Katie de Jong

Sustainability drives multi-million dollar upgrade to Woodman Point Wastewater Treatment Plant

Katie de Jong, Sinclair Knight Merz, WA; D. Higgs, Water Corporation of Western Australia; J.S. Powell, Sinclair Knight Merz

Abstract:
The Woodman Pt wastewater treatment plant (WWTP) in the southern suburbs of Perth, Australia, treats wastewater from a combined domestic and industrial catchment of around 650,000 people with a current inflow of around 125 ML/d. The WWTP is a 160 m diameter, circular sequencing batch reactor (SBR). The plant is to be upgraded to a capacity of 220 ML/d by 2040, by extension of primary, secondary, sludge and odour treatment areas. The W2W Alliance worked with the Water Corporation to develop a Planning Business Case; a strategic document that outlines required capital upgrades to
the year 2040, to continue to meet stringent effluent quality conditions and continued reduction of odour emissions.

The W2W Alliance has a strong sustainability framework that aims to drive sustainable outcomes through the use of specifically developed sustainability assessment tools. One of these tools is an expanded net present value (NPV) tool that quantifies not only conventional capital and operating costs but also externalities such as environmental and social impacts. Environmental costs are predominantly quantified via a greenhouse gas model that quantifies the carbon footprint of different design technologies. The model captures the carbon footprint related to direct emissions from site (referred to as Scope 1 emissions, including fugitive emissions such as CO2, CH4 and N2O), power consumed and generated (Scope 2 emissions) and indirect emissions such as fuel used for biosolids transport and embodied energy in chemicals consumed (Scope 3 emissions). The use of these tools enabled strategic design decisions to be made that produce the best long term value, in line with future drivers such as increasing energy prices, carbon pollution regulation, increasing community expectations regarding ocean discharge, odour emissions and wastewater reuse. This study has shown that when sustainability factors are given an economic value, the outcomes can be entirely different than when the analysis is based on conventional capital and operating cost alone. The expanded NPV analysis provided a holistic, integrated view of each design option that enabled key decision-makers to make more informed decisions to ensure the best long term value outcome for the Water Corporation, the environment and the community.