(d) Sequencing batch reactor (SBR) 已地时 The SBR system(see Table 8-15) also employs preanoxic denitrification using BOD in the invent wastewater. Mixing is used during the fill riod to contact the mixed liquor with the invent wastewater. Fo many domestic applications, depending on the wastewater strength, sufficient bod and fill time are available to remove almost oll of the nitrate remaining in the mixed liquor after the setle and decant steps ome nitrate removal also occurs during the nonaerated sede and anaerobic or anoxic contacting during the fi shoving sih os,,.@nd is periods. Separate mixing provides operating Flexibility and is for anoxic operation during the aeration period,as In eeling properties in addition to nitrogen removal. Many facilities he ave repore effluent NO N concentrations of less than 5 mg/L nedved sunye The Bio-denitro TM process has also been referred to as a phased isolation oxidation ditch technology. the process was developed in Denmark for nitrogen removal and has been installed in over 75 full- scale focilities producing effluent total nitrogen concentrations of less than 8 mg/L(Stonsel and Coleman, 2000). The technology uses ot least to oxidation ditches in a series configuration in which the operating sequence of the ditches and operation of the aeration and anoxic zones is varied. Submerged mixers are installed in the ditches so that for some operating phe continues to receive in Aunt wastewater and operates as a preanoxic cone. Similor to the SBR operation, nitrate is available from a previous erobic nitrification operation. Besides denitrification in the preanoxic cone, nitrate reduction is also possible during the aerobic operation vef. A typical duration for phe 5.日.5.1.5.do.5h15