North Lee County Water Treatment Plant Rehabilitation and Expansion

Lee County Utilities, 
Florida

North Lee County Water Treatment Plant Rehabilitation and Expansion

Awards: 
2012 Overall in the Water/Wastewater Projects under $25M - Design-Build Institute of America (Florida Section)
Service Type: 
Project Highlights: 
  • Design added energy recovery and eliminated sulfuric acid, which saves up to $784,000 per year.
  • Progressive design/build delivery.
  • Challenging project schedule with substantial completion in 15 months.
Sulfuric acid elimination
Sulfuric acid elimination reduced operating costs and improved operator safety.

The North Lee County RO WTP (NLC WTP) was constructed in response to the need for additional capacity in the Lee County Utilities’ (LCU) northern service area. LCU began operating the NLC WTP in October 2006 and since that time has faced several challenges that have resulted in the inability to meet nameplate capacity. The causes for this include:

  • Changes in feed water quality.
  • Irreversibly fouled RO membranes.
  • Process control deficiencies.
  • Undersized RO feed pumps.

Additionally, several other deficiencies were identified by the LCU staff, including:

  • Undersized or inadequately controlled infrastructure to support expanded plant flows.
  • Reliability concerns pertaining to:
    • Corroded equipment.
    • Maintainability of chemical injectors.
    • The adequacy of sulfide removal.

Carollo was selected to provide design and construction phase engineering services for the progressive-design/build delivery of the expansion of this facility to 10-mgd. As part of the design, Carollo addressed the hydraulic issues by increasing RO feed pump sizes from 75 to 250 HP and redesigning the existing and new RO trains to reduce feed pressure. An innovative turbine assisted motorized interstage booster pump was included in both the new and rehabilitated RO train designs to recover wasted energy from the concentrate stream. Reliability concerns were addressed by improving the control and chemical feed systems, eliminating sulfuric acid and providing enhanced sulfide removal by adding carbonic acid to the degasifier feed water. In all, Carollo’s design for this $16.9-million project reduces operating costs by much as $784,000 per year.