Eugene/Springfield Water Pollution Control Facility 1984-1991

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section D: PLANT OPERATIONS Page 23 The split flow bypasses the aeration basin and secondary clarifiers and goes directly to final treat- ment, where it converges with secondary treat- menteffluent and is disinfected. • Secondary Diversion Flow Control Two secondary diversion flow control gates are located at the end of the primary effluent channel. Primary clarifier effluent flow can be split at this point to control hydraulic loading to the secondary treatment process. Diversion gates can be opened in three ways: manually, by a local controller, orby the plant process computer. Under computer con- trol, the amount of secondary split flow is deter- mined by a setpoint or on a percentage of plant flow. If primary effluent flows are higher than the setpoint, they are diverted around the secondary treatment process. Operations has found the com- putercontrolledmethodisthe mostaccurate ofthe three. Operations splits the flow periodically during peak winter plant flows to ensure secondary treatment efficiency. To maintain a minimum aeration basin detention time of 30 minutes, operators begin splitting flow when plant flow reaches 105 MGD. Splitflow practices have had no significant impact on final effluent because the amount of diverted materials has been a small percentage of the total plant flow. Also, high plantflows that call for split flow are caused by heavy infiltration and inflow within the collection system, which have very low concentrations of TSS and BOD. • Heaary Solids/Secondary Scum/ Drain Pump Station The heavy solids/secondary scum/drain pump sta- tionconsist of awes well and two 25-HP vertically mounted centrifugal pumps. The pumps are com- monly referred to as the heavy solids pumps. The station receives effluent from all basin, channel, and clarifier surfaces and From floor drains at the east end of the plant. It also is designed to receive sludge lagoon decant and flow from building floor drains, lavatories, and the RV dump station. The heavy solids pumps can discharge into the primary effluent channel or to the recycle pump station at the pretreatment complex. Effluent is usually directed to the recycle pump station to remove floating materials and grit, which is not possible in the primary effluent channel. FINAL TREATMENT Flow measurement, chlorination, and dechlorina- tion are the main treatment components of the final treatment process and include four chlorine contact stabilization basins with capacities of 670,000 gallons each. The final treatment com- plexalso houses the plant's W2 pump system and an emergency chlorine scrubber system that can neutralize up to 4,000 pounds of chlorine or sulfur dioxide. • Flow Measurement Four Parshall flumes at the head of each chlorine contact basin measure plant effluent flows. Con- ductivitystrips continuously monitor liquid levels. • Chlorination Liquid chlorine is supplied in one-ton containers, and chlorine feed rates are aided by two evapora- A plant operator collects activiated sludge samples from an aeration basin.