Grantee Research Project Results
2000 Progress Report: The Use of Microfiltration and Ultrafiltration Membranes for the Separation, Recovery, and Reuse of Surfactant/Contaminant Solutions
EPA Grant Number: R825540C003Subproject: this is subproject number 003 , established and managed by the Center Director under grant R825540
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Duke University Center for Environmental Implications of NanoTechnology
Center Director: Wiesner, Mark R.
Title: The Use of Microfiltration and Ultrafiltration Membranes for the Separation, Recovery, and Reuse of Surfactant/Contaminant Solutions
Investigators: Jones, Kimberly L.
Institution: Howard University
EPA Project Officer: Hahn, Intaek
Project Period:
Project Period Covered by this Report: January 1, 2000 through December 31,2000
RFA: Hazardous Substance Research Centers - HSRC (1989) RFA Text | Recipients Lists
Research Category: Hazardous Substance Research Centers , Land and Waste Management
Objective:
The overall goal of this research is to develop a method to separate VOCs from surfactant-VOC solutions in order to reuse the surfactant in surfactant enhanced aquifer remediation (SEAR) applications. In the proposed system, a pervaporation (PV) process will be used to separate VOCs from a surfactant-VOC stream, and an ultrafiltration membrane will be used to concentrate the recovered surfactant (Figure 1). Individual objectives of this research are to: 1) evaluate the capacity of the pervaporation membrane for separating VOCs from a surfactant solution under conditions relevant to TRAC II SEAR efforts, 2) develop a suitable model to determine the optimal mass transport conditions of the system, and 3) test the pervaporation/microfiltration system under field conditions using the Bachman site. The research will be expanded to include application-specific information, such as cost and flux/selectivity models for different system designs.
Progress Summary:
Rationale: Researchers in TRAC II of the Great Lakes and Mid-Atlantic Center for Hazardous Substance Research are currently involved in research efforts designed to improve the ability to develop and implement effective solubilization and density modified displacement technologies for recovery of DNAPLs and DNAPL mixtures from natural aquifer materials. Membrane technology is an innovative method to recover surfactant monomers, resulting in an efficient, economically viable solution for surfactant reuse. The focus of the proposed study is to evaluate a combined pervaporation/ultrafiltration system for the separation and recovery of the surfactant following SEAR.
Approach: Mass transfer through a pervaporation membrane can be expressed by the resistance-in-series model, which relates the permeate flux to the concentration difference between the bulk permeate and feed phase by an overall mass transfer coefficient:
( 1
where Jvoc = flux of solute from bulk solution to permeate (mol/cm2*s), Kov = overall mass transfer coefficient (cm/s), c = concentration (mol/cm3), and the subscripts "b" and "p" represent bulk and permeate concentrations, respectively. The overall mass transfer coefficient consists of the following four individual mass transfer coefficients: ks (surfactant), kl (liquid boundary layer), km (membrane) and kg (vacuum boundary layer):
( 2
There are three phase interfaces involved in the separation - micelle/bulk liquid , bulk liquid/membrane and membrane/vacuum boundary layer. Three partition coefficients can be defined for each of the three phase interfaces:
where cs' = concentration of VOC in the liquid feed phase at the micelle/bulk interface (mol/cm3), Ka = micelle/aqueous phase partition coefficient (-), cb' = concentration in the membrane at liquid/membrane interface, Km = distribution coefficient of VOC between the liquid and membrane, cm = concentration in the membrane at the membrane/liquid interface, cv'= concentration at the of VOC in the membrane at the membrane/vacuum interface, Kv is the distribution coefficient between the membrane and the vacuum side and cmv is the concentration of VOC in the membrane at the membrane/vacuum interface.
The individual mass transfer rates can be expressed as follows:
Micelle/bulk liquid interface: (6
Liquid/Membrane interface: (7
Membrane surface: (8
Membrane/vacuum interface: (9
At steady state, the fluxes are all equal to the overall flux in equation 1, and the resistance of the vacuum side boundary layer is negligible compared to the other resistances (Das et al., 1998). The mass transfer resistance of the mono-molecular surfactant layer will be calculated and compared to the other mass transfer coefficients to determine the effect of surfactant on the overall transport process.
Current Status: The flux of PCE across different PV membranes is currently being measured under constant temperature and vacuum pressure. No accurate flux measurements have been made due to an unusual observation in the cold trap, described as follows: When methanol is added to the cold trap, the pressure in the cold trap increases, forcing vapor out of the trap. That vapor may contain volatized PCE, making the PCE measurement inaccurate. Other researchers (Vane, 1999) have documented this phenomenon, and solutions to that problem are being investigated. Present options are to either assume that a negligible amount of PCE escapes or to perform a mass balance on the PCE to attempt to quantify the amount of PCE which may escape. Previous researchers have assumed that the escaped amount is negligible, however we are performing a mass balance for quantification of the escaped amount.
Also, there is a liquid (suspected to be N2 from the air) found in the cold trap the temperature is dropped to -200°C by the addition of liquid N2 to the flask around the trap. The system is confirmed to be airtight, and the vacuum pressure inside the cold trap should prevent any air from entering the cold trap.
We are presently investigating these observations in order to gain accurate data for presentation of the flux of PCE across the PV membrane in the presence of Tween 80 at 4 X CMC.
Client/Users -Technology Transfer and Outreach Plan: Researchers in TRAC II of the Great Lakes and Mid-Atlantic Hazardous Substance Research Center are currently involved in research efforts designed to improve the ability to develop and implement effective solubilization and density modified displacement technologies for recovery of DNAPLs and DNAPL mixtures from natural aquifer materials. Although advances have been made in improving the technical feasibility of this process, a major concern with this technology is the cost of surfactant required to fill the aquifer. Thus, economics of the process require that the surfactant be recovered for reuse. Membrane technology is an innovative method to recover surfactant monomers, resulting in an efficient, economically viable solution for surfactant reuse. The focus of the proposed study is to evaluate a combined pervaporation/ultrafiltration system for the separation and recovery of the surfactant following SEAR.
Although several researchers have evaluated pervaporation for the removal of VOCs from groundwaters and wastewaters, there are fewer studies of the use of pervaporation for separating VOCs from a surfactant stream. The presence of surfactant in the PV process alters the transport characteristics of the system. This progress report focuses on the development of a suitable method to determine the flux and selectivity for a VOC/surfactant solution. The overall goal of this research is to develop a method to separate VOCs from surfactant-VOC solutions in order to reuse the surfactant in surfactant enhanced aquifer remediation (SEAR) applications. In the proposed system, a pervaporation (PV) process will be used to separate VOCs from a surfactant-VOC stream, and an ultrafiltration membrane will be used to concentrate the recovered surfactant. The research will be expanded to include application-specific information, such as cost and flux/selectivity models for different system designs. The specific objectives of this research are to: 1) evaluate the capacity of the pervaporation membrane for separating VOCs from a surfactant solution under conditions relevant to TRAC II SEAR efforts, 2) develop a suitable model to determine the optimal mass transport conditions of the system, and 3) test the pervaporation/microfiltration system under field conditions using the Bachman site.
In recent years, government and industrial researchers have developed feasibility studies to investigate surfactant-based remediation techniques. These projects are in various stages of completion, from laboratory experiments to field investigations. In any surfactant-enhanced process, large concentrations of surfactant must be pumped into the contaminated aquifer, and the economics of the process dictate that the majority of surfactant must be recovered and reused. To this end, it is important to develop technologies for recovering surfactant for reuse. Conventional processes such as liquid-liquid extraction and air stripping can achieve the necessary separation of surfactant and VOC, but they often suffer from foaming problems. Pervaporation is a promising alternative, as PV membranes have been used for recovering organic compounds from water and separating organic mixtures in order to recover a valuable product from a feed stream. The exact treatment cost for PV depends on the efficiency of the membrane separation process, which is affected by the presence of surfactant micelles in the solution. Results from this research will enable potential surfactant-aided remediation processes to become more economically feasible, and the mass transfer characteristics of the surfactant-VOC separation will be a helpful tool in general PV studies.
Supplemental Keywords:
RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, TREATMENT/CONTROL, Chemical Engineering, Contaminated Sediments, Treatment Technologies, Environmental Chemistry, Hazardous Waste, Bioremediation, Ecology and Ecosystems, Hazardous, Environmental Engineering, sequestration, contaminant transport, in situ remediation, fate and transport , bioavailability, biodegradation, contaminated sediment, kinetic studies, contaminated soil, membrane processes, bioremediation of soils, contaminants in soil, groundwater remediation, in-situ bioremediation, microfiltration, contaminated groundwater, environmentally acceptable endpoints, hazardous organic compounds, bioacummulation, ultrafiltration, bioaccumulation, alternative endpoints, contaminated soilsProgress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R825540 Duke University Center for Environmental Implications of NanoTechnology Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R825540C001 Development and Verification of A Molecular Modeling Approach for Predicting the Sequestration and Bioavailability/Biotoxicity Reduction of Organic Contaminants by Soils and Sediments
R825540C002 Molecular Modeling of Hydrophobic Organic Contaminants Uptake and Sequestration by Soil Organic Matter
R825540C003 The Use of Microfiltration and Ultrafiltration Membranes for the Separation, Recovery, and Reuse of Surfactant/Contaminant Solutions
R825540C004 A Contained Simulation of Field Application of Genetically Engineered Microorganisms (Gems) for the Bioremediation of PCB Contaminated Soils
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.