After a hot summer and an expansion project, Bridgeport's treatment plant began receiving odor complaints. Here's how they regained their good-neighbor status.
The Water Pollution Control Authority (WPCA) of the city of Bridgeport, Connecticut, operates two wastewater treatment facilities and maintains the city’s sewer system.
The customer’s needs:
After years of operating successfully in the community, the city of Bridgeport’s WPCA had developed an odor problem at its East Side Wastewater Treatment Plant. It was an exceptionally hot summer, and the plant’s expansion/refurbishment project had taken one-third of the treatment plant's facilities out of service. Equipment that was still in service was old and near the end of its life. The plant was operating with a diminished air supply in its process air blowers, and a major user expanded demand for treatment services causing a significant change in the characteristics of the wastewater received for treatment.
These factors led to odor complaints that put the treatment plant in the community spotlight. The extent of the problem was obvious to everyone, especially neighbors in condominium developments, marinas and industrial/commercial operations surrounding the treatment plant. The situation reached the point where the state of Connecticut issued a consent order, directing WPCA to eliminate the odor.
In response, WPCA commissioned an odor study that identified potential sources of odor and recommended a plan of action. The initial recommended solution was a capture-and-treat approach involving a substantial number of fixed covers over primary clarifiers, influent and effluent channels and various skimming pits, along with a central odor treatment system.
After consulting with its engineering advisors and operating staff, WPCA concluded the proposed solution was technically sound, but the fixed covers did not address the operational need for regular access to the tanks to observe the treatment process, inspect equipment and take samples. Also, because the odor sources were dispersed around the plant property, there was a concern that an elaborate and expensive piping system would be required to bring the odorous off-gas to a central treatment system.
A search was initiated for a cover system that allowed better tank access and a treatment system better suited to the dispersed odor sources. A solution was critical, but so were cost concerns. In an effort to meet both operating and cost requirements, WPCA investigated various cover systems and chose a solution consisting of three different cover styles.
WPCA chose a retractable, structurally supported cover system manufactured by Geomembrane Technologies Inc. (GTI) for the influent channel and primary clarifiers. GTI's structurally supported covers met the operational need for regular and unencumbered access to the tanks. They consist of a sheet of durable, coated fabric tensioned across a series of low-profile aluminum arches that span each tank opening.
The fabric cover is sufficiently airtight to capture the off-gases for removal to the treatment system, yet it can be detached on three sides and retracted to expose the tank contents for easy inspection or maintenance. The arched shape means that rain or snow-melt water automatically runs off the cover to the tank perimeter.
GTI's designers worked with the WPCA and its advisers to add several customized features that either made the operator's job easier or simplified connections to the odor treatment system.
Skimming pits are covered with GTI's suspended covers. The irregular shape of the pits, and the many pipe and cable penetrations, made these high-strength, flexible, tensioned fabric covers a good choice.
Narrow channels within concrete walkways are covered with aluminum diamond plate panels. The aluminum plate replaces aluminum grating and is fabricated in sections sized to allow manual removal.
Odorous air captured under the various cover systems is exhausted to individual prepackaged carbon filtration systems that are installed beside each odor source. WPCA staff also addressed odors from the sludge storage tanks. The headspace in the tanks is used as an inlet air source for a mixing air blower system in the plant's chlorine contact basin. Sludge odors are oxidized as the air curtain mixes the wastewater.
GTI’s creative cover system solution proved successful in meeting odor complaints and the fiscal budget as well as positioning WPCA well for future expansions.
The WPCA found that this solution has a double benefit: a cost savings in not having to run a pipe network from each odor source to a central treatment facility, as well as the flexibility to add more covers and treatment systems if required in the future.
Following installation of the covers and odor treatment systems, the odors were brought under control at the East Side Wastewater Treatment Plant. WPCA and the surrounding community are once again back to a harmonious relationship.