Startup and Performance of the World’s first Large Scale Primary Dissolved Air Floatation Clarifier

The Pima County Regional Wastewater Reclamation Department, in Tucson, Arizona, built the new 120 MLD (32 MGD) Agua Nueva Water Reclamation Facility (ANWRF) and started it up in early 2014. This facility includes the first large scale Dissolved Air Floatation (DAF) primary clarifiers in the world. DAF primary clarifiers were chosen for their benefits of low cost, small footprint, improved TSS and BOD removal (as compared to no primary treatment). They also eliminated the need for separate solids thickening, and improved oil and grease removal. However, the risk was that there was no full scale implementations in wastewater that could be used to validate the technology.The DAF primary clarifiers at ANWRF treat both the screened raw sewage and the waste activated solids that are combined at the head of each DAF unit. The DAFs have been found to remove between 50% and 75% of the suspended material, depending on chemical addition, and between 30% and 50% of the influent COD, while reliably producing a thickened solids (primary and WAS) approaching 4 percent. Some removal of soluble organics has also been observed, likely a result of a combination of colloidal coagulation and soluble uptake by the cothickened waste activated sludge.Primary DAF clarification at ANWRF has shown performance similar to conventional primary clarification while combining the function of WAS/Primary sludge thickening and grit removal in a single unit process. Actual operation of the DAF clarifiers has met the goals originally envisioned in the design, but with slightly higher effluent TSS values than hoped for. Continuing optimization at the facility appears to be improving overall TSS removal at lower chemical usage rates.