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centrifugal blowers (including one standby). During normal operation, only one blower may be used. The effluent from the aeration basins is equally divided between the two final clarifiers. The clarifiers are 98 feet in diameter with a 12 foot sidewater depth. Each clarifier is equipped with a spiral blade-style sludge collector that transports the sludge to a common point for retum and waste. The sludge is periodically withdrawn from the clarifiers using the RAS and WAS pumps whose operation is controlled by timers. Hoth sets of pumps are located at the secondary sludge pumping station. RAS is retumed to the head of the aeration basins by three (one stand-by) centrifugal pumps operating on a time-controlled basis, each rate at 3,300 gpm. The two (including one stand-by) WAS pumps have a capacity of 100 gpm each, and divert WAS to the primary clarifiers for co-settling with primary sludge. (E) Effluent Filters. The secondary effluent flows into the effluent filters for further suspended solids removal. There are three Infilco Degremont dual media filters, each 26.0 feet by 76.0 feet. The filters are designed to accommodate an average flow of 13.5 mgd and peak flow of 27 mgd. The filter loading rate is 2.6 gpmjsf and 5.2 gpmjsf at average and peak flows, respectively. Each filter unit is equipped with a backwash system mounted on a traveling bridge. The maximum backwash rate for the maximum flow is 25 gpmj sf. The backwash water is returned to the primary distribution box using three (including one stand- by) pumps, each at a capacity of 750 gpm. (F) Ultraviolet System. The disinfection of the filtered effluent is achieved through the UV system. Two UV channels measure 26.0 feet long and 4.75 feet wide, and have a sidewater depth of 2.0 feet. The UV lamps are located inside these channels. Each channel has two UV banks with 152 lamps each. The UV system is designed to treat an influent flow of 18.0 mgd with BODs and TSS concentrations of approximately 5 mgjL. The disinfected water flows from the UV system to the two re-aeration basins through two channels. Hoth re- aeration basins are equipped with fme bubble diffusers that are used to maintain the dissolved oxygen concentration above 6.0 mgjL. The air to the diffuser system is supplied by three (including one standby) blowers, rated at 415 scfm each. (G) Facilities Effluent. The Effluent from the Facilities is collected in a common box. A portion of the flow may be diverted to various customers for re-use (such as cooling water to a power plant customer), and the remaining flows by gravity through a 48-inch outfall to the San Marcos River. (H) ATAD Process. Until completion of the Planned ProcessjResiduals Improvement, or implementation of mobile equipment dewatering, whichever occurs sooner, the sludge from the primary clarifiers and WAS from the aeration basins are handled on-site using the ATAD process. (1) The sludge from the primary clarifiers (co-settled primary sludge and WAS) flows into a covered holding tank with a volume of 145,000 gallons before entering the ATAD system. The sludge is thickened to between 4% and 6% solids using one of two centrifuges. Each centrifuge has a thickening capacity of 100 gpm. (2) The centrate is recycled to the primary distribution box through the lift station behind the aeration basins. The thickened solids flow into the covered-top US Filter ATAD system. (3) The ATAD system consists of three reactors 26 feet in diameter and 18 feet deep. The working volume of each reactor is approximately 60,000 gallons. The remammg upper portion is for foam expansion and control. These reactors were designed to operate in series in batch mode at a thermophilic temperature range (135EF). The contents from the third ATAD reactor flow into the covered and aerated cooling tank with a volume of 0.41 mg. 1-2