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The extensive use of organic chemicals has resulted in the widespread distribution of hydrocarbon contaminants (HCs) in many ecosystems on a global scale. Many subterranean ecosystems can rapidly become anaerobic or even methanogenic following hydrocarbon contamination. Bacteria and archaea dominate communities in such systems and mediate the syntrophic processes that transform HCs into methane (CH4). The resulting CH4 is oxidized by anaerobic bacteria and archaea, either jointly or individually, in the presence of electron acceptors (e.g., sulfate, nitrate, nitrite, manganese, or ferric iron), a process that reduces CH4 emissions and, as a result, contributes to climate change mitigation. Although the possibility of the syntrophy of bacteria and archaea in the anaerobic transformation of HCs and methane oxidation is widely established, the specific pathways and syntrophic taxa involved are poorly understood. This paper reviews the syntrophy of bacteria and archaea in anaerobic HC degradation, with a focus on methanogenic processes. In addition, we discuss the role of bacteria and archaea in the anaerobic oxidation of methane (AOM) and its environmental significance. Given that much of the biotransformation of HCs driven by methanogenic and methanotrophic processes remains unknown, we propose a way forward to discover novel syntrophic partners and metabolic pathways in such anoxic systems. [ABSTRACT FROM AUTHOR]

Polyaromatic hydrocarbon, rhizoremediation, biostimulation and bioaugmentation, hydrocarbon contaminants, bioremediaiton Bioaugmentation of indigenous fungi resulted in an important shift of the bacterial populations, which was also linked to HMW-PAHs biodegradation efficiency, compared to biostimulation. Keywords: polyaromatic hydrocarbon; bioremediaiton; rhizoremediation; biostimulation and bioaugmentation; hydrocarbon contaminants EN polyaromatic hydrocarbon bioremediaiton rhizoremediation biostimulation and bioaugmentation hydrocarbon contaminants 1 3 3 07/24/21 20210722 NES 210722 Polyaromatic hydrocarbons (PAHs) are hazardous organic molecules with mutagenic, carcinogenic and genotoxic effects. [Extracted from the article]

A new method for the synthesis of nano zero-valent iron (nZVI) was developed in the present study. Ultrasonic waves, as a novel method, were used to synthesize the nanoparticles. The morphology and surface compositions of the particles were characterized by using FESEM, XRD, BET, and particle size analyzer. The synthesized nanoparticles were then utilized as a Fenton-like catalyst to degrade of hydrocarbon contaminants of soil. The effect of using ultrasonic waves in combination with nZVI for hydrocarbon degradation was also investigated. The effects of ultrasonic power, nZVI concentration, pH, hydrogen peroxide concentration, and temperature on remediation were studied. It was found that the new nZVI synthesized by an ultrasound-assisted method had high efficiency in soil remediation. The results indicated that the efficiency of removing hydrocarbons by nZVI was 98.57%. Finally, the optimum conditions of degradation were obtained when pH, ultrasonic power, nZVI concentration temperature, and hydrogen peroxide concentration were respectively equal to 3.5, 500 W, 0.4 gr.l-1, 40 °C, and 30 mM.

The presence of hydrocarbon contaminants in the vadose zone is a serious hazard for environment quality. Moreover, there is an urgent need for accurate and reliable knowledge of the hydraulics of hydrocarbon contaminants in porous media to enhance efficiency of NAPLs remediation methods. The objective of this study was to quantitatively assess the hydraulic properties of different porous media with petroleum, kerosene, diesel fuel, and gasoline. The related retention curves were then experimentally obtained. Parameters of the soils retention curves were obtained based on van Genuchten (1980), Brooks-Corey (1964), and Campbell (1974) retention models. The accuracy of models was then assessed by some statistics. The results indicated that, in most cases, air entry value was significantly increased in a petroleum retention curve despite the fact that it was decreased for other NAPLs. The pore size distribution parameters (i.e.,n,m,λ, and 1/b) of diesel fuel, kerosene, and gasoline did not change considerably compared to water retention curve. The Leverett (1941) scaling function was adopted to scale soil-fluid retention curves data in two-phase systems. The results indicated that, except for a silty clay medium and petroleum, the Leverett (1941) J-function could scale the LNAPL retention curves based on the water retention curve data. [ABSTRACT FROM AUTHOR]

Abstract: Gas hold-up (ɛ g), sauter mean bubble diameter (d 32) and oxygen transfer coefficient (k L a) were evaluated at four different alkane concentrations (0.05, 0.1, 0.3 and 0.5vol.%) in water over the range of superficial gas velocity (u g) of (1.18–23.52)×10−3 m/s at 25°C in a laboratory-scale bubble column bioreactor. Immiscible hydrocarbons (n-decane, n-tridecane and n-hexadecane) were utilized in the experiments as impurity. A type of anionic surfactant was also employed in order to investigate the effect of addition of surfactant to organic-aqueous systems on sauter mean bubble diameter, gas hold-up and oxygen transfer coefficient. Influence of addition of alkanes on oxygen transfer coefficient and gas hold-up, was shown to be dependent on the superficial gas velocity. At superficial gas velocity below 0.5×10−3 m/s, addition of alkane in air–water medium has low influence on oxygen transfer coefficient and also gas hold-up, whereas; at higher gas velocities slight addition of alkane increases oxygen transfer coefficient and also gas hold-up. Increase in concentration of alkane resulted in increase in oxygen transfer coefficient and gas hold-up and roughly decrease in sauter mean bubble diameter, which was attributed to an increase in the coalescence-inhibiting tendency in the presence of surface contaminant molecules. Bubbles tend to become smaller with decreasing surface tension of hydrocarbon, thus, oxygen transfer coefficient increases due to increasing of specific gas–liquid interfacial area (a). Empirical correlations were proposed for evaluating gas hold-up as a function of sauter mean bubble diameter, superficial gas velocity and interfacial surface tension as well as evaluating Sherwood number as a function of Schmidt, Reynolds and Bond numbers. [Copyright &y& Elsevier]

Abstract: Hydrocarbon compounds are sparsely soluble in aqueous systems but, nonetheless, their presence can influence significantly mass transfer behavior in gas–liquid systems. water–p-xylene and water–p-xylene–naphthalene mixtures were employed in order to determine the influence of dissolved hydrocarbons on mass transfer of oxygen from air bubbles to water. The surface renewal-stretch model has been modified for predicting the volumetric mass transfer coefficient, , in the presence of surface contaminant molecules, including hydrocarbon compounds and surfactants. Theory and experimental oxygen transfer results were found to be in satisfactory agreement with average absolute deviation of 15%. Pendant drop and contact angle measurements by axisymmetric drop shape analysis were carried out to determine the reduction in surface tension of water due to the addition of p-xylene and naphthalene. Molecular orientation caused by instantaneous attraction of the polar moieties of the organic compounds toward the water interface has been found to be the main cause of reduction in surface tension. It was predicated that changes in gas–liquid mass transfer behavior resulted from surface contamination and that the significant parameter was the reduction in surface tension. [Copyright &y& Elsevier]

Abstract: Coastal marine environments, especially semienclosed systems such as bays, are under unrelenting stress caused by urban and industrial development. Biomonitoring plays a vital role in strategies to identify, assess, and control stressors. However, due to the magnitude of the challenge there is a demand for new and innovative approaches to provide timely and accessible information to environmental managers and policy makers. The present work aimed to assess hydrocarbon levels in sediments from petroleum-related industrial areas at Todos os Santos Bay (Brazil) and associate them to toxicity-induced responses (neutral red retention (NRR) assay) by the burrowing clam Anomalocardia brasiliana. Surface sediments collected during the dry and rainy seasons were analyzed for aliphatic and aromatic hydrocarbons. At the control site, hydrocarbon levels were low and mainly biogenic. The aliphatic hydrocarbon (“total unresolved complex mixture,” alkanes, and isoprenoids) concentrations indicated a chronic situation with very little “fresh” oil contamination at the oil-related sites. The polycyclic aromatic hydrocarbons indicated sites moderately contaminated by chronic oil and some pyrolytic input. The effects of those contaminants were assessed by the lysosomal NRR assay applied to A. brasiliana hemocytes. Sediment toxicity at the oil-related sites was evidenced by the lowered capacity of the lysosomes to retain the neutral red dye compared to results from the control site. This research indicates that the NRR assay is a useful and efficient screening technique able to discriminate polluted from clean sites. [Copyright &y& Elsevier]

• The persistence of toxic substances causes threats to the living ecosystems. • Effective remediation of contaminated environment is of supreme interest. • Nanoparticle-stabilized surfactant foams are effective to remediate hydrocarbons. Contaminated environments posed serious threats to the ecosystems and their living beings. Suitable preventive approaches should be adopted for effective remediation of contaminated environments to remove or lower their health and environmentally-related hazardous aspects. Petroleum or traces of petroleum contamination from oil fields and refineries to exposed soil in the form of gasoline, petrol, diesel, and used motor oil are a rich source of potential damage to the environment. Conventional ways of treatment and management of hydrocarbon are complicated, insufficient, and expensive. Herein, we reviewed a smart approach for the removal of petroleum source contamination from exposed soil using environment-friendly chemical surfactants and nanoscale surfactant system. The host/guest complexes formation of surfactants with the hydrocarbons (hydrophobic contaminants) of soil and water by the encapsulation mechanism of hydrophobes into the (micelles) a self-assembly aggregation of surfactants. Recently, surfactants stabilized by nanoparticles (NPs) acquired more importance and popularity over surfactant alone. The persistence of diverse hydrocarbon-based contaminants and the mechanisms of removal using pristine surfactants or NP-stabilized surfactant foams are discussed with suitable examples. In summary, herein, an effort has been made to present the notable potentialities of pristine surfactants and NP-stabilized surfactant foams to remediate the petroleum hydrocarbon contaminated soil for a greener and sustainable ecosystem. [ABSTRACT FROM AUTHOR]