Electrostatic precipitator has electrode wires that are connected at several thousand volts, which produce a cornea that release electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plants are grounded and attract the charged dust particles. The velocity of sir between the plates must be low enough to allow the dust to fall. A scrubber can remove gases like sulphur-di- oxide. In a scrubber , the exhaust is passed through a spray of water or lime.