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ORANGE COUNTY SANITATION DISTRICT SETS THE STAGE FOR CONVERSION BETWEEN THE OLD AND THE NEW: ODOR ANALYSIS METHODOLOGY

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The Orange County Sanitation District (the Sanitation District or OCSD) has been proactive in developing overall odor control strategies to minimize nuisance odors beyond their facility fence lines. The Sanitation District's two wastewater treatment plants share boundaries with residents, the Santa Ana River Trail, and other sensitive receptors.

Until recently, odors were measured in the United States according to ASTM International Method E 679-04. However, there is a growing trend to adopt the methodology specified in European Standard EN 13725:2003 as an international standard. While there are few regulations specifying fence line odor limits, the few that have been promulgated in the United States were based on the ASTM methodology. In specific, the California Environmental Quality Act (CEQA) set guidelines of 5 D/T (preferable) and 10 D/T (acceptable) based on the ASTM methodology.

Observations of data tested by both methods indicated that analyses by the European method generally reported higher dilutions to threshold (D/T) or odor units (OU) than the ASTM standard. This was particularly important to the Sanitation District because it wanted to develop stringent, but realistic, goals using the most widely accepted techniques, but also be in compliance with CEQA guidelines. Thus they sought to have air samples tested under both methods and mathematically examine the differences between the two methods.

The major difference between the European and ASTM methods is in the presentation flow rate, the rate at which the sample is presented to the odor panelists. The European method specifies a minimum flow rate of 20 liters per minute (L/min), while the ASTM E 679 does not specify a flow rate. Historically the ASTM E 679 testing has been done at 0.5 L/min, however, testing between 3 and 5 L/min has also been used. The European method also specifies qualifications for the panelists, including accuracy and repeatability for sensing n-butanol. There are other nuances between the procedures, but they are considered to be minor for this evaluation.

The Sanitation District worked with CDM and the University of California Riverside to develop a sampling plan and protocol to determine an appropriate conversion between the two testing methods. Various sources throughout both plants were identified to provide a range of odor concentrations. Solids handling, headworks and primary treatment facilities were identified to provide variations in strength of odor and types of odorous compounds. Several samples were taken throughout these facilities and each sample was tested using both testing methodologies. The data was evaluated and itwas determined that there definitely was a difference between the two data sets that could not be described as random. While a single conversion factor did not present itself, the results supported a 2 to 5 ratio (or conversion ratio) between the two methods. In other words, an odor sample reported by the ASTM method as 5 D/T could be expected to correspond to 10 to 25 D/T under the European method. The converse is also true.

The focus of this paper is a presentation of the results supporting a conversion between 2 to 5 between the ASTM and European testing methods. This paper focuses on the experimental setup, testingmethods used, and presentation and discussion of the results. Selection of a fence line odor goal at the Sanitation District's two wastewater treatment plants is also discussed.
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Document Type: Research Article

Publication date: 2006-01-01

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