US EPA

4054227 

Journal Article 

Wastewater treatment plant odor control using a biofiltration system in Duluth, Minnesota 

Boyette, RA; Bergstedt, L 

1998 

107-118 

WOS:000081048500011 

The Western Lake Superior Sanitary District (WLSSD) owns and operates a 45 million gallon per day capacity regional wastewater treatment plant in Duluth, Minnesota. Because of the severely cold climate, all unit process structures are enclosed. Odorous process offgases from many of these structures must be collected for treatment or dispersion. The treatment plant has had a history of odor problems due to sulfide laden influent principally as a result of the high percentage of kraft paper mill wastewater being received and processed at the plant. The most odorous air emissions from influent channels are routinely incinerated in WLSSD's municipal solid waste/sludge co-disposal incinerator. However, odorous offgases from grit removal and sludge thickening rooms were vented to the atmosphere resulting in ongoing odor complaints from neighboring residents. in response to this problem, WLSSD designed and constructed an open bed biofilter system to treat 44,000 cubic feet per minute of sulfide laden exhaust gases from the grit removal room and the dissolved air sludge thickening room. The design also included the capacity for an additional 6,000 CFM of exhaust gas from the influent screw pump area which was included in 1997. The project was designed and constructed on a fast-track schedule between May and October 1996 to take advantage of the short outdoor construction season in Duluth. Construction was completed, and the system started operating in October 1996. The open bed biofilter system successfully operated in the sub-zero temperatures of Northern Minnesota during the 1996-1997 winter. No noticeable odors have been detected From the biofilter surface since start-up. Performance testing of the system was conducted in March 1997. Exhaust air samples were collected and monitored for odors per ASTM 679-91. The inlet and outlet odor concentration averaged 819 dilutions to threshold (D/T) and 9 D/T, respectively. This resulted in an overall odor removal efficiency of 99%. In addition, inlet and outlet total reduced sulfur compounds were measured in September 1997.



This paper presents design, construction, and operating information of this innovative odor control project. Design parameters, air handling, moisture control, media, and cold weather considerations will be discussed. Capital and operating costs as well as odor removal data will also be summarized. Techniques and procedures used to optimize the system's performance and reduce the overall capital and operating expenses will be presented.



This paper is significant to the cold region engineering conference because it will present information on the design, construction, and operation of a moist open bed biological system in a subzero climate Information presented will be useful to other engineers evaluating odor control options at waste treatment facilities in cold weather regions.