In starting a dissolved air flotation (DAF) system, which action is performed first?

• A. Close all drain lines and valves
• B. Open all drain lines and valves
• C. Start the air flotation pump
• D. Add coagulant to the influent

Answer: (A)

The first step is to isolate the DAF loop by closing all drain lines and valves. This keeps the system sealed so you can establish proper pressure and dissolve air without losing liquid or flow paths. If drains were opened first, process water and air would escape, making it hard to achieve the saturated conditions needed for bubble formation and effective flotation. After the system is sealed, you can proceed with starting the pumps and introducing coagulant as per the normal startup sequence.