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Preliminary Treatment
Raw wastwater flows into the raw influent wet well located in the headworks building. A small submersible grinder pump installed in the wetwell provides a continuous flow of plant influent to an automatic composite sampler.
Wastwater in the raw influent wetwell is then lifted and conveyed by a system of three 54-inch screw pumps (photo). The screw pumps provide all the lift necessary for the wastewater to flow through the plant by gravity to pressure filters influent wetwell.
After the sewage is lifted, it is screened by a mechanically cleaned fine bar screen. Waste material screened are then conveyed to a waste receptacle located on the floor below. In the event of a failure of the fine screen, it may be tipped out of the channel, and all wastewater would pass through a manually cleaned course screen.
The plant influent flow is measured by an 18" Parshall Flume located downstream of the fine screen. This flowrate is sent to the plant programmable logic controller (PLC) for display and recording purposes. The plant flowrate is also display locally.
The final pre-treatment process is grit removal. A vortex type grit removal system is employed to facilitate this process. The sytem is comprised of a 12-foot diameter grit chamber with a drive motor, grit pump and water scour system for collecting, removing, and conveying grit from the waste stream to a dewatering grit screw conveyor. The grit screw conveyor discharges dewatered grit to a waste receptacle located in the lower level of the headworks building.
Two influent equalization basins provide a measure protection for plant processes downstream of the headworks building during periods of unusually high flows. Wastewater flows by gravity to the EQ basins when the flowrate exceeds 5 million gallons per day. The flowrate relates to the level in the channel that would exceed the design level of the stop logs upstream of the inlet to the EQ basins. The EQ basin drain line is a gravity line connected to the 18-inch sanitary sewer discharging into the plant from the south.
Primary Treatment
Wastewater flows from the headworks to two 45-foot diameter primary clarifiers. Wastwater enters the clarifiers through  the center support column from the driver motor, scraper arms, and the walkway and flows down and outward from the center over a perimeter mounted wier and baffle system to an effluent trough. Sludge collected on the bottom is swept by the scraper arms toward the center of the tank for removal.
A sample pump located in the mechanical room provides a continuous flow of primary effluent to the primary effluent sampler located in the solids handling building.
Secondary Treatment
Primary effluent flows by gravity to a mixing chamber immediately upstream of the aeration tank distribution manifold pipe where it is mixed with return activated sludge before proceding to the aeration tanks. The primary effluent and return activated sludge mix flows from the mixing chamber into the four aeration tanks by gravity.
 The aeration tanks provide the majority of the biological treatment that occurs at the plant. Flow to each aeration tank is controlled by a manually operated 24-inch butterfly valve. Flow out of each tank is through a v-notch weir, which is adjustable by raising or lowering the wier until desired flow is acheived. Baffles is each aeration tank were constructed to minimize short circuiting through the tanks. Ceramic fine bubble diffusers mounted uniformly on the bottom of each tank distributes are supplied by blowers in the adjacent blower building to each tank.
The blower building contains four 125 horsepower blowers, and is the major electrical load at the plant. This building has it's own back-up power generator.
 Flow continues by gravity to a splitter box for distribution to any of three secondary clarifiers. Flow to each clarifier is controlled by a v-notch weir. The splitter box was constructed to allow for the easy addition of a fourth clarifier.
The three clarifiers are a "center-feed" type and 55-feet in diameter. Settled effluent passes over the perimeter weirs for filtration and disinfection. Solids collected at the bottom of the clarifier are continuously pumped out for recirculation or wasting to maintain the desired sludge age in the aeration tanks.
A small sample pump located in the return activated sludge building provides a continuous flow of secondary effluent to the secondary effluent sampler.
Advanced Treatment and Disinfection
Secondary effluent flows via gravity to the filter influent wetwell located just outside the west wall of the filter building where it is pumped through a system of three pressure filters. The filter effluent flows through a wet well over a weir to the ultraviolet disinfection system immediately downstream. Filtered effluent in the wetwell is used as plant service water.
Ultraviolet light is used to disinfect the wastewater prior to discharge. Disinfection is acheived by passing the secondary effluent through channels containing modules of bulbs that are specifically designed to produce the majority of their light energy at a wavelength of 254nm. This wavelength interferes with the genetic material of the passing microbes, rendering them unable to reproduce, effectively disinfecting the effluent. A small submersible grinder pump is installed immediately downstream of the UV channels for the purposes of final effluent sample collection. This pump provides a continuous flow of final effluent to a composite sampler.
Prior to discharge, the disinfected final effluent flow is measured and displayed locally, and on the SCADA system by an ultrasonic level sensor and rectangular weir.
Sludge Handling
Waste activated sludge (WAS) from the secondary settling tanks is treated using a two step process. The first step is to reduce the volume of sludge by thickening it in a rotary drum thickener. After thickening, WAS is pumped to the lime stabilization process.
Waste primary sludge is not thickened, but is stabilized with the thickened WAS prior to storage and ultimate disposal.
Primary sludge and thickened WAS are both stabilized by the addition of lime in the lime stabilization tank. This is a batch process controlled by the plant operator. Lime is added to the combined thickened WAS and the raw primary sludge by a small feed pump and mixed by a mechanical mixer in the stabilization tank until a pH greater than 12 is reached for a period of not less than 2 hours. After the 2 hour hold period, the sludge is pumped to one of three storage tanks where it stays until seasonal land application by an outside contractor.
Ferric Chloride may be added to the wastewater stream at two locations throughout the treatment plant for the purpose of chemical phosphorous removal. The two locations are the primary settling tanks and the mixed liquor splitter box.
Instrumentation
The operation of the plant has been automated by the installation of locally mounted PLC's throughout the plant. These PLC's are connected to a central Supervisory Control and Data Aquisition (SCADA) computer. The SCADA allows plant operators to control the operation of the plant through a computer interface. The SCADA system also monitors the treatment process and equipment for alarm conditions. During an alarm event, plant personnel are notified whether they are on or off site.
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