The Smell of Success: An Odor Study of the Broomfield Wastewater Reclamation Facility

Wastewater treatment facilities in urban vicinities face the continuing challenge of reducing odor emissions to maintain public favor. This is the case for the City and County (City) of Broomfield Wastewater Reclamation Facility (WRF) located outside of Denver, Colorado. The Broomfield WRF has recently undergone upgrades to proactively address odor issues but occasionally receives odor complaints from neighboring residents. This paper presents the findings from a thorough odor sampling campaign to evaluate odor generation and emissions at the Broomfield WRF.The Broomfield WRF was constructed in the 1950s in a rural area northwest of Denver. Today, the WRF is surrounded by a large community of townhomes and houses bordering on the north and west sides of the facility. Odor complaints are occasional and the City has implemented a number of improvements to reduce odor emissions. The Broomfield WRF is a secondary wastewater treatment plant that includes preliminary treatment, primary clarifiers, aeration basins, secondary clarifiers, dissolved air flotation thickening (DAFT), anaerobic digesters, solids handling, and ultraviolet (UV) disinfection. The facility underwent a plant-wide upgrade, Phase 1 completed in 2005, which included the final phase of installing foul air treatment including six odor control fans and a BIOREM biofilter. This recent study focused on identifying emission sources at the plant and providing recommendations for the Phase 2 upgrade.The odor study involved an intense liquid and gas sampling effort that included gaseous and liquid phase sulfide, air pressure evaluations in rooms and covered tanks, Nasal Ranger® testing of facility boundaries, and smoke testing of the existing biofilter which treats the foul air from the process buildings. The main sources of odors were detected around the digesters, in the digester gas, and in the centrate liquid stream and holding tank foul air. Gas from the digesters measured around 2,000 ppm hydrogen sulfide (H2S) and the gas from the centrate holding tank measured 100 ppm H2S. Also, the influent stream of the facility showed unusual daily spikes in H2S gas and it is very possible that wastewater from one of the collection system lift stations is a major contributor to the high influent sulfide in this stream. The biofilter had little odor and appeared to effectively treat the facility's foul air. However, during the smoke testing, there was a noticeable separation of the smoke on the surface of the filter media although there are no partitions to separate the air flow. The main recommendations from the odor study included the following activities:System Negative Pressures. Increase exhaust air flow from buildings and covered tanks to ensure negative pressure and avoid fugitive emissions.Sulfide Spikes. Confirm that the cause of the afternoon sulfide spike at the influent channel is an upstream pump station operation.Digesters. Consider ferric chloride addition to reduce sulfide concentration in the sludge and consequently in the digester gas and in the dewatering centrate.Centrate Recycle. Consider rerouting centrate recycle stream to an aerobic zone of the aeration tanks.Biofilter. Check air pressures and conduct smoke tests at least every year.Overall, the study found that the facility has improved its odor emission with recent upgrades and odors detected at the facility were minimal. The biofilter appears to be providing effective treatment of the collected foul air. The proposed upgrades for Phase 2 are generally in line with the findings from this study and will further improve odor control.