Odor Studies

Our Top Services

Odor Studies by Webster Environmental Associates, Inc.

WEA has completed hundreds of odor studies for municipalities (wastewater treatment plants and collection systems) and industrial clients, since 1981. WEA has all the experience and equipment necessary to evaluate treatment processes, collect air samples, conduct on-site testing of hydrogen sulfide, ammonia and other odorous compounds, perform community odor surveys and evaluate the performance of existing odor control systems.

WEA engineers plan, conduct, and evaluate results from both air and liquid phase sampling and testing to provide our clients with full-service odor control solutions.

This hands-on approach allows WEA to recommend and design the best odor control solutions for each of our clients’ unique odor control needs.

WEA typically prepares a sampling and testing protocol prior to testing that includes sampling and testing means and methods, proposed sampling locations, proposed testing schedule and other details needed to assure the project will meet the client’s goals and objectives.

A typical testing protocol would include the following:

Air samples are collected from all potentially significant odor sources during each round of testing. Two rounds of testing are conducted at many facilities to provide more reliable data. The samples are normally analyzed on-site for hydrogen sulfide (H2S) and sent to laboratories for odor panel analysis and quantification of reduced sulfur compounds.

Air samples are typically analyzed by an odor panel. The samples are shipped via overnight delivery to St. Croix Sensory for analysis. St Croix can analyze the samples for odor detection threshold (DT), recognition threshold (RT), intensity, hedonic tone (HT), persistency (dose response, DR) and characterization. All these parameters are useful in certain situations, but the samples are often analyzed for DT/RT only as DT is the input required for air dispersion modeling.

In addition to the odor panel analyses, WEA normally tests some of the samples for reduced sulfur compounds (RSC). This analysis can be as important as the odor panel analysis because of the need-to-know which compounds are in the air and in what concentrations. WEA typically tests samples from the headworks, primary clarification and solids handling sources for RSCs. This information is needed to identify the best odor control technology and select the appropriate design criteria.

VOC Testing – WEA will sometimes analyze the air samples for volatile organic compounds (VOC) if they are suspected of being present. VOCs are most commonly tested for when there are combustion sources and/or industrial sources.

The recommended sampling locations are identified during a preliminary site inspection and listed in the testing protocol. The proposed locations and the analysis to be performed on each location are presented to the client for review and approval.

Instantaneous measurements of hydrogen sulfide (H2S) concentrations are collected along with each air sample, and at other identified locations in the facilities. An Arizona Instruments Jerome 631X H2S analyzer is used to measure H2S concentrations less than 50 parts per million (ppm). OdaLog/Acrulog H2S data loggers are also used to measure higher concentrations, and to continuously log H2S concentrations at specific locations within the facility. Odalogs/Acrulogs are used to monitor H2S at all locations within the facility that have the potential for H2S. The H2S monitors are typically left in place for one to two weeks. Continuous H2S monitoring is performed to show how the H2S varies diurnally and from day to day.  It is also used to validate the odor panel testing results. For instance, if the H2S was only 1 ppm when the odor sample was collected but the H2S monitor shows that peaks of up to 10 ppm are present, then consideration is given to adjusting the odor panel test results to reflect the higher H2S readings.

Air flow rates are measured in the existing odor control ducts where accessible using a TSI Velocicalc Thermoanemometer.

Liquid samples are typically collected from the plant influent and tested for pH, oxidation reduction potential (ORP) and temperature using a Hanna Model HI98121 instrument. Total sulfides are measured using a LaMotte Model 4456-01 sulfide test kit with a range of 0.2 – 20 mg/L. Dissolved oxygen (DO) can also be tested using a YSI Professional Plus instrument.

Pressure tests are performed to identify potential sources of fugitive emissions from equipment, tanks, and buildings. Pressure testing is conducted with an Extech HD755 differential pressure manometer.

WEA provides all sampling devices, tools, supplies, instruments, and contracts with laboratories for odor panel, RSC and VOC analyses.