Thermal treatments for hazardous waste are controversial due to the risk of toxins’ being released into the atmosphere from the operation of incinerators and other combustors. Some activist groups oppose the burning of hazardous waste and have alerted the public to the risk that high levels of hazardous waste by-products could be emitted, threatening public health and the environment. The U.S. Environmental Protection Agency is putting pressure on thermal treatment operators to lower the levels of air pollutants. A recent EPA ruling forces hazardous waste treatment operators to comply with new, more stringent standards for controlling the emission of a range of combustion compounds. The ruling also requires that facilities demonstrate their compliance with the new standards by installing continuous emission monitors (CEMs) to detect the composition and concentration of pollutants in stack gas emissions continuously and in real time. The ruling requires CEMs for carbon monoxide, hydrocarbons, and particulate matter. Failure to comply with the ruling will lead to closure of facilities.

Closure of DOE incinerators and kilns would threaten DOE cleanup since thermal treatment is DOE’s only currently available permitted technology for destroying much of its inventory of mixed low-level and mixed transuranic waste. The new ruling, which establishes a deadline for compliance, is focusing the efforts of several Office of Science and Technology programs that have an interest in the development or demonstration of CEMs: Mixed Waste Focus Area (MWFA); Characterization, Monitoring, and Sensor Technology Crosscutting Program (CMST); and Industry and University Programs. In addition, the National Technical Workgroup (NTW) on Mixed Waste Treatment—established by MWFA and composed of representatives from DOE, EPA, states, and privatized facilities—is interpreting the impacts of the new ruling on the costs and regulatory burdens of DOE’s facilities and is examining how the rules, which are written for hazardous waste treatment, will apply to mixed waste treatment. NTW technical assistance teams advise mixed waste incinerator operators on compliance with the new rule.

What’s the hurry?
Under the authority of the Clean Air Act and the Resource Conservation and Recovery Act, EPA promulgated stricter standards for hazardous waste–burning combustors on September 30, 1999. Based on the Maximum Achievable Control Technology (MACT) approach required by the Clean Air Act, the MACT amendment to the Clean Air Act gives facilities three years from the date of promulgation—until September 30, 2002—to comply with a range of emissions standards for controlling the release of toxins into the atmosphere. MACT requires that operators of hazardous waste combustors file a notice of intent to comply or not to comply by September 30, 2000. Filing a notice of intent not to comply will close facilities a year earlier—September 30, 2001.

Why CEMs?
EPA’s move to require CEMs for detecting and controlling the release of carbon monoxide, hydrocarbons, and particulate matter is based on the commercial availability of CEMs for these pollutants. EPA believes these technologies are ready on a wide scale to offer better protection to public health and the environment. Multimetal and mercury CEMs are presently in the developmental stages, and their use won’t be required by the MACT rule; however, EPA is offering incentives for their use.

Apart from regulatory considerations, CEMs offer advantages to facility operators, who can minimize reliance on extensive waste characterization, operating parameter controls, and trial burns—current methods for validating compliance. When CEMs aren’t available or aren’t sensitive enough to detect pollutants at the levels necessary to establish compliance, costly trial burns are necessary during which EPA-approved manual sampling of flue gas emissions demonstrates that compliance is being achieved. Continuous compliance with the standard is then assumed by constraining incinerator operation to the operating parameters that existed during the trial burn—such parameters as waste feed composition and rate, combustion temperature, flue gas flow rate, and oxygen and carbon dioxide concentration in the stack. Limitations on waste feed composition and rate require frequent waste characterization, which can cost millions of dollars per year per facility.

CEMs replace assumptions about emissions with actual emissions data that is provided continuously and in real or near real time to control burn parameters and maintain compliance. By continuously validating compliance to the new standards, CEMs will support safer and better waste treatment and may help reverse the negative perception about hazardous waste thermal treatments that exists among some people.

Countdown to 9/30/02
OST’s CEM development and demonstration projects are in response to the critical need among DOE sites to continue operation of mixed waste thermal treatment facilities at the Consolidated Incineration Facility at the Savannah River Site, the Waste Experimental Reduction Facility at the Idaho National Engineering and Environmental Laboratory, and the Toxic Substances Control Act rotary kiln at the Oak Ridge National Laboratory. The MACT rule will, of course, also affect DOE mixed waste facilities that are in the planning stages, as well as commercially operated facilities on which DOE depends in Tennessee and North Carolina.

Laser-Spark Spectroscopy
CMST is funding the development and testing of a CEM for multimetals based on laser-induced breakdown spectroscopy. Laser-Spark Spectroscopy (LASS), developed by Sandia National Laboratories, uses a pulsed laser to create a pinpoint of plasma within the offgas stack. The microplasma dissociates and excites all metal species, in both the gaseous and particulate phases, within the plasma. Fiber optics collects the resulting spectral emissions for the simultaneous analysis of antimony, arsenic, beryllium, cadmium, chromium, lead, and mercury. LASS can measure metals embedded in particles, fine aerosols, or vapors. In addition to monitoring and compliance assurance, LASS may be readily adapted to control furnace operation, automatically correcting for conditions that signal noncompliance before hazardous metals are emitted through the stack. This capability would lower the risk of hazardous metal emission, enhance the efficiency of operations, and help assure the public that incinerators are an environmentally sound way to dispose of hazardous waste. (OST/TMS ID 18)

Microwave Plasma Analyzer
Another multimetal CEM, this one based on a microwave-induced plasma, is being developed through Industry and University Programs. The technique, being developed by the Massachusetts Institute of Technology, is similar in concept to the LASS system described above, except the MIT CEM uses focused microwave energy to create a plasma in a continuously extracted sample of off-gas. As with LASS, emitted light is captured by fiber optics and analyzed in a spectrometer for a full range of hazardous metals.

High-Resolution Interferometric Spectrometer
This CMST project is developing a spectrometer to improve the practicability of CEMs for detecting toxic metals and actinides. By monitoring spectral data collected from an air inductively coupled plasma atomic emission spectrometer (ICPAES), this high-resolution, solid-state, compact spectrometer will enable the field operation of other CEMs based on optical emissions. The system reduces the size of the optical system while providing superior resolution and reducing spectral interferences. This project also involves the Diagnostic Instrumentation and Analysis Laboratory (DIAL) at Mississippi State University, which is developing ICPAES. (OST/TMS ID 1564)

The system offers the resolution and sensitivity of a 1.0- to 1.5-meter spectrometer in a package that is less than 1/10 the usual size and weight. The system consists of a 38-centimeter echelle-grating spectrometer with an acousto-optic tunable filter (AOTF) performing grating-order selection. An array detector, either a linear photodiode array or a rectangular charged coupled device array, detects the dispersed emission. The AOTF is a quartz crystal device that selects a narrow band (0.1–0.6 nm) of emitted light and rotates its polarization by 90 degrees. When placed between crossed polarizers, only the selected wavelength band is transmitted to the echelle grating. The AOTF wavelength is tuned by changing an applied radio frequency. The AOTF enables extremely rapid sequential or simultaneous selection of wavelengths with no moving parts. The wavelength-switching rate is limited to several milliseconds by the electronics and the speed of the acoustic wave in the quartz crystal.

Compared with tunable-grating spectrometers with comparable resolution, this detection system is smaller and lighter, provides more rapid wavelength tuning, and is more flexible than direct reader spectrometers, which require moving the detector components to change selected lines.

Surface Acoustic Wave Mercury Vapor Sensor
Under development by the Sensor Research and Development Corporation (SRDC) through Industry and University Programs, the surface acoustic wave (SAW) mercury vapor sensor is targeted to meet the needs of the many small- and medium-sized emitters, who will be seeking low-cost alternatives to commercially available CEMs that are based upon spectroscopic technologies. SRDC’s prototype instrument is a SAW microsensor that employs a gold film as a sensing element to detect mercury vapor. The film’s conductivity or resistivity and its mass change in response to changing mercury concentrations. The SAW device monitors the film’s changes and outputs a frequency that is a direct measure of the mercury concentration. Through the development of other selective films, this sensor technology is extendible to the selective detection of other metal contaminants. The integration of chemiresistive and SAW technology has the potential to provide a small, low-power, portable, inexpensive, and accurate means of monitoring mercury vapor over a broad range of concentrations from subparts per billion to parts per million. (OST/TMS ID 2170)

Continuous monitoring of furans and dioxins
Another project falling under Industry and University Programs is SRI International’s development of a CEM for detecting furans and dioxins at realistic concentrations (parts per trillion or subparts per trillion) in real time (minutes). SRI’s instrument is based on supersonic jet expansion and cooling followed by resonantly enhanced, multiphoton ionization (REMPI) and a mass spectrometer. Once developed, the instrument will be used to study the emission levels of key dioxins, leading eventually to an improved understanding of the formation of these molecules and an improved means for monitoring and controlling them.

The instrument’s sensitivity and selectivity is made possible by the combination of its three main components: a pulsed gas jet, REMPI, and a mass spectrometer. A pulsed gas valve subjects a sample of molecules from the off-gas to a free jet expansion that cools the gas to within a few degrees of absolute zero. The lowered sample temperature narrows the resonance line widths through reduction in molecule velocities, which reduces the ionization of other molecular species and leads to improved selectivity. The instrument’s narrow-bandwidth, tunable laser source yields very high selectivity while REMPI simultaneously produces positively charged ions whose molecular weight can be measured by mass spectrometry. The simultaneous detection by wavelength and mass yields extremely high chemical selectivity crucial to identifying one trace compound in the midst of many other similar ones. (OST/TMS ID 2305)

CEM demonstrations on the minds of many
Improving the chances that DOE mixed waste thermal treatment facilities will remain online past September 30, 2002, is the participation of multiple federal agencies, technology developers, and technology users in jointly supported CEM demonstrations. MWFA and CMST are cooperating with EPA in conducting long-term performance testing of several CEMs for monitoring the emissions of particulate matter, mercury, multimetals, organics, polychlorinated dioxins/furans, and radionuclides. The goal is to accelerate the commercial availability of those CEMS that meet both CEM performance standards specified in the MACT amendment and DOE technical requirements specified by MWFA. Drawing solutions from industry and other agencies will augment OST’s development activities and help ensure that DOE is doing its share to lower air pollution and validate the agency’s compliance with the new tougher air standards.

For more information on the Mixed Waste Focus Area’s CEM development projects, see the Offgas Monitoring and Control page of the focus area’s Web site at http://wastenot.inel.gov/mwfa/
offgas.html, or contact Steve Priebe, the Offgas Monitoring and Control Work Package Manager, at (208) 526-0898, priebesj@inel.gov.