Grantee Research Project Results
Final Report: A Compact, Low-Cost, Near-UV Sensor for Chlorine Dioxide
EPA Contract Number: EPD06057Title: A Compact, Low-Cost, Near-UV Sensor for Chlorine Dioxide
Investigators: Bomse, David S.
Small Business: Southwest Sciences Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2006 through August 31, 2006
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2006) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Homeland Security , Small Business Innovation Research (SBIR)
Description:
The Phase I research effort was designed to determine the suitability of diode laser-based optical absorption spectroscopy for quantitative detection of chlorine dioxide (ClO2) over a concentration range spanning five orders of magnitude. Successful completion of the Phase I research will allow one type of sensor to replace the two that are now used commercially. This work is enabling technology for the use of ClO2 as a biodecontaminating agent. ClO2 is challenging to use because it is difficult to control the concentration within the delivered stream, and its high toxicity requires an effective measurement at low concentrations (sub-ppm) to allow re-entry into the treated area.
Most people associate “biodecontamination” with terrorism, such as the 2001 anthrax contamination of postal facilities and government office buildings. Although ClO2 is an effective decontaminant—and was used successfully in 2001—for such events, commercial decontamination activities include water treatment, and mold and mildew removal. These commercial activities define the significant markets for the detection technology, and help explain why research by Southwest Sciences, Inc., may lead to an enabling technology.
Although there is some debate concerning preference for hydrogen peroxide versus ClO2 for biodecontamination, most experts favor ClO2 because it is better suited to decontaminating large volume buildings, whereas using hydrogen peroxide requires partitioning the region into smaller subsections. ClO2 has been used successfully to treat a 14 million cubic foot structure; hydrogen peroxide has not yet been demonstrated for more than 200,000 cubic feet. The main arguments in favor of hydrogen peroxide are its decomposition into benign products and anecdotal reports that it is less likely to damage electronic equipment.
At the time of the Phase I proposal submission, accepted ClO2 concentration measurement ranges were 0.1 to 2000 ppm. Currently, a larger dynamic range of 0.001 to 6000 ppm is required.
Previous Southwest Sciences, Inc. work, including the development of commercial instruments, used near-infrared and mid-infrared diode lasers for gas sensing. For this Phase I research project, an attempt was made to extend the company’s technology to the near-ultraviolet (near-UV) by using diode lasers, which have recently been developed for dual-layer, DVD recording; this wavelength range is well-suited for ClO2 concentration measurements. Phase I goals included: (1) characterizing the spectroscopic performance of the new, near-UV diode lasers (scan range, scan rate, spectral linewidth, output power, etc.); (2) determining the optimum spectroscopic method for using the near-UV lasers to detect ClO2; and (3) determining the factors that define the minimum and maximum measurable concentrations of ClO2 using the optimum spectroscopic method.
Summary/Accomplishments (Outputs/Outcomes):
The Phase I effort showed that the proposed technology is feasible. The diode lasers that were used are cutting edge technology, although as with most diode lasers, these early samples have quirks, including limited wavelength tuning ranges. Supporting technology, such as optimized miniature, commercially available, aspheric collimating lenses are not yet available. These constraints will be eliminated, however, as lasers are engineered to become commodity products for the next generation of DVD players and optical hard drives. As the laser technology matures, costs will decrease and performance will improve, resulting in commercially viable applications of the ClO2 technology demonstrated in Phase I.
Phase I findings included characterization of laser performance for three near-UV diode lasers. The wavelength, optical power, and spectral width all are functions of the laser temperature and operating current. The full range of these parameters was tested to determine the optimum operating conditions for each laser. As expected, the Phase I experiments also showed pronounced optical absorption by ClO2 at near-UV wavelengths.
Several unexpected (and, in one case, unlucky) factors limited measurement sensitivity and dynamic range. These included short- and long-term drifts in the laser power and the ClO2 gas concentrations, as well as unexpectedly small optical absorbances. A set of improvements, to be implemented in Phase II, include:
- A more reliable ClO2 source. The ClO2 source should be capable of supplying known and controlled amounts of the gas at low concentrations.
- A “cleaner” gas handling system that does not adsorb ClO2. The Phase I apparatus used perfluoroalkoxy (PFA) tubing for the gas transfer lines. Better materials might include electropolished stainless steel, monel, or glass.
- Better selected lasers. The wavelengths of the three lasers used in Phase I do not overlap with ClO2’s strong absorption features. This was simply bad luck. The laser supplier was unwilling to wavelength select the devices ordered, and the current cost per device is too high to permit purchasing many lasers. In Phase II, a different supplier will be used or a different approach to the laser light source will be taken.
- More stable optics. The parameters of the collimating lenses used in Phase I were driven primarily by the dimensions of the laser package. The emitting surface is relatively far from the output window. The resulting beam characteristics—spot size and pointing stability—were strongly affected by small changes in lens position, including changes induced by repeated thermal cycling of the laser mount, and by vibrations from the fume hood fan motor. Southwest Sciences, Inc., has developed more robust and reliable optical mounts for visible and near-infrared diode lasers, and anticipates that this will result in a better engineered system.
Conclusions:
The Phase I effort showed that near-UV, diode laser optical detection of ClO2 is feasible, although commercial development will require that lower priced, wavelength-selected lasers are available. Optimization also requires the availability of a more reliable ClO2 delivery system, particularly for measurements of low concentrations. These improvements are reasonable expectations. The diode lasers are being developed for the next generation of DVD players, implying a commodity market with unit pricing well below $100.
An improved ClO2 delivery system also is possible using small volume “sachet” gas generators and gas handling materials optimized for ClO2 exposure. The most significant outcome of the market study was recognizing that the planned ClO2 analyzer is an enabling technology that will make ClO2 easier to use within the mold and mildew remediation service industry. Significant advantages include the ability to penetrate regions that are not accessible to manual cleaning and faster treatment of large structures following major disasters, such as floods or bioterrorism.
Supplemental Keywords:
small business, SBIR, chlorine dioxide detection, optical sensor, chlorine dioxide monitoring, chlorine dioxide decontamination, air quality, public health EPA, ETV, building decontamination, water decontamination, optical analyzer, laser spectroscopy, biodecontamination, air quality assessments, atmospheric chemistry, atmospheric measurements, chlorine dioxide, continuous monitoring, field detection, indoor air,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Environmental Engineering, atmospheric measurements, chlorine dioxide, continuous monitoring, optical sensor, field detection, indoor air, air quality assessmentsThe 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.