![]() ![]() The plant was designed to have two basins on line during the summer and three basins during the winter. Through trial and error, it has been determined that the process can run with half of the design aeration, which saves on maintenance and electric usage. Each blower has a throttling valve before the blower to adjust the actual scfm output. The blowers are multi-stage centrifugal blowers rated at 300 Hp with an output of 4700 scfm each. The plant annually cleans the primary clarifiers and pressure washes the sludge lines from the center of the primaries to the inlet of the raw sludge pumps with the Service Department’s flusher truck. The build up of grease is a problem in the raw sludge pumping system. The skimmers collect grease off the surface and fill a grease pit, which is decanted automatically and pumped to the anaerobic digester at least once per day, however during storm events the frequency will increase. A monthly average of 2,663,242 gallons of primary sludge are pumped to the primary digesters. The average primary sludge is 3.1 percent solid, with 75 percent volatile. He then adjusts the pumping minutes to maintain the thickest sludge and not more then one to one-and-a-half feet of sludge in the primary clarifiers. The operators take samples of the raw sludge and gauge the thickness of the sludge. Each primary can be pumped at a minimum of 4 minutes to a maximum of 15 minutes each hour and the start time for each tank is offset by 20 minutes. The progressive cavity pumps are controlled by the PLCs. The Hycor Bar Screen is locally controlled by its own control system it monitors level and function and controls the screen frequency.Īn average of 88,775 gallons of raw sludge is removed from the primary clarifiers daily through 6-inch and 8-inch lines with Monyo progressive cavity pumps to the anaerobic digestion system. The velocity with one channel open and with a flow rate of 25 MGD is 2.6 fps. The screens are sitting in a 3-foot wide channel with a maximum channel depth of 7.5 feet and normal operating depth of five feet. The two Hycor screens are front rake cleaning type with 1-inch bar openings. The two Hycor “Climber” screens that were installed in the 1988 project replaced the Dorr-Oliver back rake screens that were installed in 1972. ![]() For this reason the plant is set up to take a maximum of 23 MGD though one Hycor bar screen channel and any flow above 23 MGD will go to the Dorco bar screen and Detritus tank. Every time the flow is increased above 24 MGD the bar screens were blinded by grit and stone. However it has been found that the pipe feeding the two channels has a low spot in it that lets grit and stone settle. Each channel was designed to handle 25 MGD with a combined flow of 50 MGD. The two Hycor bar screen channels and aerated grit basins were built in 1972. ![]()
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