Integrated environmental assessment of tertiary and residuals treatment - LCA in the wastewater industry

Abstract

In the wastewater industry, decision-makers lack access to an environmental tool that can assist in further informing the non-financial analysis of a system. Such a tool should incorporate impacts beyond the effluent quality and look at the supporting processes of a plant as well as plant specific operations. Life Cycle Assessment can provide the means to fill a gap in pertinent information towards more sustainable decision-making. The project “Best Practice LCA in the Wastewater Industry” is commissioned by the CRC for Waste Management and Pollution Control at UNSW with representatives from Sydney Water Corporation(SWC), NSW Department of Land and Water Conservation and the NSW Department of Public Works. Two case studies were researched to provide a post-implementation review of changes in wastewater treatment. Case study 1: The conversion from chlorine gas to hypochlorite and UV disinfection has been completed for several inland wastewater plants at SWC. A review of operational data for each of the options has been incorporated into an LCA of each technology. Under efficient dosing conditions, disinfection with the hypochlorite system has the minimum environmental impact. Case study 2 deals with the conversion from anaerobic to aerobic digestion. Aerobic digestion minimises release of nutrients into a sidestream to be further treated in the plant. However conversion results in more biosolids production and higher electricity requirements. This study includes a consideration of the environmental impacts of biosolids production and application. On the basis of the extended system boundary including consideration of reflux composition, energy requirements and biosolids quality to potentially offset fertiliser production, anaerobic digestion performs best in 6 out of 9 impact categories. These results suggest that environmental LCA has a role in informing decision-making on unit process and treatment train selection by quantifying aspects on non-financial criteria. Also, improvement potentials are foreshadowed but not detailed.