Overcoming Challenges Associated with Implementing Odor Control Improvements – A Case Study

The 1.8 MGD (ADWF) Sausalito-Marin City Sanitary District (SMCSD) wastewater treatment plant is situated on a small (approximately 2.5-acre), constrained site on the San Francisco Bay. The plant has numerous odor sources that impact nearby residents and cause odor complaints. Spray masking agents installed in 2003 and liquid phase treatment systems have been marginally effective in controlling offsite odors. Customer surveys determined that odor control from the 50 year-old treatment plant was an important community goal and SMCSD Board of Directors authorized funding and implementation of state of the art odor control measures.An odor study was completed in 2004 that identified the major odor sources at the plant and made recommendations for odor control improvements. The SMCSD initiated an odor control improvements project immediately thereafter for addressing and controlling plant fugitive odor emissions. The initial concept design phase selected biotechnology as the preferred odor control technology based primarily on performance, safety, and ease of operation.During the detailed design phase several significant challenges surfaced, including the extremely limited footprint available at the site for new odor control facilities. This challenge was met by selecting small footprint bioscrubbers that would be installed on the roof of an existing control building. This decision triggered a seismic analysis of the existing control building (constructed in 1981), since local seismic criteria had since changed significantly since it was constructed. Structural roof improvements were implemented, coupled with the selection of multiple lightweight bioscrubbers (to spread the load). Roof weight limitation, equipment comparative performance assessment, and schedule issues drove the project to procure the bioscrubbers via a sole-source arrangement. Ongoing plant improvements that were impacting detailed odor control design had to be carefully coordinated.Two major design changes produced a significant cost savings for the project. First, a decision was made to reduce the primary clarifier cover to a launder-only cover. This accomplished a desire of plant staff to minimize confined spaces (for ease of maintenance and renewal and replacement efforts). In addition, there was an expected benefit that planned ferric chloride addition to plant influent would have on both primary clarifier performance and reduction of hydrogen sulfide (H2S) related odors. Second, the design team reversed the fixed film reactor air flow (air flow was changed to a vertical downward direction)_in order to delete the requirement for a fixed film reactor cover from the project (the downward flow pattern was expected to reduce fugitive emissions from the open top). These cover cost savings alone were realized at over 300,000 for the overall 1.5 million dollar project.During the construction phase of this project additional challenges surfaced, including an accelerated deteriorating vehicle access causeway that required the contractor to adjust construction work approaches. In addition, due to limitations related to access at the plant, an ocean barge and crane was used via San Francisco Bay to hoist the bioscrubber equipment onto the roof of the existing control building. Finally, more stringent plant effluent permit requirements imposed by the local water board required that treated plant effluent, designed to be utilized for bioscrubber irrigation, be chlorinated to greater than 5 parts per million (ppm) Cl-, a level exceeding that recommended by the bioscrubber manufacturer. This required that a separate non-chlorinated pumped irrigation system (secondary effluent) be implemented as both an irrigation and nutrient source.The various challenges encountered during implementation of the odor control improvements at the SMCSD were met with ingenuity, creativity and perseverance by both plant staff and the engineering consultant. This allowed the project to move forward, meeting both schedule and budget constraints, and accomplish the project goal of mitigating offsite odors while building community trust and demonstrating that SMCSD is acting as a good neighbor.