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~' .,. power outages or equipment breakdowns. In recirculating PBFs, the recirculation tank provides even more buffering capacity by diluting the incoming septic tank effluent with treated effluent, to mitigate the effects of organic shock loading. Most PBF designs do not allow completely untreated sewage to be released since, unlike passive gravity systems, wastewater must pass through the treatment media before discharge. This feature also prevents deliberate attempts to disable the treatment system. With passive gravity systems, it is not uncommon for users to "unplug" their system to lower their electrical bill. PBF systems with programmable timers in their control panels have the ability to detect excessive inflow caused by infiltration, leaky plumbing fixtures, or higher-than-normal water consumption by the user. This "flow management" provided by the programmable timer is a fundamental tool that allows operators to detect and diagnose problems that would otherwise go undetected until complete system failure. The programmable timer also provides improved treatment through frequent"micro-dosing"of the PBF. Operational costs are low, limited to the intermittent operation of small fractional horsepower pumps. A typical single-pass PBF for an average single family home requires between 4 and 12 kw-hr per month of electricity. At the national average of 8 cents per kw-hr, the power cost ranges from about 32 to 96 cents per month. Recirculating PBFs typically cost 3 to 5 times more to operate than single pass PBFs. Routine maintenance for PBFs is usually performed once or twice per year and normally includes inspection of effluent for clarity and odor, as well as cleaning pump filters and flushing distribution piping if necessary. Because PBFs are designed to limit cell mass growth by controlling the organic loading rate and inspiring endogenous respiration, sludge removal is not required from the PBF itself Solids do build up in the septic tank and must be removed periodically. However, the pumping of septic tank solids can be as infrequent as every 12 years or more, if solids accumulations are monitored every 2 to 3 years to determine when the tank actually needs pumping. While sand media PBFs are, and will continue to be, an excellent choice for wastewater pretreatment, certain limitations have prevented them from being considered at all sites: • Land area—Some sites lack the land area required for a sand filter. Sand filters for single-family homes typically require between 100 and 400 square feet, depending on the type of sand filter being used. • Media quality and accessibility—Good quality sand media is occasionally not locally available. In addition, getting sand to some sites---such as islands, mountainous regions, or other isolated areas—can be difficult. • Installation quality—Sand filters are typically built onsite, and quality of installation is partially contingent on the ability of the installing contractor. Textile-Based Packed Bed Filters Recent research has resulted in an advanced packed bed treatment technology that uses a textile medium. It provides all the benefits inherent in the packed bed filter design but overcomes the limitations listed above. .r. NTP-FL7-TR8-ES8-HUB-1 2100 Page 4