Applying European Olfactometry Standard EN 13725 for Odor Performance Testing in Milford Connecticut – Lessons Learned

The City of Milford, Connecticut (City) is a residential coastal community located in the south central portion of the state approximately half way between the State of New York, and the State of Rhode Island. The City owns and operates two advanced wastewater treatment facilities (WWTF). The Housatonic WWTF is a 12.0 million gallon per day (mgd) activated sludge treatment facility that was upgraded using the Modified Ludzack-Ettinger (MLE) process for removal of total nitrogen. The Beaver Brook WWTF is a 3.0 million gallon per day (mgd) activated sludge treatment facility that was upgraded using the Modified Ludzack-Ettinger (MLE) process for removal of total nitrogen. The upgrading of both facilities was completed in the summer of 2009. Each facility included improvements to the preliminary treatment and sludge processing systems that were completed at the same time as the nitrogen removal improvements. Each facility was retrofitted with a new centralized odor control system that is designed to treat foul air that is exhausted from the Headworks, and Sludge Processing Facilities. Both facilities are located adjacent to residential neighborhoods that required effective odor containment, collection, and treatment to meet the neighborhood expectation of “no odors”.The odor control systems at each facility utilize multi-stage packed bed chemical scrubbers. The scrubbers are designed to treat foul air containing peak hydrogen sulfide (H2S) concentrations of 30 parts per million by volume (ppmv). The units are required to provide 98 percent removal of H2S and 90 percent odor removal. In the past odor control system performance testing followed American Society of Testing Materials ASTM E-679-04 – “Standard Practice for Determination of Taste and Odor Threshold by Forced Choice Ascending Concentration Series Method of Limits” (ASTM, 2004). Due to the sensitivity of the community to odors near the WWTF it was decided that an additional requirement would be included in the project specifications for odor control system performance testing. The performance testing specifications included an additional requirement to follow European Olfactometry Standard EN 13725:2003 – “Air Quality Determination of Odor Concentrations by Dynamic Olfactometry” (CEN, 2003) with respect to olfactometer design, calibration, sample air flow, sample air velocity, odor laboratory operation, assessor selection, and quality assurance/quality control procedures during laboratory testing. During the odor performance testing foul air from each process area was exhausted to the scrubber system. In addition, bottled H2S gas was metered into the airstream upstream of the scrubber system to maintain inlet H2S concentrations at 25 ppmv throughout the performance test to verify that the scrubber system will perform as specified at the design peak operating conditionsThe odor control system at the Housatonic WWTF treats airflows of 21,700 cfm from the Aerated Grit Chambers, Screenings Building, WAS Holding Tanks, Septage Holding Tanks, Solids Handling Building Belt Filter Press Room, Solids Handling Building Sludge Loading Garage Bay, and covered primary clarifier effluent launders. The odor control system at the Beaver Brook WWTF treats airflows of 9,800 cfm from the Influent Lift Station, Sludge Dewatering Room, Sludge Loading Garage Bay, and WAS Storage Tanks. During the performance testing inlet odor concentrations of up to 22,000 dilutions to threshold (D/T) were recorded. Outlet odor concentrations ranged from 600 to 800 D/T. The units both successfully completed the performance tests.This paper will outline the impacts that the EN 13725 requirements had on the project with respect to locating laboratories that actually conform to EN 13725, impacts on sample collection, sample holding time, impacts on the odor test results and other lessons learned during the Milford odor control system performance testing and subsequent operation.