Evaluation of B. subtilis SPB1 biosurfactants' potency for diesel-contaminated soil washing: optimization of oil desorption using Taguchi design

Low solubility of certain hydrophobic soil contaminants limits remediation process. Surface-active compounds can improve the solubility and removal of hydrophobic compounds from contaminated soils and, consequently, their biodegradation. Hence, this paper aims to study desorption efficiency of oil from soil of SPB1 lipopeptide biosurfactant. The effect of different physicochemical parameters on desorption potency was assessed. Taguchi experimental design method was applied in order to enhance the desorption capacity and establish the best washing parameters. Mobilization potency was compared to those of chemical surfactants under the newly defined conditions. Better desorption capacity was obtained using 0.1 % biosurfacatnt solution and the mobilization potency shows great tolerance to acidic and alkaline pH values and salinity. Results show an optimum value of oil removal from diesel-contaminated soil of about 87 %. The optimum washing conditions for surfactant solution volume, biosurfactant concentration, agitation speed, temperature, and time were found to be 12 ml/g of soil, 0.1 % biosurfactant, 200 rpm, 30 °C, and 24 h, respectively. The obtained results were compared to those of SDS and Tween 80 at the optimal conditions described above, and the study reveals an effectiveness of SPB1 biosurfactant comparable to the reported chemical emulsifiers. (1) The obtained findings suggest (a) the competence of Bacillus subtilis biosurfactant in promoting diesel desorption from soil towards chemical surfactants and (b) the applicability of this method in decontaminating crude oil-contaminated soil and, therefore, improving bioavailability of hydrophobic compounds. (2) The obtained findings also suggest the adequacy of Taguchi design in promoting process efficiency. Our findings suggest that preoptimized desorption process using microbial-derived emulsifier can contribute significantly to enhancement of hydrophobic pollutants' bioavailability. This study can be complemented with the investigation of potential role in improving the biodegradation of the diesel adsorbed to the soil.     

A DFT study on the carbamates formation through the absorption of CO2 by AMP

DFT calculations in gas and aqueous solution phases have been performed to study the mechanism of carbamate formation by the absorption of CO₂ in 2-amino-2-methyl-1-propanol (AMP). The results reveal the importance of considering the effect of water as solvent for the reaction to proceed. Furthermore water molecules play an important role as a basic reactant leading to stable intermediates formation. These results point at a single-step, third order reaction as the most probable mechanism for the formation of carbamate by the absorption process.     

Detection and quantification of chlordecone in contaminated soils from the French West Indies by GC-MS using the 13C10-chlordecone stable isotope as a tracer

Chlordecone is an organochlorine insecticide that has been widely used to control banana weevil in the French West Indies. As a result of this intense use, up to 20,000 ha are contaminated by this insecticide in the French West Indies, and this causes environmental damage and health problems. A scenario of exposure was drawn by French authorities, based on land usage records. Many efforts have been made to monitor the occurrence of chlordecone and its main metabolites using different analytical methods, including GC, GC/MS, LC/MS, and NIRS. Although these different methods allow for the detection and quantification of chlordecone from soils, none of them estimate the bottleneck caused by extraction of this organochlorine from soils with high adsorption ability. In this study, we used ¹³C₁₀-chlordecone as a tracer to estimate chlordecone extraction yield and to quantify chlordecone in soil extracts based on the ¹³C/¹²C isotope dilution. We report the optimization of ¹³C₁₀-chlordecone extraction from an Andosol. The method was found to be linear from 0.118 to 43 mg kg^?1 in the Andosol, with an instrumental detection limit estimated at 8.84 μg kg^?1. This method showed that chlordecone ranged from 35.4 down to 0.18 mg kg^?1 in Andosol, Nitisol, Ferralsol, and Fluvisol soil types. Traces of the metabolite β-monohydrochlordecone were detected in the Andosol, Nitisol, and Ferralsol soil samples. This last result indicates that this method could be useful to monitor the fate of chlordecone in soils of the French West Indies.     

Air–dust-borne associations of phototrophic and hydrocarbon-utilizing microorganisms: promising consortia in volatile hydrocarbon bioremediation

Aquatic and terrestrial associations of phototrophic and heterotrophic microorganisms active in hydrocarbon bioremediation have been described earlier. The question arises: do similar consortia also occur in the atmosphere? Dust samples at the height of 15?m were collected from Kuwait City air, and analyzed microbiologically for phototrophic and heterotrophic hydrocarbon-utilizing microorganisms, which were subsequently characterized according to their 16S rRNA gene sequences. The hydrocarbon utilization potential of the heterotrophs alone, and in association with the phototrophic partners, was measured quantitatively. The chlorophyte Gloeotila sp. and the two cyanobacteria Nostoc commune and Leptolyngbya thermalis were found associated with dust, and (for comparison) the cynobacteria Leptolyngbya sp. and Acaryochloris sp. were isolated from coastal water. All phototrophic cultures harbored oil vapor-utilizing bacteria in the magnitude of 10⁵?g^?1. Each phototrophic culture had its unique oil-utilizing bacteria; however, the bacterial composition in Leptolyngbya cultures from air and water was similar. The hydrocarbon-utilizing bacteria were affiliated with Acinetobacter sp., Aeromonas caviae, Alcanivorax jadensis, Bacillus asahii, Bacillus pumilus, Marinobacter aquaeolei, Paenibacillus sp., and Stenotrophomonas maltophilia. The nonaxenic cultures, when used as inocula in batch cultures, attenuated crude oil in light and dark, and in the presence of antibiotics and absence of nitrogenous compounds. Aqueous and diethyl ether extracts from the phototrophic cultures enhanced the growth of the pertinent oil-utilizing bacteria in batch cultures, with oil vapor as a sole carbon source. It was concluded that the airborne microbial associations may be effective in bioremediating atmospheric hydrocarbon pollutants in situ. Like the aquatic and terrestrial habitats, the atmosphere contains dust-borne associations of phototrophic and heterotrophic hydrocarbon-utilizing bacteria that are active in hydrocarbon attenuation.     

A Critical Review on Natural Fibers Modifications by Graft Copolymerization for Wastewater Treatment

Graft copolymerization is a distinctive approach to modify the inherently cheap natural fibers (NFs) using different initiators to incorporate synthetic polymer side chains allowing development of novel types of hybrid materials. This method has been widely applied to develop a variety of NFs based adsorbents for decontamination of toxic pollutants from the aqueous environment. However, the development of high-performance adsorbents from NFs is steady challenged by the need to preserve the sustainability during graft modifications and applications. This article critically reviews the progress on modifications of NFs by graft copolymerization of polar monomers on NFs using various initiating methods and their applications in wastewater treatment. Particularly, the applications of the grafted NFs in removal of heavy metal ions, synthetic dyes, oil spills and extraction of precious metals from wastewater are elaborated. The critical challenges to the viability and sustainability of NFs-based adsorbents with respect to functionalization by graft copolymerization and environmental impacts are discussed and the future research directions are also outlined.