Continuous-feed, intermittent-discharge (CFID) basins have been in use for many years in Australia and the United States (Rich, 1999). In-basin sedimentation is used rather than a secondary clarifier, and sludge recycle is used. Discharge is intermittent, but flow into the basin is continuous which differs from sequencing batch reactors. These systems generally have been successful but have had problems with short-circuiting and sludge bulking; however, modifications to the system can be made to overcome these difficulties (Rich, 1999). Rich (1996, 1999) has proposed a modified CFID basin for use in aerated lagoon systems for nitrification and denitrification. The systems are designed to use in-basin sedimentation to uncouple the solids retention time from the hydraulic retention time, and the influent flow is continuous. He also has proposed a nitrification system consisting of a combination of a modified CFID with a sludge basin. The modified CFID basin serves as the reactor basin, and the sludge basin stabilizes and stores the sludge. This arrangement provides flexibility in operation. To learn more about the operation of CFID systems, consult Rich (1999).
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