Largo Wastewater Reclamation Facility Biological Treatment Improvements

Clearwater, Florida

As part of a Florida Department of Environmental Protection administrative order, the City of Largo was required to update its wastewater reclamation facility. The city selected Kiewit Infrastructure South Co. (Kiewit) to renovate its 50-year-old 18-MGD facility for biological treatment upgrades and a reduction in total effluent nitrogen.

To help reach the City of Largo’s goals, Kiewit’s engineering and procurement teams established a foundational relationship with the city to conduct a thorough understanding of the project. The team provided a strategy to construct the upgrades while keeping two-thirds of the plant operational for community use.

Kiewit’s scope of work included renovations of the existing primary, secondary, and tertiary treatment processes, and the addition of a new tertiary process in the form of disc filtration for total suspended solids (TSS) removal.

Primary treatment renovations included modifications to three Bardenpho biological nutrient removal (BNR) basins, three new chain and flight primary clarifier mechanisms, new influent flow metering, new electrical buildings associated with each train, and new backup power generation.

Secondary treatment renovations included:

• Modifications to five secondary clarifier mechanisms
• One new secondary clarifier mechanism
• Removal of a traveling bridge filter system
• A new secondary effluent pump station
• Two new disc filters
• Filter media replacement and new power logic control stations for nine denitrification filter cells
• A new methanol pumping system and structural modifications to the methanol containment area

This work also included one new electrical building and a new backup power generation system.

Tertiary treatment modification included the addition of a sodium hypochlorite pump skid, associated dual contained transmission piping and minor modifications to a chlorine contact basin.   During construction, the city identified an issue with their sodium hypochlorite mixing in the chlorine contact basins, resulting in the need to add additional basins, piping, coatings, and mixing equipment.

Kiewit separated the project into four work zones based on scope, logistics, equipment delivery dates, permitting and commissioning. This allowed the team to focus on early work design packages and minimize impacts to ongoing plant operations.

This design-build project improved the city’s biological treatment process to reduce effluent total nitrogen loading and meet the permit of by reducing the output from 27 to 19 tons per year.  Through various innovative value-engineering alternatives proposed throughout the project, the owner saved $2.4 million which was subsequently reinvested into other important facility improvements, including modifications to the chlorine contact chamber and the denitrification backwash system. These included additional baffles, walls, backwash pumps and mixing chambers to improve the disinfection process. These enhancements will contribute to additional facility process efficiencies in the plant and long-term cost savings for the City of Largo.

Learn more about Kiewit’s Water Infrastructure Capabilities