Leland M. Vane

Recent advances in VOCs removal from water by pervaporation

Pervaporation (PV) is a separation process in which minor components of a liquid mixture are preferentially transported by partial vaporization through a non-porous permselective (selectively permeable) membrane. PV is an emerging technology in environment cleanup operations, especially in the removal of volatile organic compounds (VOCs) from industrial wastewaters or contaminated groundwaters. Current state of PV membrane development in VOC removal and improvement in process engineering, and better understanding of the interactions between VOCs and membrane materials are reviewed. Among PV process parameters documented here are process temperature, permeate pressure, feed concentration, and feed flow rate. The effects of these parameters on PV selectivity and permeation flux have been studied extensively and these studies have borne fruit in a better understanding of many aspects of PV processes. The challenge in implementing PV in practical operations lies in the further enhancement of membrane quality for specific VOCs as well as improved management and control of possible adverse hurdles coming from real systems.

Effect of aqueous phase properties on clay particle zeta potential and electro-osmotic permeability: Implications for electro-kinetic soil remediation processes

Abstract The influence of aqueous phase properties (pH, ionic strength and divalent metal ion concentration) on clay particle zeta potential and packed-bed electro-osmotic permeability was quantified. Although pH strongly altered the zeta potential of a Georgia kaolinite, it did not significantly change that of a Wyoming bentonite. The zeta potential for the kaolinite ranged from +0.7 mV at pH = 2 to −54 mV at pH = 10 (0.01 M KCl) while the bentonite zeta potential changed by only 5 mV (−31 to −36 mV) over the same pH range. For both clays, ionic strength was found to have a weak effect while divalent cations made the zeta potential markedly more positive. Charge reversal was observed for kaolinite at 100 ppm Pb2+ (pH = 5) with a background ionic strength of 0.01 M KCl and only 10 ppm Pb2+ with a background of 5 × 10−4 M KCl. A theoretical relationship between the electro-osmotic permeability coefficient for packed clay beds and particle zeta potential was developed and experimentally verified for kaolinite. For example, both the electro-osmotic permeability coefficient and particle zeta potential were found to be three times greater at pH = 5 than at pH = 3. As a result, rapid zeta potential analyses can be used to predict electro-osmotic performance for expected site conditions as well as to select electrolyte control strategies to optimize an electro-kinetic soil remediation process.

STABILITY CONSTANTS FOR COMPLEXES OF THE SIDEROPHORE DESFERRIOXAMINE B WITH SELECTED HEAVY METAL CATIONS

Abstract Potentiometric titrations of desferrioxamine B were performed in the presence of Zn(II), Cu(II), Pb(II), Sn(II), Bi(III) and hg(II). Conditions were 0.1 ionic strength and 25 or 20 °C using KNO3, KCl or NaClO4 as supporting electrolyte. Stability constants for the metal complexes were estimated as follows; DFB-Zn(II): 9.55 in KNO3 at 25 °C, DFB-Pb(II): 10.00 in KNO3 at 25 °C, DFB-Sn(II): 21.14 in KCl at 25 °C, DFB-Cu(II): 13.73 in NaClO4 at 20 °C and 13.54 at 25 °C, DFB-Bi(III): > ∼ 23.5 in NaClO4 at 25 °C.

Recovery of VOCs from surfactant solutions by pervaporation

Abstract Surfactant-based processes are emerging as promising technologies to enhance conventional pump-and-treat methods for remediating soils contaminated with nonaqueous phase liquids (NAPLs), primarily due to the potential to significantly reduce the remediation time. In order to reuse the surfactant, thereby making the process more economical, the NAPLs must be separated from the surfactant solution. Pervaporation was identified as a potential technology for removing volatile NAPLs from surfactant solutions. Initial tests with 1,1,1-trichloroethane (TCA) in an aqueous solution of the non-ionic surfactant Triton X-100 showed that the surfactant had a negligible effect on both flux and selectivity at concentrations of up to four times the critical micelle concentration (4×CMC). Further tests with a 40×CMC surfactant solution yielded moderately lower TCA fluxes and selectivities than comparable aqueous solutions without surfactant. The reduced pervaporation performance at higher surfactant and TCA concentrations were found to result from two effects: (1) increases in the viscosity of the solution, which increases the liquid-side boundary layer mass transfer resistance and (2) partitioning of TCA into the micelles, thereby reducing the effective extramicellar concentration. Despite these reductions in performance, pervaporation was found to be quite capable of removing this volatile NAPL from the surfactant solutions.

The application of siderophores for metal recovery and waste remediation: examination of correlations for prediction of metal affinities

The naturally occurring metal-chelating compounds known as siderophores may be useful in environmental applications, but limited metal specificity data is available for this class of compounds. Correlations that predict ligand–metal affinity vs metal ion charge density and hydrolysis behavior are applied to the case of the siderophore desferrioxamine B (DFB). DFB–metal complex formation constants are better correlated to the first hydrolysis constant of the respective metal cations than to the ratio of charge to metal–ligand interatomic separation. Test cases of PbII, SnII and BiIII confirm this conclusion.

Reduction of concentration polarization in pervaporation using vibrating membrane module

A vibrating membrane module currently marketed for filtration applications was evaluated for the separation of volatile organic compounds (VOCs) from aqueous solutions by pervaporation. Preliminary screening experiments with three VOCs, three silicone membranes, and in the presence and absence of a surfactant were performed to determine if further consideration of the vibrating module for a field demonstration project was warranted. The primary process variables studied were vibrational amplitude and liquid flow rate. The vibrations greatly reduced concentration polarization in the system as inferred from an order of magnitude increase in the overall mass transport coefficient. Mass transfer coefficients for the vibrating module compared favorably with those for traditional spiral wound modules.

Multi-stage continuous culture fermentation of glucose-xylose mixtures to fuel ethanol using genetically engineered Saccharomyces cerevisiae 424A.

Multi-stage continuous (chemostat) culture fermentation (MCCF) with variable fermentor volumes was carried out to study the utilization of glucose and xylose for ethanol production via mixed sugar fermentation (MSF). Variable fermentor volumes were used to enable enhanced sugar utilization, accounting for differences in glucose and xylose utilization rates. Saccharomyces cerevisiae 424A-LNH-ST was used for fermentation of glucose-xylose mixtures. The dilution rates employed for continuous fermentation were based on earlier batch kinetic studies of ethanol production and sugar utilization. With a feed containing approximately 30 g L(-1) glucose and 15 g L(-1) xylose, cell washout was observed at a dilution rate of 0.8 h(-1). At dilution rates below 0.5 h(-1), complete glucose utilization was observed. Xylose consumption in the first-stage 1 L reactor was only 37% at the lowest dilution rate studied, 0.0 5h(-1). At this same flow rate, xylose consumption rose to 69% after subsequently passing through 3 and 1 L reactors in series, primarily due to the longer residence time in the 3 L reactor (0.0167 h(-1) dilution rate).

Field demonstration of pervaporation for the separation of volatile organic compounds from a surfactant-based soil remediation fluid

As part of a Department of Defense project, the US Environmental Protection Agency was responsible for designing, building and field operating a pilot-scale pervaporation unit. The field site was an active dry cleaning facility on the grounds of Marine Corps Base Camp Lejeune in Jacksonville, NC. The overall goal of the project was to remove tetrachloroethylene (PCE) from the soil beneath the dry cleaning shop using a surfactant-based soil remediation fluid and to recycle/reuse the surfactant. In order to reinject the recovered surfactant, the pervaporation unit was required to achieve an average 95% removal of contaminants from the extracted fluid over the duration of the test period. PCE removal averaged 95.8% during peak surfactant levels and exceeded 99.9% in the absence of surfactant, thereby meeting the reinjection requirement. Removal of a group of secondary contaminants at the site, termed Varsol compounds, was monitored via concentrations of three Varsol marker compounds: decane, undecane and 1,3,5-trimethylbenzene. The pervaporation system processed 100,000 gal of groundwater and surfactant solution over a period of 70 days. In order to evaluate and validate process performance, a variety of process variables and properties were monitored over the course of the demonstration. Pervaporation costs are projected to be on the order of

VOC removal from water and surfactant solutions by pervaporation: a pilot study

20 per 1000 gal of surfactant solution treated for a moderate size system (10 gpm).

Pervaporation and Vapor Permeation Tutorial: Membrane Processes for the Selective Separation of Liquid and Vapor Mixtures

Abstract The removal of VOCs from aqueous solutions via pervaporation is an established technology that has been successfully demonstrated at the full scale. The purpose of this research was to measure the effect of an anionic surfactant (DOWFAX 8390) on pervaporation system performance and mass transfer of 1,1,1 trichloroethane (TCA) and toluene. This aqueous surfactant application of pervaporation targets the recovery and reuse of surfactant from SEAR (surfactant enhanced aquifer remediation) process fluids. In this study, a pilot scale pervaporation unit with 4 spiral wound modules was used to conduct 75 eight hour runs. Process variables included temperature (30, 40, 50, 60°C), permeate pressure (15, 25, 55 Torr), flow rate (0.25–2.0 gpm), and VOC feed concentration (17–265 mg/l TCA and 5–200 mg/l toluene). Surfactant addition reduced the removal of VOCs 0.7–29% depending on the system flowrate, feed temperature, and VOC. The reduced VOC flux resulting from the addition of surfactant was found to be attributed to an increase in the liquid viscosity due to the addition of the surfactant (10–13% increase) and partitioning of the VOC into the surfactant micellar phase (63–68% of TCA and 73–78% of toluene was in micellar form) under experimental conditions. Though the addition of surfactant causes a decrease in the VOC removal efficiency, this study demonstrates that pervaporation can be used to remove VOCs from surfactant solutions without affecting the surfactant, permitting surfactant recycle.