Northwest Wastewater Treatment Plant Expansion

City of Springfield, 
Missouri

Northwest Wastewater Treatment Plant Expansion

Service Type: 
Project Highlights: 
  • Plant expansion to 9.5 mgd.
  • Improvements to influent pumping, grit removal, aeration, secondary clarification, and disinfection processes.
  • Total nitrogen and total phosphorus removal, with MLSS pump station and selector basin.
  • On-site sample collection and laboratory/bench-scale testing to optimize plant design.
Springfield’s Northwest Wastewater Treatment Plant
Carollo provided predesign, final design and construction-phase services for Springfield’s Northwest Wastewater Treatment Plant expansion.

Carollo provided final design services for an expansion of the City of Springfield’s Northwest Wastewater Treatment Plant to 9.5 mgd. Facilities included peak flow retention basin improvements, new submersible influent pumps, a new grit removal facility, screenings modifications, selector basin, aeration basin improvements, secondary clarification improvements, ultraviolet (UV) disinfection, odor control, and other related appurtenances.

As part of the preliminary design process, Carollo performed on-site sample collection and laboratory testing to evaluate key characteristics of the activated sludge mixed liquor and the treatability of the effluent for UV disinfection. The testing involved determining the settling characteristics of the mixed liquor suspended solids (MLSS). Through bench-scale testing conducted at the treatment plant, Carollo developed a plant-specific settling curve and used it to establish a correlation between secondary clarifier capacity and MLSS concentration. The project also involved a conductive microscopic evaluation that revealed the presence of filamentous organisms that are known to cause reduced sludge settleability. Carollo identified the main source of the high organic waste that contributed to the poor sludge settleability and recommended pumping this low-flow, high-strength industrial waste to the 35-mgd Southwest plant.

Work included examining effluent samples for UV transmittance, particle size distribution, and collimated-beam (CB) dose/response. Sample results indicated the effluent quality was amendable to disinfection by UV and provided a basis for economically sizing this new equipment. This testing provided additional information not available from historical operating data and allowed Carollo to optimize the plant design.

Planning workshops and regular meetings held with Springfield helped to facilitate clear lines of communication. The feedback from these meetings and other project communications ensured that all project participants understood the key factors in developing the planning alternatives and recommendations. A value engineering workshop also helped to validate process selection and confirm that the recommended alternative was economical. Carollo also assisted operations staff in automating the selector/activated sludge control process for biological nitrogen and phosphorus removal. This included implementing online dissolved oxygen measurements to allow Springfield to maintain a constant solids retention time (SRT) in the activated sludge basin and waste a constant mass to the sludge thickeners.

Carollo also provided construction-phase engineering and support services for the project, including the development of a computerized operations and maintenance manual.