The Intermittent Decanted Extended Aeration (IDEA) process developed over 30 years ago by the then NSW Department of Public Works (DPW) provided substantial cost savings over the continuous activated sludge process. This is achieved by combining the process of aeration and sludge settlement in a single tank.

The first IDEA plant was constructed at Adelong, NSW, in 1965. Since then over 100 plants have been built by DPW and Department of Land and Water Conservation (DLWC) for communities of a few hundred people to large regional centres serving over 50,000 people.

This paper presents the latest development of incorporating enhanced biological phosphorus removal (EBPR) in the IDEA process. The retrofitting of 3 IDEA plants (capacity ranging from 4000 to 55000 persons) for EBPR is discussed. Different innovative and low cost solutions of incorporating conventional EBPR technology to the single tank IDEA plant are presented. Operational data including plant loading, effluent quality and sludge handling are also discussed.