WASTEWATER TREATMENT PLANT ODOR CONTROL USING BIOFILTRATION

The Neenah-Menasha Sewerage Commission owns and operates a 13 mgd wastewater treatment facility, which is adjacent to a residential area. Odor complaints intensified when the area residents learned of a need for future plant expansion. These odor complaints prompted the Sewerage Commission to investigate odor control techniques.In the early 1990s the Commission identified the main source of odors to be from the screw pumps, headworks (grit and screening area) and biosolids dewatering operations. These odors are primarily related to hydrogen sulfide, ammonia and volatile organic compounds (VOCs). Chemical masking agents were being used at the time with limited success. Two options were considered for permanent odor treatment: chemical scrubbing and biofiltration.Preliminary cost investigations determined that chemical scrubbing could cost as much as 1,000,000 with annual operating costs of 150,000/year. Biofilters, however, may have similar capital costs but much lower operating costs. Biofilters may also have a lower capital cost depending on the adopted design. Therefore it was recommended to the Commission that a pilot test of a biofilter be conducted to evaluate the performance and to develop full-scale design parameters.A pilot biofilter was installed on the exhaust from the Dewatering Room and operated from July 2, 1999 through October 1999. Throughout the study, the unit successfully removed 82% of the ammonia to non-detectable levels and 94% of the volatile organic compounds related to odors. Hydrogen sulfide never exceeded 1 ppm in the pilot biofilter exhaust.The cost of chemical scrubbing to biofiltration was compared for systems sized at two air flow rates. The cost analysis showed the biofilter to be the most cost effective choice.Construction of a full-scale biofilter, using lava rock as the media, placed in two existing 100-ft. diameter biosolids storage tanks sized at 45,000 cfm was completed in January, 2001. Operation of the full-scale unit has shown and effectiveness in removing VOCs, ammonia, and hydrogen sulfide (when present). More importantly, the operational biofilter has decreased facility odors, increased local support for the facility, and been a cost-effective solution to odor control.