Hobart City Council has three separate wastewater catchments. Prior to 1997 one catchment discharged untreated sewage to the Derwent River estuary. The State environmental authority required this wastewater to be treated to nutrient removal standard. Following extensive investigations to determine options, Council decided to transfer this wastewater to the existing Selfs Point trickling filter plant. Augmentation of this facility to biological nutrient removal standard was selected to meet the more stringent licence conditions. Council required the new treatment process to utilise current best industry practice, to have proven performance and to make best use of the existing infrastructure, while maintaining cost effectiveness.

This paper discusses the rationale for incorporating trickling filters into the process specification. It also describes the maximal use of previously existing plant, with over 90% incorporated into the design. A significant feature is that the anaerobic digesters have been retained to ensure good biosolids stabilisation.

Selfs Point has shown that retrofitting a trickling filter plant to BNR performance can be very cost effective where existing facilities are in good condition.