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Flow Equalization Overview
 
Purpose
The purpose of flow equalization is to reduce hydraulic impacts of peak flows through the plant.  The process pumps raw sewage to the flow equalization basin and then returns the stored flow back into the influent sewer after the high flow event ends. 
Theory of Operation

Flow equalization is implemented to reduce hydraulic impacts of peak flows through the plant. The equalization basin is used when flows exceed approximately 11 MGD. Raw sewage pumps 5 and 6 discharge to a 24-inch pipeline that feeds the flow equalization basin. A single submersible pump rated for 700 gpm (1 mgd) pumps the contents of the flow equalization basin back into the influent sewer after the high flow event ends.The flow equalization basin is located west across the road from the WWTP. The basis of design for this unit process can be found in the follwing table:

Item Design Criteria
Flow Equalization Basin
Number of units 1
Type Lined pond
Capacity 1.7 million gallons
Flow Equalization Pump
Number of units 1
Type Submersible non-clog
Capacity 700 gpm
Motor 5 HP
Motor type Constant speed
Description
The flow equalization consists of a 24-inch influent pipeline from the raw sewage pump station, a membrane lined basin with sand filled membrane tubes, a concrete sump, a simplex submersible pump station with local controls, and a 4-inch discharge pipeline. A plan view of the flow equalization basin is shown in Figure 1.

Following a flow equalization event, a flushing valve can be opened to flush city water (isolated by a backflow preventer) into the pipeline to displace dilute raw sewage in the pipeline. Sodium hypochlorite can be dosed into this same water using the RAS chlorination pump.
Equipment
The Flow Equalization system includes the following equipment:
  • Wet well level instrument
  • Influent pumps 5 and 6
  • Flow equalization basin
  • Equalization basin return pump station
Wet Well Level Instrument 6
  An ultrasonic level indicator monitors the level of the influent wet well.
Influent Pumps 5 and 66
Two vertical centrifugal pumps are located in the pump room, with extended shafts connected to the motors installed upstairs in the motor room. The pump shafts have an intermediate bearing support and guards. Both pumps are constant speed.

Each pump uses seal water controlled by a solenoid valve that opens when the pump is running. The pumps are supplied from the wet well and pump raw wastewater to the flow equalization basin.
Flow Equalization Basin 6
The flow equalization basin consists of a membrane lined basin with sand filled membrane tubes, a concrete sump, a simplex submersible pump station with local controls, and a 4-inch discharge pipeline.

A plan view of the flow equalization basin is shown in Figure 1. The flow equalization basin has a capacity of 1.7 million gallons below elevation 639.0 (NAVD88).
EQ Basin Return Pump Station 6
  The Flow Equalization Basin Pump Station is located next to the EQ Basin. The equalization basin effluent pump is a simplex pump in a 72-inch diameter manhole and is removable using a guide rail system. The pump is started manually at the local control panel when the plant is ready to receive the contents of the basin.

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Last Updated: 9/16/2013 11:41:59 AM
Version 4.0.1