1997 Progress Report: A Multi-Scale Investigation of Mass Transfer Limitations in Surfactant-Enhanced Aquifer RemediationEPA Grant Number: R825405
Title: A Multi-Scale Investigation of Mass Transfer Limitations in Surfactant-Enhanced Aquifer Remediation
Investigators: Mayer, Alex , Pope, Gary A.
Institution: Michigan Technological University , The University of Texas at Austin
Current Institution: Michigan Technological University , The University of Texas at Houston
EPA Project Officer: Chung, Serena
Project Period: October 1, 1996 through October 31, 1999 (Extended to October 31, 2000)
Project Period Covered by this Report: October 1, 1996 through October 31, 1997
Project Amount: $299,792
RFA: Environmental Fate and Treatment of Toxics and Hazardous Wastes (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Objective:At Michigan Technological University (MTU), we have been conducting batch and column experiments. The batch tests have been used to measure solubilization rates with time, as a function of surfactant concentration, salinity and other chemicals. Column experiment protocols have been developed for surfactant flooding tests, including analytical techniques. We can obtain reliable results and have conducted almost 40 column experiments, where we have varied the column length, flooding velocities, initial NAPL saturations, surfactant concentration, and salinity. We expect to run about 50 more column tests next year. We have been using a Cytec Aerosol MA surfactant. We will work with at least one other surfactant, starting this Fall. We are continuing to use trichloroethylene (TCE) for our NAPL.
The batch tests are conducted under isothermal, completely-mixed conditions. The batch test results indicate that equilibrium between the surfactant solution and the TCE is reached within tens of seconds or about a minute. We have conducted a few quiescent batch tests, in order to measure rate of diffusion of TCE into the surfactant solution. The column tests indicate that equilibrium concentrations are achieved within about one pore volume. The equilibrium concentrations are maintained until the NAPL saturations are reduced to about 5%. At this point, the concentrations drop steeply below equilibrium levels. Some of this work was presented at the Fall meeting of the American Geophysical Union in December 1997. Future work will focus on determining whether the nonequilibrium behavior is due to flow bypassing, moving dissolution front, dissolution fingering, or a combination of these phenomena.
A research collaboration was initiated in June 1997 with Dr. Robert Glass' group at Sandia National Laboratory. We conducted a couple of experiments with Dr. Glass' glass micromodels in September 1997. Lirong Zhong, a MTU Ph.D. student supported by this project, will spend the summer at Sandia conducting several more micromodel experiments. The advantage of these experiments is that observations of the NAPL-surfactant system can be made at the pore scale. In April 1998, a pore network simulator will be obtained from Stanford University. The pore network simulator will be used to obtain further insights into solubilization at the pore scale. A Ph.D. student will be responsible for modifying and running the pore network simulator.
Drs. Gary Pope and Mojdeh Delshad at the University of Texas (UT) have modified the UTCHEM simulator incorporate nonequilibrium dissolution models. They will be fitting the dissolution model to the column data from MTU over the next couple of months. This work will be presented at the Batelle DNAPL conference in late May 1998. Dr. Mayer will travel to UT in late April to discuss progress on the project and set future directions for the research.
In Summer 1997, two undergraduate students worked on the project, supported by a NSF Research Experience for Undergraduates grant. In December 1998, a $32,000 grant from the Michigan Research Excellence Fund was awarded. These funds were used to purchase a spinning drop tensiometer, which can measure ultra-low interfacial tensions (IFTs). A second instrument will be purchased for measuring mid-level IFTs.
A Ph.D. student and three undergraduate research assistants have been utilized for the project thus far. A suitable candidate for a postdoctoral research assistant was not found. Instead, a Ph.D. student and an M.S. student will be put onto the project this summer.
Keywords: nonaqueous, surfactants, TCE, batch/column, models, dissolution