The primary clarifiers are used as fermenters to provide VFAs for P removal. There is a de-ox, or Johannesburg, tank at the end of the aeration basins that allows Oxygen to be depleted before returning mixed liquor to the Anoxic Zone.
Another highlight from my contract operating days was to serve as Operations Manager at the 8 MGD Caguas Puerto Rico Advanced Wastewater Treatment Plant. This plant removes Nitrogen and Phosphorous through biological treatment in the A2O process patented by Kruger, Inc.
I was chosen for the position because of my treatment process expertise. We had the plant up and running and meeting TIN < 10 mg/L and Tot P < 1 mg/L in a few months.