_O & M MANUAL - WEST LANE MOBILE HOME PARK

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Wastewater is usually removed from the equalization tank with constant speed pumps. Pumps installed in the equalization tank must be able to pass the solids found in raw wastewater. If other types of pumps are used, a bar screen must be installed at the influent to the equalization tank. Because the water level in the surge tank changes; the pumping rate of a constant speed pump will vary; as the water level is pumped down in the equalization tank and the pumping head increases, the pump will deliver less wastewater to the aeration tank. A way to overcome the problem of a changing level in the flow equalization tank is with a constant head column. Mounted within the column is an air lift pump. This air lift pump will dose the aeration tank at an adjustable constant rate. The excess waste water is return to the flow equalization tank. The U.S. Environmental Protection Agency (EPA) requires 100% standby pumping capacity in the equalization tank, which is provided for by the two submersible pumps. However, flow interruption would occur during periods of power failure; therefore, installation of emergency overflow by gravity form the equalization tank to the aeration tank is recommended. Operation of the Equalization Tank In a typical equalization tank two submersible pumps, working alternately, are used to pump the influent flow to a flow control box. Both pumps are controlled by float switches and an alternator to give the pumps equal run tirne. The top float switch is usually only for an alarm condition in the event that either pump is not working or not keeping up with the influent flow rate. An emergency overflow pipe is provided to keep from overflowing the tank. The second float down will turn on the lag purnp if the lead pump fails to turn on or cannot keep up with the incoming flow rate. The third float switch down will turn on the lead pump and blower if supplied when the equalization tank becomes approximately 25% full. The level at which the lead pump is set to turn on can vary, but generally should be low enough so the water level rarely reaches the top float switch. When this purnp is operating, is when the flow control box should be adjusted so that 1.5 times the design flow rate flows over the V-notch with the balance being returned to the equalizations tank. The lead pump and blower will continue to operate until the equalization tank is pumped down to the lowest float switch. Then both the blower and pump will turn off. This float should be located several inches above the diffuser drops. General maintenance A fixed skimming device that removes grease balls and scum in the equalization tank is impractical because the water level changes continuously. The operator must remove these floating materials manually with a wire mesh such as ordinary window screen. A simple device that is convenient for removing floating material can be made readily by mounting the mesh on a wire frame that has been fitted with a long handle. The same kind of maintenance is generally required in the clarifier. Material removed from the flow equalization tank should be put into a lined trash can with a tight-fitting lid. The best method of final disposal is at an approved landfill. pcsio 'm-prated-procescoritrol %f-.q-!