WASTEWATER TREATMENT PLANT ODOR CONTROL USING A LAVA ROCK BASED BIOFILTER

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 the need for a plant expansion. This prompted the Sewerage Commission to investigate odor control techniques.Previous work undertaken by the Commission in the early 1990's 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 organics. Chemical masking agents were being used with limited success. Two options were considered for odor treatment:Chemical scrubbing of the foul air.Biofiltration of the foul air.Preliminary investigations determine that chemical scrubbing could cost as much as 1,000,000 with annual operating costs of 150,000/year. Biofilters, however, would have similar capital costs but much lower operating costs. Therefore, McMahon Associates, Inc. recommended the Commission pilot test a biofilter at the plant to evaluate the performance and to develop design criteria.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 proceeded with the full scale biofilter, using lava rock as the media, placed in two existing 100-ft. diameter biosolids storage tanks sized at 45,000 cfm. The system was constructed during the summer of 2000 and placed into operation on November 1, 2000. The paper includes full scale operating data as well as pilot test results, design details and operating parameters.