Applications of functional nanoparticle-stabilized surfactant foam in petroleum-contaminated soil remediation.

Surfactant foam (SF) can be used to remediate petroleum-contaminated soil because of its easy transfer to inhomogeneous and low-permeability formations. Nanoparticles (NPs) not only stabilize SF under extreme conditions but also impart various functions, aiding the removal of petroleum contaminants. This review discusses the stabilization mechanisms of nanoparticle-stabilized SF (NP-SF) as well as the effects of NP size, chargeability, wettability, and NP-to-surfactant ratio on foam stability. SF stabilized by inert SiO2 NPs is most commonly used to remediate soil contaminated with crude oil and diesel. Low dose of SF stabilized by nano zero-valent iron is cost-effective for treating soil contaminated with chlorinated organics and heavy metal ions. The efficiency and recyclability of Al2O3/Fe3O4 NPs in the remediation of diesel and crude oil contamination could be enhanced by applying a magnetic field. This review provides a theoretical basis and practical guidelines for developing functional NP-SF to improve the remediation of petroleum-contaminated soils. Future research should focus on the structural design of photocatalytic NPs and the application of catalytic NP-SF in soil remediation.

[Extraction of surface active substance and analysis of demulsifying characteristics for the demulsifying strain Alcaligenes sp. S-XJ-1].

Extraction and identification of surface active substance of Alcaligenes sp. S-XJ-1, as well as description of its emulsion breaking process were conducted to reveal the demulsifying characteristics of this demulsifying strain. Alkali solvent was adopted in the extraction process with conditions optimized as 35 degrees C, 0.08 mol x L(-1) of alkali concentration, 12 g x L(-1) of sample to solution ratio, and 4 h of extraction time by launching both single-factor and orthogonal tests. Under this optimal condition, the extracted surface active substance (the extraction ratio was 36.1%) achieved 77% emulsion breaking ratio for 500 mg x L(-1) within 48 h. FT-IR showed the existence of glycolipids, lipids and proteins in the surface active substance, the molecular weight of which mainly scattered between 55 and 61 256. Saccharides, lipids and proteins were identified as the three chief components in surface active substance with the content of 22.2%, 7.5% and 13.4%, respectively. The proteins were further proved to take the most responsibility for the emulsion breaking ability. Moreover, obvious difference in the emulsion breaking process was demonstrated between the original demulsifying strain S-XJ-1 and the extracted surface active substance by real time observation of Turbiscan Lab Expert. The results suggested that the demulsifying efficiency of the strain was jointly contributed by its surface active substance and demulsifying cell morphology, and the former possessed higher functional priority than the latter.

Relationship of cell-wall bound fatty acids and the demulsification efficiency of demulsifying bacteria Alcaligenes sp. S-XJ-1 cultured with vegetable oils.

Considering that the surface properties of demulsifying cells correlate with their demulsification efficiency, the demulsifying bacteria Alcaligenes sp. S-XJ-1 with various surface properties were obtained using different vegetable oils as carbon sources. The results show that better performance was achieved with demulsifying bacteria S-XJ-1 possessing a relatively high cell surface hydrophobicity (CSH) and total unsaturated degree for the cell-wall bound fatty acids. There also appeared to be a correlation between the specific cell-wall bound fatty acid components of the bacteria, in terms of carbon chain length or degree of unsaturation, and either CSH or demulsification efficiency. The fatty acids attached to the cell wall were mainly composed of palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3). C18:1 and C18:2 had a positive effect on the formation of CSH, while C18:0 and C18:3 had the opposite effect.

Optimization of biodemulsifier production from Alcaligenes sp. S-XJ-1 and its application in breaking crude oil emulsion.

A biodemulsifier-producing strain of Alcaligenes sp. S-XJ-1, isolated from petroleum-contaminated soil of the Karamay Oilfield, exhibited excellent demulsifying ability. The application of this biodemulsifier significantly improved the quality of separated water compared with the chemical demulsifier, polyether, which clearly indicates that it has potential applications in the crude oil extraction industry. To optimize its biosynthesis, the impacts of carbon sources, nitrogen sources and pH were studied in detail. Paraffin, a hydrophobic carbon source, favored the synthesis of this cell wall associated biodemulsifier. The nitrogen source ammonium citrate stimulated the production and demulsifying performance of the biodemulsifier. An alkaline environment (pH 9.5) of the initial culture medium favored the strain's growth and improved its demulsifying ability. The results showed paraffin, ammonium citrate and pH had significant effects on the production of the biodemulsifier. These three variables were further investigated using a response surface methodology based on a central composite design to optimize the biodemulsifier yield. The optimal yield conditions were found at a paraffin concentration of 4.01%, an ammonium citrate concentration of 8.08 g/L and a pH of 9.35. Under optimal conditions, the biodemulsifier yield from Alcaligenes sp. S-XJ-1 was increased to 3.42 g/L.

[Treatment of oilfield produced water by biological methods-constructed wetland process and degradation characteristics of organic substances].

Hydrolysis acidification-aerobic-constructed wetland process and hydrolysis acidification-constructed wetland were used to treat oilfield produced water after the pretreatment of oil separation-coagulation. Gas chromatography-mass spectrometry was used to study the degradation characteristics of organic substances during the treatment process. The results showed that COD and ammonia nitrogen of both the two process effluents were below 80 mg/L and 15 mg/L, respectively, when HRT was 20 h for hydrolysis acidification, 10 h for aeration and 2 d for constructed wetlands or when HRT was 20 h for hydrolysis acidification and 4 d for constructed wetland. The results of GC-MS analysis showed that biodegradability of the oil produced water was significantly improved in hydrolysis acidification. Substantial removal of benzene compounds was achieved in aerobic and constructed wetland.

[Experimental study on the mechanism of oilfield wastewater treatment by using hydrolysis-acidification with aerobic biological processes].

Hydrolysis-acidification + aerobic biological processes were conducted experimentally to treat oilfield wastewater pretreated with physical and chemical treatment in Xinjiang oilfield. The results showed that when the COD concentration in influent was 190-220 mg x L(-1), that in effluent reduced to 65-75 mg x L(-1) under HRT of 10h in both hydrolysis-acidification process and aerobic biological process, reaching the strictest requirement of Effluent Standards for Wastewater from Petroleum Development Industry (GB3550-83). Using GC/MS technology, the relative content of various organic pollutants was analyzed to discover the transfer and degradation law in the oilfield wastewater in biological treatment process. The system of DNA extraction technique, PCR and DGGE reacting systems were practical to analyze the microbial community in the hydrolysis-acidification and aerobic biological processes. The predominant sequences of several 16S rDNA DGGE fragments were determined and confirmed in comparison in GeneBank (NCBI).