If a dissolved air flotation unit is turned off, when should the drain valves be opened?

In a dissolved air flotation (DAF) unit, it is essential to manage the system properly during and after a shutdown to prevent operational issues such as the buildup of scum and solids, which may lead to fouling or damage.

Choosing to open the drain valves only if the DAF unit has been off for a long time is appropriate because it allows for necessary conditions to be met before draining. If the unit is turned off briefly, there may still be sufficient pressure and dissolved air in the system to continue flotation processes, and opening the drain valves immediately could lead to premature loss of treated water and residual air pressure. A longer downtime, on the other hand, increases the risk of solid accumulation and may necessitate the opening of the drain valves to remove these materials, ensuring that the system remains in good condition and is ready to function effectively upon restart.

Other intervals for opening the drain valves, such as immediately upon shutdown, may not account for the operational state of the DAF unit and could result in operational inefficiencies, while a routine opening once per week or after a day could lead to unnecessary loss of water or create opportunities for system maintenance that might not yet be needed.