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ODOR CONTROL STUDY • Colorimetric sorption tubes were used to measure specific sulfur compounds , including H2S and dimethyl sulfide . The tube quantitatively changes color proportionate to the concentration of the sulfur compounds in the gas sample . • A field portable GC/MS was used to measure various organic sulfur compounds by a modified EPA Method TO - 14 . The field -portable GC/MS eliminates potential sampling errors because the sample is drawn directly from the source . Therefore , there is no sampling container, which can negatively bias results. Other common organic compounds (such as toluene and ketones ) were measured by the GC/MS method employed in this study. However, none of these other organic compounds measured at the Central WWTF are considered relevant to odor emissions . This is because the concentrations found in the samples are far below odor detection thresholds for these compounds . For example , as -shown in Table 1 toluene and acetone have odor detection thresholds of 170 and 20 , 000 ppbv, respectively. The highest concentration of toluene in any of the significant emitting sources at the Central WWTF was 82 ppbv. The highest total volatile organic compound (VOC ) concentration was 710 ppbv . Therefore , these organic compounds are considered to have little to no odor significance . By contrast, some of the significant sources at the Central WWTF contained 3 , 000 to 10 , 000 -ppbv of organic sulfur compounds . These organic sulfur compounds have . significant odor implications considering the detection thresholds are less than 1 ppbv . • Samples for each source were collected in Tedlar bags and sent to Odor Science and Engineering in Bloomfield , Connecticut for olfactory odor analyses performed in accordance with ASTM E -679-91 and E-544-99 . Odor emissions were quantified in terms of dilution -to-threshold ( D[T) ratio and intensity. Subjective characterization of the odors was also provided . 2 .2 Mass Emission Rates Once the samples were collected and analyzed , PBSU summarized the data and estimated mass odor emission rates for each treatment process at the Central WWTF . Summaries of data from the olfactory analyses , field measurements , and GC/MS analyses are provided in Tables 2 , 3 , and 4 respectively. For the point sources , the mass emission rates were calculated by multiplying the concentration of the odorant times the airflow rate of the source . For the area sources , the mass emission rates were calculated by multiplying the emission flux rates (as determined by flux chamber measurements ) times the total area of the source . Pertinent data and information about the treatment processes were obtained from County personnel , plant records , drawings , and field measurements . Airflow rates , volumetric concentrations , and flux emission rates that were used in calculating the mass emission rates for each source are presented in Table 2 . Surface areas and emission flux rates are also provided for each area source . All mass emission rates are given in terms of pounds per day of H2S . PBSJ# 5Indian River County, Central Wastewater Treatment Facility 11 PBS&J #071230, February 2003