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i <br /> f <br /> 96 cents per month. Depending on the operating recirc-ratio,multiple-pass recirculating PBFs may <br /> cost 3 to 5 times more to operate than single-pass PBFs, depending on the operating recirc-ratio. <br /> Low routine maintenance requirements—:Annual routine maintenance for PBFs is recommended <br /> and normally includes inspection of effluent for clarity (e.g.,turbidity, grease and oily films, foam, <br /> color, etc.) and odor, as well as cleaning pump filters and flushing distribution piping if necessary. <br /> Because PBFs are designed to limit cell mass growth by controlling the organic loading rate and <br /> encouraging endogenous respiration, sludge removal is not required from the PBF itself. Solids do <br /> build up in the septic tank and must be removed periodically. The pumping of septic tank solids can be <br /> e <br /> as infrequent as every 12 years or more if solids accumulations are"monitored" eve 2-3 ears to <br /> determine when the tank actually needs p1iWinfr. <br /> Ease of maintenance—Maintenance of pre-manufactured, packaged PBF's is particularly service <br /> friendly and especially suited for management programs, due to a)Training and certification of <br /> installers and service providers, b) Detailed installation and operation manuals that identify specific <br /> sevice,testing and troubleshooting techniques, c) Specially engineered mediums, as shown in Figure <br /> 9, that can be cleaned with a small pressure washer in the event of system abuse or overuse and put <br /> back into service within a matter of minutes, and d) Controls that monitor and alert service providers <br /> directly upon electro-mechanical malfunctions, as well as water usage and system functioning <br /> abnormalities. <br /> As a result, the management of onsite systems can be as user-friendly, effective, reliable, and trouble- <br /> free as the municipal gravity alternative and, in the event of an individual malfunctions,much more <br /> manageable and environmentally friendly. <br /> Figure 9: Typical servicing of AdvanTex <br /> textile medium. (An underdrain valve is <br /> opened during a filter washdown that <br /> allows sloughed solids to flush back into the <br /> process tank,so there is no removal or <br /> wasting of media.) <br /> NTP-FLT-TRB-1 <br /> Rev.1.1,11102 <br /> Pa Oe 9 of 12 <br /> 1 <br />