compound peaks (including saturated and aromatic hydrocarbons) need to be integrated for the identification and quantification of characteristic oil compounds. The speed and quality of integration are the key factors that influence both peak identification and quantification. This influence is observed not only because of the time-consuming nature of manual peak integration but also because different instrument operators may obtain different results due to different peak integration skills, especially for alkylated-PAHs, which need to be integrated into a series of peaks from one whole peak group. This study describes an automatic integration method developed for characteristic oil fingerprinting compounds, including the auto-recognition of single and multiple peaks, identification of bifurcated peaks, determination of the baseline and area integration for single peaks as well as multiple peaks and UCM (unresolved complex mixture) based on trapezoid summation theory. This method has been programmed and used in an oil data analysis and identification system in China. More importantly, this method has been applied since four years in a number of real-world oil spill case investigations and has been demonstrated to be accurate and efficient.

The efficiencies of free and immobilized microbial consortia in the degradation of different types of petroleum hydrocarbons were investigated. In this study, the biodegradation rates of naphthalene, phenanthrene, pyrene and crude oil reached about 80%, 30%, 56% and 48% under the optimum environmental conditions of free microbial consortia after 7 d. We evaluated five unique co-metabolic substances with petroleum hydrocarbons, α-lactose was the best co-metabolic substance among glucose, α-lactose, soluble starch, yeast powder and urea. The orthogonal biodegradation analysis results showed that semi-coke was the best immobilized carrier followed by walnut shell and activated carbon. Meanwhile, the significance of various factors that contribute to the biodegradation of semi-coke immobilized microbial consortia followed the order of: α-lactose > semi-coke > sodium alginate > CaCl2. Moreover, the degradation rate of the immobilized microbial consortium (47%) was higher than that of a free microbial consortium (26%) under environmental conditions such as the crude oil concentration of 3 g L−1, NaCl concentration of 20 g L−1, pH at 7.2–7.4 and temperature of 25 °C after 5 d. SEM and FTIR analyses revealed that the structure of semi-coke became more porous and easily adhered to the microbial consortium; the functional groups (e.g., hydroxy and phosphate) were identified in the microbial consortium and were changed by immobilization. This study demonstrated that the ability of microbial adaptation to the environment can be improved by immobilization which expands the application fields of microbial remediation.

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 × 105, 1.0 × 105 and 2.5 × 105 cells per mL to 1.7 × 106, 8.5 × 105 and 2.5 × 106 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.

In this work, a hydrocarbon-degrading bacterium D3-2 isolated from petroleum contaminated soil samples was investigated for its potential effect in biodegradation of crude oil. The strain was identified as Acinetobacter sp. D3-2 based on morphological, biochemical and phylogenetic analysis. The optimum environmental conditions for growth of the bacteria were determined to be pH 8.0, with a NaCl concentration of 3.0% (w/v) at 30 °C. Acinetobacter sp. D3-2 could utilize various hydrocarbon substrates as the sole carbon and energy source. From this study, we also found that the strain had the ability to produce biosurfactant, with the production of 0.52 g L−1. The surface tension of the culture broth was decreased from 48.02 to 26.30 mN m−1. The biosurfactant was determined to contain lipopeptide compounds based on laboratory analyses. By carrying out a crude oil degradation assay in an Erlenmeyer flask experiment and analyzing the hydrocarbon removal rate using gas chromatography, we found that Acinetobacter sp. D3-2 could grow at 30 °C in 3% NaCl solution with a preferable ability to degrade 82% hydrocarbons, showing that bioremediation does occur and plays a profound role during the oil reparation process.

•3% (v/v) of four crude oil was used as sole carbon source by an individual bacteria.•The microbial degradation efficiency is relevant to the API value of the crude oil.•The Corexit-derived compound DOF could be metabolized by M-25 strain.•The different structural response of PLFAs was sensitive to petroleum composition.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 30 days, 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.

•The oil/water volume ratio influences the residence time most, the dosage of dispersants comes second and salinity least.•The optimum residence time 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.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 2387 s, 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.Download high-res image (178KB)Download full-size image

•Microbial community structure shifts when crude oil invaded was presented.•Bacterial composition and biodegradation potential were linked to temperature.•Dispersants were used in response to crude oil and impacted on microorganisms.•Fertilizer applications increased microbial populations and improve bioremediation.This study tracked structure shifts of bacterial compositions before, during and after invading by crude oil to determine the microbial response and explore how temperature, dispersants and nutrients affect the composition of microbial communities or their activities of biodegradation in artificial marine environment. During petroleum hydrocarbons exposed, the composition and functional dynamics of marine microbial communities were altered, favoring bacteria that could utilize this rich carbon source such as the Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes phyla. Low temperature as a dominant factor decreased bacterial richness and catabolic diversity due to abated enzymes activities in correlation with the process of biodegradation. Dispersants exerted no negative consequences on microbial composition, however, bacterial composition by the Chloroflexi, TM6, OP8, Cyanobacteria and Gemmatimonadetes phyla increased. It seemed that more frequent fertilizer application could be equally safe to bacteria and increased significantly the abundance of bacterial strains but Actinobacteria phyla decreased.Download high-res image (182KB)Download full-size image

•The PAHs may exert potential health risk to urban residents and have a strong inhibitory effect on microbial growth.•The rhamnolipid which was produced by Bacillus Lz-2 was applied to enhance the solubilization of PAHs.•The influencing factors on PAH solubilization capacity were mainly discussed.Rhamnolipid biosurfactant-producing bacteria, Bacillus Lz-2, was isolated from oil polluted water collected from Dongying Shengli oilfield, China. The factors that influence PAH solubilization such as biosurfactant concentration, pH, ionic strength and temperature were discussed. The results showed that the solubilities of naphthalene, phenanthrene and pyrene increased linearly with the rise of rhamnolipid biosurfactant dose above the biosurfactant critical micelle concentration (CMC). Furthermore, the molar solubilization ratio (MSR) values decreased in the following order: naphthalene > phenanthrene > pyrene. However, the solubility percentage increased and followed the opposite order: pyrene > phenanthrene > naphthalene. The solubilities of PAHs in rhamnolipid biosurfactant solution increased with the rise of pH and ionic strength, and reached the maximum values under the conditions of pH 11 and NaCl concentration 8 g·L− 1. The solubility of phenanthrene and pyrene increased with the rise of temperature.Download full-size image

•Rhamnolipid enhanced the oil biodegradation efficiency by approximately 9.22%.•Microbial species present unique response in biosurfactant-enhanced biodegradation.•The chemical dispersant GM-2 did not enhance the petroleum hydrocarbon biodegradation.The application of surfactants as dispersants for the remediation of contamination by a variety of petroleum hydrocarbons has received much attention from researchers worldwide because petroleum hydrocarbons may cause great potential harm to the marine environment and human health. A simulated bioremediation of a marine offshore oil spill was carried out to determine the contribution of chemical dispersants and biosurfactants on bioremediation of Haierzhan crude oil. Compared to chemical dispersants, biosurfactants were more effective at bioremediation of oil-contaminated marine environment. Rhamnolipids did enhance the bioremediation of petroleum hydrocarbon compounds with a coefficient of 9.02 using the RSM equation, which is much higher than a coefficient of 4.42 observed with the commercial chemical dispersants GM-2. There was a synergistic effect between Dioctyl Sodium Sulfosuccinate (DOSS) and GM-2 on the bioremediation of crude oil, with the coefficient for the two factors being 16.58, while, the contribution of rhamnolipid with GM-2 resulted in a negative effect on crude oil biodegradation, with a coefficient −7.72. The strain LSH-7′ grew very well when the medium were amended with biosurfactants as the sole carbon source, indicating that the biosurfactants have no toxic effect on the hydrocarbon-degrading microorganisms.Download high-res image (136KB)Download full-size image

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.

In this work, a hydrocarbon-degrading bacterium D3-2 isolated from petroleum contaminated soil samples was investigated for its potential effect in biodegradation of crude oil. The strain was identified as Acinetobacter sp. D3-2 based on morphological, biochemical and phylogenetic analysis. The optimum environmental conditions for growth of the bacteria were determined to be pH 8.0, with a NaCl concentration of 3.0% (w/v) at 30 °C. Acinetobacter sp. D3-2 could utilize various hydrocarbon substrates as the sole carbon and energy source. From this study, we also found that the strain had the ability to produce biosurfactant, with the production of 0.52 g L−1. The surface tension of the culture broth was decreased from 48.02 to 26.30 mN m−1. The biosurfactant was determined to contain lipopeptide compounds based on laboratory analyses. By carrying out a crude oil degradation assay in an Erlenmeyer flask experiment and analyzing the hydrocarbon removal rate using gas chromatography, we found that Acinetobacter sp. D3-2 could grow at 30 °C in 3% NaCl solution with a preferable ability to degrade 82% hydrocarbons, showing that bioremediation does occur and plays a profound role during the oil reparation process.

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 × 105, 1.0 × 105 and 2.5 × 105 cells per mL to 1.7 × 106, 8.5 × 105 and 2.5 × 106 cells per mL, respectively, which illustrated that the quality of seawater contaminated by crude oil was significantly improved by the bioremediation.

The efficiencies of free and immobilized microbial consortia in the degradation of different types of petroleum hydrocarbons were investigated. In this study, the biodegradation rates of naphthalene, phenanthrene, pyrene and crude oil reached about 80%, 30%, 56% and 48% under the optimum environmental conditions of free microbial consortia after 7 d. We evaluated five unique co-metabolic substances with petroleum hydrocarbons, α-lactose was the best co-metabolic substance among glucose, α-lactose, soluble starch, yeast powder and urea. The orthogonal biodegradation analysis results showed that semi-coke was the best immobilized carrier followed by walnut shell and activated carbon. Meanwhile, the significance of various factors that contribute to the biodegradation of semi-coke immobilized microbial consortia followed the order of: α-lactose > semi-coke > sodium alginate > CaCl2. Moreover, the degradation rate of the immobilized microbial consortium (47%) was higher than that of a free microbial consortium (26%) under environmental conditions such as the crude oil concentration of 3 g L−1, NaCl concentration of 20 g L−1, pH at 7.2–7.4 and temperature of 25 °C after 5 d. SEM and FTIR analyses revealed that the structure of semi-coke became more porous and easily adhered to the microbial consortium; the functional groups (e.g., hydroxy and phosphate) were identified in the microbial consortium and were changed by immobilization. This study demonstrated that the ability of microbial adaptation to the environment can be improved by immobilization which expands the application fields of microbial remediation.