Franklin R. Alvarez

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.

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).

Cross-Flow Filtration of Synthetic Electroplating Wastewater by Ceramic Membranes Using High Frequency Backpulsing

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.

Separation process using pervaporation and dephlegmation

Cross-flow microfiltration (MF) was investigated as a viable option for separating colloidal particles from electroplating wastewater. Filtration experiments with Cr(OH)3 suspension as synthetic electroplating wastewater were performed on a pilot filter unit equipped with a backpulse device using porous alumina ceramic membranes of various pore sizes (0.2-5.0 µm). The membranes were characterized by nitrogen and clean water permeation. In filtration with Cr(OH)3 suspension, water permeate flux decreases with decreasing membrane pore size and increasing solute concentration in suspension. All membranes are fouled in filtration primarily due to the cake formation. With backpulse in operation, a constant water permeate flux can be maintained using membranes with pore size smaller or larger than the size of solid aggregates in the suspension. The rejection coefficient of suspended solid is about 100% for the smaller pore membranes but drops to only 70% for the larger pore membrane. The backpulse is not effective in maintaining a constant water permeate flux for filtration using membranes of pore size close to the suspension aggregate size due to entrapment of fine aggregates in the membrane pores. The fouled membranes could be completely regenerated by a chemical rinsing method with NaOH and HNO3 solutions.