The 5 mgd Wilsonville WWTP was experiencing odor complaints from the adjacent residential neighborhood. An existing in-ground, bark and wood-chip biofilter was not performing well. In December 2004, the City of Wilsonville contacted BioReaction Industries (BRI) requesting the design of a bio-oxidation system with guaranteed performance criteria. The project required an understanding of the nature of the odor problem and quick implementation of a solution to reduce odors under the agreed-upon performance criteria. The design necessitated a small footprint due to site limitations, and rapid construction and installation to address the recurring odor problems. An induced draft, multi-stage system consisting of a 12’d x 24’h biotrickling filter followed by a 12’d x 24’h biomatrix tower was the solution, providing greater than 99% reduction of H2S and reduce organo-sulfur compounds to below the odor threshold in the 8,000 cfm process airstream. Construction and installation was rapid and the bio-oxidation system has been in continuous operation since start-up in early June 2005 with no malfunctions and no increases in back pressure or other operational issues. Data collected on system performance demonstrated that the engineered biofilter is achieving all performance criteria.
In December 2004, the City of Wilsonville contacted BioReaction Industries (BRI) and asked if they could design a bio-oxidation system that would treat the odors emanating from the WWTP (located in the Willamette River flood plain and adjacent to a residential area); and provide the City this equipment under a ‘guaranteed performance criteria’. Wilsonville had some experience with BRI’s odor control equipment in a pilot demonstration several years earlier that was very successful in eliminating the odors from a ‘grit box’. The Wilsonville WWTP had fully-enclosed and ducted odor containment and collection system in place, but the two year old existing inground biofilter odor abatement system was not able to accomplish the task of 99% odor removal. The problems were excessive back pressure, channeling and added maintenance (bed tilling and replacement) in the existing forced-draft system. BRI was successful in providing Wilsonville the odor control system they needed without extensive maintenance and without replacing the bed annually, if not more often, and at a cost-effective price.
GOALS AND OBJECTIVES
The primary goal of this project was to understand the nature of the odor problem and quickly implement a solution to reduce odors under agreed-upon performance criteria. Two additional requirements were: 1 -design of a system with a small footprint due to site limitations, and 2 - rapid construction and installation to address potential odor problems during the upcoming summer season.
IDENTIFYING THE PROBLEM
During the summer months, with warmer temperatures and winds from the south, the 5 mgd Wilsonville WWTP experienced odor complaints from the residential neighborhood located approximately 50-75 feet above its north property boundary. A forced draft in-ground biofilter system was installed in 2003 and was very successful initially. However, after approximately 12 months severe backpressure problems developed (compaction), and repeated attempts to ‘till the bio-bed’ only resulted in short-term fixes with secondary short-circuiting and finally, compaction again, which severely limited the airflow. After several months of working on the problem the existing ‘bed’ was removed and a new bed installed with a different mix of materials, designed to provide longer bed life without compaction. This new bed lasted a relatively short time, developing the same problems encountered in that first bed. At this point, the City determined that an alternative odor control system was necessary. At that time BRI was contacted for evaluation of the system and potential design of a complete odor control system.
A characterization of the emissions air stream was initiated so that the bio-oxidation unit could be appropriately designed for the type and concentration of odor emissions, as well as the air flow (volume) that it would receive. This project was required to be a turn-key installation, from design and construction to installation - including connecting to the existing duct work - followed by commissioning. Tedlar bag samples were collected and analyzed for H2S and reduced sulfur compounds. These data were compared with data that had been previously collected and analyzed. It was determined that the primary odor causing compounds were H2S (up to 10 ppm) and several additional organic sulfur compounds at less than 500 ppb. Ammonia was present in the emissions stream at relatively high levels (up to 180ppm) which could have an effect on the optimal operation of the system and had to be addressed in the design and operation of the system so that it could be removed from the airstream.