CH2M HILL made a twist on the usual placement of a dissolved air flotation (DAF) system, placing it at the beginning of the process train rather than in the solids-treatment train, where it is usually located in wastewater treatment facilities.
The DAF has six basins with a series of chains and crossbars, or flights, across the top of the tank to collect the solids that have floated up as a result of the air added to the liquid. The removed solids are then sent by pipeline for processing at the Ina Road facility.
Meanwhile, the cleaner water flows under a baffle and to a bioreactor for further treatment. The system "allows for the separation of solids and water inside the DAF," says Greg Fischer, projects program manager for CH2M Hill.
Putting the DAF at the beginning of the process, rather than in the solids train, eliminates the need for extra clarifiers and thus reduces capital costs.
Fischer notes that the entire plant process, including the DAF, saved the county approximately $75 million over previous estimates.
"If we were to go with standard primary clarification, we would have had to build four much larger clarifiers up front," in addition to the four clarifiers at the end of the process, Fischer says.