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Process Flow Diagram


The design and construction of the treatment facility was funded by a loan from the State Revolving Loan Fund (SRF). The SRF will loan money for facilities such as this at an interest rate 2% below the current state bond bank level, provided all applicable state and federal regulations are followed. The York Sewer District borrowed approximately $6.8 million for design and construction of the facilities.

PROCESS FLOW DIAGRAM - See Process steps below:


A. Headworks
In the headworks wastewater receives preliminary treatment by mechanical screening and grit removal prior to flowing to the aeration basins. Preliminary treatment is provided to protect the downstream piping and equipment from damage and plugging, and to reduce the quantity of grit collected in the aeration basins.

B. Aerations Basins
From the headworks wastewater flows to the existing aeration basins where bacteria provide secondary treatment by breaking down wastes and converting it to cell mass (sludge), water and CO2. This biological treatment requires air which is introduced into the aeration blowers and fine bubble ceramic diffusers.

C. Clarifiers
From the aerations tanks the wastewater flows to two new 70 foot diameter clarifiers each covered by an aluminum dome. In the clarifiers, sludge settles to the bottom of the tank and clarified wastewater flows out to the chlorine contact tank for disinfection. A portion of the settled sludge is pumped back to the aeration tanks to maintain the bacterial population and a portion is wasted to the sludge holding tanks.

D. Disinfection System
From the clarifiers, treated wastewater (effluent) flows to the chlorine contact tank where liquid chlorine is introduced to disinfect the effluent. Before the disinfected effluent is discharged to the ocean in York Harbor, sodium bisulfite is added to remove any residual chlorine that was not used during the disinfection stage.

E. Sludge Pumps

1. Return Pumps
The return sludge pumps return activated sludge from the clarifiers to the aeration basins. The sludge can be returned to the headworks, the aeration flow splitter box or directly to the aeration tanks.

2. Waste Pumps (existing)
The waste sludge pumps waste excess sludge generated during the biological treatment of the wastewater and pump the sludge to the sludge holding tanks.


3. Screw Press Feed Pumps
The screw press feed pumps feed the sludge stored in the sludge holding tanks to the screw presses which dewater the sludge prior to disposal.

F. Dewatering System
The dewatering system is comprised of two screw presses, polymer feed, and a lime stabilization system. This system reduces the volume of sludge that must be disposed of.

G. Plant Water System
The plant water system provides washwater to the screw press, to hydrants located around the treatment plant and to a foam control system located in the aeration tanks.

H. Influent Pumps
The majority of the wastewater flow coming to the treatment facility is pumped to the plant by the Long Beach Pump Station. The gravity portion of the flow enters the treatment facility at the influent pump station where it is pumped to the headworks. In addition, screw press filtrate and spray wash water flows to the influent pump station.

I. Sludge Holding System
Excess sludge generated during the biological treatment of the wastewater is wasted to the sludge holding tanks where the sludge is stored until it is dewatered by the screw presses. The sludge is aerated while it is stored to prevent odors and to further stabilize the sludge.

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