Odor Threshold Emission Factors for Common WWTP Processes

Odor threshold values of waste water treatment plant (WWTP) processes (i.e. screenings, primaries, aeration, dewatering, etc.) have frequently been reported in individual case study presentations, however, no one source has provided an overview of many odor samples collected at various locations.A review of over seven years of WWTP odor sample results (over 1,000 samples) tested by a commercial laboratory yielded a statistical overview of odor threshold values of common WWTP processes. Emissions from each stage of WWTP as well as odor control processes were reviewed. These results can be used as emission factors for comparison to actual odor study testing results and for estimating odor emissions from plants under development. The geometric mean value would be used as a value for a typical process running under normal conditions. The 3rd quartile value (75th percentile) can be used as a more conservative value or as a likely maximum value for a typical process.All test results were performed following the protocols of dynamic olfactometry testing standards: ASTM International E679-04, EN13725:2003, and AS/NZ 4323.3-2001. The review of odor threshold values also provides correlations of 1) odor threshold values with hydrogen sulfide concentration and 2) samples processed at two olfactometer presentation flow rates (i.e. 0.5-LPM vs. 20-LPM).