Effects of rhamnolipid biosurfactants on removal of phenanthrene from soil

Solubilizing agents may enhance remediation of-soils contaminated with hydrophobic organic contaminants by diminishing sorption of the contaminants or increasing desorption rates. The effectiveness of rhamnolipid biosurfactants to enhance the removal of sorbed contaminants from soil was determined using column studies. Soil columns were contaminated with phenanthrene and subsequently eluted with electrolyte solution or with electrolyte solution containing 500 mg/L rhamnolipid. For the four soils studied, removal of 50% of the phenanthrene from the soil columns was accomplished in a 2-5-fold shorter time period, and the time required for 90% removal was reduced up to 3.5-fold when elution was performed with the rhamnolipid-containing solution as compared to the treatment without rhamnolipid. The effect of rhamnolipid on the removal of phenanthrene was satisfactorily simulated using independently obtained parameters with a two-component advective-dispersive model accounting for micellar solubilization and admicellar sorption. A more detailed analysis of the system showed that desorption rates of phenanthrene in the presence of 500 mg/L rhamnolipid were higher than predicted on the basis of desorption rate constants of phenanthrene determined in the absence of rhamnolipid. It is concluded that rhamnolipid enhanced the removal of phenanthrene mainly by micellar solubilization and also by influencing sorption kinetics

Assessment of the use of partitioning and interfacial tracers to determine the content and mass removal rates of nonaqueous phase liquids

It was assessed whether partitioning and interfacial tracers can be used to determine the content and mass removal rate of nonaqueous phase liquid (NAPL) in porous media. Retardation factors for these tracers were determined for five different model matrices contaminated with hexadecane as NAPL. The retardation of the partitioning tracer 2,4-dimethyl-3-pentanol was correlated with the degree of NAPL saturation for four of the five matrices (r(2) = 0.93, n = 8), The observed retardation factors matched the retardation factors predicted with the independently determined hexadecane-water partitioning constant and the degree of NAPL saturation, indicating that this tracer may be used to estimate the degree of NAPL saturation of porous media. The mass removal rates of NAPL from columns packed with different matrices were determined by measuring the amount of hexadecane in the column effluent during elution with electrolyte solution. These removal rates differed over 3 orders of magnitude, dependent on the matrix used. The retardation of the interfacial tracer alkylbenzenesulfonate was higher for matrices with higher NAPL mass removal rates but was not correlated to the degree of NAPL saturation. This indicates that the retardation factors of alkylbenzenesulfonates in NAPL-contaminated media contain information related to the NAPL mass removal rates

Rhamnolipid Stimulates Uptake of Hydrophobic Compounds by Pseudomonas aeruginosa

The biodegradation of hexadecane by five biosurfactant-producing bacterial strains (Pseudomonas aeruginosa UG2, Acinetobacter calcoaceticus RAG1, Rhodococcus erythropolis DSM 43066, R. erythropolis ATCC 19558, and strain BCG112) was determined in the presence and absence of exogenously added biosurfactants. The degradation of hexadecane by P. aeruginosa was stimulated only by the rhamnolipid biosurfactant produced by the same organism. This rhamnolipid did not stimulate the biodegradation of hexadecane by the four other strains to the same extent, nor was degradation of hexadecane by these strains stimulated by addition of their own biosurfactants. This suggests that P. aeruginosa has a mode of hexadecane uptake different from those of the other organisms. Rhamnolipid also enhanced the rate of epoxidation of the aliphatic hydrocarbon α,ω-tetradecadiene by a cell suspension of P. aeruginosa. Furthermore, the uptake of the hydrophobic probe 1-naphthylphenylamine by cells of P. aeruginosa was enhanced by rhamnolipid, as indicated by stopped-flow fluorescence experiments. Rhamnolipid did not stimulate the uptake rate of this probe in de-energized cells. These results indicate that an energy-dependent system is present in P. aeruginosa strain UG2 that mediates fast uptake of hydrophobic compounds in the presence of rhamnolipid

Adsorption of a Multicomponent Rhamnolipid Surfactant to Soil

The adsorption of rhamnolipid, a multicomponent biosurfactant with potential application in soil remediation, to two sandy soils was investigated using batch and column studies. The surfactant mixture contained six anionic components differing in lipid chain length and number of rhamnose moieties. Batch adsorption experiments indicated that the overall adsorption isotherms of total surfactant and of the individual components leveled off above a concentration at which micelles were formed. Column experiments showed that the retardation factors for the total surfactant and for the individual components decreased with increasing influent concentration. Extended tailing was observed in the distal portion of the surfactant breakthrough curve. The concentration-dependent retardation factors and the extended tailing are in accordance with the nonlinear (concave) adsorption isotherms found in the batch adsorption studies. The more hydrophobic rhamnolipid components were preferentially adsorbed, but adsorption was not correlated with the organic carbon content of the soil. This suggests that adsorption of rhamnolipid to soil is not a partitioning process but mainly an interfacial adsorption process.

Kinetics of hydrolysis in aqueous solution of 1-benzoyl-1,2,4-triazole; the role of pairwise and triplet Gibbs energy interaction parameters in describing the effects of added salts and added alcohols

Kinetic data are reported for the spontaneous hydrolysis of 1-benzoyl-1,2,4-triazole in aqueous solutions at ambient pressure and 298.2 K, in aqueous solutions containing added ethanol, propanol and sodium chloride. Kinetic data are also reported for the same reaction in aqueous mixtures of sodium chloride and ethanol. When either ethanol or propanol are added the rate constant k decreases, plots of ln(k) vs. molality of alcohol being linear. The patterns are accounted for using pairwise Gibbs energy interaction parameters. The rate constant k decreases more dramatically when sodium chloride is added. This pattern is accounted for using pairwise and triplet interaction parameters. The dependence of rate constant on molality of added ethanol in solutions containing fixed molalities of sodium chloride deviates from that predicted using the pairwise interaction parameters indicating a non-additivity of salt and alcohol effects on the rate constant. The deviations increase with increase in molalities of both added salt and added solvent in a direction consistent with a disruption of the substrate-alcohol hydrophobic interactions by added salt.