The development of two different denitrification systems is described in this paper. An attached growth denitrification process was developed for the 29 mgd (1.27 m3/sec) Lower Molonglo Water Quality Control Centre which will serve Canberra, Australia’s national capital. A suspended growth denitrification process was adapted for use at the 30 mgd (1.32 m3/sec) Central Contra Costa Sanitary District’s Water Reclamation Plant in the U.S. Testing data and design details are given in the paper.