Raina M. Miller

Removal of Cadmium, Lead, and Zinc from Soil by a Rhamnolipid Biosurfactant

Complexation of cadmium, lead, and zinc (singly and in a mixture) by a monorhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 was studied in batch solution and soil experiments. Conditional stability constants (log K L ) for metalrhamnolipid complexation in a buffered medium (0.1 M Pipes, pH 6.8) were determined in duplicate using an ion-exchange technique and averaged 6.5 (Cd 2+ ), 6.6 (Pb 2+ ), and 5.4 (Zn 2+ ) ; these values are similar or slightly higher than literature values for Cd 2+ and Pb 2+ complexation with fulvic acid and activated sludge solids. To determine the ability of rhamnolipid to desorb soil-bound metals, rhamnolipid solutions (12.5, 25, 50, and 80 mM) were added to soil containing sorbed Cd 2+ (1.46 mmol kg -1 ), Pb 2+ (1.96 mmol kg -1 ), or a mixture of Pb 2+ -Cd 2+ -Zn 2+ (3.4 mmol kg -1 ). At 12.5 and 25 mM rhamnolipid, rhamnolipid sorption to soil exceeded 78%, and less than 11% of soil-bound Cd 2+ and Zn 2+ was desorbed. However, ion exchange of bound metals with K + present in the rhamnolipid matrix could account for the removal of between 16 and 48% of the sorbed Cd 2+ and Zn 2+ . At 50 and 80 mM rhamnolipid, rhamnolipid sorption to soil decreased to between 20 and 77%, and the removal of Cd 2+ and Zn 2+ could exceed the removal by ion exchange by as much as 3-fold. The behavior of Pb 2+ was quite different. Less than 2% of soil-bound Pb 2+ was desorbed due to ion exchange, although up to 43% was desorbed by 80 mM rhamnolipid.

Biosurfactant-enhanced removal of residual hydrocarbon from soil

Abstract An anionic monorhamnolipid biosurfactant produced by Pseudomonas aeruginosa was investigated for its potential to remove residual hexadecane from sand columns. In a series of column experiments, residual hexadecane saturation was established by pumping 14C-hexadecane into water-saturated sand columns and then flushing with water at a velocity of 25 cm h−1. Monorhamnolipid solutions of varying concentration were then applied to the columns at a velocity of 15 cm H−1 to remove the residual hexadecane. Of the rhamnolipid concentrations tested, which ranged from 40 to 1500 mg l−1, the optimal concentration for residual removal was 500 mg l−1, approximately ten times the critical micelle concentration (cmc). Approximately 84% of the residual was removed from the column packed with 20 30 mesh sand, and 22% was removed from the 40 50 mesh column. The primary mechanism for residual removal was mobilization (displacement and dispersion), whereas solubilization was found to be insignificant. The performance of monorhamnolipid was compared with that of two synthetic surfactant solutions on a mass basis (500 mg l−1) for the 40 50 mesh sand. Sodium dodecyl sulfate (0.2 X cmc), and polyoxyethylene (20) sorbitan monooleate (38 × cmc), removed 0% and 6.1% of the residual saturation, respectively.

Complexation of cadmium by a rhamnolipid biosurfactant.

The potential of microbially-produced surfactants (biosurfactants) to complex heavy metals was investigated in this study. Batch solution studies using a model metal, cadmium, and an anionic monorhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 showed that complexation of the metal and biosurfactantwas rapid and stable and achieved high reductions in the free Cd 2+ concentration. For example 92% of Cd 2+ (0.72 mM) was complexed by 7.3 mM rhamnolipid, and 97% of Cd 2+ (0.36 mM) was complexed by 3.9 mM rhamnolipid. Under the experimental conditions used, the maximum complexation capacity of the rhamnolipid was 0.2 Cd 2+ /rhamnolipid on a molar basis

Influence of cation type, ionic strength, and pH on solubilization and mobilization of residual hydrocarbon by a biosurfactant

This study investigated the effect of cation type, ionic strength, and pH on the performance of an anionic monorhamnolipid biosurfactant for solubilization and removal of residual hexadecane from sand. Three common soil cations, Na+, Mg2+, and Ca2+, were used in these experiments and hexadecane was chosen to represent a nonaqueous phase liquid (NAPL) less dense than water. Results showed that hexadecane solubility in rhamnolipid solution was significantly increased by the addition of Na+ and Mg2+. Addition of up to 0.2 mM Ca2+ also increased hexadecane solubility. For Ca2+ concentrations greater than 0.2 mM there was little effect on hexadecane solubility due to competing effects of calcium-induced rhamnolipid precipitation and enhanced hexadecane solubilization. Efficiency of NAPL solubilization can be expressed in terms of molar solubilization ratios (MSR). The results showed that MSR values for hexadecane in rhamnolipid solutions increased 7.5-fold in the presence of 500 mM Na+, and 25-fold in the presence of 1 mM Mg2+. The presence of cations also reduced the interfacial tension between rhamnolipid solutions and hexadecane. For example, an increase in Na+ from 0 to 800 mM caused a decrease in interfacial tension from 2.2 to 0.89 dyn cm−1. Similarly, decreasing pH caused a reduction in interfacial tension. The lowest interfacial tension value observed in this study was 0.02 dyn cm−1 at pH 6 in the presence of 320 mM Na+. These conditions were also found to be optimal for removal of hexadecane residual from sand columns, with 58% of residual removed within three pore volumes. The removal of residual NAPL from the packed columns was primarily by mobilization, even though solubilization was significantly increased in the presence of Na+.

Sequential degradation of chlorophenols by photolytic and microbial treatment

Using the radiolabeled model pollutants 2,4-dichlorophenol (DCP) and 2,4,5-trichlorophenol (TCP) the authors demonstrated that the brief UV (300-nm) photolysis greatly facilitates the removal of the two chlorophenols from sewage through accelerated mineralization and binding of polar products. The addition of 0.1 M H/sub 2/O/sub 2/ strongly accelerated the photolysis process resulting in the half-lives of 1.68 and 0.87 min for DCP and TCP, respectively. In natural sunlight, half-lives of the chlorophenols were less than 1 day when H/sub 2/O/sub 2/ was present. During 4 days of incubation in activated sewage sludge, only 3% of unphotolyzed DCP and 1% of unphotolyzed TCP were mineralized. Mineralization rose to 79 and 59%, respectively, after photolysis in the presence of H/sub 2/O/sub 2/. Photolysis without H/sub 2/O/sub 2/ resulted in removal of chlorophenols from solution chiefly by binding. Increased mineralization and binding were observed also upon incubation of photolyzed chlorophenols in soil. Disruption of carbon-halogen bonds by brief photolysis followed by traditional biological effluent treatment offers an alternative to activated charcoal treatment for removal of xenobiotics from industrial effluents.

Field-scale biofiltration of gasoline vapors extracted from beneath a leaking underground storage tank

Approximately 15000 L of unleaded gasoline werereleased into the surrounding vadose zone from aleaking underground storage tank. Initialremediation was by soil vapor extraction andcombustion which soon became cost prohibitive, asadded propane was required to reach the combustionlimit of the extracted vapors. As a cost effectivealternative, a field-scale compost based biofilterwas used in conjunction with soil vapor extractionto remediate the vadose zone. The biofilter wasconstructed on site using 4:1 diatomaceousearth:composted horse manure. Results of a fivemonth study showed that the biofilter removedapproximately 90% of total petroleum hydrocarbons(TPH) and >90% of the BTEX compounds (benzene,toluene, ethylbenzene, xylene), achieving thestringent permit requirements set at either 90% TPHreduction or less than 1.36 kg per day of volatileorganic compounds (VOCs) released to theatmosphere. The biofilter showed the capacity toreadily adapt to changing environmental conditionssuch as increased contaminant loading, andvariations in temperature and moisture. Thebacterial population in the biofilter was uniformlydiverse throughout the biofilter, suggesting that aconsortium of bacteria was needed for efficientbiodegradation. The cost of biofilter set up andoperation saved 90% in the first year alone of theoperating expenses incurred by soil vapor extractionand combustion.

A method for the detection and quantitation of PCR template in environmental samples by high performance liquid chromatography

This study describes methodology for the detection and quantitation of PCR amplified DNA. Specifically we report the estimation of the prevalence of E. coli in marine waters and other environmental samples from Mamala Bay, Hawaii. High performance liquid chromatography (HPLC) was used to quantitate PCR products containing between 1 and 250 ng DNA. PCR was used to amplify E. coli DNA through the use of lamB primers. A standard curve was generated that related initial cell template concentrations to amplified product DNA concentrations within a template range of 520 to 5.2×107 cells. The standard curve was used to determine initial template concentrations of the lamB gene sequence present within 11 different environmental samples. Quantified PCR analyses were most useful when samples contained only low numbers of target organisms, and when environmental samples contained few PCR inhibitory substances, as for example in marine water samples. Quantitation of amplified DNA and comparison with culture data also suggested the presence of viable but nonculturable organisms in some environmental samples. Overall these data are unique in that they indicate the successful use of HPLC to quantitate PCR amplifications with concomitant estimation of PCR template within environmental samples.

Optimization of arbitrarily primed PCR for the identification of bacterial isolates

Abstract Arbitrarily primed polymerase chain reaction (AP-PCR) has been used extensively for genetic mapping, and the identification of bacterial isolates. To ensure that the results will be reproducible and due to true genetic variations, the AP-PCR reaction conditions must be optimized. In this study, three cultured bacterial isolates were screened with 100 arbitrary primers. Of these, five were chosen for the optimization study. The parameters optimized included: the operating conditions of the thermal cycler, the agarose gel concentration, the annealing temperature, and the concentrations of Taq polymerase enzyme, magnesium chloride, primer, and template. The final optimized PCR reaction conditions were 1 × buffer (3.5 mM MgCl 2 , 10 mM Tris-HCl, 50 mM KCl and 0.1 mg ml −1 gelatin), 200 μM dNTP, 0.4 μM primer, 2.5 U AmpliTaq® (Perkin-Elmer Cetus) polymerase enzyme, and 5 μl of template (at least 10 6 lysed bacterial cells). The Perkin-Elmer Gene-Amp™ 9600 PCR System was used with the following cycling conditions; a 94°C 15 s denaturation step, a 45°C 15 s annealing step, and 72°C 30 s extension step for a total of 35 cycles. Reproducible, unique fingerprints were generated for the three isolates using each of the five arbitrary primers.

Effect of four alcohols on adsorption, desorption, and movement of cadmium, nickel, and zinc through soils

Abstract Miscible-displacement experiments were conducted to compare the effects of aqueous soil solutions with ethyl alcohol, ethylene glycol, diethylene glycol, and triethylene glycol on the movement of metals through soils. Aqueous or alcohol solutions containing 1 mM each Cd, Ni, and Zn and 5 mM Ca were perfused through columns containing River Sand, Canelo loam (Canelo 1) or Mohave sandy clay loam (Mohave scl) until effluent metal concentrations (C) equaled influent concentrations (C 0 ) or CC 0 −1 = 1. In general, the order of sorption was Zn > Ni > Cd in aqueous-perfused columns, while in alcohol-perfused columns sorption of Ni ⪢ Cd ≥ Zn. In comparison to aqueous solutions, alcohols reduced total metal sorption by at least 25%. Metal sorption was best correlated to cation exchange capacity of the soil, sorption of metals being greatest in the Mohave scl and least in the River Sand. After CC 0 −1 = 1 was reached, columns were leached with deionized water. While leaching did not affect the sorption of metals in columns which had been perfused with aqueous solvents, sorption behavior of metals changed significantly in columns which had been perfused with alcohol solvents. Leaching caused desorption of 5 to 30% of the sorbed Ni. In general, Cd was desorbed (up to 45%) from the soils tested. The exceptions were River Sand columns perfused with diethylene and triethylene glycol in which additional Cd was sorbed to the soil from the soil solution. Additional Zn was sorbed in all columns tested with the exception of the Canelo 1 column perfused with ethyl alcohol.

Estimation of Kinetic Rate Coefficients for 2,4-D Biodegradation during Transport in Soil Columns

The Monod model is used increasingly to simulate the kinetics of biodegradation in soil environments with distinctly different hydraulic properties than the well-mixed batch reactor environments for which the model is known to be appropriate [17,19,20]. This paper investigates the use of a transport model with Monod kinetics to describe the fate of 2,4-D in soil columns. The research includes development of a mathematical model for the biodegradation of 2,4-D in the presence of an acclimated biological population and an optimization model to calibrate results of the mathematical model with experimented observations. The model is applied to experimental data from two independent soil column experiments to qualify the generality of the numerical results. Fitted kinetic parameters ?we compared with well-mixed batch reactor test data and goodness of fit is compared with a linear model of transport with first-order substrate decay. The fitted model is used to discuss strategies to minimize transport of 2,4-D into lower soil horizons and groundwater.