A major planning effort undertaken in the mid 1950’s by the Melbourne and Metropolitan Board of Works resulted in the decision to construct a major wastewater purification plant to serve the rapidly growing eastern, north eastern and south eastern suburbs. The first step in implementation of the plan was to undertake a study to determine initial and ultimate plant capacity, effluent quality requirements, and type of treatment required. That study resulted in the establishment of design loading as summarized in Table 1, together with a conclusion that the effluent quality requirements would best be met by the activated sludge process. A simplified flow diagram of the plant is shown in Figure 1. Detailed design of the South Eastern Purification Plant was commenced in 1968 by an international team of consultants who were confronted with many interesting design problems among which was the development of an aeration system that would be both reliable and efficient. This paper describes the design criteria established for the aeration system, final design of the aeration system and performance testing of prototype air diffusion units.