Council Bluffs, IA

Wastewater Treatment Disinfection

  • Client City of Council Bluffs
  • Type Wastewater
  • Services Evaluation, Design
  • Project Manager Keith Hobson, P.E., BCEE
  • Project Engineer Laurie Twitchell, P.E., BCEE

Challenge

FOX teamed with the city on a project resulting in the largest UV installation in the state of Iowa (2011). The disinfection study phase included evaluation of various options for implementation; FOX worked extensively with plant staff to evaluate options specifically suited for the Council Bluffs facility.

UV Electrical Cabinets

UV Electrical Cabinets

Solution

The trickling filter solids characteristics and wastewater effluent quality were tested and compared to disinfection alternatives specifically sized for this use. In addition to capital cost quotes, quotes were also obtained for operation, maintenance, and replacement items in each alternative. The present worth cost evaluation was performed utilizing all cost factors. An evaluation was conducted with plant staff on non-economic issues such as safety, reliability, ease of operation, risks to effluent quality, and space requirements. The alternative selected by the city was the ultraviolet disinfection using high intensity lamps.

A unique aspect of this investigation included testing of the required chlorine dosing on the Council Bluffs effluent and testing of the effectiveness of the chlorine contact basin. The basin was a circular tank with center feed similar to a clarifier. Theoretical contact time in the basin was 30 minutes at average flows. However, using dye testing it was shown that short circuiting was experienced after less than 5 minutes as illustrated in the photo. This highlighted the importance of providing modifications for improved clarifier performance.

A thorough hydraulic evaluation was needed for this facility because of the constraints presented by Missouri River flood levels and the hydraulic conditions of the original plant design. Insertion of a UV light disinfection facility between the final clarifiers and flood levels required detailed calculations on various conditions through pipes, open channels, weirs, and troughs. A design was implemented utilizing the trough elevations of two clarifiers and modifying the weirs and troughs in the other two final clarifiers, and modifying the depth of troughs in all basins. Special dewatering was implemented to allow for construction of the units as well as the final clarifier modifications.

Thorough research and lab testing are necessary when applying UV technology to trickling filter effluent. FOX provided detailed research and guidance on the appropriateness of UV for the city’s unique effluent, so that the city would feel comfortable selecting UV technology.

UV Outfall

UV Outfall

Outcome

UV equipment was procured in September 2009 to incorporate energy efficiencies and operating and maintenance costs into the overall equipment selection. Outstanding bids were received for equipment procurement and construction. This allowed FOX and the city to tailor the design to meet the particular needs of the city and manufacturer. The final design and construction implemented the hydraulic requirements, final clarifier modifications, piping changes, effluent flow meter, and flow splitter boxes as well as the UV disinfection facility. Missouri River flooding during construction was extensive for extended periods but the dewatering operation sustained the excavations and clarifier structures.