Treatment Process


  • 42 MGD Annual Average Flow
  • 54 MGD Peak Month (30-day rolling)
  • 128.4 MGD Peak Instantaneous Influent
  • 90 Million Gallons On-site Emergency Storage
  • 7.5MW Emergency Generator Capacity

Key Permit Requirements

  • Chemical Oxygen Demand (COD) < 10 mg/L
  • Total Phosphorus (TP) <0.1 mg/l
  • Total Suspended Solids (TSS) <1.0 mg/L
  • Total Kjeldall Nitrogen (TKN) <1.0 mg/L
  • Turbidity <0.5 NTU

Conventional Treatment

Conventional Treatment removes over 90% of incoming pollutants and provides a high-quality effluent for subsequent advanced waste treatment polishing steps.

  • Mechanically cleaned bar screens (0.5-inch openings)
  • Vortex grit chambers, 24-ft diameter
  • Circular center-feed primary clarifiers with primary scum collection, 125-ft diameter
  • Archimedes screw primary effluent lift pumps
  • Aerobic biological selectors
  • Activated sludge aeration basins
    • Most basins fine-bubble diffusers
    • All basins operate in nitrifying mode with active D.O. control
    • Four basins have modified Ludzack–Ettinger denitrification process, can achieve 6-10 mg/L nitrate
  • Neuros energy-efficient turbo blowers supply air for the bioreactors
  • 125-ft diameter circular center-feed secondary clarifiers with draft tubes, slot-valve draft control, and biofoam collection
  • Continuous monitoring of secondary effluent TSS, Nitrate, and Ammonia  

Chemical Advanced Treatment

Process water leaving Conventional Treatment enters the high-lime process, to reduce phosphorus to below 0.10 mg/L. This process also serves as a barrier to viruses, captures organics leaving Conventional Treatment, and precipitates heavy metals.

  • Silos with total storage for 240 tons of calcium oxide as pebble quicklime
  • Detention-type lime slakers with lime aging tanks
  • Rapid mix basins for lime slurry addition computer controlled to pH 11
  • Declining-rate flocculation basins
  • Chemical clarifiers, 125-ft circular
  • First stage recarbonation lowers pH to 10. Second stage lowers pH to 7 (neutral).
  • Both stages use coarse-bubble diffusers and introduce exhaust stack gas containing waste carbon dioxide from digester boilers, carbon furnace, and pelletizer furnaces, capturing greenhouse gas from emissions.
  • Recarbonation clarifiers between first and second stages to collect precipitated calcium carbonate
  • Gravity thickeners to concentrate chemical and recarbonation sludge
  • Recessed chamber plate and frame filter presses to dewater sludge
  • On-site 2 million cubic yard captive landfill for dewatered lime solids

Physical Advanced Treatment

Process water leaving Chemical Advanced Treatment enters a Physical Advanced Treatment process. The UOSA permit requires TSS below 1 mg/L and COD below 10 mg/L. To meet these stringent levels, multimedia depth filtration and activated carbon are used.

UOSA has two process trains, one with pressure filtration/carbon and one with gravity. The gravity system is as follows:

  • Six 100-hp vertical turbine pumps transfer effluent from Chemical Advanced Treatment to filters
  • Alum is used as a filter aid
  • Ten multimedia filters with 36-inch bed of anthracite, silica, and garnet
  • Continuous online turbidity analyzers
  • High-rate backwash with air scour
  • Intermediate filter effluent pump station pumps filter effluent to carbon
  • Eight upflow/downflow carbon contactors with 2 million pounds of activated carbon
  • Carbon transfer facilities to facilitate carbon regeneration or replacement

The pressure process train is similar.

Activated carbon is regenerated onsite with a multi-hearth furnace


Process water leaving Physical Advanced Treatment enters a disinfection process prior to discharge. Disinfection creates the final barrier to pathogens. UOSA uses a chlorination and dechlorination process. Sodium hypochlorite and sodium bisulfite are used for the disinfection process.

  • Bulk storage of 36,000 gallons of sodium hypochlorite
  • Three primary disinfection chlorination pumps and three backups (52 gph)
  • Two mix chambers and four 345,000-gallon labyrinth contact basins
  • Continuous online measurement of Total and free residual chlorine at mix chamber, and after 30-minute contact time
  • Bulk storage of 20,000 gallons of sodium bisulfite and transfer pumps for day tanks
  • Three bisulfite feed pumps (52 gph)
  • Continuous online measurement of pre-dechlorination total chlorine residual for bisulfite pacing
  • Continuous online measurement of post-dechlorination total chlorine residual
  • Outfall to 180-million-gallon final effluent reservoir

Digestion and Sludge Handling

Organic sludges from the Conventional Treatment processes are stabilized into a biosolids product used as a soil amendment and chemical fertilizer alternative. Primary sludge and waste activated sludge are screened, digested, blended, dewatered, and ultimately dried to produce fertilizer pellets.

  • Parkson strain presses remove particulates greater than 5 mm from primary sludge and WAS
  • Dissolved air floatation thickeners and Westfalia thickening centrifuges thicken WAS to 5-6 percent
  • Three one-million-gallon mesophilic anaerobic digesters with IDI gas cannon mix systems
    • biogas is burned for digester heating, steam for carbon regeneration and facility heating
    • exhaust gasses are captured and used as primary acid to adjust pH after high-lime process
  • Blending and storage tanks (260,000 gallons) with mix and transfer pumps
  • Sharples and Westfalia dewatering centrifuges
  • Berlie and Andritz pelletizer systems
    • rotary drum dryers
    • 800 tons of pellet storage
  • RDP lime stabilization system as backup
  • High-quality fertilizer product