Converting rectangular and circular primary tanks into the AAA biologically enhanced clarification settler

Abstract

The frequent design challenge for existing water resource recovery facilities targets the accommodation of an ~50% load increase within the existing infrastructure and footprint. Off‐loading this organic load at the top‐end of the plant and redirection toward the digesters has proven the most efficient way of process intensification. The Triple A settler is an “activated primary treatment,” stands for alternating activated adsorption, and can be retrofitted into existing rectangular or circular (mostly) primary tanks at a hydraulic retention time of 2 h and a sludge retention time of about 0.5 days. Several technology implementations demonstrate flexible designs adjusting to existing tank geometries and depths of 2.5 to 5.0 m. Different implementation scales from dry‐weather flow rates ranging from 0.1 to 10 mgd show generic applicability of the functional principles at any scale: Biosorption, bioflocculation, and assimilation provide the key added value in pretreatment efficiencies of ~60/25/33 in %COD/%N/%P removal compared with application of pure physics in primary settling with typical 33%/9%/11% removal, respectively.Practitioners Points Triple A is a hybrid form of A‐stage and contact stabilizer for advanced primary treatment. Besides COD and TSS, also, P and N can be removed via Triple A. Triple A can be retrofitted in existing rectangular or circular tanks. This high‐rate process does not worsen the conditions for enhanced biological phosphorus removal. Energy efficiency, capacity increase, and operational benefits are the main goals of Triple A.