Influent Pumping
Raw sewage from all the sewage collection systems combines into one influent pipeline that divides between two influent pump stations each with a trash rake at the inlet of the pump stations’ wet wells.  The trash rakes allow water to pass through, but remove large debris such as paper towels, plastic wrappers, rags, washcloths, baby wipes, and diapers.  This enables the raw sewage to be pumped, without clogging, to the fine screen building via three flow sensors.

 
Influent Pump Station

Fine screens remove solids and debris to prevent damage to downstream pumps and other mechanical equipment.  They also increase the efficiency of the facility by reducing solids buildup in downstream basins.  The captured screenings are dewatered before being discharged to a dumpster to be hauled off site for disposal. 

The screened wastewater flows by gravity to two pairs of grit removal units where dense particles, particularly grit, is settled out of the wastewater.  The captured grit is pumped through grit cyclones and classifiers to wash organics from the grit and then hauled off site for disposal. 

Primary Clarification
Two primary clarifier junction boxes distribute flow to four primary clarifiers.  Sludge that settles to the bottom of the clarifier is removed as primary sludge and scum that floats on the surface of the clarifier is removed as primary scum.  Primary sludge and scum are pumped to the fermenters.  Ferric chloride can be added to the primary clarifier junction box for chemical precipitation of phosphorus.  The precipitated phosphorus settles and is removed with the primary sludge.  The primary clarifiers overflow treated wastewater to the biological reactor inlet box.  The primary clarifiers can be bypassed at the primary junction box allowing flow from the grit removal units to be sent directly to the biological reactors.

Secondary Biological Treatment
The biological reactor inlet box distributes flow to an Enhanced Nutrient Removal (ENR) system that includes twelve biological reactors, six secondary anoxic tanks, and six final clarifiers for biologically and chemically removing nutrients from the wastewater.

Biological Reactors and Secondary Anoxic Tanks
The biological reactors receive incoming wastewater from the primary clarifiers and discharge to the secondary anoxic tanks where treatment continues.  A large population of microorganisms consumes organic carbon compounds, nitrogen, and phosphorus.  The resulting mixture, called activated sludge, flows from clarified effluent and discharges to the tertiary filters.  Most of the settled activated sludge is recycled back to the biological reactors.  A small percentage of the settled activated sludge is wasted from the system.

 

Final Clarifier
Mixed liquor from the biological reactors flows to six clarifiers where the solids, mostly microorganisms, settle by gravity and the scum rises to the clarifier surface leaving treated wastewater to overflow to the clarifier weirs and discharge to the tertiary filter.  Most of the settled solids are returned to the biological reactors, as return activated sludge (RAS).

Final clarifiers collect secondary scum from the liquid surface and settled RAS from the bottom of the clarifiers.  RAS pump stations draw the secondary scum and RAS from clarifiers and discharge to the biological reactors.  After this process is performed throughout the clarifiers, sludge is discharged into storage tanks.

A small controlled portion of the RAS and scum is removed as WAS by a variable position motorized valve and directed to a gravity belt thickener.  The thickened WAS from the gravity belt thickener is pumped to the digesters.  The volume of WAS is controlled to maintain a target concentration of solids in the biological treatment system.

RAS Junction

 

Final Clarifier