Mark the incorrect statement about electrostatic precipitator.

Electrostatic precipitators operate on the principle of the attraction of a charged particle for an oppositely charged collector. They are filter-less devices.Electrostatic precipitator has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall.