Grantee Research Project Results
Final Report: Development of an Integrated Optic Interferometer for In-Situ Monitoring of Volatile Hydrocarbons
EPA Grant Number: R825513C018Subproject: this is subproject number 018 , established and managed by the Center Director under grant R825513
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: The Southeastern Center for Air Pollution and Epidemiology: Multiscale Measurements and Modeling of Mixtures
Center Director: Tolbert, Paige
Title: Development of an Integrated Optic Interferometer for In-Situ Monitoring of Volatile Hydrocarbons
Investigators: Walsh, J. , Hartman, N. F
Institution: Georgia Institute of Technology
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1992 through January 1, 1994
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (1989) RFA Text | Recipients Lists
Research Category: Hazardous Substance Research Centers , Land and Waste Management
Objective:
In this project a microsensor was developed and demonstrated which was suitable for monitoring BETX (benzene, ethylbenzene, toluene and xylene) chemicals. Although current laboratory instrumentation is satisfactory for chemical diagnostics, these instruments are of limited value for field monitoring applications due to size, cost and speed. Monitoring pplications generally require real time in-situ measurements using sensors that are 1) economically viable, 2) suitable for long term field operations, 3) easily maintained or repaired in the field, and 4) require minimal fixed equipment for operation.
Summary/Accomplishments (Outputs/Outcomes):
The microsensor technology is based on an integrated optic (IO), interferometric device capable of continuously measuring an individual chemical species in the ppmv or lower range. The sensor approach relies on the detection of very small refractive index changes in a thin film on the surface of an optical waveguide. Sensitivity to benzene, toluene, and xylene have been demonstrated at concentrations in the low ppmv range. Further, the sensor technology has been shown to be capable of detecting the presence of gasoline in sedimentary soils. This technology offers the potential of monitoring several different chemical species on a single, multi-channel waveguide package only 1.5 inches in diameter and a few inches in length (including electronics). Moreover, techniques for negating many of the effects associated with a soil-water environment such as moisture changes, temperature variations, and chemical contamination have been developed and demonstrated. The sensor technology reported herein overcomes many of the disadvantages of existing techniques for measuring these substances including prohibitively high expense, excessively long measurement times, and inherently complex instrumentation that restricts field use.
The chemical species selected from the BTEX group as target analytes include benzene, toluene and xylene. Detection and monitoring capabilities depend on detection, sensitivity and specificity. The latter represents the most challenging problem because the organic species are small, simple molecules with similar chemical properties. The efforts in this program focused on realizing useful detection sensitivity levels and only demonstrating techniques for achieving class specificity.
Vapor phase measurements were utilized since this approach offers greatest flexibility where both sedimentary soils and aqueous phase environments will be encountered In the case of sedimentary soils, the sensor can only detect the presence of trace vapors not bound to the soil molecules. In the case of aqueous environments, the relative solubility difference between water (very low) and the selective polymer layer (relatively high) limits the reversibility of the process. For measurements in the aqueous phase, a separation membrane, a hydrophobic filter, is required. The separation membrane also provides other advantages as it serves to protect the waveguide sensing surface from mechanical abrasion and contamination.
Waveguide Sensor/Coating Response
The evanescent field of a low
order mode in a properly designed waveguide is tightly confined to the waveguide
and so does not see changes in the cover film. In contrast, because the
evanescent field associated with a higher order mode extends into the cover
film, it is sensitive to index changes occurring therein.
The single mode version of an interferometric sensor operates on the same principles as the multimode but utilizes two guided beams spatially separated on the waveguide surface. In this instance, however, the waveguide is designed such that the evanescent field of both guided waves penetrates into the superstrate. One of guided beam path is covered with a chemically selective layer (signal beam) while the other is covered with an isolating layer (reference arm). Again, the interaction with the chemically selective film alters the phase of the guided beam under it and by interfering that guided wave with the reference beam, the chemically induced phase shifts are easily detected.
For the test measurements, air saturated with the organic species of interest was mixed with flowing nitrogen to dilute the flow impinging on the polymer coated waveguide surface. The phase change was then detected and the relative response determined based on the known vapor pressures for the organic species of interest. The waveguide element used for these experiments consisted of a fused silica (SiO2) substrate overcoated with a 110 nanometer (nm) silicon nitride (Si3N4) waveguide film and a 40 nm fused silica film. The 40 nm fused silica layer only serves to provide different chemistries for attaching chemically active films to the waveguide surface. The overall sensitivity is dependent on several factors including; 1) waveguide design and parameters, 2) polymeric coating, 3) polymer thickness, and 4) sensing channel length.
Sensor Response for Contaminated Sedimentary Samples
To test the
sensor response using contaminated soils a soil sample was contaminated with
small sample volumes of gasoline and toluene. The response of the sensor was
recorded as a function of time. The time dependent response is strictly defined
by the diffusion of the specimen through the thickness of the sediment layer
which was 1 cm. The specimen, having a volume of approximately 1 microliter, was
placed directly on the top surface of the sediment for these test. The typical
response was a high detected phase change signal between the first and fourth
minute of the test for both gasoline and toluene. The slow recovery time (full
recovery required 30 minutes) occurs because the test species as release from
the selective polymer film was entrapped.
Waveguide Surface Protection
Because the waveguide surface is
sensitive to mechanical abrasion and its throughput can be attenuated by opaque
residue deposited directly on the waveguide surface, the sensing surface must be
protected. As previously noted, a separation membrane was used as a means of
overcoming the lack of reversible absorption observed in an aqueous media. The
waveguides were tested in a variety of aqueous environments. In particular, the
most harsh condition included a flowing stream at a temperature of approximately
60 C and a pH of 10.6, Under these conditions, damage to the waveguide was
observed when the waveguide surface was exposed directly to the hot caustic
media. The damage included actual etching and destruction of surface films. In
the case of dry soil samples, the hydrophobic filter provided adequate
protection against dust contamination.
Sensor Probe Design and Configuration
Although a complete prototype
sensor system suitable for field testing was not a part of the HSRC funding
effort, through synergism with other projects a prototype system was developed.
The probe configuration is compatible with the design requirements for the cone
penetrometer.
Summary of Results:
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other subproject views: | All 3 publications | 2 publications in selected types | All 1 journal articles |
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Other center views: | All 392 publications | 154 publications in selected types | All 106 journal articles |
Type | Citation | ||
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|
Walsh JL, Ross CC, Hartman NF. Sensors can find and monitor contaminants. Centerpoint 1993;1(1):10. |
R825513C018 (Final) |
not available |
Supplemental Keywords:
BTEX, microsensor, and detection., RFA, Scientific Discipline, Air, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Chemical Engineering, air toxics, Contaminated Sediments, Environmental Chemistry, Monitoring/Modeling, Analytical Chemistry, Hazardous Waste, Ecology and Ecosystems, Hazardous, Environmental Engineering, vaporization, environmental technology, sediment treatment, hazardous waste management, hazardous waste treatment, risk assessment, environmental monitoring, volatile air toxics, contaminated sediment, in situ sensor, air pollution, air qialty model, chemical contaminants, contaminated soil, airborne metals, BETX, hydrocarbons, microsensor, Volatile Organic Compounds (VOCs)Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R825513 The Southeastern Center for Air Pollution and Epidemiology: Multiscale Measurements and Modeling of Mixtures Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R825513C001 Sediment Resuspension and Contaminant Transport in an Estuary.
R825513C002 Contaminant Transport Across Cohesive Sediment Interfaces.
R825513C003 Mobilization and Fate of Inorganic Contaminant due to Resuspension of Cohesive Sediment.
R825513C004 Source Identification, Transformation, and Transport Processes of N-, O- and S- Containing Organic Chemicals in Wetland and Upland Sediments.
R825513C005 Mobility and Transport of Radium from Sediment and Waste Pits.
R825513C006 Anaerobic Biodegradation of 2,4,6-Trinitrotoluene and Other Nitroaromatic Compounds by Clostridium Acetobutylicum.
R825513C007 Investigation on the Fate and Biotransformation of Hexachlorobutadiene and Chlorobenzenes in a Sediment-Water Estuarine System
R825513C008 An Investigation of Chemical Transport from Contaminated Sediments through Porous Containment Structures
R825513C009 Evaluation of Placement and Effectiveness of Sediment Caps
R825513C010 Coupled Biological and Physicochemical Bed-Sediment Processes
R825513C011 Pollutant Fluxes to Aquatic Systems via Coupled Biological and Physicochemical Bed-Sediment Processes
R825513C012 Controls on Metals Partitioning in Contaminated Sediments
R825513C013 Phytoremediation of TNT Contaminated Soil and Groundwaters
R825513C014 Sediment-Based Remediation of Hazardous Substances at a Contaminated Military Base
R825513C015 Effect of Natural Dynamic Changes on Pollutant-Sediment Interaction
R825513C016 Desorption of Nonpolar Organic Pollutants from Historically Contaminated Sediments and Dredged Materials
R825513C017 Modeling Air Emissions of Organic Compounds from Contaminated Sediments and Dredged Materials title change in last year to "Long-term Release of Pollutants from Contaminated Sediment Dredged Material"
R825513C018 Development of an Integrated Optic Interferometer for In-Situ Monitoring of Volatile Hydrocarbons
R825513C019 Bioremediation of Contaminated Sediments and Dredged Material
R825513C020 Bioremediation of Sediments Contaminated with Polyaromatic Hydrocarbons
R825513C021 Role of Particles in Mobilizing Hazardous Chemicals in Urban Runoff
R825513C022 Particle Transport and Deposit Morphology at the Sediment/Water Interface
R825513C023 Uptake of Metal Ions from Aqueous Solutions by Sediments
R825513C024 Bioavailability of Desorption Resistant Hydrocarbons in Sediment-Water Systems.
R825513C025 Interactive Roles of Microbial and Spartina Populations in Mercury Methylation Processes in Bioremediation of Contaminated Sediments in Salt-Marsh Systems
R825513C026 Evaluation of Physical-Chemical Methods for Rapid Assessment of the Bioavailability of Moderately Polar Compounds in Sediments
R825513C027 Freshwater Bioturbators in Riverine Sediments as Enhancers of Contaminant Release
R825513C028 Characterization of Laguna Madre Contaminated Sediments.
R825513C029 The Role of Competitive Adsorption of Suspended Sediments in Determining Partitioning and Colloidal Stability.
R825513C030 Remediation of TNT-Contaminated Soil by Cyanobacterial Mat.
R825513C031 Experimental and Detailed Mathematical Modeling of Diffusion of Contaminants in Fluids
R825513C033 Application of Biotechnology in Bioremediation of Contaminated Sediments
R825513C034 Characterization of PAH's Degrading Bacteria in Coastal Sediments
R825513C035 Dynamic Aspects of Metal Speciation in the Miami River Sediments in Relation to Particle Size Distribution of Chemical Heterogeneity
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.
Project Research Results
1 journal articles for this subproject
Main Center: R825513
392 publications for this center
106 journal articles for this center