The invention relates to apparatus (1) for distributing a gas in a liquid, particularly for "floating" particulate matter from raw or flocculated sewage, comprising an inlet (2) for a gas entrained in a liquid carrier such as recycled sewage, a sinuous part (16, 18) of a flow path (3) through the apparatus, and a downstream outlet (4, 11) of substantially uniform cross section adapted to allow gas to be released from the liquid carrier and to be dispersed laterally of the flow path (3).