Small-scale beds of granular activated carbon (GAG) have been tested in this research using challenges of volatile organic compounds (VOCs) in air at concentrations ranging from approximately 0.5 to 100 ppm. The research linked the performance of GAG from high-concentration quickly completed tests to performance at low concentrations near those encountered indoors. For all tests, the carbon bed was approximately 2.54 cm thick and operated with a residence time of 0.11 s. The tests were conducted at 25 °C and 50% relative humidity.The measured 10% breakthrough times ranged from about 0.5 hour to several hundred hours. For the individual compounds, the relationship between the logarithms of breakthrough time and concentration was approximately linear over the experimental range, with different compounds producing lines having different slopes. The measured breakthrough times compared favorably to published data and models. The results suggest that higher-concentration single-component breakthrough tests, which are short and easily obtained, may be cautiously extrapolated to indoor concentrations for these compounds. IMPLICATIONSVolatile organic compounds (VOCs) have been identified as important contributors to poor indoor air quality (IAQ). Indoor VOC concentrations can be reduced through local control or source reduction, increased ventilation, and air cleaning. Beds of granular activated carbon (GAC) are the most commonly used air cleaning technology for VOCs at indoor concentrations. However, design and operating data at the low concentrations encountered indoors are scarce and difficult to obtain. Extrapolation of more available high-concentration performance data to indoor concentrations has not been demonstrated. These test results are directly applicable to constant, low-concentration challenge applications, and they support the use of conventional sorption models to predict performance at indoor concentrations.
A test method based upon the adsorption of chloroform onto charcoal was evaluated for the collection and analysis of chloroform emissions from stationary sources. In this method, a source gas sample is pulled through adsorption tubes containing activated charcoal (to adsorb the chloroform), and chloroform is extracted from the charcoal with a hexane/methanol mixture. The extract is analyzed by gas chromatography with an electron capture detector. Procedures in Environmental Protection Agency (EPA) Method 301 were utilized to test the suitability of the method under field conditions at two sampling sites (paper mills). EPA Method 301 requires that four separate trains ("quad train") operate simultaneously in each run. During each run, two of the four sampling trains were spiked with a known amount of gaseous chloroform. The quad train sampling was performed six or more times. In the first field test, the stack emissions of chloroform were approximately 300 ppm, the mean spike recovery was 82%, the precision of the method for unspiked samples was within 5%, and the sampling bias was -43 ppm. Modifications were made to the sampling method and the spike gas introduction system. The revised method was then tested at a second field site which had chloroform emissions of approximately 220 ppm. The mean spike recovery improved to 95%, the unspiked sample precision was within 5%, and the sampling bias improved to -8.5 ppm.
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