Grantee Research Project Results
Final Report: Real-Time Analysis of Metals in Aqueous Waste Streams
EPA Contract Number: 68D02022Title: Real-Time Analysis of Metals in Aqueous Waste Streams
Investigators: Thomas, Rhys N.
Small Business: Fayette Environmental Services Inc.
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2002 through September 1, 2002
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)
Description:
The primary purpose of this Phase I research project was to prove that a complex absorption spectrum in the x-ray region could be resolved into its elemental composition in a short period of time. Existing technologies for determining the concentrations of metals in wastewater rely on sampling and remote testing, requiring several hours to several days to obtain results. In that period before analysis is complete, wastewater with unacceptable concentrations of regulated metals may be discharged. Fayette Environmental Services, Inc.'s proposed instrument was designed to make the same measurement in minutes through a high-density polyethylene wastewater pipe section or window, without sampling or sample treatment, and with the capability of controlling the outlet valve of the wastewater system.
The same instrument will find application in the monitoring of process baths. A real-time monitor would provide the information necessary to decide when a bath requires adjustment or replacement. Real-time data would reduce the total quantity of waste by allowing baths to be used to the exact end of their useful lives. Signaling bath problems immediately also will be useful in reducing production waste.
Summary/Accomplishments (Outputs/Outcomes):
In this research, a prototype x-ray spectrometer was assembled from commercially available components to collect spectra from surrogate wastewater spiked with a variety of elements, from chlorine to uranium. Elements were measured as ions, polyatomic ions, and suspended solids. Limits were established for the: (1) initial estimate required by the software, (2) noise tolerance of the software, (3) ability of the system to quantify elemental composition as low as 100 ppb, and (4) ability of the system to correctly separate responses from elements of adjacent atomic number.
Aqueous solutions containing 2 to 14 analytes were examined. The number of possible analytes (not only those that were present) was varied from the number of analytes that were present up to 94 (hydrogen through plutonium). In each case, the software resolved the sample spectrum into its elemental composition. Calculation time varied with the number of possible elements. With two elements present, only milliseconds were required. When allowing for 94 elements, as many as 8 seconds were needed. In practice, factor analysis and generator knowledge will be used to reduce the number of possible analytes, allowing the software to generate a quick response.
The initial estimate for the composition of the sample was required to be within 75 percent of the actual value, or the software would become trapped in a local minimum of the multidimensional surface generated by comparing each element of the proposed elemental composition with recorded spectrum. If the solver became trapped, the results were always unreasonable, yielding either a zero concentration for all elements or a very large concentration (limited by the operator to 500 ppm) for at least one element. If an unreasonable result was returned, the software generated another estimate, continuing until a reasonable result was obtained.
The software was shown to tolerate up to 7 percent noise inherent in the constants of the system. The mass absorption coefficients calculated from literature values were stored in the spreadsheet in which the calculations were performed. When these were perturbed by noise before being used, the system still reached the correct elemental composition. The investigated concentration range was from 100 ppm to 0.1 ppm. The software scaled all values into the same order of magnitude as the first step of the calculations to avoid having the standard deviation of one value swamping a smaller value.
Conclusions:
The instrument, being cost comparable to existing analytical methods, will be attractive to industries that generate metal-laden wastewater. In addition to meeting the analytical burden cost effectively, the instrument will reduce liability by documenting all discharges in small increments of time. The instrument also will find application in monitoring process baths for trace metals contamination and for primary metal concentration. Monitoring trace metal contamination will allow the user to determine when a bath requires replacement or cleanup. Monitoring primary metal concentration will allow the user to extend the life of a process bath to the maximum. Furthermore, because these analyses require no sampling or sample treatment, personnel who are not trained in analytical chemistry may monitor the baths.
The same instrument may be modified to analyze metals in gaseous effluent with detection limits below current regulatory levels. This is feasible because the absorbance mathematics depend on the product of pathlength and density. To compensate for the low density of gaseous effluent, the pathlength needs only to be lengthened proportionately. A gaseous effluent stack is more than tall enough to contain such an analytical beam of photons aimed diagonally up the inside. The instrumentation would be placed entirely outside the stack in environmental housings. Coal-fired power plants, cement kilns, and waste incinerators could be fitted with such spectrometers to monitor the metals content of their fly ash in real time. Elemental mercury vapor also may be monitored. The software method developed in this research has application to all forms of spectroscopy in which complex spectra must be resolved into a list of known elemental or molecular components.
Supplemental Keywords:
monitoring, spectrometry, spectroscopy, metals, aqueous waste stream, wastewater, real-time analysis, fly ash, elemental mercury, trace metal contamination, SBIR, RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Wastewater, Monitoring/Modeling, Analytical Chemistry, Environmental Monitoring, Ecology and Ecosystems, Biology, Engineering, Chemistry, & Physics, Environmental Engineering, monitoring, wastewater treatment, spectrometry, real time analysis, contaminant transport, contaminants, field portable systems, field portable monitoring, municipal sewers, field monitoring, detection system, municipal wastewater, stormwater, water quality, field detection, water contaminants, aqueous waste stream, real-time monitoring, aqueous waste streamsThe 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.