The process uses a three-stage batch cycle structure, depicted in Figure 2, eliminating supplementary tanks such as clarifiers and selector basins and the mechanical equipment associated with return activated sludge and internal recycle which contribute to significant footprint and energy savings. The initial phase consists of a simultaneous fill/draw under anaerobic conditions. Raw wastewater enters the tank from the reactor floor through the settled sludge bed under vertical plug flow operation. The dominance of slow-growing bacteria in this phase, such as polyphosphate-accumulating organisms (PAOs), encourage phosphorus release. The second and longest of the treatment phases occurs is in an aerobic environment in the bulk liquid and aerobic/anoxic conditions within the granules resulting in a reduction of organic constituents in addition to simultaneous nitrification/denitrification and phosphorus uptake. The cycle then ends with a rapid settle phase. A portion of time into settling, sludge wasting occurs at approximately half of reactor depth. This allows the reactor to waste the lighter flocculent sludge while retaining the denser, fast-settling particles and granules. This hydraulic selection, in addition to the granule backbone developed by extracellular polymeric substances during the anaerobic feed, is integral to the formation of true aerobic granules capable of BNR.
Aerobic granular sludge (AGS) possesses inherent BNR capabilities as the layered microbial community of the granules enables simultaneous nitrification/denitrification and enhanced biological phosphorus removal (EBPR) to occur within the granular biomass. This technology therefore eliminates the need for clarifiers, carrier media, and return sludge pumping stations, as well as selectors or separate compartments for plants looking to achieve BNR.
For more information on AquaNereda technology, visit www.aquanereda.com or contact Aqua-Aerobic Systems directly at 815-654-2501.
