Diffuser for aeration of a fluid

An elongate diffuser, having a length of at least one metre, comprising:

• a diffuser base comprising a diffuser body;
• a membrane attached to the diffuser body;
• wherein the membrane is connected to the diffuser body so that introduction of gas at a working pressure into the diffuser displaces part of the membrane from contact with the diffuser body to provide an elongate sealed compartment between the membrane and a surface provided mainly or wholly by the diffuser body, the compartment having a first lateral side interface region where the membrane contacts the diffuser body, a laterally intermediate region where the membrane is spaced apart from the diffuser body and a second lateral side interface region where the membrane contacts the diffuser body, and wherein gas can pass from the compartment through the membrane for aeration of a fluid in which the diffuser is immersed;
• wherein the diffuser body surface which bounds the compartment comprises a base surface which comprises a recessed base surface portion which is recessed away from the membrane between the first lateral side interface region and the second lateral side interface region, compared to a planar surface extending between the first lateral side interface region and the second lateral side interface region, to thereby provide the compartment with larger transverse cross sectional size than would be provided by a planar surface extending from the first lateral side interface region to the second lateral side interface region;
• and
• wherein at least one axial end region of the compartment comprises a base surface end portion which is shaped to provide a smooth and gradual transition from a substantially convex transverse cross sectional shape of an end region of the base surface, to the recessed base surface portion.