Established in 1966, the Bolivar Wastewater Treatment Plant (WWTP) treating approximately 70 per cent of metropolitan Adelaide’s wastewater and serving approximately one million customers. A comprehensive and staged upgrade of legacy PLC-5 controllers were upgraded to Allen -Bradley® ControlLogix® for centralised control requirements and Flex™I/O and CompactLogix™ for control of field devices. The original ControlNet network was upgraded to Ethernet/IP for improved diagnostics and communications. The upgrade was conducted with no impact on wastewater treatment. Plant performance was optimised, yielding operational savings and significantly lowering environmental risks.