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Developed to directly attempt to resolve the return of nitrate to the anaerobic zone, this P removal process is a three stage Bardenpho process with a small denitrification reactor in the return sludge stream.
While secondary denitrification is slow, the positioning of the reactor in the return sludge line where the MLSS may be twice the concentration of solids in the process proper or even higher, permits a higher rate of denitrification to occur. The secondary denitrification reactor must be kept small otherwise the it will adversely affect the unaerated mass fraction of the process.
This process configuration does not share the international popularity of many of the other NDEBPR processes due to limitations in efficiency.
This N & P removal process is a three stage Bardenpho process with a small denitrification reactor in the return sludge stream which uses the slowest rate of denitrification (endogenous) to denitrify the return sludge prior to its
entry into the anaerobic zone. Sizing of this zone is important as the high MLSS (2x-3x the aerobic MLSS) gives it a disproportionate impact in terms of its size which may have a deleterious effect upon the efficiency of the process layout.
It is the high MLSS which provides a sufficiently high denitrification rate to achieve its design role, but operationally it places one more variable in the consideration of the ‘s’ recycle rate which is primarily designed to provide latitude in the classifier operations control. Too large a sludge denitrification zone will limit the overall size of the remaining unaerated zones.
The addition of a small supply of biodegradable or readily biodegradable organic carbon (raw sewage, settled sewage or methanol) to the sludge denitrification zone allows the zone to be smaller, but it must be kept anoxic and not permitted to become anaerobic.
Able to deal with typical in-fluent TKN/COD ratios of 0.09-0.12,  the process is usually operated at 15-25 days sludge age.