Step 2 – Bardenpho Process

The District employs a unique five stage treatment process for the removal of nutrients and organic pollutants. The Bardenpho Process was first developed in South Africa. The Payson facility was the first to use this innovative technology in the Western United States.

The first stage is the fermentation zone, where the incoming flow from the VFA basin waste is mixed with return activated sludge (RAS) from within the treatment process. Stored phosphorus is released by the microorganisms, which are then able to reabsorb very large amounts at a later stage in the process.

From the fermentation zone, flow enters the first anoxic zone where it is mixed with recycled liquor from the nitrification zone. In the absence of dissolved oxygen, the microorganisms scavenge under stressed conditions to strip oxygen from the nitrates contained in the recycle flow, reducing the nitrates to nitrogen gas.

As the flow continues on into the nitrification zone, oxygen is provided by fine bubble diffusion to oxidize the biochemical oxygen demand (BOD) remaining from the first anoxic zone and to oxidize the ammonia nitrogen to nitrate nitrogen. The biomass in this cell is recycled to the first anoxic zone to assure complete nitrogen reduction. Phosphorus uptake occurs in this treatment cell. The second anoxic zone is used as a polishing stage to remove more nitrates coming through the prior basin. Finally, a short reaeration zone is used to provide oxygen for microorganisms and to prevent phosphorus release further in the treatment process.

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