Electrochemical Studies on De-Emulsification: Effect of a Biosurfactant Produced by Bacillus subtilis MO-1

Model emulsions were de-emulsified using a biosurfactant produced by Bacillus subtilis MO-1 mixed with chemical de-emulsifiers. The speed and efficiency of de-emulsification by polyether type de-emulsifier (G-17) were enhanced by combined use of a biosurfactant produced by B. subtilis MO-1 (BS); this effect was more apparent at low concentrations. Polyether/biosurfactant synergy was confirmed by electrochemical measurement of the interfacial film electrical resistance (R _m ) and capacitance (C _m ) during de-emulsification. These values were closely related to the rate of water removal, demonstrating that electrical techniques are suitable for studying de-emulsification phenomena.     

Production and properties of a biosurfactant applied to polycyclic aromatic hydrocarbon solubilization

Microorganisms isolated from a soil sample collected from a gasoline filling station (located in Guwahati) were tested for their pyrene- and anthracene-degrading potential. Preliminary studies showed the ability of the organism to grow on carbon-free mineral medium (CFMM) supplemented with pyrene as the sole source of carbon. The organisms were found to produce a bioemulsifier when grown on CFMM with glucose or glycerol and/or pyrene as the carbon source. The organisms could also utilize anthracene when grown on mineral salt medium along with 2% glycerol. Within 2 d, anthracene concentration dropped less than 30% of the original concentration. Approximately 100 mg of the emulsifier was isolated from 25 mL of the 5-d-grown culture. The emulsifier was tested to produce emulsion with both an aliphatic and an aromatic group of hydrocarbons and resulting emulsions were found to be stable for a long period of time when keptat 10–15°C. The emulsifier was also quite stable in a pH range of 3.0–11.0. In a concentration range of 0.5–10 mg/mL, it resulted in a linear increment of apparent pyrene and anthracene solubility in water.     

生物表面活性剂的特性及应用

生物表面活性剂可分为五类:糖脂、多糖脂、脂肽、磷脂及中性脂。木文简述了生物表面活性剂的特性,着重介绍了糖脂化合物的结构,物理化学性质及应用。     

Dispersion of Colloidal Alumina using a Rhamnolipid Biosurfactant

Dispersability of colloidal alumina in water has been studied using a rhamnolipid containing biosurfactant. Zeta potential measurements revealed that the surface charge of alumina was altered due to adsorption of the biosurfactant and the iso‐electric‐point of alumina shifted from pH 9 to 6.3. Sedimentation tests indicated that the alumina suspension was completely dispersed for 3–5 hours in the presence of biosurfactant after which some settling was observed. Stability of the suspension in the time period studied was found to be independent of pH. Capillary suction time measurements showed that the alumina suspension was dispersed in the presence of the biosurfactant and varied with pH. Maximum dispersion is obtained in the pH range of 3.5–5 and 7–11 while a minimum is obtained around pH 6. This behavior is consistent with the changes in zeta potential in the presence of the biosurfactant and thus capillary suction time measurements appeared to be more reliable than the sedimentation tests. Optimization studies showed that about 60 mg/g of biosurfactant was necessary for best dispersion and dispersion could be done up to 40% solids. The application of a natural biosurfactant for dispersing colloidal alumina has been demonstrated.     

Silver nanoparticles formed in bio- and chemical syntheses with biosurfactant as the stabilizing agent

In this work, the comparison of the physical properties of silver nanoparticles (AgNPs) obtained via the reduction of silver nitrate (AgNO₃) in biological and chemical (model) syntheses supplemented with the biosurfactant surfactin is described. In the studies, two strains of Bacillus subtilis (denoted T’1 and I’1a) were used. The biological synthesis of AgNPs was performed using supernatants obtained from cultures of bacteria growing on brewery effluents, molasses, and Luria–Bretani (LB) medium. In model experiments, ascorbic acid served as the reductant; surfactin acted as the stabilizing agent. The surfactin concentrations were adjusted to 5 and 30?mg/L, which corresponded to minimum and maximum surfactin concentrations as measured in the supernatants obtained from the B. subtilis cultures. The chemical synthesis was carried out at acidic as well as alkaline pH. Dynamic light scattering (DLS) revealed that in model and biological samples, single AgNPs were accompanied by aggregated structures. Transmission electron microscopy showed that the contribution of the aggregates in bacterial supernatants and in chemical synthesis is negligible under acidic conditions. However, in the alkaline environment, this contribution predominates. In the model experiments, smaller nanoparticles were formed with higher concentrations of surfactant. The presence of surfactin significantly increased the stability of AgNPs in both bio- and chemical syntheses.     

Bioremediation of Aged Petroleum Oil Contaminated Soil: From Laboratory Scale to Full Scale Application

Large quantity of aged petroleum oil contamination such as dehydrated oil sludge, generated in the disposal process of oil-containing sewage in Indonesia. This study aims to investigate the OSCS removal by mean of bioremediation technique. Results found that petrofilic consortia and biosurfactants addition increased the removal efficiency up to 46% and 85%, respectively. At full scale application, this technique succeed in removing of 46 g TPH per kg soil from 4 883 m³ of OSCS during 16 mo of treatment. These results suggest that petrofilic consortia and biosurfactants addition stimulate the biodegradation and overcome the limitation of OSCS degradation process.     

生物表面活性剂鼠李糖脂及其复配体系界面行为和性质的介观模拟

采用介观模拟耗散颗粒动力学（DPD）方法研究不同结构的鼠李糖脂在油/水界面行为差异和结构对活性的影响,并探讨了其与不同类型表面活性剂如十二烷基硫酸钠（SDS）、十二烷基苯磺酸钠（SDBS）、脂肪醇聚氧乙烯醚（AEO3）复配时体系的界面性质,给出不同结构的鼠李糖脂的行为特点及与常用合成表面活性剂在油/水界面的相互作用规律...     

Biodegradation of n-hexadecane by bacterial strains B1 and B2 isolated from petroleum-contaminated soil

Two hydrocarbon-biodegrading bacterial strains,B1 and B2,were isolated from petroleum-contaminated soil collected from Tianjin,China.The strains were identified as Pseudomonas aeruginosa(B1) and Acinetobacter junii(B2).The degradation rate of n-hexadecane by B1 and B2 reached 96% and 78% respectively after 7 days,though the strains employed different mechanisms of degradation.The results showed that B2 was not able to use glucose as carbon source.B1 could produce glycolipid surfactants using glucose as the carbon source,according to the results of blue agar plate analysis and thin layer chromatography(TLC),and the bacterial culture of B1 had a high oil discharge and emulsification activity.Both B1 and B2 could produce biosurfactants with hexadecane as the sole carbon source,but their modes of action were different.The carbon source was found to affect the cell surface hydrophobicity.Cell surface hydrophobicity was poor with glucose as the carbon source,but enhanced when hexadecane was used as the carbon source.     

Adsorption of tricarboxylic acid biosurfactant derived from spiculisporic acid on titanium dioxide surface

In the present study, adsorption isotherms of a polycarboxylic-acid-type biosurfantant, the sodium salt of (2-(2-carboxyethyl)-3-decyl maleic anhydride) (DCMA-3Na), on TiO₂, zeta potential, and changes in particle aggregate size as a function of biosurfactant concentration, solid-liquid ratio and pH were systematically investigated. The adsorption of DCMA-3Na on the surface of TiO₂ shows a relatively weak dependence on pH, unlike the adsorption behavior of chemically-synthesized surfactants. Adsorption of DCMA-3Na still occurs at pH above the isoelectric points of TiO₂ due to the buffering capacity, which is due to three carboxylate functional groups in the hydrophilic moiety of DCMA-3Na. Since DCMA-3Na has three anionic head groups, the zeta potential of TiO₂ at pH 3 decreases very steeply from positive to negative values as the surface charges are neutralized by the adsorption of biosurfactants. Trends in zeta potentials as a function of equilibrium DCMA-3Na concentration are quite closely related to the changes in flocculation of individual TiO₂ particles.     

Development of continuous surfactin production from potato process effluent by Bacillus subtilis in an airlift reactor

The biosurfactant surfactin has the potential to aid in the recovery of subsurface organic contaminants (environmental remediation) or crude oils (oil recovery). However, high medium and purification costs limit its use in these high-volume applications. In previous work, we showed that surfactin can be produced from an inexpensive low-solids (LS) potato process effluent with minimal amendments or pretreatments. Previous research has also shown that 95% or more of the surfactin in Bacillus subtilis cultures can be recovered by foam fractionation. In this work, we present the results of research to integrate surfactin production with foam fractionation. Experiments were performed in an airlift reactor, with continuous collection of the foam through a tube at the top of the column. Preliminary results using both purified potato starch and unamended low-solids potato process effluent as substrates for surfactin production indicate that the process is oxygen limited and that recalcitrant indigenous bacteria in the potato process effluent may hamper continuous surfactin production.