W10 AM Life Cycle Approaches to Water Resources
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 341-342

(MON-1117-222921) Applying life cycle assessment to wastewater treatment: concepts and implementation.

Monteith, H¹, Bagley, D², MacLean, H², ¹ Hydromantis, Inc., Hamilton, ON, Canada² Dept. of Civil Engineering, the University of Toronto, Toronto, ON, Canada

ABSTRACT- The life cycle assessment (LCA) approach has migrated from beginnings in manufacturing and production to many other aspects of contemporary human activity, including environmental impacts. For example, a recent paper has investigated water treatment, use and wastewater treatment in terms of a complete human hydrologic cycle. In this paper, issues related to two conceptual examples of LCA application to wastewater treatment will be examined. In the first example, most current wastewater treatment practices rely on aerobic treatment, an energy intensive process resulting in large volumes of solids for stabilization and disposal, and potentially significant upstream air emissions (e.g., greenhouse gases, NO_x, SO_x and PM₁₀). Anaerobic processes, conversely, are net energy producers, generating much smaller quantities of biomass for disposal. Due to slow growth kinetics at ambient wastewater temperatures, however, the process applicability in temperate climates may be limited. Another example, disposal of residual wastewater solids is a divisive issue. Wastewater biosolids have substantive nutrient value that can replace energy-intensive chemical fertilizers in agriculture or other applications. However, stabilization of the solids, their transport and application at the ultimate destination also have inherent costs, in terms of energy consumption, social stigma and environmental impact. Incineration of the solids at the treatment plant site may offer reduced overall energy and environmental costs. Recovery of energy from biogas produced by anaerobically digested wastewater solids will be discussed to illustrate a LCA approach in greater detail. Energy recovery and use by processes such as boilers, engine-generators, micro-turbines, fuel cells were examined. Factors assessed include capital and operating costs of biogas cleaning and recovery processes, value of energy recovered, and emissions produced, both from on-site biogas use and off0site electricity generation. Examples of the sensitivity of process sustainability to the value of purchased and recovered energy will be provided.

Key words: LCA, wastewater, energy, recovery