WRHSRC Research Program:
Physical and Chemical Abiotic Processes

Focus Group Leader:

Martin Reinhard, Stanford University

Technical Description:

The research group associated with abiotic processes addresses chemical reactions for in-situ treatment of CAH contamination and innovative physical removal methods. Center researchers have been actively involved in basic research using palladium catalysis with hydrogen (Schreier and Reinhard, 1995), ultimately with field applications (McNab et al., 2000). Mass transfer issues associated with the treatment of dilute plumes, such as desorption are also being investigated. Mechanisms for slow desorption of chemicals from aquifer solids have been studied by Reinhard (Werth and Reinhard, 1997).

Project 1-SU-02:

Chemical, Physical and Biological Processes at the Surface of Palladium Catalysts under Groundwater Treatment Conditions

Principal Investigator:

Martin Reinhard, Stanford University and John Westall, Oregon State University

Project Initiated: 2002

 

Project Summary:

This project is an investigation of the chemical, physical, and biological processes at the surface of palladium catalysts under groundwater treatment conditions by Martin Reinhard and Stanford University and John Westall at Oregon State University. This project approaches optimization of the abiotic process for CAH reduction using Pd catalysts. The project aims at obtaining a through understanding of changes in the catalyst surface during treatment and correlating these to changes in catalytic activity. Research conducted during the second year of this project demonstrated that deactivation of the catalyst was consistent with sulfide poisoning. Treatment with sodium hypochlorite was able to fully regenerate the catalyst. The research is being undertaken in collaboration with a field study at Edwards Air Force Base (EAFB) near Lancaster, California.

Project 1-SU-03:

Effects of Sorbent Microporosity on Multicomponent Fate and Transport in Contaminated Groundwater Aquifers

Principal Investigators:

Martin Reinhard, Stanford University

Project Initiated: 2002

 

Project Summary:

In this project the effects of sorbent microporosity on multicomponent fate and transport in contaminated groundwater aquifers is being studied. This project is investigating the importance of one of the most fundamental processes of organic sequestration on porous sorbents—micropore sorption. The impacts of the environmental variables affecting micropore sequestration is being quantified. The competitive sorption/desorption of multiple contaminants on the natural soils is being studied to elucidate the interactions among molecules with different properties during micropore sequestration. The kinetics of contaminant uptake and release from micropores is being measured and compared with other sorption/desorption pathways. Over the past year an apparatus has been developed specially for measuring slow sorption and desorption kinetics of VOCs on solid materials packed in columns. This design has expanded the investigative capabilities in several ways: data are acquired in real-time with high resolution over the entire contaminant desorption profile, contaminant detection is extremely sensitive, and sorption and desorption of multiple volatile organic contaminants can be studied. The initial experimental results suggests that the property of micropores in geosorbents, rather than the total volume of the micropores, plays key role in controlling contaminant sequestration and desorption.

Project 2-SU-05:

The Role of Micropore Structure in Contaminant Sorption and Desorption

Principal Investigator:

Martin Reinhard, Stanford University

Project Initiated: 2004

 

Project Summary:

Sorption of organic molecules on geosorbents plays a key role in controlling the availability and rate of contaminant biotic and abiotic degradations. Of practical significance is sorption in the micropore domain (i.e., in pores with diameters less than 20 Å) that acts as a sink for hydrophobic contaminants. Substantial fraction of nonpolar organic compounds can be sequestered in micropores, and the uptake and release kinetics are very slow when micropore sequestration is the dominant sorption mechanism. Contaminant interactions with microporous solids are influenced by the sorbent microporosity and the contaminant properties. The overall objective of this research is to gain a better mechanistic understanding of the mechanism of contaminant sequestration in and desorption from microporous solids.

Specific objectives for this project are:

• to determine the impact of micropore geometry on long-term desorption of contaminants sequestered in micropores;
• to assess the pore wall polarity of micropores and quantify the impact of micropore hydrophobicity/hydrophilicity on contaminant sorption and desorption;
• to study the sorption and desorption kinetics of hydrophobic organic contaminants in and from micropores, and to assess the competitive effects of water and other hydrophilic species on these processes; and
• to evaluate the influence of pore gas composition on desorption kinetics of organic contaminants sequestered in micropores.

The approach will be to study the sorption and desorption kinetics of contaminants on microporous engineered solids and geosorbents under various conditions and infer molecular level interactions of contaminants with microporous solids. Sorption and desorption rates of chlorinated solvents and other volatile organic compounds (VOCs) will be measured using an experimental apparatus that has been developed under prior WRHSRC support. The influence of pore geometry and structure, particularly pore throats, on contaminant desorption kinetics will be inferred from the rate measurements, and the impact of pore wall polarity will be studied by competitive sorption of hydrophobic and hydrophilic species on the microporous solids. Influence of molecular size of the purging gas used in desorption and effectiveness of hydrophobic organic gas species at enhancing contaminant desorption under ambient conditions (in presence of water molecules) will also be evaluated.

The expected benefits from this work include:

• improved understanding of the mechanism of micropore sequestration, particularly with respect to pore throat restriction of mass transfer rate during desorption;
• fundamental understanding of the competition among multiple species during sorption and desorption on geosorbents;
• development of a technique to characterize hydrophobic and hydrophilic micropores, and evaluation of the effect of pore wall polarity on competitive sorption of multiple species;
• knowledge of how sorbent microporosity (including pore wall polarity and pore geometry) and purging gas properties (e.g., molecular size, polarity) may affect the contaminant desorption kinetics; and
• evaluation of the impact of micropore sequestration on contaminant fate and transport in subsurface, prediction of timescale for releasing of micropore sequestered contaminant from geosorbents, and assessment of risk of contaminated aquifers when micropore sequestration is the dominant sorption mechanism.

Project Update Slide (November 2004):

To download a copy of this slide, right click here.