Apparatus for treating gas comprises a casing (100) containing a gas scrubber section (118) and an electrostatic precipitator section (120) located above the scrubber section. A partition (136) may be located within the casing (100) to separate the precipitator section (120) from the scrubber section (118). The casing has a gas inlet (102) for supplying gas to the scrubber section, a gas outlet (104) for exhausting gas from the precipitator section, a scrubbing liquid inlet (106) for supplying scrubbing liquid to the precipitator section, and a scrubbing liquid outlet (126) for draining scrubbing liquid from the scrubber section. In one embodiment the partition comprises a set of apertures (138) through which scrubbing liquid drains from the precipitator section into the scrubber section, and a set of gas passages (140) for conveying gas from the scrubber section to the precipitator section.